0031-3998/86/2010-0920$02.00/0 PEDIATRIC RESEARCH Vol. 20, No. 10, 1986 Copyright © 1986 International Pediatric Research Foundation, Inc. Printed in U.S.A.
Prenatal Starvation Retards Development of the Ventilatory Response to Hypoxia in Newborn Guinea Pigs
ANDREW J. LECHNER AND DEBRA S. TULL Department ofPhysiology, St. Louis University School ofMedicine, St. Louis, Missouri 63104
ABSTRACT. Prenatal starvation causes pulmonary hy Prenatal caloric restriction (starvation) severely retards pul poplasia in newborn guinea pigs, and is associated with monary growth and development in guinea pigs, which are postnatal cyanosis, hypothermia, and respiratory failure. normally born with functionally mature lungs (1,2). Starvation To determine the effects of such starvation on ventilation, during the last trimester of pregnancy causes high perinatal neonates from litters either fed ad libitum throughout mortality, pulmonary hypoplasia, reduced surfactant prOduction, gestation (control) or given 50% rations in the last trimes altered tissue elastic recoil, and decreased anatomical diffusing ter of pregnancy (starved) were studied at 29 0 C by pleth capacity (3-5). Many of the starved newborn guinea pigs are ysmography in 21, II, and 5% O 2, After 15 min (steady cyanotic and hypothermic, and subsequently die of apparent state) in II% and then 5% O2, 13 of 14 controls (mean = respiratory failure (3, 6). Similarities in survivorship as well as in 95 g) sustained increases in weight-specific minute venti lung structure and function between prenatally starved animals lation of 46 and 75% compared to values in air (p < 0.01), and human premature and small-for-date infants suggest that due to increases in respiratory frequency. Seven of II these animal studies are excellent models ofsuch clinical condi starved neonates (mean =76 g) also sustained increases in tions and their postnatal consequences (7-13). respiratory frequency and weight-specific minute ventila In humans, the few reports concerning the effects of malmitri tion in II and 5% O 2 similar in magnitude to those of the tion on ventilatory control have been performed using normal normal controls, although at higher weight-specific tidal adult volunteers (cj Ref. 14). Low birth weight infants show volumes. One abnormal control (85 g) and four starved reduced V02, VE, and thermoregulatory ability (15-18), but neonates (mean = 70 g) hyperventilated in air, did not ethical considerations preclude measurement oftheir ventilatory respond to 11% O2, and then hypoventilated in 5% O2 due abilities beyond minimal levels. Thus the impact of prenatal to a reduced weight-specific tidal volume. Neonates with malnutrition, while probably present to varying degrees, cannot normal ventilatory patterns did not alter weight-specific be assessed despite its undisputed global importance to infant minute ventilation in 100% O 2 and did not show a biphasic survival (19). Animal studies concerning the effects ofprematur response in acute (1-5 min) exposures to moderate hy ity on respiratory volumes and ventilatory control (20, 21) have poxia, as noted for newborn ofother species. Thus, hypoxia focused only on normal interrupted gestations rather than intra identified those starved neonates in which pulmonary im uterine growth retardation such as occurs with prenatal starva maturity or other starvation-induced pathologies necessi tion. This report represents the first description of ventilation tated a maximal ventilatory effect in air. The sustainable immediately following the stress of prenatal starvation, in both hyperventilation among normal guinea pigs during hypoxia normoxia and hypoxia. The results on respiratory impairment emphasizes the precocial development in this species at correlate with comprehensive pulmonary data recently presented birth, which may be compromised by intrauterine starva elsewhere for this same animal model. tion. (Pediatr Res 20: 920-924,1986)
