Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations

1980 Cardiovascular responses to diving in the turtle, Pseudemys scripta Stuart Keith Ware Iowa State University

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Recommended Citation Ware, Stuart Keith, "Cardiovascular responses to diving in the turtle, Pseudemys scripta " (1980). Retrospective Theses and Dissertations. 6813. https://lib.dr.iastate.edu/rtd/6813

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University Microfilms International 300 N. ZEEB ROAD, ANN ARBOR, Ml 48106 18 BEDFORD ROW, LONDON WCl R 4EJ, ENGLAND 8028642

WARE, STUART KEITH

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Iowa Slate University PH.D. 1980

University Microfilms 1 nt0r nBt i O n âl 300 N. Zeeb Road, Ann Arbor. MI 48106 18 Bedford Row, London WCIR 4E]. England Cardiovascular responses to diving in

the turtle, Pseudemys scripta

by

Stuart Keith Ware

A Dissertation Submitted to the

Graduate Faculty in Partial Fulfillment of the

Requirements for the Degree of

DOCTOR OF PHILOSOPHY

Department: Zoology Major: Zoology (Physiology)

Approved:

Signature was redacted for privacy.

n Char/^e of Major Work

Signature was redacted for privacy.

For the Major DepartmentIT

Signature was redacted for privacy.

5 V ! U! WW WW « w i » v.-^v-

? ^ ^ Am ^ ^^ 1UWG O UC UC u 11 I V c: o I u j Arnes,

1980 ii

TABLE OF CONTENTS

page

INTRODUCTION 1

REVIEW OF THE LITERATURE 3

Historical Perspective 3

Respiratory System and Metabolism 6

Cardiovascular System 22

Nervous System and the Integration of Physiological Responses to Diving /2

MATERIALS AND METHODS 37

Animal Maintenance 87

Heart Rates, Electrocardiograms and Blood Pressures 87

Hardiac Output, Shunting and Tissue Blood Flow 92

RESULTS 104

Heart Rates, Electrocardiograms and Blood Pressures 104

Cardiac Output, Shunting and Tissue Blood Flow 132

r\rr*r*}te*r'rr\\iUlOVUOOlUn

SUMMARY 177

LITERATURE CITED 180

ACKNOWLEDGEMENTS 204 1

INTRODUCTION

The physiological responses elicited when animals dive or are experi­ mentally submerged have been of interest to zoologists for many years.

Since 1870, studies have been carried out to elucidate these responses in an attempt to explain the long dives made by natural divers. As a result, we now understand many of the circulatory and respiratory adaptations which allow for long, and sometimes deep, dives. The results have im-

vci: ivc uc jVMU G * & vW M ty i u: a:i uuuc: ^ oauu liiy v : u: ic ptij^iuswyi^ai i c— sponses to submergence per se. There are situations, of much more immedi­ ate interest and importance than diving itself, which, apparently, elicit

a physiological response not unlike the response to submersion in divers.

Such situations include birth, trauma such as shock, burns, surgery,

hemorrhage or cardiac failure. It appears that the physiological mecha­

nisms employed by natural divers to remain submerged for prolonged time

periods are present in all vertebrates during all stages of life and may

simply be the perfection of a corraion defense mechanism against asphyxie

condi tions.

Despite all the information available on the physiology of diving,

comparatively little is known about lower vertebrates. Mammals and birds

have been studied extensively, but it is not known to exactly what extent

Tra H 1 rtn i.fX 4 X -yc. -r yi &v~rr:c n :: c aX r? 4 \ / •? « rt

» X. T? lûC^ ^ 3 I T— 11y» 3/4/44^4I V I vrw-: 11 ) III».* itjr/ wr\^ I ^iis»In o w 41« *f 4I wy

• •SiMVs» Kooîn Hnna^wtiw nnI é «-/ * \w/r\riHor! W t Vf \rov^*^ûKv»a4-oçVWt W * L»pv*o « ^ /-'rs*nrl4/-»+4*^nt t ovp»r»nloVa^/xCklll^tC)

turtles have been shown to show a reduction in heart rate upon diving by

most workers, but not by all - even when the same species was used. The 2 situation is even more confusing with amphibians where, apparently, the cardiac response varies with water oxygen content, temperature, species used, and furthermore, may be seasonal. Based on indirect evidence, tur­ tles have been reported to show either reduced blood flow or maintained

blood flow to muscles during submergence. No direct measurements of tis­ sue blood flow in any diving reptile have been attempted. In fact, cir­ culatory studies of any nature for diving amphibians or reptiles are

scarce.

It was the purpose of this study, therefore, to measure the cardio­

vascular responses to submersion in the turtle, Pseudemys scripta. This

animal was chosen because of its availability, size, and relative ease of

surgical manipulation. Furthermore, more physiological information is

available for this turtle species than for any other.

The overall study was divided into two parts. The first part was con­

cerned with measurements of heart rates, electrocardiograms, blood pres­

sures and external respiration. These parameters were recorded from

vu I un ud r I I V uivjjiu uu r u i o a:> we i-1 ai» i rmn cm nna i cAucf inicfi i » v 5UU-

merged. The second part of the study involved measurements of cardiac

output, stroke volume, intra-cardiac shunting of blood, and blood flow to

various tissues. Due to the nature of these procedures^ voluntarily div­

ing turtles could not be studied. 3

REVIEW OF THE LITERATURE

Historical Perspective

Studies into the physiology of diving began over 100 years ago with the work of the French physiologist Paul Bert (1870). Although there had been earlier mention in the literature of the ability of divers to sur­ vive prolonged submersion, Bert was the first investigator to try to ex­ plain this phenomenon. He is, therefore, considered by most workers as the founder of diving physiology. Bert attempted to explain the differ­ ence between divers and non-divers by comparing the hen and the duck. He felt that the difference between the two species which allowed the duck to remain submerged for a longer time than the hen (15 minutes vs. 3 minutes) was the fact that the duck had a greater blood volume per unit body weight

(10%) than the hen (4%). Thus, the duck had a greater oxygen store to draw upon during diving. Performing the crude experiment of bleeding the duck until its blood volume/body weight ratio had been reduced to that of the hen, he demonstrated that the ability to dive had decreased corres­ pondingly.

Twenty-four years later Bert's conclusion was challenged by another

French physiologist, Charles Richet (1894a). He argued that, even though the duck did have a larger weight-specific blood volume than the hen,

-rV-.-- c Civ-f-v-a n\r\rt~.ci!r. -...'n : Tr. macr f ha !-..Qar; Ç r.T a 1 nnn Hiup.

Analysis of gas in the respiratory system of diving clucks (Langlois and

Richet, 1898) shewed that oxygen consumption decreased during submergence.

Furthermore, Richet (1399; showed that immersion itself was important to

survival during respiratory arrest. Tracheal occlusion in two groups of 4 ducks demonstrated that those which were immersed lived about three times as long as those left in the air. Richet concluded that physiological ad­ justments to submergence take place which cause a decrease in oxygen con- ciimn+imn THi< tha qiihmornnrl Hiirtn pyi 1 nnqfir on nyvnon stores available than those left to perish in air.

After these initial studies no more papers on the subject appeared until 1913. It had been suggested by Bert (1870) that submersion apnea was voluntary. Huxley (1913a) demonstrated that submersion apnea takes place in decerebrate ducks as well as normal ones, thus proving that higher brain centers are not required. She also showed that submersion bradycardia occurs in decerebrate ducks as well as in normal ones (Huxley,

1913b).

Lombroso (1913) made a study of the causes for submersion bradycardia in ducks. He noted that tracheal occlusion of birds in air did not pro­ duce a cardiac slowing. He also reported that consistent results were not obtained when the lungs of submerged ducks were ventilated with a

Lie» c ' n a C nmnrrîcôC on n M 3 l mo or ï.rov»o a c — sociated with the bradycardia of diving.

Orr and Watson (1913) published a paper dealing with the respiratory

C i * CLf wi Ck IL* ) (V/rV v ^ ^ i * ) ^ ti4 vi » C >uw«voi\«

-ri ma -rlni c nanov* k s c r- 4 4- oH a X 4 4- rt o o v»v«»rv»^ Q/M t ç concept that CO2 does not stimulate respiration in diving animals. Many

people have even interpreted this paper to mean that CO2 actually inhibits

respiration in divers. Tn IQ'^Hc an<4 1 0/1. Dc ri v-» Oa r\v»/\/nv*occ i.'ac nn3/4o 4 w

physiology of divir:g. Lawrence Irving and ?. F. Scholancer pub'iishea a 5

number of papers dealing with diving during this time. It is probably

fair to say that these two men have contributed more to our understanding of diving physiology than anyone else.

Irving (1934) rejected the idea that vertebrate divers carry enough

O2 for prolonged dives. He pointed out that the brain and heart of homeo-

therms are damaged by Og lack, and stated that the muscles may safely be

left for long periods of time without O2. He felt that reflex adjustment

was the mechanism used by divers to allow for adaptation to submergence.

In the latter half of the 1930s, Irving showed that CO2 stimulates

respiration to a lesser extent in beavers, muskrats, and seals than in

strictly terrestrial mammals (Irving, 1938b). He showed that brain blood

flow is increased during the arrest of breathing, whereas that of muscle

is reduced (Irving, 1938b). He also demonstrated that the physiological

responses to diving are not unique to diving vertebrates, but rather are

just better developed in them than in their terrestrial relatives (.Irving,

1937).

in JL J aiiucr' uu u i i^neu a luuriuu r*a un ur' urse uri vb 1 u » uu 1 cc 1

sponses to diving in birds and mammals. He investigated primarily res­

piratory and metabolic parameters in divers. This publication may well

be th^ "T^t rnûinrahor.ci \/o rH -'rr.noyrs nt c i rr1 a af fnrt i n tkio f i al H nf

diving physiology. His ingenious methods permitted the accumulation of a

tremendous amount of information on diving animals previously unavailable.

By 1940, Irving and Scholander had united in their efforts. As a

result, today we largely understand the basic physiological modifications 5

Since the 1940s, many further studies into diving physiology have been made. The diving responses, as outlined by Irving and Scholander, have been found to exist in all terrestrial vertebrates studied (includ­ ing man) and in fishes removed from water. Sophisticated techniques have been employed to measure blood flow to tissues during diving, especially in the past few years. Many control mechanisms have been examined in de­ tail during submergence. This is especially true with regards to the con­ trol and integration of respiratory and circulatory responses to diving.

The results indicate that the postulates of Irving and Scholander in the

1930s were essentially correct.

Respiratory System and Metabolism

Lung volumes compared to body weight are not always larger in divers compared to non-divers. In fact, some whales have weight-specific lung volumes much smaller than non-divers, such as man (Irving et al., 1941a;

Scholander and Irving, 1941). This small lung volume may be an adapta­ tion to diving in animals which descend to great depths (Andersen, 1955), such as Sperm whales which have been found entangled in submarine cables

A f npnfhc ov/on AyrooHi nn T 00.0 mof ore 1 Q!>7 ^ Mr 5/aa n anri Pav»!+nn

(1977) have shown that beavers have a smaller lung volume/body weight ratio than man. They found that a larger ratio in the beaver would give

• u ^V 11 kvwj'ÛI VI lu u ! ^MCI » :! ! ! OU ;u vc u • i ! Î u'-i ! '-» « :ivrf— ever, Kcc^-man (1973) stdtes that all marine mammals show a trend towards larger lung volumes than terrestrial mammals, especially when lung volume is expressed relative to lean body weight. This was interpreted as an adaptation which a"lows the animals to rest at sea due to the increased 7 buoyancy (Kooyman, 1973; McKean and Carl ton, 1977). It has been shown that the lung volume of sea snakes is conspicuously larger than that of terres­ trial species (Wood and Lenfant, 1976).

T n Haon H 4 fko 1 « mnc rnlTançû X i iv~i nn H ccr on f a nri a i on f may become contained wholly within the respiratory dead space (Scholander»

1940). Of course, whether total lung collapse is possible or not depends on the size of the lungs relative to the size of the dead space. Thus,

small lungs may be adaptive in this regard (Andersen, 1955). The chest

wall of a seal or whale can collapse completely around, the deflated lungs,

in contrast to the situation in man. In seals, which usually expire be­

fore diving, alveolar collapse occurs at 100 to 200 meters (Scholander,

1964). It has been shown that the airways of diving mammals are rein­

forced with a larger than usual amount of cartilage which, in some species,

extends to the openings of the alveolar sacs. Thus, the alveolar gas is

forced into the non-absorptive airways as the weaker alveoli collapse dur­

ing descent (Kooyman, 1973).

I M T" vm ^ 4 % f ^ W T<<~ ? A ^ • ••W V I \A W WL«>» >a/W IIIWW^I 1VNAW

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1971, 1973a). In addition, studies have shown that isolated sea lion

lungs empty much more completely upon compression than do dog lungs, pre-

KorSiiCa +ho uioaai vi.,ia \/c n f -r'oo X f\n Inmnc n nl 1 s r\c a 3 i-\X + r,3 c

- - /rv... ^ .1 1 \ C.C - _ _ ,_ - ' ill ui ic c, 1 » cu I 1 \L;cii I au 11 c L. C.I., 3/ J. ; . 111c uii iuiiuu uc 1 1 i cr Tcq ucu 8 blood of a deep-diving mammal and, thus, they need dispose of only a small amount of nitrogen during ascent. This helps to prevent dysbarism.

Kooyman et al. (1972) compressed seals in a hydraulic chamber to a depth equivalent to 30-270 meters (4-28 Arteri?! and centT?.! venous blood samples were taken during various phases of the compression process and analyzed for nitrogen tension. In all cases, N2 tension remained low.

This indicates that little of the N2 in the lungs was absorbed into the

blood.

It is imperative that mechanisms be present to prevent decompression sickness in diving animals, especially marine mammals which are known to dive very deep and to remain submerged for long periods of time. Sperm

whales are known to dive as deep as 1134 meters (Heezen, 1957) and Bottle-

nosed whales have been oDserved to remain submerged for 2 hours after har­

pooning (Gray, 1882). Kooyman (1955) has shown that Weddell seals can dive

to 500 meters, and that they may remain submerged for over 43 minutes.

Lung collapse during a deep dive also means that diffusion of O2 from Tina lr»r»/nc mtl mr\ n 3 / H T n ko n 3 T v* o/^ * 4- 3 4- 3r\no3v^C +K3T

few of the diving vertebrates take full advantage of the lungs as a

potential oxygen store anyway. Seals are known to exhale before diving

' hn"! a nriay , 10^.0; n n \/m a n a-r a 1 _ " G7 1 079 ^ _ anri rH-iv/inn Kivn'c 'n-iaccpn

1950) and reptiles (Andersen. 1951) are commonly observed to dive On ex­

piration. Expiration before submergence in deep divers may help to pre­

vent decompression sickness, or it may be necessary for buoyancy adjust­

ment (Andersen, 1955). Even in divers that do not go deep, exhaling of

A 1 y~ i c "Fv^^ni :ûn"r1 \/ conn Ko-rriv»^ c i : m o T-r i c I/nnwm -rna-r nTv»/ic k

s* V «iw^ » « V» * C u/ CZ . w I \Z ^ V* ^ I \y ' » i vw C * C * v kV ii k^tC» vCil VilCL vI M 9 slowly (Eliassen, I960; Andersen, 1953a, 1953b). White (,1970) reported

that diving alligators would not show a dive bradycardia until at least

part of the lung gas was expelled. However, Kooyman et al. Cl973b) report­

ed that penguins dive ?.n inspiration: rather than after an expira­

tion as in seals. It is also known that whales dive on inspiration

(Scholander, 1964), as well as sea lions and porpoises (Kooyman, 1973).

In these animals which inhale before diving, lung O2 stores may be a

significant portion of total body O2 stores and may extend the diving time

of such animals when the dives are rather shallow (Kooyman, 1973).

Pacific green turtles have been observed feeding at 290 meters under

the ocean surface (Landis, 1965). Berkson (1967) found that the brady­

cardia of submersion is accentuated in such animals when pressure is ap­

plied externally to the animal. In fact, from 28-68% of the time that

the animals were under 9-19 atmospheres of pressure, there was no cardiac

activity. This reduces the distribution of gases from the lungs to the

tissues and thus reduces the chances for decompression sickness. In ad-

ri 4 T 4 n "f- M c î»mnc 3 c r-r» 1 ! 3 m c a /^r\mn 1 of-o i -f-kn o n e

9-19 atm. This reduces the surface area across which gas exchange occurs.

However, even though equilibration of Nn tensions between I'jr.g air and

r\l Ç «oo\,'OV^ 5 -ri-s 4 0.3 in în or>'T«ov^O'^ ^r»o 3 ^ 4 X

artorv f n vonHoy rho f i ir +1 a ci Kronf i SI o f n ns ç amhr.l-in rha i n f Tny^

emergence.

The blood volume of diving animals is usually greater than for non-

divers (Scholander, 1940). Expressed relative to body weighty it has

I w# 11\.* Ill t ijw w k/ O Cktiiiw^v III Incite :iC» vwC; t i v C1 O 10 as in non-divers (Andersen, 1964). However, the O2 carrying capacity may or may not be greater, depending upon the particular animal species.

Oxygen affinity of the blood varies among reptiles, but appears to be

a i-oH i.ri +k -f-hû H an rxf AV* Ç1 I 1 nn T C hrvoç Ç diving habits (see Heatwole and Seymour, 1975). Seymour and Webster

(1975) found that hemoglobin (Hb) concentration and Hb-02 affinity in sea snakes were no different than for terrestrial snakes, and Mutton (.1958) found no consistent difference in hematocrit or red cell count between semi-aquatic and terrestrial snakes. Moreover, significant concentrations of methemoglobin occasionally observed in reptiles reduce the 0? storage capacity of the blood. For example. Rough (1959) found 14 to 21% methemo­

globin in the blood of 4 species of freshly captured lizards. Gaumer and

Goodnight (1957) found that Kb concentrations yere higher in the more

aquatic turtles but Burggren et al. (1977) could find no difference in

hematocrit or Hb concentrations between the aquatic turtle Pseudemys

scripta and the terrestrial turtle Testudo graeca. Wood and Johansen

\ V / "T / i\yutiVJ uiiuu u: ic lit I c nivi : 1 w 1 1 : 1 vj o : 11\^ 1 w v ~ f 1 oc fnaf :1 ri na mnç-înûv^ûn c a n A nf a f i nnc f n n i \/ 4 nn Thoco wny~((Ar

alsn rniinri fnaf lÎTpyrlç nonora 11 v hav/o similar hlnnrl r;^ nari ti

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which show an increased Oo capacity usually do so by virtue of an in­

creased hematocrit and/or cellular Hb concentration (Lenfant et al.,

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especially at reduced tauperatures (Guard and Murrish, 1973). Snyder

(1971) demonstrated that transport of O2 by reptile blood is limited net 11 only by the O2 capacity but also by the viscosity. Oxygen transport in active animals is best served by a relatively low affinity blood, whereas

O2 storage, which could be of advantage in animals spending long periods resting underwater^ is best served by ?. high affinity. Of course, the actual amount of O2 carried by the blood will depend on both blood volume and O2 carrying capacity. Due to the larger weight-specific blood volume of divers compared to non-divers, coupled with a larger O2 capacity in most cases, most diving animals store a larger amount of O2 in the blood

than do terrestrial animals (Andersen, 1965). This extra amount of Og,

however, only corresponds to an extension of the submergence diving time

of mammals of from 3 to 5 minutes based on predive metabolic rates (Blix,

1976).

It has been shown that the Bohr effect is more pronounced in the

crocodile and alligator than in the chuckwalla and gila monster (Dill and

Edwards, 1931b, 1935; Dill et al., 1935; Edwards and Dill, 1935). Thus,

in the crocodilians, unloading of 0, from the blood is facilitated while

i/ao T D/n ina nav*-t--r3 r r*v-kocc*'v«o 'Dfi ^ c I o) f a fcM 1 ^ cnnirin Ko nnnnTorî

out, however, that a large Bohr effect will retard Og loading from the

lungs during the progressive acidosis of diving. Therefore, the lung 0^

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nA aKl o 3r\ 4- r"r\ 111 X KQ A omr\ *nç*r-v*a'ron f ^ o\/rr:AT 1 anH Kc i"

1975). However, since the skin of sea snakes is permeable to O?, a low

arterial P02 (P2O2) would be advantageous to limit O2 loss to the sea

îAiSrav Has r'lA.T.l o s nri *sa\/T7ini 107!^^ Tlri ç a cci ;rnoc nf fhs f fho PH.

^ o *. 4" ^V» "'C : L"« T» ^ ^ ^ D i i 3 1 / 1 07 7 \

^ I « «m W ^ Q ^ ^ ^ ^ «mm ^ ^ ^ I ^ ^ ^ ^ ' arterial blood (PaC02) of about 7 torr (from 24 to 31 torr); this would increase the Pa02 at which

4" ko UK c balf c a ur*î "f h A _ ^ D _ ^ ^ K\/ Anl 1 — 9 t'A

The O2 affinity of the blood of diving lizards has been shown to be

relatively temperature insensitive (Wood and Moberly, 1970; Wood and

Johansen, 1974). This would serve to minimize the increase in O2 affin­

ity of the blood (decrease in P50) when these lizards enter water after

basking in the sun.

The muscles of diving mammals and birds (but not reptiles (Berkson,

1966)) are known to have a higher myoglobin (Mb) concentration than in

most non-divers (Scholander, 1940). It has been suggested that this is a

valuable store of O2 in permitting divers to remain submerged for long

periods of time, and Robinson (1939) estimated the O2 contained here to

be 47% of the total amount available in seals during submersion. It ap­

pears though that this store cannot be as important as first thought since ^ — f— A ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^^11^ I ^ ^ ^ # t ^ 5^ ^ ^ ^ u: ic \_f ^ : a 11 vi % * v uv vi ic * 11 » ^ itw , ^ v*.

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extremely important for muscle activity underwater for it would prolong

the time until the muscle must switch from aerobic to anaerobic metabolism

\ « % I l\.AX V.Qv*e I ar% 1 A

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stores of non-civers (Lenfani ex al., 197Ob; McrCaan and Ccrlton, 1977). 13

There are exceptions, such as the beaver which has a total weight-specific

O2 store less than man and about one-third that of the Harbor seal (McKean and Carlton, 1977). Despite the large difference in O2 stores, the maxi­ mum diving times for the Harbor seal and the beaver are 20 ?.nd 15 minuteS; respectively (Irving, 1964), It has been postulated that this similarity in the dive durations is due to the smaller weight-specific heart and brain masses of beavers compared to seals. During diving, the heart and brain use most of the O2, and in the seal these organs would deplete a greater amount of the O2 stores owing to their larger fraction of body mass (McKean and Carlton, 1977).

Comparisons between the O2 available from Û2 depots and resting O2 consumption have been made for a few divers (Scholander, 1940; Andersen,

1959a). From this data can be calculated an estimated dive duration, as­ suming the dive is dependent upon aerobic metabolism at the predive level.

Comparison of this value to the observed dive durations of the animals shows that the diving vertebrates are able to remain submerged for 2-4

•i' ^ r' 11 t f 4- I'COO ^ Û ^ T^"?C >0/^ I I I I I IVI II V: I I « V ^ fW V» I I ^ w the postulate that enough energy is derived from an increase in anaerobic processes to fully CG~pensate for the ci-inished O2 consumption (Dill and

^ J. _ « yj ^ ^ \ M ^^000^ ^ ^ WS V» ^ \ r liwy'v'wVCl y TNIWIICO \ ^ W .V Z/ y • is^Vs^vu vLr LfVL » V. * I rriQ-^a11 w v* -i cm 1.0rvckO c > ;,u^ /- oXV* V* 1w 1 Iv» i*111^ nrt cOw4 1 ' Kmc> I ^ 4I wr\nI « » T vr\\ ^ ûv*-r mnn-!-ç umov^û» * * » >.» * H. r r\ nc t :mr\ t-t r»n has been measured before and after diving have since shown that in ducks and seals (Scholander, 1940), the manatee (Scholander and Irving, 1941), and the alligator (Andersen, 1961), the excess intake of O2 after a pro-

J Viiycu u » V C ndo 1 c;) ^ una;» CA^CW uCu, COj^Cv-. :û»ijr miCn Ui IC vujvC oO. ^ Civ-pN-pUni — paniea by little activity or struggling. Furthermore, it has been shown 14 that ducks experience a decrease in body temperature when only the head is submerged. At the same time, changes in the peripheral circulation in­ dicated an improvement in the insulation. A decreased body tenperature cccLirrip.g at the same time that insulation is actually increased can only indicate a lowering of total energy metabolism (Andersen. 1959a: Hoi 1en- berg and Uvnas, 1953). On emersion, body temperature fell even more than during the dive. This was probably due to the redistribution of the core heat to all parts of the body upon the re-establishment of a general cir­ culation. During the dive the slowed circulation had conserved the heat in the body core (Andersen, 1959a, 1954). A decreased metabolism has al­ so been reported in frogs (Poczopko, 1959-60b), toads (Leivestad, 1950) and turtles (Jackson and Schmidt-Nielsen, 1965) during submergence, and in fish when exposed to air (Leivestad et al., 1957). All these findings support the postulate of Richet (1899) that total energy metabolism is re­ duced during submersion.

Jackson and Schmidt-Nielsen (1955) thought that the decreased metab-

,w* 4»1 t.»OC ***0 I 1 1M f W V 1 i ^ 111 U Wll 111^ t ^ ^ I I w ^ 111 ^ W I W* W W VT\A W w# ^ W «VVVW* W w V ^ V » wv ^ »

They found that predive ventilation with pure O2 delayed the onset of the metabolic depression (which resulted in a reduction in heat production

— k — !^ O r\C/\ T ^ ^ T /- V ^ z ^ ^ 4.-î Ç U ^ rN ^ 1 Ci U L* O W /O J » ill ^ ^ VJW g O & ^IX ^V/ 1I Vm. /\L* vI ^ I W Nmp

olisr, and body stores of O2 in submerged P. saripta. He found that dur­

ing the first 20-25 minutes of submergence, heat loss remained at the pre­

dive level despite the fact that lung and blood O2 stores were being rapid­

ly consumed. This was the time required for the lung O2 pressure to drop

^ .. — / n^ ^ \ ^ L. ^ On «M» «a » « ^ ^ ^M ^ ^ UV j UZ V I 1 U ) VC : vaiUC \ cv —W: 1 Jm W C1 VI ic mCAw m * * :w vC ^ iC uCCiu 15 loss declined to 40% of the predive rate while the Og reserves were ex­ hausted. Normal metabolic rate cannot be maintained once the Og critical pressure is reached. For the rest of the 4 hour dive, the heat loss gradually' decreased to 15% of the predive rate while the Oo reserves re­ mained low (about 1%) and constant. This indicates that anaerobic metab­ olism cannot continue indefinitely, even in the turtle. Body temperature decreased in parallel fashion to heat loss. The tissues initially re­ stricted from the circulation during the dive will be the first to suffer a decrease in metabolic rate. Within time even the perfused tissues will

become anoxic as the O2 supply decreases. At this time the animal must

surface or vital organs must then become dependent upon an anaerobic

source of energy. Thus, Jackson (1958) demonstrated that metabolic rate

falls during diving as a result of a reduction in tissue O2.

Kooyman (1975) has calculated that a penguin should be able to extend

its underwater survival time from 2.5 to 6 minutes if aerobic metabolism

is decreased by 30% during a dive. The weight-specific oxygen stores are

v^rs— Afo/i-T3 nonmiin ann a c:op1 nrA f.np sAA 1 rA n û1vP

for 70 minutes, it is surprising that the penguin cannot dive for corres­

ponding periods of time. During a dive blood lactate in the penguin in-

4 4- In <3 c? 1 Tniic mn AAn nl \/ f1 nw< TflY^niinh rhp

muscles of penguins than seals during a dive and thus more of the O2 stores

are utilized by them (Kooyman, 1975).

Eliassen (1950) has taken exception to the idea of a decreased metab­

olism during diving. However, his argument is based on experimental dives 1 3 c + 4 Mm r\n" \/ 1 cQ»-nrv-ic Wo rnnciriovc i f vpsconphlp fhaf i f f hp mP+A -

uu 1 ; C ra uc i b r ca i i r cuu(^cu, uiicii : u luuiu uc osuc ivji nuiiucii u , 16

1-2 minutes duration as well as for prolonged ones. The observed meta­ bolic decrease is probably a response to the cardiovascular changes which channel O2 away from metabolically active tissues such as muscles. Such circulatory changes usually take longer than 1-2 minutes to develop, especially during a forced submergence (Andersen. 1966).

Many experiments have been done with diving reptiles (Dill and

Edwards, 1931a; Johansen, 1959), birds (Orr and Watson, 1913; Hiestand and Randall, 1941) and mammals (Irving et al., 1935; Irving, 1938b) in which the sensitivity of respiration to COg was investigated. In some of

the studies the animals had been anesthetized or decerebrated (Orr and

Watson, 1913; Irving et al., 1935; Irving, 1938b). Usually 5 to 20% CÛ2 was given to the animal in the inspired air, even though Johansen (1959)

gave 25, 50 or even 100% CO,. Many of these reports show decreased

respiration, or only slight increases in respiration as the result. Data

of this sort have led workers to believe that insensitivity to COg or

inhibition of respiration by CO2 are normal characteristics of vertebrate

I. 1 H Ko r» rs nr» onf "T T nn f H _ u/niiiri

increase to such high values during diving (Andersen. 1966). Analysis of

lung gas fro~ alligators has shown the CO2 concentration to be well-below

^ 3 ^ /"> ^ C*' ^C "* ^ 1"nû 11 IMn c

of ducks and seals have also never been observed to contain as much as 10%

CO2 even after prolonged dives (Scholander, 1940; Andersen, 1959a, 1959b).

McCutcheon (1943) reported that in the diamond back terrapin (turtle),

lung CO2 increases progressively from 4.7 to 12.9% during dives of up to

<^0 minutes. Basoglu (1951) "^ound a lung CC2 of 19 = 8% in a pond turtle.-

I / V*/-N-1 CO 3 Q IV» m 4 o "T no iimrr Pi 17 were less than 1%. Berkson (1955) showed that after 1 hour of diving in a sea turtle, tracheal 0^ concentration was less than 1%. Carbon dioxide in­ creased and leveled off at 8-10% during the dive. The animals could re- iiiaii. unuc.vvQcer fcr 5 hours after the Q, was depleted.

More reccïcently, the relationship between respiration and CO concen­ trations has been re-examined. Robinet al. (1953) compared the ventilatory response in the seal and man when breathing 4, 6 or 10% CO2 in O2. They showed that ventilation increased much more in man than in the seal when the PCO2 was increased. However, respiratory minute volume increased in every seal tested over the whole range of PCO2's studied (40-80 torr).

Andersen and L0v0 (1954) gave ducks gases ranging from 0-15% in CO2. The respiratory minute volume increased in every duck except one which showed a decrease above 5%. The other ducks showed a doubling of the minute volume when the COg concentration of the inspired gas reached 7.5%. It has been shown that alveolar ventilation is doubled in man when the PCO2 rises by 0.2% of an atmosphere (Haldane and Priestly, 1905). Therefore,

une auuvc c yiuuicS 5,10» ^ûnaû L* ^ ^ ^ûr.£ X». rcjp;r^tcry response or ai vers lo

is less than that of man and terrestrial animals. However, they also v^tcci ij OJiuyv UMÛ u v/w2 stimulates respiration in seals and ducks over the

range of hypercapnia experienced during submergence (Andersen, 1955).

It has recently been shown that 6% CO? increases the respiratory minute

volume in sea turtles by about 2-fold: the response was mediated solely by

an increased tidal volume (Jackson et al., 1979). Jackson et al. (1974)

showed that the turtle p. scripta responds markedly to inspired CO, up to

at least 6%. Tnis was achieved by approximately equivalent increases in

tidal volume and frequency. 18

Reports on the respiratory effects of hypoxia in divers are few. Orr and Watson (1913) reported that, in ducks under ether anesthesia, in­ spired gas containing less than 10% O2 increased respiration, especially when 5% or less O2 '/.'as given. However = when ducks are submerged for 15 minutes» half of this period is endured with less than 5% O2 in the lung gas (Andersen, 1959a). Therefore, a low O2 content in the inspired air does not impose an immediate threat. Seymour and Webster (1975) found that lung and aortic O2 contents converged until just before voluntary emergence in sea snakes, when the lung PO2 was about 50 torr and the blood

PO2 was 34 torr. Thus, only about half of the available O2 had been used;

the arterial blood was still 44% saturated. Blood lactate concentration and blood pH remained relatively stable. Spontaneous breathing also oc­ curs with a considerable store of O2 remaining in the turtle cheiys fimbriata

(Lenfant et al., 1970a). However, the diving lizard, varanus niioticus,

uses about 90% of the blood O2 before emerging (Wood and Johansen, 1974).

Ackerman and White (1979) demonstrated that the turtle P. scripta would

iw sz-'o I * Dfl. VV In •rnv^'rtûC 4 T

appears that a lung PO? of 20-26 torr characterizes the critical PO?

(Bennett and Da\^'son^ 1976). However^ during forced dives in turtles;

Ui Is.. w 2 I C {V V » ^ ^ O wiiCkii ^

1O C1 • D «a C .1 3 1/ C 10 ^ Q ^ X ^ X 9 Sv I vI *; V Li ^ V I & ) X w / «

Boyer (1966) recorded respiratory rate and amplitude in various rep­

tiles over a range of Og tensions (room air to 15 torr). Snapping turtles

showed progressively greater rates and amplitudes with increasing hypoxia,

i.fX 4 1 A Kiill /-îôcov*+ 4/-tiianac a nn an % 11 4 ma -rnv» c nn\i/o/4 an 4n/^y«oaco 4 n

^ L*. . X ^ ™ X X 1 fS A \«» ^ ™ «/* ^^ ^ ^ V M ^ ^ ^ I.I ^ ^ ^ —s ^ ^«« A I vw s.* C ) wwtv I 1 V V * C V I 11w ^2. 19 consumption was maintained at a constant 1eve! in the turtles at all 0^ tensions, while at 75 torr (10% Og), the other reptiles began using less

O2. Heart rates increased with hypoxia. Therefore, the above studies shov.' that hypoxia stimulates respiration over the range encountered in diving reptiles.

During prolonged dives, asphyxia may become severe. Large amounts of lactic acid are formed in the muscles, but only small amounts appear in the blood. When the animal surfaces, however, blood lactic acid concen­ tration immediately increases, and the blood pH follows the concentration of blood lactate. This response appears to be similar in seals, ducks, alligators, snakes and man (Scholander, 1940; Andersen, 1959b; Andersen,

1951; Murdaugh and Jackson, 1962; Scholander et al., 1962b; Andersen et al., 1965). Berkson (1966) reported the same phenomenon in the marine

turtle, however, Jackson and Silverblatt (1974) found the blood lactate to

steadily increase during diving in P. scripta with no increase in concen­

tration upon emersion. Moberly (1968a) reported that blood lactate in-

/"* c •+»v^ /^rri I \ / I « V» n n \ / a c f k» O 1m I 3 fia

Acid-base status during diving has been analyzed in ducks (Andersen

et al.; 1965)= A 10-13 minute submersion caused a decrease "-n Oo satura-

— —I .y,I V— W —/ V/ /O ^ V ^ ^ V» ^ mc/^ /'J m "T u»^ P ^ V \.M w Piw* ^ linn "T c

bleed PCO2 increased throughout the dive and sometimes reached 2 times

the resting value. The acid-base pattern depends, in part, on the ability

of the animal to retain its lactic acid in the muscles during a dive.

Upon emersion, vigorous ventilation causes a rapid drop in the bicarbon-

^/Mr.or>-r V* a "T-i y> a y\/4 ori11-r 1-? -r *? nr» n-r hi Anri ann lîjnn na c Toncinnc Thûv^o —

I W 1 C ^ ^ VCt VW ^ Cl I I kV ^ 111 VS/ ^ ^ ^ ^ y I I « I V * Ct * 20 respiratory acidosis after the dive; 2) later, a combined respiratory and metabolic acidosis; and 3) metabolic acidosis in the early stages after emersion.

Jackson and Silverblatt (1974) investigated the acid-base status of the turtle p. scripts during and after diving at 24°C. Plasma lactate concentrations reached high levels during the dive with very little in­ crease following emersion. Arterial pH reflected this change in plasma lactate. The turtles were anoxic for the majority of the 2-4 hour dive and, therefore, lactate was probably being produced by most tissues. The lactic acid was being buffered by bicarbonate and this was promoting an elevated PaC02. This elevated PaCÛ2 caused extrapulmonary CÛ2 loss to occur thereby making the acidosis less severe. In 1976, Jackson showed

that the turtle loses CO2 to the water during a dive which minimizes the

acidosis of apnea. This loss is especially prominent because blood lac­

tate increases during the dive in the turtle rather than after. During a

4 hour dive, ?aC02 increases to about 4 times the predive concentration

c'psorr.fj p*i irni n;=5 rinn fn fho wA fax" _ ."î^ric^înn ;^nn 1 vArnl H ft !

further showed that hyperventilation following the dive caused the PaOg

to rise above normal values within 30 minutes. The pH was back to normal irA Kn i *f Tf 1 c tnnn -hna-J- -fiv^ç-r '50 m*:nii-roc -rrxl _

lowing emersion, peak ventilation was occurring despite the fact that Pa02

was already above normal and PaC02 was at or below normal. At this -:ime

the hyperventilation must be due to the acid pH. Recovery of blood lac­

tate levels was much slower (20-24 hours). Some of the lactate vv-as ex- The buffer capacity of the blood of good mammalian divers is signif­ icantly higher than for non-diving mammals (Lenfant et al., 1958, 1970b).

This minimizes changes in blood pH during and immediately following a dive. Hov/eve*"; Seymour and Webster (1975) found the buffering capacity of sea snake blood to be similar to that of land snakes. Buffering capacity of aquatic turtles is generally higher than in terrestrial tur­ tles (Robin et al., 1964; Lenfant et al., 1970a). Plasma bicarbonate is generally 2-3 times higher in turtles than in other reptiles and as a re­ sult, their blood pH is relatively alkaline (Dessauer, 1970). However, sea turtles do not show higher blood buffering capacities than their ter­ restrial relatives (Berkson, 1966). It has been reported that no consis­ tent relationship exists between blood bicarbonate concentration and div­ ing within any reptile group. Any possible relationship between blood buf­ fering capacity and diving behavior in reptiles may be obscured because even non-diving forms exhibit extensive powers of anaerobiosis and most are tolerant of markedly reduced blood pH (Moberly, 1958b; Bennett and

1131."G7v. MonnQ-r-7- 3mri iirnf 1077) If 1c Icnnwn triM i. inûst nSt.— ural dives of reptiles are aerobic (Seymour and Webster, 1974; Ackerman ar.d White; 1979: Seymour. 1979) and some can exchange gases with the

'•1^ / 0/-\ /"s 4- "O^O* C-Ï v-»rt "îç • Pal !/ 4 m Inam 107ZL^

Freshwater turtles possess a considerable volume of coelmoic fluid with a pH more alkaline than plasma and a bicarbonate concentration about

3 times as high (Smith, 1929). It has been suggested that this fluid might serve as a repository for lactate generated during long dives

^ ^ ^ L. ^0^0* ^^ ^ 1 0^ \ ^ «m « y / 1 07^ \ T* 1 3 1/ O Q n 1 _ y ^I I I I I : ) «L ^ ^ ^ VL * * ; .k V TT y ) h/v* \ ^ ^ * "i y ««•••

verolaiu (1974) have snowr. inai lactate Goes nor accumulate in this 22 coelonic fluid during long dives in P. scripta, even though blood lactate

concentration may increase as much as 37-fold.

Cardiovascular System

It was found over 100 years ago that bradycardia developed in ducks

during diving (Bert, 1870). This has been confirmed for almost every div­

ing vertebrate investigated (Scholander, 1940; Scholander and Irving,

1941; Irving et al., 1941a, 1953; Grinnel et al., 1942; Johansen, 1959;

Poczopko, 1959-603; Eliassan, 1950; Harrison and Tcmlinson, 1960; Wilbur,

1950; Andersen, 1961; Murdaugh et al., 1951b; Bel kin, 1954; Eisner et al.,

1954; Jones and Shelton, 1964; Catlett and Johnston, 1974). It has also

been observed in non-divers, including man, upon submergence (Scholander

and Irving, 1941; Irving et al., 1942b; Olsen et al., 1962a, 1962b;

Scholander et al., 1952b; Irving, 1953; Wolf, 1954; Eisner et al., 1955b;

Campbell et al., 1969). The reptiles which have demonstrated this re­

sponse include crccodilians, freshwater and marine turtles, terrestrial,

semi-aquatic and marine lizards, and terrestrial, semi-aquatic and marine

snakes (Johansen, 1959; Andersen, 1961; Murdaugh and Jackson, 1952; Bel kin.

1953b; Bel kin, 1954; Bartholomew and Lasiewski, 1955; Berkson, 1965; white

and Ross, 1955, Rough, 1973; Wood and Johansen, 1974). It should be noted

that, although most studies show a diving bradycardia in turtles. Mill en

et al. (1954) reported thai "bradycardia, wnich is an important aspect of

Trip^ taWW nv*ninnna/H sm t w » t t ^ n w*a mSifl W* «a Vk 4-4W < ^/-* rv»5rrw2.l<-« Ii vwt H a IM * ^ IIW ^ V ^^ u I 1 { (

fr.p T! irfl p**

The bradycardia is reported to be independent cf underwater physical

^ y ^ —» « V g ^II) ^ ^ ^ y # t Iw TV ^ V I ^ 11 i ^ CII 1^ ! O O 23

(1956) indicate that when forcibly submerged turtles struggle to surface, heart rate increases for a short time. The same thing occurs with sub­ merged Pacific green turtles (Berkson, 1956, 1957) and sea snakes

vncauwujcs/ « I a.. ±y/oj*

The rate and extent of bradycardia may depend upon whether the animal is forcibly submerged or if it is naturally diving. In the alligator,

the heart rate slows down more rapidly, but then remains at a higher

level if the dive is natural (Andersen, 1951). On the other hand, Johan-

sen (1959) observed an 85% reduction in heart rate within 2-20 seconds

following forced submergence in a water snake. The turtle p. concinna,

when voluntarily diving, shows a 41% bradycardia immediately upon sub­

mergence (Belkin, 1954). However, during forced dives in p. scripta,

predive heart rate persisted for 8-10 minutes (Jackson. 1958), 8-180

minutes (White and Ross, 1965) or took anywhere from a few to 50 minutes

(Penney, 1974) to decrease following submergence. Heath (1978) reported

that freely diving tiger salamanders showed little bradycardia compared

"CO TOrCSG Q ! YKb . ! Si! LU C\J !il ! nu LCS WCr C I CUU l t cu i u: i u i i ucv c ivjwiucii u u i

the bradycardia in the latter case. Irvine and Frange (1975) found brady­

cardia to be immediately elicited in voluntarily diving water snakes.

During forcea dives it took longer to develop. Similar conclusions were

reached by Jacob and McDonald (1975) who studied 4 species of aquatic

snakes. The gradual development of bradycardia in many forcibly sub­

merged animals may be an artifact of the involuntary nature of the dive.

The rapid onset of the decreased rate during natural dives, and its

rapiû reversal curing rne firsz oreatn after emersion, argues against 24 asphyxia as a major stimulus for the induction and maintenance of the bradycardia (Johansen, 1959; White and Ross, 1956; White, 1969, 1975).

