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Glossary of terms for thermal physiology

Glossary of terms for thermal physiologyThird Edition

revised byThe Commission for Thermal Physiology of the International Union of Physiological Sciences

(IUPS Thermal Commission)

PrefaceThe first Glossary of Terms for Thermal Physiologywas published in the J. Appl. Physiol. (1973, 35: 941–961) by J.Bligh and K.G. Johnson, under the auspices ofthe I.U.P.S. Commission for Thermal Physiology. Thesecond revised glossary was again collated with thehelp of the members of the I.U.P.S Commission forThermal Physiology and consulted experts and waspublished in Pflügers Arch. (1987, 410: 567–587) by E.Simon. Once again the members of the I.U.P.S. Com-mission for Thermal Physiology and consulted expertswhose names are listed in APPENDIX 3 have contrib-uted to the revision of this 3rd edition.

This revised edition obeys the following rules outlinedin the first and second editions:

UnitsUnits used in the Glossary are based on the Système In-ternationale (SI). Where such units would be inconve-niently small or large, SI convention permits increasesor decreases by multiples of 103, e.g., m to mm (m ×10–3) or to nm (m × 10–9), but not to cm (m × 10–2). Thebasic, supplementary, and derived SI units used in theGlossary are given in APPENDIX 1.

SymbolsThe symbols used in the Glossary are listed in APPEN-DIX 2. These symbols conform generally to those spec-ified in the “Proposed Standard System of Symbols forThermal Physiology” (J. Appl. Physiol. 27: 439–446,1969). Minor changes have been suggested. In thebody heat balance equation, the symbol M is nowused to denote the rate of metabolic energy transfor-mation (=metabolic rate); metabolic heat produc-tion is identified by the symbol H. The symbol ε(epsilon) is used for emissivity and not for emittance,and the term exitance has replaced emittance (seeAmerican National Standard Institute, Nomenclatureand Definitions for Illumination Engineering, RP-16,1967, p. 32 (UDC 653.104.8:621.32)). k is used forconductance and λ for thermal conductivity.

Order of Presentation of TermsTo bring similar or related terms closer together in theGlossary, the common term is given first followed bythe descriptive term, e.g., emissivity, hemispherical.In use the order is reversed: hemispherical emissivity.To avoid confusion such entries have a cross-reference,e.g., hemispherical emissivity. →Emissivity, hemi-spherical. If the same root of a term is used in morethan one grammatical form, however, with analogousmeaning, it is defined only once without referring ex-plicitly to the other forms; example: homeothermy,homeothermic, homeotherm.

Use of Fonts and Markers in Text

Horizontal arrows in the headings of the definitionpoint to cross-references.Bold-face letters mark the terms and their cross-refer-ences which are being defined and, further, those termsin the text of the definitions which are defined else-where in the glossary.

Abbreviations

Multiple DefinitionsWhere more than one definition of a term is given, theyare listed in order of preference.

Although this Glossary expresses the preferences of thecommission, it is not a rule. It is a norm for a bettercommunication between the scientists within the samefield, scientists working in other fields and the generalpublic. Any speciality produces its own jargon. It ishoped that this Glossary will help transform jargon intogeneral vocabulary.

cf. compare OED Oxford Englishe.g. for example DictionaryFr. French ref ReferenceGk. Greek SD Standard

Deviationi.e. that is SOED Shorter OEDL. Latin ( ) Symbols[ ] Unit

The Japanese Journal of Physiology Vol. 51, No. 2, 2001 245


Communications concerning the glossary may be sentto the Chairman of the IUPS Thermal Commission, orto the Publisher.

AcknowledgementThis revision was initiated by James Mercer during histerm as Chairman of the I.U.P.S. Commission for Ther-mal Physiology. Thermal Commission member JurgenWerner was responsible for producing the first workingdraft and further updating of the glossary followedfrom numerous additional suggestions for new entriesand modifications by the current commission membersand other consulted experts. In the revised glossary, 11terms have been removed, 49 of the original entrieshave been modified and the definitions of 37 new termshave been added, increasing the overall number of en-tries to 479.