Abbreviations MATERIALS AND METHODS Animals. Pregnant Hartley-strain guinea pigs with verified V0 , oxygen consumption (ml/min) 2 dates of insemination were obtained from Camm Research In VE, weight-specific minute ventilation (ml/min/l00 g) stitute (Wayne, NJ) when 3 wk pregnant, individually caged at VT, weight-specific tidal volume (ml/IOO g) f, respiratory frequency (per min) 22° C, and provided water ad libitum. Control sows received food ad libitum (Guinea Pig Chow No. 5025, containing 18.5% TT' total breath duration (s) T.. inspiratory duration (s) protein, 4.0% fat, 11.0% fiber, and approximately 175% of known vitamin and mineral requirements, Ralston Purina Co., F102, inspired oxygen concentration (%) St. Louis, MO) throughout gestation. The experimental animals VTfT" mean inspiratory airflow (ml/s/IOO g) ANOVA, analysis of variance were fed ad libitum until day 45 of gestation, and then given 50% rations (Starvation) equal to 22 g of Chow per day during their last trimester (until about day 67 in both groups) (3.-6). Ventilation and metabolism measurements. V02 and VE were determined using whole-body plethysmography. Neonates were tested in one of two procedures within 12 h of birth and before Received March 10, 1986; accepted May 12, 1986. adlibitum feeding ofthe mothers. In the first procedure (protocol Correspondence Dr. Andrew J. Lechner, Department of Physiology, St. Louis A), animals were placed in the apparatus for 30-45 min to University School of Medicine. 1402 South Grand Boulevard, St. Louis, MO 63104. provide baseline resting data in 21 % O2 (air) of V02, VT, f, TT, This work was supported by the American Lung Association and by Grant HL and T.. using modified equations from Drorbaugh and Fenn (22) 29640 from the National Heart, Lung, and Blood Institute. and Blake and Banchero (23). In this protocol, only steady-state 920 VENTILATION IN NEWBORN GUINEA PIGS 921 ventilatory responses to hypoxic gases were measured. FC?llowing exposure to air, the chamber was purged with 11 %O2, V02was determined for 15 min, and then VT, f, TT, and T l measured for "'0'"NN"'; '"NNN\0 \0 approximately 30 s. The chamber was then purged with 5% O2 +1 +1 +1 +1 +1 +1 and the procedure repeated. In St. Louis, these three levels of '" \0 r•
N'" N RESULTS +1 o E (p o Protocol A. In 13 of 14 controls, V significantly increased r- < 0.0 I) during 15 min of 11 and 5% O2due to sustained increases in f(Table 1, Fig. 1); 10 of 14 animals also increased VT while four showed no change or slight decreases. In 12 of 14 controls, both T) and TT also decreased (p < 0.05) as F102 was decreased from 21 to 5%, although TdTT did not change (Table 1). Thus, e '0 VT/T1increased 70% as F102 decreased from 21 to 5% O (p < .., 2 co u G 0.01, Fig. 1). Both resting V02 and rectal temperatures (Tr) decreased significantly (p < 0.05) when F102 was reduced from til '" ....E til 11 to 5% (Table 1). The single abnormal control (85 g) was o ::: E.... characterized by high normoxic VE and VT, which did not change .D o during exposure to 11 %O2 but declined during 15 min of 5% <: Z O2; values for f, TI, and TT did not vary in this animal during 922 LECHNER AND TULL 600 40 ,-- ,I I -... I I ,I if::::::]/ I / 0> I 0>400 0 30 I o 0 I
o I () c --Q) - (/) E --E E / / J------J / 200 / w • control / .> / o starved } / SEM) - normal r -- abnormal *
o r I I °ll-l-'----_L---_------' ° 5 II 21 ° '5 II 21 Fr0 2 ("!o) Fr 0 2 ("!o) Fig. I. Minute ventilation, VE, and mean inspiratory air flow, VT/Tr, in newborn guinea pigs exposed to stepwise hypoxia (protocol A); data were collected after 15 min at each F'02' Thirteen of 14 controls showed the normal pattern ofsustained hyperventilation, as did seven of II neonates whose mothers were starved with 50% rations in their last trimester. Values for VEand VT/T, significantly increased for both normal starved and normal controls with decreasing F102 compared to values for each group in air (p < 0.01). The remaining four starved animals and a single control showed abnormally high VE's at 21 %O2, which did not increase at II %O2, and which declined at 5% O2. See Table I for body weights and other details on these groups. *p < 0.05 versus normal controls at the same F102.