Lund and Dingle (1968) found that the heart rates of unrestrained frogs were lower than those of restraineu animals. Restraint stresses the animals; heart rate and presumably metabolism increases. With forced immersion, bradycardia follows because restraint and immersion imposes demands which cutaneous respiration cannot meet. Under natural environ­ mental conditions, when the animal is not stressed, bradycardia may not occur. Lillo (1979a) found that freely diving frogs would show a dive bradycardia but that it was less than that developed if the animal was forced under. It was also slower to develop. He ascribes the difference

in the magnitude of the heart rate reductions to be due to the shorter

times that the freely diving animals remained underwater. Heatwole et

al. (1979) report that during voluntary dives, sea snakes remain aerobic

and that bradycardia does not occur. Graham (1974) has shown that such

snakes can get O2 cutaneously during a dive. Seymour and Webster (1975)

found no relationship between submergence and heart rate in bea snakcb

-t k"! v* o î-vv* + o s

when the totally-aquatic Elephant Trunk snake voluntarily submerges. He

argues that since apnea (with associated bradycardia) and anaerobic

metabolism are basic features of reptilian physiology, physiological

vw w iwtio w/ là i w}ll^

basic features. The reptiles major adaptations for aquatic life are

probably behavioral (willingness to enter water and dive, modifications of

methods of locating and capturing prey, etc.) and morpnological (flattened

body, nostrils at tip of snout, lack of ventral body scales, etc.). 25

Anticipatory increases in heart rate have been observed prior to voluntary emersion or breathing in seals (Eisner, 1955; Kooyman and Camp­ bell, 1972), turtles (Boyer, 1953; Bel kin, 1964; Burggren, 1975) and

C -I 1/ r» / Q yx * ,r» T «m ^ / 1 O ^ \ ^ oii

It has been reported that animals which do not exhale prior to sub­ mergence develop diving bradycardia only slowly (Eliassen, 1960; Murdaugh and Jackson, 1962; Andersen, 1953a, 1953b; White, 1970). This may help to explain the variation in the time of onset of bradycardia.

A natural dive may differ in its effects from an escape dive. Unre­ strained Caiman crocodiius shows a much greater bradycardia when diving in response to an approaching person than when doing so spontaneously (Gaunt and Gans, 1969). In fact, during voluntary diving heart rates decreased only by 1-2 beats/minute, or not at all. Similar responses were observed

Ml LI (c luuGiJG lyooù J âîîu âiilyâuùr CT; cû â i . . Mppû r-

3 4" 1 O a c "T Titi r* Ovyius. I iCo uitxu : i IL* I «u g ^^ / w / . uu^uiiv Uiiva

(1959) also reported that the classical diving bradycardia would occur if the animals were disturbed when outside the diving tank. Bel kin (1953b)

reported that fright may produce apnea and bradycardia in reptiles.

Bel kin (1954) has shown that the long-term mean heart rate of the

turtle ?. concxnna approximates more nearly the rate associated with diving

than -char occurring in air. Tne turtles woula voluntarily remain suomergeo 26 from 4-141 minutes (mean of 63 minutes). Only 2% of the time was spent at the surface breathing. He also showed that the O2 stores could allow 2-3 hour dives without any physiological compensation. He, therefore, argues that the variations in heart rate should not be considered as indicating submersion bradycardia, but rather as reflecting a breathing tachycardia.

The function of the tachycardia would be to achieve a rapid equilibration of blood and tissue O2 and CO2 with that of lung gas during the brief periods of time spent at the surface breathing.

In the seal, unrestrained diving results in a more profound degree of bradycardia than when the animals are forcibly submerged (Murdaugh et al., 19ôlb). This is, of course, opposite to what Andersen (1951) found in diving alligators.

In seals, bradycardia may be induced by sound or visual stimuli when out of water (Irving et al,, 1942a). On the other hand, it may not devel­ op even when the seal is completely submerged, provided the animal is free to reach up and breath whenever it wishes. Therefore, there is apparently

A ^fr-nnn ncvrnn"! nnir-pl f^rfnr invnlvpn ^ h?"; he>pn ('f^iïiOris !;rrt î.ëd fûr CrûCO- dilians by Gaunt and Gans (1959).

White and Ross (1965) showed that the bradycardia of diving would de-

mrvvQ v^an-irl"; \/ 4 ri oc fkaf 'nan alraaHv HiwoH t.n fhin 'hho ny»ororl4nn few minutes= ThuS; previous diving history may also be a factor which de­ termines the physiological characteristics of submergence. There is general agreement that the cardiac slowing upon submersion in reptiles, birds and mammals results from vagal stimulation of the heart, since vagotomy abolishes the response (Harrison and Tcmlinscn, 1950;

rvnii p»»rtr» ot a i _ ' "fO ' 0 ' . ' \ CUiUVIHC '«nCVCii iC 27

bradycardia as was initially shown by Richet (1894b) for ducks (Murdaugh and Jackson, 1962; Belkin, 1953b; Bel kin, 1964; White and Ross, 1966;

White, 1969; Lin, 1974). However, Johansen (1959) found that atropine

nnf + + ahnlicl-i -rioo -in çr.a lroc;

This contrasts with the study of Murdaugh and Jackson (1952) in which div­

ing bradycardia in a species of water snake was shown to be vagal in ori­

gin. Heath (1978) found that atropine would only partially block the div­

ing bradycardia of tiger salamanders.

Even though bradycardia is also observed in frogs during diving,

Jones and Shelton (1954) report that it is not vagally induced. When bi­

laterally vagotomized frogs were submerged, heart rate fell to the same

low level as in controls. Curiously, the predive heart rate of the vagoto­

mized frogs was lower than in the intact controls. This is strange since

section of the vagi generally produces cardio-acceleration. The authors

explained the bradycardia of the vagotomized frogs as due to a decrease in

sympathetic tone even though they also remark that "such a possibility is

i t» ^ \ f ^ v —» i "3 3 ^4 (YV^t I WV I W I I V. • * 1 Mit VA> VS» • I I W Vf « * I S./ I *

fna\/ c'^racr fnar -rno 4 c Trc nf n acnnwYir' ot top r

rirorflv nr fno no% —

J. u J id 6 L;cc ; 1 ucu ux&L, v u: .c : ciii--' 11 . u * a ; ;i> a i iu b i iuv\ a i m i i à i

uc V c ; u JCU U)V:ny u; uiC i LVi) c..»u uu!icz> ) z2u/

Lund and Dingle (1958) found that in restrained frogs, 2 types of diving

bradycardia would occur. A rapidly attained bradycardia could be abolished

by atropine or bilateral vagotomy, and thus was of vagal origin. A slowly

3t*"r3":non %;/-» î r" m -..oc r\ -f \ / 3 r" 31 wf/miln

also occur. Lund and Dingle felt that "che slowly developing bradycardia 28 was due to asphyxia (hypoxia and/or hypercapnia). They suggested that asphyxia may act directly on the heart, that it may act to decrease sym­ pathetic activity, that it may act on the central nervous system as a

Av* T-f- ma>r :: r- f p 4- 4-ko ficsuo 1 ol K\/ T n — creasing the concentration of metabolic products. Though both forms of inhibition of the heart may occur in any one dive, the form predominating was dependent on temperature and season. A seasonal variability in the

tonic vagal discharge also occurs in the toad (Iriuchijima, 1959). Lillo

(1978) could find no evidence that diving bradycardia in frogs was medi­

ated reflexly, but rather that such changes in rate were developed in

response to a decrease in blood 0? tensions. However, in a later study

(Lillo, 1979a) he found that atropine fully blocked the bradycardia of

diving in frogs and that the sympathetic system was not involved.

Lin (1974) found a 64% decrease in the heart rate during experimental

submersion of white rats. This bradycardia resulted primarily from an

increase in parasympathetic tone, but a decrease in the sympathetic tone

cxi^u icu. 1 : v uu uiicu w/ o iiitniv.ioiVi/M>

V C : J' : : 's,' : : : 4: %Yf -,:::y V.~ L.' : jr C : 'u : : : : v. ^: î ^ -r]r\ "• mn v nor^ov*..* s#

W^li^= r\r'r^\-.v>c « « -r1.» nI « -roo « II \/n rvr1 ^-'"A \/ mn\/omon"hli«v » ** OT A^ 1« w g

^rooa: AiTitc; 1202:m ^ ^ ^ f-sDuuier anaI —.ay,or, • ±5/0: ourggren, /»> ~7 r~ T^rvine • ana1

3-, 1 r-.-j c . • --"1- \ — : ^u- r:ci:yc, 12/u, \^z>i zic. j .uu:;u u.iai,, iii uuiiiiuya, une

immediate increase in heart rate upon emersion was due to a decrease in

vagal tone. The sympathetic nervous system was not involved. He also

*-» /"m . i/'\ ^ ^ 4- i /-» c «.«oc *" SI I wwc I CiCUbC :I LVI.I :i v /\ 1 ui **ui) i

ing the animals into an atmosphere low in G2 gave the same responses as 29 emerging them into an atmosphere of air (Lillo, 1979b). White and Ross

(1955) showed that emerging a turtle into a 100% CO2 atmosphere did not al­ low a reversal of the diving responses. However, they also demonstrated

— —uo 4-11'/^-j-1 ci c"oc 100^' m.. wa< hrowpn just as rapidly as if it had surfaced into air. Therefore; it appears that the diving bradycardia may be remitted upon emersion even though the animal is still hypoxic. However, hypercapnea may prevent the in­ creased heart rate.

The bradycardia of diving is due to a prolongation of diastole. The electrocardiogram is thus characterized by an increased T-P or T-R inter­ val (Johansen, 1959; Andersen, 1951; Bel kin, 1953b; Rough, 1973). Other changes in the EKG include a progressive lengthening of the P-R interval

(Johansen, 1959; Andersen, 1951; Pough, 1973), eventual disappearance of the P wave (Andersen, 1966), and an elevated T wave that sometimes appears diphasic or inverted (uonansen, 1959; Andersen, 1955). Johansen (1959) ascribed the T wave changes to changes in the concentration of CO2 in the

— —..—, j — — — '. — ^ ^ ^ f ^ 'z /j ^ o ««"x ^ u wiiic i y cu ii :a .%c . uguuu/ wjiu \ j.^ j 1 v w * ww «-.c. crease in 3 of 4 aquatic snake species curing submergence. The fourth species snowec no change. There is no change in the P-R interval during u,v:xy 1 ;: u.'ic: a.iiycuu; iv : !uu ; , j.'SOU j. i i.c iuyycio

hyp£r.

tion of plasma potassium as much as 3-fold in ducks during S minutes of

submersion. The changes in plasma potassium associated with diving largely

follow the same pattern as those 0- lactic acid and pH, reaching a maximal

V ^ W I i ^ r<-^-r-ov^« W • omo«^4 . • v^c 4 r\r ^ V Sw# .V . ^ ^ * . < . np rvo i J ^ i P.T i U^ PHC^ ^ 0^

cl c ci i ^ Vw c- -i-v V* ic <- 111— ^w r- ^ /"M. ' C: » ' C, 5 i v»» w»»s» •L/ uf?>/o'**«»» »»• • ^ w* ^ ^ s»». «.•> tt r\o^ n- 30 emersion despite a maximally elevated plasma potassium, and the P-R inter­ val is shortened in correspondence with the postdive tachycardia. The T wave may remain elevated and peaked for several minutes (Andersen, 1955) or

-f-loû hi wo to ^ pffv^tonçlv/

Bel kin (1964) reported that the T wave would decrease in amplitude during

voluntary diving in the turtle. This is the reverse of that seen in other divers, Johansen (1959) showed that the QRS interval increased 25% during

forced submergence in the snake. Heath (1973) reported a change in the

amplitude of the EKG in freely diving tiger salamanders, although he did

not specify the direction in which it changed. Berkson (1965) noted that

the EKG amplitude decreased during diving in a marine turtle.

In alligators during submergence, a transient arrhythmia would always

occur until the diving bradycardia was developed (Andersen, 1951). The

same thing occurs in snakes (Johansen, 1959) and frogs (Jones, 1968).

Arrhythmias are commonly observed in human divers (01 sen et al., 1962a).

Such periods of cardiac arrhythmia occur in both voluntary and forced

u j v ci> •

The length of ventricular systole (q-T interval) increased 51% during

i n a an-n 1 - n f .Irs iqnq^i

0u u : i I Uu!iu u: io. u u: :c y- ; 1 j » i-c ; v c i ixu; ccacu in w : uu uo. ; i » y uiv —

liiL, :>! id xc:). uavuu aiiu nuL/unaiu \ / \j j icvvi ucu une i\- . :nuciv&i 1:1-

crease during diving in 4 aquatic species of snakes. The q-T interval is

known to be rate-dependent (Bazett, 1920).

d ^ 1 !/ -» i 3v^v^/-nc"^ a /n x : 1 n n i T\ - ' ; u 1 v* 1 * v.aii\u w ^ w «

voluntary diving in the iguana. 31

Boyer (1956) found that hypoxia increased the heart rates of reptiles.

In lizards, it decreased both conduction (P-R) and repolarization (R-T)

time and in snakes and an alligator it decreased the conduction time.

1t-a- U iiQ^ M wvfs i. « wcCi««is I I CO, i i -t.UMC*. l»i ^ u v; iC /"4 — k/,v* Ci wj/-! 1 f ^ ^ v* /"i ^ ^ wii*jr^ n \ / o N-. ^• o™ iT.ent of the overall cardiovascular response to diving. A picture is

emerging that in all essentials substantiates the physiological responses

envisioned by Irving and Scholander more than 40 years ago.

The relationship between the degree of bradycardia and the period of

underwater exposure endured by seals was studied by Irving et al. (1941b).

They found that the earlier the diving bradycardia develops, the longer

the animals are able to extend their O2 stores. This does not mean that

the decrease in O2 consumption simply depends upon heart rate, as they

subsequently pointed out (Grinnel et al.. 1942). Obviously, the heart

will consume less O2 if its rate is suddenly reduced, but this alone does

not explain a prolonged extension of the 0, stores.

Further research showed that, despite the reduced heart rate, arterial

uiuOu sr; une Feiiiur'a : ar'Lèrv wâS wcl ; iTidl ûtâl ilcd ( I-'V lily cû âl .,

y». 1 ^ . w-v» 4» oc ^ a r\v^oî2t~j*>_ u . vc ucovc; jucu ^;auuG;ij' & i cvj acuac») w wi w y u « j' w* « >-*-«. #

ine air. Tne large increase in stroke volume which would be necessary to

compensate for the bradycardia and explain the slow descent of diastolic

pressure was dismissec, and they concluded that "a large part of the pe­

ripheral circulation is probably restricted as a unit when the heart slows.

f ; i ! ^ liiL- ease ! Î ! jJC •: l yiC • c. ! u; UC ; JCvC; uco : v » iC

extreme oradycarcia. 32

Regulation of blood pressure has been studied in avian divers

(johansen and Krog, 1959; Hollenberg and Uvnas, 1963; Johansen and Aakhus,

1953; Butler and Jones, 1971). Johansen and Krog (1959) showed that mean

(I I uci iQi in uuc Nauv. ai-» v*4» uci /-\v* 1 i a T» 1 i pressure fell by as much as 25%. Hollenberg and Uvnas (1963) found that mean arterial pressure increased on the average 17% during submergence in ducks. All dives lasted 1-2 minutes. Johansen and Aakhus (1963) reported a fall in mean aortic pressure in ducks for even short dives lasting 40-60 seconds. Butler and Jones (1971) found changes in arterial pressure to be variable in diving ducks; there was either no change or a slight de­ crease in the systolic, mean, and diastolic pressures. Eliassen (1950) found that puffins^ cormorants and guillemots maintain arterial blood pressure during a dive, despite the bradycardia. Jones et al. (1979) report that mean arterial blood pressure die not change when ducks were submerged for as long as 250 seconds. Heart rate fell by 78%.

Srit;• LL-ïî end'jurieb (1955; T'e^jurc tndt drceridl blood pressurcb ucureebe

uv iju uicoaujc I ci 1 ixv. c unci., uv i .v vicaauic, uuciciuic) puioc — su"e decreasea curing submersion. However> uillo {1979a} reports pressure

to be maintained or slightly elevated in frogs during a 25 minute forced

r.T\/û urforial ç — n: : nr! fn hn rzfrar wnll-msinfaincH 4 n f no

xV. 4I »V / 1I y-*I I ny uu , u I C ^ A i ; ) ^c, C G.kU3 v\ x p'^ccisv-/ bb , '0^^*—:j

1959). However, Andersen (1351) showed that systolic and diastolic pres­

sure would fall inrougnoui a aive in alligators (afier an initial increase

upon submersion). Toward the end of the dive, diastolic pressure would be near zero. Upon emergence, both pressures increased above predive levels and did not recover until 30 minutes later. Berkson (1955) found systolic pressure to be maintained in a diving marine turtle for up to 1 hour after

. . L». «—» ^ «s ^ ^ — X» ««» ^ T ^ L* ^ « t ^ ^ ^ n » f ^ >-s ^ ^ • i ^ o ^uutiici yc ( (L. c. uia^ uv ^icaauic * c & * ui M »_/ uy i«v/ uu u* «c * v c . v« * ^ > co ^ v* « co returned to noiTial within several minutes after the turtle emerged. After

45-50 minutes of diving, not only did systolic blood pressure begin to de­ crease, but blood lactate concentration began to increase. Apparently, some of the circulatory responses to diving were breaking down.

The mean arterial pressure in the sea lion (Eisner et al., 1964) and the seal (Irving et al., 1942a; Van Citters et al., 1965; Murdaugh et al.,

1965, 1958; Zapol et al., 1979) are quite well-maintained during diving.

The same is true for the nutria (Ferrante and Opdyke, 1959), beaver

(Irving, 1939; Scholander, 1940) and man (Scholander et al., 1952b). How­ ever, in the dog (Eisner et al., 1966b), cat (Ferrante and Frankel, 1971), sheep (Tchobroustsky et al., 1959) and rat (Lin, 1974), diving is associ­ ated with elevated pressure.

wner! biuud pr'ebbuft; , une reuuCL'iû!! 1 ;; u lâStûl IC ûi'cSSUî'ê 1S

^UlCïC ^1 W I C IC) ^u ^ ou IllCU u I C V C: I CCl l ub iivym ui i C i i vC., ut" ture seem to indicate "chai: poikilothermic divers do not regulate their blood pressure as well as homeothermic divers when submerged. Prolonged submersion in most divers apparently results in a decreased pressure

(Andersen, 1955). However, any fall in mean pressure that does occur is not nearly as great as the reduction in cardiac output which scccmpanies a Give. Tne perioneral vascular resistance musu, znerefore, be increased 34

A substantial increase in central venous pressure during the develop­ ment of diving bradycardia in ducks has been observed (Johansen and Aakhus,

1963; Folkow et al., 1967), as well as a decrease in left ventricular con- tracti1 'I ty of birds and m anuria1 s (r errante and Gpdyke, 1959; B i i x et al.,

1976; Gross et al., 1976). This increased venous pressure probaoly pro­ duces an elevated ventricular filling pressure which may, in turn, pro­ mote an increased ventricular end-diastolic volume. The bradycardia, with increased filling time, wouldalso promote greater ventricular filling.

Despite these changes, however, an elevated peripheral resistance (which may increase afterload pressures) and a negative inotropic effect (via the autonomic nervous system) may cause a reduced stroke volume during diving

(Gross et al., 1976). Such a reduced stroke volume has been demonstrated

in man during simulated diving (Kawakami et al., 1957; Skillman et al.,

1967). Zapol et al. (1979) showed that central venous pressure remained

constant in diving seals.

During diving bradycardia, the heart rate may be reduced to one-tenth

"che predive level. Mosi workers agree thai: a full cuii-penz^dtiun uf Lne

u3 1 4i li3 /M . wjry a3 v i 1 ^ /-s v%c^ 4111 v. wtlw rocri 4- v L" c, •.v ;r\ w * ; :rr.^11 i c^ ~i rr. ht r'. r'. c —

^ «ri u ^i e . uuuan:)Cfit t— ^ ^ aiiuj naf^iiu:^ iroo^ ^ ;\ jlufic ^ juu #lmuiic l» A *#»per A • A »i vu»

K'l r>nri -rv^nm f'no i n rn rhci a nv^f p -in rinr i/c \»rpc nnf ri-irrov^onr iinriov^ nro-

dive and dive conditions. They concluded that stroke volume remained un-

/-* x 3 ys rr ctl c r* v* o"^ 3 1 ^ 1 0 ^ /i ^ <^0^0 v^rr* n %r, o /-« 3 v^/4 4 a i i f : : v»l n n c i : km & v»__ SarllCfcil^WV^a ^IOIIVmI (.A I * ^ ^^ TJ Ill ll*\..\.i ^Lt I W I L* VW W V V* I « I *^ OV# k/lI I

gence in a sea lion from pulmonary blood flow measurements. An ultrasonic

•rl Aunrjci-r \»i^c mAnnron nn -r na n: : 1 mAm:) ;5 a nrî n aa y~ T C f rA / a wAl —

ume and cardiac output were determined. Tne stroke volume was found to

remain constant during submergence, while the cardiac output decreased in 35 proportion to the bradycardia. Shelton ar.d Jones (1965) measured stroke volume in frogs and determined the cardiac output. They found a decreased stroke volume during submergence. Cardiac output fell to between one-half

^ -1— ^ ^ ^ ^ ^ 1,1 w t ^ ^ ^ o ^ ^ ^ ^ ^ ^ ct flU uric— I I I uj" 1 u I Uf tube \ cw I ucu au une a u » « e. **1 * * u».. \ w y found cardiac output to decrease in forcibly submerged turtles by 95% and to be maintained for over one hour. On the other hand, Jones and Holeton

(1972) found the stroke volume to increase slightly in submerged ducks.

They reasoned that the conditions for cardiac pumping were favorable for this during diving since the preload (right atrial pressure) is increased while the after lead is decreased or unaltered. Nevertheless, the vagal tone is increased during diving, and this, along with a decreased sympa­ thetic input, is known to produce a negative inotropic effect in ducks

(Fclkow and Yonce, 1957; Ferrante and Opdyke, 1959), which may negate the conditions favoring increased stroke volume. Jones et al. (1979) found that stroke volume increased 2.5x beyond predive values in ducks during the early part of a dive, but was not different from control values after

144-250 seconds of subiiieryence.

Diving or head immersion has also been found to reduce the cardiac u ^ U^L* u i 1 * UI «e ^ ' /l..,uj/ a u v u v w v /o y r lu ( v y M c/-\ —u L*3 &i * ^ v v ; ^1 ^c m» s..^ « 0*f"s-w ^a1 ;

1978; Sinne-L ex al. ^ 1978; Zapol ex al.. 1975), domestic goose (Cohn et al., 1958) and rat (Lin, 1574). It also reduced blood flow in the as­ cending aorta in the dog (Eisner et al., 1955b). Face immersion with breath-holding reduced the cardiac output and stroke volume in man

i !<'h it:"i û'i" ^ 1 1 q a"7 1

cnus seems safe to concl uae zns.z in verieora ûe ai vers rhe carciac output decreases upon diving. There is usually either a decrease or no change in stroke volume with submergence (Johansen and Aakhus, 1963;

Eisner et al., 1964; Shelton and Jones, 1955; Murdaugh et al., 1965;

Folkow et al., 1967; Lin, 1974) so that reduction in cardiac output is near pr u^ur uiuiia i uv une : a i i in vue nca» v « a vc.

As mentioned earlier, changes in the peripheral resistance must occur if blood pressure is to be maintained in the face of a falling cardiac output. Butler and Jones (1971) showed that although the vascular resis­ tance in the carotid artery increased 1.24 times during submersion in ducks, that in the sciatic artery increased 7.97 times. This would not only help to maintain blood pressure during diving but would also redis­ tribute the blood flow. Jones et al. (1979) found that total peripheral resistance rose 2.25x after 20-72 seconds of diving in ducks, and after

144-250 seconds it was 4x the control value. The increase in vascular re­ sistance may involve constriction of large arteries as well as the resis­ tance vessels (Folkow et al., 1966; Heistad et al., 1968) and is due to activation of sympathetic adrenergic fibers (Butler and Jones, 1971). ru'kuw et d; . [i9ooj : uui'.j una u uric icrOe cX "CrârûuSCUl c':' à rteri c5 Of GUCkS were heavily innervated in comparison to such vessels in cats or turkeys=

Vasoconstriction ouxside the muscle is advantageous in that metabolic vaso cilazors produced by muscles during underwater activity do not compete with the neurogenically constricted blood vessels. Thus, resistance is maintained during diving and muscle blood flow is effectively curtailed.

Lin (1974) found a 4-fold increase in the total peripheral resistance

during submergence in rats. The increase in flow resistance in ducks is

accompaniea oy venous cons'cricûion (ûjojosugiûo et al., 1969). 37

The brain and, to some extent the heart, are irreversibly damaged in hcmeotherms by hypoxia (Barcroft, 1920-21). Most other tissues are far less vulnerable. Survival in a prolonged asphyxie dive, therefore, de- nûv^rîç iinnrj +'r>o aK*îl*î*h\/ ta nv^nxMrlo Ho f n î 4- i c mryç-f- nooHûH anH v^o — strict it from tissues that can go without.

Only small quantities of O2 are conserved by the cardiovascular changes to diving per se. However profound the bradycardia, it does not

in itself extend the O2 stores appreciably. Conservation of O2 on a large scale is only possible if all tissues that are not critically dependent

upon O2 participate. In other words, if O2 is circulated only to those

tissues requiring O2 at all times (brain and heart in homeotherms), and

is restricted from the rest, a saving of O2 can be achieved during sub­

mersion (Andersen, 1955). Such a circulatory response was visualized by

Irving in 1934. He provided some support for this idea in 1938 (Irving,

1938a) when he showed that blood flow to tine brain increases during

respiratory arrest in dogs, while flow to the muscles decreases-

^ ^ 1 ^ xs ^ ^ ry y ^ îa ^ ^ ^ I • ^ ^ ^ ^ ^ ^ ^ ^ IIV I iwL : iw C I \ u. .y-r V y o : i\w'yvcu ui iLt u vaui : 1 ly u v i w: i\4Cw 1 v c in o Cu : ^ ;

niirî/C prin nonnM^nc rvlnnn 1 = r- -? ri 1 nr ccri 9 n v'*:,.nc onl \/

0V0r> Upon EHiErsion it, rnlQh't ir.cr0aS9 to 10 tirnss th0 pr0div0 V2.1 u0. H0

^ V o uw I w, uw G V VI iC I Civ, vO. oC vvU^ ( Ci.iCt i i : i : ly j i k oiiC mu* t cb i w y buiui:ict~

I r\ m riiio T D I x -^1 /^i.. •—/^ x 4 c — - C C « ' w\ 1 \ / r\ k/-\ «. '3 c r\ « , 4- S«vii v v* v. w v* : w i \.f w i iw« w wiiio v * * k jf vv l/c y«ci.^i:ou v w v i1 i w

the circulation upon emersion when blood flow to the muscles resumed.

This hypothesis was later proven to be true (Scholander et al., 1942a)

u;wûn i -h i.fac clani.fn -i-las-r 3 m s 1/ .0 x n co n mtiçr«*]o 1

GCCurrcu clufiny diving with aû parallel rise in blood lactate. On sur­

facing, the blood was rapidly charged wiin laciic acid wnile ine 38 concentration of lactate in the muscles decreased. It was also shown by the same group of workers that the muscle Og store was consumed during the first few minutes of submergence, at which time the arterial blood was still mors than 50% saturated. This proves that muscle circulation has essentially stopped. Otherwise, the myoglobin; due to its greater affin­ ity for O2 than that of hemoglobin, would not be reduced at such an early stage, but would remain oxygenated throughout the major part of the dive.

The retension of lactic acid in the muscle during diving would be impos­ sible if the circulation remained unchanged. The lactic acid changes

have been verified in the duck (Andersen, 1959b; Andersen et al,, 1955), alligator (Andersen, 1961), turtle (Berkson, 1955) and snake (Murdaugh and Jackson, 1952) as well as in various other animals including man

(Scholander et al., 1952b). However, Jackson and Silverblatt (1974) re­

ported that blood lactate concentration increased during a dive in the

turtle p. scripta with little or no further increase upon emersion. Blood

lactate was also found to increase tremendously during dives of the iguana

thco-' ^ ^ ^ \ f ^ p i a j!!ttmptoi\/ \ i jw lv c i i ^ j «l ^ w,/ u y » xii ^ i v» v* ^ ^ j # v* ) ^ - .«p..

breaks down and lactate is releasee into the general circulation (Scho-

1 anXav- o-h a 1 1 Q9K - Rovl/cnr. 1 Qnri ^

a l, 1^ iltucl uw iiv lfc umcl v w iv v w 1 vcl «./ww»

snakes during voluntary dives, but during forced submergence these snakes

show the pattern discussed above for other animals forcibly submerged

(see Heatwole and Seymour, 1975). Thus, voluntary dives are predominantly

aerobic. The elevated blood lactate levels and depressed pH lasted for

over 4 hours after émergence from a forced dive. Long recovery periods 39 like this are typical in reptiles artificially stimulated into activity or submerged (Andersen, 1951; Berkson, 1965; Bennett and Licht, 1972).

Reduced blood flow to the muscles has also been demonstrated in many

V L! ICI aittiitaiâ u a i uy ui ic ici tnva v i vuiu: 11 i u i i yuc. inio p-iv^ucuuic mcu ou « co the heat conductivity in muscles vvitn a hou vvire. Such measurements per~ formed on muskrats, beavers, dogs, cats and rabbits (Irving, 1937, 1938a), seals (Grinnell et al., 1942), and ducks (Andersen, 1959a), showed a marked rise in the heated wire temperature during a dive or apnea, in the thigh muscles of the duck, the wire temperature rose nearly as high as it did when the blood flow was stopped by a tourniquet. Similar experiments have shown that brain circulation is normal or even increased (Irving, 1937,

1938a).

Johansen (1964) studied the regional distribution of circulating blood in submerged ducks using the radioactive isotope Rb®°Cl. The rate at which this isotope is taken up by tissues depends upon their extraction coefficients, the arterial concentration of the isotope, and the blood

1 ; ur/ Ldr ÛUÛÛ Crlc SSucS vocO'i T b Cc MI 5 ivjoj. ' nc 1 zavuuuc naa % njcv ucu

Iw I ^vCO tuuCi^ yx V» ^VI L-x ic iiCUl u «.vvuO I ? f Or- usj y r-\ w : vu Ow,/— VU I u vCvi 1/i\w I uitNu3 /I w I y u I iC> 3 M fv 1« OC ^C u ' ' x..C& CC*

removed; counted and compared to control values. Lin and Baker (1975) did a similar study on forcibly submerged white rats using the isotope

C < ^ ^ C1 r? nr! i ;; r niirniirc mo? c i ly^ori i r. nno nrni m n f r;; f < wpv^o mi il f t n1 t or! hv

the fractional distribution of the Cs*^" isotope in the tissues of a sec-

U! :u y ' u u u ' o.;ii":!aiS uu C5 u i ria vc a ua v i u LC u ; vvu i i uyya . j.n vmc uco u wu y i c

years, blood flow nas been measured "co tissues of diving mammals and birds using the radioactive microsphere technique (31ix et al., 1975; Eisner et al., 1978; Jones et al., 1979; Zapol et al., 1979; McKean et al., 1980).

If such small polystyrene spheres containing a ganma-emitting nuclide, and slightly larger than red blood cells, are well-mixed in the circula­ tory systeiT! upon injection; they will then become blocked in tissue capil­ laries in direct proportion to the blood flow through the tissue. In this manner tissue blood flows can be quantitated.

Johansen (1954) reported that the skeletal muscles of diving birds showed very little radioactivity, which indicates that the muscles had been essentially shut off from the circulation. The activity of the jaw muscles and other muscles of the head showed more activity than muscles elsewhere in the body. The eye also showed a high activity. These parts of the animal are used when the duck searches for food and during eating. Thus, apparently, the nervous system is not limited to an on-off response in con­ trolling blood flow during diving, but rather is discriminating in its ability to provide blood to tissues that may need it, Jones et al. (1979) found that blood flow to the muscles of diving ducks was completely o y 0/4 J 3 wr' r 1 û"7x ^ c iTÇ-înrT " c1 o / T i T n a f" Kjnnrî -r1 nur -rn the gastrocnemius muscle in submerged rats decreased by about 50%. whereas the fractional distribution of the cardiac output to this tissue was al-

11iv ^ V ViC/ w w I * iitC CiL/^kv w O i L& * v* s/ w Vf "

r\ 11 4- ».»aç K\/ ~7 /"i cm nmû v* c "i Tanr\l o+ 3 1 / 1 Q 7 Q ^ H o+ 4 n a/4

blood flow to organs in diving Weddell seals by use of radioactive micro­

spheres. They found that blood flow to the skeletal muscle was essentially

rhar /cH eii-.-r-. r.n ci ;h—nrqi nn F1 cner of MQ7R^ A rri vor Af thp rnn- 41

Myocardial blood flow in ducks was measured by Oohansen (1964) using the Rb®^Cl technique discussed earlier. He found a 4-fold increase in the blood flow to the heart during submersion. Jones et al. (1979) found blood flcv; tc the myocardium to be unchanged during diving in ducks although the proportionate share of cardiac output to the heart increased 5-fold.

However, Blix et al. (1976, 1978) and Eisner et al. (1978) found that myo­ cardial blood flow in submerged seals was only 7-16% of the predive value.

This they attributed to the decreased O2 requirement of heart muscle dur­

ing diving bradycardia as evidenced by a decrease in the ventricular work

during submergence. Lin and Baker (1975) found blood flow to the ventri­

cles to be maintained at the predive value and the fractional distribution

of the cardiac output to this organ to be increased about 3-fold in sub­

merged rats. Zapol et al. (1979) found that blood flow to the walls of

the right and left ventricles in diving seals was reduced about 85%.

Since cardiac output in these seals decreased 86%, and since mean arterial

and central venous pressures remained the same, coronary vascular resis-

-—. w.. —. ^ — c v* — v» 3 ^ ct r" / \ ^. Li mopnanicit! ^CX I 1 c 1 % i ^ ^^ ^ I I ^4 # II I W I ^ ^ , V # .. . ^ V * . V . * * W .. .

which coordinates myocardial work and coronary flew is thus suggested.

Millard et al. (1980) demonstrated that coronary flow is markedly reduced

L41 I I « ^ Li I V I i I lit ^ L» U CW j/ 1 i 1 v C 1 * ^ v'sA^^./wwiiOwt » s,» v » v « * yj »

coronary arteries. Myocardial flow is also known to decrease in diving

beavers (McKean et al.. 1980).

Irving ei: al. (1942a) were the first to measure blood flow changes to

the gastrointestinal system of a diving animal. They exposed a part of

•t m^ m ,* «,| ^ ^ ^ # ,* # , .— i-iIB bllicil iiiLebUMit; u: ic icc; lui viaucii iiiipc»- oiuu auu i v ui iv: a y i cuua :

vasoconstriction of the sm.all arteries to occur in response to submersion. 42

Hollenberg and Uvnas (1953) found intestinal blood flow to decrease marked­ ly in avian divers using a drop-counter to operate an ordinate plotter.

Johansen (1954) found an increased blood flow to the esophagus in sub-

—-J ^ 4-r\ -ï-Uo n4-y? a r) am/) 4 OÇ+Tnû Hor- ÇûH 11ic i ^ c u v.1 ci^ rs o ) vv 11 i ^ i t w ** v ^ * ê ^ ^ i Su w* i » «.» "«» v ^ -

Jonas et al. (1979) demonstrated that blood flow to both the small intes­ tine and spleen was completely stopped during diving in ducks. In sub­ merged rats blood flow to the intestine and spleen was decreased about

95% (Lin and Baker, 1975). In the diving seal, blood flow was reduced

8-fold to the ileum and 61-fold to the spleen.

Scholander (1940) observed that superficial incisions in penguins

which would bleed profusely before or after diving, would cease to bleed

during a dive. He suggested that this was due to a reduced skin circula­

tion during submergence. Scholander et al. (1942a) made similar observa­

tions in seals with a wound in the muscles. Johansen (1954), using Rb®®Cl,

found that most of the skin of a diving duck was without circulating blood.

However, skin in the head region showed a greater flow during submersion.

nu q s z>u r cyur ucu una l i< of;c uuvf\ wca ouujcu ucu ul/ u wcu u u: one.

-rn o T

skin blood flow increases during diving, making possible maximum use of

cutaneous respiration. Such a change ir, circulation will allow the sub­

merged frog to get enough O2 to meet requirements imposed when the water

temperature is as high as 15°C (Poczopko; 1959-503, 1959-50b). The in­

crease in circulation to skin was due to a reduction of the circulation to

other organs, Lin and Baker (1975) found bleed flow to the skin and tail

— ."T — ^ ^ — — — I—. - ^ rs rf .C » ^ . ««—«-« « « O * ^ T ^ ^ Ui buu:i:er ycu r a u:) uu ucv-i ca^c uj uiu\j«a i i\jn wj s/-, v * vv

skin in seals during submersion (Zapol et al., 19/9). 43

Renal ischemia with impaired glomerular filtration rate, or a com­ plete cessation of renal function, has been reported in diving seals

(Bradley and Bing, 1942; Murdaugh et al., 1951a; Eisner et al., 1978) and

/1—^ 07/i ^ L,L4 I V I C ^ \ V C( v.» I\ ^ W ! I Cill^ «.Jl IV\—* WiLAV*#) ^ m/ t ~C J 9 «V y\ p» s# « 4i

(jo^=hansen, 1954; Jones at al., 1979) have also shown a reduction in renal

blood flow in diving ducks. In submerged white rats, blood flow to the

kidneys decreased by 97% (Lin and Baker, 1975). In diving seals, renal

blood flow decreased 91% (Zapol et al., 1979). Thus, it is probably safe

to conclude that renal blood flow is greatly curtailed in diving verte­

brates.

Johansen (1964) showed that pancreatic circulation was completely

stopped, whereas the liver blood flow was not changed in diving ducks.

Both thyroid and adrenal glands showed an increased flow during submergence.

The high rate of blood flow through the adrenal gland during diving may in­

dicate that the cardiovascular responses to submergence are controlled by

an interplay between nervous and hormonal elements (Andersen, 1956).

uuncz* co cl» 1z7 / :7 / i cyu\ ucu u: i c u tivci uiuuu iiuw wu o i cu uwcw * ** i ici cw j

that to the adrenal gland increased during diving in ducks. Zapol et al.

/ 'i 07 g \ i i tr\) i rivi ^t-\3 ^ ^ i "tww ^ i v i ^v t> r\ 1 /4 -mm! « » « ^ h^ 1 « \/» i« hh » « ^ 1••• h i~hos«..w

Wecdell seal. Liver flow decreased 12-folc. thyroid flow decreased 5-fold

and adrenal flew was not changed. Blood flow to the pituitary also re­

mained the same. Eisner et al. (1978) found the liver of diving seals to

be completely ischemic. In a study of blood glucose levels during diving

ht v uv r\ z> ; mw yvgc> o » una u v ; «c ysaonio. w <. vd ^ a v » v : i u cv- i wu : 11 ly a j. w

minute dive. This may indicate char liver blood flow was decreased or

stopped during the dive, since glycogenolysis does not require O2 (see 44

Andersen, 1954). However, during diving in seals (Blix, 1975) and turtles

(Storey and Hochachka, 1974a, 1974b) blood glucose concentrations increase.

Lin and Baker (1975) have shown a 50% decrease in blood flow to the liver w i awl/iiic* ycw ic i * cix., u 4 v/1«û i w « o ui * l/l« l, * v/i * v i uiic w * w».. w/-*ii4-r>tt+ u vpci u vw 4-U'îcvi i * a viVTT y c11p m iiivin-ir\v«o 4"viigii K 3 wv/uk/r\i i K1 * » TXoi « is., wK1 * r\r\rl f 1 4-A 4» Ha warlv^onalc w i decreased by 75%.

An estimate of brain blood flow may be obtained from the work of

Johansen (1954). It must be kept in mind that Rb^G has a smaller extrac­

tion ratio in brain tissues than elsewhere, so one cannot compare cerebral

blood flow to flow in other organs and tissues in the same animal when

using this technique (Sapirstein, 1958). Nevertheless, Johansen found a

3-fold increase in blood flow to the brain in ducks compared to those

breathing air. He also found about a 4-fold increase in flow to the eye.

Most workers believe that cerebral tissues do receive an adequate Og sup­

ply while diving since divers usually emerge from prolonged underwater

exposures with no visible signs of motor disturbances and appear to remain

a ; cf C aiiu Yu ; uui) ûui 1;:y . irvv; . uunci> c u

1 -r —» v* «k OPl ~0 /-v ^ rv v* W r» 1 /? /Î OCO I I IS^ I CLtOCu IMW I C VMUM ±U\J /C U> UCI C.U— / L. .5 CWW I IVAO V/ I UtVlliy^ U.I VCI iT-r-"

seconds it had increased to 755% of predive value. Blood flow to the

eyes did not change. Murdaugh and Jackson (1952) found that water snakes

would show no ill effects of diving for 30 minutes =, but cyanosis and un-

cnmc/-"": r\i:cnccc r\r\cx od rr 4 i 4- o c m t (Osm> « vy c« ^ t ix-^ ^ vu w V I «J v.. s.* ^ i i , I y lu i « «L* ^ wi & 12 L/ I CC VI 1 I n y •

The same proble~ with moveïnent of isotope across the blood-brain bar­

rier exisôs for Cs-^~ as for RD°°. however, as wiin Jonansen's worK (1954),

relative differences in brain flow are informative. Lin and Baker (1975), using the Cs^^^ isotope, found blood flow to the brain to be unchanged during diving although the fractional distribution of the cardiac output

to cerebral tissues increased more than 3-fold. Kerem and Eisner (1973),

(-"bU'iy c ùùppiér" u i ûràSùrri C ï i ù'wTrié'iier , Tuunû una u v-cfcur a i uiuuu i i uW lii- creaseQ slightly in Submerged Harcor seals, wmle Biix et al. (1976) found

that cerebral flow had decreased by one-third during diving in a single

gray seal. Dormer et al. (1977) showed an increase in cerebral blood flow

in the sea lion of about 100% after 3 minutes of submergence. Zapol et

al. (1979) demonstrated that blood flow to the cerebral cortex, cerebellum,

thalamus, and hypothalamus was maintained during diving in the Weddell

seal. Blood flow to the medulla, however, increased slightly. Flow to

the spinal cord and retina remained at predive levels. Eisner et al.

(1973) showed that cerebral cortex blood flow in submerged seals decreased

early in the dive but then increased above predive values later along with

elevated PCOg and The brainstem received a decreased flow. McKean

et al. (1980) found that brain blood flow was 2« of the cardiac output in

beavers predive. During a cive "che percentage increased to 55%. Thib

1 y •-''O: C VI3 IV". I !-n c" O ky * V w -rli i ft 4 v-. c.^ = ^C .3v— ,4 :v* : i T r: c v#: : Km11 c, ^.'z c r:c.» i s.» s— *

• -L. L% M A ^ *% w. ^ ^ ^ I . ^ J 4 A ^ ^ ^ i / T ^ ^ ^ -A* ^ » f hm I a ^ J. L na ucc: i uu i m ucu vu u u j rijiic;; c u u:. j ui la v) even ui luuy 11

the "curile orain can function anaerobically and mus does not need O2, a

continued blood supply to this organ is necessary to provide it with sub-

C+V>3-!"O -rnv^ C

It should be kept in mind that maintenance of blood flow at the pre-

v * vv/ w v ^"'CC'''*^Cv ; ^ ^ l* c ^ T» 1i w 1: l. o z 4" ^c Iw I w r\l^ 1 \v / ^»^OCO r\ l&5 v»1: ^c i.fiviwii 4 -r X

02 ac cue prsQive race si nee cne raG2 cecreases during submergence L1 n 46 and Baker, 1975). It may be therefore, that even the central nervous sys­ tem must reduce its metabolism during diving or else utilize anaerobic metabolism to some extent (Blix, 1975).

^ ^ ^ A-t- ^ f ^ ^ \ jC^ ^ ^ m ^^ •»>^ ^ "» ^ ^ ^ ri z_o^v 1 c u o i. \ ±Z> / :? J i vuuli ui ici u v1ic i i v « vi « i m i s.., # 11j cs., vcv*

^ w% 4./> 4. im /> 4*1^3 4- 1 r\ ri^ 4 y\ +'»-*o 1 t i m m c i.is c /4 4 kof/\ v^o 3 v%fl I Ii OU UilC I C I U V CI I L I * k, I C VI iCl u I \_/\uyC*u 111 u: i v* :ly ^ vvuo v* i i i »w.i v.i i v i w i w i *w during diving in seals. Predive the lungs received 7.9% of the injected spheres while during the dive it increased to 29.9%. This indicates that there is an increase in peripheral arteriovenous shunting during the dive and/or increased bronchial artery blood flow in seals. Jones et al.

