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Glossary of terms for thermal Glossary of terms for thermal physiology Third Edition revised by The Commission for Thermal Physiology of the International Union of Physiological (IUPS Thermal Commission)

Preface Order of Presentation of Terms The first Glossary of Terms for Thermal Physiology To bring similar or related terms closer together in the was published in the J. Appl. Physiol. (1973, 35: 941– Glossary, the common is given first followed by 961) by J.Bligh and K.G.Johnson, under the auspices of the descriptive term, e.g., , hemispherical. the I.U.P.S. Commission for Thermal Physiology. The In use the order is reversed: hemispherical emissivity. revised glossary was again collated with the To avoid confusion such entries have a cross-reference, help of the members of the I.U.P.S Commission for e.g., hemispherical emissivity. →Emissivity, hemi- Thermal Physiology and consulted experts and was spherical. If the same root of a term is used in more published in Pflügers Arch. (1987, 410: 567–587) by E. than one grammatical form, however, with analogous Simon. Once again the members of the I.U.P.S. Com- meaning, it is defined only once without referring ex- mission for Thermal Physiology and consulted experts plicitly to the other forms; example: , whose names are listed in APPENDIX 3 have contrib- homeothermic, homeotherm. uted to the revision of this 3rd edition. Use of Fonts and Markers in Text This revised edition obeys the following rules outlined in the first and second editions: Horizontal arrows in the headings of the definition point to cross-references. Units Bold-face letters mark the terms and their cross-refer- UnitsusedintheGlossaryarebasedontheSystèmeIn- ences which are being defined and, further, those terms ternationale (SI). Where such units would be inconve- in the text of the definitions which are defined else- niently small or large, SI convention permits increases where in the glossary. or decreases by multiples of 103,e.g.,mtomm(m× 10–3)ortonm(m×10–9), but not to cm (m × 10–2). The Abbreviations basic, supplementary, and derived SI units used in the cf. compare OED Oxford English Glossary are given in APPENDIX 1. e.g. for example Dictionary Fr. French ref Reference Symbols Gk. Greek SD Standard The symbols used in the Glossary are listed in APPEN- Deviation DIX 2. These symbols conform generally to those spec- i.e. that is SOED Shorter OED ified in the “Proposed Standard System of Symbols for L. Latin () Symbols Thermal Physiology” (J. Appl. Physiol. 27: 439–446, [] Unit 1969). Minor changes have been suggested. In the body balance equation, the symbol M is now Multiple Definitions used to denote the of metabolic transfor- Where more than one definition of a term is given, they mation (=metabolic rate); metabolic heat produc- are listed in order of preference. tion is identified by the symbol H. The symbol ε (epsilon) is used for emissivity and not for emittance, Although this Glossary expresses the preferences of the and the term exitance has replaced emittance (see commission, it is not a rule. It is a norm for a better American National Standard Institute, Nomenclature communication between the within the same and Definitions for Illumination ,RP-16, field, scientists working in other fields and the general 1967, p. 32 (UDC 653.104.8:621.32)). k is used for public. Any speciality produces its own jargon. It is conductance and λ for . hoped that this Glossary will help transform jargon into general vocabulary.

The Japanese Journal of Physiology Vol. 51, No. 2, 2001 245 Glossary of terms for thermal physiology

Communications concerning the glossary may be sent the term to describe the adaptive to the Chairman of the IUPS Thermal Commission, or changes that occur within an in response to to the Publisher. changes in the natural . Refs:Eagan,C.J.,Federation Proc. 22: 930, 1963; Acknowledgement Greenleaf, J.E., & C.J. Greenleaf, NASA Tech. Mem. This revision was initiated by James Mercer during his X-62, 008, 1970; Hart, J.S., Rev. Can. Biol. 16: 133, term as Chairman of the I.U.P.S. Commission for Ther- 1957. mal Physiology. Thermal Commission member Jurgen Werner was responsible for producing the first working Acclimatization: Physiological or behavioral changes draft and further updating of the glossary followed occurring within the lifetime of an organism that reduce from numerous additional suggestions for new entries the strain caused by stressful changes in the natural cli- and modifications by the current commission members mate (e.g., seasonal or geographical). → acclimation. and other consulted experts. In the revised glossary, 11 Note: What is termed acclimatization mayalsobe terms have been removed, 49 of the original entries specified as a particular phenotypic ;there- have been modified and the definitions of 37 new terms fore, the usefulness of the term may be questioned. have been added, increasing the overall number of en- tries to 479. Acute- response (APR): The multifactorial ste- reotyped response of an organism to infection, injury or James Mercer, Chairman trauma. The APR comprises changes in con- I.U.P.S. Commission for Thermal Physiology centrations of trace metals, (so-called Department of Medical Physiology “acute phase proteins”), , intermediary me- Institute of Medical tabolism, neutrophilia, and “sickness behavior”, which Faculty of includes the development of , loss of appe- University of Tromsø tite, increased , decreased motor activity, and de- N-9037 Tromsø. creased alertness. The acute-phase response (APR) is Norway. considered an early, non-specific host-defence re- sponse, and is triggered by the release of cytokines such as interleukin-1 (IL-1), IL-6, and tumor necrosis Glossary factor α (TNFα).

Absolute . → Humidity, absolute. Adaptation: Changes that reduce the physiological strain produced by stressful components of the total , total radiant. → Radiant absorptance, environment. This change may occur within the - total. of an organism (phenotypic) or be the result of ge- netic selection in a species or subspecies (genotypic). Accidental . → Hypothermia, acciden- Acclimation as defined in this Glossary relates to phe- tal. notypic to specified climatic components. In thermal physiology, the use of the term adaptation Acclimation: Physiologicalorbehavioralchangesoc- does not require specification of the climatic compo- curring within an organism, which reduces the strain or nents of the total environment to which the organism enhances endurance of strain caused by experimentally adapts, but the most obvious component is often de- induced stressful changes in particular climatic factors. noted (e.g., adaptation to heat). There are no distinct Note: The terms acclimation and acclimatization are terms that relate genotypic adaptations to the climate etymologically indistinguishable. Both words have or particular components of climate. been assigned several and different meanings (- Note: In comparison to adaptation as defined in neuro- leaf & Greenleaf, 1970). The most useful of the as- physiology, the adaptive processes in thermal physiol- signed meanings, adopted here, would seem to be those ogy usually occur with larger time constants. of Hart (1957) and Eagan (1963) who use the term ac- climation to describe the adaptive changes that occur Adaptation, genetic. → Adaptation, genotypic. within an organism in response to experimentally in- duced changes in particular climatic factors such as Adaptation, genotypic: A genetically fixed condition ambient in a controlled environment, and of a species or subspecies, or its , which

246 The Japanese Journal of Physiology Vol. 51, No. 2, 2001 Glossary of terms for thermal physiology favours survival in a particular total environment. → some conditions) are also endogenous antipyretics. adaptation. All, however, have distinct mechanisms of action.

Adaptation, nongenetic. → Adaptation, phenotypic. Antipyretics, exogenous: Pharmacological agents (e.g.,cyclooxygenase inhibitors [NSAID’s]) that pre- Adaptation, phenotypic: Changes that reduce the vent or attenuate the development of fever. physiological and/or emotional strain produced by stressful components of the total environment and oc- Area, DuBois (AD): The total area in square curring within the lifetime of the organism. Synonym: meters of a nude human as estimated by the of adaptation, nongenetic. DuBois based on the height, H[m], and , W[kg]. Note: acclimation relates to phenotypic adaptation to Ref.: DuBois, E.F., Basal in and individual climatic components of the total environ- , Philadelphia, P.A, Lea & Febiger, 1927. AD = ment. 0.202·W0.425·H0.725 [m2]

→ . Estivation. Area, effective radiating (Ar): The surface area of a body that exchanges with the environ- Afebrile: The thermoregulatory state of an organism ment through a angle of 4 π . [m2] where core temperature is , and thermoeffec- tors are not attempting to increase or maintain core Area, projected (Ap): The area of a body (or surface) temperature at an elevated level. Antonym: febrile projected on a plane perpendicular to the direction of a collimated beam (projected through an aperture) of ra- : Generally, the changed of a diation. [m2] given peripheral resulting from the stimula- tion of internal sensors; in thermal physiology, the de- Area, (As): The area of a body pro- pendence of thermal sensation on both and core jected perpendicularly to the ’s rays. [m2] .(Gk.alloioo-to alter; aisthesia-sensa- tion) Area, total body (Ab): The area of the outer surface of Note: Positive alliesthesia indicates a change to a more a body, assumed smooth. [m2] pleasurable sensation, negative alliesthesia a change to Note: Direct of surface area are difficult a less pleasurable one. and subject to appreciable error. Surface area is usually estimated from a formula such as that of Meeh (1879) Ambient temperature. → Temperature, ambient. that relates total body area (Ab) to body weight (W): 2/3 Ab =k·W .ThisisaparticularcaseofHuxley’sallo- Anaerobic metabolism. → Metabolism, anaerobic. metric law. Estimates of the value of k vary widely be- tween and within species but are generally between 2 Anapyrexia: A pathological condition in which there 0.07 and 0.11 when Ab is in m and W is in kg (Spector, is a regulated decrease in core temperature. Anapyr- 1956). The DuBois formula (→Area, DuBois), used in exia is distinct from hypothermia in that thermoregu- the estimation of the total body area, relates total latory responses indicate a defence of the anapyretic body area to both mass and height. Estimates of total level of core temperature.(Gk.ana-reverse; pyre- body area made with either Meeh's formula or the tos-fever). DuBois formula have limited accuracy, and reference Note: Anapyrexia may be caused by exogenous or en- should be made to the original direct measurements dogenous substances (→ Cryogen); e.g., the activation from which total body area was calculated. Refs: Hux- of heat loss underlying the menopausal hot flushes ley, J.S., Problems of Relative Growth, London: Meth- may be considered as due to temporary anapyrexia uen, 1932; Meeh, K., Z. Biol. 15: 425, 1879; Spector, caused by GnRH. W.S., Handbook of Biological Data, Philadelphia, P.A.: Saunders, 1956. Antipyretics, endogenous: Hormones and cytokines that limit the of fever. The hormones in- Area, wetted (Aw): The area of skin which, if covered clude arginine (AVP), α-melanocyte stim- with sweat (), would provide the observed rate of ulating (αMSH), and . The under the prevailing condition. [m2] → cytokines IL-4, IL-1α and possibly TNF-α (under Wettedness, skin.

The Japanese Journal of Physiology Vol. 51, No. 2, 2001 247 Glossary of terms for thermal physiology

Autonomic temperature regulation. → Tempera- body). ture regulation, autonomic. Note: The equation is designed to describe the prevail- ing physiological situation of a homeothermic (e.g. Autonomic . → Temperature reg- human) subject. At a given metabolic energy trans- ulation, autonomic. formation, the subject transfers some mechanical en- ergy to its ambiance (→work rate, positive), and, if the Bacterial pyrogen. → Pyrogen, bacterial. ambient thermal conditions permit it, heat from the body to the environment by evaporation, conduction, . → Metabolic rate, basal. , and radiation, which eventually results in the stabilization of body heat content with storage S = Behavior, thermoregulatory. → Temperature regu- 0. However, there are physiological conditions in lation, behavioral. which mechanical energy is absorbed by the body, ulti- mately as heat (→work rate, negative), and/or one or Behavioral temperature regulation. → Temperature the other of the terms describing the exchange of heat regulation, behavioral. flow with the environment may become negative. In a core/ treatment of the body we get two heat Behavioral thermoregulation. → Temperature reg- balance equations: ulation, behavioral. Score =M–(W)–(H)–REHL Sshell =H–(E)–(C)–(R)–(K) Blackbody. → Radiator, full. with REHL = → respiratory evaporative heat loss (REHL) and H = → (conductive and Body heat balance: The steady-state relation in which convective heat flow) between core and shell. The lat- total heat gain in the body equals its heat loss to the en- ter is proportional to the difference of mean core and vironment. mean with the proportionality con- stant → conductance k. Body heat balance equation (actually: heat flow bal- ance equation): A mathematical expression that de- Body heat content. → Heat content, body. scribes the net rate at which a subject generates and exchanges heat with its environment (First Law of Body heat storage. → Storage of body heat and Heat ). The dimension of the equation and storage, change in. its terms respectively, are in [W] thereby consti- tuting heat flows, but often are also expressed in rela- Body temperature, mean. → Temperature, mean tion to unit area of body surface [W · m–2], to unit body body. mass [W · kg–1], or to unit body [W·m–3]. S = M – (W) – (E) – (C) – (K) – (R). Bradymetabolism: The low levels of basal metabo- lism of and other nonavian and nonmammalian S = storage of body heat (positive = increase in body relative to those of and of the heat content; negative = decrease in body heat con- same body size and at the same temperature. (Gk. tent). bradus-slow, sluggish; metabole-change) Antonym: M = metabolic energy transformation (always posi- tachymetabolism. tive in a living organism) = metabolic rate. Note: As a synonym cold-bloodedness is unsatisfac- W = work rate, positive (= useful mechanical tory and is falling into disuse. This relatively low level accomplished; negative = mechanical power absorbed of basal metabolism is sometimes described as poiki- by body: work rate, negative). lothermy, which is incorrect since poikilothermy sig- E = evaporative heat transfer (positive = evaporative nifies conformity of body and ambient temperatures heat loss;negative=evaporative heat gain). and not all bradymetabolic species are temperature C = convective heat transfer (positive = transfer to the conformers;someareectothermic temperature reg- environment; negative = transfer into the body). ulators. K= conductive heat transfer (positive = transfer to the environment; negative = transfer into the body). cooling, selective. → Selective brain cooling. R = radiant heat exchange (positive = heat transfer to the environment; negative = heat absorption by the (): A particular form of ad-

248 The Japanese Journal of Physiology Vol. 51, No. 2, 2001 Glossary of terms for thermal physiology ipose tissue with selected distribution. It differs from the heat transfer. white adipose tissue both structurally and functionally; Note: The most common method of indirect calorim- its colour is brownish ( to reddish), depending on etry is to measure the uptake of and/or the elim- its content of (mitochondrial) cytochromes and of fat ination of , and to convert these values to which is distributed in multipledroplets (multilocular) an equivalent quantity of heat. The calorific equivalent as compared to white fat cells (monolocular) and also of a of oxygen is approximately 20 kJ of heat. on its dense vascularization. ap- pears to be restricted to mammalian species, especially Calorimetry, partitional: The estimation of any single of smaller body size, including the hibernators (→ Hi- term in the body heat balance equation from direct bernation), but is also in newborns of larger measurements of all other terms in the equation during species including humans. Regulatory heat production the . Ref: Winslow, C.E.A., L.P. Herrington, has been identified as its main but possibly not its only &A.P.Gagge,Am. J. Physiol. 116: 641, 1936. . Its heat-generating capacity relates to the rate of fatty acid oxidation which is not constrained by cel- Cenothermy: The condition of a temperature regula- lular ATP catabolism. This property correlates with the tor when its core temperature is within +1SDofthe presence of a specialized component in the inner mito- range associated with the normal postabsorptive resting chondrial membrane named UCP1 (the uncoupling condition of the species in the thermoneutral zone. or thermogenin, which establishes a proton (Gk. koinos-common, shared; therme-heat) Synonym: shunt bypassing oxidative phosphorylation). The activ- euthermy, normothermy. ity of brown adipose tissue is controlled by the sympa- Note: Ceno (common) seems a more appropriate prefix thetic through release of . than eu (well, good). Note: Chronic to cold (→ nonshivering ther- mogenesis) and to excess food intake (→ diet-induced Change in heat storage. → Heat storage, change in. ) enhance the heat-generating capacity of brown adipose tissue by hypertrophy (including in- Chemical temperature regulation. → Temperature crease in UCP1 amount) and hyperplasia. The total regulation, chemical. process is referred to as recruitment. In accordance with the sympathetic control of brown adipose tissue,the Circadian: Relating to the approximate 24-h periodic- increase in metabolic energy transformation of an ity of a free running biological rhythm, or to the exact in a thermoneutral environment after systemic 24-h periodicity of an environmentally synchronized injection of noradrenaline is considered as an estimate biological rhythm that persists with an approximate of the thermogenetic capacity of brown adipose tissue. 24-h periodicity when not environmentally synchro- nized. (L. circa-about, approximately; dies-) Brown fat. → Brown adipose tissue. clo: A unit to express the relative thermal insulation Calorimetry: The of heat. In thermal values of various assemblies. physiology, the measurement of the heat transfer be- 1clo=0.18°C·m2 ·h · kcal–1 = 0.155°C ·m2 ·W–1 tween a tissue, an , or an organism and its envi- ronment. (L. calor-heat; Gk. metria-act of measuring) Note: The clo is a unit developed to express thermal → calorimetry, direct and calorimetry, indirect. insulation (→ ) in practical terms and represents the insulation provided by the normal Calorimetry, direct: The direct physical measurement indoor clothing of a sedentary worker in comfortable of heat, usually the rate of transfer of heat (→ heat indoor surroundings (Ref: Gagge, A.P., A.C. Burton, & transfer) between a tissue, an organ, or an organism H.C. Bazett, 94: 428, 1941). The term is used in and its environment. heating and ventilation engineering in the determina- tion of environmental conditions for human comfort. Calorimetry, indirect: The measurement of the rate of transfer of a material involved in the transformation of Cold-blooded: The thermal state of an animal in which chemical energy into heat between a tissue, an organ, or core temperature remains close to ambient tempera- an organism and its environment. The process requires ture when subjected to a low ambient temperature. the calculation of the heat transfer from an empirically Synonym: bradymetabolic, poikilothermic.Ant- established relation between the material transfer and onym: warm-blooded.