James Mercer, ChairmanI.U.P.S. Commission for Thermal PhysiologyDepartment of Medical PhysiologyInstitute of Medical BiologyFaculty of MedicineUniversity of TromsøN-9037 Tromsø.Norway.

Glossary

Absolute humidity. → Humidity, absolute.

Absorptance, total radiant. → Radiant absorptance,total.

Accidental hypothermia. → Hypothermia, acciden-tal.

Acclimation: Physiological or behavioral changes oc-curring within an organism, which reduces the strain orenhances endurance of strain caused by experimentallyinduced stressful changes in particular climatic factors.Note: The terms acclimation and acclimatization areetymologically indistinguishable. Both words havebeen assigned several and different meanings (Green-leaf & Greenleaf, 1970). The most useful of the as-signed meanings, adopted here, would seem to be thoseof Hart (1957) and Eagan (1963) who use the term ac-climation to describe the adaptive changes that occurwithin an organism in response to experimentally in-duced changes in particular climatic factors such asambient temperature in a controlled environment, and

the term acclimatization to describe the adaptivechanges that occur within an organism in response tochanges in the natural climate.Refs: Eagan, C. J., Federation Proc. 22: 930, 1963;Greenleaf, J.E., & C.J. Greenleaf, NASA Tech. Mem.X-62, 008, 1970; Hart, J.S., Rev. Can. Biol. 16: 133,1957.

Acclimatization: Physiological or behavioral changesoccurring within the lifetime of an organism that reducethe strain caused by stressful changes in the natural cli-mate (e.g., seasonal or geographical). → acclimation.Note: What is termed acclimatization may also bespecified as a particular phenotypic adaptation; there-fore, the usefulness of the term may be questioned.

Acute-phase response (APR): The multifactorial ste-reotyped response of an organism to infection, injury ortrauma. The APR comprises changes in plasma con-centrations of trace metals, liver proteins (so-called“acute phase proteins”), hormones, intermediary me-tabolism, neutrophilia, and “sickness behavior”, whichincludes the development of fever, loss of food appe-tite, increased sleep, decreased motor activity, and de-creased alertness. The acute-phase response (APR) isconsidered an early, non-specific host-defence re-sponse, and is triggered by the release of cytokinessuch as interleukin-1 (IL-1), IL-6, and tumor necrosisfactor α (TNFα).

Adaptation: Changes that reduce the physiologicalstrain produced by stressful components of the totalenvironment. This change may occur within the life-time of an organism (phenotypic) or be the result of ge-netic selection in a species or subspecies (genotypic).Acclimation as defined in this Glossary relates to phe-notypic adaptations to specified climatic components.In thermal physiology, the use of the term adaptationdoes not require specification of the climatic compo-nents of the total environment to which the organismadapts, but the most obvious component is often de-noted (e.g., adaptation to heat). There are no distinctterms that relate genotypic adaptations to the climateor particular components of climate.Note: In comparison to adaptation as defined in neuro-physiology, the adaptive processes in thermal physiol-ogy usually occur with larger time constants.

Adaptation, genetic. → Adaptation, genotypic.

Adaptation, genotypic: A genetically fixed conditionof a species or subspecies, or its evolution, which

246 The Japanese Journal of Physiology Vol. 51, No. 2, 2001


favours survival in a particular total environment. →adaptation.

Adaptation, nongenetic. → Adaptation, phenotypic.

Adaptation, phenotypic: Changes that reduce thephysiological and/or emotional strain produced bystressful components of the total environment and oc-curring within the lifetime of the organism. Synonym:adaptation, nongenetic.Note: acclimation relates to phenotypic adaptation toindividual climatic components of the total environ-ment.

Aestivation. → Estivation.