(1979), however, found the lungs to receive 0.6% of the cardiac output in ducks before diving and 0.7% during the dive.

Since it is well established that most of the mass of an animal be­ comes hypoxic during submergence, investigations into the biochemical adaptations to anaerobiosis should prove rewarding. Kerem et al. (1973) found that brain and heart glycogen concentrations are 2-3 times higher in seals than in most other mammals, whereas skeletal muscle glycogen is b iinilcir to levels found in Lhe duy ur cdL. The fr-ee FaLL_y au lù COîiCcnLfà-

WiWtl k—/ I \w/ Iw4 I Vk W

^ ^ k /OT»»» n iCT \ C «.. < « ,k» Lk y» \>% , vm ^ r\ ^I i f <-usc 1 iiu I caici \.oiia5 J.ZI! ^ j . o ; Mc c ;jiuu^c; ucuiwi a : uo uic iiwi- pciiuocj curing a dive, bui -.?e porral circulaiion is operational , it may be that

free fatty acids and glucose are fuel sources for the heart at the begin-

m'nn nf -f-ha Ht\/o Ac f H î x/n r 11 -hi n n i nr yoa c ac ni ir o nlumco iiigjym 3 \ f iv% cr\ utic bf", u , ivb u ) gi iwiV» ^uivu

tt- x a r c -r in 3 +- <- /-» ? v. 3 o 3 3 1 3 4 n O /-»r\V-K^Ot^'hv^3^Tn»-»C

>11 ui:c l/ i v i ui i\c ^locii .^cck vu* . v i ^ i i>c^wvcijr itv^m nuitiii^^ vvcti 47 as the levels of lactate and pyruvate. Identical results have been ob­

tained during simulated diving in man (see Blix, 1975).

Succinate has been shown to accumulate in rat cardiac muscle during

t ^ drx-mw, lc7ai\ 3 4 ^ <33 1 tx/qv» 3 1/4 fc lutaw/nica ^ i l*i «*-» w»» * w« «>— « « • wj « «vw» %»»<•%.•

of altitude acclimated guinea pigs (DeSilva and Cazorla» 1973). Experi­

ments by Cascarano (1974) and Cascarano et al. (1976) have shown that

under O2 deficiency, peripheral tissues convert fumarate or alpha-keto-

glutarate to succinate with the concomitant production of ATP. Succinate

is then carried to the lungs by the circulatory system where it is oxi­

dized to fumarate and malate. These products may then return to the pe­

ripheral tissues and provide energy for processes which might not be

maintained by glycolysis (such as the maintenance of heart Ca levels).

Thus, it may be that energy-yielding mitochondrial reactions also occur

in diving vertebrates to prolong the submersion time (Hochachka and

Storey, 1975). Penney (1974) found succinate in the turtle liver follow­

ing a 24 hour dive and suggested that, not only might reduction of fuma-

I eue uu 3UUU J I iG uc vi:c( c ucui-cr j/ : c i u vjt r-. jr» ivu u u: :ci u luaj uc

T-r nzic X omrs — in 3 i- ms>n\/ \/ nn -rnû C i m t: 1 _

Lc hcvuZ> ua ucou i i uT a.:; i :iu au J ui gi iu ucuu;i Vui c uci uui :iiy cX ucnucC uci 1 uub

ui cijuajc nuuncv^ ji ng gilu ."iu :) ug1 g) J LJ ^ g:> suyycsucu cg: i ici :ui u1 v 1ny

vertebrates. Such a scheme of anaerobiosis allows for the maintenance

of redox balance indefinitely during anoxia, and is associated with a

^ M ^ A . ' ^ "t - ^ )' Ci : u c I r\M I , J \V i c : v; u c v%1 .iiv-/iCT>-\ I VJ ( \_G; f/m c uc ^ « v-» I — f GiOJiCI wG;; u;v-»~^

duce (Hochachka et al., 1573). 48

The lactate dehydrogenase system has been studied in seals and ducks

(Blix and From, 1971; Blix et al., 1973) and beavers (Messelt and Blix,

1975). There are 2 types of lactate dehydrogenase, the M type being a pyruvate reductase and functioning in an anaerobic environment, and the H type being a lactate dehydrogenase and functioning largely under aerobic conditions (Kaplan and Everse, 1972). It was found that the heart and

brain of the divers had a much higher M subunit content than sheep, but

that the skeletal muscles of the seal and beaver had a lower M subunit

content than skeletal muscle from sheep. Messelt and Blix (1975) have

shown that sheep muscles are composed almost totally of white (anaerobic)

fibers and M subunits, whereas the skeletal muscles of the beaver are

made of both white and red (aerobic) muscle fibers in a proportion com-

pCi 1 u u > c uv oilC^ I c I Ci V I V C Cmvu n u v/^ : dm Qnva^ w-i /h uii owwuuivor- i i l-m i n ^ o it> umC miiuuov...iC* i ^ r* 1 ^ "tl^ii^itiuoj

the lactate dehydrogenase is fiber-specific and it is the fiber composition

which reflects an adaptation to diving. The red fibers, and the associ­

ated H subunits, in the seal and beaver muscles are probably adaptive to

iC I :Ci L/ I u : 11 u: :Ci u u: iCjr irru u : vu lOvii i vO uC u * Ci y i w tC^v-/vCijf

emergence (Blix, 1976).

Blix (1971) has shown that there are no specific energy stores (créa-

u * M C y It; uiiC uibbuCb Ui uiv , iiy

It has been demonstrated that seal cardiac muscle has a myoglobin con-

vex u; c u 1 vu Will un ; :> uuuuic uncu ui iiica. nuwcvct > uuc vciucs i vi see is aic

probably an underestimate of the actual concentration since the investiga-

w 10 u u I I 1 i_Cw poco I {icvu It via yd 1 wcuo utiA.9

HGcnacnxa a no Storey (.1975,) nave constructed a rather complete scheme

of biochemical adaotations to anaerobiosis in divino animals based uoon 49 data gathered from diving and non-diving animals. Briefly, they found that there have been only a few modifications of the basic biochemical machinery present in non-divers (such as the white rat) for allowing

3 4 ma1 c a -Fr\ pnjic.v^r'. Stactc nryy^r^ ûv>-î-v»a*f-îr\toç nf a few glycolytic enz^/mes are increased (along with glycogen reserves) which reflect a greater overall glycolytic potential and improved capacity to maintain the NAD/NADH ratio when O2 is lacking. Baldwin and Seymour

(1977) showed that in ten species of terrestrial and aquatic snakes, there was no correlation between diving behavior and levels of glycolytic en­ zymes.

At the water surface, diving mammals use primarily fat for energy.

During a long dive, fatty acid oxidation is reduced due to an increase

in the lactate concentration and a decrease in the transport of hor­ mones to the muscles (vasoconstriction of muscle arteries). Glycogen is

then relied on as a source of energy. On emergence, fatty acids are again

mobilized and burned and gluconeogenesis occurs in the liver and muscles

t I uni : av^ uu uc a nu ni\ju : : i z-cu Gn;i:iu av-.:uo \ : laci irs.a g i lu o uv i ej ; zv/vy.

iv* cr>mo "tl'v^t-ioc , J jv i!V : :Y v. ::'w.; ::: : vv;•

a nr! C 2 w- f z r» n'^i \/nr\n c^n 4 c 1 n_ -f nl A n n r; nov' f Xa n "in ^ • I I IW» w • 4 t N M I > SP« w I ^ / wy* V \«* * i « ».« « «*»* * " » i i

Jm ^ — —^ ^ ^ ~ v« •" V* Z-* — ~ —, ——— — ^ ^ /",-/%/"• — ucjfcoosia» gwu t-w/ u 1 mcz) u 1 y i ic : uuau lu u ( v iiiy :iiaiiuiiai:> \ i\ci en»

c L. ai.j t o J m I : 1 I Z: 3 ^vu^tcu W i uii iiiyii vci en ui o. u 1 v 110 u i cumc yijvuijuiu

enzymes, gives turtles a large glycolytic potential (Hochachka and Storey.

1975). The heart is very tolerant of the high lactate levels which occur

/4 i i 1 m 3 \y -1 ^ /"x — /-1i ifyz-xl /-n »-> -r \ f r>-i ^ 4- » Nuwi tiiv< LA i I u. oi(> wuMit LA I I L* i I i tLA w I \-i I f I V I C: I V j: iC ^ \VW: C v

â:':G nocûâcûkâ, 19/^bj ûnci incrêûSêd ûuTTôr'ing cûpâcvcy ^udckson and

Silverblatt, 1974). Turtle heart lactate dehydrogenase is of the M type 50

(Altman and Robin, 1959) which is tolerant of anaerobiosis. A high oxida­ tion potential occurs in the turtle heart (high NAD/NADH ratio) due to glycolytic enzyme modifications (Lai and Miller, 1973).

in buiiiiiiaf\y , a iliyii uv vci i u i a . >11 vj.w.ny ù.,.. . o to: a) high glycogen concentrations for anaerobic use, b) the tolerance of high lactate accumulation via more efficient buffering, more acid pH optima of enzymes, and a means to remove (metabolize) the lactate after a dive, and c) the high NAD/NADH ratio (Hochachka and Storey, 1975).

It is known that glucose remains an important energy source for the turtle brain even during prolonged diving (Clark and Miller, 1973). The

Cori cycle remains functional and thus lactate formed may be transported

to the liver in exchange for glucose. Blood glucose increases 5 to 24- fold during anoxic dives, or when in 100% N., in Pseudemys and the pH

drops from 7.9 to 5.8 (Johlin and Moreland, 1933; Penney, 1974; Storey

and Hochachka, 1974a, 1974b). However, blood glucose does not increase

during diving in the lizard (Moberly, 1958a). Cardiac glycogen is de-

-•--=ngsd (Clark and "'"lier, 1973). Penney (1974) found that blood

^ z ^ ^ 1 j i /"> «.m /i : i /n n \ m dm ; C.U UC LC I nu I cc^ CU O / ~ : VJ l U Uuiu CU icucij I w I LA t_-r iKw'Mi

luriles are breathing lOOh N? blood lactate increases about 2G-fold

(Johlin and Moreland, 1933). Jackson and Silverblatt (1974) demonstrated,

however, that blood lactate "in the submerged turtle increased throughout

the dive and Moberly (1958a) found a similar situation in lizards which

the .nso.rt- or

brain during diving may circulate to tne lungs wnere, cue to tne ûg whicn 51 is usually present in at least small amounts, it is oxidized back to pyruvate. This could then be used in the heart or brain to oxidize NADH, thus keeping the NAD/NADH ratio high. This could explain how the redox uuLên'ù'jQi UÏ uûc 'C'lbbucb ; nia i m ua i i»cu uu ; : iiy a;;uAia auu storey, 1375).

Penney (1974) reported thaz extensive glycogen depletion occurred in the heart (95%) and liver (83%) of ?. scripva as a result of a 24 hour dive in N^-bubbled water. Lactate increased in these 2 organs 8-fold.

Clark and Miller (1973) believe that the long anaerobic survival of the turtle is the result of a number of factors, including a low metabolic re­ quirement, a capacity for sustained anaerobic glycolysis and very high blood and extracellular fluid buffer capacities. They state that the fail ure of anaerobiosis to maintain adequate levels of ATP and creatine phos­

phate in key organs (due to the low efficiency of glycolysis) is the major factor that ultimately limits anaerobic survival. However, substrate depletion and lowered pH may contribute to this.

In SLiiiirnary, ix appears iha% "che 0? scores uf vertebra i-t; diverb are

uiic r'cb l i 5 G ; r- ur CG l: s i uc. gu » : ; uv r cuig i iuumci ycu i u ;

prt\/ r\y»n*! -r-^rno r. rn^-r

involves most vascular beds. 31 cod flow is reduced or curtailed to most

r\ ^ ^ rr*i ,c m3 ^ S ^ ^ <"*3 Mal C WC 4" w l vi i\- iulâ ^ o ) iiig j 1 1 l/ i luic ^ ^ )

the kidneys, and most glands. An animal thus becomes a "heart-brain-lung

ny^or^3v-»a-rTnr^'' I'wirv 3 vrn v*0C0v^\'0C "f-no "rn r» -rno -ttcci'ûç iirn i r- n X omz rv

1%. After muscle O2 is used, anaerobic metabolism occurs and. due to an 52 enhanced capacity for anaerobiosis, can function to supply the energy needed for locomotion during the dive and that necessary for emergence.

The bradycardia, and the corresponding reduction of cardiac output, can be v'iéwed as a nièans Lù kèép prèSSurê VvVthli'i rèâSûn CùnS'iûcnûQ tné IntcnSc generalized vasoconstriction which occurs, and to reduce the blood flow to a level necessary to perfuse only myocardial and cerebral tissues at a work level which requies minimal O2 and/or substrates.

In amphibians and reptiles, which have a single ventricle, shunting of systemic venous blood directly to the systemic circulation is possible under some circumstances, thus effectively by-passing the lungs (see

Figure 1). This is referred to as a right-to-left (R-L) shunt. Recircu­ lation of pulmonary venous blood back through the lungs is also possible and is referred to as a 1 eft-to-right (L-R) shunt (White, 1959). Foxon et al. (1955) have shown that, in a lizard, when a R-L shunt occurs, it is the left aortic arch which receives the systemic venous blood. Khalil and

Zaki (1954) found that the left arch received 62% of the R-L shunt in the cna/o* rno ynnnr s v^rn T nc ~ n 1 nn

• ujoiv-ij »j{\c O. I : uv&l-'vi wvu I I iCiu iCyuiiCOg uuvC u. CC iiiL* jv/ *

leading fron: the single venxricle; a pulmonary artery, a left aortic arch,

« I V L* I I \J in ïllltV'ki & I I I ^ I I V Vk I I i ,

brachiocephalic artery provides blood to the head and anterior body. The

tI C^ I -i»u Civn buywiicaf* I I f» -rvue o iivCi GiiUw. yCbuiWiuvcaviuG;/-«—• oc^'o*^j o vCiii /"\rrr • ; : i 1i /-Iy u ^ v u3 iw* iu /"M

left aortic arches unite to form the common dorsal aorta which supplies

r\" rv/->/-! -rrv -r rt o l/*?/nno>/C 3 r\ o c — o n r» v-« ;/ t Ôcnlaw w I w \u vv Ut tw i\ I su 11wjr O ) w I ^ I I^ 1 v 1 \i tOi*# «m. 9

1955). By channeling most of the R-L shunted blood Into the left aortic rigure 1. Schematic diagram of the turtle heart. Systemic venous blood enters the right atrium (RAt) by way of the sinus venosus (SV). This blood then enters the single ventricle (V) where it is pumped either to the lungs through the pulmonary arteries (PA) or back to ttie tissues via a right-to-left (RL) shunt. The Rl. shunted blood (dotted 1 ine) is dis­ tributed primarily to the left aorta (LA). Blood returning from the lungs via the pul­ monary veins (PV) enters :he left atrium (LAt) and then the ventricle. Here it may be pumped to the tissues or back to the lungs through a 1 eft-to-right (LR) shunt (dotted line): The brachiocephal k: artery (b) gives rise to the right aorta (RA), left and right subclavian (S) and eft and right carotid (C) arteries. The right and left aortae curve posteriorly where they meet to form the common dorsal aorta M

en

R Al LAt

SV PV 55 arch, the brain, heart and major sense organs are insured relatively well- oxygenated blood. White and Sonnenschein (1954) have shown that blood flow in the left systemic arch of the iguana is lower, or at best equal to, flow

•in -f-ho pvrh

Evidence exists showing that, despite the single ventricle, the sys­

temic and pulmonary venous returns of lizards and snakes can be separately distributed (White, 1959) or show a R-L shunt (Tucker, 1955; Heatwole and

Seymour, 1975). Maintenance of a high degree of separation of the 2 venous

returns to the heart has also been snown to occur in the turtle (Steggerda

and Essex, 1957).

Turtles show both R-L and L-R shunts. Mi 11 en et al. (1964) and white

and Ross (1965) have shown that air-breathing Pseudemys exhibit a L-R shunt.

Steggerda and Essex (1957) have also shown this to be true in chelydra

serpentina, .the snapping turtle. However, these latter workers used

either pithed or anesthetized turtles with the plastron removed. The

animals were supported by a respiratory pump. The above papers also showed

-? v-s/-* T v«/-> oMTwc u coMioT c urirh p k —î < hi ) ni.

This was accompanied by an elevation of the pulmonary vascular resistance

and a decrease in systemic vascular resistance (White and Ross, 1955).

-s — 0_' ^ ^ ' «m. ^ 4 V» /-I /-Î I : 4 m 1M "T ( 1 7"! ^ ^ ^ (illU ^ ^i i ^^ I I I\ ^ t É ^ ^ ' « • •^ Si* • • • • •^ ^ ^ ^ • "w ^ W

pt.p nulmnrzrvJ hvpass (Mi 11 en et al., 1964) to a readiustment frorrom

60% of the total heart output directed to the pulmonary circuit during

air breathing (L-R shunt) to 40% during diving (R-L shunt) (White and Ross,

1966). The cardiac output curing the bradycardia of diving falls to as

low as 5% 0"^ the grad^ve uaiue i'U'hite end Ross- 19661. The level of the

vq( i c^ wiuli lfi ic ) i ( c* ^ * l/ ui » v>3<*wi* 56 a L-R shunt occurs whereas during apnea there is equality of systanic and

pulmonary blood flow (no mixing) (White and Ross, 1965). It appears that

the direction and magnitude of shunting is determined by the balance be­

tween systemic ana pulmonary vascular resistances (white, 1976). Mil Ten

et al. (1964) report that the stimulus for the development of the R-L

shunt in turtles is due to blood or tissue 0 tension. The shunt was pro­

duced by diving and Ng inhalation, but not by the administration of cyanide

(which inhibits Og utilization and results in high blood O2 tensions).

The hypoxemia effected a R-L shunt by increasing the impedance of the pul­

monary artery.

In the chelonian reptiles selective perfusion of the systemic or pul­

monary circulation is achieved to a large extent by alterations in pulmon­

ary impedance while the impedance of the systemic circulation is maintained

at a more constant level (She!ton and Burggren, 1976). This impedance

change within the pulmonary circulation may occur in the vascular bed it­

self (White, 1970) or in the vasculature proximal to that within the lung

(Luckhdrdt and Carlson, i92i; berger, 1973). Surggren (lS77a) has shown

that the pulmonary resistance of turtles increases upon vagal stimulation

or when perfused with acetylcholine and is prevented by prior treatment

viizh atropine. However, sympathetic stimulation produced no vasomotor

changes, but adrenaline perfusion caused a vasodilation. He suggested

that an abrupt increase in catecholamines occurring at the same time as a

fall in parasympathetic tone might be responsible for the decrease in

pulmonary vascular resistance accompanying active ventilation.

White and Ross (1966) founc %na% tne pulmonary vascular resistance

increased during diving in turtles while the systemic vascular resistance 57 decreased. As discussed above, a net R-L shunt then would occur. At the same time, the pulmonary arterial pressure rises to equal the pressures in the aorta during systole, both in magnitude and time course. Such pres­ sure overlap is probably the force uel'iind the directicnal shunting.

Millard and uohansen (1974) found that, although the pulmonary vascular resistance increases during diving in the varanid lizard, aortic pressures remain higher than pulmonary pressures. This indicates that the systemic and pulmonary arteries are perfused by functionally distinct pumps and that no shunting can occur inside the heart during systole. Intra-cardiac shunting can occur only during diastole (during cardiac filling or from systolic residual blood), and the authors believe that, due to the small ventricular chambers, shunting would be minor.

In the Crocodilia, the right and left aortas arise from the left and right ventricles, respectively. The ventricle is completely separated as

in homeotherms; however, the 2 systemic arches are connected at their

bases by the foramen of Panizza (White, 1956). The pressure in the right

ventricle is not sufficient to eject blood intu the lefl aOrLa during air

breathing, thus when the alligator is above water both systemic arches

are perfused with blood by the left ventricle. Obviously, the left arch

must receive blood from the right via tne foramen of Panizza under these

circumstances. However, during diving the pulmonary vascular resistance

increases such that right ventricular pressure becomes sufficient to force

blood into the left aorta. Then a R-L shunt occurs. And, as in lizards,

this R-L shunt is directed to the left aortic arch. The shunt is associ­

ated with bradycardia, as in turtles (white, 1959, 1970). however, in turtles the increased pulmonary vascular resistance results from 58 vasoconstriction within the pulmonary vascular circuit (White and Ross,

1955, 1955) whereas the increased resistance in crocodiles and alligators results from an increase in the pulmonary outflow tract resistance, an in­ tracardiac event (White, 1969). A L-R shunt in crocodilians is impossible.

Meyers et al. (1979) have shown, using radioactive microspheres, a net

R-L shunt in submerged bullfrogs (58% R-L shunt, 23% L-R countershunt).

However, when in air the shunt was variable and did not consistently demonstrate a net shunt toward the lungs. Moalli et al. (1978) have shown

that bullfrogs increase the skin blood flow during a dive. This is bene­ ficial since the gas exchange organ during a dive switches from pulmonary- cutaneous to cutaneous only. Poczopko (1959-50a) showed that the cutaneous capillaries open in frogs during diving; the greater the reduction of

4" IDOo ^6 5 "^noI nv-'op-rov -f-lnoVI «S— ?VAIIIV./V4I1VI» : i n 4- n-rV I nnon-irsn

Intravenous administration of acetycholine in alligators breathing air resulted in a bradycardia and a R-L shunt. In addition, atropine

prevented the normal development of a large pressure gradient between the

ncHT snn n: : : mr\ ns niiv^-nn a niwo inûÇû v^ûc»mtç nnriT —

ui (cl u , ill ciiiyc uw i ^ ; ui i c 3!iu:iu uiy incv i la t i : otu to i i rvc une

ur'GuyLcr'u• j jid _ v/aiiLCj 1303, 13/uj.r\~7 r\\ \wnice \i3Vo;^ \ iXUiLCLCb.t j ^ ^ .u - ^ i.una _ j.u ,u'--trit: —uuiiiiuri- . n »...

2 -- — 3 vw i v i s.» ~ci .d v* ^ v m v 1 iv. \ f a «r m c »nov*>roo

since vagotomy or atropine produces pulmonary vasodilation while acetyl-

X, I IV !) 4* Iv, I ^ V/"x v*: \VU^Ul / p p 1 «''VtiUUIULUiU/ll3 + i^UIVW. lU^lClWlC) t cy U t O

tion of ventilation/perfusion relationships in turtles is of reflex cho-

rr^nry^rsl ^ 1 1 r» r u/rMiln nr\T- no 3r\rvv^r»r^v*T_.

ate in a bird or mammal since iz would cause rignû veniricular overloaa

anc pulmonary hypertension. 59

By Lise of a tracheal T-tube it was found that the intratracheal pres­ sure remains quite constant during a dive in alligators. Even after ex­ piration during a dive the pressure remained relatively constant. This

I a i 1 i vci ca V I My I V naa L/CCI * WWOCIV cva W, w VI IC k>{ Ci wjf waisuiû V/ I * V * I III

i ' ^ 4 1 »->pv*4- ' v» m naç ina c koo>^ ovp ot t orl ct : : iyd wlo uwcb uvv vv^u; unuii pcli u sv i vii l. « ui *y yvk o mco k/v.cii ii n^sa •

It appears that pressure receptors are not involved in these changes, but that lung or thorax mechanoreceptors (stretch receptors) may be important in initiating the cardiovascular responses to submersion. After brady­ cardia had developed during a dive, replacement of lung volume by N2 in­

jected through a tracheal T-tube produced a reversal of the bradycardia, whereas withdrawal of the volume was following by a return to the brady- cardic state (White, 1970).

Lillo (1978) demonstrated that diving bradycardia in bullfrogs was

correlated with a decreased concentration of O2 in the blood. However,

if PaOa was decreased, and the animal allowed to breath N2, no decrease

in heart rate would occur. This suggests that inhibition of lung ventila-

uiuu ; : j Y v i : n ; u i a u 1 u: ; v : u iv;i;u ui cujvc i u j a • nvwcv ci • uc

' T» ^ vm ^ L"» I. « /"x — «m ^ \ I _ ^ I « * W» ^ ^ I i fMI I

-I /M V-» 4- V» r\ fI I I 4- 1*"« /-x n v» 4- ^ : n 1 : 10/0^^ uî/*\ vu I iv^Ouiv Ml OciuOL'taiik/iUi iiCUi u luvC v..»iiuiiyOO ^i. 1 :1 v* ^ i^ kj j» iiC

suggests that stretch receptors do not play a role in the recovery from

bradycardia upon emergence. These results agree with those of Bnilio

;5nH Shol+nn /107?\ -fny c Kiir rnnf^acr uii-rh fhnco nf Jnnac

{1 0^^^ ^rw*

cif a1 1 C77 ^ Xa \/ c c nn;wn \;cn fnlaTinn nf rînû VvV W» » « ^ t I y aiVkVN.» WltViV W»< W* • «W'W»» « ^ » W I » W» w I < • w • ^ *w

:u « lya v1 r'• SCSI p Ccc n:ii 1 î iv-: CG z>c :iCG : u zGuc Gnu puuiiuiiGij' uîuuu iivn.

Termination of ventilation caused the rate and flow to decrease towards 50 pre-ventilation levels. Step-wise reductions in lung volume caused a de­ crease in heart rate and pulmonary stroke volume immediately upon rénovai of each volume of gas. Injection of equivalent amounts of air rapidly re­ turned values to near control levels. Similar results -A'ould occur whether the gas used was air, 100% M2, 100% 0% or 5% CO2 in air. Thus, chemo- sensitive receptors inside the pulmonary system cannot be responsible for the changes. These workers found that the intra-pulmonary pressure would increase in proportion to the depth that the turtle was submerged, and that as the depth of descent and intra-pulmonary pressure increased,

heart rate and pulmonary blood flow would decrease. However, after cho­ linergic blockade (atropine), the cardiovascular changes were abolished.

Since diving will cause a decrease in lung volume and an increase in intra-

pulmonary pressure, and since removal of lung gas will result in a smaller

lung volume and a reduction in intrapulmonary pressure, changes in lung

volume rather than pressure are probably responsible for the cardiovas­

cular responses demonstrated. The investigators did not state, however,

: iLJvv a 'CLcy uu ; ui: y;iu ui5i,:i;yui3;i uc urtccn vv^iumv.

Therefore, these authors have shown that a diving turtle moving vertically

through the water column will experience heart rate and pulmonary blood

flow changes tuned to its depth and consequent compression of its lungs.

Tnis vagal reflex may help to explain heart rate changes in anticipation

of breathing during ascent.

The significance of intra-cardiac shunting is not definitely known.

There are only two situations known where R-L shunts develop in reptiles:

~ ^ t" *' ^ — .j ^ ^ *1 lit i 1^0» l* ^ lilî « 121^ cl1 1 w vuv»it 11:^ i w • 'w j

and sea snakes. Tucker (1955} suggested that the R-L shunt during thermal 51 loading in lizards may be to increase the systemic cardiac output. This increased output could increase thermal conductance (and thus accelerate heating) and the shunt could reduce thermal losses across the pulmonary vascular bed (Baker and White, 1970). It has been suggested that R-L shunting during diving is advantageous in that it redirects cardiac energy expenditure toward systemic rather than pulmonary perfusion. This would occur at a time when perfusion of the lungs would yield little in the way of loading the blood with O2 (White, 1959).

Arterial PCO2 levels have been found to exceed 100 torr in p. scripta after 2 hours of submergence (Jackson, 1968; Jackson and Silverblatt,

^ *7 ^ \ ft ^ .im ^ A A w. -Im — «1^ M ^ n ..AM ^ T T «La A «A T . * —# Jm ^ ^ ^ ^ ML Liic :^aiisc oiiiic rv2 vaiues jcm tu um j a i cw uuc i . inci civic, as apnea progresses, lung O2 concentration falls and COg levels increase and both of these changes are unfavorable to blood oxygenation owing to the

Bohr shift. Wilson (1939) has shown that as apnea in Pseudemys progresses,

the respiratory exchange ratio in the lungs becomes smaller. This suggests

a R-L shunt. A similar progressive reduction in CO2 elimination from

ms /"x 1 i i w ^ * .i—^ x* m «fs y—? _ t .. _ ^ "n o mm m i i ^ k/ I VfWW I I I UW Ul IC !U!IV ruao \-»U^Cl VwU Ml VU Ul IIJV U U\J I:: I I lU UC Uï CW Ul I

(Lenfant et al., 1970a). The p5o(lungs) will become progressively greater

as apnea continues. However, a R-L shunt may reduce this rate due to the

shuntina of CO, awav from the resoiratorv orcan. Consecuentlv, a lower

lung blood flow may become as effective in removing 0? from the lungs as

a higher flow rate. In addition, there will be an intensification of the

Bohr effect at the tissue level due to the intra-cardiac mixing of systemic

and pulmonary venous blood. This will augment tissue uptake of Og (white,

1978; Ackerman and White, 1375). The R-L shunt may be very important in

w'OOn'^nn iiinrr iii 1 1 ^ irvt.i çnor-o 111 -r *1 çtimm o v* C* 62 p. scripta is minimal. The stored CO2 will be released into the lung during active ventilation; thus lung COg concentrations are pulsatile

(Ackerman and White, 1979).

Simultaneous mpAsurements of PO2 i^ the lung and dorsal aorta of sea snakes show that a significant difference exists, with the blood giving a lower value. Either a R-L shunt occurs to dilute the pulmonary venous blood entering the arterial system or else there is incomplete equilibrium of the O2 gas in the lung and blood, or both. Calculations indicate that

this corresponds to a 50-70% R-L shunt (Heatwole and Seymour, 1975;

Seymour and Webster, 1975). Since it is known that cutaneous gas exchange occurs in sea snakes (Graham, 1974), it has been suggested that the shunt

serves to keep arterial POglow, thus allowing O2 uptake fran the water

when the snake is at or near the surface and preventing O2 loss to water

during a deep dive when the lung PO2 increases (Heatwole and Seymour,

1975; Seymour and Webster, 1975). Seymour (1974) argues that the shunt

also may help to prevent decompression sickness following deep dives by

rîîîtîtnnn v^-'r-n ninnx rnc it'rrrç fno -tîççmûç

where equilibration with the sea water occurs.

With regard to cutaneous respiration in submerged sea snakes, it has

imnûv^ rTNnn-i-r T nnc nnv^mallx/ -i r luncn

was reduced to about 16 torr, survival time became as short as 23 minutes

(Graham, 1974).

During diving in turtles (Robin et al., 1964), iguanas (Moberlys

G. I O. I I I y Ci. w 1 ^ ^ x j ^ uCtww * 1 ^ 1 1 * 1 63 pathways. The increased pulmonary vascular resistance causes a partial pulmonary bypass due to development of a R-L shunt.

White and Ross (1965), Bel kin (1959), Burggren (1975), Johansen et al. (1977) and Lucey and House (1977) have found that turtles have a higher heart rate during active ventilation than during apneic periods. This is associated with an increased blood flow to the lungs (White and Ross, 1966;

Shelton and Burggren, 1976; Johansen et al., 1977). Such heart rate and blood flow changes during respiration may provide a more efficient ventilation/perfusion relationship. Findings similar to this have been found for alligators (Muggins et al., 1970), marine snakes (Heatwole and

Seymour, 1975) and lizards (Millard and Johansen, 1974), and evidence indicates that the lower heart rates during apnea may be vagally induced

(Burggren, 1975). This reduction in heart rate during apnea may be related to the bradycardia of diving.

Burggren (1977b) did not observe this heart rate-respiratory response in garter snakes. It should also be noted that Lucey and House (1977)

4 u'sc iif'non T no nnnv Tpmnpr*^ — tare was decreased to 1G°C.

The cardiovascular changes which accompany breathing in many reptiles

^ ^ — "2 ^ ^ O^ * r\ /~v-r +-1^0 1I T m C I : 1 n 111Ct y L/ ^ I ^a * o w I ^ J ^ Ê I /\ I a^ w I I ^ ^I V w I • w • ^ * V» « * ^ w » • • •^ ventilation. However, Burggren (1975) found that artificial lung infla­ tion with various gas mixtures did not alter the heart rate in turtles.

Lucey and House (1977) and Burggren (1975) suggest that the responses noted are probably due to inhibition of the cardio-inhibitory center and

/-V* X ^ ^ r\^ / -r-Pno 3 r*^ 4 I/O r'OnT'OV* ^ all

U; vJiMUii a: c luva ucu i1iC wcuuiic, uuivnyaua uiiw a i c i\i iw/v*, w *,i w0 4 a w ^ with each other in mammals. Lucey and House (1977) also observed a slight rise in systemic systolic and diastolic pressures in the turtle during active ventilation at 25 and 30°C. Jones (1966) has reported that spike activity in the pulmonary vagus afferents increases when the lungs of frogs are artificially inflated. An increase in heart rate then follows due to a decrease of activity in the cardiac vagus. Jones hypothesizes that some type of proprioceptor or pressoreceptor input resulting from the lung inflation initiates this reflex response.

Boyer (1953) found that the time which the snapping turtle spent in apnea declined with decreasing ambient O2 while the heart rate increased.

Kinney et al. (1977) found the same phenomenon with the turtle P.

fioridana. The pulmonary blood flow was greatest during ventilation, simul

•f-snoniicS(» «.A » • ^ un+h•* • ^ i-ho^ • 4 nhsco^ • 4 ^ n-rV • msvimiim4*4 4 * « t • t • Inoavf44 ft v-^ra4 V-* nwrinnS-* • • • • ^ a niyan^ 4 # Sw# 4 • 4 ^ ^ 4 4 S.» Sf 4 ^ cycle, pulmonary vascular resistance would increase as apnea progressed and the POg of the lung gas declined. White and Kinney (1975) observed the pulmonary microcirculation of the turtle through a window placed in r'no raranara nnno nwcr tdo ; : i nn Q Hwnnvir nvne^rannir infrn —

i~\ k I r\ A -IW-1-Î-/N 1 i y-» 4-» X I , %. » ; Tk I I 1 3 O 3 ui il. & w 11y o oiu mw u u^^cui uw u uu microcirculatory level, as would be expected for nianinials. Evidence indi- r'3'^C.Ç u>:cau ^'r»0 s..4 vii v1 i r\w —) ^wt : Iiii rr i*câ 3 v~i jf\ / 1iii ri ^itv»^ioçuc«i

lizards, and snakes is probably neurogenic (Luckhardt and Carlson, 1921: Roy^nov^ 1 079 • i to 1G7P^ Tno cifa f nv^ wacnrnncfr^rfinn i c a f a binb

level in the vascular circuit because pressure measurements between the ni î"! mAna v*\/ av^rov^x/ noav -rho anri email nt 11mrsna v-»\/ noav^ f Xo

this pressure differencial (Bercer, 1972). Since zhe changes in heart 65 rate and pulmonary blood flow rapidly follow changes in respiration, such a control system is probably regulated by mechanical factors rather than by alterations in alveolar or blood gases (White, 1976).

It is also possible that cuemoreceptors in the lungs responsive to

CO2 would help regulate blood flow and heart rate. A reduced PCO2 could increase heart rate and increase flow via a reduced pulmonary vascular

resistance. The opposite would occur when the PCOg was increased. How­ ever, during diving when the PCOg increases, some mechanism must inhibit

the drive to respire since 1-6% CO, is known to stimulate respiration in

air-breathing turtles (Jackson et al., 1974; White, 1975; Jackson et al.,

1979). Such intrapulmonary CO, receptors have been demonstrated in the

reptilian lung (Milsom and Jones, 1976; Fedde et al., 1977). The turtle

receptors also respond to mechanical stimulation, in contrast to those in

the lungs of birds and lizards.

No defined baroreceptor sites have been described in reptiles

(White, 1976). Glomus bodies have been described which appear to be

mùrpnûlùyiually bimildr to mammalian carotid and aortic bodies (Aaams,

1953); however, functional evidence shewing their role in the control of

circulatory or respiratory phenomena are lacking (White, 1976).

Reptiles appear to nave DOth augmenter and ceceierator nerves in­

nervating the heart. Cardiac sympathetics run with the cervical vagus in

turtles (Qaskell and Gadow, 1884) and lizards (Khalil and Malek, 1952).

The sympathetic fibers behave on stimulation like those of mammals

(Berger, 1971), and the principal catecholamine released inthe turtle is

iitC \ I O inc h » 1\\J C u & : . ) J. Z/\J J • 1 1 :C : C CiC CwiCHCiyiV I i UC( ^ I IL

the caval veins, sinus venosus, auricles, ventricle, and coronary arteries 56 of reptiles (Furness and Moore, 1970). Catecholamines produce both posi­ tive chronotropic and inotropic responses in reptiles (Akers and Peiss,

1953; Kirby and Burnstock, 1959b). Stimulation of the cardiac vagal fibers

l

the left (Khalil and Malek, 1952).

Although only a few species have been investigated, an extensive

autonomic innervation of the vascular system occurs in reptiles (Burnstock,

1959). Most fibers supplying large arteries are adrenergic*, however,

evidence exists for excitatory cholinergic fibers (Kirby and Burnstock,

1959a). The coronary arteries of turtles differ from those of mammals

in their response to catecholamine?. Juhasz-Nagy et al. (1963) showed

that epinephrine produces vasoconstriction rather than vasodilation.

Acetycholine produces vasodilation. From (1950) reported that sympathetic

drugs will decrease the capacitance of the turtle venous system markedly

and Furness and More (1970) have shown that the major veins and their

iii u; z> ; i i z.c lu ci-s ,,

less so than the arteries. The pulmonary arteries of reptiles appear to

be innervated by cholinergic and adrenergic fibers. In turtleS; choliner-

y IL vaya: ^uimuiauiuu uiuuucci yuiiiiuiiQij' ai uc ; i a . vaivv-Oiiiv,! wn, ..

as epinephrine produces vasodilation (Luckhardt and Carlson, 1921).

Berger (1972) showed that the adrenergic innervation to the turtle lung

\/3 cru 1 a f : i rc nrnHurcc wacnrilafinn ç -îrnj 11 a rori

Many workers have reported that a temperature sensitive area of the

ill V U I U & C^ /VlllWil v^rC^ii Ct I V CI I I « V I IV*

(Rodbard et al., 1949, 1950; Heaûn et al., 1958). Heating was associated 67 with a rapid rise in heart rate and pressure, but the effects are largely absent when the body temperature is below 20°C. The rise in the heart rate is probably not the result of secondary reflexes resulting from the n V-» oc c • • D v> r» ûc 4- K a H-î "hî r>*-> n-T 4 c v»\/ v»o— sponses as understood from studying mammalian pressoreceptor reflexes.

Data bearing on the central neural components of vascular function in reptiles are scarce.

The ability of reptiles to undergo anaerobiosis is remarkable (Johlin and Moreland, 1933; Bel kin, 1963a, 1968a; Jackson and Schmidt-Nielsen,

1966; Jackson, 1968; Gatten, 1974). Bel kin (1963a) exposed a vari­ ety of reptiles to an atmosphere of pure N2 at 22^C. They survived for periods ranging from 20 minutes (some lizards) to 33 hours (a turtle). He found that reptiles fell into 2 groups on the basis of their resistance to anoxia: one with a minimum tolerance time of more than 4.5 hours

(usually about 12 hours), and the other with a maximum tolerance time of less than 2.5 hours (usually about 45 minutes). The first group included

UL* I u 1 CO \ C/Ww, CL/ U iMUl lliC Ok /CV, ICO/ www VI IC O oiivi inn. ^)

^•î*7av^nç a nrl n v^nr-nn1 1 4 sn c •fnv«-r"ioc anncs y*on rn no 4 nto v^or! 4 a TO in

fhic rona^H T'no mannv rnrrolato annoa^c fn ho taynnnnir rafhor than

cuw I Uy I \^a I • Occ, 6na Wvuiu iGii 111 uv one c>c:s-»umu yivuv Q. u\j v c oi ai »ani 5

J. / -T; • ; J icjf aic uiv I C acnaiuivc uu \j 2 : f\ uiiQii muO v ic^uiico

land snakes). Robin et al. (1954) reported that submerged ?. scripta

could survive for 5 days at 17°C.

Bel kin (1963a) found that freshwater turtles were over 10 times more

vw >c> 14 u \J I ci i iv/x i c& uiiciii t1c1 c w u: id i i ic<^ ^ vi ic « i ittcciii c« i i c w»iito twi

i1 2 d ^ y ' j' « lt u ^ C.U -w -t • / w" t \jk i o y • w.dcr*4.^^ uo \ yl& i c J 68 can survive submersion for over 2 days at 25^C and over 3 months at 1.5°C

(Musacchia, 1959). Robin et al. (1954) report that p. scripta can survive dives of up to 2 weeks at 15-18°C. Penney (1974) reported that 30 hour

death. Since the turtles can survive longer while submerged than when in a N2 environment, it is suggested that their metabolism and energy demands are reduced while underwater (Penney, 1974). That this is indeed the case

has been shown by Jackson and Schmidt-Nielsen (1955) and Jackson (1958).

Pseudemys concinna has 0? reserves to allow for a 2-3 hour supply at a normal rate of metabolism (Belkin, 1954). For short-term dives of 30 minutes or less, p. scripta can carry on normal aerobic metabolism (Jack­

son and Schmidt-Nielsen, 1955). As the O2 stores become depleted in long

dives, however, the metabolism decreases until, when no 0? remains,

metabolism is about 20% of predive and is primarily anaerobic. Extra­

pulmonary O2 extraction during diving in most turtles has been considered

to be minor (Robin et al., 1954). Jackson and Schmidt-Nielsen (1955)

• wiiCkw VY w^ III z'. TT«-*o I vi-vj u _/~T/o wu I Illy .awwuici O:v:i«

Tho\/ DHT -rna-r niiv^-inn c ; 1 nmo o umor» "frv-rsl n c

nnl V 90" that nf nranivo thic P."/. rnnlH ho cinnifirant -fnv ciiv^i/TV/al Uinui

^ t 1 —K j J. t,« — —» - "A - ^ ^ , li.v CVCIJ t^C.fxin \ 5 0. J lOUMU unGu bulVlVCI LI IIIC UI ^. scnovâ. :>uu-

4 1.-4 1-» <^4 ^ v» ^, v» /-s a m •-•^c ^ •)! I I I wi L& UC'U VII cI Ul iC I yulC V2 VI l%2 MVU UillCICIIU*

He also showed that the rhythmic gular movements which result in bucco­

pharyngeal ventilation stopped after submersion. In addition, Bel kin

ç hn'ia/ori that wantilatinn n f t xo iwol 1 _ ol ^ — —' — *N_pi w I I^ tts»! • ^$ WV* W^ I WW I L* VII L* I1

tta vci 5 nil I v^i » wuu uj o yt MCI1 ^, scri.pZcL ) :> I I CC uu ui caui: a 11 , uups wncn une 69 animal is completely submerged. Obstruction of the cloaca did not reduce survival time underwater.

Extra-pulmonary O2 uptake may be more important for the musk turtle '

(Belkin, i968a) and Nile turtle (Girgis, 1961) than for Pseudemys. Girgis

(1964) has demonstrated a large pharyngeal branch from the carotid artery of the Nile turtle breaks up to form an extensive rete mirabile in the wall of the pharynx. From this rete, capillaries enter small respiratory processes that form a dense mass on the surface of the pharynx. It is thought that gaseous exchange between these vascular processes and the water enables these turtles to remain submerged for longer periods of time than would otherwise be possible.