The Japanese Journal of Physiology Vol. 51, No. 2, 2001 249 Glossary of terms for thermal physiology

Note: The existence of only a small temperature gradi- Comfort. → . ent between the organism and its environment results from the low rate of metabolic heat production Conductance, thermal. → Thermal conductance. (bradymetabolism)ofcold-blooded animals relative to the high rate of metabolic heat production (ta- Conductive heat transfer (K): The net rate of heat chymetabolism)ofwarm-blooded animals. Thus, the transfer in a solid material or a non-moving or terms bradymetabolic and tachymetabolic are pre- fluid (i.e., by conduction) down a thermal , ferred to the terms cold-blooded and warm-blooded, within an organism, or between an organism and its ex- because the first pair of terms relates to a more basic ternal environment. The latter is usually expressed in physiological distinction and because the second pair of terms of unit area of the total body surface, i.e. as a heat terms has been used with various meanings not all of , and is the quantity (K) in the body heat balance which are entirely consistent with the definitions given equation in which (–K)=heat gain,and(+K)=heat here. Since their core temperatures follow ambient loss.[W·m–2], [W], [W·m–3], [W·kg–1] temperature, all cold-blooded animals are poikilother- mic (i.e., many temperatured). Thus, cold-blooded, Conductive heat transfer coefficient. → Heat trans- poikilothermic,andbradymetabolic are descriptions fer coefficient, conductive. of related phenomena. The same cannot be said of warm-blooded, homeothermic,andtachymetabolic Conductivity, thermal. →Thermal conductivity. (→ warm-blooded). Control: 1. the process by which a physiological vari- Cold . → . able becomes a function of information generated lo- cally or transmitted from remote sources by neural or Cold tolerance: The ability to tolerate low ambient hormonal signals ( control); 2. the process temperatures. This term comprises a variety of physi- by which a physiological system stabilizes (“regu- ological properties. Certain homeotherms (tachymet- lates”) a variable, generally by means of an information abolic species) are described as cold tolerant, because loop with negative . The control loop com- they are able to balance heat production and heat loss in prises the controlled (passive) system (e.g., the heat the state of cenothermy at particularly low ambient transfer processes) and the controlling (active) system, temperatures. This may be due to the development of which may be divided into sensor, processor and effec- insulation or to the efficiency of metabolic heat pro- tor components. duction and is often combined with an improved abil- Note: With the adoption of definition #2 from the ter- ity to protect appendages from freezing by effective minology of technical control, further terms like vascular control of local .Inhomeo- set-point, controlled variable, load-error, nega- therms, cold tolerance mayalsobeachievedbygen- tive-feedback, servo-control, etc., have been introduced eral heterothermy, including , i.e., by to describe the various components of the physiological controlled forms of hypothermia. processes of regulation. Control in the of defini- (bradymetabolic species) are characterized as cold tion #2 and regulation are analogous terms in physiol- tolerant, if they are able to survive low and even sub- ogy. However, the use of the term regulation should be freezing body temperatures, either in the state of cryo- generally given preference in order to avoid confusion thermy, or because intracellular formation of between the two definitions of control. is avoided during freezing. All forms of cold tolerance may be subject to adaptation or accli- Control, proportional: A control concept with nega- mat(izat). tive feedback, obviously present in thermoregulation, Note: While some types of what is termed cold toler- in which the controller activates thermoeffector mech- ance have already been specified (cryothermy, hiber- anisms to an extent dependent on the deviation of the nation), further specification and agreement upon controlled variable from its set-point. If the distur- additional definitions seem necessary. bance (external or internal thermal load) persists, such a control concept implies a load error, i.e., a permanent Combined nonevaporative heat transfer coefficient. deviation of the controlled variable. However, such a → Heat transfer coefficient, combined nonevapora- deviation is much smaller than that which is present tive. without feedback control.

250 The Japanese Journal of Physiology Vol. 51, No. 2, 2001 Glossary of terms for thermal physiology

Controlled temperature lability. → Temperature la- a section of the thermal core: however, in several bility, controlled. mammalian and avian species its temperature may de- viate to some extent from that of the remaining thermal Convection, circulatory: Flow of in the vessels core due to selective brain cooling. of the . In thermal physiology, con- vective transfer of heat with the blood stream from the Crepuscular: Occurring daily during the phases of thermal core through the thermal shell to the heat dis- twilight. → diurnal.(L.crepusculum-twilight) . sipating of the body is a thermoeffector of au- tonomic temperature regulation. Its efficiency in Critical temperature for evaporative heat loss. → transferring heat is a function of flow rate and the tem- Critical temperature, upper. perature gradient between core and heat dissipating surface, and may be modified by the of heat ex- Critical temperature for heat production.→ Critical change by conduction between the vessels to and from temperature, lower. these surfaces (e.g., due to the counter-current arrange- ment of arteries and veins). Critical temperature, lower: The ambient tempera- ture below which the rate of metabolic heat produc- Convective heat transfer (C): The net rate of heat tion of a resting thermoregulating tachymetabolic transfer in a moving gas or fluid (i.e., by convection) animal must be increased by and/or nonshiv- between different parts of an organism, or between an ering thermogenesis in order to maintain thermal bal- organism and its external environment; it may develop ance. Synonym: critical temperature for heat and be amplified by thermal (natural convec- production.[°C] tion) and by forces such as , fans, pumps or body movement (forced convection) usually expressed in Critical temperature, upper: The ambient tempera- terms of unit area of the total body surface (→ Area, to- ture above which the rate of evaporative heat loss of a tal body), i.e., as a . The quantity (C)inthe resting thermoregulating animal must be increased body heat balance equation in which (–C)=heat gain (e.g., by thermal tachypnea or by thermal sweating) and (+C)=heat loss.[W·m–2], [W], [W·m–3], [W·kg–1] in order to maintain thermal balance. Synonym: criti- cal temperature for evaporative heat loss.[°C] Convective heat transfer coefficient.→ Heat trans- Note: Upper critical temperature hasalsobeenused fer coefficient, convective. to define the ambient temperature above which the capacities of the mechanisms of heat transfer to the Convective . → Mass transfer, convec- environment of a resting animal are exceeded, such that tive. core temperature is forced to rise and, as a conse- quence, metabolic energy transformation,i.e.,thein- Convulsions, febrile: Convulsions (epileptic seizures) ternal heat load, is further increased. This use of the occurring before or during fever episodes. Febrile con- term should be avoided, however, because it does not vulsions occur mostly in children between the of 6 accurately describe the upper temperature survival and 3 . They are rare after the age of 8 limit. years. Note: Due to its rare occurrence, this term has become Cryogen: An endogenous or exogenous substance that obsolete in many developed countries. lowers the set-point of body temperature and causes anapyrexia. Antonym: pyrogen.(Gk.kruos-cold; < Core temperature. → Temperature, core. gen-become).

Core, thermal: Those inner tissues of the body whose Cryothermy: The thermal status of a supercooled or- temperatures are not changed in their relationship to ganism (i.e., with the temperature of the body mass be- each other by circulatory adjustments and changes in low the freezing point of the tissue). (Gk. kruos-cold; heat dissipation to the environment that affect the ther- therme-heat) mal shell of the body. Note: The term is used mainly to describe the deep body Cutaneous evaporative heat loss (CEHL): Rate of tissues of homeotherms whose temperatures are repre- heat dissipated by evaporation from the skin. [W], sented by the core temperature. The brain is generally [W·m–2], [W·m–3], [W·kg–1]. Cutaneous evaporative

The Japanese Journal of Physiology Vol. 51, No. 2, 2001 251 Glossary of terms for thermal physiology heat loss (CEHL) plus respiratory evaporative heat of activity) occurring during the day, as distinct from loss (REHL) constitute → evaporative heat loss. the night. 2. Occurring daily (during each 24-h period). (L. diurnus adj < dies-day). Cutaneous water exchange, passive. → Passive cuta- Note: Terms relating to other phases of entrained 24 h neous water exchange. periodicity, i.e., to definition #1, are: nocturnal (during the night) and crepuscular (during twilight); nych- Cutaneous water exchange, passive. → Pas- themeral corresponds to definition #2. sive cutaneous exchange. Dry bulb temperature. → Temperature, dry bulb. Cytokine: A class of immunoregulatory polypeptides produced by various types, but, at the outset, pri- Dry heat loss. → Heat loss, nonevaporative. marily by mononuclear phagocytes activated by vari- ous signals provided by exogenous pyrogens. DuBois area. → Area, DuBois. Cytokines may act as endogenous mediators of fever (endogenous pyrogens). The most prominent among Eccritic body temperature. → Preferred body tem- the fever producing cytokines are interleukins perature. (IL)-1β and -6, tumor necrosis factor (TNF)-α, and interferon (IFN)-α. Ectothermic temperature regulator. → Tempera- ture regulator. Deep body temperature. → Temperature, core. Ectothermy: The pattern of temperature regulation (ρ): Theratioofthemasstothevolumeofa of animals in which body temperature depends mainly substance. [kg · m–3] on the behaviorally controlled exchange of heat with the environment. Autonomic thermoeffectors may be Dew-point temperature. → Temperature, temporarily important in a few ectothermic species dew-point. (panting in lizards, warming-up of ). (Gk. ek- tos-outside; therme-heat) Antonym: endothermy. Diet-induced thermogenesis. → Thermogenesis, diet-induced. Effective radiant field. → , effective.

Diffusivity, mass (D): The constant of proportionality Effective radiant flux. → Radiant flux, effective. relating the rate of of a gas to the gradient of its in another gas, e.g., water vapor in air. Effective radiating area. → Area, effective radiat- If the rate of diffusion of mass is m[kg· · s–1] in a direc- ing. tion specified by a coordinate y [m] and if the concen- tration over a plane at a given value of y is p[kg ·m–3], . → Temperature, effective. the rate of flow through an area A is given by the Fick- ian equation, m=–DA(· ∂p/∂y), where D is the mass Emissivity (ε): The ratio of the total radiant energy diffusivity or diffusion coefficient and ∂p/∂yistheap- emitted by a body to the energy emitted by a full radi- propriate concentration gradient. More complex equa- ator atthesametemperature. tions are needed to describe diffusion in two or three 2 –1 ε directions simultaneously [m ·s ] Emissivity, directional ( (θ,φ)): The ratio of the ther- mal (Le,th) of a body in a given direction to Diffusivity, thermal (α): The thermal conductivity of that of a full radiator (Le,(ε=1)) at the same temperature. ε θ φ a substance divided by its density (ρ)andspecific heat (θ,φ) =Le,th(θ,φ)/Le,(ε=1) in which and are the angular 2 –1 at constant (cp)·[m ·s ] coordinates defining the given direction. ε Direct calorimetry. → Calorimetry, direct. Emissivity, hemispherical ( h): The ratio of the total radiant energy emitted by an element of a surface into Directional emissivity. → Emissivity, directional. a hemisphere to the energy by a similar element on the surface of a full radiator. The element forms the center Diurnal: 1. Indicates biological processes (e.g., phases of the equatorial plane of the hemisphere, but it is not

252 The Japanese Journal of Physiology Vol. 51, No. 2, 2001 Glossary of terms for thermal physiology necessary to define its radius. components in the body heat balance equation.