hypoxia. This abnonnal ventilatory pattern was not attributable within 2 min to 135% of the value in air via both VT and f; after to body weight since three smaller controls (weighing 63, 73, and 15 min VE was still 85% greater than in air (p < 0.01) due to the 82 g) showed the nonnal pattern as defined herein. 70% elevation in f. All six controls were nonnal based on the Although average gestational age at tenn (67.1 days) and litter criteria detailed above. size (4.0) were the same for control and starved litters, prenatal Among randomly selected starved neonates, five ofsix animals starvation resulted in a 22% decrease in body weight (p < 0.05) (mean = 81 g) demonstrated a similar ventilatory pattern to that among liveborn neonates (Table 1). Seven starved neonates of the controls. Ventilation in these animals was unaffected by sustained hyperventilation during hypoxia and resembled nor 100% O2 and the subsequent return to air. Although the 32% mal controls with respect to body temperature at all F102s and increase in VE in 11 % Oz (p < 0.05 versus in air) was sustained decreased V02in 5% O2, although their average VTs were larger for 15 min, this was due to a smaller relative increase in f than at all levels of F'02. All seven animals increased f during the in controls (Fig. 2). Reducing FJOz to 5% caused a doubling of reduction in F'02 from 21 to 5%. Thus VE also significantly VE compared to the air value within 2 min (p< 0.01), comprised increased with hypoxia (p < 0.01), and values were higher in the of 40-50% increases in both VT and f. After 15 min at 5% Oz, normal starved neonates than in controls at both 21 and 5% O2 VE was still 77% higher than in air (p < 0.01), due to elevations (p < 0.05, Fig. I). Six of the seven nonnal starved animals of22 and 46% in VT and f, respectively (p < 0.05 for both). The reduced both T, and TT during hypoxia, such that VTIT, in sixth starved neonate (61 g) hyperventilated in air as described creased in a manner parallel to that seen in nonnal controls (p above for other abnonnal animals. Exposure to 100% O2resulted < 0.01, Fig. I). in parallel fluctuations in f and VE, followed by a return to Four of the 11 starved neonates demonstrated an abnonnal nonnoxic values (Fig. 2). Reducing F102 to 11 % resulted in two ventilatory response to hypoxia, which was a significantly higher periods of hyperventilation within the first 5 min, associated 2 rate of occurrence than in controls (p < 0.01 by the x distribu with increases in VT ; within 15 min all ventilatory parameters tion). As noted for the single abnonnal control, these four had returned to nonnoxic levels. In 5% Oz, VE rapidly increased animals were similar in size to three starved neonates which and then decreased, reflecting changes in both VT and f, such demonstrated the normal ventilation pattern. In these animals, that f was substantially lower in this animal than the sustained f VE in air was approximately twice that in nonnal controls (p < levels for the 11 other neonates tested in this procedure. 0.001) and did not increase further following 15 min in 11% O2; subsequent exposure to 5% O2 led to a pronounced decline in DISCUSSION VE (p < 0.05, Fig. I). None of these animals altered f during hypoxia, and at 5% O2, mean inspiratory airflow (VT/T,) de Sustained hyperventilation during hypoxia has been consid creased significantly (p < 0.05). Although all neonates remained ered a property ofmature mammalian respiratory systems which conscious throughout protocol A, the abnormal starved animals develops in the weeks or months after nonnal birth. Except for were cyanotic, hypothennic, and feeble by its conclusion (Table newborn lambs, other neonates including premature and tenn I). infants show a biphasic response to hypoxia: VE increases within Protocol B. Six randomly-selected control neonates (mean = 1-2 min of exposure but then declines to basal or lower levels 104 g) were studied for their acute ventilatory responses to F'02 under continued stress (15, 20, 21, 27-31). This response has of21, 100,21, 11, and 5% (Fig. 2). Hyperoxia did not affect VE, been reported in resting, unsedated newborns using plethysmog f, or other parameters compared to values in air, nor was venti raphy or facial masks (15, 22, 28) as well as in anesthetized, lation altered by the subsequent return to 21 %O2.A 33% intubated animals in which more rapid response patterns to an increase in VE (p < 0.05 versus in air) occurred within 1 min of ideal step reduction in F102 can be achieved (20, 21, 29, 30). exposure to 11 % Oz due to both increased VT and f; at 15 min Although the methodology used here obscured VE changes during this sustained increase in VE was primarily due to the 27% the 30-60 s required to alter chamber F,oz, the plethysmography increase in f. When F102 was further reduced to 5%, VE increased clearly documented persistent increases in VE during hypoxia. VENTILATION IN NEWBORN GUINEA PIGS 923
250 -. normal control (n=6) 0--0 normal starved (n=5)
200 0- -0 abnormal starved (n=1l .S E "-
0 150
.Q'" 100 aLI FI 0 2 (%11 21 100 21 II 5 800 R I , 600 I ' 0'" I 'b I , "- I ' c: I ' I 'b. E 400 I ' "- E
234 5 2 3 4 5 10 2 3 4 5 15
Exposure Time (min) Fig. 2. Sequential changes in f and VEamong normal control (mean = 104.4 ± 9.4 g) and normal starved (mean = 81.8 ± 12.1 g) newborn guinea pigs exposed to F102 of 21, 100, 21, II, and 5% for the times shown (protocol B). For both control and starved normal animals, acute increases in VEoccurring within 1-3 min (p < 0.05 versus air) during II% O2 were sustained throughout exposure to that gas. Subsequent exposure to 5% O2 led to large initial increases in \IE which declined slightly with time to values which were still significantly elevated at IS min compared to VE's in air (p < 0.01). An abnormal starved neonate (61 g) excessively hyperventilated in air, hypoventilated for several minutes in 100% O2, but then reversed that decline while still in hyperoxia. Subsequent exposure to 11 and then 5% O2 led to acute but unsustained increases in VEwhile f in this animal did not differ in hypoxia from values in air. Values are means ± SEM.