Afebrile: The thermoregulatory state of an organismwhere core temperature is normal, and thermoeffec-tors are not attempting to increase or maintain coretemperature at an elevated level. Antonym: febrile

Alliesthesia: Generally, the changed perception of agiven peripheral stimulus resulting from the stimula-tion of internal sensors; in thermal physiology, the de-pendence of thermal sensation on both skin and coretemperatures. (Gk.alloioo-to alter; aisthesia-sensa-tion)Note: Positive alliesthesia indicates a change to a morepleasurable sensation, negative alliesthesia a change toa less pleasurable one.

Ambient temperature. → Temperature, ambient.

Anaerobic metabolism. → Metabolism, anaerobic.

Anapyrexia: A pathological condition in which thereis a regulated decrease in core temperature. Anapyr-exia is distinct from hypothermia in that thermoregu-latory responses indicate a defence of the anapyreticlevel of core temperature. (Gk. ana-reverse; pyre-tos-fever).Note: Anapyrexia may be caused by exogenous or en-dogenous substances (→ Cryogen); e.g., the activationof heat loss underlying the menopausal hot flushesmay be considered as due to temporary anapyrexiacaused by GnRH.

Antipyretics, endogenous: Hormones and cytokinesthat limit the magnitude of fever. The hormones in-clude arginine vasopressin (AVP), α-melanocyte stim-ulating hormone (αMSH), and glucocorticoids. Thecytokines IL-4, IL-1α and possibly TNF-α (under

some conditions) are also endogenous antipyretics.All, however, have distinct mechanisms of action.

Antipyretics, exogenous: Pharmacological agents(e.g.,cyclooxygenase inhibitors [NSAID’s]) that pre-vent or attenuate the development of fever.

Area, DuBois (AD): The total surface area in squaremeters of a nude human as estimated by the formula ofDuBois based on the height, H[m], and mass, W[kg].Ref.: DuBois, E.F., Basal Metabolism in Health andDisease, Philadelphia, P.A, Lea & Febiger, 1927. AD =0.202·W0.425· H0.725 [m2]

Area, effective radiating (Ar): The surface area of abody that exchanges radiant energy with the environ-ment through a solid angle of 4 π steradians. [m2]

Area, projected (Ap): The area of a body (or surface)projected on a plane perpendicular to the direction of acollimated beam (projected through an aperture) of ra-diation. [m2]

Area, solar radiation (As): The area of a body pro-jected perpendicularly to the sun’s rays. [m2]

Area, total body (Ab): The area of the outer surface ofa body, assumed smooth. [m2]Note: Direct measurements of surface area are difficultand subject to appreciable error. Surface area is usuallyestimated from a formula such as that of Meeh (1879)that relates total body area (Ab) to body weight (W):Ab = k·W2/3. This is a particular case of Huxley’s allo-metric law. Estimates of the value of k vary widely be-tween and within species but are generally between0.07 and 0.11 when Ab is in m2 and W is in kg (Spector,1956). The DuBois formula (→Area, DuBois), used inthe estimation of the total body area, relates totalbody area to both mass and height. Estimates of totalbody area made with either Meeh's formula or theDuBois formula have limited accuracy, and referenceshould be made to the original direct measurementsfrom which total body area was calculated. Refs: Hux-ley, J.S., Problems of Relative Growth, London: Meth-uen, 1932; Meeh, K., Z. Biol. 15: 425, 1879; Spector,W.S., Handbook of Biological Data, Philadelphia, P.A.:Saunders, 1956.

Area, wetted (Aw): The area of skin which, if coveredwith sweat (water), would provide the observed rate ofevaporation under the prevailing condition. [m2] →Wettedness, skin.



Autonomic temperature regulation. → Tempera-ture regulation, autonomic.

Autonomic thermoregulation. → Temperature reg-ulation, autonomic.

Bacterial pyrogen. → Pyrogen, bacterial.

Basal metabolic rate. → Metabolic rate, basal.

Behavior, thermoregulatory. → Temperature regu-lation, behavioral.