Emissivity, spectral (ελ): The ratio of the radiant flux Energy metabolism. → Metabolism, energy. emitted by an element of surface per unit interval to the flux emitted by a full radiator at the Environment. → Total environment. same temperature and in the same waveband. Estivation: A state of lethargy (often during the sum- ε Emissivity, window ( w): The ratio of the radiant en- mer) with a reduction in body temperature and metab- ergy emitted by an element of surface between - olism demonstrated by some animals that are λ λ 1 and 2 to the flux emitted by a full radiator at temperature regulators when active. The term is usu- the same temperature and in the same waveband. The ally, but not exclusively, applied to ectothermic tem- quantity is a special type of spectral emissivity and is perature regulators.(L.aestivus adj < used because some biological materials have a low aestas-summer) emissivity in parts of the or . These parts are known as windows. Eurythermy: The tolerance by of a wide range of environmental temperatures, or the accommo- Emittance. → . dation to substantial changes in the thermal environ- ment. (Gk. eurus-wide; therme-heat) Antonym: Endogenous antipyretic. → Antipyretic, endoge- stenothermy. nous. Euthermy. → Cenothermy. Endogenous pyrogen. → Pyrogen, endogenous. Evaporative heat gain: → evaporative heat transfer Endothermic temperature regulator. → Tempera- from the ambiance to the body (i.e., gain of heat en- ture regulator. ergy) due to of vapor on the skin and/or the surfaces of the respiratory tract, usually expressed Endothermy: The pattern of thermoregulation in in terms of energy per unit time and unit area of total which the body temperature depends on a high (ta- body surface. [W], [W · m–2], [W · m–3], [W · kg–1] chymetabolic) and controlled rate of heat production. Note: evaporative heat transfer most frequently oc- Behavioural responses are often used by . curs by of water from body surfaces and is (Gk. endo-inside; therme-heat) Antonym: ectothermy. → evaporative heat loss. Note: The use of endothermy to denote the production of heat within an organ or organism is etymologically Evaporative heat loss: → evaporative heat transfer correct but may be found confusing as the same term is from the body to the ambiance (i.e., loss of heat energy) used in to mean the uptake of heat during a by evaporation of water from the skin and the surfaces . of the respiratory tract, usually expressed in terms of heat flow [W] or heat flux [W·m–2] (energy per unit Endotoxin: Heat stable compounds that are intrinsic to time and unit area of total body surface) or in [W·kg–1] the cell walls of Gram-negative . The term de- or [W·m–3]. rives from the noxious effects on the infected host; in Note: Evaporative heat loss comprises passive com- addition, endotoxins act as potent exogenous pyrogens ponents, i.e., water vaporizing from respiratory sur- and stimulators of the acute-phase response, respec- faces at normal and water diffusing through tively. Endotoxins contain lipopolysaccharides (LPS) the skin and vaporizing at the surface (→ insensible of high molecular weight. Other cell wall components, ); its thermoregulatory components are e.g., peptidoglycans, may have partially similar effects. established by autonomic thermoeffectors,likether- mal sweating and thermal panting, and behavioral Energy: Energy may occur either as chemical, electro- thermoeffectors,likesaliva spreading, wallowing, magnetic, or mechanical energy. [Ws = J]. Synonymous and other modes of behavioral surface wetting. to mechanical energy (force length, height or dis- tance) is work, synonymous to is heat. Evaporative heat loss coefficient. → Heat loss coef- Work or heat per unit time (→ work rate or → heat ficient, evaporative. flow) constitute physically → power, and are used as

The Japanese Journal of Physiology Vol. 51, No. 2, 2001 253 Glossary of terms for thermal physiology

Evaporative heat loss, respiratory. → Respiratory named pyrogens. Endogenous pyrogens (e.g., pros- evaporative heat loss. taglandin E2) are usually the obligatory mediators of fe- Evaporative heat transfer (E): The rate at which heat ver, but direct actions of exogenous pyrogens are not energy is transferred by evaporation from or condensa- ruled out. Fever can also result as an idiopathic condi- tion on the skin and the surfaces of the respiratory tract, tionofthebody.Itcanalsobecausedbyemotional usually expressed in terms of unit area of total body sur- (→ stress fever). The exact mechanisms of fever face. The quantity (E)inthebody heat balance equa- induction are not yet clear. tion, evaporation and heat loss from the body are Note: Typical natural fever in response to bacterial in- indicatedby(+E), condensation and heat gain to the fection is induced by interleukin-1 (IL-1), IL-6 and bodyby(–E).[W]or[W·m–2]. other cytokines which are formed as mediators in the multifactorial humoral host-defence response termed Exertional : An acute syndrome caused by acute-phase response. Limited febrile rises in core an excessive rise in body temperature as the result of temperature are apparently harmless, as long as bodily overloading or failure of the thermoregulatory system functions are not compromised by other disturbances or during exposure to heat stress while exercising in a stressful conditions. Fever may contribute to the bene- warm environment. ficial effects of the humoral host-defence responses to Note: Exertional heat stroke, in contrast to classical infection. heat stroke, occurs most commonly in healthy young or middle-aged adults; cutaneous vasodilatation is re- Fever, stress. → Stress fever. duced and thermal sweating may decrease but is often still conspicuous. Freezing cold injury (FCI): Tissue damage (frostbite) resulting when tissue temperature falls below its freez- Exitance. → Radiant exitance. ing temperature (ca. –2°C). 90% of FCI’s occur in ex- posed skin and the extremities. The development of Exogenous pyrogen. → Pyrogen, exogenous. FCI is primarily determined by the ambient tempera- ture, Antonym: Non-freezing cold injury (NFCI). Febrile: A term used to describe the state of an organ- ism during a fever. Antonym: afebrile Full radiator. → Radiator, full.

Febrile convulsions. → Convulsions, febrile. Genetic adaptation. → Adaptation, genotypic.

Fever:Astateofelevatedcore temperature which is Genotypic adaptation. → Adaptation, genotypic. often, but not necessarily, part of the defensive re- sponses of organisms (host) to the invasion by live (mi- Globe temperature. → Temperature, globe. croorganisms) or inanimate recognized as pathogenic or alien by the host. The rise in core tem- GDP-binding protein. → UCP1. perature is usually designated as due to a change in the thermocontroller characteristics resulting in an eleva- Gular fluttering: The rapid oscillations of the hyoid tion of the set-point of body temperature. The higher apparatus and hence of the gular region of some birds as temperature is actively established and defended by the a characteristic form of thermal panting during expo- operation of heat-producing and heat-conserving ther- sure to high ambient temperature,bywhichmeansair moeffectors. Time courses and extent of natural is moved across the moist surfaces of the upper respira- are variable, but an upper temperature limit (41°C in tory tract. humans) is seldom exceeded, at which level core tem- perature is maintained for some time and eventually Habituation: Reduction of responses to or perception reduced when the set-point of temperature regulation of a repeated stimulation. returns to its normal level. While any rise in body tem- perature may be due to fever, those rises which are not Heat. → Energy. accompanied by supportive changes in thermoeffector activities, are termed .Thehumoral Heat balance equation. → Body heat balance equa- mechanisms underlying fever consist of the alteration tion. of the neural control of body temperature by agents

254 The Japanese Journal of Physiology Vol. 51, No. 2, 2001 Glossary of terms for thermal physiology

Heat capacity: The product of the mass of an object refers to convection only and does not include other and its specific heat.[J·°C–1] forms of heat transfer.

Heat content, body: The product of the body mass, its Heat loss, evaporative. → Evaporative heat loss. average specific heat, and the absolute mean body temperature.[J] Heat loss, insensible. → Evaporative heat loss. Note: The actual value of this term is seldom calcu- Note: The term insensible heat loss should be avoided lated. It is used only in the determination of heat stor- in favour of evaporative heat loss, because of possible age. → Storage of body heat. confusion with insensible water loss which implies evaporative heat loss but relates to . Heat cramps: Painful spasms of skeletal muscles re- lated to prolonged heat stress. Heat loss, Newtonian. → Heat loss, dry. Note: Heat cramps are usually strong painful tetanic contractions of groups of extremity or abdominal mus- Heat loss, nonevaporative. → Heat loss, dry. cles. They are related to prolonged heat stress, pro- found thermal sweating and water but not salt deficit Heat loss, sensible. → Heat loss, dry. replacement. Heat production, metabolic. → Metabolic heat pro- Heat endurance.→ Heat toleranc. duction.

Heat exhaustion: Muscular weakness, fatigue, and Heat production (excess), postprandial: The increase distress, resulting from prolonged exposure to heat. in metabolic heat production, relative to its postab- Core temperature is elevated and thermal sweating sorptive resting level, in the following food in- and cutaneous vasodilatation are commonly but not in- take. Its relationship to specific dynamic effect,or variably reduced. This condition is aggravated by mus- diet-induced thermogenesis is not clear. cular exertion, and . Note: While the term postprandial heat production is Circulatory abnormalities may occur. coming into use, it is recommended to include the spec- ification excess, because the definition means heat pro- Heat flow [H]: The amount of heat transferred per duction in excess of resting metabolic rate (RMR). unit time between parts of a body at different tempera- tures, or between a body and its environment when at Heat production, total. → Total heat production. different temperatures. [W]. Physically it constitutes → power. Heat protein (HSP): Intracellular proteins present in every species, from bacteria to humans. Heat flow balance equation.→ Body heat balance Among the multiple functions ascribed to these pro- equation. teins they protect nascent proteins, halt proteins de-folding etc. Their generation may alter the threshold Heatflux:Heatflowpassing through unit area of a for thermal injury. given surface. [W · m–2] Heat shock response. → Thermotolerance. Heat gain. → Heat transfer. Heat, specific. → Specific heat. Heat loss. → Heat transfer. Heat storage, change in: → Storage of body heat. Heat loss coefficient, evaporative. → Heat transfer coefficient, evaporative. Heat stroke: An acute syndrome caused by an exces- sive rise in core temperature as the result of overload- Heat loss, dry: The sum of heat flows or heat ing or failure of the thermoregulatory system during by radiation, convection, and conduction from a body exposure to heat stress. It is characterized by a large va- to the environment.[W]or[W·m–2] Synonyms: sen- riety of pathophysiological alterations of bodily func- sible heat loss; heat loss, Newtonian. tions, including mental disturbances, with a high Note: In meteorological literature, loss incidence of permanent or fatal damage.

The Japanese Journal of Physiology Vol. 51, No. 2, 2001 255 Glossary of terms for thermal physiology

Note: Classical heat stroke, in contrast to exertional combination of these processes) and for evaporation heat stroke, occurs under sedentary conditions, most (see below). commonly in very old or very young people; cutaneous vasodilatation is greatly reduced and thermal sweating Heat transfer coefficient, combined nonevaporative is commonly absent. (hcomb): The ratio of total heat transfer per unit area by radiation, convection, and conduction to the temper- Heat : Collapse, usually with loss of con- ature difference between the surface and operative sciousness, during exposure to heat. The symptoms are temperature of the environment. similar to those of the vasovagal syndrome (fainting). –2 –1 hcomb =hr +hc +hk [W· m ·°C ] Heat tolerance: The ability to tolerate high ambient temperatures. This term comprises a variety of physi- Heat transfer coefficient, conductive (hk): The net ological characteristics. Homeotherms (tachymeta- heat transfer by conduction per unit area between a bolic species) are often characterized as heat tolerant, surface and a solid or stationary fluidic medium in con- if they remain comfortable or are able to balance heat tact with the surface per unit temperature difference production and heat loss at particularly high ambient (∆T) between the surface and the substance with which temperatures. Homeothermic species are also char- it is in contact. acterized as heat tolerant, if they are capable to main- ∆ –1 –2 –1 tain normal functions, or to survive, at body hk = K· T [W·m ·°C ] temperatures exceeding their normal range; this may involve the facility of selective brain cooling.–Poiki- Heat transfer coefficient, convective (hc): The net lotherms (bradymetabolic species) may also be spec- heat transfer per unit area between a surface and a ified as heat tolerant, if they are able to survive very moving fluidic medium per unit temperature difference high body temperatures. All forms of heat tolerance (∆T) between the surface and the medium. may be subject to adaptation or acclimat(izat)ion. ∆ –1 –2 –1 Synonym: heat endurance. hc = C· T [W· m ·°C ] Note: In the OED the words tolerance and endurance are almost synonymous. From a physiological point of Heat transfer coefficient, evaporative (he): The net view a distinction is sometimes made between heat tol- heat transfer per unit gradient caused erance and heat endurance, the former term is some- by the evaporation of water from a unit area of wet sur- times used in a more general sense and includes all face or by the condensation of water vapor on a unit forms of tolerance, while the latter is sometimes used in area of body surface. The driving force is the vapor a more specific sense as in tolerance with time during a from Pws (on the surface) to Pwa (of sustained stress, e.g., exercise endurance. the ambient gas). Thus

–1 –2 –1 –2 –1 Heat transfer: Process of heat flow [W], i.e., the rate he = E(Pws –Pwa) ·[W·m ·Pa ]or[W·m · ]. at which heat energy is transferred from one part of an organism to another especially between body core and In terms of the of vaporization (λ or LHV) shell. In this case the heat transfer is a combination of of water, the for water vapor (Rw), the conduction and convection. A more frequently investi- mean temperature (T) of the medium in °K and the gated topic of thermal physiology is heat transfer be- mass transfer coefficient (hD) tweenanorganismanditsenvironment,by λ –1 –1 conduction, convection, radiation, evaporation, or a he =hD· ·Rw ·T combination of these. Net transfer from the organism to the environment is heat loss, and from the ambiance Note: In most physiological applications the vapor into the organism is heat gain. → Body heat balance pressure gradient instead of the concentration gradient equation. can be considered as the driving potential for the evap- orative process since the temperature difference be- Heat transfer coefficient: A parameter (h) [W · m–2 tween the evaporating surface and the ambient air is ·°C–1] which determines the amount of heat flux (H) small in relation to the average temperature of the sur- due to a temperature difference (∆T): H =h·∆T. H may face-water vapor medium. be defined for conduction, convection, radiation (or the

256 The Japanese Journal of Physiology Vol. 51, No. 2, 2001 Glossary of terms for thermal physiology

Heat transfer coefficient, radiative: The net rate of perature and metabolism of some animals that are ho- heat transfer per unit area by the exchange of thermal meothermic temperature regulators when active. (L. radiation between two surfaces, per unit temperature hibernare- to pass the winter) difference between the surfaces. [W · m–2 ·°C–1] Note: Body temperature is regulated in the state of hi- bernation,however,withset-point differing from that Heat transfer coefficient, radiative (linear) (hr): Ac- in the state of cenothermy (euthermy). cording to the Stefan-Boltzmann Law, the exchange of radiation between two surfaces at temperatures Hidromeiosis: The swelling of keratinized layers of σ 4 σ T1 and T2 [°K] is proportional to T ,where is the the skin, due to prolonged exposure to water or sweat, Stefan-. When the ratio (T1 –T2)/T which blocks sweat ducts and reduces sweating rate. σ 4 4 ≈ σ 3 is small, where T = (T1 +T2)/2, (T1 –T2 ) 4 T · (Gk. hidros-sweat; -decrease) σ 3 (T1 +T2)andtheterm4 T can be treated as a linear heat transfer coefficient.[W·m–2 ·°C–1] : General term characterizing the relative constancy of physico-chemical properties of the inter- Heliothermy: The regulation of the body temperature nal environment of an organism as being maintained by of an ectothermic animal by behavioral adjustments of regulation.(Gk.homoio-similar, resembling; sta- its exposure to solar radiation. (Gk. helios-the sun; sis-standing) therme-heat) Homeothermy: The pattern of temperature regula- Hemihidrotic response: Suppression of thermal tion in a tachymetabolic species in which the cyclic sweating,duetotheskin pressure effect, if one half of variation in core temperature,eithernychthemerally the body is affected. or seasonally, is maintained within arbitrarily defined limits despite much larger variations in ambient tem- Hemispherical emissivity. → Emissivity, hemispher- perature, i.e., homeotherms regulate their body tem- ical. perature within a narrow range. (Gk. homoio-similar, resembling; therme-heat) Synonym: homoiothermy. Heterothermy: The pattern of temperature regula- Note: A number of homeothermic species may tempo- tion in a tachymetabolic species in which the variation rarily enter states in which their set-range of body tem- in core temperature,eithernychthemerally or sea- perature regulation is not definable or much lower sonally, exceeds that which defines homeothermy. than during their normal state of homeothermy (→ (Gk. hetero-different; therme-heat) heterothermy, hibernation, ). Note: This is an arbitrary term in two : i) because hetero = a difference from (i.e., a difference between Homoiothermy. → Homeothermy. two) rather than a wide range, and ii) because the dis- tinction that is being made between thermostable and Humidity, absolute (γ): Mass of water vapor in air per rather less thermally stable species depends on an arbi- unit volume of air/water vapor mixture. [kg · m–3] trary division. →: 1. poikilothermy (diversified tem- peratures) although etymologically satisfactory has Humidity, relative (φ): The ratio of the mol fraction of already been given a more restricted meaning. 2. steno- water vapor present in a volume of air to the mol frac- thermy (narrow temperature range) and eurythermy tion present in saturated air, both at the same tempera- (wide temperature range) would have suited the cir- ture and pressure; in thermal physiology, the ratio of the cumstance well, but these terms are already in use to saturated vapor pressure at the dew point tempera- describe animals that are able to adjust to narrow ranges ture (Ps, dp) of the enclosure to the saturated vapor and wide ranges respectively, of ambient tempera- pressure at its dry bulb temperature (Ps, db) [ND]. ture. When the relative humidity is expressed as a percent- age, the symbol is RH. Heterothermy, local: The pattern of temperature in those parts of the body which comprises the thermal Hyperpnea, thermal. → Thermal hyperpnea. shell of homeotherms. Hyperthermia: The condition of a temperature regu- Hibernation: The state of winter (sometimes late fall lator when core temperature is above its range speci- or early spring) lethargy with a reduction in body tem- fied for the normal active state of the species. (Gk.