In turtles, it appears that a lung PO2 of 20-26 torr characterizes the critical PO2 (Bsnnstt and Dawson, 1976). Ackerman and Whits (1979)

have estimated that it would take about 45 minutes for the lung PO2 to reach 22 torr at 22°C based on predive O2 consumption data. The maximum voluntary submergence time they observed in ?. scripta was 44 minutes,

ui vuu:3c, cvuiviuy nniic iuuniC! ycu w i : i i:lu ; ucx ui:i3 u :sue aiuuc une

O2 will be used at a greater rate. Therefore, even though P. scripta

possess a well-developed anaerobic capacity, they may not routinely reach

Pv2's which evoke anaerobiosis. Instead, routine submergence will be

terminated as the lung 0? concentration approaches 22 torr (Ackerman and

Wmte, 197S). Wood and Johansen (1974) state that voluntarily diving

monitor lizards are stimulated to emerge when the Pa02 decreases to about

o / i * /"\ vmt,» sj v uw i i • 70

Jackson (1958) found that tne internal 0. stores of the turtle p. scripta were depleted within one hour of forced submergence at 24°C. At this time lung and blood Og content was approximately 1%. Once the criti-

and by about 45 minutes the entire animal became anoxic. However, ever, during anaerobiosis, heat loss continued to fall indicating that anaerobio- sis was slowing. This was probably due to the accumulating lactic acid inhibiting the reduction of pyruvate to more lactate (Jackson, 1968),

Therefore, once the O2 stores of a diving turtle are depleted, even though

the animal is in no immediate danger, its range of activities are probably

limited to hiding or resting or minimal activity which would propel it

toward the surface.

Seymour (1979) and Seymour and Webster (1975) found that blood lactate

levels usually do not increase in freely diving sea snakes. This means

that routine dives are accomplished aerobically. However, in 2 snakes

(out of 18) high blood lactate levels showed that anaerobic dives do

vwcaiumv \-.u;icia ucu uuiauinu uicv ur

predators. Seymour (1979) estimated that severe anaerobiosis may occur

i n nno nnf nf OV/OV^X/ \/nl t tni-a 4 m -f-i-ioco cp - - • V « • V V ^V ^ ^ ^ V % W • 11^ t ^ • r ^ ill ^11 ^ ^I I rN ^ ^ J y? I O ^

analysis of lung gases during experimental dives of the marine iguana

implies aerobic metabolism during normal dives of 3-5 minutes duration

(Hobson. 1965; Ssymour. 1979). However, during "escape" dives the marine

iguana may build up high blood lactate levels (Bartholomew et al., 1975)

a «vc f x (3 -îim«.4ui>ic4 m « 3 \ i i w c/ : : y * 'i 0 c o \

wj iv-;s-iwa\-.cu«v^ uj!w c>uiviva; oiiiic u 1 au u—

merged turtles, but permits incefinite survival in air (Belkin, 1962; 71

Jackson, 1958). This indicates that anoxic turtles are dependent upon anaerobic glycolysis. The bicarbonate concentration of turtles is high which suggests that there is an increased buffering capacity for acid mofahnlifos fRolkin Rovlcçnn <;hnwon that lartatp dnçs nnt appear in the carotid arterial blood of submerged sea turtles during the

first 30-60 minutes. However, longer dives result in increasing concen­

tration of blood lactic acid. On emergence, blood lactate increases

markedly suggesting a diminished muscle blood flow during submergence.

In p. scripta and the iguana, blood lactate increases throughout the dive,

and there may be no increase upon emergence (Moberly, 1968a; Jackson and

Silverblatt, 1974).

As O2 is depleted in the lung and blood during a dive, CO2 concentra­

tions rise. They may rise to high levels in long dives. Andersen (1961)

found a lung CO2 concentration of 10% after a 105 minute dive of an

alligator. McCutcheon (1943) found it to be 12.9% 40 minutes after

submergence of a turtle. Since it is known that both hypoxia and hyper-

^ z v* r- r» ^ m 1 ^ ^ r- — *« 1 7 ^ 3 i 1 û/1 /i * V4I X* I IVi I ^ «II \ I \Vk IIWtVAl* W

Rnwor lOn^ "Gnn^ -it T c nn-r i/nnum nnvi t'no roGniratnrv morhpnism i<

msHo in

i'iCu. MQli J v-.a I pC I J o ; C u i uI iC M CCi i u lii uci i ^ lu iiG. i i CO oCU Uj

01^ f» \/ 41 Cl ; C^vCp/-\ \/ -f-u iu> O.^ 0(iy:JU

more than 15 hours of anaerobic work could be carried out in vitro at

23-25°C, provided some plasma was added to the medium. Bing et al, (1972)

/-Amnav^or! f ha nav^r nv«rna nr* û nr icnlarcH crv^Tnc nr frrtlo a nri

: c u ; ICC : u Giiu : vunu uuc lucviicii i vc i cuuivic^ v : nj ^ vui uic iiijuuQ i u ; uni

to function much longer than that of ine rat. The increased hypoxia 72 tolerance of turtle heart is due to an enhanced capacity for anaerobic glycolysis (Reeves, 1953b). It has been suggested that a dependence on anaerobic energy sources exists even for the central nervous system dur-

Nervous System and the Integration of Physiological

Responses to Diving

Nervous mechanisms which initiate and control the respiratory and

v-»oc Ç oÇ -rw \^4vllt^ ilx^vv^U^x/o k/s. iitlcawll 1ts^ooo c c oç-rv l*i tr? n« orîv. wllsiatt Tv iKo l\.. responses themselves. However, contemplation of such mechanisms has been apparent in the writings of many people beginning with Richet in 1894b.

The first modern studies were carried out concurrently, but independently,

by workers in three Swedish laboratories. Their reports were all pub­

lished within six months of each other in the same journal (Andersen,

1963a, 1953b, 1953c; Feigl and Folkow, 1963; Hollenberg and Uvnas, 1953).

All studies used domestic ducks.

Three of the reports (Andersen, 1953a, 1953b; Feigl and Folkow, 1953)

described experiments to differentiate between the effects of asphyxia and

water immersion per se. Diving bradycardia was used as an index of the

cardiovascular changes elicited by immersion. The ducks were provided

with tracheal cannulas which could be attached to respiratory pumps or

uv Oiivn uv iicc oii in au umc i ycu an i uia i .

hairi a nri nnl i/rw.f fn r ; r'h^r T'r^a ufh^rh nmiv^c ritjv»—

Înr nivirin ic nnr r'no rn ci m nl \/ acnnwvia Orr": wcir^r\ nf rhn

cannula caused a cardiac slowing, but it was less than the slowing seen

Hurinn : K*r.nv»ç-Inn 1 'non -rho r-a nvni ,1 p ç /^itv**?nn 73 submergence, surfacing would only bring the heart rate back to approxi­ mately 75% of the predive rate, whereas if the duck was allowed to breathe upon surfacing the heart rate would immediately return to the predive level. Bradycardia in submerged ducks that were artificially ventilated was immediate; however, it did not decrease to the same extent as that normally seen during submersion. Using gas mixtures to produce hypoxia or hypercapnia, these investigators found that elevated COg levels poten­ tiated the submersion bradycardia more markedly than Og lack. They con­ cluded that diving bradycardia depends on at least 3 factors: 1) a ner­ vous reflex resulting from the head immersion, 2) progressive hypercapnia, and 3) increasing hypoxia.

Andersen (1953a, 1953b) carried out similar experiments using essen­

tially the same techniques. His findings were very similar. He found

that the area around the nostrils and the nasal cavity of ducks would in­

crease the degree of diving bradycardia when such areas were imnersed in

water (Andersen, 1953a). He also found that as long as essentially normal

fluctuations in heart rate could not be effected regardless of the gas com­

position used. However; if large "tidal" volumes were delivered, brady-

/J ^^ ^ ^ — «m. ^^ ^ 1 v% ^ TD^ ri^ ^ ^ ^ I V.U À ill V V CÀ I Va* I ^ aa^it «W « iI w * * r" w

Kv^pp-t-'op Tvaz-lnosl nrrlucimn /~ancori rarHiar clnunnn hn+ i f wa c; nnf a <

pronounced as during a dive. Asphyxia alone never caused apnea (Andersen,

i963b).

In another paper, Andersen showed that the physiological adjustments

-rrx c M r\mov-»c •: nn mo/-'m1 1 a / v^ûtiûvoc /ûnnarcan î-io TAnnri f^AT

VC*»* ClV./i4S^Cfc Ct I 1 ^ W * V» 4 L* ll'wt ^ u* ^ Ct, ^ readily as they did before the procedure. However, these responses were not present after cutting both trigeminal nerves. After sectioning these nerves, submerged birds would continue to breathe through the tracheal

CQIIUUIQ CLllU WiOll MVJ S^llCxiiyC Ml ilCCil v iUoC* vvs./c<«vu i C gardless of whether the central nervous system was left intact cr net.

Further investigation showed the ophthalmic branch of the trigeminal nerve to be the most important limb in the afferent pathway. Animals in which the central nervous systems had been left intact, but in which the trigeminal nerves had been sectioned, were panic-stricken when submerged.

They struggled violently and attempted to breathe through the tracheal cannulas. Such a response appeared very similar to the response to sub­ mersion in non-divers and it looked very much like voluntary breath-holding

It was concluded that the nervous impulses which arise in the area in and around the nasal cavity upon water immersion inhibit the respiratory cen­ ter and, directly or indirectly, elicit the cardiovascular responses to diving (Andersen, 1953c). However, even though higher brain centers are

Û0 L rcOu'srcu ;0r Luc br'du vCà ruà Oi u i v 1î': û . 1 u 1S wc i i "NHOWn thâ u tûc Tê-

( 11 vCiV, u yr-vii-uCi OC»!, uc I I i I ) ^^ u-r 3 vjCi uuu unu UO.HO5 j, ^ ^ j •

Hypercapnea seems uo play a role in maintaining bradycardia since

emersion of turtles into pure CO, did not allow a reversal of the diving

rosnnrcos iwnoraac intn r a : 1 fho hrAHvrarHia to hp ro-

4 I ,c 4- PC -Î "F »o/-\ pi 3 4 4-o 3nX Dncc >111 V u*—w J w^ V i I Ow I I G I I I y iiiuN^ iiwimCt Gti ^ « 1 * vs.. Gir^i * O^ ^ \J U y *

J Iic 5 c ! u f c; CilxjA • 0. a • vj f }c c. : !; ! V u uc vMC vauac v ) vi ;c iiiui caocu vcy G » w;;c

during diving. Johansen (1959) reached similar conclusions using snakes 75

It is reported that the major cause of diving bradycardia in frogs is O2 lack. When frogs are submerged in water that has a PO2 of 760 torr,

O2 consumption continues at the predive rate and there is no bradycardia

/ 1 s f /\ v* -» w ^ r\ -« ^ VVI #C O CitlVJ OllC 1 UL/11 9 X ^\J'T ) J. V-/ / J m IIS/>IV»(^C» ) Iii w l*

t v..ickuiwtiOiiij^+ wwovvwv.liKo+».roo>^ UoavH+t I ^ I u uw www3 r»/H Hwp r\v~wi fwwC) H anwii wtiw«jr^t^snalwcnc n-Fw> *^»ww\4 yw O concentrations is necessary. This was not done in the above studies. How­ ever, Lillo (1978) did measure blood gases during submergence in frogs and found that when blood Og levels would decrease, a bradycardia would occur. Blood CO2 or pH levels were not correlated with the bradycardia.

The bradycardia was not reflexive (took 8 minutes to develop) and was de­ pendent upon an inhibition of lung ventilation.

Bel kin (1964) reported that bradycardia is not elicited in p. concinna. when the nostrils are filled with water. He reports the same thing with

the iguana (Belkin, 1963b). However, Murdaugh and Jackson (1962) found evidence suggestive of the involvement of the nares in the diving brady­ cardia in snakes. During their study, 2 snakes had difficulty shedding

LUC I I ua^a « svaics. DuCf'i ncO r cbUî'Ccû Cv lûuu C:1 Of ca Cninu v i' vû-

-f-\!• -T- v-n-N<-C o 4vt -rl-i o ^OC"^ -r -roo c"^Ol/'OC kj I W Wjr WWIWtW) N,,.WItVtWljr U W Ul I W IWO^Wmc^W «m V I I W IW^^ W I VI IW OlWfNWO*

Receptors around the nose and on the face are also responsible for

uu Uii UMC ui cujcc; u ; a uuuui : i iiy in ma : : ui i wa uci i uuuc f :5 J ui i \ M: icjnc cf :u

Killip: 1967: Heistad and Wheeler, 1970), and the limb vasoconstriction

(Heistad and Wheeler, 1970). Dykes (1974) reported that seals with faces

ypnriprpri ane^rhsfir Sv cxhrntanonnc iniorfinnc n-r liHnraino

a x 1 * 4 ir» /i 4 ç a rs\r^ ^ 4 m 4 1 3 v» -t-r\ +^3^ 4ws ^ ^ m ^

seals without immersion. When these animals were ventilated below water. 75 the heart rate was the same as when breathing above water. Thus, a cessa­ tion of respiratory movements and neural activity from facial receptors were thought necessary for immersion bradycardia.

n 1 1 ^ y» —. V-. J Uv —> ^ m ^ • I T ^ ws ^ /-» rvnyci »—vciiiicz) anu uaij \ ± u^ x Jt l.kidney, and splanchnic vascular

bed, but not in the common carotid circulation. A reduction in cardiac output also occurred. Similar studies have also shown an increased secre­

tion of adrenal catecholamines in the rabbit (Allison and Powis, 1971)

and splenic contraction in the dog (Angel1-James and Daly, 1972a) result­

ing from nasal stimulation. These cardiovascular responses from the nose

still occur when the apnea is prevented by artificial respiration, al­

though they may be reduced in size. The evidence suggests that these

responses are the result of primary reflexes from the nose rather than

secondary effects due to respiratory or blood pressure changes (Angel1-

James and Daly, 1972a). The afferent pathway is the trigeminal nerve,

âilû the c r Tcrcn u Og uiîwg v lOi u'lc CârO'iâC r'cSpOî'iScS IS vâyuS i'tcr'VcS

;=îr.h fnr thp- vasrxlar fiherc

.lamoc anrî T f cz-vz-M-nc 4- X 3 4- -r 3 o3 1 r\v* L.» V» I jr ; .!._// L-W J • O y t V/ WW I VfllUU U l l V. I ILA I V I

receptors around the nose and on the face (Eisner et al., 135oa: Kavvakami

et al., 1957), initiate the cardiovascular responses to diving. The brady­

cardia actually produced is the sum of that produced by face immersion and

that resulting from apnea (Feigl and Folkow, 1953; Kawakami et al., 1957).

thû nr man 4 c rno 1 uiafcmnn^a+u^o f \iVr\^\/r>ci

1974). 77

Asphyxia has been shown to cause a reduction in muscle blood flow in the dog (Irving, 1938a), seal and sheep (Eisner et al., 1970). At the same time, blood flow to the brain and heart increased (Irving, 1938a;

^"v j- —1c7 \ *.iti fo »*mit ^» f \ f ^1 ^ Il|./ W C. I I C, V LA I # ) J m liV^V«V«VCl 9 VVVA.O I * C* I J V 4 « V I * L* V * S,/ I I w^

/-Iwbti* iv^v»T r^rr iI MI I fkocawiiv^Ov» snnmaleI I I uiL* * O # TXII n Xnnc vvii^ii -hWûwtts- acnkwvia^^ »jr /\ * v» 4* ^c a c cnr» t p-{-ûrîu\.. w i.fi«t • fw Int i

hyperventilation, a vagal reflex initiated from the lungs overrides these

responses and little or no changes occur in heart rate and systemic vascu­

lar resistance (Angell-James and Daly, 1959a). Therefore, in diving ani­ mals apneic asphyxia is important in initiating the cardiovascular re­

sponse and also probably the vasoconstriction.

In addition to respiratory control, arterial chemoreceptors play an

important part in the reflex regulation of the cardiovascular system.

Situated in the carotid and aortic bodies, they are stimulated by arterial

hypoxia and to a less extent by hypercapnia and acidemia. The primary

cardiovascular reflexes caused by stimulation of the carotid bodies in­

clude bradycardia and vasoconstriction in skin, muscle and the splanchnic

vcu uaij. itic avr Ù :u ûvuics cvunc i f iucn:>c va^uvvnsurivuiun

in the dO- 1 Qf^.7 ^ ^r\r. % 1 1Qr.P>V h.'.'.f i

C 4" Î 1 1 c/^rno rîrvitKr- r» »->/-» o ^ -r v»/-\1 r\ -P v^a-r.-v / H 3 1 \ ^ \f s » t ^ \^H I \m Ill 11^ S;, WlI VI W I vy I IIS. ».* I L» l\AWV,. ^I./ I^ ^ ^ t tmm J •

Both bradycardia and systemic vasoconstriction occur in apneic asphyxia

and are due to excitation of the arterial chemoreceptors (Angel 1-James

and Daly, 1959a).

It thus seemed likely that the chemoreceptors, stimulated by hypoxia

A nH hx/novr s nn~? s u;nwlrl rnni-VT Si;ro tn -f-'no rzrninwacrular vocnnncûc nf Hiw_

Illy 111 uu<-n;5 aiuci ucucivauivjii ui vai u u iu ui icuiu- aiiu uai ui cuc^ ou! i . rut 78 technical reasons they could not denervate these receptors separately.

The result was that no submersion bradycardia or initial pressor response occurred. Since these authors were aware of the fact that baroreceptors

—« •^ -a ^ m a ^ m j— a ^l» ^ ^^ u ^5^ ^ o ^ ^11 n ^ ^n n ^ i ^ a f c Ilu u I cspv 1 iz> 1 V c uv in ptij •^*-'2 ^ ' « ^2 c ^ j ^ they concluded that the chemoreceptors in diving animals are stimulated by the progressive asphyxia which produces an increase in peripheral re­ sistance and a fall in heart rate.

On the other hand, Johansen and Aakhus (1963) never observed an in­ crease in blood pressure during the initial stage of submersion. This,

they said, means that the bradycardia of diving cannot be due to increased

baroreceptor activity. However, as Andersen (1956) has pointed out, this

does not eliminate the possibility that baroreceptors determine the rate

of cardiac slowing. It is the function of baroreceptors to prevent changes

in arterial blood pressure. The baroreceptors are rate-sensitive; that

is to say. their rate of firing is determined by the rate of change of

blood pressure (Landgren, 1952). The system for blood pressure regulation

tnub inUIUUKS IGCIiiUlCb !Ut uuh-n ; csuun sc wi i i n nuu ! u CI IIII II la uc laiyc

pressure changes in an intact diving animal. As peripheral vasoccnstric-

^ a ^ r /- \#/-\v^*ro>rn"^»a-ro 3m \/ 1 n V I W :( \_/yi i(i Li itwiiiCw VIC: m i\., vO> i v v. i ) vk

blood pressure is automatically compensated for by further cardiac slowing.

In the end when peripheral resistance is maximal, bradycardia has become

fully developed and the blood pressure has not shown any obvious changes.

Kobinger and Oda (1969) treated ducks with drugs to prevent peripher-

a ' !! r\r\ r, c, , Xm o^ c r\ -P H i i c1/ c c + 4 11 n _ S.** Iw* I I V I S.» V* ) WI ^Nxtjrs^^i s* I V « t I V

curred. They concluded that the baroreceptors were not of primary impor-

tance in initiating ihe lower heart rate. Lin (1974) reported thai: 79 bradycardia still occurred during diving in reserpine-treated rats while aortic pressure was actually falling (reserpine blocks adrenergic activity).

Lin felt, therefore,that the baroreceptors were not a contributing factor

til VIiC wI V * My wI C*wjf O.I uI L& *

\/p cr\/-/Ma Ç nii^uiwii ^ i +v#jr r\*Pwi 4-w nai Kv*a/Hak/i sa>ujr *1 a *îiii n rlnx/nnn

(Murdaugh et al., 1958). These authors maintained the heart rate of a

harbor seal constant via intra-cardiac pacing and found that vasocon­ striction still occurred during submergence.

It is possible, however, that resetting of the baroreceptors could occur. In other words, the curve representing the normal relationship be­

tween the heart rate and mean arterial pressure could be shifted, so that

at the same blood pressure, the heart rate was lower compared to the pre-

dive value. Also, the curve relating vascular resistance and mean blood

pressure could also be shifted such that at the same mean pressure the

vascular resistance during submersion is greater than predive. Indeed,

evidence exists indicating that this resetting of the baroreceptors

cvuuaiiv vuvuTS \miuc i 5-ua;:ic:> anu uaiv. 12/v? 12/cu;. i u ayycars una c

v*^ -r nv-i vy* I ^ i , w» i—4»um/»», i ^ t VI (C uu t w I Cv^ vv I 1 C 1 I C/\ C O vaul iiiy L/inC i .5 : v w; yi couuiLiw i viiiuuyu

a central mechanism (Angell-James and Daly, 1972b).

Jones and Furves (1970b) found that when the chemoreceptors of ducks

wnro Honorv/s tori . •fhcyo wzc nn rhanna i n t 'no latonrv nf nncof nf Hiwinn

bradycardia, but the rate of initial fall in heart frequency and the size

+»-tO V*OC'^'^»^CO Lîr\«.f 4» X ry ^ w I VI I»-. VLivi Y v.ijiiti>itOiiv.\a» iiwri vi i ;Cn>aiOvi i i./u v : w : : Vi

vitC C* I s-i I O. v^vwwv VMÛV V wv.» vaut ijiy iviuC : .a : v;i C&iiCw vCva uj^ v :iOiiU"

receptor denervation is not known. 80

If during water immersion, which reflexly produces apnea, the chemo- receptors are stimulated to such an extent that they contribute to the cardiovascular responses, why do they not stimulate the respiratory cen­ ters and force the animal to surface earlier than it does? Jones and

Purves (1970b) have shown that ventilation hypoxia in ducks causes an in­ crease in pulmonary ventilation of 3-fold when the PaOg is lowered to 38-

47 torr (PaC02 held constant). And yet, apnea produced by head immersion in ducks resulted in the same PO2 with the animals able to remain sub­ merged (Jones and Purves, 1970a). Diving reptiles also show lung gas con­ centrations which would stimulate an increased ventilation when above water (McCutcheon, 1943; Randall et al., 1944; Basoglu, 1951; Andersen,

1951; Boyer, 1963, 1966; Jackson et al., 1974; Jackson et al., 1979).

It is possible that during diving the chemoreceptor-respiratory re­ flex is blocked to some extent, possibly by inhibitory impulses from the facial receptors. In addition, it is possible that whereas the respira­ tory reflex response is inhibited by facial receptors, the cardiac re-

nrx "is ér!nrtrî(":hcl ni" triril i iêrî . Asd'îvxi.^ S t irnhnhi v nnî" rfip f^r-

UW 1 MllUldulMM UiiC VUIVISIM ICOUUIIOCO j « I U U:*lU(Gib% V U U I U inùj/ 1 1) UCi 1 b i I

them (Angell-James and Daly, 1972b).

Î wnrr -i n-r "i a -rn r- 2 t : c cc 'r\\r na1 /Hal \/ a w/n

Scott; 1958; Jones ; 1966) and vasodilation in the splanchnic vascular

bed, skin, and muscle by reducing the activity of adrenergic sympathetic

fibers (Daly et al., 1967). The receptors responsible for initiating

these changes are the pulmonary stretch receptors (Daly and Robinson, 1968;

Hainsworth et al.. 1970). Tne vagus nerves arp the afferent pathway

r") i c mil na y~ \/ n;a : v^ot-iov : ha 1 \/ ot tga/* a m/"; d/-\r\tr»çr\»i lo^q» 81

Angel 1-James and Daly, 1969a). The importance of this reflex is that it can modify cardiovascular responses initiated in other ways. Hyperventila­ tion (increased pulmonary stretch) may partially or wholly override the primary c9.?^diovascul?.r responses effected by the chemnreceptors. Alter­ natively. if the activity of the pulmonary vagal reflex is reduced (as

by apnea in the expiratory position), the primary cardiovascular responses from the arterial chemoreceptors are enhanced (Angel1-James and Daly,

1959a). This may help to explain the observation that artificial ventila­

tion of submerged ducks, especially when the "tidal" volume is greater

than normal, either can override the bradycardia (Andersen, 1963b) or

else does not allow the development of a diving bradycardia in the first

place (Reite et al., 1963). However, it has been reported that denerva­

tion of the lungs in ducks did not change the time course of diving brady­

cardia from that of intact animals (Bamford and Jones, 1975). This in­

dicates that the enhancement of the chemoreceptor reflex during apnea

in birds may not occur. This response may, therefore, be limited to mam-

mp ic TT TC AFCN nnccnKûo CNANNOC i n i n-RV^A -RNNV^AR* n n ny»oc çii VO m M i ri

produce changes in the venous return. This could then modify arterial

pressure and alter heart rate by eliciting a baroreceptor reflex (Craig,

4<

AT r'hanrro n*r 4-ka nv^ûcÇMvo

Since many animals exhale before diving (Scholander, 1940; Andersen,

1961; White, 1970; Kooyman et al., 1970, 1972), this pulmonary vagal re-

fley TT,;;v hp! n fn intanrafo t'no rarHinvasrxlar snri rncnirafmrv rocnnncoc

C>CCii i:#y û/\ i iCi > Ci u i wu L/C ivic v : V ; 1 ly VYII i iC^Ui^ sii a iCi i CA

slowing of the heart (Anrep et al., 1936), and in reflex vasoconstriction 82

(Daly et al., 1957). It will also result in less inhibition of the chemo- receptor primary reflex pathways. Thus, the primary cardio-inhibitory and vasoconstrictor responses to arterial hypoxia and hypercapnia will be nrann+ant- Tho voHiiroH nnlmnnarv vznpl innuf 11 siinmpnt thp ro- sponses resulting from stimulation of the nasal reflex (Angell-James and

Daly, 1972b).

A marked bradycardia occurs in man during submersion (Olsen et al.,

1952a; Scholander et al., 1952b; Craig, 1963; Irving, 1953) or simply in response to face immersion (Scholander, 1953; Wolf, 1954) and is equally pronounced in good and poor swimmers. This bradycardia occurs in spite of vigorous exercise just as in most other diving vertebrates (Olsen et al., 1952a; Scholander et al., 1952b). Apnea combined with face immersion also causes vasoconstriction in the limbs (Eisner et al., 1955b; Heistad et al., 1958; Campbell et al., 1959) and fingers (Heistad et al., 1958).

Kawakami et al. (1957) showed that face immersion in man causes a decrease in cardiac output and stroke volume.

f -« v-» w, t v"* /"s 4- i sv* l n III IMVkll \AINm ^IXtllS.»! W V• • W W W •• •

Other vertebrates, including the natural divers, with the exception that man may experience more arrhythmia and sinus arrest (Olsen et al=; 1962a).

L. I IW 1 Û M WCl C U Cll. \ j.^\j l.u j ^ UU Và t CV-i Ul IC va4V ( liy l U/l l^V-G. I » NU I V w I ^

liUiii UliC iviiCO OuiÛJMiiu C. iPU luatiw wu :

similar to those of other vertebrates. This included: marked bradycardia

during 50-90 seconds of submersion, blood pressure maintained or slightly

increased despite the cardiac si owing^ and venous lactic acid concentra-

•f-TPvn m-:r>"ÎTr.^l ri 11 n rr -r'no n'T\/o -ta : 1 K\/ a /-io*r"inT"ro i nr Co r\ m çi i v~-F3 r- *: nrr 83

01 sen et al. (1962b) studied American skin divers during apneic dives and found essentially the same thing.

Thus, the cardiovascular responses to submersion in humans are es-

+ -rWo camo 3c fbnca mf Hiwinn xrov+oKva+dc Hi ip n + i-f-iv/Dl \/ çnoalr- ing, however, they are not so marked.

Respiration has been studied in the Korean diving women by various investigators (Hong et al., 1953; Kang et al., 1963; Song et al., 1963).

These women typically dive to about 5 meters for approximately 30 seconds and average 60 dives per hour. They hyperventilate slightly and fill their lungs to about 85% of vital capacity before descending. Due to com­ pression at the bottom, both O2 and COg diffuse from the lungs into the blood. On ascent, CO2 is removed from the blood by the lungs (Hong et al.,

1963). The vital capacity of these women was found to be larger than in non-diving women due to their higher inspiratory capacity. The maximal

breathing capacity of the divers was about 15% higher than in the non- diving women. Also, the ventilatory response of the divers to high COg

nu,a icoa u: id : 1 111 uiic 11 ic: c wci v 1 * , u* 1%.

-rr» irw.r nvx/rron 'çnnn ;3» V • f V. V*-/ ' J" • ^ V W ! V '^•«7 ^ t » m ^ ^ ^^ -

SfnHioc 'na\;o c'n.-vi.in f'na-f- fofal acnh\/v-'3 ic inovifahlo in alnncf ovorv

uciivctj aiiiCZ) CO ai • ^ ;n 16 icsuiua in g ^unuiuiun ui av&wubiS v1

icbUiicLVij anu mcucuv : i v v: lytn \vcnic:) cu ct ., , nciouivu cu ai.j

1958). There appears to be a post-delivery maximum in lactic acid con­

centration — enough to indicate that the lactate is washed out from a non-

in asphyxiated infants and is usually interpreted as due to this condition. 84

Thus, the physiological changes in the human infant strongly suggest that oxygen-conserving reflexes similar to those seen in diving vertebrates operate during delivery (Andersen, 1956).

+ t.rnrln o on ç ûn11 on-r na Ç "f"v*n i n + ûç inp 1

ischemia and necrosis have been reported in patients with myocardial in­ farction, ventricular aneurysm, or coronary arteriosclerosis. Gastro­

intestinal necrosis may also follow from mesenteric angiospasm after

hemorrhage, traumatic shock, surgery, burns, cardiac arrhythmias, and con­

gestive failure (Corday et al., 1962). This response is basically iden­

tical to the physiological adjustment the vertebrate divers employ to

survive prolonged submersions (Eisner et al., 1964).

The physiological responses to diving are developed to near perfec­

tion in vertebrate divers. They are also present in other vertebrate

animals and man. Phylogenetically, these reflexes are old, because they

also exist in fish when removed from water. Bradycardia occurs (Dehadrai,

1962; Garey, 1962; Leivestad et al., 1957; Otis et al., 1957; Scholander

^ ^ ^ n o^ o ^ ^ yj «r ^ jt a . < ^ j ^ a ^ ^ a lk 4^ ^ ^ /x t ^ ^ r • •• t ^ c u u. i .) « u mu i u wu a swuuu u: i u u u vwui i o; i ouiumvi i ;ly v:* tuiisa wu i t nuo

! I ^ •n ri 4 -4 rVDic-^'^C *.' >> 4 n c TiATTv f «n r\IOr*n ï.fDOn

•ri^o fncn n c rmt-r xa r- !/ 4 y. cf- a 1 10^7^ I I I i^ii i\ III r«\.AUs.»i \u. i v *....) ^ Vf v* * »; ^ ^/ y #

et al._ (19o2a) have shown the same response for blood lactate in the

y I UI11V113, c I i5ii v^wjuM spawns uuu ui wcuci un u: ic ocijiuiimc uccvi icz>. n

prompt bradycardia is also observed in the flying fish during a simulated

flight (Garey, 1962). On the other hand, the mudskipper of tropical man-

y ) w V c CiiCCa O uc: {w Z> u: :C , vjr u i uiuic v^uu w : uC i ivi CC, u j i i ^ Ci»;

from its enlarged gill pouches. When frightened, it disappears into a

mudhole filled with hypoxic water and immediately develops a bradycardia 85

(Garey, 1952). This fish has so reverted to an aerial existence that it acts physiologically like a normal vertebrate diver and shows an asphyxiai defense reaction in water.

x o viiua u i o vi v vi ic i lû 11 t cmp i cw wjf i tu vu i u i divers to remain submerged for prolonged time periods are present in all vertebrates during all stages of life. They are not simply defensive mech­ anisms unique to vertebrate divers, but rather the natural divers have perfected a fundamental facility common to all vertebrates.

In summary, it appears that many of the integrative mechanisms of diving are known. However, extreme caution may be in order when attempting to extrapolate the work done on terrestrial mammals to those that naturally dive. To what extent these mechanisms operate in non-mammalian organisms is not known.

Head immersion initiates a trigeminal nerve reflex which causes apnea and stimulates cardio-inhibitory and vasomotor centers resulting in brady­ cardia and selective vasoconstriction. The gradual development of hypoxia cud hypcrCâpiVtc fur't'ficr 6 Û tutu i d uc uîê Card lù-! rnV! u'l LOr'y ânu vdSOiiiOLOr" uer!-

t h : n H artier r.r. rhc fill

vncoc wic: ciinajjwcu wj a ; cuuv viuu iii civ u : v i v^ vi :c puiuiuiiai^ vagal reflex engendered by apnea anc expira-icn preceair.g suomersicn.

This is effected through the vagus nerves. The arterial chemoreceptor

arfinn nn f ho ^ 11 c cX K\/ n>;nr»v-ÎD s r,/-! capnia) is overridden by the inhibitory action of the trigeminal nerve im­

pulses. Excitation of the trigeminal and chemoreceptor reflexes may reset

"che barorecepior-caraiac anc oaroreceptor-vasomotor reflexes: tne cardiac 86 reflex is reset in the direction of bradycardia, the vasomotor reflex in the direction of vasoconstriction (Angell-James and Daly, 1972b).

The selective vasoconstriction which occurs essentially stops the flow

^ ^ ^ . .l» z ^ ls «i» ^ —» «m "k \ ^ ^ ^ n f ^ ^ û*t>t>^ t t \ / u 1 uluuu uu ate \j 1 ut * .v/\ » ) v. i-. tcw4««w • w. • •^ •

Such tissues include the muscles, the gastrointestinal system, kidneys, liver, most glands and the skin. While the blood flow to the heart muscle is usually decreased somewhat, flow to the central nervous system is es­ sentially maintained. This is explained by the fact that the amount of work performed by the heart during the dive is decreased and the heart and central nervous system are not tolerant of O2 lack. The vasoconstriction increases the peripheral resistance to blood flow thereby helping to main­

tain blood pressure despite a decreased cardiac output.

On surfacing, a reversal of the above pattern occurs. There is hyper­

ventilation and, within 1-2 seconds, tachycardia, which increases cardiac

output and blood pressure. About 10-15 seconds later, systemic vascular

resistance falls. Eventually all parameters return to predive values.

o u ! i!!U !d t i uîi u! une lju ! iiiusia ' y vayai rcficA u_y uuc iij^uci vcu o i i a o luu \uwiicu

is broken by a decreased trigeminal nerve reflex once the face is out of

water) may be an important mechanism initiating these postcive cardiovas­

cular effects through inhibition of the trigeminal and cnemoreceptor re­

flexes (Daly et al., 1957; Daly and Robinson, 1968; Angell-James and Daly,

1959a). "Central irradiation" of impulses from respiratory to cardio­

vascular neurones, or feedback from pulmonary stretch receptors, may

terminate the cardiovascular responses to diving in ducks (Bamford and

Jones. 1976). 87

MATERIALS AND METHODS

Animal Maintenance

Red-eared turtles {pseudemys scripta) used in this study were pur­ chased from Southern Biological Supply (McKenzie, Tenn.). Upon arrival

they were housed in 85 x 74 x 37 cm tanks (5-8 animals per tank) and pro­

vided with running tap water. The ambient temperature was approximately

18°C, and the lighting was regulated with a light-dark cycle of 14-10

hmiv^c Tho animale mnwan l*?>/ûv» ar»rl/rvv* ficH urûoi^lx/ anri

were usually observed to be eating. Lettuce was occasionally provided,

but it was not eaten. Cod liver oil was given orally as a source of

vitamins A and D. Animals which appeared unhealthy or had obviously lost

weight either were not used, or were used only to study anatomy or to

practice surgical techniques. Most animals were used within three months

of arrival. Before experimentation, the turtles were placed in a tank at

room temperature (20-22°C) for at least 48 hours to allow for temperature

acclimation. They were not fed during this time.

Turtles of both sexes were used; weights varied from 1054 to 507

yi cimo vjiicgh - occ

Heart Rates, Electrucaroiograms and Sloocl Pressures

1 u ; 1 uW 11ly avu i iuia u :vu uu ï uuiii Lciupcr G uuMC ;u i G u * CGi v c UGJ a ^ uui -

ties were placed in a refrigerator at 1°C for 12-14 hours (White and Ross.

1955). This resulted in a body temperature of about 4°C and allowed for

çiiv*

the actual Surgical procedure, the animal s were placed in cracked ice to 88 keep them in a Hypothermic state. After surgery, the turtles always re­ covered rapidly and appeared to be in good physical condition.

During surgery, a flexible shaft drill fitted with a cutting disk was

"C a/4 v»Q>nn\/o a car+ 4 n-f n" a c + von nnno \/i nn tha hpsrt and ma inr blood vessels. Bleeding during surgery was usually minimal and was stopped by cauterizing the tissue. A polyethylene catheter (PE 50; 0.955 mm OD, 0.58 mm ID) filled with a heparin-reptilian saline solution (100-

200 lU heparin/ml) was placed into the left ventral cervical artery and

the tip pushed upstream into the left subclavian artery. The catheter was

then secured in place by tying it firmly into the ventral cervical artery

with 000 silk. A SVE 6 catheter (described in the next section) was

placed in the right atrium in 2 turtles for the measurement of central

venous pressure. In 4 animals, a needle tipped catheter was inserted

into the left pulmonary artery 2-3 cm downstream from the heart for re­

cording pulmonary arterial pressures. The catheter was held in position

with a drop of Eastman 910 adhesive. The removed plastron bone was

i iv i i i iw iw.. i v i * i v i wiin— v * •m'sawtn «taw ^ v —' »

T*7nn : ' c1 nn 3 n : i -ro Tno -r 4 f n-r Tna 1 ^ ron nnno Ç fi n % f

cnn; inn fn in c i : y*c fna t m ûnnv>/ onrov^ûr! r'nû Snn\/ r A vi fv

n u i cao u j. c iivju t o wci c a i i uwcu i ui i cvu v cj j'" » i vm i)ui yc i J wc i v * c

C.V uuG. i I cuui U i uy^ ne: c mauc.

The catheter(s) was attached to either an RP-1500 (Narco Bio-Systems,

Houston, Texas) or Statham P23Db pressure transducer which had been pre-

\ i C 1 \ / i.f-i 4" X s m / m 3tn o "To v* nv^OCCMV^û ti/ac ^ -p-f- q

yuo 1 L i v; i I iiy u»ic ur a ii:)uuvc! c u u; ic yvauci icvci v i one uiviny oauK.. jiiu^ 89 calibrated, movement of the transducer catheter through the water column did not produce any change in the recorded pressure.

Pressure recordings were made with either a Physiograph Four-B

/ m v» d ^ \ ^ d x» «m r\^ — v» r) v* \ 11Û.I s-V L/ * \J ~ sjjr a vCiiiO / V I

c\fc 4 t ?c+z-xl 4 3 n»itço nvoççmv^oc v.i<^v*q r* a 1 r*! 11 a "t-oh fv^r\m 4- ko ojr ^ s^\j :*%.,) \jici^witv.»5 d i iw v* *^ v. ^i ow * s..^ \^l& » * vl i i wiu i w

pressure tracings at various times. Pressures were averaged for about

10-15 heart beats and the mean value recorded. Mean pressure was calcu­

lated as systolic pressure + 2 diastolic pressure / 3 (Burton, 1965).

Small wood screws were placed about 3 mm into the carapace after

first drilling small holes in the bone to accon^nodate them. The screws

served as electrodes for the purpose of recording both electrocardiograms

and ventilatory movements. Three screws were used; one was placed in

each second costal scute and one in the right fourth costal scute. The

latter electrode served as a ground. Respiratory movements were recorded

by impedance pneumography. Electrocardiograms were obtained by jumping

the signal from the Impedance coupler of the Physiograph Four-B to a

nl-vaâ'in COupsêî V!! L;;c Same rcCOruer'. i :Vi î âiiOwêu bûui ;'ûCv:'ùl nyS tû uû

rïi> iiiy nûa ù u vuy,I icu eau11 ov,i CM a ilu a; iv, nv i eu n i un cpw i ov, i en

was then insulated from the water by a generous amount of silicon rubber.

Respiratory records were analyzed for the percentage of time spent

i n snnpa . thp nnmhpv nf \/on fi T fn w/ connor.roc nov hniir^ anH +ho rlt ;ra f i nn

of each sequence (see Lucey and House, 1977). Electrocardiograms were

anal -fa y* 4*'o<û -r4'r«o a a 4 11 c ina oc 4 ».owr\ \t7 aa i » wi * >-. —» l_ i 111 ^ * jw w i f y v * » v w ^ ti; vvuvc

« v « » i w * ttwoki *fc*0 m i i i viii wiio i v i k/ # w ^i c w * c ic*

V.V I u I ; ly uj wun u wiy vue iiumuc ( V i ucc per VXC m i ! lu UC lilUClVGi a'C YCTlOuS 90 times (forced diving records) or by averaging the number of beats over the entire duration of a voluntary dive or emersion (voluntary diving records).

i I une uujcv u I V C wvai uu JHQNC I CV^UI U * IIY wiiiic une animai waa uiviiiy

^ ^ ^ N 1 A «A ^ J* 1 ^ ^ T ^ ^^ M YM ^ ^ T ^ ^ ^ J* ^ I / / 7 C \/ O 1 % / O ^ \ iiQuuiai IJ, uiicii uiic LU f ulc waa piaucu in a y i aaa uanr\ ^ / v A uz A w uni; filled with water to a 20 cm depth for at least 5 hours following the 12 hour postsurgical waiting period. This time was usually sufficient enough for the animal to become adjusted to the tank environment. Thermal dis­ turbances were minimized by insuring that the water in the diving tank was

near the same temperature as that of the room. The tank itself was cov­ ered on all sides and the top by black plastic, except for the upper

half of one side which allowed for observation of the turtle. The room was darkened and a lamp directed toward the tank. Thus, it was possible

to observe the animal without disturbing it. The chart recorder was marked

when the turtle surfaced and submerged by the use of a remote control

event marker. Most of the time the turtle would remain very quiet either

un Lhe tank bottom or near tne wi^er surface. When underwaterj its eyes

: 1i .4 r-.-P-f-CkV.v , vs.» i Ko v, * w ) 1^03 c n<1 -T oc 1i r, 4, i /-t * Tl-»i i o 4-u i rr.ills, .3 ^ r*. o— "î"v ^v* %.C, is— ouiC : ; 4\a>..fs—

uz,uc 1 i j :)nu r L. vCCcbluxcjij 0(16 âniiïic i WOLi i u z^vvl lu biuwiy i rOiii zsl u6

rn c:i n a in too r;3n"> ny~ Tv~\/ "rr»i ? vr " 4 T c -'msro 1 or fori -fynm rna •r;ani/

glass.

^T f « 4**now>tsa> r» K "î or» \/o v ' -r^<1^ Xo ^ (fvaoi.'sç fr\ r 3 v*n'r rk\/3 cr i t 1 a v* sw/^rvsv^z-roc i il* i i^

which result from forced siibmergence, then the animal was attached to a

diving platform and positioned over the glass tank immediately after sur­

gery. During nypoinermia, four small noles were ariIlea znrougn me cara­

pace at the left and right second and ninth marginal scutes. Heavy string 91 was used to secure the anterior and posterior ends of the animal to the platform. This procedure proved adequate to hold the animal tightly to the platform despite occasional bouts of intense struggling. The platform

C ^ OO O 0 i.fr\ ^ X 3 r* KaX 4-r\ + 1 Kpv»ç wo^ mowc I I Va/ill o /\ W /\ .y ^lli ^ V i ffWNiyW» W w>KW •••w v*— » -V «0. — which spanned the width of the tank. The setup was designed so that the wood platform could be raised above the tank or lowered to its bottom.

A V-shaped notch was made in the top of the wood platform near one end to accommodate the catheter(s) leaving the body cavity through the plastron bone. Predive and postdive measurements were recorded with the animal at the water surface, the platform was adjusted so as to position the animal's heart slightly below the surface of the water. When desired,

the turtle could be lowered into the tank which had been filled with water

to a 28 cm depth. Under these conditions the animal could not surface,

but limb and head movements were not restricted. Care was taken not to

disturb the animal unnecessarily while recordings were being made. The

turtle was usually left alone with the lights off during the experiment,

WlLrlî U :H yCr 1 UU l v V TICV UV J IliU I C UNO V u:ic cuu I wiiici I u Mu o i wi i\., v i v* * * i

f ^•

Data were recorded in the predive state for about 30 minutes, during

the forced dive which lasted for variable periods depending upon the ex­

periment, and then postdive for an additional 30 to SO minutes.