Considering the advanced appearance and function ofthe normal near-maximal ventilation in normoxic thermoneutrality, these guinea pig lung at term (1-3), it is perhaps not surprising that animals may have been incapable of any additional ventilatory the animal's ventilatory persistence in hypoxia is normally well response to reduced P02 or increased V02• In adults, ventilatory developed at birth (Fig. I). drive and respiratory muscle function are both compromised by The resting V02 and VEreported herein for normal newborn malnutrition and reflect decreased respiratory muscle mass, gly controls in air agree well with predictions based on body weight, cogen stores, and muscle strength due to multiple myopathies although VTand VTIT1 are slightly higher than reported by others (14,34-36). In young animals, these effects of malnutrition on (24, 32, 33). The sustained increases in VE to II and 5% O2 muscle performance would be in addition to any starvation (Figs. I and 2) were larger than noted for adult guinea pigs, induced retardation of respiratory muscle development (37). although those adults experienced a smaller change in inspired Such impairment of the respiratory muscles is suggested by the P02 (about 38 mm Hg) in breathing 21 and then 15% O2 at the frequency data among abnormal control and starved neonates: f altitude of Denver (32). Regardless of feeding regimen, many is not only invariably high in 21 and 11% O2, but peak values of neonates which sustained normoxic V02 in II %O2 did not do fin 5% O2 were always less than in normal animals (Table I). so in 5% O2, and thus rectal temperature declined in many Normal control and starved guinea pigs sustained elevations animals during this part of protocol A (Table I). Although of VEin II%O2 (Fig. 2), an F102 at which the newborn of other ventilatory parameters remained stable during this 15-min period species show a biphasic ventilatory pattern (27-31). The expla (Fig. I, Table I), it is possible that longer exposures to 5% O2 nation for a biphasic response may be general immaturity of would have eventually reduced ventilatory capacity. ventilatory control in other neonates, or specific effects of hy Many of the starved guinea pigs also sustained changes in VE poxia such as depressed medullary activity, respiratory muscle during hypoxia, although their reliance on greater VTs suggests fatigue, or altered lung and chest wall compliance (15, 20, 21, some degree of respiratory impairment among even the normal 28-31, 33, 36). Imposition ofa stress such as starvation in these starved group. More importantly, there was a significant increase other animal models of neonatal respiration might clarify the in the percentage ofabnormal animals following starvation, from mechanism involved. 5% (one of 20) in controls to 30% (five of 17) among starved (p < 0.0 I, both protocols). This altered percentage is consistent REFERENCES with the relative number of starved neonates whose lungs were J. Lechner AJ, Banchero N, 1982 Advanced pulmonary development in newborn severely retarded as measured by cellularity and anatomical guinea pigs (Cavia porcellus). Am J Anat 163:236-246 diffusing capacity (3-5). Since low birth weight was a better 2. Gaultier C, Harf A, Lorino AM, Atlan G 1984 Lung mechanics in growing predictor of pulmonary hypoplasia (3, 4) than of ventilatory guinea pigs. Respir Physiol 56:217-228 abnormality (present study), other factors such as sex, litter size, 3. Lechner AJ 1985 Perinatal age determines the severity of retarded lung devel opment induced by starvation. Am Rev Respir Dis 131 :638-643 or gestational length may also have influenced development of 4. Lechner AJ 1985 Starvation-induced organ hypoplasia in prenatal and post the abnormal ventilatory pattern. natal guinea pigs. BioI Neonate 48:36-42 All abnormal neonates were distinguished by their excessive 5. Lechner AJ, Winston DC, Bauman JE 1986 Lung mechanics, cellularity, and surfactant after prenatal starvation in guinea pigs. J Appl Physiol hyperventilation in air which was usually accompanied by frank 60:1610-1614 signs ofcyanosis, hypothermia, and respiratory distress. Thus, if 6. Lechner AJ 1984 Growth retardation and mortality in guinea pigs following inadequate pulmonary development orother factors necessitated perinatal starvation. Nutr Rep Int 30:1435-1447 924 LECHNER AND TULL
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