The Japanese Journal of Physiology Vol. 51, No. 2, 2001 257 Glossary of terms for thermal physiology hyper-over; therme-heat) body and/or inactivation of heat conservation and heat Note: Hyperthermia may be regulated (e.g., in fever production by physical and/or pharmacological means. or during dehydration) or may be forced if total heat Note: Induced hypothermia is employed in surgery to production exceeds the capacity for heat loss. reduce the oxygen demand of tissues that are particu- larly sensitive to circulatory arrest. Hyperthermia, induced: The state of hyperthermia produced purposefully by increase in heat load and/or Indirect calorimetry. → Calorimetry, indirect. inactivation of heat dissipation by physical and/or phar- macological means. Induced Hypothermia.→ Hypothermia, induced. Note: Induced hyperthermia is used in a few specific conditions as a therapeutical adjuvant. It may also be Infrared. → Radiant energy. locally induced (e.g., by or organ Note: The infrared wave band is radiant heat. ). Induced hyperthermia should be distin- guished from fever induced by administration of pyro- Insensible heat loss. → Heat loss, insensible. gens, which is an obsolete technique to produce elevations of body temperature in medicine for thera- Insensible perspiration: The mass of water passing peutical purposes. through the skin by diffusion per unit area in unit time. [kg · m–2 ·s–1] Synonym: passive cutaneous water va- Hyperthermia, malignant: A pharmacogenetic my- por exchange. Insensible perspiration represents a opathy characterized by a rapid rise in body tempera- fraction of the insensible water loss. ture in genetically susceptible subjects during Note: Hitherto, rates of insensible perspiration and of anaesthesia (triggering agents: halothane, succinyl cho- sweating have been expressed most commonly in [g · line, etc.). Malignant Hyperthermia stems from im- m–2 ·h–l], but this does not conform with SI conven- pairment (genetically originated) in the sarcoplasmic tions. The most convenient SI term appears to be [mg · reticulum, leading to alteration in handling of the ex- m–2 ·s–1](3.6g·m–2 ·h–1 =1mg·m–2 ·s–1). cess cytosolic Ca++, rigidity and spas- ticity and, in-turn, increased heat production.The Insensible water loss: The sum of the water lost by dif- often fatal hyperthermia is the result of heat produc- fusion through the skin and water lost in , and tion in skeletal muscle and supported by the limitations excluding any water excreted (e.g., in sweat, urine, fe- of active heat dissipation during anaesthesia. It is com- ces). [kg · s–1]or[kg·m–2 ·s–1]Lossofwaterasvapor plicated by sympathetic activation, excessive lactate implies loss of heat according to the latent heat of va- production and , muscle rigidity, myoglobin- porization of water. aemia, and disturbances of cellular permeability. Note: Restricting the term water to its state as a fluid is obsolete, as is the designation of water loss as insensi- Hypothermia: The condition of a temperature regu- ble if it is lost as water vapor. However, the term insen- lator when core temperature is below its range speci- sible water loss is still used, mainly in the literature fied for the normal active state of the species. (Gk. pertaining to farm animals. In thermal physiology its hypo-beneath; therme-heat). use should be avoided because of possible confusion Note: Hypothermia may be regulated (e.g., Torpor, with insensible heat loss; passive evaporative water Hibernation)ormaybeforced if heat loss exceeds the loss should be considered as an alternative term. capacity for total heat production. Insulation. → Thermal resistance. Hypothermia, accidental: The condition of a temper- ature regulator following an accidental or deliberate Interleukin-1 (IL-1): Heat labile proteins produced by im- decrease in core temperature below its range specified mune cells (e.g., mononuclear phagocytes) when activated for the normal active state of the species. The condition by or their products. There are two forms usually occurs in a cold environment and is associated of IL-1 (α and β). The production of interleukin-1 (IL-1) is with an acute problem, but without primary caused by infection, injury and trauma. It (as well as other of the temperature regulating system. cytokines) produces the acute phase response. IL-1 is con- sidered an important endogenous pyrogen, as are interleu- Hypothermia, induced: The state of hypothermia kin-6 (IL-6), tumor necrosis factor α (TNF α),andsome produced purposefully by increasing heat loss from the other cytokines.

258 The Japanese Journal of Physiology Vol. 51, No. 2, 2001 Glossary of terms for thermal physiology

Interthreshold zone. → Thermoeffector threshold Mass transfer, convective: The transport by convec- zone. tion of one component of a nonreactive mixture (usu- ally air-water) across an interface caused by a (E): The radiant flow incident on or pass- concentration gradient often accompanied by a trans- ing through unit area of a surface. [W · m–2] formation of phase and by a simultaneous transfer of heat. Katathermometer: An instrument which measures the heat flow from a surface to a cooler environment. Mass transfer rate (m):· The rate of transfer of mass. [kg · s–1] Latent heat of fusion: The quantity of heat absorbed, or released, in the reversible change of state, or Maximum metabolic rate. → Metabolic rate, maxi- freezing, of unit mass of solid or , without change mum. of temperature. [J · g–1] Note: The melting of 1 g of ice to water at 0°C absorbs Maximum oxygen consumption. → Oxygen con- 333.15 J. sumption, maximum.

Latent heat of vaporization (λ or LHV): The quantity Mean body temperature. → Temperature, mean of heat absorbed (or released) by a volatile substance body. (fluid) per unit mass in the process of its reversible change of state by evaporation (or condensation) under Mean radiant temperature. → Temperature, mean isobaric and isothermal equilibrium conditions. [J · g–1] radiant. Note: For water: λ = 2490.9 – 2.34 T, with T = temper- ature of water in °C, e.g., l g of water, when changing Mean skin temperature. → Temperature, mean from fluid to vapor at T = 34°C, absorbs 2411.3 J. skin.

Least observed metabolic rate. → Metabolic rate, Menopausal hot flush (flash): An abrupt heat dissipa- least observed. tion response, provoked or unprovoked, occurring in hypoestrogenic women following the decline of ova- Lower critical temperature. → Critical tempera- rian function. The response typically lasts about 5 min- ture, lower. utes and consists of peripheral , sweating and reports of intense warmth. Lower temperature survival limit. → Temperature survival limit, lower. Met: An assigned unit of measurement to designate "sitting-resting" metabolic rate of man. Malignant hyperthermia. → Hyperthermia, malig- nant. 1 met = 58.15 W · m–2 =50kcal·h–1 ·m–2

Mass diffusivity. → Diffusivity, mass. It is an empirical unit of measurement to express the metabolic rate (M or MR) ofamanwhoseclothinghas Mass transfer coefficient (diffusion) (hD): Therateof an insulative value of 1 clo when he is sitting at rest in mass transfer (m)· from a vaporizing liquid (usually wa- comfortable indoor surroundings (21°C). ter) to a moving gas (usually air) in contact with it, per unit area (A) of the liquid surface and per unit differ- Metabolic body size: The function of an animal's body ence between the vapor density (saturated) at the sur- size to which standard metabolic rate (SMR) (or face (pws) and the vapor density of the ambient gas basal metabolic rate (BMR)) is directly proportional. (pwa), expressed in the equation Synonym: metabolically effective body mass. Note: Metabolic body size is often calculated using · –1 –1 –1 b hD = m·A (pws – pwa) [m · s ] body mass raised to a power (W ) as in the expression M=aWb. That the resting metabolic rate (RMR) of → heat transfer coefficient, evaporative; mass adult animals (both tachymetabolic and bradymeta- transfer rate. bolic) changes in proportion to the 3/4 power of body mass is an empirically established fact, and the use of

The Japanese Journal of Physiology Vol. 51, No. 2, 2001 259 Glossary of terms for thermal physiology

W3/4 as the metabolic body size permits comparisons Metabolic rate (M or MR): = metabolic energy to be made between the metabolic levels of different transformation.[W],[W·m–2], [W·m–3], [W·kg–l], animals. When W2/3 is used, this implies proportional- [W·kg–3/4] The rate of transformation of chemical en- ity of metabolic body size to the animal's surface area ergy into heat and mechanical work by aerobic and (→ surface rule). The relation between metabolic rate anaerobic metabolic activities within an organism, usu- (M or MR) and body size (M = aW3/4) is a particular ally expressed in terms of unit area of the total body case of the general allometric equation (y = axb)which surface, i.e., as a heat flux. The quantity M in the body says that plotting a biological variable, y, against an- heat balance equation. other biological variable, x, after logarithmic transfor- Note: Metabolic energy transformation may not all mation (i.e., log y = log a + b · log x) will result in a result from aerobic metabolic activities and may there- straight line with slope b. Ref: von Bertalanffy, L., Hel- fore exceed that indicated by the rate of oxygen con- goländer Wiss. Meeresuntersuch. 9: 5, 1964. sumption. Part of the metabolic energy transformation maybeusedtodoworkonanexternal Metabolic energy production. → Metabolic energy system, and therefore the rate of heat production may transformation. be less than the metabolic energy transformation. Terms in the body heat balance equation are often ex- Metabolic energy transformation (M). → Metabolic pressed as quantities of energy perunitsurfacearea rate. and per unit time [W · m–2], because heat exchange is a function of area. Metabolic rate (M or MR) is given as Metabolic heat production (H): Rate of transforma- the total energy production in the organism in unit time tion of chemical energy into heat in an organism, usu- [W] or often as the energy production per unit mass of ally expressed in terms of unit area of the total body tissue in unit time [W · kg–1]. For comparison of meta- surface (→ total body area). H is equal to M–(W)in bolic rates of animals of different body sizes, meta- the body heat balance equation.[W·m–2], [W · kg–1] bolic rate (M or MR) is usually related to (body or [W] mass)3/4 (→ metabolic body size). Note: During positive work rate (+W)orintheab- sence of work (W =0)metabolic heat production (H = Metabolic rate, basal (BMR): metabolic energy M–(+W)), i.e. positive work rate subtracted from the transformation calculated from measurements of heat rate of metabolic energy transformation (=meta- production or oxygen consumption in an organism in a bolic rate), equals total heat production.Whenwork rested, awake, fasting* sufficiently long to be in is being done on the body by an external source (nega- post-absorptive state, and thermoneutral zone (a par- tive work), total heat production is the sum of meta- ticular case of standard metabolic rate (SMR)).[W], bolic rate (M or MR) (which is equal to metabolic heat [W · m–2], [W · m–3], [W · kg–1], [W · kg–3/4] production in this condition) and the heat liberated Note: In these conditions, when the amount of work be- within the body due to negative work (M–(–W)). ing done on an external system is negligible, the rate of heat production is equal to the rate of metabolism Metabolic level: The metabolic heat production (metabolic energy production).*Theperiodoffast- measured under standard conditions (→ metabolic ing needs to be specified as this may be for days in large rate, standard (SMR)) during a 24-h period divided by animals, and for much shorter periods for very small the metabolic body size.[kJ·kg–3/4· (24 h)–1]* mammals and birds. Note: *1 kJ . kg–3/4 ·(24h)–l = 0.2388 kcal · kg–3/4 ·(24 h)–l. Metabolic levels are approximately constant Metabolic rate, lowest observed (LOMR): The lowest within phylogenetic groups but may vary between observed rate of metabolism during specified periods groups. For example, mammalian and avian species of minimum activity. [W], [W · m–2], [W · kg–1], [W · (tachymetabolism)havehighermetabolic levels than kg–3/4] → metabolic rate, minimum observed other species (bradymetabolism), while the metabolic (MOMR). The rationale and objective of lowest ob- levels of birds are apparently higher than those of mam- served metabolic rate (LOMR) and minimum ob- mals, and those of prototherian () and met- served metabolic rate (MOMR) are identical: to atherian (marsupial) mammals are lower than those of measure the metabolic rates of small and wild animals eutherian (placental) mammals. during periods of minimal activity as the nearest that (Poczopko, 1971). Ref: Poczopko, P., Acta Theriolog- can be made to a measurement of a standard meta- ica 16: 1, 1971. bolic rate (SMR).

260 The Japanese Journal of Physiology Vol. 51, No. 2, 2001 Glossary of terms for thermal physiology

Note: There are small but significant differences in [W], [W· m–2], [W · m–3], [W · kg–1], [W · kg –3/4] technique: Minimum observed metabolic rate Note: A particular case of standard metabolic rate (MOMR) is the average metabolic rate (M or MR) (SMR) used when the subject cannot be brought to a during periods of minimum activity; lowest observed fasting condition, e.g., ruminant animals. The period of metabolic rate (LOMR) is the lowest recorded meta- food deprivation should be stated. bolic rate (M or MR) during periods of minimum ac- tivity. Such brief low values may be influenced by Metabolic rate, standard (SMR): metabolic energy physical characteristics of the . transformation calculated from measurements of heat Note: lowest observed metabolic rate (LOMR) may production or oxygen consumption in an organism un- be lower than basal metabolic rate (BMR) (e.g., dur- der specified standard conditions*. [W], [W · m–2], [W ing some stages of sleep). ·m–3], [W · kg–1], [W · kg–3/4] Note: The conditions are usually such that the amount Metabolic rate, maximum (MMR): The highest met- of work being done on an external system is negligible. abolic rate (M or MR) during a specified period of The rate of heat production is then an acceptable index work compatible with sustained aerobic metabolism of the rate of metabolism. * The specified standard con- (i.e., when there is no progressive accumulation of lac- ditions are usually that the organism is rested (or as near tic acid in the blood). [W], [W · m–2], [W · m–3], [W · to rested as is possible), fasting (if possible), awake, kg–1],[W · kg–3/4] and in a thermoneutral environment. The extent to Note: There may be some confusion between maxi- which standard conditions can be achieved varies with mum and peak metabolic rates (PMR).Bothtermsin- species. → Metabolic rate, minimum observed dicate maximum rates. The distinction is in usage: (MOMR). maximum relates to work, peak relates to cold expo- sure. The terms should also be distinguished from max- Metabolic rate, summit. → Metabolic rate, peak. imum oxygen consumption. Metabolic scope. → Scope, metabolic. Metabolic rate, minimum observed (MOMR): Aver- aged metabolic rate during specified periods of mini- Metabolically effective body mass: → metabolic mum activity. [W], [W · m–2], [W · m–3], [W · kg–l], [W body size (preferred synonym). ·kg–3/4] Note: The term metabolically effective body mass Note: The metabolic rate (M or MR) of small animals may be wrongly understood to be that part of the body in particular, but also of larger wild animals, cannot be mass which is metabolically active in contrast to a part measured under basal or other standard conditions (→ that is metabolically inert. Its use should be avoided. metabolic rate, basal (BMR),andmetabolic rate, standard (SMR)). A practical solution to the problem Metabolism. → Metabolism, energy. (Gk. metab- is to measure metabolic rate (M or MR) continuously ole-change) and accept the average metabolic rate (M or MR) dur- Note: Metabolism is a general term which relates to ing periods of minimum activity as the best possible es- chemical and physical changes occurring in living or- timate of standard metabolic rate (SMR). ganisms. In thermal physiology metabolism invariably relates to the transformation of chemical energy into Metabolic rate, peak (PMR): The highest metabolic work and heat. In other divisions of physiology the rate (M or MR) that can be induced in a resting animal term is used in relation to other changes in state of by any cold environment. [W], [W · m–2], [W · m–3], chemical energy (e.g., from storage compounds to [W · kg–l], [W · kg–3/4] Synonym: summit metabolic readily available compounds, including the energy rate. → Metabolic rate, maximum (MMR). transferring polyphosphates, and vice versa), or to turn- Note: Although summit metabolic rate (SMR) is now an over of material between different states (e.g., accepted term, peak metabolic rate (PMR) is prefera- salts from ionized to solid, and vice versa). ble because the abbreviation SMR is indistinguishable from that for standard metabolic rate (SMR). Metabolism, anaerobic: Transformation of matter and energy without uptake of oxygen. Metabolic rate, resting (RMR): The metabolic rate (M or MR) of an animal that is resting in a thermoneu- Metabolism, energy: The sum of the chemical tral environment but not in the postabsorptive state. changes in living matter in which energy is trans-

The Japanese Journal of Physiology Vol. 51, No. 2, 2001 261 Glossary of terms for thermal physiology formed. (Gk. metabole-change) → metabolism. mogenesis, nonshivering (obligatory).