Data were usually recorded for both natural and forced dives in the

same animal. The natural dives were cone first with the forced dive

usually taking place about 12 hours later. In addition, a few animals

were inscrumented for recording only EKG's during tlie diving maneuvers so 92 as to remove any possible effects caused by the surgical implantation of catheters.

Cardiac Output, Shunting and Tissue Blood Flow

Turtles were made torpid for surgery as described previously and a section of the plastron removed. Clear vinyl SVE 6 catheters (Durai

Plastics and Engineering, 592 Old Northern Road, N.S.W., Australia 2158) were placed into both right and left atria. The catheters were tied into ui iC Ci3^ VI 4iC. VY, 4 I 4»Vil k VnnO w coiir\ 41 (/ Cif I ^vC ^ V» ( i cmv/"xm \ v t ^i irii ly rt ^O crnoniCxii 31 1 ^t^nO'^OC i \..o \j i v: r\ 4 5 V*»/4 4 i ITT>

The catheters had an inside diameter of 0.45 mm (00 = 0.75 mm) at the cannulating end tapering to an inside diameter of 0.9 mm at the other end. These catheters were then attached to lengths of ?E 90 tubing after leaving the body cavity.

A SVE 5 catheter tipped with a short 24 gauge needle was inserted into the left pulmonary artery 2-3 cm downstream from the pulmonary trunk.

The catheter had previously been cut to a length of about 15 cm to minimize

1 onn-rh n-r 4-ko cma 1 1 /44 T'nû n oa/41 o u/s c f4^mlw a -hi'a r* koH

to the vessel with a small drop of Eastman 910 adhesive. A similar SVE 5 catheter was inserted into the left aorta or subclavian artery. The larger diameter end of each vinyl catheter was then attached to a longer

segment of PE 90 tubing after emerging from the body cavity.

i uc icj V GUI V I V VI OU uu I c V 4 a n va vi i ever WQO WMMCVVCU VV G ovavnaui

nv^oççi!v*û h 4 r* h p n rsadr^ r» p i 4 ;5Ç /4oc^v*4So/H ûav>l4ûv*

R : nnri nvûCCMV^o o.H nn ^ n nin ZL * 1 v^nrTiv^z-iav» Trio 1 cf4-

pulmonary arterial catheter was connected to a Sage Model 351 Syringe Pump 93

(Orion Research, Inc., Cambridge, Mass.) for collecting pulmonary arterial blood at a known withdrawal rate.

Bleeding tissues were cauterized as required. A notch was then made

\/1/-> >0 i viio t ^ v/mws kyw * ww 3vkwsi'vi/iiutis./suv^ws.» ^ r\rr>'^r\ w* at /^a4-l-io4-ov^cw^w>>wws«i «./ a (a x 1» +"w •vwkwc • ori a nrl co/~i i ur-î-f-t-i a ^^m4nii+o ûnr\v\/ \Aii<»4 0\»w>s.4t\..Na ** * V * * w iiititwaww w ^ v jr •

Screws were attached to the carapace (as described earlier) for recording EKG's and respiratory movements with impedance pneumography.

The turtle was then secured to the diving platform and allowed to recover for at least 6 hours; 12-15 hrs of recovery were allowed for most animals.

After recovery, and provided that blood pressure was normal (occasion­ ally there was a problem with post-surgical bleeding once the animal had warmed to room temperature), the experiment was begun. The atrial cathe­

ters were each connected to separate small glass chambers (volume approxi­ mately 1.0 ml) which were, in turn, connected to 10-ml syringes through

lengths of PE 90 tubing (see Figure 2). The glass chambers could be load­

ed with radioactive microspheres through a third opening attached to a

aiuc : I acyricii v v : r L. uv uu u :: ly . ii k^iiamuci wc 3 i i i i cu w: uu ^gi mic un—

m \ * ^ I/» w»,-. *1*/-* ^ t/* ^ 1 ^ W rv> M /"x ^ Li

( a /IciX v.f n "T X Q nA_ ^ AA m 4 4 3 X 4 m4^v-»r>çr\lnov*0 ci:cr»OK»C

(3M Company Nuclear Products Division, St. Paul, Minn.) by the use of a

250- or 500-microliter gas tight syringe (Unimetrics Corp., Anaheim,

Calif,)- The microspheres were supplied in vials with 10 ml of 10% dex-

tran and 0.05% Tween 80 and containing 1 mCi of a gamma-emitting isotope.

r\ V» f-z-s ».l4 ^ r»«4 V*a i.»a 1 r\ -P C -Pv-«/-\rr-i -4- X ^ ^ I I 4- 4 r\ 4» X ^ l f 4 1 ^ >1 I wI WW ffiw<«wivir«w.i wt 0W11C1U.0 itwsi; wtiv. Ovw w r*. .awtwwiwiim v 1 Li : ^ *1C : C

V'iyûrûuSiy ayvcaccu and chen sorricaceo Tor approximaceay 5 minutes, iney Fiaure 2. Diaqram illustratinq the experimental setup used to ir.easut c blood flows, cardiac output and intracardiac shunting. The animal (A) is shown attached to the diving platform which is suspended over the diving tank (DT). Two glass injection cham­ bers (IC) were attached atop a centrifuge tube which fit the neoprene cup of a vortex mixer. The two injection chambers were attached side-by-side to the centrifuge tube. Each was connected to a 10 ml syringe attached to a single infusion pump and, from the other end, each was connected to a different atrium of the animal. All tubing (other than that used for cannulation of atria and vessels) was PE-90 tubing (FT). The injection chambers were filled with microspheres through a small port (shown at the upper left). For withdrawal of microspheres, the left pulmonary artery catheter was attached to a third 10 ml syringe connected to a withdrawal pump. Although not shown, systemic arterial pressures were measured through a fourth catheter during the process of injecting and withdrawing micro- . ciiu o K i tfL. C.r CLuaurJCU uu one uc.'auauc wci c u acu cu record EKG's and impedance pneumograms 95 95 were then vortexed immediately before being drawn into the microliter syringe. The spheres used were of two types, containing either a Ce-141 or Sr-85 nuclide.

The diameter of the microspheres was approximately 25-miCrons (Sr-

85, 25.8 microns ± 2.5 (S.D.)j Ce-141, 25.2 microns z 1.8 (S.D.)).

While loading each chamber with microspheres from the microliter syringe, the atrial catheter was pinched closed near the glass chamber and the other catheter disconnected at the 10-ml syringe. This allowed saline

to be displaced from the chamber during the filling procedure. All microspheres would remain in the chamber if the loading rate was slow.

The cathéter was then reconnected to the syringe. The loading port was

closed by crimping and tying the PE 50 tubing after removing the micro­

liter syringe. Care was taken to insure that no air bubbles were in the

system.

Occasionally, a sample of the vortexed stock solution was placed on

a slide and observed under a light microscope. Very rarely was microsphere

r\r\ ojîimnnnr: n r> ç wa r»/^I I v.* 11^ k/ I cnn^voc o\;or»>_•*>.>>• Tnjtnn' s/ I « <— » «win a cm s

y WU itllAlny (li UMC V-.lIV-.UlGL.Ulj UCU! j I u : ^ COaCM V i Ci I vMLt v ui (C

dû iiot fùriïi clusters, a phenornenor, which is observed more Trepuently in

smaiîûv*«itvkliw» h1 mnr'v«açnhov»ûç

The cylindrical glass injection chambers were fastened to a flat

J-/JCWC^ \jO^ I *-*^ n i O.^ a4» V I V ^/ *yv ., ( I m(VII /"* «.»•>/»wGi y i w v cu uv *^4»i i u 4»u- L\/-\ »c X"* I/»j lOiuuc ^ v-r« i o / * i c* »

bands. The plastic piece had previously been glued to a centrifuge tube

which snugly fit the neoprene cup of a vortex mixer. During the injection

of microspneres into tne animal, tne cnamoers were constanuly snaKen oy

the mixer. This constant agitation of the chambers' contents insured 97 that the microspheres were thoroughly mixed when they entered the heart.

A small glass bead placed in each chamber facilitated the mixing of the spheres during agitation. During the injection of aerial animals, 1.5 ml of saline was injected f^om. each 10-ml syringe and into the animal over approximately 90 seconds. This flushed about 85% of the microspheres placed in the chambers into the animal.

Beginning about 30 seconds before injection of the microspheres, and lasting until one minute after, left pulmonary arterial blood was withdrawn at 1.0 ml/min by the syringe pump. This served as an "artificial organ" in calculating cardiac output (Hales, 1973).

In the submerged animals, the infusion of microspheres was made at a slower rate (0.3 ml/min) than for the animals above water, and blood was also withdrawn at this slower rate. This was necessary since cardiac out­ put would decrease during diving and high infusion and withdrawal rates would sometimes result in blood pressure changes and/or problems in with­ drawing blood at a steady rate. The microsphere infusion was made over

-s/-S^ /-> "C 7 m-t J »c 2*0/^ t.r - *• ln/-i v-»3 ^C "fO vm *7 n a "T ûrî anoMT 1 minutes later. This slower infusion rate also helped insure that the microspheres remained well-mixed within the circulatory system — a situa-

^ ^ — —». j — £ ^ ^ ^ l... —« ^ 1 . . l& «"k ^ a ^ ^ 7 c o c ^ w o yw n V I \w/ i : 11 iCiW C I ( iw « C Va^iii Ci ^tSa/yt IJOC^I W L# ^ V wi w«»• v

spheres placed into the injection chamber were flushed into the animal.

Blood pressure was recorded during the entire procedure. When sig­

nificant changes in blood pressure and/or heart rate due to the injection

m v^o aKcovv/oz-i +'oo Hafa HicrarXoX Pytamal vac n*: y;5 T"? nn

wci 11IV: I : uvTcu uui i:;y liic ^î'uucuuTc *v i un nnpcucn^c pwcwinwy : apjij . All animals were secured to the diving platform and positioned at the water surface as previously described. Predive heart rates, blood pressures and ventilation rates were obtained no sooner than 5 hours after

JL. ^ ^ ^ H • T ^ VA ^ /J T ^ IM ^ \ ^ T ^ ^ ^^ ^^ \ f ^ one Ù-Uiyi^ai yivvCUU l ca WCIC wnip» l CUCW . xi ic luw * Z> v w W(«>WV4 w. k/v V c water, the same procedure was followed but with the a ni uial remaining at the water surface. If diving information was desired, the animal was lowered into the water and the procedure was initiated once a significant brady­ cardia had developed. Individual animals were used either above or below water, but not both.

Approximately 20 minutes following the procedure, the animal was

killed by an overdose of sodium pentobarbital.

The withdrawn blood was placed into counting tubes and the withdrawal syringe and catheter repeatedly rinsed into others. The injection chambers and atrial catheters were likewise repeatedly rinsed into counting tubes.

Tissues of interest were removed from the animal, weighed, and placed into

counting tubes also. The height of the tissues in the tubes was kept

ui!uef 2 L!!i LU iTiiure Û relaLivclj COïiSuàriL COuntinO GcOmctry. ihc Vcutri-

w I # f ^ ^ 1 i ^ a t w t ^ ^ 4 f ^ i ^ ^ ^ ^ ^ • « w » • V

^ ^^ ^ ^ n » # ^ ^w t ^^ m ^ ^ \ ^ ^i i m ^ ^ ^^ ^ ^ ^ o^ ^ ^ ^ ^ a ^: ic [ ca wuiuii acuu; cu in one i * ca t u v^ui :iiy luj v:vu. > vi

Done from zne carapace were removea fro^ 5 aifferenu places and placed

in counting tubes. All the tubes were then counted for 2 minutes each

1r 2 D-îrrd rrrm ^ TT r\v> Tv^ar»r\v^ + /-AMn-J-Tnn ç\/ç-f-nm ;5 nr! -hh^ a 4-4

ity of the two isotopes in each sample resolved.

i I c( v c^uc; y#C i C w ; ;: O u i C ujiCiw u:i c uijv^i cb

were being completely trapped by the capillary beds. In three aniiTials, subclavian artery and from the abdominal vein during injection of micro­ spheres into the left atrium (at 1 ml/min). Since radioactivity in the withdrawn venous blood was never greater than background, it was apparent

uiiauait lutvivapucica ncic wc i i ly w # 111 ajr a uoii i v, vCi piiiat ica, xii addition, microspheres were injected into a carotid artery in 2 turtles.

Subsequent counting of tissues showed that few microspheres were lodged in any tissues other than those of the head and neck.

To test for microsphere passage through pulmonary capillaries, a known amount of microspheres was injected into a pulmonary artery in 2 animals. A subsequent count of the lungs showed that approximately 97% of the injected dose had lodged in the pulmonary capillaries. Counts of other tissues showed no activity above background. This, as well as

the tests on systemic capillaries, was not done on animals underwater.

Microspheres were also compared to actual red blood cells and capil­

laries for a determination of relative size differences. When placed on s slide with heparinized turtle blood and observed under a light micro­

scope, SpiiereS were usually fuunu Lu ue laryer' Li id!: Lne r eu uells by

M ml ^ A ^ ^ ^ ^ ^ 1 \f 1 i A ^ f ^^ ^^ ^ ^ A ^ r-. oo-L ucL :>nuvy a v i v. ± A — u.i in i viio ^iiicaii u iauic uci a

of -[he eliptical cells z S.t.) (Musacchia and Sievers, 1962).

Microspheres were also compared microscopically to capillary tufts

obtained from, corrosion casts of the circulatory system. In all cases the

spheres were observed to be larger than the capillary casts. However, it

lb IIW u X- i ca I 1 i UMC VC O UO VG Y : : : G ; J V ! Gl'IC vC: UUC LV SLICLLA::

of the vessel walls during injection of ihe material inro -ne circulatory 100 system, or underestimate it due to shrinkage of the vessels before the material hardens.

In order to calculate cardiac output and intracardiac shunting, the t» u. />-c ^ ^ ^ ^ ko !/ 1 4" ko r4 n r f i ^ Vtl I * I V i ,\ t i\y rw » • iw ••'w s^vii*

/^nl4- +rv r>r\titrx-h fKc 4-, : v~+"l o an alinnnf nr rho mn rv^ncnhov*o innorfinn Vi»Vi

Also calculated was the isotope activity per microsphere. A dilution of the original microsphere stock solution was made and, using a hemocy- tometer, the number of spheres per microliter in this diluted solution was determined. Once the number of microspheres per microliter of stock solution was known, the counts per minute (cpm) per sphere could be easily calculated.

Based on the above results, approximately 2-5 x 10= microspheres

(200-500 microliters of the stock solution) were injected per cardiac

output and blood flow determination. Any tissue or organ found to have

:ca :> una j i "tvju uv uu i luivivauucica rva a ( iv u u acw i 11 w :www i i w vt wu i wu i w. v « wwo

/-) « i o^ 3 i f 0 / ) \

P iww f c r\c^ l/\— i ^ i siaiis^a «n/4 iUoTC^ov^ is— * ^i w) ^1G77\ i / j MÇûn -r>w( A V rl 0T0y>m *î ninm

cardiac output and tissue blood flow were:

V fU ^iii 1 / 111 ! P. j — tr'.\p X n i J\

u('n£3y«o \/Dn = wanfrirnlar' niiTmnnavv/ nifrnni-- u! = fHo rafo nf nMimnnaw hinnri

withdrawal; Apç = the total activity of microspheres which enter the pul­

monary system (counts in lungs -r counts in withdrawn blood); Ap ^ =

the total activity of blood withdrawn from the pulmonary artery. 101

Ventricular pulmonary output can be calculated for each of the 2 isotopes injected. When the 2 VPO values were different, streaming of the shunted and unshunted blood in the pulmonary artery was assumed and the data

\.rovo rl-i Çf-a vrloH

Intracardiac shunting of blood (right-to-left (r-l) and left-to- right (l-r)) was also determined. Equations used were:

% L-R shunt = X 100

% R-L shunt = X 100

where A.^j^ = the activity of the injected left atrial microspheres measured in the lungs and withdrawn pulmonary blood; = the

total activity of spheres injected into the animal at the left atrium;

Amg = the total activity of spheres injected into the right atrium minus

that found in the lungs and withdrawn pulmonary blood; A-j-j^ = the total

activity of spheres injected into the animal at the right atrium.

Ventricular systemic output (VSO) can be calculated from the known

^ \/ o T» m «i» V/h —» ^ "V ^ ^ ^ ^ « OVfc V/tl fl V IllVt «éA^VAI

VSO (ml/iïîin) = (1- % L-R shunt/100) VPO (ml/min) / (1 - % R-L shunt/100)

The volume of shunted blood (VSO ) can be calculated once the % R-L

CliiU Ul IC VOU O. i C rvilUvVli ^G.ÏIU ic^icbcnu5 uiic V v * UmC Oi

n /"> ^ *.* w n 1 ^ • uiwuw. niiivfu uj—ui ic i uily a y .

VSO (ml/min) = VSO (ml/min) x % R-L shunt/100

The volume of the ventricular systemic output which is unshunted

\ -le- \•^•

wca — \/co \/c^ \iu * / iii i u/ — * ov \iiii/jijiny - \»j»«/iuiii/ 102

Total heart output (THO) is the sum of all the blood pumped from the ventricle:

THO (ml/min) = VSO (ml/min) + VPO (ml/min).

^ \ ^^, z «en «y» ^o v» ^ 1 1 ^ /-j ^ a veil I XV» U 4 ^ L4 C I IV/VV.^ VVV»l v. 1^1 t W«4«WI

blocd as TO1 lows.

Unshunted Tissue Flow (ml/min) = VSO^^ (ml/min)

X fractional distribution of systemic

isotope injected into the left atrium;

Shunted Tissue Flow (ml/min) = VSO^ (ml/min)

X fractional distribution of systsnic

isotope injected into the right atrium.

Tissue blood flows were calculated on a weight specific basis (ml/min

X 100 gram tissue).

In one animal, surgery was performed as above except that the right

atrial catheter was not implanted. In this animal, injection of one micro­

sphere label into the left atrium above water and one below gave a mea-

autc vj 1 u [ wu : ;u w k, ( (C: uui ::iy u ; v : ny tii ui ic acmic un iit:u i vu o i iim ic

^3 r» -mi.iyx r\w\ -Tv-k/-^'^\/-î/-l»tTv^» 3y» X X 4 \ 3 m4 rm 3 I c I!*^T^v*"rirr>a"rû- i lu( c^ wl/oci vv.vu wc ccl * *|jvl iv |s_«l4u1 ^1 uiivu i v ^i ;i i wv|4 i

ly, with this procedure, % R-L shunting, VSO, and absolute tissue flows

could not be determined.

Resistances to blood flow in the pulmonary and systemic circulations

were calculated from the mean arterial blood pressures and blood flows in

t !•_ /_t — o ! i \ / c R '^imii ny/Jii 1 / 111 i :i ; — r ny ; / i 103 where R is resistance, P is mean arterial pressure and F is blood flow.

For calculation of pulmonary resistance, P was mean pulmonary arterial pressure and F was VPO. Systemic resistance was calculated using mean

^^r»V*J-^ ^1 r> ^Ç» IV* ^ \l^C\ V>«> 41 I W VA I ISpAl » V v »

If there is a 1 mm Hg pressure difference between 2 points in the circulatory system, and if there is a blood flow of 1 ml/min between those

2 points, then resistance to flow is said to be one peripheral resistance unit, or PRU (mm Hg/ml/min) (Berne and Levy, 1972).

Mean values were calculated for the measured parameters and are listed in the Results section as means ± 1 standard deviation (S.D.). The data were analyzed statistically using either the Students' t-test or an F-test.

A coefficient of correlation was established for some of the data

(Snedecor and Cochran, 1957). 104

RESULTS

Heart Rates, Electrocardiograms and Blood Pressures

Upon voluntarily submerging, most turtles would show an immediate re­ duction in heart rate. This bradycardia would usually occur within a couple of heart beats after diving and usually would not develop much farther. A recording showing this heart rate response has been reproduced in Figure 3. Upon emersion, the bradycardia would be immediately broken and the animal would usually ventilate its lungs before diving again.

Typically, this ventilation would consist of from 1-4 respiratory sequences with diving closely following the last sequence. Ventilation would begin with an expiration after emerging from a dive, and the animals were com­ monly observed to dive after an inspiration. On various occasions, the

turtles would give off bubbles through the nares after diving, although

this was more common during forced dives. As can also be seen in Figure

3, the apneic periods at the surface are spent with the lung in an in­

spiratory position.

Occasionally, the heart rate would increase before the turtle emerged.

Sometimes this would occur at the same time that the animal began to move

toward the water surface. However, there were times when this would

occur before the animal would begin to move (Figure 4). In fact, in many

T rnulH n -î r»-i- 2 n ex ro hvy wafrhinn f ko

+0 v>n n nr?

Although the heart rate during diving would usually rapidly stabilize

to a lower rate than in air, the rate above water was very labile due to

ventilation tachycardia. Furthermore, the apneic surfaced rates would 105

EKG

I.II.t.inn 111 1 1] l{ II " 'UUi-iUi 1 h h ^ h IN II lilU; u u u

5 SEC n 9

gure 3. Recording of the electrocardiogra™ (EKG) and impedance pneumo- gràm (I?) of a voluntarily diving turtle. Three respiratory sequences are shown. Arrowheads indicate where the animal . i ^ v 4- M a iD u/Swfn: mu i ll&V V WillWl I V I 8xpir&^ 105

DOWN

igure 4. Heart rate of a voluntarily diving turtle. The thin arrow O I IV/ (T# I I I I v_> IIVIIIV» t • w I < vy I V* t I ^ I w w«vii w air v w ^ 107 sometimes be as low, or lower, than the mean dive rate. Very low heart rates would occasionally occur in animals above water if left undisturbed for a long time. In one animal this approached 8 beats/minute.

Figure 5 shows the heart rate responses of a typical animal to re­ peated voluntary dives over approximately 75 minutes time. The heart rates indicated are averages for the diving and emergence times shown.

The upper horizontal lines represent the heart rates at the water surface; the lower lines while submerged. For this animal, bradycardia occurred each time the animal dived and, as indicated earlier, this response was usually immediate.

Tables 1 and 2 give the heart rate data for voluntarily diving turtles which showed a diving bradycardia. These animals spent about 75% of the recorded time underwater. Individual dives would last about 3.5 times as long as the time at the surface following each emergence (P<0.01). For

this reason, the overall heart rate more closely approximated the sub­ merged heart rate (P<0.10) than the heart rate at the water surface

t' ^< n . M1 ^ un fno to wp r^pniiron ^nnur nt :r i no vnlim-

tary diving (P<0.01). It should be pointed out that 2 animals out of the

eleven (18%) used for recording voluntary diving heart rates did not show

Hi vi nn Tn farf _ thov ri iH nnt a nu rnn(:i c+on+ na+foyn

of heart rate response and. therefore, they were not included in the data

for Table 1. It should also be pointed out that there were occasional

dives of almost every turtle that did not produce a bradycardia. This

was especially true of very short dives. Occasionally animals would seem

a rri +3f-an a mri Kan 4 n ri 4 4 nm a n/n c i i a"î n v*a r\T/-i1 TWoço c

were not used in the heart rate calculations for that animal. 108

a» ^ 25 -••Av* A [•i V- 20

50 >-

il i ^voll J jr DIVE 40 i h CD HELD UNDER 30 RELEASED L_ /

'^1 0 20 40 6 0 80 M!N

gure 5, Heari raie changes during repeated voluntary dives in a TSLirne, upper horizontal lines indicate the mean surfaced raTe; lower lines correspond to the mean dive rate. Breaks in the record ^^ ^ m ^ i* ^ ^ j— «»* /"» » «—» <"» ^ ^ ^ vuv u( wiictc vi:c i cl,vi u ( ny wq^ mviuci i uu i i i jr o w b w i «w diastolic systemic arterial pressures are shown for one volun­ tary emergence. Also shown are the results of grasping the ani-

ma1 3-r-fov 3 \/r\"! ? :m-rs v^\/ rî i ann nnl n 4 nr: l* r i :innorwA Table 1. Heart rate data for voluntary dives in 9 turtles ®

Mean Mean Percent — Heart rate submergence surface tinio Percent time (min) time (min) submerged Overall Surface Submerged reduction

10.0 ± 5.7 2.8 ± 1.8 7!) ± 1:1.0 18.7 ± 6.2 24.6 ± 7.7 17.7 ± 5.3 27.9 ± 9.7

mean length of recording periods = 164 ± 80 min

^Va lues are means i 1 S.D.; heart rates are in beats/minute. 110a

Table 2. Statistical significance levels for voluntary dive heart rates®

Data compared Significance level

Mean submergence vs. mean surface time P

Overall vs. surface heart rate P<0.01

Overall vs. submerged heart rate P<0.10

Surface vs. Submerged heart rate P<0.01

^These data accompany Table 1.

As indicated earner, the voluntarily diving turtles would usually either slowly sink to the tank bottom after submerging (20 cm of water), or remain suspended in the water just beneath the surface. Occasionally,

they would slowly swim back and forth in the tank and this would usually have no effect on their heart rate.

I could determine no correlation between the lengths of the voluntary dives and the degree of bradycardia which was developed, nor between the dive duration and the subsequent heart rate when surfaced, nor between the

length of the dive and the duration of the following emergence. However,

there was a positive linear correlation between the neart rate at the

surface of the water and the rate during the dive (r = 0.8784; P

and between the overall heart rata and the heart rate while submerged

f y- = n Q7 9A. D^n ni ^ 110b

When the turtles were forcibly submerged, the heart rate response was clearly different. Rarely would the bradycardia be immediate, as when voluntarily diving. Instead, the heart rate would usually gradually decrease over a period of minutes. In some animals, it would net sven begin to decrease until about 30 minutes after submergence - and then additional minutes would be required before the bradycardia would become maximally developed. In some animals a slight tachycardia would occur immediately after being forcibly submerged. On average, it took 38.1 ±

28.9 minutes (S.D.) for maximum bradycardia to develop after diving the animal.

Figures 6-8 give typical heart rate responses to a forced dive. Dur­ ing a long dive (Figure 5), following the initial strong bradycardia, the heart rate would increase and then level out at a rate somewhere above the minimum. This rate would then be maintained for the duration of the dive, which occasionally lasted 24 hours. Struggling during the dive would usually cause a transient tachycardia, as shown in Figures 7

nH drop to very low values. This some­ times would reach 1 beat/minute or less and was always much lower than the minimal heart rate recoraec curing Yolunxary diving. Tables 3 and 4 show the heart rate data for forced dives. The dive heart rates were calculated every 5-15 minutes following submergence and the average rate

used as the dive heart rate for that animal.

Predive and postdive heart rates were calculated every 5 minutes for

each animal and then averaged. Predive heart rates were recorded for an average of 30.2 ± 5.5 minutes; postdive this was 44.0 = 29.6 minutes. Ill

at SO min 30

20

10

0

0 I 2 3 5 10 15 20 30 min MRS

igure 5. Heart rate during a prolonged forced submergence in the turtle 112

30

20

50

40

30

MOVEMEN

20

0 30 60 90 120 ISO MIN

Mgure /. nearz raze ar.c cir;,srici: O:Oùù pressures curing a forced dive lasting approximately one hour. Upper blood pres­ sure line is systolic pressure; lower line is diastolic pres­ sure. Notice the transient tachycardia due to struggling dur- "i nn r'no n i vo 113

40 •DOWN •COWN

0

0

"-UP 0 30 60 90 120 150

Figure 8. Heart rate during 2 successive forced dives. The dive brady­ cardia was developed faster in this animal than in the animal represented in Figure 5, and it v;as developed to a greater ex­ tent despite the shorter dive. In almost all animals, the bradycardia was broken immediately upon surfacing 114

down

45-

0- co ou •

15-

30 60 90 120 150 MIN

Figure 9. Heart rate response to forced submergence, struggling while submerged (S) and to atropine (A) in a single turtle. One- half ml of Ringers solution (R) was injected through an arterial catheter a few minutes preceding the atropine (0.5 mg/kg in 0.5 ml Ringers solution) to serve as a control 115 fable 3. Heart rates before, during, and after forced dives in the turtle, Pseudemys scripta

Predive Dive Postdive Percent heartrate heartrate heartrate reduction

31.4 ± 10.9 14.7 ± 7.2 35.0 ± 9.3 53.2

mean dive duration = 480 ± 531 minutes

^Values are means of 14 animals ± 1 S.D.; heart rates are in beats/

III I IIU LC.

Table 4. Statistical significance levels for forced dive heart rates^

Data compared Significance level

Predive vs. dive heart rate P<0.01

Predive vs. postdive heart rate P<0.05

a-.rheiço riara arrnmnsnv tphlp 1

As shown in Table 3, there was a reduction in heart rate of 53% when considering the entire time period that the animals were submerged. This

represents a significant bradycardia for animals undergoing forced dives

v?

v»»^ i , w v , l* i i & w \w. v i w i v ivivxc v i i i w i o ;ii vv^iwii i v i i ly vu i

"Cias. iiowever, wnen cr.iy considering the minimal heart r

forced submergence, the bradycardia v.'ould approach 98% in some animals

_ oc. _ in i i i o *.'3yiv.4 ^c t « v f 1 i un -^3 1 \ f 4\ 116 animals. There appears to be no correlation of degree of bradycardia ob­

served during a voluntary dive with that later developed when the animal

was forcibly submerged.

The overall reduction in heart rate observed on long dives was not

much greater than that for short dives. This was probably due to the fact

that, in long dives, the heart rate increased after 1-2 hours of submer­

gence, so that the degree of bradycardia calculated over the entire dive

ï.o ç 4- k 3 -pr\ v* +w3+* tf ori rl*?\/oc vvu ^ IIV u uiwv, I: y : CU vOi vi fct 11 i v i vi iL* v v i oiiv/i i .li uitw

would produce an immediate bradycardia, the shorter dives would yield

greater degrees of diving bradycardia than the longer ones.

Six of the 14 animals used for the heart rate response to forced

dives were used in August, 1978. The mean predive heart rate of this

group was 21.7 = 2.2 beats/minute. The remaining S animals were used from

November, 1978, to February, 1979, and their mean predive heart rate was

38.5 ± 8.8 beats/minute. The difference in the rates was probably a sea­

sonal effect and helps to explain the variability in the predive heart

rate value shown in Table 3. However, despite the large difference in pre­

dive heart raies between the 2 groups, the mean percent reduction in rate

for the entire dive was similar, as was the maximum percent reduction in

heart rate. For these reasons, the data for the 2 groups were combined

"in Tahlo Two mif nf the 1 A fny^ri hi v ci:hrnaynoH tiiytloc fshniit 1

riiri nnf chnu: a Hi nn hvan \//~a vH •• a a\/an i»ihan ri 4 ^;ori f nr 1 r»nn T^mD noyinric-

they were not included in Table 3.

The postuive heart rate typically shows an overshoot from the predive

1 ma 5 c c 4 m tsklo *5 4- in 4 c rw/ov* ç ^ n ori 1 i r» 1a +iiv^+ loc —* * IV fX « I III I \.

used (?<0.Q5) when calculated over 44.0 ± 29.5 minutes oostdive. 117

There were no detectable differences in the heart rate response to either forced or natural dives between animals fitted with only EKG elec­ trodes compared to those with surgically implanted blood pressure catheters.

Û rpv/H-iar svvhv/thmia WA < Almnqt WA vg obse'^ved f.hp devpl nn- ment of the diving bradycardia in forcibly submerged animals. Occasionally the beats would come in groups of 2-4, especially when the heart rate began to increase again after 1-2 hours of submergence. In general, the latter

half of a long dive was much less arrhythmic than the first half.

Ventilation tachycardia could be observed in many animals, especially

postdive. However, this would only occur when the heart rate was rather

low. Figure 10 shows an example of this phenomenon.

The bradycardia of diving appeared to be broken with the first post-

dive breath, although sometimes the heart rate gradually increased over a

1-2 minute period following emergence at which time ventilation was occur­

ring. Therefore, it appears that bradycardia will not be broken unless

the turtle breathes, but breathing does not always insure that it will

/-* -• rww — /-.i kv * vk ^ i v i i #

Disturbing a turtle while it was out of water resulted in a brady­

cardia that resembled that of voluntary diving = Prodding an ani^'o.l to

V Ui U 1 J UÛ; * 1 ^ buumciyC Cv-i vi fC yC C« G i 5 1 vC*. v * »

— -i 4 m -, 1 t» o^ 4- x3 r) \fr\l i \ / iiçiidi 3 ic c* i : )»,,ci i (aiuci i v : lu w vv^iutii wwk t : i ^ r'v* ai \v i w^ v* w i - m va

tachycardia. Preventing the animal from voluntarily surfacing after a

natural dive (such as grasping the animal with the hand or lowering a

c "hx/v^nr nam 1 4 ri Kolnu; f no ura + ii'r' c ; i y~f ;= r c. ^ ;.;n: :1 ri Y~ac i il t i n a ri\/r A rn i a

I lii i 1 c I uv 01 la u u uI 1 ny i v f ucu o uumo y ci luc . 118

EKG A

IP r-^ i ) l/WWWl yi

5 SEC

1 i I 1 1 i r~i I i i n i 1 i n i i i i n i i i i i m n n i i i i r~i i i i i i r

Figure 10. Electrocardiogram (EKG) and impedance pneuniogram ClP)_demon- strating the phenomenon of ventilation tachycardia. Three respiratory sequences are shown; the shill-jwer, broader v/aves between ventilations are impedance changes caused by heart 119

Figure 5 shows the results of turning a voluntary dive into a forced dive. After the turtle had made a voluntary dive, the animal was grasped and held underwater. The heart rate would decrease to a rate not achieved during sr.y cf the previous voluntary dives. Even though most voluntary dives were not long in duration^ 5 animals remained underwater voluntarily for longer time periods than it subsequently took to develop a severe

bradycardia on forced submergence. This indicates that the greater degree of bradycardia developed during forced dives was not due simply to a

longer submergence time. Figure 5 also supports this contention.

Figure 11 shows the results of injecting air or Ng into the left lung of a submerged turtle. When 5 successive 5 ml volumes of air were inject­

ed, the heart rate increased to the predive value. Even injection of a

single 5 ml volume of air caused a transient tachycardia. The injection

of 10 ml of M2 also increased the heart rate.

Figure 9 illustrates the effect of atropine on the heart rate response

to submergence. Immediately after injection of the drug, the heart rate

t i 1^ I CU OCVii OlMlii) I ^VI I $ I ^ ) WW V ^ • N4 I iv^ ^ I ^VA I » »** ^ ^ V « « — — «

facing; the rate increased further and actually exceeded the heart rate

Kû-rAv-»û rii

n.ii CiCUU/uuaiuiUMfain i-'ciujc Gnu uui ) wy a m « ww x^.vc tiC-i cc, ..**

lustrated in Figure 12. Table 5 gives the results of the standard EKG in­

tervals for 7 forcibly submerged animals. As indicated, there was no

change in the length of the P-R or QRS intervals. The dive bradycardia

(P<0.01) was due to an increase in the S-T {?<0.01) and T-P (P

1 T" ^ ^ ^ ' o ^ -r 4- r\y» 3\/Qv*»arTo -r Xa D _ D

— » ^ . «» — /» /— j— '. — «««^ ^ ».•"« f" (j• » ^ i^ . ifiLcr Vc ; 1 DLi caz>cu c/ O/o \r

5x5 ml

i 20 m ml

lOmiN

5 ml

a

0 iO 50 50 70 30

Figure 11. Graph showing the heart rate response to a forced submergence f , vm; n A vv w, nwf . -rw. n.w a 1. -i: s^rt wh t 1 ^ ci i k«. merged in a single turtle. Single 5 and 10 ml volumes of room air and 5 successive 5 ml volumes of room air were introduced into the left lung through an intrapulmonary catheter passing through the overlying carapace bone. Ten ml of pure N2 were also in.iacted Figure ]2. Turtle electrocardiogram predivc (PD) and 157 minutes after being forcibly submerged (D-157). Intervals of tfie predive EKG are shown as they W(îre measured (PR = beginning of P v;ave to beginning o1" Q or R wave; QRS = beginning of Q or R wave to end of S wave; ST = end of S wave to end of T wave; TP = end of T wave to beginning of P wave). Note the prolonged ST and TP intervals during the dive ORS

PR ST TP

PD

D 157 M(M

——-

SEC Ta 1)1 G 5. inectrocardiogram time intervals before and during diving in seven turtles®

Heart Condition P-R QRS S-T T-P P-P rate

Predive .45 :L .14 .20 ± XI .89 ± .28 .55 + .40 2.09 ± .75 28.7 + 11.4

Dive .45 .10 .21 ± .C7 1.26 ± .36 5.87 ± 6.02 7,79 ± 5.92 7.7 ± 5.6

% change 0.0 I5.0 +41.6 +967.3 +272.7 -73.2

Sig. level N.S. N.S. <0.01 <0.05 <0.05 <0.01

^Values are means ;• 1 S.D.; P-R through P-P are in seconds, heart rates are in beats/minute. 124

1.4-fold increase in the S-T interval (42%) and to an increase in the T-P interval of 10.7-fold (967%). Electrocardiograms analyzed for voluntarily diving animals showed the dive bradycardia to be due to the same phenomena.

The T I'/aves became biphasic during diving in 3 of the 7 forcibly dived animals (43%), increased in amplitude in 1 animal (14%) and de­ creased in 1. The QRS amplitude decreased in 3 animals, and the P wave decreased in amplitude or disappeared in 3 animals. Two of the 7 animals

(29%) showed no changes in wave amplitude or form during the dives.

Tables 6 and 7 give the results of the blood pressure recordings for

the forcibly submerged turtles. Recordings were analyzed for 10 animals

and dive pressures were calculated only after at least a 20% reduction in

heart rate (mean = 50%) had occurred. The mean dive duration was 77 ± 52

minutes and it took an average of 29 ± 29 minutes for at least a 20%

bradycardia to be effected. No animal in which blood pressures were being

recorded was kept submerged longer than 200 minutes. Predive pressures

were recorded for a mean duration of 19.4 ± 14.5 minutes; postdive this

• oc o to "7 ,, 4- ^^ a f r- n v, ts^loc ^ nvoccliv^ûç ** VL ^ x/ e / <•« w V» ««s* • y «« —

increased (?<0.05) and diastolic pressures decreased (P<0.G5) during diving

which caused the pulse pressure to increase by 123% (P<0.01). There was

r»-» —v .-vf- < < >>» /-v /"j /x c ^ ^"3 a v* rl t a IIW I ^ i ) I^ C iii 141^ CX It ^ t O • « W * ^ I ^ ^ M • W >>4 ^ «V px I W «À • '<«i> • wa

(?<0.01). There were no significant differences in any of the measured

parameters shown in Table 5 between predive and postdive conditions.

In the 2 animals kept submerged longer than 2 hours, the mean pres­

sure began to decrease somewhat after about 130-140 minutes. Figure 13

shows systemic arterial pressure in an animal before^ during (61 minutes)

Gnu / injuu l.c^ CjuCJ g luuvcw wivc. 1 lywic ; ojf ^w Cmé . gi wc> « g » 125

Table 5. Blood pressures before, during, and after forced diving in 10 specimens of Pseudemys scripta^

Arterial Pulse Mean Heart Condition pressure pressure pressure rate

28.2 ± 4.1 Predive 5.2 ± 1.2 24.8 ± 4.1 38.8 ±8.7 23. 1 4.1 31. 3 + 3. 6 Dive 11.6 ± 2.3 23,6 ± 3.6 10.3 ± 4.3 19.7 + 3. 9 27. 5 ± 4. 2 Postdive 5.4 ± 1.3 23.8 ± 3.9 40.2 ± 7.1 22.1 ± 3.8

Values are means ± 1 S.D.; pressures are in mm Hg, heart rate in beats/minute.

Table 7. Statistical significance levels for forced dive blood pressure'

Data compared Significance level

Predive vs. dive P<0.05 systolic pressure

Predive vs. dive i m vj t uo w j i

ive vs. .. .1 ?

Predive vs. dive P<0.01

cant differences between predive and postdive measurements or for mean pressures bet.'/een any of the 3 conditions. 126

EKG

I II |i I' 1' !' I' r !'

IlimilllUIUi.., I ,ll'll»l!!ll»l!n!!!lllil!!ii!!lll!illli!i •sn")

1 mm MG

PD D-61 MIN PTD

MIN

IlililliilllllilillilillllliillillllliiiliiilllliiHillilllHIIHIIIi liliillililiiiiiliilillliiil'iiiriiiniiiillilil'iiiiii iiiisiiiiiii iiii:{ni'iiiiiiiii.!iiiiiiiiiii;iiiiiiiiiiiiiiiiiiiiiiibiiiMiii>iii

Figure 13.

turtle. After submergence, the EKG recording sensitivity was increased. The IP shows bozh heart rate and venu11auiOn \a predive ventilation sequence is r.arked with arrows; 3 sequences occur Dostdive). Notice increased pulse pressure during div­ ine ano tne decrease i r. uhi wu nrpssijres ventilation 127 pressures and heart rates before, during and after a one-hour dive.

Pressures would increase above predive values immediately after emergence in some animals. Afterwards, or in other animals, it might decrease be-

1 vw prcuivc pf ca.

Figure 14 shows left aortic blood pressure recorded after a 31 minute forced dive. The diastolic run-off pressure has about the same slope before and during the dive. This slope can be used to approximate rela­ tive changes in peripheral vascular resistance. Therefore, it appears that in this animal systemic vascular resistance does not change appre­ ciably during diving. In some animals this diastolic pressure run-off be­ came slightly less during diving, indicating that systemic vascular resis­

tance increased somewhat. Also shown in Figure 14 is pulmonary arterial

blood pressure. In this case, the slope of the diastolic limb of the

pressure curve is much less during the dive than before. This was the

case with 3 of the 4 turtles in which pulmonary pressures were measured

and indicates that pulmonary vascular resistance usually increases during

uivitiy, b udutniet! uS âuûu ù one Cnâtiyè vt iâC\ OV Cfiâriûc 1!"i VôSCUiâT

-i c r = r-..-^ 4 r,r'.r.r: =cc:;rr:£. = rr.r, c f = nf r.: :1 rr.-, r.% r\,' r.ri <: v ct T -.t: r c f rf-.l's

v u 1 uuic. na w i i i uc yu i : i ucu u u u i c uc i , uu«cvci , oncoc o uù ucmci i vo mu o v uc

modified since ine srro;

turtles (see Discussion).

Pulmonary arterial pressures were measured in 4 animals during forced

submergence. Despite a profound bradycardia (mean = 77%), mean pressure

r CMtQ {! W! UG. ! I U \ 1 / t

u i ca if'uiii 1^1, o 2: .o uu 61 — 6. v iuhi ny a : lu wa o i co uv ; cu u v u i "cu ; v c

levels within 1 mir.u"ce after emergence. 123

1 i il 1 111 i

31 MIN DfVE

Figure 14. Left aortic (LA) and left pulmonary arterial (PA) blood près- tiv*/^c ki^^ov»/-n t\ vi ^1 m-»w-«t«+"0c d f4- -f/> v»/- /gx cm km o a 4 m 3 4"i! v^_ SU4i\.0 I \j I Gjt\a sj M iitiiituuw^ Lt : vC i twiv.>WNu tit *»» vw i •^ «..• .1 ..a !• , ^ 1* I /"il ^ T'iQ m 1^ O T•"! _)T" T-r-vo n~>^OT-r>i tr~ iTmf"» r'>"^ L" * v. » WIIW v*«w«0ww« I \x I I lié hmf V « «^IIW ^WAttON/tlWk* J ^ I W trace is not as steep during the dive 129

Right atrial pressure was measured in 2 animals during forced sub­ mergence. Predive pressures were 2.5 ± 0.5/1,8 ± 0.3 cm H2O, During diving, in which a maximum bradycardia of about 90% occurred, pressures

^ ^ -j- n 7 /i /! -l a q u^o ^ v^r> r» s v» n c» n »»» ^ v»a 1

\;onnnc nv^ûcçiiv^û rl n v~ 4 nm fk^cc annv~f\v4ma+nl \/ ^0 m4r>n*f-o H4\/ûc

In some animals, during voluntary diving, both diastolic and systolic systemic arterial pressures would decrease, especially the former. Pulse pressures would, therefore, increase and mean pressure would fall somewhat.