Microwave: Part of the with Operative temperature. → Temperature, operative. wavelength from 1 to 100 mm. are ab- sorbed by metal and water and thus permit deep heating Optimal body temperature range: The range of body of aqueous or metallic bodies exposed to them (→ ra- temperatures in which a species carries out its normal diant energy). daily activity. Note: This “ecological optimum” integrates internal Minimum observed metabolic rate. → Metabolic and external forces acting on a species; it applies rate, minimum observed. mostly to . · Natural convection. → Convective heat transfer. Oxygen consumption, maximum (VO2max): The maximum rate at which an organism can take up oxy- Negative work. → Work rate, negative. gen. [ml · s–1], conventionally [ml · min–1], [l · min–1] Note: Determination of this parameter requires very Neuroleptic malignant syndrome: The development high motivation of the subject and can probably be of severe muscle rigidity, elevated core temperature, done only on humans. Criteria used to show that a hu- · and a disturbance of mental status associated with the man subject has reached the VO2max although not as yet use of neuroleptic medication. agreed upon, include an indication of no further in- crease in oxygen uptake during further increase in work Nocturnal: Occurring during the nighttime, as distinct load. from daytime. (L. nocturnus adj < nox-night) Antonym: diurnal. P 32000 polypeptide. → UCP1

Nonevaporative heat loss. → Heat loss, nonevapora- Panting, thermal. → Thermal panting. tive. Partitional calorimetry. → Calorimetry, partitional. Non-freezing cold injury (NFCI): Tissue damage re- sulting from prolonged exposure to ambient tempera- Passive cutaneous water exchange: The passage tures between 15°C down to –0.5°C. In NFCI the through the skin in either direction of water down an os- normal thermoregulatory responses of the injured body motic gradient per unit area in unit time. [kg . m–2 ·s–1], are disturbed. All types of tissue may be damaged by also [mg · m–2 ·s–1] sustained cooling, but the most serious effects occur in Note: Passive cutaneous water exchange occurs only the nerves and blood vessels. Antonym: Freezing cold when the skin is covered with water or an aqueous so- injury (FCI). lution.

Nongenetic adaptation. → Adaptation, phenotypic. Passive cutaneous water vapor exchange: The pas- sage through the skin in either direction of water vapor Nonshivering thermogenesis. → Thermogenesis, down a water vapor pressure gradient per unit area in nonshivering. unit time. [kg · m–2 ·s–1], also [mg · m–2 ·s–1]. Syn- onym: insensible perspiration. Nonthermal sweating. → Sweating, nonthermal. Passive temperature lability. → Temperature labil- Normothermy. → Cenothermy. ity, passive.

Nychthemeral: Relating to an exact period of 24 h. Peak metabolic rate. → Metabolic rate, peak. (Gk. nux-night; hemera-day). Phenotypic adaptation. → Adaptation, phenotypic. : A period of 24 h, consisting of a day and a night (SOED). Physical temperature regulation. → Temperature regulation, physical. Obligatory nonshivering thermogenesis. → Ther-

262 The Japanese Journal of Physiology Vol. 51, No. 2, 2001 Glossary of terms for thermal physiology

Physical thermoregulation. → Temperature regula- attributed the letter H [W]. tion, physical. Note: All quantities in the so-called body heat balance equation constitute power (either heat flow or work Physiological temperature regulation. → Tempera- rate). For convenience, they may be expressed in [W], ture regulation, physiological. in [W · m–2], in [W · m–3], or in [W · kg–1].

Physiological thermoregulation. → Temperature Preferred ambient temperature: The range of ambi- regulation, physiological. ent temperature, associated with specified radiation intensity, humidity, and air movement, from which an Piloerection: Involuntary bristling of hairs or ruffling unrestrained human or animal does not seek to move to of feathers; in thermal physiology an autonomic ther- a warmer or colder environment. [°C] moeffector response often associated with behavioral (e.g., postural) adjustments. Preferred body temperature: The range of core tem- perature within which an ectothermic animal seeks to Poikilothermy: Large variability of body temperature maintain itself by behavioral means. [°C] as a function of ambient temperature in organisms without effective autonomic temperature regulation. Pressure (P): The force exerted per unit area. [Pa, , As a rule, bradymetabolism implies poikilothermy Torr] A liquid or gas enclosed in a container will exert with only temporary exceptions in some species (e.g., an uniform pressure on its walls, if the influence of active warming-up of insects before flight). Synonym: gravitational forces is excluded or of little importance Temperature conformer. Tachymetabolism excludes as in case of . poikilothermy, except in pathological conditions (im- Note: The SI-derived unit of pressure is the Pascal (Pa), pairment of temperature regulation), but permits het- which is defined as a per square meter (N·m–2). erothermy or torpor to occur in a number of species. An alternate SI-derived unit of pressure is the bar (bar) (Gk. poikilos-changeful, diversified; therme-heat) Ant- defined as 105 Pa. The unit of pressure currently ap- onym: homeothermy. proved by the International Commission of the IUPS Note: For ectothermic organisms without effective for Respiratory Physiology is the Pascal [Pa] which is thermoregulatory behavior, poikilothermy is synon- synonymous with the pressure unit mmHg (an obsoles- ymous with temperature conformity. Poikilo- is in- cent unit). One Torr is equal to 1.33322 millibars or consistent with other uses of this root in biology; it 133.322 Pa. should, perhaps, be poecilo- or pecilo-; cf. poeciloblast, poecilocyte (OED). Pressure, atmospheric (P): The pressure due to the weight of the as indicated by a . Polypnea, thermal. → Thermal polypnea. Standard is the pressure 101.325 kilopascals (kPa) (or the weight of a 760 mm Positive work. → Work, positive. column of at 0°C with density 13.5951 × 103 kg · m–3 under standard of 9.80665 m · s–2)and Postprandial (excess) heat production. → Heat pro- is equivalent to 1,013.25 millibars or to 760 Torr. duction (excess), postprandial. Pressure, water vapor (Pw): Thepressureexertedby Potohidrotic response: The instantaneous intense water vapor. If water vapor is confined over its liquid so sweating appearing when hyperthermic dehydrated that the vapor comes into equilibrium with the liquid, humans drink. (Gk. poto-drink; hidro-sweat). and the ambient temperature Ta of the medium is held constant, the vapor pressure approaches a maximum Power (W): Physically power [W] is energy per time value called the saturated vapor pressure (Ps,Ta)or unit. In the case of mechanical energy per time unit it is (Psa). The term vapor pressure (water) is always syn- called mechanical power or, particularly in thermal, onymous with a saturated vapor pressure at a temper- sports and occupational physiology, work rate and at- ature T. [Pa, millibar, Torr] tributed the letter W. Note: The water vapor pressure (→ vapor pressure Note: W, e.g., in the heat balance equation,iswork (water)) of an enclosure may be calculated from the rate in [W] and not work in [Ws = J]. In the case of ther- observed wet bulb and dry bulb temperatures and the mal energy (heat) per time unit it is called heat flow and atmospheric pressure, by using standard steam or mete-

The Japanese Journal of Physiology Vol. 51, No. 2, 2001 263 Glossary of terms for thermal physiology orological tables and (Ref: Chambers, A.B., A Temperature and Life, Berlin-Heidelberg-New York, psychrometric chart for physiological research, J. Appl. Springer, 1973, p. 17 ff.). Physiol. 29: 406–412, 1970). The water vapor pressure in an enclosure is equal to the saturated vapor pres- Radiance (Le): Radiance at a surface element (dA) of sure at its dew-point temperature (Ps,Tdp)ortothe a source or receiver is the (dI) from product of the relative humidity (N) and the saturated direction θ divided by the orthogonal projection of this θ vapor pressure at its dry bulb temperature (NPs,Tdp). surface element (dA ·cos ) on a plane perpendicular to the direction θ. θ is the angle between the normal to the Projected area. → Area, projected. element (dA) of the source or receiver and the direction of the observation. [W · sr–1 ·m–2] Pyrexia: The condition of being febrile. Note: Pyrogen: The generic term for any substance Radiance thermal (Le,th): radiance due to thermal ra- whether exogenous or endogenous that causes fever diation. [W · sr–1 ·m–2] when introduced into or released in the body. (Gk. pur-;

Pyrogen, exogenous: A substance which, when enter- Microwave 1–100 mm ing the inner environment of a multicellular organism (host) will cause fever. Stimulation of the production Radiant energy, spectral (Qλ): The radiant energy and/or release of endogenous pyrogens is, at least in per unit wave length interval at wavelength λ.[J·nm–1] most instances, the humoral effect from which fever ul- timately results. Radiant exitance (Me): The radiant flux leaving an Note: The most potent exogenous pyrogens are element of a surface. This quantity includes radiation heat-stable lipopolysaccharides intrinsic to the cell emitted, reflected, and transmitted by the surface. walls of gram-negative bacteria (→ endotoxin). Many φ θ Ω –2 exogenous pyrogens of different molecular composi- Me =d e/dA = ∫ Le ·cos ·d [W · m ] tion exist; they comprise compounds intrinsic to bacte- ria, , fungi, mycobacteria, and some protozoa, as Note: The name radiant emittance previously given to well as foreign proteins and some . this quantity is abandoned because it has given rise to confusion. Thus, the term emittance is used to desig-

Q10: The ratio of the rate of a physiological process at nate either the flux leaving a surface whatever the ori- a particular temperature to the rate at a temperature gin (emitted, reflected, or transmitted), or the flux 10°C lower, when the of the rate is an ap- emitted by a surface (originating in the surface), or a proximately linear function of temperature (Ref. Pre- quantity without dimensions similar to emissivity but cht, H., J. Christophersen, H. Hensel, & W. Larcher. applicable only to a specimen.

264 The Japanese Journal of Physiology Vol. 51, No. 2, 2001 Glossary of terms for thermal physiology

Radiant exitance, self (Me,s): The radiant flux emit- Radiant intensity, spectral (Iλ): The radiant inten- ted by a surface. The flux considered does not include sity per unit wave length interval. [W · sr–1 ·nm–1] reflected or transmitted flux. [W · m–2] Radiation . → Reflectance, radiation. Radiant exitance, thermal (Me,th): The radiant flux emitted as by a surface. Radiation shape factor (Fij): A dimensionless quan- Note: In the case of a full radiator,theradiance (Le)is tity expressing the fraction of the diffuse energy emit- uniform in all directions. In consequence, when the ted by a surface (or a source), denoted by the subscript solid angle is measured in steradians, the radiant exi- i, that is received by another surface, denoted by the π tance has the numerical value Me =4 Le. subscript j, visible by it and in known geometric rela- tion with it. Synonym: radiation view factor. Radiant field, effective. → Radiant flux, effective. Radiation . → Transmittance, radia- Radiant flow (φ): The amount of radiant energy per tion. . [W] Radiation view factor. → Radiation shape factor. Radiant flow spectral (φλ): The radiant flow per unit wavelength interval at wavelength λ.[W·nm–1] Radiative heat transfer coefficient. → Heat transfer coefficient, radiative. Radiant fIux (dφ/dA): The radiant flow per unit area. [W · m–2] Radiative (linear) heat transfer coefficient. → Heat Note: The radiant flux emitted by a surface is the ther- transfer coefficient, radiative (linear). mal radiant exitance. The radiant flux incident on or passing through an area is the irradiance. Radiator: An emitter of radiant energy.

Radiant flux, effective (Hr): The net radiant flux ex- Radiator, full: A radiator of uniform surface temper- changed with all enclosing surfaces and with any in- ature whose radiant exitance in all parts of the spec- tense directional sources and sinks for exchange of trum is the maximum obtainable. The emissivity of a radiant heat by a human or human-shaped object whose full radiator is unity for all . Synonym: surface temperature is hypothetically at ambient air blackbody. temperature.[W·m–2] Note: If the same object, with surface temperature at Radiator, graybody: A radiator whose spectral ambient air temperature, is assumed to exchange ra- emissivity is less than unity, at least in the waveband diant heat at a given effective radiant flux with a hy- for thermal radiation (3–30 µm), but is the same at all pothetical black surface enclosure of corresponding wavelengths. wall temperature, then this condition defines the effec- tive radiant field transferring the amount of heat per Radiator, selective: A radiator with a spectral emis- unit time and per unit surface of the object which is sivity less than unity which varies with wavelength. quantified by the effective radiant flux.Inthissense, Note: Human and animal have high effective radiant field and effective radiant flux are in the waveband 3–30 µm but not between 0.7 and 3 synonymous terms. µm.

Radiant heat exchange (R): The net rate of heat ex- Reflectance, radiation (p): The ratio of the radiant change by radiation between an organism and its envi- flux reflected by a surface or medium to the incident ronment, usually expressed in terms of unit area of the flux. total body surface, i.e., as a heat flux. The quantity (R) Note: Measured values of reflectance depend upon the in the body heat balance equation where (–R)=heat angles of incidence and view and the spectral character gain and (+R) = heat loss. [W] or [W · m–2] of the incident flux; these factors should be specified.