In other animals no change in systolic pressure would occur during diving with only slight decreases in diastolic pressure. Therefore, changes in systolic pressure resembled the changes seen in forcibly dived animals while the diastolic pressure did not decrease as much. This was probably due to the higher heart rates during voluntary diving compared to forced dives. Blood pressures during voluntary dives are shown in Figures 5 and

15.

Tables 8 and 9 summarize the data on respiration before and after

• v I 111 -u vt :I * iiiu 1 a . ) Iic yc i v, ci 1 uciy c w 1 uw uu : 1 cvw 1 wcvi u ui:c a uc:: u 212

A nw no ^ s-A ^nor* , s_ ^cori -r n « 1r\i.;4 mm^ -riio;! _ /-i4\/oc.^ ! y o 1 !0 <^r\ w: A1 ^ y^ 5 iT*-»: t : u 4-v j o: U>/?-vov*>wo»^"'"4"îp_: g. f"1 An u;h 4 A % immoH 1a Tnl \/ "fn1 1 riwiorî mn ç-r X 4 \/z3C c r\ o/4 ç na -r c 4 mr- o T-no pGStuiVc data are aVcrayco over approximately one-naiT nour. Neveruneiess.

V CI 1 u 1 1 a u I uiI «va a i ni_ i caacu luiiuwiiiy ui;c uivc aiiu Liiii was au'wuiuu i ii iicu lij an increase in the number of respiratory sequences per unit time (P<0.01).

The mean duration of each sequence was not significantly different at the

0.10 level. Figure 13 shows a respiratory recording for one animal before aid after di^'-'^o. 130

0 SEC

mm hi g

10

V

i iQLire 15. Recording of systemic arterial blood pressures during a single voluntary emergence in the turtle. Arrow-heads show where the animal emerged (up) and subsequently submerged (down) 131

Table 8. Respiratory data before and after forced diving in 5 specimens of Pseudemys script^^

Percent time Number respiratory Duration of Condition in apnea sequences/hr resp sequence

Predive 89.2 ± 3.7 24.5 ± 9.7 16.8 ± 2.6

Postdive 75.5 ± 8.7 52.9 i 18 13.8 ± 3.3

Mean dive duration = 88 ± 51 min

Length of postdive recording = 35.8 ± 16.1 min

Values are means ± 1 S.D.; duration of respiratory sequences is in seconds.

lable 9. Statistical significance levels for forced dive respiratory data"^

Data compared Significance level

Predive vs. postdive P<0.01 % apnea

Predive vs. postdive P<0.01 sequences/hour

Predive vs. postdive p

ihese data accomoanv Table 8. 132

The number of respiratory sequences per hour was negatively corre­ lated with the length of the postdive recording period (r = -0.9070;

P<0.05). The number of respiratory sequences per hour and the percentage

3 4 \ \ f r* r\v^v^c»1 a 4-orl / = —0 om ^ hi ^ nç*înn ^ liltC ^^ CI 1 ly III Ct y/1I f K t ^ I 4 ^y s* * — y_ the combined predive and postdive data.

As described earlier, during voluntary diving the animal would venti­ late its lungs with 1-4 respiratory sequences while at the water surface between dives. Following the last inspiration of the final sequence it would dive. The first cycle of the first sequence upon emerging would then be an expiration (Figure 3). Occasionally an animal would be ob­ served to expire some of its lung gas after submergence. However, this occurred more often, and to a greater extent, in those animals which were forcibly submerged.

Cardiac Output, Shunting and Tissue Blood Flow

To use the microsphere technique properly it is necessary that the injected microspheres be blocked in the capillary beds during their first passage. As described in the Materials and Methods section, experiments were performed to insure that this was happening.

To test for microsphere passage through systemic capillaries, blood was withdrawn from one of the 2 large abdominal veins during injection of microspheres into the left atrium. It was found that radi'jdctivity '.r. the withdrawn venous blood was never greater than background. This proce­ dure was performed on 3 turtles. It should be noted that blood leaving the capillary beds in the posterior body may enter either the renal portal

ci/c + om nv fko a KrI Am-i n s "! \;ai ne lAi'n-ir'n f ri o \/annt i c hlnnr! tn the hona r 133 portal system. However, should microspheres have passed through the first capillary bed in the posterior body, some of them should have entered the abdominal veins. It appears, therefore, that essentially all of the 25- iivicron diameter microspheres were blocked in the posterior systemic capil­ lary beds on their first passage through these tissues.

The same results were obtained when microspheres were injected into a carotid artery in 2 turtles. Venous blood draining the head was not col­ lected, but the heart, lungs, kidneys, liver, spleen, brain and eyes were later counted. Little radioactivity could be found in any tissues other than the brain and eyes. It was concluded that, at most, only 2-3% of the injected dose could have passed through the capillary beds.

To test for microsphere passage through the pulmonary capillaries, a

known amount of microspheres was injected into a pulmonary artery in 2 ani' mals. The lungs as well as other organs were then counted for radioactiv­

ity. Results showed that only about 2% of the injected dose of micro­

spheres had passed through the capillaries of the lungs. It is possible,

nowever, tnat a slignrly larger percentage initially passed inr-uuyh Lhe

capillaries and was then blocked on their second transit after going throu

a left-to-right intracardiac shunt.

In 2 animals, 15-micrcn diameter microspheres were injected inro a pul

monary artery. Results showed that about 56% of the injected spheres

became trapped in the lungs. In another animal these microspheres were

injected into the brachiocephalic artery downstream from the origin of the

right aorta. It was determined that the lungs had trapped about 21% of

this injected dose, presumably after the microsoneres naa passed tnrougn 134 systemic capillary beds. Judging from the results on these 3 animals, it appears that 15-micron diameter microspheres are too small to use success­ fully in the turtle.

J-JU»^ I ^ I V,/1 lU I UCi ^rJ-V o 4-UD^w* *w* ^ 4"^««w A 9^_mTr'v*nn*— v rnnr'v*n çnhov^oç ^ •••_•. — being trapped in the capillaries on their first passage were obtained by comparing the microspheres with turtle red blood cells on the same micro­ scope slide. The microspheres were almost always larger than the blood cells. The same conclusion was reached when the microspheres were micro­ scopically compared to capillary tufts of the circulatory system made from corrosion cast material. The capillary diameters were not measured but, in comparison to the microspheres, appeared to approximate 20-microns.

It is necessary that the microspheres injected into the circulatory system be well-mixed with the blood. In this way they will be distributed in direct proportion to blood flow and can be used to measure regional per­ fusion rates. To insure that the spheres were well-mixed during the actual injection procedure, they were agitated in their injection chambers by a

VUr'UtJX i'llAtif. i!!!Ub!U!! U I U!lè ipIICICi Was ucyuii Uiiijr ai uci i iiaycv, u iu:: u i the chamber contents revealed that the microspheres v/ere well-mixed with the saline solution. Shaking of the chambers was continued until the in­ fusion was terminated.

In an attempt to verify that the infused microspheres were being well- mixed within the circulatory system, blood was withdrawn from the left aorta and left subclavian artery in 3 animals. If the injected spheres were well-mixed in the heart, and if R-L shunted blood was being well-mixed

wizn Dlooa from rne left azrium oefore ejection inro "che systemic arches. 135 equal amounts of isotope would be expected in the blood withdrawn from each artery. The results showed that the activity of the blood withdrawn from the left aorta during the injection of microspheres into the left atrium

, ~ ^ -A. ' - — J- "k jZ •- - —«C V* 4" ^ WdS d 1 Wày s I uwè r tfiaii lugl u i une uiuw'a o uuu i vu wcv/wo » Jr » u» • w.m w..>« left subclavian artery. It is difficult to believe that the explanation for these results is that the spheres are not well-mixed with the blood in the heart. The withdrawn blood from the left subclavian artery was always higher in radioactivity than the blood withdrawn from the left aorta (mean of 251/0 higher). Apparently blood shunted from the right atrium to the systemic arteries is preferentially directed to the left aorta at the ex­ pense of the brachiocephalic artery.

Even experiments in which blood was simultaneously withdrawn from the

1 eft carotid and subclavian arteries (near their connection with the brach­ iocephalic artery) resulted in different total counts of nuclide. In 2 animals, microspheres were injected into the left atrium and simultaneously withdrawn from the above 2 sites. In both cases, the blood witndrawn from me carotid artery had a greater rauiuauLiv i Ly (mean oT 2GC% higher).

In a thi^^d animal, microspheres of a different label were injected into

each atrium and blood withdrawn as above. Considering the microspheres

injected into ihe left atrium, the DIOOQ wiinarawn from the carotid artery

contained over 48 times as many as that withdrawn from the subclavian

artery. Of those spheres injected into the right atrium, 75% more were

withdrawn from the subclavian artery. This procedure was repeated 90 min­

utes later in the same animal with the microsphere labels injected into

each atrium being reversed. The same pattern was observeo: the carotio 135 withdrawal contained 57% more of the left atrial spheres while the sub­ clavian artery received 56% more of the right atrial microspheres. Thus,

it is possible that the shunted blood which does enter the brachiocephalic

arucij uvea :ivu IIJIA yv i ui i une unouui i ucu uiuuu, uu u ; iia ucau maj i UMU a i>cpa-

fa uc :: u( cam Wi11 uii r ciiia u):> uuiii i ACU W i ui* ui ic i c i u a ui i a i u i uuu ^ cv cn uin

dovmstream from the ventricle.

Despite the reasons for the above results, it was apparent that using

the left aorta or any of the branches of the brachiocephalic artery for

blood withdrawal to determine cardiac output would give erroneous results.

A measure of the mean concentration of microspheres leaving the "left

side" of the ventricle was necessary to calculate ventricular systemic out­

put. Since the blood leaving the "left side" is made of two separate frac­

tions (pulmonary venous blood and R-L shunted blood), and since they appear

to be leaving without thoroughly mixing with each other, another site for

blood withdrav/al had to be located.

Subsequent experiments showed that L-R shunted blood usually mixes

WO I I ufTTH c \/<: Tom Î r \/onnnc ninnn na-fn^d no inn oi ocf or: infn thp n? î i mnn;^ r»\/

5 f U-I^o V 1 ^ C. 17 \ TA o 3 7-^: ;1 mfx v» \Ai«4wijr XN./ Uiiiva A. / J • w I I V» i w:

wionurawai ciiuWs lur une LCiuuicuiuH ui Vcu ur iuu iar pu iiiiuncrj

QiiTnîî'T i.'inon n'Mmnri^Y^v/ n-irnMr nn mo Sa c ? q r.-f nnf n 4 ni or Tori

isotopes (one from each atrium) is the same, thorough mixing of the 2 blood-

C Tvoamc nc Z riX 4 r-z -r oX 3 r\ I 11 m/"\ v* n v»\ / r\ : I -rr-^, , 4- \ ; 3 1 i»o 3 3 c C /-• V» /> /- 4- -* I 10 « I I lymA ^ W * MIW 4 4W, I jr W L* L* V V L» I W X— LA 1 j L/\_ I |CV U *

Additional equations can then be used to calculate the ventricular systemic

A: A; : T ^nn y~or: 4r\na 1 r r\r»X «ni.fc icoo T^'a-rov^": 3I c 3 nX r.'o 4- r\ Xr ^ ,3/^ «r» 4 ^ v s»i i" w ^ i v * » w i \l ^^ vattnrf i viin i vw ^ ."\M J 9 137 riguro 1(3. Relative weight-specific blood flows to a lung of the turtle. Microspheres containing the nuclide Sr-85 were injected into the right atrium and their distribution to the lungs was therefore representai;ive of uns hunted blood flow to the lung. The Ce-14] isotope was representative of shunted blood since these microspheres were injected into the left atrium. The anterior and posterior ends of the lung are labeled A and P, respectively. Ten cross-sectional cuts were made through the lung moving in an anterior-posterior direction after dividing the lung into rougly equal dorsal and ventral halves. (See Figure 17). Weigtit-spec ific blood flow to the most anterior-ventral section was arbitrarily designated a.s 100 for comparison with other lung sections DORSAL SF(-85

91 36 136 247 227 265 129 83

101 60 61 1(15 2A5 275 74 100

1-1 (s)

82 77 137 262 232 235 256 192 122 139 89

113 62 54 187 237 262 201 156 104 72 100

VENTRAL i-i(jure :17. Diagram il lustrating hov/ the lungs v/ere sectioned prior to being weighed and counted. The bronchi (B), trachec (T), left (LL) and right (RL) lungs are drawn from a ventral porse|)ctivo. À side view of the lei^t lung is also shown (which corresponds to figure 16). Lines drawn throucih the left lung show how the lungs were sectioned into approxi­ mately equal size piece*, for weighing and counting ANT

DORSAL

VENT 141

Table 10 gives the results of the cardiac output and intracardiac shunting determinations. The values shown are the means for at least 5 aerial and 5 submerged animals. As indicated, L-R shunting decreased 57%

(P<0.10); whereas R-L shunting increased 59% (P<0.10) in submerged animals.

This means that blood was shifted from the pulmonary circuit to the system­ ic circuit during diving. The table also shows that a mean net R-L shunt existed in turtles both above and below water.

Both ventricular pulmonary output (P

Therefore, the total heart output decreased 52% (P<0.01) in the diving animals. Stroke volume increased 96% (?<0.01), thus partially offsetting

the potential cardiac output reduction effected by the 75% bradycardia

(P<0.01). Although there was no significant change in the volume of the

ventricular systemic output composed of R-L shunted blood in submerged

animals, the volume made of unshunted blood decreased by 69% (P<0.01).

This again illustrates that a smaller proportion of blood is circulating

Tnm; inn f no 1i ;nn<;

Using the values for mean systemic and pulmonary arterial pressures,

and knowing the amount of blood pumped through each circuit by the heart,

the resistances to blood flow can be calculated. In aerial animals, total

pulmonary vascular resistance, corrected for body size, is 0.48 mm Hg/ml/

min/kg or 0.48 peripheral resistance units (pru). In submerged animals,

this increases to 1.61 PRU, an increase of 235%. Systemic vascular re­

sistance in animals above water is 0.52 PRU compared to 0.84 PRU in diving Table 10. Blood flow data for aerial and submerged Pseudemys scripta^

Condition % LR % RL VPO' VSO THO

Aorial 15.8 i 14.3 (13)^ 40.9 ± 25.6 (7) 35.2 ± 12.0 (6) 46.8 ± 13.2 (5) 79.3 + 9.4 (5)

Submerged 5.3 i 6.1 (7) 65.0 + 21.8 (6) 10.5 ± 4.5 (6) 28.8 ± 15.7 (5) 38.1 ± 17.2 (5)

% Change -66.5 +58.9 -70.2 -38.5 -52.0

Sig. level <0.10 <0.10 <0.01 <0.10 <0.01

SV VSO, vso. MR" Condi tion us

Aerial 2.3 :L 0.3 (5) 19.0 ± 18.9 (5) 27.8 ± 7.2 (5) 33.8 ± 3.3 (5)

Submerged 4.5 ± 1.0 (!3) 20.3 ± 14.7 (5) 8.5 ± 3.3 (5) 8.5 ± 2.1 (5)

7o Change +95.7 +6.8 -69.4 -74.9

Sig, level <0.01 N.S. <0.01 <0.01

^AVI values are means ± 1 S.D. Abbreviations: LR, left-to-right shunting; RL, right-to-left shunting; VPO, ventricular pulmonary output; VSO, ventricular systemic output; THO, total heart out­ put; SV, stroke volume; VSOg, shunted portion of VSO; VSO^^, unsliunted portion of VSO; HR, heart rate

'\P0 through VSO^^g are values in ml or ml/min per kg body weight.

"^Number of observations.

^As beats/minute. turtles. This represents an increase of 62%. Therefore, peripheral resistance increases during diving in both the pulmonary and systemic vasculature, and the increase in pulmonary resistance was 2.0 times the

; MU 1 CQ a C id Ul IC ^ wCtll 1U

D1 \ ^ I y 114» u O. vI ICi ! utooouic '-'^CvtC^ i u laaT Ci i* ni 11y\ 4-r\ uw 4iii Sfnyirr systemic vascular resistances since central venous pressure does not change during diving. For the calculations of pulmonary impedance it was assumed

that left atrial pressure is also maintained constant during diving in

turtles.

Results of the tissue blood flow experiments are given in Tables Il­

ls and Figure 18. For many tissues, especially in submerged turtles, less

than 400 microspheres were trapped. Therefore, in Tables 11-12 and Figure

18, flow values for these tissues are shown as "something less" than the

value calculated on the basis of exactly 400 microspheres. Since the flow

could not be accurately determined to these tissues, a mean and standard

deviation could not be established. For this reason. Tables 14 and 15 do

nO L y ; V e b Lc L :b L !Ua : bcynifiucnLe leveib Tur" Lhe L i SSvèS wiLh icSS Lnûn 4GG

^ ^ « • • « ^ « t ^ 4 W w' ^ i t I ^ W W Wk ^ W 4 • ^ I W W « W # # # ^ « A ^ • V ^ « 4 • ^

I Û u ^uC! ^ L.O ^ ^ u I CO^ ^I wK( ^ ^I vcixs ^ ^vCO ^ ^Vi Lm :C ^ Oiynii^ m ^ ^ ^ mi ^ ^ ^ icvcirN \i 1 ^: O ^;ii C/w.»^ v/ coo^ ^ ^ ^w *i

0.10 for -chose -cissues.

As shown in Tables 11, 13 and 14, and Figure 13, the brain, eyes and

q hoi 1 sll rami \/ori 1 oqç çhnntoH f ha n nnichrnfon hi ap.ri i r A ori snimalq.

Tn4MiO 4 c '.'PCviCÂo i-VI w' Co i VI Kr\i^wvw 4- X do kVOwK c » wt i 4-vs., ^ iiwrvo CL « ys.. v»/^% v, on« i v^ n .a r\Tv/ i oa X flI«VM« *Tr* i&

i c V u; VI V : cv c ; V cu c L/O V : u vc i j/ ; )v o : ;v n ucu u ; vv u. jwcic wao i :v o vo u ;

uical ly significanu difference between absolute snur.oed and unshunred flow "co 144

Table 11. iissue blood flows for aerial pseudemys scripts^

Tissue Unshunted Shunted Total

Ventricle 20.0 + 13.6 (5)b 33.4 ± 13.1 (5) 55,2 ± 17.4

Thyroid 32.4 ± 11.0 (4) <45.5f (4) <77.9

Liver 3.8 3.8 (5) 4.1 ± 3.8 (5) 7.9 ± 3.7

Esophagus 2.8 ± 2.9 (5) < 7.3 (5) <10.1

Stomach 1.4 ± 1.1 (5) 1.1 ± 1.1 (5) 2.5 ± 0.5

Pa nc rea s 5.7 ± 5.6 (5) 25. 9 ± 40.0 (5) 32.9 ± 33.1

Spl een 42.3 + 48.9 (5) 378. 6 ± 437.9 (5) 426.6 ± 434.1

Small Intestine 4.0 3.2 (5) 6. 7 ± 7.2 (5) 10.8 ± 4.5

Large Intestine 9.0 ± 5.6 (5) 8.,9 ± 12.2 (5) 18.1 ± 9.2

Kidneys 10.5 + 5.8 (5) 6.,8 ± 9.1 (5) 17.3 ± 10.2

Anterior Skeletal 5.0 ± 2.1 (5) <2.3 (5) <7.3 Muscle Posterior Skeletal 3.7 ± 1.4 (5) <2.6 (5) <6.3 Muscle Brain 6.0 3.4 (4) 00.0^ (4) 6.0 ± 3.4

= r\r\ r\ r \ nr n /I r Eves 24.5 4.5 VV .u J c.-r . sj

Sh el 1 11. T/ 0.9 (5) r\ £ (5) 1= 9 ± 1= 3

•^Values are means ± 1 S.D., units in ml/min per 100 grams tissue.

°Nu"ber of measurements.

^Tissues with less than 400 total microspheres are shown with "less than" signs.

M ""Brain and eyes gave counts no greater than background. 145

Table 12. Tissue blood flows for 5 submerged Pseudemys scripta^

Tissue Unshunted Shunted Total % Change^

Ventricl e 13. 3 ± 7.5 28. 9 ± 13.1 42. 0 ± 18.1 - 23.9

Thyroid <9.1^ <45.5 <54.6

Liver 0.1 ± 0.2 1.7 ± 2.0 1.8 ± 2.1 - 77.2**

Esophagus 1. 4 ± 1.7 <8.2 < 9.6

Stomach <0.1 < 0.9 < 1.0 - 60.0

Pancreas <0.5 <4.9 < 5.4 - 83.6

Spleen <0.5 < 4.9 < 5.5 - 98.7

Small Intestine <0.1 < 0.2 < 0.3 - 97.2

Large Intestine 0.,2 ± 0.2 < 1.3 < 1.5 - 91.7

Kidneys <0.5 < 4.5 < 5.0 - 71.1

Anterior Skeletal 1.,4 ± 1.4 4..3 ± 2.8 5,.7 ± 3.0 Muscle Posterior Skeletal 2.,2 ± 0.9 10..6 ± 8.1 12,.5 ± 7.6 Muscle Brain 30,.2 z 16.7 8..0 ± 5.5 38 .2 ± 13.1 +536.7*

Eyei 27,. ! - i5,3

A = 0.1 n n Shel 1 ' * " ± 0.7 ± 0.8

^Values are means 1 S.D., units are ml/min per 100 grams weight.

^Represents % change between total blood flow for aerial {Table 11) and submerged animals; -, ?<0.01: ?

^Ticciioc with Iocs rrirsl rv-r,c:-,hprp<; ïilble 13. Distribution of ventricular systemic output for aerial and submerged Pseudemys scripta^

-- - Mer Id 1 —— Submerged ——— Tissue %VSO^^ %VS0g %VSOyg %VSOg

Ventricle 123 .8 i 61.4 (10)b 263.8 ± 198 .6 (5) 225.9 + 81.0 (8) 256.6 ± 143.4 (7)

Thyroid 27 2,,0 ± 181.1 0) <363.6' (5) <90.9 (3) <363.6 (7)

1. iver 23 .3 i 21.8 (10) 61.3 ± 51.9 (6) 2.0 •± 2.0 (8) 7.7 ± 8.0 (7) l'.:;ophagus 16,.0 i 17.7 (B) < 36.7 (6) 17.8 19.5 (8) < 36.7 (7)

îitomach 9,.3 ± 9.9 (10) 9.2 i 9,.5 (6) < 1.0 (8) < 4.2 (7)

Pancreas 29,,4 ± 16.4 (9) 167.8 ± 213,,9 (6) < 5.4 (8) < 21.5 (7)

Spleen 150. 8 1 103.G (10) 1572.0 i 1313,,0 (6) < 5.5 (8) < 21.9 (7)

-Small Int. 15. 0 ± 17.0 (10) 40.5 ± 16.,8 (6) < 0.3 (8) < 1.1 (7) large Int. 42. 4 ± 30,5 (10) 66.7 ± 42. 9 (6) 1.9 + 2.5 (8) < 5.6 (7)

Kidneys 59. 5 18.5 (10) 28.3 ± 25. 8 (6) 6.9 + 11.5 (8) < 20.0 (7)

Anterior Sk. 3 ± 32.1 (9) <11.4 (6) 30.7 + 18.6 (8) 46.4 ± 18.7 (7) Muscle 45. I'ostorior 3R. 5 ± 19,0 (0) <11.8 (6) 48.3 + 23.8 (8) 67.7 ± 30.5 (7) Sk. Muscle O C lirai n 75. 3 (9) 00.0^ (B) 580.8 + 232.6 (8) 72.6 ± 49.3 (7) lyes 185.8 ± 55.4 (8) 00.0 (5) 533.2 ± 259 .3 (8) <200.0 (7)

Shel 1 6. 9 ± 5.8 (9) 1.4 ± 1. 5 (6) 3.8 ± 3.7 (8) 1.4 ± 2.6 (7) ^Values are means ± 1 S.D. and are based on 100 grams tissue weight.

'Number of observations.

^Tissues that contained less than 400 total microspheres.

'•'counts in brain and eyes were never above background.

-r^ Table 14. Statistical significance levels for blood flow data'

Data Compared

Acïrial aninals - - Submerged animal s Tissue Shunted vs unshunted Shunted vs unshunted Shunted vs unshunted Shunted vs unshunted ml/min-lOOg %VS0/100g ml/min-lOOg %VS0/100g

Ventricle **"• d Thyroid 1.1 ver •k-k-k -kk-k [.liophagus Stomach f'ancreas -k-k-k Spleen Small Intestine large Intestine Kidneys •k-k Ant. Muscle Post. Muscle *** [îrain -kk -k -k-k Eyes -k -k Shel 1 k k •k-k

'These data accompany Tables 11, 12 and 13. ')*** denotes statistical significance at the 0.10 level. denotes statistical significance at the 0.05 level. "Tissues with less than 400 total microspheres. denotes statistical significance at the 0.01 level. 149

Table 15. Statistical significance levels for blood flow data&

Data compared (aerial vs dive) Tissue Shunted Unshunted Shunted Unshunted ml/inin-lOOg ml/tnin-lOOg %VS0/100g %VS0/100g

Ventricl e

Thyroid ***d Liver •k-k •k-k

Esophagus -

Stomach - - -

Pancreas - - -

Spleen - - -

Small Intestine - - -

•k Large Intestine -

k Kidneys - -

Anterior Muscle - ~k-k-x Post. Muscle -

Brain ** •k-K •k •k

Eyes -

one 1 1 *

^These data accompany Tables 11, 12 and 13.

denotes statistical significance at the 0.05 level.

"Tissues with less than 400 total microspheres.

denotes statistical significance at the 0.10 levai,

denotes statistical significance at the 0.01 level. Figure 18. Absolute blood flows to various tissues in aerial (A) and submerged (S) animals. Total flow is represented by the height of the column. Shunted flow is that part of the col­ umn blackened; the remainder is unshunted flow. A question mark indicates that the flow is "something less;" than the value shown (see text). Bars indicate ± 1 S.D./n 50

4 0

EYES SHELL Figure 18. continued INI MS "Ids NWd OXS

Ê FigurG 19. Percent systemic Hows :o various tissues in aerial (A) and submerged (S) turtles. Percent of unshunted VSO (u) received is shown in the first column of each pair, per­ cent shunted (s) is the second solumn. A question mark indicates that the i'low is "something less" than thi3 value shown (see text).. Bars indicate ± S.D./n 2,64 1:50 /2%'B c. ^ 1^ « 267 40 10 27 g"

G» o o o œ > •><

A S

50 II u

10 « 7 ; • __ J_1 r-m VENT THYF^OID STOMACH Figure 19. continued 15ig

H a

jc-'i I—

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H-i

Cm C5 CO iS- \ Cvj 3 1C^.! Sis s r" , 1 i ; 5 1 i i. —' ^ _J L. Ii

a

(O jO'l ii.

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I V o S. o /% t ^ w; / V&/Wo / Figure 19. continued \i\0 581 (53:; 186 200 110 / 29 / 32 c» C' c>

C' a> A S

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^iO ï ï

0 10 (i u 0 i I fk-Ù^ ANT MUc POST MUS BRAIN EYES SHELL 152 the other tissues to which flow could be quanti tated accurately despite the large differences in mean flov;s to tissues such as the spleen and pancreas.

Blood flow to these 2 tissues was tremendously variable, and weight-specif­ ic flow to the spleen was usually greater than flow to any other tissue in the body. The spleen, pancreas, liver, heart and small intestine each re­ ceived a greater percent shunted than unshunted flow despite the fact that absolute flows were not significantly different. The %VSO to the kidneys of aerial animals was less than the %VSO to them, but absolute flows were equal.

When considering only submerged animals (Tables 12, 13 and 14 and

Figure 18), the ventricle received more shunted than unshunted blood, but percent flows were the same. The brain received less absolute and percent­ age of shunted blood than it did of unshunted blood. Shunted flow could not be accurately measured to the eyes in submerged animals, as v/as the case with many of the other tissues. Shunted flow was greater to the shell, skeletal muscle and liver than was unshunted flow, but statistically

tn9S9 di ff0'*^0"C°S nn-r c i nr f i ra nf ? f rhp n.'w lO t.nê posterior skeletal muscle. Percent shunted flow to the liver was greater

than percent unshunted flow.

r\c .3#-, 4- -rr»v» -rr\ -rz 1 r\l nnri f 1 r&uf "TTCCUOC

when aerial animals (Table 11} are compared to those which were submerged

(Table 12). Blood flow to the ventricle decreased, but not significantly.

Flow to the liver decreased 77% (?<0.05), whereas that to the brain in­

creased by 537/0 (P<0.01). Blood flow to the shell decreased by 5S%

(P<0-10}. Total blood flow to the stomach, pancreas, soleen. small and 153 large intestine and kidneys was calculated to be reduced by at least the amount shown in Table 12 (from 50 to 99%), but significance levels could not be established for this data. Blood flow changes, if any, to the

thyroid and esophagusv.-ere impossible to assess since total flow to these organs could not be quantitated in either aerial or submerged turtles.

Total blood flow to the skeletal muscles increased slightly, but probably

not significantly.

Submerged animals showed a reduction in shunted blood flow to many

tissues when compared to aerial animals (Tables 11-13 and 15), but the level

of statistical significance could not be ascertained for most of these tis­

sues since they trapped less than 400 microspheres. Absolute shunted flow

increased to the skeletal muscles, brain and eyes and this increase was

significant at least to the brain. Percent shunted flow decreased to the

liver even though the absolute flow did not change; it increased to the

brain as did the absolute shunted blood flow. Unshunted flow appeared to

decrease to many tissues in submerged animals - definitely so to the large

V_> ) I I V I 4_4l|V^ •«>l\ I I I I g VTI IW W ^ « VV V « » w

brain increased. Percent unshunted flo'.v to the ventricle, brain and eyes

increased, but decreased to the liver, large intestine and kidneys,

Ài U I VC 1 VCI I L, W 1 O U: I L/L* V 1 L/M V f G,) i w iv i s/Vf A

changes during diving, this will indicate that changes in the distribution

of blood flow have occurred. Changes in absolute shunted and unshunted

flow to specific tissues, however, may result not only from changes in the

distribution of flow to such tissues, but also from changes in the volume

V I ^ 1 lu 11 LCU CÀ nu u ua MUI : ucu u i v uu i i vm uuc i iC 0.i u. i i iC > c i v > c; ^ v * ; * jr 154 measurements of %VSO and %VSO^^ to tissues under various experimental con­ ditions will insure an accurate assessment of changes in peripheral blood flow resulting from alterations in flow effected at the tissue level.

Furthermore, if the unshunted and shunted blood in the "left" ventricle are well-mixed, changes in %VSO should parallel changes in %VSO,,g. There­ fore, percent distribution of the 2 blood streams to various organs will give us information on flow patterns.

Tables 13 and 15 show that the percent of unshunted and shunted flow decreases to many of the tissues during diving; however, it could only be shown statistically to decrease to the liver, large intestine and kidneys.

It increased to the heart, brain and eyes.

Tables 13 and 14 indicate that %VSO and %VSO to some tissues are

not equal. Thus, streaming of the 2 bloodstreams could be occurring. This

is probably the case for blood within the brachiocephalic artery since the

to the brain (end probably eyes) is always greater than the %VSO

to this tissue, whereas this is not always the case for either the heart

Or- the anterior skeletal muscles (all 3 tissues ûre supplied with blood

from the brachiocephalic artery). Percent distribution of shunted and un­

shunted blood to the gastrointestinal tract and kidneys may not always be

equal as shown in Tables 13 and 14, In fact. Table 13 seems to show a

pattern in this regard. The gastrointestinal tract and spleen of aerial

animals receive a greater %VSO^ than while the opposite appears to

be the case with the kidneys and posterior skeletal muscle. The gastro­

intestinal tract and spleen receive their blood supply from the left

aorta ? the comor dorsal aorta supplées the kidneys and posterior skeletal 155 muscle. Diving may alter this distributional pattern due to the changes in peripheral vasomotion and intracardiac shunting which accompany such maneuvers. It was pointed out earlier that the majority of the R-L shunted blood is directed towards the left aorta rather than being well- mixed in the ventricle with pulmonary venous blood, and it is this initial separation of the 2 streams of blood which could form the basis for differ­ ences in %VSOg and %VSO in the more peripheral tissues.

In summary- it appears that:

1) When considering aerial animals only:

a) Shunted blood is not directed to the central nervous system;

u J I V mua L uoiici u I aauca artun ucu a ilu ui la i lu 11 vcu uiuuu i i VM au : uuyii i j

equal rates despite the fact that the percent of shunted and un-

shunted flow that each tissue receives may not be the same.

2) When considering submerged animals only:

a) Shunted flow to the ventricle is greater than unshunted flow to

this organ;

K\IV / Qw/WMiN_ c 1KI: u I :y»I + V*—ii>^rT /-i/n 4to c w/4 4i i ww +1^/3wi ix.. r'MCvi ; ivv w iiwi*) r\i»» fTvww T».#« »l * C—» ?"w l • «-iC —

sue is composed mainly of unshunted blood;

c) Percent distribution of shunted and unshunted flows to tissues

are not always equal.

3) When comparing aerial turtles to submerged animals:

a) Total blood flow to many tissues decreases because unshunted and

shunted flows decrease, especially the former;

bj Flow to the brain increases, due mainly to an increase in un­

shunted flow to this tissue: 156

c) Blood flow to the ventricle and skeletal muscles remains the

same. Flow to the muscles is probably maintained because of an

increase in the flow of shunted blood to this tissue since the

unshunted flow appears to decrease;

d) Percent distribution of shunted and unshunted flows indicates

that blood flow is redistributed away from the viscera and to­

wards the brain, heart and skeletal muscles.

Microspheres were injected into the left atrium of a turtle above water and followed by a second injection of microspheres of a different radioactive label after the animal had been submerged. Th"s procedure allowed for the comparison of data in the same animal both above and below water. With only a left atrial catheter, however, only VPO, %L-R shunting and %VSO, could be calculated. The experiment was performed on only one turtle.

Results indicated that the same overall response to submersion oc­ curred as would be predicted based on a comparison of blood flows between separate aerial and submergeu animals. Ventricular oulmcnarv cutout de­ creased 67% (from 48.9 to 16.3 ml/min-kg) and L-R shunted blood decreased by 77% (from 3.1 to 0.7%). Percent unshunted flow increased to the ven­ tricle. skeletal muscles, brain and eyes and decreased to the gastro­ intestinal system, spleen, kidneys and thyroid. 157

DISCUSSION

A significant bradycardia was observed during diving in most of the turtles used in this study. This is consistent with the majority of re­ sults obtained for other animals including mammals, birds and reptiles.

Mil 1 en et al. (1954) found that no bradycardia accompanied submersion in the turtle p. scripta. However, a significant bradycardia has been re­ ported during diving in snakes (Johansen, 1959; Murdaugh and Jackson, 1952;

Pough, 1973; Irvine and Prange, 1975), lizards (Bartholomew and Lasiewski,

1955; Wood and Johansen, 1974), crocodilians (Wilbur, 1950; Andersen, 1951) and turtles including p. scripta (Belkin, 1954; Berkson, 1965; White and

Ross, 1955; Penney, 1974).

In birds and mammals the bradycardia of diving is reported to be inde­ pendent of underwater physical activity (Scholander, 1940; Andersen, 1959a).

In the present study, however, struggling was accompanied by a transient tachycardia which occurred at times in almost all forcibly submerged tur­ tles. This response may be common in reptiles as it has been previously observed in turtles (White and Ross, 1955; Berkson, 1955, 1957) and sea cnal/oc r Wca o 1 Q7^ ^

It was found that voluntary diving in p. scripta was accompanied by a

2S'o reduction in heart rate. This is to be compared to an average reduc-

L, Î V Î 1 V Î C ~'A ! !! !GL L,C î J' W .'0 ? I S U f t ! »lîU 1C» i W i i L/ i vjiv of bradycardia in these latter animals approached 98% in a few instances, a phenomenon never observed in a voluntarily diving turtle. Clearly, forced submergence effects a more pronounced reduction in heart rate than is the case during voluntary diving. Not only were there differences in the 158 degree of bradycardia attained between the 2 types of dives, but the time course over which the bradycardia was developed was clearly different.

When the animals would voluntarily submerge, heart rate would usually he reduced within 1-2 cardiac cycles. However, the response to a forced dive was variable with heart rate being reduced only over a period of min­ utes. On average, it took about 38 minutes for the heart rate to reach its lowest value during a forced dive. These results are similar to obser­ vations made in the alligator where heart rate slows more rapidly during a natural dive, but remains at a higher level than when the animal is forcibly submerged (Andersen, 1961). Bel kin (1954) found that a 41% brady­ cardia developed immediately when p. condnna would dive naturally, and other studies have demonstrated that the heart rate of forcibly dived p. scripts develops slowly (White and Ross, 1966; Jackson, 1968; Penney,

1974). Similar differences in the onset of a diving bradycardia depen­ dent upon the nature of the dive have been reported in tiger salamanders

(Heath, 1978) and water snakes (Irvine and Prange, 1976; Jacob and

The rapid onset of the bradycardia during natural dives indicates that

the response is probably not dependent upon the development of asphyxia as 1 '2^ C Q « ^ X 0/^çç *0^^» 1 07 ^ \

3 3 mav/ Ka 4 mr\n anf 4 n o-f-r -t": nn Tnn ri \/ra Y~r! ia nKcûv*\/ûr!

during a forced dive and it is possible that this effect is mediated through

the chemoreceptors once the PO2 of the body fluids decreases. Evidence in­

dicates that chemoreceptors are responsible, at least in part, for the in-

u I ccicu pici J :c! a 1 i ci i iua iiuc a i lu ui aujv_a luiû lu uivijiy uuv-isi \ Tiu i i ci ii/c i y 159 and Uvnas, 1953; Jones and Purves, 1970b). The bradycardia which gradually develops in diving frogs is also thought to be due to O2 lack (Jones, 1967;

Lille, 1978), although this effect may result from a direct action of asphyxia or. the heart rather than through chenio receptors (Lund and Dingle.

1968). Glomus bodies have been described in reptiles which appear to be morphologically similar to mammalian carotid and aortic bodies (Adams,

1953), but knowledge of their function is lacking.

In the seal, unrestrained diving elicits a greater bradycardia than when the animals are forcibly submerged (Murdaugh et al., 1961b). This

is opposite to the response in reptiles.

Gaunt and Gans (1959) reported that unrestrained caiman crocodiius

show a greater reduction in heart rate when diving in response to an ap­

proaching person than when doing so spontaneously. The iguana (Belkin,

1953b) and alligator (Smith et al., 1974) show similar responses. It is

also known that fright will produce apnea and bradycardia in reptiles even

when they are not in water (Belkin, 1968b; Gaunt and Gans, 1959). The -C-.. ^ ^ ^ I"» /-y — ' ! V» —1 c 1. rt-* I f ^ ov* M I n I ^ < I L# O ^ U V I LZ • t W J I a O v.* low U * III ^ V * I ^ V* I W I ^ T T < t ^ W • —

produce a bradycardia siir.ilgr to that developed during voluntary diving an

that the same general response would occur when the animals would dive to

escape a prodding. If the turtles were disturbed when underwater, they

would usually respond with a tachycardia, while preventing voluntarily div

ing turtles from surfacing would result in a bradycardia resembling that

when forcibly submerged. Clearly, the cardiac reflex response to submer-

31 VU w;i, vii . i> i fiucycriuerio UT nicher brain centers, at least in ducks

(Huxley, 1915a; Andersen, 1955c), is certainly modified by such centers, 150

The overall reaction to any particular situation is very complex and it appears that a strong psychologic component may be involved in the cardiac response to a dive.

That higher brain centers may modify the characteristics of the dive reflex may be appreciated when one considers the anticipatory increases in heart rate which occur prior to voluntary emersion in turtles. This has been previously reported in seals (Eisner, 1965; Kooyman and Campbell,

1972), turtles (Boyer, 1953; Bel kin, 1964; Burggren, 1975) and snakes

(Rough, 1973). Grinnel et al. (1942) reported that heart rate sometimes increased in seals which were forcibly submerged when the animals observed activities of the investigator which they had learned to be associated with being brought back to the surface. Irving et al. (1942a) found that when a seal is completely submerged, but is free to raise its head out of the water to breathe, bradycardia may not develop.

Bel kin (1954) reported that the overall mean heart rate of p. conciima was similar to the heart rate obtained when the animals voluntarily sub-

Timo -rov- T'no i, nf a 1 \/ ri i wi nn ly^fl oq i n thiQ <:+i:ri\/ cnonf

nf tho t-imo cnhmovnoiH Tlierofnro rhp n\/oyal1 hparl" rsfo A nH thp hPA rt

I a Lc yyui;c uiviiiM vïcic biiniiai . O 111 Lc ui i c uu: u i cb Wu u i u i oiia i 11

V» rv» ^ 4- ^ V/m /-\ /"* /^ ^

rate response a breathing tachycardia rather than a diving bradycardia.

That the dive bradycardia is at least partly mediated by an increased

parasympathetic tone has been demonstrated in one turtle of this study.

T r\ a ^ ^ /4 ^ ^ ^ « II/» 4» V» ^ V ^ 1 ^^ /\ vI V* it wiw ««wv»* tv^vw # s.» vs..

: u:> jjicviuu:? icvci. o i ncc unc wz>c v i a uf up i i:c JcCjuif cu uu c>u i u i : j 161 effect a 30 minute blockade of the cardiovascular responses to intravenous injections of acetylcholine in toads is reported to range between 1-5 mg/ kg (Kirby and Burnstock, 1969b), it is possible that the atropine did not k "7 ^ o "7 1 a vsa c" s +[^<3+ 4 r» 4" o 4-A haa y* MnUfûV/OV* Roi !(' ln ^ 1Q^Zl 1 states that 0.2 mg/kg atropine blocks the cardiac vagus in turtles. It is also possible that a decreased sympathetic tone and/or a direct asphyxie effect on the heart is also responsible for the cardiac slowing observed during forced submergence. Caution should be used here in applying these results since the drug was given to only a single animal. An increased parasympathetic tone is usually reported to be the mechanism of effecting the diving bradycardia in reptiles since vagotomy (Andersen, 1951;

Murdaugh et al., 1961b) or atropine (Murdaugh and Jackson, 1952; Bel kin,

1963b; White and Ross, 1966) prevents this response. There are studies, however, which indicate that in grass snakes (Johansen, 1959), tiger salamanders (Heath, 1978), frogs (Jones and Shelton, 1954) and white rats

(Lin, 1974), the dive bradycardia is not simply due to increased parasympa-

VI ic V 1 V uv: *c •

J.T : : 4 C 4-4 '-it;3 4 V. ^ 4in4-/-> -rioov ; 1 11 yrm^ J'c v "r; S.« Dçi»v ^nmo v«n^ on -tm • -rv i• on«. 4• nn• y»oa ^C on

4-no m ca v^a*ro Cnmil a-TTz-xn n-r ^ v«ocn4v-»a'^nv^\/ n \/n 1 OC A "F n mi o3 n % y»û"hiiv^nori the heart rate to its oredive value. This tachycardia in response to lung inflation is known to be associated with an increased pulmonary blood flow in p. scripta and both responses are abolished by atropine (Johansen et al.

1977). A similar increase in heart rate in response to the intrapulmonary

^ A I _ T C «n t ç-1 i r\rr> I I J J u iKJli \J I I IU.O ivCC I ' I 1 »»; OiuuntiCi

L/u L, Ct k/iwv^Cw\^i^ I ) * WW I * I I V y vuivu 1Zf ^ v* wC* vw iiviCii

rate cnanges i^lIisO, ly/ yo;. I'c "cnereTore appears "cna'c apnea may oe an 152

important prerequisite to the dive bradycardia and that lung stretch re­ ceptors may be responsible for modifying the heart rate response to sub­ mergence. Additionally, it has been shown that a diving bradycardia is not

cffectcd in alligators until part of the lung gas is expelled f^White. 1970).

Observations of turtles in this study indicate that they commonly exhale

after diving (especially in response to a forced dive), but upon emersion

the animals would always first expire further before filling the lungs with

air.

Johansenetal. (1977) state that this vagal reflex from lung mechano-

receptors may explain the heart rate changes which occur in anticipation

of surfacing from a dive. Turtles in this study, however, were observed

to show this anticipatory tachycardia before beginning any movenent to­

wards the surface. In fact, Bel kin (1964) could correlate this phenomenon

in several turtles to the time that they merely raised their eyes to look

at the water surface.

In the present study it was usually found that the diving bradycardia

was rapidly reversed upon emcrsicr.. It appeared that ventilatory rnover^enis

•were necessary for this response even though the heart rate only gradually

increased in a few animals which were actively ventilating their lungs

postalve. ihis correlation between venti ;at".or.

ing from emergence has been observed in various animals including snakes

(Irvine and Prange, 1976). turtles (Burggren, 1975), alligators (White,

1979) and bullfrogs (Lillo, 1979b). The bradycardia can be broken after

emergence even though the animal remains hypoxic (White and Ross. 1966;

Lillo, 1979b), but r.ypercarbia prevents the heart rate reversal in turtles

(white and Ross, 1966). 163

Upon surfacing after a forced dive the turtles would hyperventilate.

This was especially true after long dives. Since p. scripta becomes anoxic after about 1 hour of diving (Jackson, 1968), any metabolism after that time will produce a metabolic acidosis. This promotes an elevated PaC02 since the lactate is buffered by bicarbonate (Jackson and Silverblatt,

1974). The hyperventilation following the dive is probably in response to the acidosis, increased PaCOa and/or reduced PaOz, and this vigorous venti­ lation has been shown to restore the PaOz and PaCOz levels to normal within

30 minutes following a 4 hour dive. The pH was back to normal in about 2

hours, whereas blood lactate levels recovered only after 20-24 hours

(Jackson and Silverblatt, 1974).

The present study found the bradycardia of diving to be due primarily

to an increase in the length of diastole and secondarily to an increase in

the length of ventricular systole. An increase in the length of diastole

has been demonstrated in other diving reptiles (Johansen, 1959; Andersen,

1951; Bel kin, 1953b; Pough, 1973) as well as an increase in the Q-T or

k-T inforwal 'Jnnanson 1 IQnl" Pnunr. 1Q7?: .I^rnh A nri

McDonald. 1976). The R-T segment is reportedly increased in reptiles

when they are made hypoxic (Boyer. 1956). Tnovo ».r3 Ç nrv /^n^r-ino 4 0"î*rn0v^ -rno Tr>-rov^\/al ri v* nftv^a*fTAn A-r f" no

QRS wave during diving in the turtles. This indicates that the spread of

depolarization from the atria to the ventricle, and then over the ventricle

itself, was not changed during submersion. That there was not a prolonga­

tion of the ?-R interval during diving was interesting since A-V conductiv-

4 T\/ "Î c Î :c M 31 1 \/ /nonv^occo/^ r\\ / ç;"^v»'^nn CT-imiil 3-r4r\n t.»loir»n n ç

VI iC inCt J w I 1 CCt iwi uitC u I Cl ujf Wk w i V * i . xit Cxsuuiv^iwit^ i ij u\j/\ t Ci i 164 known to increase the length of the P-R interval in reptiles (Boyer, 1955).

An increase (Johansen, 1959; Andersen, 1961; Rough, 1973) or decrease

(Jacob and McDonald, 1976) or no change (Wilbur, 1950; Jacob and McDonald,

1975) has been reported for the P-R interval of diving reptiles.

In this study, 43% of the diving turtles showed biphasic T waves,

Johansen (1959) found biphasic T waves in diving snakes and ascribed them to increasing levels of CO2 which accumulate during the dive.

The decrease or disappearance of the P waves in 3 of the 7 animals has

been reported for other diving animals (Andersen, 1955) as well as the de­ crease in the amplitude of the ORS complex (Berkson, 1955). Since the P wave changes are quite rapid in response to the dive and emersion, they may

be mediated neurally. The change in the QRS ampl itude, however, appeared

more slowly as if in response to humoral changes within the body fluids.

The transient tacr^cardia which occurs during the development of the

dive bradycardia, and the groups of beats which may occur during the first

couple of hours of a long dive, are commonly observed in other divers 1 C) ^ ^ 4» 3 : ] U % V a ) U KJ ^ / s l~\ t I ^I aj ^ ^ V ^ g V I ^* I ^ # e ^ — laM y »

Mean systemic arterial blood pressures were well-maintained in the

turtles during diving. Pulse pressures increased 123% due to a slight

increase in systolic pressure and a drop ir. diastolic pressure. Systolic

pressure probably increased ir, response to the increased systemic stroke

volume during diving (146%) and the increased peripheral resistance (62%)

of the systemic circuit. Diastolic pressure dropped, despite a greater

resistance to flow because, with a 73% bradycardia^ blood has a longer

CO aCCYC V MC CL t I* C [ 1CLÎ ! CC LV C ! W 1 C u: ) C iiC/\ v Ci 1 1 C* >.<• 155

Diving in alligators is known to produce a decrease in both systolic and diastolic pressures and towards the end of a 15 minute dive the dia­ stolic pressure would be about zero (Andersen, 1961). Berkson (1965) found systolic pressure to be maintained in a diving marine turtle for as long as 50 minutes after submergence. Diastolic pressure fell throughout the dive. Once the systolic pressure began to decrease after 45-60 min­ utes, blood lactic acid concentration began to increase. The circulatory responses to diving were presumably beginning to break down. In the 2 turtles dived for longer periods of time than the average of 77 minutes, mean arterial pressure began to decrease after about 2 hours. This may indicate that the circulatory response to diving in these turtles was being remitted after 2 hours in comparison to about 1 hour in Berkson's study of marine turtles. Bel kin (1963a) has shown that freshwater turtles are more tolerant of anoxia than are marine turtles and this fact may be reflected in their differential circulatory responses to a prolonged dive.

Mean pulmonary arterial pressures remained constant during forced sub- merCenCe "in 'np?<^"r rffp. Piils^ H>

68% in response to the decreased heart rate despite the fact that pulmonary vascular resistance increased by 235% and pulmonary stroke volume by 19%.

Û q 4 -f-no Ç V/C-r orri-i ^ v-r-i ir -r f ^ C» olcwaf-nX niilçû Q 1 rV* Û i< nrnnahlv A rnn—

sequence of the decreased heart rate allowing the diastolic pressure to

fall below predive levels. The increased stroke volume probably causes

the increased systolic pressure.

Central venous (right atrial) pressure did not change during diving

4 ri -ni-io 0 4-1 I "^1 c 1.1 X-% X -rinnc woe rnODCJiv^O/^ 4 C 1 n /^An'TVSÇT TA T n O

S, 4-,. ^ J--.* ^ ^ / o y» ' t e T-\v*o Ç Ç ' ' v-»o v» oP Ç o ^ /"i 11 T n rt ri*7\/nnn 166

(Folkow et al., 1967). Therefore, the ventricular filling pressure is not increased in diving turtles as it is in ducks.

Since the introduction of the microsphere technique for measurement of total and regional blood flows (Rudolph and Heymann. 1967). the proce­ dure has been applied to a number of different animals and has become well accepted with cardiovascular physiologists. In order to use the technique properly it is imperative that the microspheres be blocked during their first passage through a capillary bed and that the spheres be well-mixed within the circulatory system (Archie et al., 1973; Bartrum et al., 1974).

Tests (see Results) showed that nearly all of the 25-micron diameter micro­ spheres were being trapped in the capillary beds during their first pas­ sage. Only about 3% of the microspheres were found to be passing the pul­ monary capillary beds while even less passed through the systemic capil­ lary beds in the head and posterior body. Microspheres of a 15-micron diameter were found not adequate for blood flow determinations in p. scripta due to their small size relative to the red bloc?d cells which measure ap-

rw O" TO wm -« V* /"> f- K < v/\ I I"W V»— Ijr t— J. /\

In an attempt to verify that the microspheres were well mixed within the circulatory system^ "ultiple withdrawal sites were used to simultaneous-

T ^ »-»•»« /J •• ^ ^^ ^ y* ^ ^ — I L-» ^ ^ It ^ -f- I j ^L& )I i ^ * C W I www il Will L* I I I CZ I WI » V I ^^ I iWW W I V * «X# ^ w«i Sfw «L- w«

fi c Xi n.-r znTA fna lo^T Q P r8^; : 1 f it was found that the R-L shunted blood does not mix well with the blood leaving the left atrium before being ejected into the systemic arteries.

Instead it appears that the R-L shunted blood is directed preferentially

towards the left aorta at the expense of t:ne brachiocephalic artery. This noo*^ v»f^nr\\r«T-or* -rm mo -rno r- a q a -rn 'f-rjynr! d-r A1 157 and snakes (Khali! and Zaki, 1964) and may serve to keep deoxygenated blood from the central nervous system.

Blood which was simultaneously withdrawn from 2 branches of the brach­

iocephalic artery (the left carotid and subclaviar arteries near their

origin from the brachiocephalic artery) contained unequal numbers of micro­

spheres which had been injected into the 2 atria. The carotid artery

withdrawal always contained more microspheres from the left than from the

right atrium; the opposite occurred for the subclavian withdrawal. It,

therefore, appears possible that the R-L shunted (right atrial) blood

which does enter the brachiocephalic artery remains unmixed with the left

atrial blood even 2-3 cm downstream from the heart. Therefore, streaming

of left atrial (oxygenated) blood may occur to the carotid arteries, while

the shunted (de-oxygenated) blood streams to the subclavian arteries. This

would exclude the de-oxygenated blood from the brain and major sense organs.

Indeed, regional blood flow results indicate that, in turtles above water,

no R-L shunted blood finds its way to the brain or eyes. But, since the

V C t I U1 t ^ 1 C ) Ul I Y ! V ) VI U 1w* 1 v_i^ U 11 UC I t t O (N Vw I Vm vw i 111V*' t r-—» y» 1I ^ Tt I ! • V C O ^ Ml î M f O/M

blood; the brachiocephalic artery must receive part of the R-L shunted

bl cod

S*"I i I C U « iC^ U I ^ U1^ I WU.. W . •!•U ••I ««wW I * Wi^ ^ ^ ^ V*^ w*I * rvi 1 f s—. w f M O

lungs was usually the same (as verified by both counting the dissected

lungs for regional distribution of the 2 microsphere labels and by the

equality of the pulmonary output measurements based on calculations of the

amount of each microsphere label withdrawn), the microspheres were assumed

uv I cn;a 1 i I nc i * ; /\cu ai uc i c:i uci iiiy une i i Ctvtvi:. sv : u, * 1O.1 • iwriC>

to the right and left kidneys, right and left halves of the liver and 168 and right and left eyes were usually obtained, which further indicates good mixing of microspheres and blood.

Total heart output was reduced by 52% in submerged turtles in com­ parison to aerial animals. However, the output was not reduced in exact proportion to the decreased heart rate because the stroke volume was 9.6.% greater in submerged animals. Stroke volume into the systemic arches in­ creased by 146%, while in the pulmonary arch, the stroke volume increased only 19%. It is a common observation that cardiac minute volume is reduced in diving animals and, among ectotherms, this has been reported for frogs

(50-80% decrease) (Shelton and Jones, 1955) and turtles (95% reduction)

(white and Ross, 1966). In frogs, the stroke volume decreases during sub­ mergence (Shelton and Jones, 1965) or else increases initially only to be­ come equivalent to predive values after 144-250 seconds (Jones et al., 1979).

The bradycardia, with increased filling time due to a prolongation of diastole, could promote greater ventricular filling even though central venous pressure did not change. This may be responsible, at least in part,

for the ir.CreîSeci x/nlnmo nf ni vino turtles. nOwêVêV'. thy nc05t"iVc

inotropic effect which may occur through an increased parasympathetic tone

and/or decreased sympathetic tone may not allow the stroke volume to in-

ac mur^'n a c 4 -r u/rnilH

Since total heart output decreases in the submerged turtles, and since

mean arterial blood pressures do not change, the resistance to blood flow

must increase. Since the decrease in ventricular pulmonary output was 70%

compared to a 39% decrease in ventricular systemic output, peripheral re-

-î V» o S OiH m/>v%o 4 4 i 4 T riîrv^4nn X4w4nn Tnsn 159 did resistance in the systemic circuit. Assuming the decrease in VSO to be real 5 the increase in peripheral resistances was 235% and 62%, respective­ ly, representing a 2,0-fold greater increase in the pulmonary arterial re­ sistance than in the systemic circuit. This increase in pulmonary imped­ ance relative to that in the systemic circuit causes blood to be shifted from the pulmonary vasculature to the systsnic system. This can be seen in Table 10 where submerged animals show a 57% decrease in L-R shunted blood (blood which immediately recirculates through the lungs) and a 59% increase in R-L shunted blood (systemic venous blood which by-passes the lungs). Even though the VSO is 39% less in submerged animals compared to aerial turtles, the total shunted volume of this VSO does not change.

Therefore, the decrease in VSO is due entirely to a 70% decrease in the un- shunted portion of VSO.

The greater increase in pulmonary impedance relative to systemic can be seen in the blood pressure tracings in Figure 14. Compared to predive tracings, the decay of pressure during diastole in the pulmonary artery

submerged animals, this probably represents an increase in pulmonary vas­ cular resistance. There appears to be little change in the slope of the

^ 111 oiiO lOi u Ci V/1 vCl Qit I 11 I lii VI iC ^ • t i w ^ v i v r\C

\/nl I :TT:(3 nf 1 Zl Tr. -Îc !" X 3 -r r\i'lmr\r>3-^\/ more than does systemic vascular resistance during diving and is consistent with the data presented in Table 10. Indeed, systemic resistance may actually decrease in this animal during diving if systemic stroke volume

increases as indicateo. 170

The mean arterial pulmonary pressure in aerial turtles is less than the mean arterial systemic pressure (17.2vs. 24,8 mm Hg) due to a lower diastolic pressure in the pulmonary system. However, pulmonary blood flow is less than systemic blood flow (35.2 vs. 46.8 ml/min/kg) which indi­ cates that the peripheral resistance of the pulmonary and systemic circuits

is about the same in aerial animals (0.49 compared to 0.53 mm Hg/ml/min/kg).

Despite this rough equivalency of peripheral resistances, a net R-L shunt

exists in aerial animals of 25%, increasing to 50% when pulmonary impedance

increases relative to systemic resistance in submerged turtles.

The overall shunting pattern observed in the heart of reptiles is

J-unuuyiit L. L. ^ J-—.uu I»uc «1. ui ic Mcauiu^ . n u. ^vi £ uiiicicnucoA i^ £ «"s ^y* ^ ^ ucunccu puiiuuuaijrv» \ f uu^vN ^ o vciun * % f 3 f _

cular resistances (White, 1975). In turtles, selective perfusion of either

circuit is effected primarily by changes in pulmonary impedance with the

resistance of the systemic circuit being relatively constant (Shelton and

Burggren, 1975). This observation is supported by data from the present

study. However, White and Ross (1965) found that pulmonary impedance in-

^ ^ ^ ^ J , . m ^ ^ m ^ I. » n /"s ^\ t c ^ __ o I uu: jjjvj U2VII1VJ iii r". j. ul.g. m wjiiic icoio uu i i\-^ c w i » v « w vi ic ->^7 o uv^u —

ic circulation actually decreases. This may be the case with the animal

shown in Figure 14. Of course, whether systemic impedance remains the same

or falls, a larger R-L shunt will occur when pulmonary resistance increases.

The impedance change within the pulmonary system may occur in the vas­

cular bed (White, 1970), but more probably in the vasculature proximal

to tne lung (Berger, 1973; wnite, 1978). The reduced pulmonary impedance

accompanying ventilation is thought to be of vagal origin since atropine

picvc:jub una a yiic: ivinci :v: ; -i-z/a;. Ac3u lua U) c/vpci une:: ua vu ai— 4 4» ^ 4- *1 , , v» ^ ^ "^C 171 the bradycardia of diving (White, 1970). Mill en et al., (_1964) report that the development of the R-L shunt during diving in turtles is effected by a decrease in blood or tissue O2 tensions; in other words, the hypoxemia elicits an increase in the impedance of the pulmonary vasculature. How­ ever, this implies that the response occurs gradually. White and Ross

(1965) have shown that when anoxic turtles emerge into a Ng environment, vagal tone is decreased, thus allowing the heart rate to increase even though the animals must certainly remain hypoxemic.

Previous reports indicate that a net R-L shunt occurs .vhen turtles

(Millen et al., 1964; White and Ross, 1955) and frogs (Meyers et al.,

1979) submerge. When turtles are above water and actively ventilating their lungs, a net L-R shunt occurs, whereas during apnea, there appears to be equal flow to the systemic and pulmonary circulations (White and Ross,

1965). Estimates of the degree of R-L shunting during diving in turtles ranges from complete pulmonary by-pass (Millen et al., 1954) to a net R-L shunt of about 20% (White and Ross, 1955). Diving frogs show a net 45%

R-l shunt, whereas the shunting Dattern in a.r was variable (Meyers et al.,

1979). In this study, turtles showed a net R-L shunt both above and below water. A net L-R shunt was not observed in aerial animals possibly because when the animals did ventilate their lungs curing the microsphere infusion procedure, it would consist of only a few cycles. Many animals were in apnea throughout the infusion procedure. It is probable that they were somewhat disturbed by the shaking of the vortex mixer end tne general activity accompanying the experimental procedure.

A net R-L shunt in diving reptiles is thought to be important in help­ ing to keep the CO? concentration of the lung gas lev; while at the same 172 time increasing the PCOg of the peripheral tissues. This aids the blood in picking up Og from the lungs and in delivering it to the tissues during a dive (White, 1978; Ackerman and White, 1979). Such a shunt may also helD to keeo blood N. tensions low and, thus, helo to prevent dysbarism.

The increase in heart rate observed during active lung ventilation in the turtles of this study has been observed previously (Johansen et al.,

1977; Lucey and House, 1977). This tachycardia is associated with an in­ creased blood flow to the lungs (Shelton and Burggren, 1975; Johansen et al., 1977) and may provide a more efficient ventilation/perfusion relation­ ship. The lower heart rates during apnea may be vagally induced (Burggren,

1975) and the tachycardia accompanying ventilation may be mediated by stretch receptors within the pulmonary system or may be due to inhibition of the cardio-inhibitory center by the active respiratory center (Burggren,

1975; Lucey and House, 1977). This reduction in heart rate during apnea may be related to the bradycardia and vasoconstriction of diving (Angell-

James and Daly, 1969a). Indeed, the apneic heart rate of a voluntarily

nivinn furfle, wnilg Af f ho wafAr oirf,H r wn i ;1 n i nP ^ < low. Or*

lower, than the mean dive heart rate.

The pulmonary vagal reflex (stretch receptors overriding the primary

arfifirial nf cnhmov^norl riîv^rloc ran nworrino rhp hraHvrarHÎA

However, some workers believe that this response only occurs in mammals

since denervation of the lungs in ducks does not change the time course of

diving bradycardia from that of intact animals (Bamford and Jones^ 1975). 173

Total blood flow was reduced to many tissues in submerged turtles as shown in Table 12. Tissues to which flow was reduced included the liver and shell and probably the stomach, pancreas, spleen, small and large in­ testine and kidneys. Flow was maintained to the skeletal muscles and heart; it increased to the brain and possibly the eyes. Actual values for blood flow to many of these tissues could not be determined accurately, since they trapped less than 400 microspheres, especially in diving animals.

However, the general pattern appeared to be a reduction in flow to many tis­ sues in the animals which were submerged compared to values for aerial turtles. A similar vascular response has been observed in diving ducks

(Johansen, 1954; Jones et al., 1979), seals (Eisner et al., 1978; Zapol et al., 1979) and white rats (Lin and Baker, 1975) with any differences noted below.

Blood flow to skeletal muscle has been reported to decrease in most diving animals studied (Johansen, 1964; Lin and Baker, 1975; Zapol et al.,

1979). However, skeletal muscle flow in the submerged turtles appeared to

-> CO 3 +" jjnn Tni< f1 WAS n rA—

sumably because shunted blood flow to the muscle increased: unshunted flow

to the tissue decreased during diving. That flow to the muscle was main- C" "2 , X 4 w. /-I -^1 -rvrvm -rno mtiç^loc : 11 ri

appear to be important in conserving the in the blood for tissues which

might be more sensitive to 0? lack, such as possibly the heart and brain.

Blood lactic acid concentrations in turtles are reported to increase only

after a dive (Berkson, 1965) or else throughout the dive with no postdive 174 snakes (Murdaugh and Jackson, 1962) and alligators (Andersen, 1961) show an increase in blood lactate levels, but it was found to increase tremen­ dously during dives in the iguana (Moberly, 1958a). It appears, therefore, 4-U ^ ^ m» 4 r» 3 c 4r> mamma 1 ç "i ç

Hi ir or! Hi :y~i nn Hiwinn hi i f 4 n nfHcrc i f i c nn f

Blood flow to the ventricular muscle in submerged turtles was not sig­ nificantly different than for aerial animals, even though the %VSO^g to this organ increased. Blood flow to the myocardium of diving ducks is re­ ported to increase 4-fold (Johansen, 1964) or to remain unchanged (Jones et al., 1979). Myocardial flow in submerged seals decreased by 84-93%

(Blix et al., 1976, 1978; Eisner et al., 1978; Zapol et al., 1979). It should be noted that even though the ventricular blood flow did not change in the turtles studied here, total heart output decreased by 52% (due to a

75% bradycardia) and mean arterial pressure did not change. Therefore, the heart is probably receiving a greater blood flow relative to work out­ put during diving than before.

A A ' • . ^ *1 A A M T ^ . Jmm J— ^ « M ^ ^ ^ ^ « • C O "7 0/ m «M ^ ^ ^ ^ ^ ^ ^ muaw: u vc i-r i \ i \jn vw u: ic wiuiM cuccu L/jr / /o i 11 ui isi y 4-1 oc a n/-i fmic uta ç o-r-ro/^-roH f>\/ a r% nn^^^acc 4 n nr»*rn chnnTon anri imcnunron

-fl m.tc fn r'n-ic nvnan- anri "i nr-yoa cori 1 i Vowi CO rlnw fn i"hp

c_y Ci ne. s cii,;ici uii_i cabeu 3 i i uii o i _y uC 1 ciiia 1 1 icu unoi laiiycu . n O-iOiu iii-

s-1 ccic in I IUM uu une via 111, wiuii a -t-iuiu iiiu: caic uu uiic cjc3 , naj iuuii

in ducks during submergence (Johansen, 1964). Jones et al., (1979) found

blood flow to the brain to increase in diving ducks by 130% after 20-72

C\-.v<«Jiwo w : nwciCCa CiiL-Ci OC»wW;iv-;^ * u t.jv^jcciicva f /O•

'he.-'c wcs no change in blood flow to the eyes. 175

It is interesting that blood flow increases to the brain during diving in turtles since the brain can function anaerobically for an average of

15 hours in P. concinna (Bel kin, 1968c). However, Bel kin also found that the brain would only function anaerobically for about 1 hour in this species when blood flow was prevented by removing the heart. Apparently blood flow is needed for brain function, not to carry Og to this tissue, but rather to provide the CNS with substrate for anaerobiosis (Millen et al., 1964; Belkin, 1968c).

There were differences in the percentage of shunted and unshunted flows to some of the tissues in which such flows could be accurately mea-

r cu• ru( aci lai ciinuai^ ucc uicmi) cjr co9 (\ * w ucj^ UMw one» * , c1 v cw less percent shunted than unshunted flow. The spleen, pancreas, liver, heart and small intestine received more. It appears, therefore, that the

2 bloodstreams are not being mixed before entering most tissues, and/or that the shunted and unshunted blood is being preferentially distributed to the systemic vessels leaving the heart. It has already been pointed vjliu lu u o v r ccllmtllm w : un c w: ; o mw m ucw i hi cephalic artery probably occurs, and the tissue blood flew data substan­ tiates such a statement. Furthermore, it appears that the gastrointestinal tract and spleen receive a greater fraction of shunted than unshunted

blood while the opposite may be true for the more posterior structures.

This presumably results from the fact that the R-L shunted blood is directed primarily to the left aorta rather tnan being distributed equally

to both the left and right aortic arches. It is interesting to note in

this regard that in each of tne 2 corrosion casts made of the circulatory 175 system of the turtle, the left aortic arch, which, together with the right arch, forms the common dorsal aorta, was much smaller than the right arch where the 2 joined. Apparently, most of the left aortic blood is used

to perfuse the gastrointestinal tract and associated structures. There­

fore, the right aortic arch blood may be the major source of perfusate for

the structures supplied by the common dorsal aorta itself.

In aerial animals, VSO^ and VSO^^ are about the same and the brain re­

ceives none of the shunted blood. During diving, VSO^^ decreases while

VSOg is maintained. However, despite the fact that the VSO^ is now 2.4-

fold greater than the VSO mechanisms are still operative to prevent uS right atrial blood from perfusing the brain. Therefore, even though O2

is not essential for short-term brain function, there appears to be a

selective advantage for keeping it supplied with blood of maximum PO2 and/

or minimum PCO2.

It is possible that future studies should use greater quantities of

microspheres in an effort to accurately quantitate blood flow to all the

tissues cf a diving reptile, it wnnin however, to verify

that such a quantity of microspheres does not disturb normal hemodynamics,

especially if multiple injections are used in the same animal. 177

SUMMARY

(1) The cardiovascular response to diving in the semi-aquatic turtle

{pseudemys scripta) was examined.

(2) Voluntarily diving turtles showed a reduction in heart rate of

28% when averaged over the entire dive. The bradycardia occurred immedi­ ately and appeared to be relatively stable throughout the dive. Upon emersion, the bradycardia was immediately broken. In some animals, the heart raie would increase shortly before surfacing, presumably in anticipa­ tion of the emergence. Occasionally, apneic heart rates at the water sur­ face would be as low, or lower, than the mean dive rate in that animal.

(3) An average decrease in heart rate of about 53% occurred when turtles were forcibly submerged; however, the maximum degree of bradycar­ dia developed was much greater. The heart rate decreased slowly after submergence and was more labile than the rate observed during a voluntary dive, at least partially due to such things as struggling and cardiac arrhythmias. The emergence tachycardia was usually correlated with taking the first breath, and usually showed an overshoot from predive values.

(4) The dive bradycardia was primarily due to a prolonged period of diastole and secondarily to an increased period of ventricular contraction.

(5) Artificial inflation of the lungs would override the dive brady­ cardia. Atropine caused an increase in the heart rate of submerged tur­ tles, although not to the predive level.

(6) Mean arterial blood pressures (systemic and pulmonary) did net change during diving. Pulse pressures were increased due to an increase 178 in the systolic pressure and to a decrease in the diastolic pressure.

Central venous pressure did not change during diving.

(7) Total heart output decreased by one-half in forcibly submerged animals. Blood flow to the lungs decreased 70% while flow towards the systemic tissues decreased 39%.

(8) Stroke volume increased 96% during forced diving.

(9) Since the pulmonary and systemic flows decreased in submerged animals, and since mean arterial pressures remained constant, peripheral

resistance in each of the 2 circuits increased. Quantitatively, pulmonary

resistance increased 235% while impedance to systemic flow increased by cnc/

(10) The vasoconstriction which allows blood pressure to be main­

tained at predive levels during a forced submergence acts selectively to

redistribute the blood flow to the brain, heart and skeletal muscles at

the expense of most other tissues,

(11) A net 25% R-L shunt in aerial animals was found compared to a

\j\j /o Iic ^ ^u i\—L.O t aI lu 11 u in i v^ i v •»i uW Ti «y » auumciw• 4 y-\ ^ /"Scu /J ^11uu : ^uica. 1 ^ y» :\c i ci u ( v c : y aveu f\ * uy m

blood flow is shifted away from the lungs and towards the systemic tissue

during diving.

(12) R-L shunted blood is preferentially directed towards the left

aorta rather than being well-mixed with left atrial blood before ejection.

The shunted and unshunted bloodstreams appear to remain separated to many

ti ssues.

(13) Hyperventilation occurs after a forcibly submerged animal is

brought to the water surface, when animals voluntarily dive, they do so 179 after an inspiraticn and are observed to exhale immediately upon surfacing.

(14) The data are discussed in light of known reptilian physiology

and the ohysiology of diving animals in general. LITERATURE CITED

Ackerman, R. A,, and F. N, White. 1979. Cyclic carbon dioxide exchange in the turtle Pseudemys scripta. Physiol. Zool. 52:378-389.

Adams. W. E. 1953. The carotid arch in lizards with particular reference to the origin of the internal carotid artery. J. Morphol. 92:115-155.

Akers, T. K., and C. N. Peiss. 1953. Comparative study of effect of epinephrine and norepinephrine on cardiovascular system of turtle, alligator, chicken, and oppossum. Proc. Soc. Exp. Biol. Med. 112:396- 399.

Allison, D. J., and D. A. Powis. 1971. Adrenal cathecholamine secretion during stimulation of the nasal mucous membrane in the rabbit. J. Physiol. 217:327-340.

Altman, M., and E. D. Robin. 1959. Survival during prolonged anaerobio- sis as a function of an unusual adaptation involving lactate dehydro­ genase subunits. Comp. Siochem. Physiol. 30:1179-1187.

Andersen, H. T. 1959a. Depression of metabolism in the duck during div­ ing. Acta Physiol. Scand. 46:234-239.

Andersen, H. T. 1959b. A note of the composition of alveolar air in the diving duck. Acta Physiol. Scand. 46:240-243.

Andersen, H. T. 1951. Physiological adjustments to prolonged diving in the American alligator. Alligator rnississippiensis. Acta Physiol. Scand. 53:23-45.

Andersen, H. T. 1953c. riorpr-rm'^ino ihê circulatory adjustments to diving. I. Water immersion. Acta Physiol. Scand. 58:173-185.

Andersen, H. T. 1963b. Factors determining the circulatory adjustments to diving. II. Asphyxia. Acta Physiol. Scand. 53:186-200.

Andersen, H. T. 1963c. The reflex nature of the physiological adjust­ ments to diving, and their afferent oathway. Acta Physiol, Scand. 58:263-273.

Andersen, H. T. 1964. Stresses imposed on diving vertebrates during pro­ longed underwater exposure. Pages 109-127 in G. M. Hughes, ed. Homeo­ stasis and feedback mechanisms. Symposia of the Society for Experi­ mental Biology, No. XVIII. Academic Press, New York.

Andersen, H. T. 1965. Hyperpotassemia and electrocardiographic changes 181

Andersen, H. T. 1966. Physiological adaptations in diving vertebrates. Physiol. Rev. 45:212-243.

Andersen, H. T., and A. L0v0. 1954. The effect of carbon dioxide on the respiration of avian divers (ducks). Comp. Biochem. Physiol. 12: 451-456.

Andersen, H. T., B. E. Hustvedt, and A. L0v0. 1965. Acid-base changes in diving ducks. Acta Physiol. Scand. 53:128-132.

Angell-James, J. E., and M. de B. Daly. 1959a. Cardiovascular responses in apnoeic asphyxia: role of arterial chemoreceptors and the modifica­ tion of their effects by a pulmonary vagal inflation reflex. J. Physiol. 201:87-104.

Anaell-James. J. E., and M. de B. Daly. 1969b. Nasal reflexes. Prcc. R. Soc. Med. 52:1287-1293.

Angell-James, J. E., and M. de B. Daly. 1970. Comparison of the reflex vasomotor responses to separate and combined stimulation of the carotid sinus and aortic arch baroreceptors by pulsatile and non-pulsatile pressures in the dog. J. Physiol. 209:257-294.

Angell-James, J. E., and M. de B. Daly. 1972a. Reflex respiratory and cardiovascular effects of stimulation of receptors in the nose or the dog. J. Physiol. 220:673-595.

Angell-James, J. E., and M. de B. Daly. 1972b, Some mechanisms involved in the cardiovascular adaptations to diving. Symp. Soc. Exp. Biol. 26:312-341.

Anrep, G. V., W. Pascual, and R. Rossier. 1935. Respiratory variations of the heart t. The reflex mechanism of the ressirctcry ar­ rhythmia. Proc. R. Soc. Ser. 3 119:191-217.

Archie, J. B., 0. E. Fixler^ D. J. Ullyot. J. I. E. Hoffman, J. R. Utley, and L. E. Carlson. 1973. Measurement of cardiac output and organ trapping of radioactive microspheres. J. Appl. Physiol. 35:148-154.

Ashley, L. M. 1955. Laboratory anatomy of the turtle, wm. C. Brown Co., Dubuque5 Iowa. 48 pp.

Baker, L. A., and F. N. White. 1970. Redistribution of cardiac output in response to heating in iguana iguana. Com2. Biochem. Ph\/ci ol Xh - 253-262.

Baldwin, J., and R. S. Seymour. 1977. Adaptation to anoxia in snakes: levels of glycolytic enzymes in skeletal muscle. Aust. J. Zool. 25:9- 182

Bamford, 0. S., and D. R. Jones. 1975. Respiratory and cardiovascular interactions in ducks: the effect of lung denervation on the initiation of and recovery from some cardiovascular responses to submergence. J. Physiol. 259:575-595.

Barcroft, J. 1920-21. Physiological effects of insufficient oxygen sup- p I jr • lia UUI c xuu. X •

Bartholomew, G. A., and R. C. Lasiawski. 1955. Heating and cooling rates, heart rate and simulated diving in the Galapagos marine iguana. Comp. Biochem. Physiol. 15:573-582.

Bartholomew, G. A., A. F. Bennett, and W. R. Dawson. 1976. Swimming, div­ ing and lactate production of the marine iguana, Axni>iyrhynchus cristatus. Copeia 1976:709-720.

Bartrum, R. J., D. M. Berkowitz, and N. K. Hollenberg. 1974. A simple radioactive microsphere method for measuring regional flow and cardiac output. Invest. Radiol. 9:126-139.

Basoglu, M. 1951. Experiments on the composition of the alveolar air in Testudo graeca and Clemmys rivulata. Rev. Rac. Sci . Liniv. Istanbul. 158:89-94.

Bazett. H. C. 1920. An analysis of the time relations of electrocardio­ grams. Heart 7:353-370.

Bel kin, 0. A. 1952. Anaerobiosis in diving turtles. Physiologist 3:105.

Bel kin, D. A. 1963a. Anoxia: tolerance in reptiles. Science 139:492- 493.

uc7-^.1 I ix 1:1. u.rs fl n. ^uo u« usvwiu^ ^ l^[auvuaivaia 3. ' 2 _ -lu J.1ui ic luuajia. iiiroiwsu^iou C-v . 137.

Bel kin, D. A. 1964. Variations in heart rate during voluntary diving in t" mû ^vw1 iI ^uT I o ^ ) iT7^ ^ » yw "« y»«-k —. —•v ^w^ -iI Ci—> Tx c\^^ v-r %• yjO O T O O^ •

f-reshwater turtle species. Respir. Physiol. 4:1-14.

oci^iii, u. r\. X 3uou. di auyualuia in icijjvjiisc uu uiii cqu. rua, ^.uu i . o . 775.

Bel kin, D. A. 1958c. Anaerobic brain function: effects of stagnant and a n r\v1 r» annvna nn o r\ f Kv* oa 4 4 w 4 onr-a 1X mw J. -7/ —XV1m xuo •

Belkin, û. A. 1565. Tachycardia associated with breathing in turtles. Dk\/c4 ml r\r:4 183

Bennett, A. F., and W. R. Dawson. 1972. Aerobic and anaerobic metabolism during activity in the lizard Dipsosaurus dorsaiis. J. Comp. Physiol. 81:289-299.

Bennett, A. F., and P. Licht. 1972. Anaerobic metabolism during activity in lizards. J. Comp. Physiol. 81:277-288.

Bennett, A. R., and W. R. Dawson. 1976. Metabolism. Pages 127-223 in C. Gans and W. R. Dawson, eds. Biology of the Reptilia. Volume 5. Academic Press, New York.

Berger, P. J. 1971. The vagal and sympathetic innervation of the heart of the lizard Tiiiaua rugosa. Aust. J. Exp. Biol. Med. Sci. 49:297- 304.

Berger, P. J. 1972. The vagal and sympathetic innervation of the isolated pulmonary artery of a lizard and a tortoise. Comp. Gen. Pharmacol. 3: 113-124.

Berger, P. J. 1973. Autonomic innervation of the visceral and vascular smooth muscle of the lizard lung. Comp. Gen. Pharmacol. 4:1-10.

Gerger, P. J., and N. Heisler. 1977. Estimation of shunting, systemic and pulmonary output of the heart, and regional blood flow distribution in unanesthetized lizards {varanus exanthematicus) by injection of radioactively labelled microspheres. J. Exp. Biol. 71:111-121.

Berkson, H. 1955. Physiological adjustments to prolonged diving in the Pacific areen turtle {chelonia mydas agassizii). Comp. Biochem. Physiol.'18:101-119.

Berkson, H. 1967. Physiological adjustments to deep diving in the Pacific

507-524.

Berne, R. M., and M. N. Levy. 1972. Cardiovascular physiology. 2nd edition. The C. V. Mosby Co.; St. Louis= 265 np,

t m I \CCl w I i ) y^ Oil VI Vu i iw/ Ci I Ck u * V C C»V»V» (in French). Bai Hi ere, Paris. 525 pp.

Tolerance of isolated heart muscle to hvDOxia: turtle vs. rat. Amer. V. Knysioi. 1401-1403.

B1ix; A. S. 1971. Creatine in diving animals - a comparative study. rnmn nr Dn\/ci ^'RH^_R

ui lAj n. o. iiic :lu^u i uo11 vc vi v;i c ucv c < wpuicii vi divine bradvcardia in ducks. Acta Phvsiol. Scand. 95:41-45. 184

Blix, A. S. 1975. Metabolic consequences of submersion asphyxia '.n mammals and birds. Biochem. Soc. Symp. 41:169-178.

Blix, A. S., and S. HJ. From. 1971. Lactate dehydrogenase in diving animals - a comparative study with special reference to the eider [somateria moilissima). Co'.Tip. Biochem. Physiol. 408:579-584.

Blix, A. S., E. B. Messelt, and S. HJ. From. 1973. Lactate dehydrogenase in the eider - an unusual pattern. Comp. Biochem. Physiol. 448:525- 627.

Blix, A. S., E. L. Gautvik, and H. Refsum. 1974. Aspects of the relative roles of peripheral vasoconstriction and vagal bradycardia in the establishment of the diving reflex in ducks. Acta Physiol. Scand. 90: 289-296.

Blix, A. S., J. K. Kjekshus, I. Enge, and A. Bergan. 1975. Myocardial blood flow in the diving seal. Acta Physiol. Scand. 96:277-280.

Blix, A. S., R. Eisner, R. Hoi, and J. K. Kjekahus. 1978. How diving seals avoid myocardial ischemia. Physiologist 21:10.

Boyer, D. R. 1963. Hypoxia: effects on heart rate and respiration in the snapping turtle. Science 140:813-814.

Boyer, D. R. 1966. Comparative effects of hypoxia on respiratory and cardiac function in reptiles. Physiol. Zool. 39.307-315.

Bradley, S. E., and R. J. Bing. 1942. Renal function in the harbour seal [Phoca vituiina L.) during asphyxiai ischemia and pyrogenic hyper­ emia. J. Cell. Comp. Physiol. 19:229-237.

L/Lfv r\L/ c I y » ^v-i* L/^ .» \j1 m ^V/ # i_I .u « ««» r\7, ^ uO » Oiv . I 1iV:. *jr « ««« 1 T ^ « i iCti^ «m i ) T O n V* ^ yx ^ and D. E. Fixler. 1971. Some sources of error in measuring regional -tI rw.t i.f-i -r n ri t ns-r-i\/o m-î ç n nca .1 Zlnnl Dh\/CTn1 1 ' ^QA — cr\fluvj-r .

Burggren, W. W, 1975. A quantitative analysis of ventilation tachycardia âPiG its cûrrcrûi in two cnsionians, Pssudemus sczi^jta and issz-udo crraeca. J. ExD. Biol. 53:357-380.

LvuI y y I ClI ) ii« ± _/ / / ct. moroholoov. haemodvnamics and oharmacolocv. j". Como. Phvsiol. 115: 303-323.

Burggren, W. 1977b. Circulation during intermittent lung ventilation in •flno c r» 3 I/o r a ri .1 1 • 1 79 P._ *1 7 9^

Bufygrcfi, A. , u. 2. A. nànf:, crû r. rOêX. x97/, rrOpcfCléS ûï biOOd OXy- non tra nqnnrr 4 n fho fi ir f1 n -T 3 nri f ho rov+n-ico /po o•<-'t ox CO2 and pH. Respir. Physiol. 31:39-50 185

Burnstock, G. 1959. Evolution of the autonomic innervation of visceral and cardiovascular systems in vertebrates. Pharmacol. Rev. 21:247- 324.

Burton, A. C. 1965. Physiology and biophysics of the circulation. Year Book Medical Publishers, Inc., Chicago. 217 pp.

Butler, P. J., and D. R. Jones. 1971. The effect of variations in heart rate and regional distribution of blood flow on the normal pressor response to diving in ducks. J. Physiol. 214:457-480.

Butler, P. J., and E. W. Taylor. 1973. The effect of hypercapnic hypoxia, accompanied by different levels of lung ventilation, on heart rate in the duck. Respir. Physiol. 19:175-187.

Campbell, A. G. M., G. S. Dawes, A. P. Fishman, and A. 1. Hyman. 1967. Regional redistribution of blood flow in the mature fetal lamb. Circ. Res. 21:229-235.

Campbell, L. B., B. A. Gooden, and J. D. Horowitz. 1959. Cardiovascular responses to partial and total immersion in man. J. Physiol. 202:239- 250.

Cascarano, J. 1974. The role of mitochondria in oxygen-deficient mam­ malian cells. Pages 19-25 in M. D. 3. Burt, ed. Proceedings of the Canadian Society of Zoologists Annual Meeting. University of New Brunswick, Fredericton, N. B., Canada.

Cascarano, J., I. Z. Ades, and J. D. O'Connor. 1975. Hypoxia: a suc­ cinate fumarate electron shuttle between peripheral cells and lung. J. Exp. Zool. 198:149-154. ^ O ' TO~7/' T» •*" /I 1\ /1M rr i V./ Cl I C I \# VAJIVal L/ # ^• W V/ 1 11 t ^ II» ^ * VVk • ^(VKW • w » w « « «^ ••• W1ild ducks. Comp. Biochem. Physiol. 47A:925-931.

Clark, V. M., and A. T. Miller, Jr. 1973. Studies on anaerobic metabolism in the fresh-water turtle (pssuds-ys scripta eiegans). Com?. Biochem, Physiol. 44A:55-52.

Cohn, J. E., 0. Krog, and R. Shannon. 1958. Cardiopulmonary responses to head immersion in domestic geese. J. Appl .Physiol. 25:35-41.

Cordav; E., D. W. Irving. H. Gold, H. Bernstein, and R. B. T. Skelton. 1962. Mesenteric vascular insufficiency: intestinal ischemia induced by remote circulatory disturbances. Amer. J. Med. 33:355-375.

Craig. A. 3., Jr. 1953. Heart rate responses to apneic underwater diving and to breath holding in man. J. Appl. Physiol. 18:854-852. 186

Daly, M. de B. 1972. Interactions of cardiovascular reflexes. Scient. Basis of Med. Annu. Rev. 1972:307-332.

Daly, M. de B., and M. J. Scott. 1958. The effects of stimulation of the carotid body chemoreceptors on heart rate in the dog. J. Physiol. 188:331-351.

Daly, M. de B., and B. H. Robinson. 1958. An analysis of the reflex systemic vasodilator response elicited by lung inflation in the dog, J. Physiol. 195:387-406.