Radiant intensity (I): The radiant flow proceeding Regulation: The processes by which a biological sys- from a source per unit solid angle in the direction con- tem stabilizes variables, generally by information loops sidered. [W · sr–1] ( control). The regulated (controlled)

The Japanese Journal of Physiology Vol. 51, No. 2, 2001 265 Glossary of terms for thermal physiology physiological variables can usually be described as a Selective brain cooling: Lowering of brain tempera- function of physical variables. In the case of changes of ture, either locally or as a whole, below aortic (arterial a regulated variable due to external or internal interfer- blood) temperature. Cool venous blood returning from ence, the processes of regulation will alter certain cephalic heat dissipating surfaces acts as a heat sink, ei- bodily functions, the effectors in the regulatory process, ther for brain tissue directly or for arterial blood supply- which act to minimize the deviations of the regulated ing brain tissue. Special vascular arrangements, e.g., variable from its set-point. the ophthalmic or carotid retia mirabilia, support arte- Note: In thermal physiology, core temperature is often rio-venous heat exchange underlying selective brain considered as the regulated variable in homeothermic cooling. Its existence in many species has been proven, species, because its changes are most effective in acti- but the situation in humans is still debated. vating the thermoeffectors of heat production, heat conservation, or heat loss in such a way that deviations Sensible heat loss. → Heat loss, dry. of core temperature are minimized. Mean body tem- perature, if representing the weighted contributions of Set-point: The value of a regulated variable which a core and shell temperatures to the entire thermal infor- healthy organism tends to stabilize by the processes of mation, may be a better estimate of the regulated vari- regulation. It is found in the condition when the effec- able. tor activities tending to counteract alterations of the regulated variable are minimal. With thermal load Relative humidity. → Humidity, relative. present, the regulated variable, due to proportional con- trol, does not stabilize at, but near the set-point.Inhy- Resistance, thermal. → Thermal resistance. per- or hypothermia, body temperature deviates substantially from the set-point, mostly because of in- Respiratory evaporative heat loss (REHL): Rate of sufficient capacity and thereby lack of stabili- heat dissipated by exhalation of air saturated with water zation. In biological systems, the apparent set-points of vapor, [W], [W·m–2], [W·m–3], [W·kg–1]. many regulated variables may change with time, either Note: Respiratory evaporative heat loss (REHL) periodically or temporarily (e.g., nychthemerally, an- comprises a passive (obligatory) fraction associated nually, with the ovulatory , or in connection with with normal breathing and, in many animals, a regula- other physiological events). In temperature regula- tory fraction which depends on the rate at which the wa- tion the set-point may change temporarily, due to inter- ter vapor dissipating respiratory surfaces are ventilated ference with the regulations of nonthermal variables (e.g., during thermal tachypnea),andonsurfacetem- (e.g., in states of dehydration and starvation, etc.), or perature depending on circulatory convection (→ due to pathological, nonthermal influences (e.g., in fe- convection, circulatory) transferring heat to these sur- ver or anapyrexia). Also, the processes of accli- faces. Net dissipation of evaporated water and, conse- mat(izat)ion and adaptation may change the set-point quently, of heat with the exhaled air is possible only as of temperature regulation. Hibernation is a special long as the inhaled air is not saturated with water vapor condition in which the set-point differs distinctly from at the temperature of the moist respiratory surfaces. that existing in the same animal in the state of ceno- thermy. The change of set-point in these processes is Resting metabolic rate. → Metabolic rate, resting. thought to be due to changes in the thermal controller characteristics, particularly changes of thresholds (→ Saliva spreading: The spreading of saliva on the body thermoeffector threshold temperature)and/or surface, often a deliberate (behavioral) thermoeffector changes of thermoeffector gain, which obviously have action to cool the surface by evaporation. Sometimes neuronal correlates, too. inaccurately termed grooming. Note: The term set-point has evoked much confusion, as it has been used for different phenomena: (1) for Saturated vapor pressure. →Pressure, water vapor. steady state of body temperatures (which can be very different in the thermoregulatory system depending on Scope, metabolic: Metabolic rate (M or MR) at max- environmental and internal conditions). (2) for a central imum oxygen consumption divided by least observed reference signal (which obviously does not exist explic- metabolic rate (LOMR). itly in the thermoregulatory system). (3) for thermoef- fector threshold zone of (mean) body temperature, Second phase panting. → Thermal hyperpnea. which is correct only in the non-acclimated and afe-

266 The Japanese Journal of Physiology Vol. 51, No. 2, 2001 Glossary of terms for thermal physiology brile state. In fever (also in acclimat(izat)ion and Originally described as “spezifisch-dynamische other adaptational or periodical processes) the thermo- Wirkung” by Rubner, the term “Wirkung” has been controller characteristics change (particularly effector translated as “action” as well as “effect”. The phenom- threshold), and by this the set-point, which then does enon is assumed to be related to the catabolism of food not fall into the interthreshold zone. With non-exces- stuffs, particularly proteins. (Kleiber, M. TheFireof sive additional thermal load, body temperature stabi- life, Huntington, N.Y., R.E. Krieger Publ. Co., 1976). lizes near this febrile set-point. Note: The term is becoming obsolete, because it cannot be distinguished precisely from other factors that stim- Shape factor, radiation. → Radiation shape factor. ulate metabolic energy transformation in the hours fol- lowing food intake and, with the inclusion of the Shell, thermal: The skin and mucosal surfaces of the specific dynamic effect, account for postprandial (ex- body engaged directly in heat exchange with the envi- cess) heat production. Synonyms: specific dynamic ronment and, in addition, those tissues under these sur- action; diet-induced thermogenesis. faces whose temperatures may deviate from core temperature, due to heat exchange with the environ- Specific heat (c): Thequantityofheatrequiredtoraise ment and to changes in circulatory convection (→ the temperature of unit mass of a substance by one de- convection, circulatory) of heat from the core to the gree . [J · kg–1 ·°C–l] heat exchanging surfaces. Antonym: thermal core. Note: For gases, it is necessary to specify whether the Note: The temperature of the shell of temperature reg- pressure (cp)orthevolume(cv) is held constant during ulators depends on ambient temperature, heat loss to its determination. The specific heat of body tissue is the environment, and on rate and geometry of blood usually taken to be 3.48 kJ · kg–1 ·°C–1 (i.e., 0.83 kcal flow to and from the skin. ·kg–1 ·°C–1). Ref: Schafer, E.A., Textbook of Physiol- ogy, London: Hodder & Stoughton, 1898, vol. I, p. 838. Shivering: Involuntary tremor of skeletal muscles as a thermoeffector activity for increasing metabolic heat Specific heat, volumetric: The product of the density production (→ thermogenesis, shivering). Its elec- ρ of a material and its specific heat.[J·°C–1 ·m–3] tromyographically distinct pattern of motor unit dis- charges may be quantified as the integrated voltage (V) Spectral emissivity. → Emissivity, spectral. deflections per unit time (t): Σ(∆V·∆t)·t–1·[V].(→ ther- moregulatory muscle tone). Spectral radiant energy. → Radiant energy, spec- tral. Sickness behavior: A group of signs or symptoms which accompany cytokine-producing events (e.g., in- Spectral radiant flow. → Radiant flow, spectral. fection), usually with the elevation of body tempera- ture. The behaviours include, among others, loss of Standard atmospheric pressure. → Pressure, atmo- , lethargy, depression and decreased motor ac- spheric. tivity, and are thought to be mediated by the action of cytokines, not necessarily those which mediate the rise Standard metabolic rate. → Metabolic rate, stan- in body temperature, as a result of the infection. dard.

Skin pressure effect on sweating: The inhibition of Steady state: The state of body heat balance in which sweating in the dermatomal area of skin when mechan- there is no positive or negative heat storage when heat ical pressure is locally applied (→ hemihidrotic re- gain and heat loss between the body and the environ- sponse). ment are equivalent. The body temperatures reached in a steady state depend on the extent of external or inter- Skin wettedness. → Wettedness, skin. nal thermal load. If the thermoeffector capacities are exceeded due to excessive load or pathological pro- Solar radiation area. → Area, solar radiation. cesses, a steady state will not be reached, leading to Specific dynamic action. → Specific dynamic effect. hypo- or hyperthermia.

Specific dynamic effect: Temporary increase in meta- Stefan-Boltzmann law: The thermal radiant exi- bolic energy transformation following food intake. tance of a full radiator is proportional to the fourth

The Japanese Journal of Physiology Vol. 51, No. 2, 2001 267 Glossary of terms for thermal physiology

σ 4 power of its absolute temperature, Me,th = T .Thecur- Sweating, thermal: A response of the sweat to rently recommended value of the Stefan-Boltzmann a thermal stimulus. Rate [mg · m–2 ·s–1] constant (σ)is5.6696× 10–8 [W · m–2 ·K–4]. Note: 1mg·m–2 ·s–1 =3.6g·m–2 ·h–1.

Stenothermy: Descriptive of organisms, which occur Sweating topography, thermal: The sequence of the naturally in a narrow range of environmental tempera- onset of thermal sweating and the differences in sweat tures and which, singly or collectively, are intolerant of rate observed between different skin regions. or accommodate ineffectually to wide changes in their thermal environment. (Gk. stenos-narrow; therme- Tachymetabolism: The high level of basal metabo- heat) Antonym: eurythermy. lism of birds and mammals relative to those of reptiles and other nonavian and nonmammalian animals of the Storage of body heat (S): Therateofincrease(+)or same body mass and at the same tissue temperatures. decrease (–) in the heat content [Ws = J] of the body (Gk. takhus-fast; metabole-change) Synonym: caused by an imbalance between heat production (met- warm-blooded. Antonym: bradymetabolism, abolic heat transformation)andheat loss, usually ex- cold-blooded. pressed in terms of unit area of total body surface (→ Note: This relatively high level of basal metabolism in Area, total body). The quantity S in the body heat bal- mammals and birds is a precondition for the relative ance equation.[W],[W·m–2], [W · m–3]or[W·kg–1]: stability of core temperature during exposure to cold (warm-blooded)andofendothermic homeothermy Stress fever: A rise in body temperature due to expo- and heterothermy. sure of a person or an animal to a psychological stres- sor. Synonym: Stress hyperthermia. Tachypnea, thermal. → Thermal tachypnea.

Stress hyperthermia. → Stress fever. Temperature: A measure of the mean of the in a volume. Sunstroke: An acute and dangerous reaction to heat exposure caused by a failure of the heat regulating Temperature, ambient (Ta): The average temperature mechanisms of the body. It is characterized by high of a gaseous or liquid environment (usually air or wa- core temperature, usually above 40.6°C, cessation of ter) surrounding a body, as measured outside the ther- thermal sweating; headache, numbness, tingling and mal and hydrodynamic boundary layers that overlay the confusion prior to sudden or , fast , body. [°C] Synonym: temperature, dry bulb (in a gas- rapid and elevated . eous environment).

Surface area. → Area, total body, and area DuBois Temperature coefficient: The ratio between the (for humans only). change in any temperature dependant activity and the defined temperature range within which this change oc- Surface rule: A statement that the basal metabolic curs. rate (BMR) is proportional to the 2/3 power of body mass. Temperature conformer: An organism, the core tem- Note: The rule is based on the proposition that basal perature of which varies as a proportional function of metabolic rate (BMR) is related to surface area and ambient temperature; an animal without effective that surface area varies with the 2/3 power of body temperature regulation by autonomic or behavioral mass. However, this is not experimentally verifiable, means. Synonym: poikilothermy. Antonym: tempera- for when basal metabolic rate (BMR) is expressed per ture regulator. 2/3 power of body mass it increases systematically with body size (Kleiber, 1947). Basal metabolic rate Temperature conformity: The thermal relation be- (BMR) is more nearly proportional to the 3/4 power of tween the environment andanorganism,thecore tem- body mass (→ metabolic body size). Ref: Kleiber, M., perature of which varies as a proportional function of Physiol. Rev. 27: 411, 1947. ambient temperature, i.e., an absence of effective temperature regulation by autonomic or behavioral Sweating, nonthermal: A response of the sweat means. glands to a nonthermal stimulus.

268 The Japanese Journal of Physiology Vol. 51, No. 2, 2001 Glossary of terms for thermal physiology

Temperature, core: Ideally, the mean temperature of thermolability, passive. the thermal core. In practice it is represented by a specified core temperature, usually rectal or (in hu- Temperature, mean body (Tb): (1) Ideally, the sum of mans) sublingual temperature. More reliable in condi- the products of the heat capacities (ci ·mi)andtemper- tions of changing core temperature are esophageal (at ature (Ti) of all tissues of the body divided by the total the cardia) or aortic (arterial blood) temperature. heat capacity of the organism: Note: Brain temperatures are core temperatures.They Σ Σ may differ regionally within the brain or from other Tb = (ci ·mi ·Ti)/ (ci ·mi). core temperatures outside of the brain, due to selec- tive brain cooling, which directly influences brain (2) The total temperature signal generated by all ther- temperature, locally or as a whole, in a number of spe- mosensors distributed in the core and shell. (2) should cies. be different from (1). For discussion, see Minard, D., In: Physiological and Behavioral Temperatuve Regula- Temperature, deep body. → Temperature, core (pre- tion,editedbyJ.D.Hardy,A.P.Gagge,&J.A.J.Stol- ferred synonym). wijk, Springfield, I11., Thomas, 1970, p. 345. Mean body temperature often is estimated approxi- Temperature dependence: The influence of the local mately from measurements of a representative core temperature upon the rate of all molecular transforma- temperature (Tc)andmean skin temperature (Tsk) tions and thereby upon practically all cellular and phys- according to: → iological processes. Q10. Tb =al ·Tc +a2 ·Tsk,withal +a2 =1, Temperature, dew-point (Tdp): The temperature at which condensation first occurs when an air-water va- in which the factors al and a2 represent the empirically por mixture is cooled at constant pressure. [°C] determined contributions of thermal core and shell to mean body temperature. Temperature, dry bulb (Tdb): The temperature of a gas or mixture of gases indicated by a Temperature, mean radiant (Tr): The temperature of shielded from radiation. [°C] Synonym: temperature, an imaginary isothermal "black" enclosure in which a ambient. solid body or occupant would exchange the same amount of heat by radiation as in the actual nonuniform Temperature, effective (Teff): An arbitrary index enclosure. [°C] which combines in a single value the effect of temper- ature, humidity, and air movement on the sensation of Temperature, mean skin (Tsk): The sum of the prod- warmth or cold felt by human subjects. The numerical ucts of the area of each regional surface element (Ai) value is that of the temperature of “still” air saturated and its mean temperature (Ti) divided by the total body with water vapor which would induce an identical sen- (surface) area. sation. [°C] Σ Tsk = (Ai ·Ti)/Ab [°C] Temperature, globe (Tg): The temperature of a black- ened hollow sphere of thin (usually 0.15 m di- Note: Mean skin temperature can be used as a physi- ameter) as measured by a thermometer at its center; Tg cal variable in the calculation of heat balance or of heat approximately equals temperature, operative.[°C] content of the body. It is, however, not necessarily a good estimate of what might be sensed as a mean skin Temperature lability, controlled: An expression of temperature according to the integrated neural input the extent of the daily and seasonal variations in the of the cutaneous , because different levelatwhichcore temperature is being regulated. surface regions may differ in their importance as ther- Synonym: thermolability, controlled. mosensor sites. Temperature lability, passive: An expression of the Temperature, operative (To): The temperature of a extent to which core temperature fluctuates passively uniform (isothermal) “black” enclosure in which a solid (i.e., without the recruitment of thermoeffector activi- body or occupant would exchange the same amount of ties) when either the rate of heat production or of heat heat by radiation and convection as in the actual non- exchange with the environment is varied. Synonym: uniform environment. [°C]

The Japanese Journal of Physiology Vol. 51, No. 2, 2001 269 Glossary of terms for thermal physiology

Temperature receptor. → Thermoreceptor. nomic temperature regulation is a potential result of behavioral temperature regulation which, however, Temperature regulation: The maintenance of the tem- competes with other, nonthermal, behavioral drives perature or temperatures of a body within a restricted (e.g., search for food). range under conditions involving variable internal Note: Behavioral temperature regulation is charac- and/or external heat loads. Biologically, the existence terized as operant, if it is acquired in an experimental of body temperature regulation to some extent by au- condition only after training guided by an experi- tonomic or behavioral means. Antonym: temperature menter. Otherwise, it is defined as natural,butthis conformity. may also involve learning. In humans the distinction between natural and operant behavioral temperature Temperature regulation, autonomic: The regulation regulation becomes arbitrary in many instances. of body temperature by autonomic (i.e., involuntary) thermoeffector responses to heat and cold which mod- Temperature regulation, chemical (obsolete): Body ify the rates of heat production and heat loss (i.e., by temperature regulation involving changes in heat sweating, thermal tachypnea, shivering, nonshiver- production. ing thermogenesis,andadjustmentsofcirculatory Note: This can be due to: 1. voluntary muscle move- convection of heat to the surfaces of the body). (Gk. ments; 2. involuntary muscle movements (e.g., shiver- autos-self; nomos-law, i.e., self-governing, SOED). ing); 3. nonshivering thermogenesis; 4. increase or Note: In this definition the term autonomic is used in its decrease in basal metabolic rate (BMR). more general sense and does not imply that all re- sponses are controlled by the Autonomic Nervous Sys- Temperature regulation, physical (obsolete): Body tem (sympathetic and parasympathetic efferents). temperature regulation involving control of the rate Autonomic temperature regulation is frequently de- of heat flow into or out of an organism. scribed as physiological temperature regulation,a Note: The responses involved in such regulation consist term which should be used for both autonomic and be- of those autonomic and behavioral responses that vary havioral thermoregulatory processes. the thermal conductance of peripheral tissues, but not of those behavioral responses which involve alteration Temperature regulation, behavioral: Any coordi- of the local environment. For example: 1. changes in nated movement of an organism ultimately tending to peripheral vasomotor tone; 2. piloerection;3.evapora- establish a thermal environment that represents a pre- tion of water from skin (following sweating, saliva ferred condition for heat exchange (heat gain, heat spreading, wallowing) and from respiratory tract sur- loss,orheat balance) of the organism with its environ- faces; 4. changes in body conformation. ment. The distinction between thermoregulatory be- havior and thermotropism is ill-defined. A may Temperature regulation, physiological: 1) Both auto- exhibit thermotropism but is not considered to be ther- nomic and behavioral temperature regulation (pre- moregulating. Some aquatic unicellular organisms ferred). 2) Obsolete synonym for autonomic move to a preferred ambient temperature,however, temperature regulation. whether this is thermotropism or thermoregulatory Note: Traditionally, mammalian thermoregulatory behavior may be disputed. For these reasons the term physiology has been concerned with those responses to is usually restricted in thermal physiology to patterns of heat or cold which do not depend on behavior. These re- behavior controlled by a nervous system. The complex ponses are autonomic (SOED self-governing; Gk. au- patterns of somato-motor activities that serve as behav- tos-self, independently; nomos-law). Autonomic ioral thermoeffector responses to heat and cold of responses are generally referred to as physiological re- temperature regulators in modifying their conditions sponses, but behavioral responses are also physiologi- of heat exchange with the environment, involve a wide cal (Physiology = the science of the normal functions variety of performances (e.g., moving to a different and phenomena of living things, SOED). Thus, physio- thermal ambiance, changes in posture, wetting of body logical thermoregulatory responses properly consist of surfaces, change of microclimate by nest building, pa- both autonomic and behavioral responses. rental behavior, huddling) and, in humans, also include voluntary exercise and cultural achievements (clothing, Temperature regulator: An organism which regulates housing, air-conditioning etc.). In endothermic tem- its body temperature to some extent by autonomic perature regulators, the reduced demand for auto- and/or behavioral processes. Antonym: temperature

270 The Japanese Journal of Physiology Vol. 51, No. 2, 2001 Glossary of terms for thermal physiology conformer. which a human in specified clothing expresses indiffer- Note: Tachymetabolism is the property of endother- ence to the thermal environment for an indefinite pe- mic temperature regulators in which core temperature riod. [°C] appears as the controlled variable, with arbitrarily de- fined degrees of thermostability (homeothermy, het- Thermal conductance (k): Therateatwhichheatis erothermy). Bradymetabolism does not exclude that transferred between unit area of two parallel surfaces in such species may be ectothermic temperature regula- a medium when unit temperature difference is main- tors, although mainly by means of behavioral temper- tained between them, or the rate of heat transfer dur- ature regulation, because thermoeffectors of ing steady state when a temperature difference of 1 °C autonomic temperature regulation are vestigial or is maintained across a layer of tissue, either expressed absent. per unit area [W · m–2 ·°C–1] or in absolute terms [W · °C–1]. Temperature responsive. → Thermoresponsive. Note: This term relates to the total heat transfer (no matter which physical processes are involved) down a Temperature sensitive. → Thermosensitive. temperature gradient from any tissue to its immediate environment, e.g., from a tissue to circulating blood, as Temperature sensor. → Thermosensor. well as from the body core through peripheral tissues to the body surface (due to conductive as well as convec- Temperature survival limit, lower: The environmen- tive processes). In practice tissue thermal conduc- tal temperature below which thermal balance cannot be tance of living tissues within the organism is not maintained for a long period and animals become pro- amenable to direct measurement. Calculated values are gressively hypothermic. At this temperature → basal usually based on several assumptions, e.g., mean tissue metabolic rate (BMR) can be measured. temperature, mean blood temperature, and the surface areas of blood vessel walls. Temperature survival limit, upper: The environmen- tal temperature above which thermal balance cannot be Thermal conductivity (λ): A property of a material maintained for a long period and animals become pro- defined by the flow of heat by conduction through unit gressively hyperthermic. thickness of the material per unit area and per unit tem- perature difference maintained at right angles to the di- Temperature, tolerated ambient range. → Tolerated rection of heat flow. [W · m –1 ·°C–1] ambient temperature range. Thermal contact coefficient. → Thermal inertia for Temperature, tympanic (Tty): The temperature of the radiant heat. tympanic membrane. Thermal core. → Core, thermal. Temperature, wet bulb (Twb): The thermodynamic wet bulb temperature of a sample of air is the lowest Thermal diffusivity. → Diffusivity, thermal. temperature to which it can be cooled by evaporating water adiabatically. This measurement is compared to Thermal expansion coefficient of volume (β): The that read by an ordinary thermometer, or dry bulb ther- change in volume (V) at constant pressure of a sub- mometer, to estimate the ambient humidity. [°C] stance (solid or fluid) per unit volume, per degree Note: The term is usually applied to the temperature re- change in temperature (T; degree ). corded by an aspirated thermometer covered with a wet β =V–1 · dV/dT (gases only) [K–1] sleeve that is approximately equal to the thermody- namic wet bulb temperature when the bulb is shielded Thermal hyperpnea: An increase in tidal volume associ- from radiation. ated with an increase in alveolar ventilation occurring dur- Thermal comfort: Subjective indifference to the ther- ing severe heat stress which has caused a large rise in core mal environment. temperature. In animals capable of thermal panting the phase of thermal hyperpnea with its slower, deeper Thermal comfort, zone of: The range of ambient breathing is also named second phase panting, since it is temperatures, associated with specified mean radiant usually preceded by a phase of typical panting (rapid, shal- temperature, humidity, and air movement, within low breathing). (Gk. hyper-above, over; pnoia-breath)

The Japanese Journal of Physiology Vol. 51, No. 2, 2001 271 Glossary of terms for thermal physiology

Thermal indifference, zone of: The range of ambient temperature regulation; 2. Any activation of thermo- temperatures, associated with specified water vapor effector activities in response to thermal stress that pressure, air velocity, and radiant exchange, within cause sustained changes in the state of other, nonther- which 80% of active people do not complain of the mal, regulatory systems. thermal environment. [°C] Cf. thermoneutral zone. Thermal stress: Any change in the thermal relation be- Thermal inertia for radiant heat (√kpc): One of the tween a temperature regulator and its environment properties of a material which determines the rate of in- which, if uncompensated by temperature regulation, crease of surface temperature during an exposure to ir- would result in hyper-orhypothermia. radiance (E). For nonpenetrating radiation incident upon a semi-infinite solid with uniform properties, the Thermal sweating. → Sweating, thermal. value of the thermal inertia for the surface can be deter- mined in appropriate units by √kpc =2π–1/2 ·t1/2 ·E· Thermal tachypnea: A rapid respiratory ac- ∆T–1 in which ∆T is the rise in surface temperature at companied by an increase in respiratory volume time, t. and, commonly, a decrease in tidal volume, in response to a thermoregulatory need to dissipate heat. (Gk. ta- Thermal insulation. → Thermal resistance. khus-swift; pnoia-breath) Synonym: thermal polyp- nea. Thermal insulation, clothing (Icl): The intrinsic insu- lation of a clothing assembly. The effective insulation Thermoeffector: An organ system and its action, re- of clothing is (Icl +Ia)whereIa is the reciprocal of the spectively, that affect heat balance in a controlled thermal conductance of the ambient environment. (Icl + manner as part of the processes of temperature regu- Ia) is usually measured as the temperature gradient lation. from the surface of a heated man-sized manikin to the Note: A multitude of thermoeffectors is involved in ambient air divided by the heat production per unit area both autonomic and behavioral temperature regula- of manikin surface. [°C · m2 ·W–1] The value is some- tion. times expressed in clo units. Thermoeffector gain: The derivative of the thermoef- Thermal panting: Increased respiratory evaporative fector output with respect to body temperature devia- heat loss (REHL) due to increased respiratory minute tion from the set-point. volume. Note:The gain may change due to fever, adaptation Note: Thermal panting in animals can occur both with and other processes. In combination with thermoeffec- a closed and open mouth. tor threshold temperature, thermoeffector gain is an important characteristic of thermoeffectors. Thermal polypnea. → Thermal tachypnea. Note: Although polypnea is more commonly used, ta- Thermoeffector threshold: The level of activity of a chypnea is etymologically more correct. potential thermoeffector that is transgressed when it becomes actively involved in temperature regulation. Thermal radiance. → Radiance, thermal. Note: For some of the thermoeffectors, thresholds can be precisely determined, e.g., as the level of basal met- Thermal radiant exitance. → Radiant exitance, abolic rate (BMR) or resting metabolic rate (RMR) thermal. of a tachymetabolic animal above which metabolic heat production (H) will increase in response to a suf- Thermal resistance (R): The reciprocal of thermal ficiently strong cold exposure. The thresholds of other conductance.[°C·m–2 ·W–1]or[°C·W–1] Synonym: thermoeffectors are arbitrarily defined, or agreed upon thermal insulation. by convention, because basal or resting levels are diffi- cult to define, e.g., in case of circulatory convection of Thermal shell. → Shell, thermal. heat to the skin and the underlying cutaneous vasomo- tor tone. Thermal strain: In temperature regulators:1.Any deviation of body temperature induced by sustained Thermoeffector threshold temperature: Describes thermal stress that cannot be fully compensated by the level of a specified body temperature (e.g., core

272 The Japanese Journal of Physiology Vol. 51, No. 2, 2001 Glossary of terms for thermal physiology temperature or mean body temperature)thetrans- nonshivering thermogenesis (NST), observed partic- gression of which in one direction, either upward or ularly in small mammals, is the brown adipose tissue downward, will activate a certain thermoeffector.Asa (BAT). rule, the threshold core temperature determined for a given effector will be a function of skin temperature, Thermogenesis, nonshivering (obligatory) and vice versa; similar interdependencies exist with and (NST(O)): That component of nonshivering thermo- among the threshold temperatures determined for spec- genesis (NST) (i.e., heat production unrelated to the ified thermosensor regions in the body core (e.g., hy- contractions of voluntary muscles) that is independent pothalamus, ). Evaluation of mean body of short-term changes in ambient temperature (Ta). temperature threshold values tries to account for the Note: NST(O) corresponds to basal metabolic rate entire thermal input from the body. Specified threshold (BMR) or standard metabolic rate (SMR). Although temperatures for certain thermoeffectors may change NST(O) is unaffected by short-term exposure to cold, it during the processes of fever, acclimat(izat)ion and may be changed by processes of acclimat(izat)ion to adaptation. Threshold temperature and thermoeffec- sustained cold or heat stress or feeding conditions. tor gain are the dominant parameters describing the thermoeffector output as a function of body tempera- Thermogenesis, nonshivering, (thermoregulatory) ture, thus, they constitute essential characteristics of the (NST(T)): Theincreaseinnonshivering thermogene- thermal controller. sis (NST) in response to acute cold exposure. The prin- cipal effector organ is the brown adipose tissue Thermoeffector threshold zone (Interthreshold (BAT). which may adaptively increase its capacity for zone): The temperature range between two threshold heat production in the course of acclimat(izat)ion and (body) temperatures, for activation of any thermoef- adaptation to cold stress. fector responses, particularly of metabolic heat pro- Note: The term nonshivering thermogenesis (NST) duction (H) and of evaporative heat loss when no usuallyreferstoNST(T). thermal load is present. This special steady-state may be called set-point. Thermoeffector threshold zone Thermogenesis, shivering: An increase in the rate of should be distinguished from thermoneutral zone heat production during cold exposure due to increased (TNZ). contractile activity of skeletal muscles not involving voluntary movements and external work. [W], [W· Thermogenesis, diet-induced: Increase of obligatory kg–1], [W · m–2]or[W·m–3] nonshivering thermogenesis occurring especially in Note: Shivering thermogenesis progresses, as its in- when transferred from standard food to a highly tensity increases, from thermoregulatory muscle palatable cafeteria diet, of which the animals consume tone, to micro-, to clonic contractions of both more but dissipate part of the surplus caloric intake by flexor and extensor muscles. All shivering thermo- enhanced heat production. The brown adipose tissue genesis is blocked by curare. (BAT) is considered as the main effector organ of diet-induced thermogenesis. Thermogenin. → P 32000 Polypeptide. Note: The relationship between postprandial (excess) heat production and diet-induced thermogenesis is not , infra-: The recording of the tem- presently clarified. perature distribution of a body from the infra-red radi- Thermogenesis, nonshivering (NST): Heat produc- ation emitted by the surface. tion due to metabolic energy transformation by pro- cesses that do not involve contractions of skeletal Thermolability, controlled. → Temperature lability, muscles, i.e., tone, microvibrations, tremor (→ shiver- controlled. ing), or tonic or voluntary contractions. In thermal Thermolability, passive. → Temperature lability, physiology this term is conventionally used to indicate passive. thermoregulatory (cold-induced) nonshivering ther- mogenesis (NST). [W], [W · m–2], [W · kg–1] Thermoneutral zone (TNZ): The range of ambient Note: While all organs contribute to obligatory non- temperature at which temperature regulation is shivering thermogenesis according to their rates of achieved only by control of sensible heat loss,i.e., resting metabolism, the principal effector organ re- without regulatory changes in metabolic heat produc- sponsible for the short-term or adaptive activation of tion (H)orevaporative heat loss. The thermoneutral