Daly, M. de B., J. L. Hazzledine, and A. Ungar. 1967. The reflex effects of alterations in the lung volume on systemic vascular resistance in the dog. J. Physiol. 188:331-351.

Dawes, G. S., B. V. Lewis, J. E. Milligan, M. R. Roach, and N. S, Talner. 1968. Vasomotor responses in the hind limbs of foetal and new-born lambs to asphyxia and aortic chemoreceptor stimulation. J. Physiol. 195:55-81.

Dehadrai, P. V. 1962. Observations on certain physiological reactions in Ophicephaius striatus exposed to air. Life Sci. 1:653-657.

Denison, D. M., D. A. Warrell, and J. B. West. 1971. Airway structure and alveolar emotyina in the lunqs of sea lions and dogs. Respir. Physiol. 13:253-260."

DeSilva, E. M., and A. Cazorla. 1973. Lactate, alpha-GP, and Krebs cycle in sea-level and high altitude native guinea pigs. Amer. J. Physiol. 224:669-672.

Dessauer, H. C. 1970. Blood chemistry of reptiles, physiological and cvvjiuuivjnnij^ u a ucv- ua. r cyca / c. ±ri ^ • vjui io umvi i . sj » o • Biology o the Reptilia. Volume 3. Academic Press, New York.

U I I I ) u • 0-5 ajjLi D. J. cuwa r ui> • x rO ig. r\c:> u j { a u i ur: ciiu n:c uauu % i oiu 11 j a \/r\t inn /- -«^,,-1-,,,-. r: i\/ î ^ Pnnûîa ^ V ^ I V ^ V «— I I Sw. ^ ^ I J m ^ ^ ^ ^ '— — « — w*

iJlllj U, O. ; QllU n. 1 . CUVVaTuS • lU. yr Vy C L V 1 C:) uI crocodile blood {crocodyius acutus, Cuvier). J. Biol. Chem. 90:515-

Dill. D. B.; H. T. Edwards, A. V. Bock, and J. H. Talbot. 1935. Prcper- "cies of reptilian biood. III. ihe cnuckwaMS \Saurorp^ius cb^sus^ Baird). J. Cell. Comp. Physiol. 6:37-42. n41 1 n Q a n/4 U T CWwo c 1 0 Q ^ Dv^nr\ov*T"noc r» f v»nn*r414^n Kl n IV. 1 he alligator [Alligator misslssippiensis; Daudia). J. Cel i. uuiTip. rûysiûi. 0:. 187

Djojosugito, A. M., B. Folkow, and L. R. Yonce. 1959. Neurogenic adjust­ ments of muscle blood flow, cutaneous A-V shunt flow and of venous tone during 'diving' in ducks. Acta Physiol. Scand. 75:377-385.

Dooley, M. S., and T. Koppanyi. 1929. The control of respiration in the domestic duck {Anas boseas). J. Pharmacol. Exp. Ther. 36:507-518.

Dormer, K. J., M. J. Denn, and H. L. Stone. 1977. Cerebral blood flow in the sea lion {zalophus caiifornlanus) during voluntary dives. Comp. Biochem. Physiol. 58A:11-18.

Dykes, R. W. 1974. Factors related to the dive reflex in Harbor seals: sensory contributions from the trigeminal region. Can. J. Physiol. Pharmacol. 52:259-265.

Edwards, H. T., and D. B. Dill. 1935. Properties of reptilian blood. II. The gila monster {Heioderma suspectum. Cope). J. Cell. Comp. Physiol. 6:21-35.

Eliassen, E. 1950. Cardiovascular responses to submersion asphyxia in avian divers. Arbok Univ. Bergen, Mat.-Naturvitensk., Ser. No. 2:1-100.

Eisner, R. 1965. Heart rate response in forced versus trained experi­ mental dives in pinnipeds. Hvalradets Skr. 48:24-29.

Eisner, R. W., and P. F. Scholander. 1953. Selective ischemia in diving man. Amer. Heart J. 65:571.

Eisner, R. W., D. L. Franklin, and R. L. Van Citters. 1964. Cardiac out­ put during diving in an unrestrained sea lion. Nature 202:809-810.

Eisner, R., D. W. Kenney, and K. Burgess. 1965a. Diving bradycardia in u; u I u f MC w WL/..j nf w*y l»M «# ( f . < a oc. J.t o .• —r^ n\^7 / —r^ n o •

Eisner. K., D. L. Franklin. R. L. Van Citters, and D. V. Kenney. 1955b, Cardiovascular defense against asphyxia. Science 153:941-949.

Eisner, R., D. 0. Hammond, and H. R. Parker. 1970. Circulatory responses

Wecdell seals and sheep. Yale J. Biol. Med. 42:202-217.

zisner, y,. icinu u. Kjekshus. 1378. Tissue pe'fTusion and ischemia in diving seals. Physiologist 21:33.

Emilio, M. 6., and G. Shelton. 1972. Factors affecting blood flow to the lungs in the amphibian^ xenopus laevis. J. Exp. Biol. 55:67-77. 188

Euler, U. S. von, G. Liljestrand, and Y. Zotterman. 1941. Baroreceptor impulses in the carotid sinus and their relation to the pressure re­ flex. Acta Physiol. Scand. 2:1-9.

Fedde, M. R., W. D. Kuhlmann, and P. Scheid. 1977. Intrapulmonary recep­ tors in the tegu lizard: I. Sensitivity to CO2. Respir. Physiol. 29: 35-48.

Feigl, E., and B. Folkow. 1953. Cardiovascular responses in 'diving' and during brain stimulation in ducks. Acta Physiol. Scand. 47: 99-110.

Ferrante, F. L. 1970. Oxygen conservation during submergence apnea in a diving mammal, the nutria. Amer. J. Physiol. 218:363-371.

Ferrante, F. L., and D. F. Opdyke. 1959. Mammalian ventricular function during submersion asphyxia. J. Appl. Physiol. 26:561-570.

Ferrante, F. L., and H. M. Frankel. 1971. Cardiovascular responses of anesthetized nutria and cats during apnea. Amer. J. Physiol. 221:

Folkow, B., and L. R. Yonce. 1967. The negative inotropic effect of vagal stimulation on the heart muscles of the duck. Acta Physiol. Scand. 71:77-84.

Folkow, B., K. Fuxe, and R. R. Sonnenschein. 1966. Responses of skeletal musculature and its vasculature during 'diving' in the duck: perculiar- ities of the adrenergic vasoconstrictor innervation. Acta Physiol. Scand. 67:327-342.

Folkow, 8., N. J. Nilsson, and L. R. Yonce. 1967. Effects of 'diving' r\v-i /Mi + rMi4- 4 M A I ir» 4- 3 0 kn\/c" n n I Cz-anrt

Foxon, G. E. H., J. Griffith, and M. Price. 1956. Mode of action of the heart of the green lizard, zacerta viridis. Proc. Soc. Zool. London 126:145-157.

From, A. H. L. 1950. Induced changes in the capacitance of the turtle venous system. Fed. Proc. 19:93.

Furness- J. B.. and J. Moore. 1970. The adrenergic innervation of the cardio-vascular system of the lizard Trachysaurus rugosus. Z. /eMTorscn. lue:iou-l/D.

Garey. w. F. 1962. Cardiac resoonses of fishes in asohvxic environments. Biol. Bull. 122:362-368.

Geskell; w. H.. and H. Gadow. 1884. On the anatomy of the cardiac nerves in certain cold blooded vertebrates. J. Physiol. 5:352-372. 189

Gatten, R. E,, Jr. 1974. Effects of temperature and activity on aerobic and anaerobic metabolism and heart rates in the turtles Pseudemys scripts and Terrapene ornata. Physiol. Zool. 48:24-35.

Gaumer, A. E. H., and C. J. Goodnight. 1957. Some aspects of the hema­ tology of turtles as related to their activity. Amer. Midi. Nat. 58: 332-340.

Gaunt, A. S., and C. Gans. 1969. Diving bradycardia and withdrawal bradycardia in caiman crocodiius. Nature 223:207-208.

Girgis, S. 1951. Aquatic respiration in the common Nile turtle, Trionyx triunguis (Forskal). Comp. Biochem. Physiol. 3:206-217.

Girgis, S. 1954. Studies on the arteries in the common Nile turtle, tzzr . PyO C - Z,00 1 wOC. '0*^ciQ^ i/LP"i0i—

Graham, J. B. 1974. Aquatic respiration in the sea snake Peiamis piaturus. Respir. Physiol. 21:1-7.

Gray, 0. 1882. Notes on the characters and habits of the Bottlenose whale {tiyperoodon rostratus). Proc. Zool . Soc. London 1882:725-731.

Grinnell, S. W., L. Irving, and P. F. Scholander. 1942. Experiments on the relation between blood flow and heart rate in the diving seal. J. Cell. Comp. Physiol. 19:341-350.

Gross, P. M., R. L. Terjung, and T. G. Lohman. 1975. Left-ventricular performance in man during breath-holding and simulated diving, u'nderseas Biomed. Res. 3:351-350.

Guard, C. L., and D. E. Murrish. 1973. Temperature dependence of blood I : i Li 11 vci i u : v, i iwi n\:;w u i i mso* IIIJ I

iainswcrth. R., 0. H. Comrce, jr.. and L. Jacobs. 1970. Evidence that

pu Ii I!iu: la I I ^j/ J CUCV uv1 O Wl l i U U uauiC uUV VII iu::y I ,1 I « V* V I VII ^ cifuafciH 1n a î \/c TpH PtHT

'_J ^ ^ ^ ^ ^ ^ ^ m ^ 1 ^^ ^ ^ ^a ^ ^^ ^w#» ^^ ^ t t a mm^ 1 id i LiC WC ^ V » V » ) Oll^ V « Oa i I I C ^ ^ I IiC i I 0>IV- # VI I ^ ventilation. J. Physiol. 32:225-255.

output and regional tissue blood flow in the sheep. Pflugers Arch. J44:119-1jz.

Harrison; R. J.^ and J. D, W. Tomlinson. 1950. Normal and experimental niwinc ir, -rl-iQ r.-immrvn coal ,r , 7 \ ~v-^v Msm

ncaCn, M. u. irï/o. ucfOicC .'""cSpOfiScS ûï CiÇjèr Se i ciTicfiûcrS ûû SuOiTièrycnCc A nH omorror.ro Pnvsirlnnicf 91 -n? 190

Heath, J. E., E. Gasdorf, and R. G. Northcutt. 1958. The effect of thermal stimulation of anterior hypothalamus on blood pressure in the turtle. Comp. Biochem. Physiol. 26:509-518.

Heatwole, H. 1978. Adaptations of marine snakes. Amer. Sci. 56:594-604.

Heatv/ole; H, = and R- Seymour. 1975. Diving physiology. Pages 289-327 in W. A. Dunson, ed. The Biology of Sea Snakes. Univ. Park Press, Balti­ more.

Heatwole, H., R. S. Seymour, and M. E. D. Webster. 1979. Heart rates of sea snakes diving in the sea. Comp. Biochem. Physiol. 62A:453-456.

Heezen, B. C. 1957. Whales entangled in deep sea cables. Deep-Sea Res. 4:105-115.

Heistad, D. D., F. M. Abboud, and J. W. Eckstein 1958. Vasoconstrictor response to simulated diving in man. J. Appl. Physiol. 25:542-549.

Heistad, D. D., and R. C. Wheeler. 1970. Simulated diving during hypoxia in man. J. Appl. Physiol. 28:652-556.

Heistand, W. A., and W. C. Randall. 1941. Species differentiation in the respiration of birds following carbon dioxide administration and the location of inhibitory receptors in the upper respiratory tract. J. Cell. Comp. Physiol. 17:333-340.

Hobson, E. S. 1955. Observations on diving in the Galapagos marine iguana, Ambiyrhynchus cristatus (Bell). Copeia 1955:249-250.

Hochachka, P. W., and T. Mustafa. 1972. Invertebrate facultative anaero- binosis. Science 178:1056-1050.

Hochachka, P. W., and K. B. Storey. 1975. Metabolic consequences of diving in animals and man. Science 187:613-521.

Hochachka, P. W., J. Fields, and T. Mustafa. 1973. Animal life without oxygen: basic biochemical mechanisms. Amer. Zool. 13:543-555.

Hollenberg, N. K., and B. Uvnas. 1963. The role of the cardiovascular response in the resistance to asphyxia of avian divers. Acta Physiol. r 1 .TO - rrr* ".a

Hong. S. K., n. Rahn, D. H. Kang, S. H. Song, and S. Kang. 1963. Diving pattern, lung volumes, and alveolar gas of the Korean diving woman (Ama). u. Appl. Physiol. 18:457-455.

Huggins, S. E., H. E. Hoff, and R. V. Pena. 1970. The respiratory-heart 191

Hutton, K. E. 1958. The blood chemistry of terrestrial and aquatic snakes. J. Cell. Comp. Physiol. 52:319-328.

Huxley, F. M. 1913a. On the reflex nature of apnoea in the duck in diving: I. The reflex nature of submersion apnoea. Q. J. Exptl. Physiol. 5:147-157.

Huxley, F. M. 1913b. On the resistance to asphyxia of the duck in diving. Q. J. Exptl. Physiol. 5:183-195.

Iriuchijima, J. 1959. Sympathetic and vagal discharges in the cardiac nerve of the toad. Tohoku J. Exp. Med. 71:109-119.

Irvine, A. G., and H. D. Prange. 1975. Dive and breath hold metabolism of the brown water snake,watrix taxlspiiota, Comp. Biochem. Physiol. 55A:61-57.

Irving, L. 1934. On the ability of warm-blooded animals to survive without breathing. Sci. Mon. N. Y. 38:422-428.

Irving, L. 1937. The respiration of beaver. J. Cell. Comp. Physiol. 9: 437-451.

Irving, L. 1938a. Changes in the blood flow through the brain and muscles during the arrest of breathing. Amer. J. Physiol. 122:207-214.

Irving, L. 1938b. The insensitivity of diving animals to COg. Amer. J. Physiol. 124:729-734.

Irving. L. 1939. Resoiration in diving mammals. Physiol. Rev. 19:112- 134.

Irving, L- Br-ad vcsrdia in human divers. J. AdoI . Physiol. 13: 489-491.

Irving, L. 1954= Comparative anatomy and physiology of gas transport mechanisms. Pages 177-212 in 0. B. Dill, ed. Handbook of Physiology, Sect. 3. Respiration. American Physiological Society, Washington, n r

Irving, L., 0. M. Solandt. D. W. Solar.dt, and K. C, Fisher. 1935. The respiratory metabolism of the seal and its adjustment to diving. J. Cell. Comp. Physiol. 7:137-151.

Irving, L., P. F. Scholander, and S. W. Grinnell. 1541a. The respiration of the pcrnoise, Tursiocs truncatus. J. Call. Como. Phvsiol. 17: 145-168.

Irving, L., P. F. Scholander, and S. W. Grinnell. 1941b. Significance of the heart rate to the diving ability of seals. J. Cell. Comp. rpysiOi. 192

Irving, L., P. F. Scholande.-, and S. VJ. Grinnell. 1942a. The regulation of arterial blood pressure in the seal during diving. Amer. J, Physiol. 135:557-566.

Irving, L., P. F. Scholander, and S. W. Grinnell. 1942b. Experimental studies of the respiration of sloths. J. Cell. Comp. Physiol. 20: inn n'y n

Irving, L., L. J. Peyton, C. H. Bahn, and R. S. Peterson. 1953. Action of the heart and breathing during the development of fur seals [callorhinus urslnus). Physiol. Zool. 36:1-20.

Jackson, D. C. 1958. Metabolic depression and oxygen depletion in the diving turtle. J. Appl. Physiol. 24:503-509.

Jackson, D. C. 1975. Non-pulmonary CO2 loss during diving in the turtle, pseudemys scripts, eleg ans. Comp. Biochem. Physiol. 55A:237-24i.

Jackson, D. C., and K. Schmidt-Nielsen. 1956. Heat production during divinq in the fresh-water turtle, Pseudemys scripts. J. Cell. Physiol. 57:225-231.

Jackson, D. C., and H. Silverblatt. 1974. Respiration and acid-base status of turtles following experimental dives. Amer. J. Physiol. 225:903-909.

Jackson, D. C., S. E. Palmer, and W. L. Meadow. 1974. The effects of temperature and carbon dioxide breathing on ventilation and acid-base status of turtle. Respir. Physiol. 20:131-145.

Jackson, D, C., D. R. Kraus, and H. D. Prange. 1979. Ventilatory re­ sponse to inspired CO^ in the sea turtle: effects of body size and LC!!!yCT GLUT --C, r, r00-"7nr 13 1 v : . 01

Jacob, J. S., and H. S. McDonald. 1976. Diving bradycardia in four soecies of North American aquatic snakes. Comp. Biochem. Physiol. 53A: 69-72.

uames; l. 5. i^ou. ncioosis or tne newborn anc its reiac-cr. asphyxia. Acta Pediat. Suppl. 122:17-28.

James, L. y. , I. M. weisbrot, C. E. Prince, D. A. Hc-laday, and V. Apgar. 1958. The acid-base status of human infants in relation to birth asphyxia and the onset of respiration. J. Pediat. 52:379-394.

Jchansan, K. 1959. Heart activity during experimental diving of snakes. Physiol. 197:504-606.

Jonansen, K. 1564. Regional distribution of circulating blood curing sub­ mersion asphyxia in the duck. Acta Physiol= Scand, 62:1-9. 193

Johansen, K., and J. Krog. 1959. Peripheral circulatory response to sub­ mersion asphyxia in the duck. Acta Physiol. Scand. 45:194-200.

Johansen, K., and T. Aakhus. 1963. Central cardiovascular responses to submersion asphyxia in the duck. Amer. J. Physiol. 205:1167-1171.

.Irihançûn K' Ul Riiv^nnv~Qn. pnri M Alass 1 Q77 Pi'lmnnsw stretch rprPD- tors regulate heart rate and pulmonary blood flow in the turtle, Pseudemys scripta. Comp, Biochem. Physioi. 58A:185-191.

Johlin, J. M., and F. B. Moreland. 1933. Studies of the blood picture of the turtle after complete anoxia. J. Biol. Chem. 103:107-114.

Jones, D. R. 1965. Factors affecting the recovery from diving brady­ cardia in the frog. J. Exp. Biol. 44:397-411.

Jones, D. R. 1957. Oxygen consumption and heart rate of several species of anuran Amphibia during submergence. Comp. Biochem. Physiol. 20: 591-707.

Jones, D. R. 1958. Specific and seasonal variations in development of diving bradycardia in anuran Amphibia. Comp. Biochem. Physiol. 25: 821-834.

Jones, D. R., and G. Shelton. 1954. Factors influencing submergence and the heart rate in the frog. J. Exp. Biol. 41:417-431.

Jones, D. R., and M. J. Purves. 1970a. The carotid body in the duck and the consequences of its denervation upon the cardiac responses to immersion. J. Physiol. 211:279-294.

Jones, 0. R., and M. J. Purves. 1970b. ihe effect of carotid body

the duck. J. Physiol. 211:295-310. .T/-vmoc n 0 3 «nX C C LI/-\T/-v *1 1070 c" ^ a o r* r\i i f if rîiiv-»*7nn !_/ * I \ ) uiivu w « I • iiv^iC vw It* ^ ^I C.• sy 1 suiuwino w i *: * ^ diving. Comp. Bioche", Physiol, -lA:639-545,

« ^ ^» I \* g I \ » I I # W I ^ I I g Wi * ) Ma «w* , #1 ^^9 * < * ••• ^L/ I ^3 1979. Regional distribution of blood flow during diving in the duck ^ Par,w v* i i # .1 ^=7.caK_-nn9 s./

Juhasz-Nagy, A., M. Szentivanyi, M. Szabo, and B. Vamosi. 1953. Coronary circulation of the tortoise heart. Acta Phvsiol. Acad. Sci. Huno. 23:33-48.

rs ^ ^ M ^rinn P ^ Çiir, a nr Ç / Wnnn Phannoc 4 n body temperature and basal metabolic rate of the ama. J. Appl. Physiol. -i.»-/ . -roN-»— -TOW • 194

Kaplan, N. 0., and J. Everse. 1972. Regulatory characteristics of lac­ tate dehydrogenases. Adv. Enzyme Regul. 10:323-335.

Kawakami, Y., B. H. Natelson, and A. B. DuBois. 1967. Cardiovascular effects of face immersion and factors affecting diving reflex in man. J. Appl. Physiol. 23:964-970.

Kerem, D., and R. Eisner. 1973. Cerebral tolerance to asphyxia! hypoxia in the harbor seal. Respir. Physiol. 19:188-200.

Kerem, D., D. Hammond and R. Eisner. 1973. Tissue glycogen levels in the Weddell seal: a possible adaptation to asphyxiai hypoxia. Comp. Biochem. Physiol. 45A:731-735.

Khalil, F., and S. R. A. Malek. 1952. Studies on the nervous control of the heart of uromastijy, aegyptia (Forskal). Physiol. Comp. Oecol . 2: 386-390.

Khalil, F., and K. Zaki. 1954. Distribution of blood in the ventricle and aortic arches in reptilia. Z. Vgl. Physiol. 48:553-589.

Kinney, 0. L., D. T. Matsuura, and F. N. White. 1977. Cardiorespiratory effects of temperature in the turtle, Pseudemys fioridana. Respir. Physiol. 31:309-325.

Kirby, S., and G. Burnstock. 1959a. Comparative pharmacological studies of isolated spiral strips of large arteries from lower vertebrates. Comp. Biochem. Physiol. 28:307-319.

Kirby, S., and G. Burnstock. 1959b. Pharmacological studies of the car­ diovascular systems in the anaesthetized sleepy lizard {Tiiiqua rugosa) and toad {sufo marlnus). Comp. Biochem. Physiol. 28:321-331.

Kobinger, VJ., and M. Oca. 1959. Effects of sympathetic blocking sub­ stances on the diving reflex of ducks. Eur. J. Pharmacol. 7:289-295.

Kooyman. G. !.. 1966. Maximum diving capacities of the Weddell seal; Leptonychotes weddeiii. Science 151:1553-1554.

Kooyman, G. L. 1973. Respiratory adaptations in marine animals. Amer.

Kooyman, G. L. 1975. Behaviour and physiology of diving. Pages 151-137 in B. Stonehouse; ed. The Biology o'F Penguins. Macrrril 1 an PresS; Ltd.

(«(nPiX/Tn;; n I Dr*. «arrmnnr^ a nrl .1 D and tracheograms of seals under pressure. Science 169:82-84. 195

Kooyman, G. L., D. H. Kerem, W. B. Campbell, and J. J. Wright. 1971. Pulmonary function in freely diving Weddell seal, Leptonychotes weddelii. Respir. Physiol. 12:271-282.

Kooyman, G. L. and W. B. Campbell. 1972. Heart rates in freely diving Weddell seals, Leptonychotes weddelii. Comp. Biochem. Physiol. 43A: 31-37.

Kooyman, G. L., J. P. Schroeder, D. M. Denison, D. D. Hammond, J. J. Wright, and W. P. Bergman. 1972. Blood nitrogen tensions of seals during simulated deep dives. Amer. J. Physiol. 223:1015-1020.

Kooyman, G. L., D. H. Kerem, W. B. Campbell, and J. J. Wright. 1973a. Pulmonary gas exchanges in freely diving Weddell seals, Leptonychotes weddelii. Respir. Physiol. 17:283-290.

Kooyman, G. L., J. P. Schroeder, D. G. Greene, and V. A. Smith. 1973b. Gas exchange in penguins during simulated dives to 30 and 58 m. Amer. J. Physiol. 225:1457-1471.

Lai, F. M. H., and A. T. Miller, Jr. 1973. Effect of hypoxia on brain and liver NAD+/NADH2 ratios in the fresh-water turtle [pseudemys scripta el egans). Comp. Biochem. Physiol. 443:307-312.

Landgren, S. 1952. On ttie excitation mechanism of the carotid barore- • ceptors. Acta Physiol. Scand. 25:1-34.

Landis, A. T., Jr. 1965. Research. Under Sea Technol. 5:21.

Langlois, P., and C. Richet. 1898. Expired gases of submerged ducks (in French). C. R. Soc. Biol. 5:483-485.

; p-iup^THo. n. T960. The effect of prolonged submersion cn the metabolism and the heart rate in the toad. Arbok Univ. Bergen, Mat.-Nat., Ser. No. 5:1-15.

Leivestad, H., H. Andersen, and P. F. Scholander. 1957. Physiological response to air exposure in the codfish. Science 125:505.

Lenfant, C., 0. W. Kenney, and C. Aucutt. 1968. Respiratory function in the killer whale (orcinus orca , Linnaeus). Amer. J. Physiol. 215: 1cncZWV- 1J. mi 1 •

Lenfant, C., K. Johansen, J. A. Petersen, and K. Schmidt-Nielsen. 1970a. Respiration in the fresh water turtle, cheiys firnbriata. Respir. Physiol. 8:251-275.

Lenfant, C., K. J ohansen, and J. D, Torrance. 19/Ob. Gas transport and v ^ f m V» a T-TV/ -i m c-^mo a nH rho Çûp Pocniv* w ^ ^ w»^w Physiol. 9:277-286. 195

Lillo, R. S. 1978. The effect of arterial-blood PO2, PCO2, and pH on diving bradycardia in the bullfrog Rana catesbeiana. Physiol. Zool. 51:340-346.

Lillo, R. S. 1979a. Autonomic cardiovascular control during submergence and emergence in bullfrogs. Amer. J. Physiol. 6:R210-R215.

Lillo, R. W. 1979b. Recovery from diving bradycardia in bullfrogs. J. Comp. Physiol. 133:193-198.

Lin, Y. C. 1974. Autonomic nervous control of cardiovascular response during diving in the rat. Amer. J. Physiol. 227:601-605.

Lin, Y. C., and D. G. Baker. 1975. Cardiac output and its distribution during diving in the rat. Amer. J. Physiol. 228:733-737.

Lombroso, U. 1913. Reflex inhibition of the heart during respiratory inhibition in various animals (in German). Z. Biol. 51:517-538.

Lucey, E. C., and E. W. House. 1977. Effect of temperature on the pat­ tern of lung ventilation and on the ventilation-circulation relation­ ship in the turtle, Pseudemys scripta. Como. Biochem. Physiol. 57A: 239-243.

Luckhardt, A. B., and A. J. Carlson. 1921. Studies on the visceral sensory nervous system. VIII. On the presence of vasomotor fibers in the vagus nerve to the pulmonary vessels of the amphibian and reptilian lung. Amer. J. Physiol. 56:72-112.

Lund, G. F., and H. Dingle. 1968. Seasonal temperature influence on vagal control of diving bradycardia in the frog {Rara vipiens). J. Exp. Biol. 48:265-277.

Matsuura, D. T., and G. C. Whittow. 1973. Oxygen uptake of the California sea lion and harbor seal during exposure to heat. Amer. J. Physiol. ppc.7Ti_7ic:

McCutcheon, F. 1943. The respiratory mechanism in turtles. Physiol.

McKear,, T., and C. Carlton. 1977. Oxygen storage in beavers. J. Appl. n r\. 1»11 w./ ' r—wmt /! I-— —xjl i

McKean, T.. W. J. Cutright, R. M. Thornton, and R. Landon. 1980. Cardio­ vascular changes durina exoerimental divinq in beavers. Fed. Proc. 3S:&71.

Messelt, E. B., and A. S. Blix. 1976. The lactate dehydrogenase of the u., r* .m.trym . O "Z ^y» Lm \ ff" m 1 QO 197

Meyers, R. S., R. Moalli, D. C. Jackson, and R. W. Millard. 1979. Micro­ sphere studies of bullfrog central vascular shunts during diving and breathing in air. J. Exp. Zool. 208:423-430.

Millard, R. W., and K. Johansen. 1974. Ventricular outflow dynamics in the lizard, varanus niloticus: responses to hypoxia, hypercarbia and diving. J. Exp. Biol. 50:871-880.

Millard, R. W., J. Kjekshus, A. S. Blix, D. Franklin, and R. E. Eisner. 1980. Coronary vasoconstriction in diving seals: a natural model of vasospasm. Fed. Proc. 39:398.

Mil 1en, J. E., H. V. Murdaugh, Jr., C. B. Bauer, and E. D. Robin. 1954. Circulatory adaptation to diving in the freshwater turtle. Science 145: 591-593.

Milsom, W. K., and D. R. Jones. 1975. Reptilian pulmonary receptors: mechano- or chemosensitive? Nature 261:327-328.

Moalli, R., R. S. Meyers, D. C. Jackson, and R. W. Millard. 1978. Functional mapping of arterial supplies to the skin of anuran amphibia. Physiologist 21:81.

Moberly, W. R. 1958a. The metabolic responses of the common iguana. Iguana iguana, to walking and diving. Comp. Biochem. Physiol. 27: 21-32.

Moberly, W. R. 1968b. The metabolic responses of the common iguana. Iguana iguana, to activity under restraint. Comp. Biochem. Physiol. 27:1-20.

Murdaugh, H. V., Jr., B. Schmidt-Nielsen, J. W. Wood, and W. L, Mitchell. iQo'rt. Cêssrttion of rénal function during divine in the trained seal [phoca vituiina). J. Cell. Comp. Physiol. 58:251-265.

Murdaugh; H. V.^ Jr.. J. C. Seabury, and W. L. Mitchell. 1961b. Electro­ cardiogram of the diving seal. Circ. Res. 9:358-351.

Murdaugh, H. V.- Jr.. and J. E. Jackson. 1962. Heart rate and blood lactic acid concentration during experimental diving of water snakes. Amer, J. Physiol. 202:1153-1155.

Murdaugh, H. V., E. D. Robin, J. E. Mill en, W. F. Drewry, and E. Weiss. 1955. Adaptations to diving in the harbor seal: cardiac output during diving. Amer. J. Physiol. 210:176-180.

Murdaugh, H. V., Jr., C. E. Cross, J. E. Mill en, J. B. L, Gee, and E. D Robin. 1968. Dissociation of bradycardia and arterial constriction curing diving the the seal Phoca vituiina. Science 162:364-365. 198

Musacchia, X. J. 1959, The viability of chrysexays picta submerged at various temperatures. Physiol. Zool. 32:47-50.

Musacchia, X. J., and M. L. Sievers. 1962. Effects of induced cold tor­ por and fasting on the erythrocytes of the turtle, Pseudemys eiegans. Trans. Amer. Microsc. Soc. 81:198-201.

01 sen, C. R., D. D. Fanestil, and P. F. Scholander. 1952a. Some effects of breath holding and apneic underwater diving on the cardiac rhythm in man. J. Appl. Physiol. 17:461-466.

Olsen, C. R., D. D. Fanestil, and P. F. Scholander. 1962b. Some effects of underwater diving on blood gases, lactate and pressure in man. J. Appl. Physiol. 17:938-942.

Orr, J. B., and A. Watson. 1913. Study of the respiratory mechanism in the duck. J. Physiol. 46:337-348.

Otis, L. S., J. A. Cerf, and J. Thomas. 1957. Conditioned inhibition of respiration and heart rate in the goldfish. Science 126:263-264.

Paulev, P. -E. 1969. Respiratory and cardiovascular effects of breath- holding. Acta Physiol. Scand. Suppl. 324:1-116.

Penney, D. G. 1974. Effects of prolonged diving anoxia on the turtle, Psaudemys scripta eiegans. Comp. Biochem. PhySTOl. 47A:933-941.

Penney, D. G., and J. Cascarano. 1970. Anaerobic rat heart; effects of glucose and tricarboxylic acid-cycle metabolites or. metabolism and physiological performance. Biochem. J. 118:221-227.

Poczopko, P. 1959-6Ga. Changes in blood circulation in Rana escuienta, L.1 . » *.Ml * I 1I ^C ^ «i » # ^ ^ 7l_vfx 1I • Ir) W 1I • /ioTsJ •

Poczopko, p. 1959-605. Respiratory exchange in p.ana escuienta, L., in different respiratory media. Zool. Pol. 10:46-55.

Pough, F. H. 1969. Environmental adaptations in the blood of lizards. Comp. Biochem. Physiol. 31:885-901,

Pough, F. H. 1973. Heart rate, breathing and voluntary diving of the r 1 onha nf Tv'uriL' c na I/a ^ r.rtrr.n Rinrhnm Phv^inl . 44A:183-189.

Randall, W. C., 0. E. Stulken, and W. A. Hiestand. 1944. Respiration of reptiles as influenced by the composition of the inspired air. Copeia 1944:133-138.

Reeves : B, 1963a. Energy cost of work in aerobic and anaerobic turtle heart muscle. Amer. J. Physiol. 205:17-22. 199

Reeves, R. B. 1963b. Control of glycogen utilization and glucose uptake in the anaerobic turtle heart. Amer. J. Physiol. 205:23-29.

Reite, 0., J. Krog, and K. Johansen. 1953. Development of bradycardia during submersion of the duck. Nature 200:583-685.

Ric'net; C- 1894a. The resistance of ducks to asohvxia fin French'). C. R. Soc. Biol. 1:244-245.

Richet, C. 1894b. ihe influence of atropine on the duration of asphyxia in the duck (in French). C. R. Soc. Biol. 1:789-790.

Richet, C. 1898. The resistance of ducks to asphyxia (in French). C. R. Soc. Biol. 5:685-686.

RicheX; C. 1899. The resistance of ducks to asphyxia (in French). J. Physiol. Pathol. Gen. 1:641-550.

Ridgway, S. H., B. L. Scronce, and J. Kanwisher. 1959. Respiration and deep diving in the bottlenose porpoise. Science 165:1651-1654.

Robin, E. D., H. V. Murdaugh, Jr., W. Pyron, E. Weiss, and P. Soteres. 1963. Adaptations to diving in the harbor seal - gas exchange and ventilatory response to CO2. Amer. J. Physiol. 205:1175-1177.

Robin, E. D., J. W. Vester, H. V. Murdaugh, and J. E. Millen. 1954. Pro­ longed anaerobiosis in a vertebrate: anaerobic metabolism in the fresh­ water turtle. J. Cell Comp. Physiol. 53:287-297.

Robinson, D. 1939. The muscle hemoglobin of seals as an oxygen store in diving. Science 90:276-277.

s V v, q1 / U —oin pn/-" i Ta \/l n 10^0 pnl a nf rhca central nervous system in the body temperature-arterial pressure rela­ tionship. Amer. J. Physiol. 158:135-140.

Rod bard, S., F. Samscr.. and D. Ferguson. 1950. Thermosensi ti vity of the turtle brain as manifested by blood pressure changes. Amer. J. .An9_/inQ

Root, R. W. 1959. Aquatic respiration in %he musk turtle. Physiol. V :. 0O.T-7O.1c- -Î-702V .

^^T MS L* A «N w.. ypJ *.«-s» T O. ^"7 L* «m. ^ « n ^ ^ 4" • . r\uu V : uu, n. giiu i'l. n. ncj/ii.a» 1:,. 10 / . ijic utivuiguiuij ui une i uuo in utero. Methods for studying the distribution of blood flow, cardiac output and organ blood flow. Circ. Res. 21:153-184.

Sapirstein, L. A. 1958. Regional blood flow by fractional distribution 200

Scholander, P. F. 1940. Experimental investigations on the respiratory function in diving mammals and birds. Hvalradets Skrifter Norske Videnskaps-Akad., Oslo 22:1-131.

Scholander, P. F. 1953, The masterswitch of life. Sci. Amer. 209:92-105.

oCflU 1 ciHucr, r. r . • mi & ima * a i m ctyua u * v ciiv«iuiuuc.»io.o. , -, and birds. Pages 729-739 in 0. B. Dill, ed. Handbook of Physiology, Sect. 4. Adaptation to the Environment. American Physiological Society, Washington, D. C.

Scholander, P. F., and L. Irving. 1941. Experimental investigations on the respiration and diving of the Florida manatee. J. Cell. Comp. Physiol. 17:159-191.

Scholander, P. F., L. Irving, and S. W. Grinnel. 1942a. Aerobic and anaerobic changes in the seal muscles during diving. J. Biol. Chem. 142:431-440.

Scholander, P. F., L. Irving, and S. W. Grinnell. 1942b. On the tempera­ ture and metabolism of the seal during diving. J. Cell Comp. Physiol. 19:67-78.

Scholander, P. F., E. Bradstreet, and W. F. Garey. 1952a. Lactic acid response in the grunion. Comp. Biochem. Physiol. 5:201-203.

Scholander, P. F., H. T. Hammel, D. H. LeMessurier, E. Heirmingsen, and W. Garey. 1962b. Circulation adjustments in pearl divers. J. Appl. Physiol. 17:184-190.

Seymour, R. S. 1974. How sea snakes may avoid the bends. Nature 250: 489-490.

Seymour, R. S. 1979. Blood lactate in free-diving sea snakes. Copeia 1 070 •dG^._dQ7

Seymour, R. S., and M. E. D. Webster. 1975. Gas transport and blood acid-base balance in diving sea snakes. J. Exp. Zool. 191:159-181.

Shelton, G., and 0. R. Jones. 1955. Central blood pressure and heart output in surfaced and submerged frogs. J. Exp. Biol. 42:339-357.

Shelton, Q., and W. Burggren. 1976. Cardiovascular dynamics of the

a ^C TI o T ^C ^C * g ! W*. liNU ^C • I8 \ m L' ^1C7!^ ^ I W • D;I il circulation of the harbor seal. J. Aool. Phvsiol. 45:718-727. 201

Skillman, J. J., J. E. Olson, J. 0. Lyons, and F. D. Moore. 1967. The hemodynamic effect of acute blood loss in normal man, with observations on the effect of the Valsalva maneuver and breath holding. Ann. Surg. 166:713-738.

Smith, E. N., R. D. Allison, and W. E. Crowder. 1974. Bradycardia in a free ranging American alligator. Copeia 1974:770-772.

Smith. H. W. 1929. The inorganic composition of the body fluids of the chelonia. 0. Biol. Chem. 82:651-551.

Snedecor, G. W., and W. G. Cochran, 1967. Statistical methods. 5th edition. Iowa State University Press, Ames, Iowa 593 pp.

Snyder, G. K. 1971. Influence of temperature and hematocrit on blood viscosity. .Amer. J. Physiol. 220:1657-1672.

Song, S. H., D. H. Kang, B. S. Kang, and S. K. Hong. 1963. Lung volumes and ventilatory responses to high CO? and low O2 in the ama. J. Appl. Physiol. 18:465-470.

Steggerda, F. R., and H. E. Essex. 1957. Circulation and blood pressure in the great vessels and heart of the turtle {cheiydra serpentina). Amer. J. Physiol. 190:310-325.

Storey, K. B., and P. W. Hochachka. 1974a. Enzymes of energy metabolism from a vertebrate facultative anaerobe, Pseudemys scriota. J. Biol. Chem. 249:1417-1422.

Storey, K. 3., and P. W. Hochachka. 1974b. Enzymes of energy metabolism from a vertebrate facultative anaerobe, Pseudemys scripta. J, Biol. Chem. 249:1423-1427.

Takehiko, A., A. Binia, and M. B. Visscher. 1955. Adrenergic mechanisms in the bullfrog and turtle. Amer. J. Physiol. 209:1287-1294.

TchobroustskV: C.: C. Merlet, and P. Rev. 1959. The diving reflex in rabbit, sheep and newborn lamb and its afferent pathways. Respir. P ' 1 no_ 117

Tucker, Y. A. 1966. Oxygen transport by the circulatory system of the green icuana (iguana iguana^, at different bodv tsmcsratures. J. EXD. Biol. 44:77-92.

Van Citters, R. L., D. L. Franklin, 0. A. Smith, Jr., N. W. Watson, and R. W. Eisner. 1955. Cardiovascular adaptations to diving in northern elephant seal iHrounaa anaustirostris. Como. Biochem. Physiol. 15: 257-275. 202

Weisbrot, I. W., L. S. James, C. E. Prince, D. A. Holaday, and V. Apgar. 1958. Acid-base homeostasis of the newborn infant during the first 24 hours of life. J. Pediat. 52:395-403.

Whayne, T. F., Jr., and T. Killip, III. 1957. Simulated diving in man: comparison of facial stimuli and response in arrhythmia. J. Appl . Physiol. 22:800-807.

White, F. N. 1955. Circulation in the reptilian heart icaiman scierops)- Anat. Rec. i25:417-432.

White, F. N. 1959. Circulation in the reptilian heart isauamata). Anat. Rec. 135:129-134.

White, F. N. 1959. Redistribution of cardiac output in the diving l 1 n rr 3 4-/-\ v* aI I :y LA vvv I • Copeia 1969:567-570.

White, F. N. 1970. Central vascular shunts and their control in reptiles. Fed. Proc. 29:1149-1153.

» 11 I J.Lc ^ ) rr- . H . 1976. Circulation. Pages 275-334 in C. Gans and W. R. Dawson, eds. Biology of the Reptilia. Volume 5. Academic Press, New York.

White, F. N. 1978. Circulation: a comparison of reptiles, mammals and birds. Pages 51-60 in J, Piiper, ed. Respiratory function in birds, adult and embryonic. Springer-Verlag. New York.

White, F. N., and R. R. Sonnenschein. 1954. Ventricular output in the iguana. Physiologist 7:285.

White, F. N., and G. Ross. 1955. Blood flow in turtles. Nature 208: •7//uw• cn -7 cn

White, F. N.: and G. Ross. 1955. Circulatory changes during experimental Giving in zhe ûurûle. Amer. J. Physiol. 211:15-18.

White, F. N., and J. Kinney. 1976. Ventilation-perfusion relationships in the turtle. Physiologist 19:409.

WiI bur, C. G. 1950. Cardiac responses of Alligator mississippiensis to riiuir.g. f.nmp . R inc. hem. Physiol. 1:154-167.

Wilson, J. W. 1939. Some physiological properties of reptilian blood. J. Cell. Comp. Pnysiol. 13:315-326.

Wolf, S. 1964. The bradycardia of the dive reflex - A possible mechanism of sudden death. Trans. Amer. Clin. Climat. Assoc. 75:192-200. 203

Wood, S. C., and W. R. Moberly. 1970. The influence of temperature on the respiratory properties of iguana blood. Respir. Physiol. 10:20-29

Wood, S. C., and K. Johansen. 1974. Respiratory adaptations to diving in the Nile Monitor Lizard, varanus niioticus. J. Comp. Physiol. 89: 145-158.

Wood, S. C., and C. J. M. Lenfant. 1976. Respiration: mechanics, control and gas exchange. Pages 225-274 in C. Gans and W. R. Dawson, eds. Biology of the Reptilia. Volume 5. Acadenic Press, New York.

Zapol, W. M., G. C. Liggins, R. C. Schneider, J. Qvist, M. T. Snider, R. K. Creasy, and P. W. Hochachka. 1979. Regional blood flow during simulated diving in the conscious Weddell seal. J. Appl. Physiol. 47:968-973. 204

ACKNOWLEDGEMENTS

Sincere appreciation is extended to the chairman of my advisory com­ mittee, Dr. James R. Redmond, for his friendship, advice and encouragement during my doctoral studies. I would also like to express thanks to the other members of my advisory committee: Drs. S. Robert Bradley, Richard

L. Engen, Leslie C. Lewis, and John A. Mutchmor, and to Dr. Hugh I. Ellis and the physiology graduate students with whom I have been associated at

Iowa State university. Thanks are also due the Zoology Department at

I.S.U. for providing research equipment and lab space, to Dr. Franklin A.

Ahrens of the Department of Veterinary Physiology and Pharmacology for

allowing me unlimited access to his gamma counter, and to Dr. Jim McFall

for the loan of his surgical equipment. I also express my appreciation to

Dan Mowrey of the I.S.U. Statistics Department for his help with the

analysis of data.

This thesis is certainly not mine alone. My wife, Diane, sacrificed

in innumerable ways so that this research could be completed and T thank

her dearly. My parents have been a constant source of encouragement to me

throughout my college studies and to them I express heartfelt thanks.

This dissertation is dedicated to Douglas and Jeffrey who have added

immense joy to my life and who allowed me to spend many evenings and week­

ends ai "zhe animal school."