The Japanese Journal of Physiology Vol. 51, No. 2, 2001 273 Glossary of terms for thermal physiology zone (TNZ) will therefore be different when insulation, Thermoregulatory nonshivering thermogenesis. → posture or basal metabolic rate (BMR) vary. The term Nonshivering thermogenesis (thermoregulatory). thermoneutral zone (TNZ) does not apply to ecto- therms.Thethermoneutral zone (TNZ) should be Thermoresponsive: Neural element which changes its distinguished from thermoeffector threshold zone. activity in response to changes of its own temperature. Synonyms: temperature responsive, thermosensi- Thermopreferendum: The thermal conditions that an tive. individual organism or a species selects for its ambient Note: In comparison to the more general term temper- environment in natural or experimental circumstances. ature dependence, neuronal thermoresponsiveness implies at least the possibility of generation or modula- Thermoreactive: Descriptive of neural elements tion of information by temperature, either non-specific whose activity changes with the temperature of a re- or as a specific temperature signal. The synonymous mote region of the body, due to synaptic input from this term thermosensitive implies the specificity of the region. thermoresponsive neural element as a temperature sig- Note: A central nervous may be both thermore- nal generator. active and thermoresponsive (thermosensitive). Thermosensitive: Descriptive of thermoresponsive Thermoreceptor: Thermosensitive neural element neural with the implication that the neural el- for which both its afferent function and its response ements involved provide specific temperature signals. characteristics are electrophysiologically identified (→ Synonym: temperature sensitive. thermosensor). Synonym: temperature receptor. Note: Thermoreceptors have been unequivocally Thermosensor: Neural element or circuitry of neural identified, so far, only in the skin and mucous surfaces elements for which it is established by psychophysical as cold receptors, warm receptors, and infrared re- criteria or analysis of thermoeffector responses or ceptors. changes of core temperature that they transduce tem- perature in such a way that thermal sensation is elicited Thermoregulation. → Temperature regulation. and/or temperature regulation is adequately stimu- lated. Thermoregulatory behavior. → Temperature regu- Note: Thermosensors may not (yet) be accessible to lation, behavioral. electrophysiological identification, but their function is equivalent to that of thermoreceptors which are elec- Thermoregulatory behavior, natural: → Tempera- trophysiologically identified thermosensors. ture regulation, behavioral. Thermotolerance: A rapid, short acting molecular Thermoregulatory behavior, operant. → Tempera- process associated with the synthesis of several fami- ture regulation, behavioral. lies of heat shock proteins (HSP) of different molecu- lar weights elicited as a result of acute short sublethal Thermoregulatory conditioned reflex: The physio- heat injury. It is thought to protect cells from noxious logical (autonomic and behavioral) responses of an stimuli as well as to accelerate their repair. It is also de- organism to changes in its thermal environment, which fined as heat shock response (HSR).Thetimecourse can also be elicited by a conditioned stimulus. of heat shock proteins (HSP) vary in different cells but, on the average, heat shock proteins (HSP) in the Thermoregulatory muscle tone: Theincreaseinthe intact body seem to operate several hours following the electrical activity of the skeletal musculature of a rest- stress and retains its activity for a few days. The re- ing tachymetabolic temperature regulator during sponse is not heat-specific and can be elicited subse- moderate cooling. During more intensive cooling, quent to subjection to several other (e.g., thermoregulatory muscle tone will be superimposed ischemia, some chemicals, etc.). Synonym: heat shock by microvibrations and eventually shivering tremor. response (HSR). The corresponding electrical activities can be deter- mined qualitatively and quantitatively by means of Thermotropism: The turning or movement of a plant electromyographical recording (→ shivering). or animal in response to a temperature stimulus. (Gk. therme-heat; trope-turn)

274 The Japanese Journal of Physiology Vol. 51, No. 2, 2001 Glossary of terms for thermal physiology

Thigmothermy: The dependence of the core temper- agocytes) when activated by microorganisms or their ature of an ectothermic animal on the conductive ex- products. The production of tumor necrosis factor change of heat with its immediate environment, e.g., (TNF-α) is caused by infection, injury and trauma. It water, air, soil. (Gk. thigma-touch; therme-heat) (aswellasothercytokines) produces the acute phase response. Tumor necrosis factor-α (TNF-α) is con- Threshold temperature. → Thermoeffector thresh- sidered an important endogenous pyrogen, as are inter- old temperature. leukin-1 (IL-1), interleukin-6 (IL-6), and some other cytokines. Threshold, thermoeffector. → Thermoeffector threshold. UCP1: Specialized protein with a subunit Mr 32000 of the mitochondrial inner membrane of brown adipose Tissue thermal conductance. → Thermal conduc- tissue (BAT); collapses the electro-chemical proton tance, tissue. gradient generated by respiration and thus, prevents ATP synthesis; the amount of this mitochondrial com- Tolerated ambient temperature range: The range of ponent is increased when brown adipose tissue (BAT) ambient temperature (Ta) within which the body core is in a recruited state. Synonym: thermogenin, uncou- temperature can be kept, by means of autonomic pling protein, P 32000 polypeptide. thermoregulatory processes, within certain limits typ- ical for the species or the individual under consider- UCP2, UCP3: Proteins of similar sequence ation. [°C] to UCP1, but found in tissues other than brown adi- pose tissue (BAT), discussed as being involved in ther- Torpor: A state of inactivity and reduced responsive- mogenesis ness to stimuli (e.g., during hibernation, hypother- mia,orestivation). Ultraviolet. → Radiant energy.

→ Total body area (Ab). Area, total body. Uncoupling protein. → P 32000 Polypeptide.

Total environment: All environmental factors that ex- Upper critical temperature. → Critical tempera- ert an influence on an organism and to which an organ- ture, upper. ism must be adequately adapted in order to survive (i.e., competitors for food sources and predators as well as Upper temperature survival limit. → Temperature the many components of the physical environment and survival limit, upper. the climate). Useful work accomplished. → Work, positive. Total heat production: The rate of transformation of chemical energy into heat in an organism (metabolic Vapor pressure (water). → Pressure, water vapor. heat production (H)) plus any heat flow liberated within the body resulting from work done on the or- Volume, thermal expansion coefficient of. → Ther- ganism by an external force (negative work rate). mal expansion coefficient of volume. [W], [W · m–2], [W · m–3], [W · kg–1] Note: During positive work andwhennoworkisbeing Volumetric specific heat. → Specific heat, volumet- done on or by the organism, total heat production ric. equals metabolic heat production (H). Total radiant absorptance. → Radiant absorptance, Wallowing: The thermoregulatory increase in evapora- total. tive heat loss by spreading an aqueous fluid (e.g., water, mud, urine) on the body surface. Transmittance, radiation (τ): The ratio of the radiant energy transmitted through a body to the total radiation Warm-blooded: The thermal state of an animal that incident on it. maintains its core temperature considerably higher than that of the environment when subjected to a low α α Tumor necrosis factor- (TNF- ): Heat labile pro- ambient temperature (Ta). Synonym: tachymeta- teins produced by immune cells (e.g., mononuclear - bolic (preferred). Antonym: cold-blooded.

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Note: This maintained temperature gradient between chanical energy, work production, useful work ac- the organism and its environment is dependent on the complished. Antonym: workrate, negative. relatively high rate of metabolic heat production (H) (tachymetabolism) of warm-blooded animals com- Work production. → Work rate, positive. pared with the low rate of heat production (bradyme- tabolism)ofcold-blooded animals. Thus, the terms Zone of thermal comfort. → Thermal comfort, zone tachymetabolic and bradymetabolic are preferred to of. the terms warm-blooded and cold-blooded because the first pair of terms relates to a more basic physiolog- Zone of thermal indifference. → Thermal indiffer- ical distinction and because the second pair of terms has ence, zone of. been used with various meanings not all of which are consistent with the definitions given here. Zone of thermoneutrality. → Thermoneutral zone. Warm-blooded is not a synonym of homeothermic, because the definition of warm-blooded does not spec- ify the degree of temperature stability consistent with homeothermy:thecore temperatures of some warm-blooded animals vary considerably either nych- themerally or seasonally.

Warm receptor. → Thermoreceptor.

Water loss, insensible. → Insensible water loss.

Wet bulb temperature. → Temperature, wet bulb.

Wetted area. → Area, wetted.

Wettedness, skin (w): The fraction of the total body area (Ab) that is covered by sweat (the wetted area (Aw)), i.e., Aw/Ab. Note: For man the total skin area would usually be takentobetheDuBois area (AD).

Window emissivity. → Emissivity, window.

Work efficiency (η): Work done on an external system per unit of energy expended by an organism in the per- formance of that work (i.e., total energy expended by an organism during the performance of work less that of basal metabolism). [%]

Work rate, negative (–W): The rate of work (→ power) done on an organism by an external force. The quantity (–W) in the body heat balance equation. [[W], W · m–2], [W · m–3], or [W · kg–1] Antonym: work rate, positive.

Work rate, positive (+W): Therateofwork(→ power) done by an organism on an external system. The quantity (+W)inthebody heat balance equation. [W], [W · m–2], [W · m–3], or [W · kg–1] Synonym: me-

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APPENDIX 1. Système Internationale (SI) Units Used in the Glossary Quantity Symbol for SI Units Abbreviations Quantity Basic I A temperature T degree Kelvin K mass m kg length l meter m time t second s Supplementary plane angle θ rad solid angle Ω sr Derived temperature T degree Celsius (0 °C = 273.15 K) °C energy E (kg · m2 ·s–2) J force F newton (J · m–1) N V (J · A–1 ·s–1) V difference power W (J · s–1) W pressure P pascal (kg · m–1 ·s–2)(=N·m–2) Pa or bar (= 105 Pa) bar or torr (= 133.3 Pa) Torr

APPENDIX 2. Symbols Used in the Glossary Symbol or Term SI Units (Abbreviations) Abbreviation (ND = No Dimensions) 2 Ab area, total body m 2 AD area, DuBois m 2 Ap area, projected m 2 Ar area, effective radiating m 2 As area, solar radiation m 2 Aw area, wetted m BMR metabolic rate, basal W, W · m–2,,W·m–3,W·kg–1,W·kg–3/4 C convective heat transfer W, W · m–2,W·m–3,W·kg–1 CEHL cutaneous evaporative heat loss W, W · m–2,W·m–3,W·kg–1 D diffusivity, mass m2 ·s–1 E irradiance W·m–2 E evaporative heat transfer W, W · m–2,W·m–3,W·kg–1 F radiation shape factor ND H body height m H heat flow W, W · m–2,W·m–3,W·kg–1 HP metabolic heat production W, W · m–2,,W · m–3,W·kg–1,W·kg–3/4

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APPENDIX 2. Symbols Used in the Glossary –2 Hr radiant flux, effective W·m I radiant intensity W·sr–1 –1 –1 Iλ radiant intensity, spectral W·sr ·nm 2 –1 Icl thermal insulation, clothing m ·°C·W K conductive heat transfer W, W · m–2,W·m–3,W·kg–1 k thermal conductance W·m–2 ·°C–1,W·°C–1 –1 –2 Le radiance W·sr ·m –1 –2 Le,th radiance, thermal W·sr ·m LOMR metabolic rate, lowest observed W, W · m–2,W·m–3,W·kg–1,W·kg–3/4 –2 Me radiant exitance W·m –2 Me,s radiant exitance, self W·m –2 Me,th radiant exitance, thermal W·m M, MR metabolic rate (metabolic energy W, W · m–2,W·m–3,W·kg–1,W·kg–3/4 transformation) MMR metabolic rate, maximum W, W · m–2,W·kg–1,W·kg–3/4,W·m–3 MOMR metabolic rate, minimum observed W, W · m–2,W·kg–1,W·kg–3/4,W·m–3 NST thermogenesis, nonshivering W, W · m–2,W·kg–1,W·kg–3/4, W·m–3 NST(O) thermogenesis, nonshivering W, W · m–2,W·m–3,W·kg–1,W·kg–3/4 (obligatory) NST(T) thermogenesis, nonshivering W, W · m–2,W·m–3,W·kg–1,W·kg–3/4 (thermoregulatory) P pressure Pa,bar,Torr

Ps,T pressure, vapor (saturated) at Pa,bar,Torr temperature T

Pw pressure, water vapor Pa,bar,Torr PMR metabolic rate, peak W, W · m–2,W·m–3,W·kg–1,W·kg–3/4 Q radiant energy J –1 Qλ radiant energy, spectral J·nm 3 –1 –1 Rw gas constant (water vapor) 3.47 m · Torr · kg ·K R thermal resistance °C · m2 ·W–1,°C·W–1 R radiant heat exchange W, W · m–2,W·m–3,W·kg–1 REHL respiratory evaporative heat loss W, W · m–2,W·m–3,W·kg–1 RH humidity, relative % RMR metabolic rate, resting W, W · m–2,W·m–3,W·kg–1,W·kg–3/4 S storage of body heat W, W · m–2,W·m–3,W·kg–1,W·kg–3/4 SMR metabolic rate, standard W, W · m–2,,W·m–3,W·kg–1,W·kg–3/4 SWR sweat rate mg · s–1,mg·m–2 ·s–1

Ta temperature , ambient °C Tc,Tco temperature, core °C Tb temperature, mean body °C Tdb temperature, dry bulb °C

278 The Japanese Journal of Physiology Vol. 51, No. 2, 2001 Glossary of terms for thermal physiology

APPENDIX 2. Symbols Used in the Glossary

Tdp temperature, dew-point °C Teff temperature, effective °C Tg temperature, globe °C To temperature, operative °C Tr temperature, mean radiant °C Ts,Tsk temperature, mean skin °C Twb temperature, wet bulb °C TNZ thermoneutral zone °C · –1 –1 VO2max rate of oxygen consumption, maximum ml · s ,l·min W body mass* kg W work rate (mechanical power) W, W · m–2,W·m–3,W·kg–1,W·kg–3/4 c specific heat J·kg–1 ·°C–1 h general heat transfer coefficient W·m–2 ·°C–1 –2 –1 hcomb.,h heat transfer coefficient, combined W·m ·°C nonevaporative –2 –1 hc heat transfer coefficient, convective W·m ·°C –1 hD mass transfer coefficient (diffusion) m·s –2 –1 –2 –1 he heat transfer coefficient, evaporative W·m ·kPa ,W·m ·Torr –2 –1 hk heat transfer coefficient, conductive W·m ·°C –2 –1 hr heat transfer coefficient, radiative W·m ·°C (linear) m· mass transfer rate kg · s–1 w wettedness, skin ND α radiant absorptance, total ND α diffusivity, thermal m2 ·s–1 β thermal expansion, coefficient of volume K–1 γ humidity, absolute kg · m–3 ε emissivity ND

ε(θ,φ) emissivity, directional ND ελ emissivity, spectral ND ε h emissivity, hemispherical ND ε w emissivity, window ND η work efficiency % θ angular coordinate, vertical rad λ thermal conductivity W·m–1 ·°C–1 λ,LHV latent heat of vaporization J·g–1 λ wavelength m, µm, nm ρ density kg · m–3 ρ reflectance, radiation ND σ Stefan-Boltzmann constant W·m–2 ·K–4 (5.67 × 10–8) τ transmittance, radiation ND φ angular coordinate, horizontal rad

The Japanese Journal of Physiology Vol. 51, No. 2, 2001 279 Glossary of terms for thermal physiology

APPENDIX 2. Symbols Used in the Glossary φ humidity, relative ND φ radiant flow W –1 φλ radiant flow, spectral W·nm Ω solid angle sr * The term weight (instead of the correct term mass) is conventionally used

APPENDIX 3. Panel of contributors

Blatteis, C. (University of Tennessee, U.S.A). Boulant, J. (The Ohio State University, U.S.A). Cabanac, M. (Universite Laval, Canada). Cannon, B. (Stockholm University, Sweden). Freedman, R. (Wayne State University, Mi, U.S.A.). Gordon, C.J. (United States Environmental Protection Agency, NC, U.S.A.). Hales, J.R.S. (The University of Sydney, Australia). Horowitz, M. (The Hebrew University, Israel). Iriki, M. ( Yamanashi Institute of Environmental Science, Japan). Janský, L (Charles University, Prague, Czech Republic). Jessen, C. (Justus-Liebig-Universität, Germany). Nielsen-Johannsen, B. (University of Copenhagen, Denmark). Kaciuba-Uscilko, H. (Polish Academy of Sciences, Poland). Kanosue, K. (Osaka University Medical School, Japan). Kluger, M.J. (The Lovelace Institutes, USA). Laburn, H.P. (University of the Witwatersrand, South Africa). Nielsen-Johannsen, B. (The University of Copenhagen, Denmark). Mercer, J.B. (University of Tromsø, Norway). Mitchell, D. (University of the Witwatersrand, South Africa). Simon, E. ( Institute, Bad Nauheim, Federal Republic of Germany). Shibata, M. (Yamanashi Institute of Environmental Science, Japan). Székely, M (University Medical School, Pécs, Hungary). Szelényi, Z. (University Medical School, Pécs, Hungary). Werner, J. (Ruhr-Universität Bochum, Federal Republic of Germany). Kozyreva, T. (Medical Academy of Russia, Novosibirsk, Russia).

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