Behavioral temperature regulation. → Temperatureregulation, behavioral.

Behavioral thermoregulation. → Temperature reg-ulation, behavioral.

Blackbody. → Radiator, full.

Body heat balance: The steady-state relation in whichtotal heat gain in the body equals its heat loss to the en-vironment.

Body heat balance equation (actually: heat flow bal-ance equation): A mathematical expression that de-scribes the net rate at which a subject generates andexchanges heat with its environment (First Law ofThermodynamics). The dimension of the equation andits terms respectively, are in watts [W] thereby consti-tuting heat flows, but often are also expressed in rela-tion to unit area of body surface [W · m–2], to unit bodymass [W · kg–1], or to unit body volume [W·m–3].S = M – (W) – (E) – (C) – (K) – (R).

S = storage of body heat (positive = increase in bodyheat content; negative = decrease in body heat con-tent).M = metabolic energy transformation (always posi-tive in a living organism) = metabolic rate.W = work rate, positive (= useful mechanical poweraccomplished; negative = mechanical power absorbedby body: work rate, negative).E = evaporative heat transfer (positive = evaporativeheat loss; negative = evaporative heat gain).C = convective heat transfer (positive = transfer to theenvironment; negative = transfer into the body).K= conductive heat transfer (positive = transfer to theenvironment; negative = transfer into the body).R = radiant heat exchange (positive = heat transfer tothe environment; negative = heat absorption by the

body).Note: The equation is designed to describe the prevail-ing physiological situation of a homeothermic (e.g.human) subject. At a given metabolic energy trans-formation, the subject transfers some mechanical en-ergy to its ambiance (→work rate, positive), and, if theambient thermal conditions permit it, heat from thebody to the environment by evaporation, conduction,convection, and radiation, which eventually results inthe stabilization of body heat content with storage S =0. However, there are physiological conditions inwhich mechanical energy is absorbed by the body, ulti-mately as heat (→work rate, negative), and/or one orthe other of the terms describing the exchange of heatflow with the environment may become negative.In a core/shell treatment of the body we get two heatbalance equations:Score = M – (W) – (H) – REHLSshell = H – (E) – (C) – (R) – (K)with REHL = → respiratory evaporative heat loss(REHL) and H = → heat transfer (conductive andconvective heat flow) between core and shell. The lat-ter is proportional to the difference of mean core andmean skin temperature with the proportionality con-stant → conductance k.

Body heat content. → Heat content, body.

Body heat storage. → Storage of body heat and Heatstorage, change in.

Body temperature, mean. → Temperature, meanbody.

Bradymetabolism: The low levels of basal metabo-lism of reptiles and other nonavian and nonmammaliananimals relative to those of birds and mammals of thesame body size and at the same tissue temperature. (Gk.bradus-slow, sluggish; metabole-change) Antonym:tachymetabolism.Note: As a synonym cold-bloodedness is unsatisfac-tory and is falling into disuse. This relatively low levelof basal metabolism is sometimes described as poiki-lothermy, which is incorrect since poikilothermy sig-nifies conformity of body and ambient temperaturesand not all bradymetabolic species are temperatureconformers; some are ectothermic temperature reg-ulators.

Brain cooling, selective. → Selective brain cooling.

Brown adipose tissue (BAT): A particular form of ad-



ipose tissue with selected distribution. It differs fromwhite adipose tissue both structurally and functionally;its colour is brownish (yellow to reddish), depending onits content of (mitochondrial) cytochromes and of fatwhich is distributed in multipledroplets (multilocular)as compared to white fat cells (monolocular) and alsoon its dense vascularization. Brown adipose tissue ap-pears to be restricted to mammalian species, especiallyof smaller body size, including the hibernators (→ Hi-bernation), but is also present in newborns of largerspecies including humans. Regulatory heat productionhas been identified as its main but possibly not its onlyfunction. Its heat-generating capacity relates to the rateof fatty acid oxidation which is not constrained by cel-lular ATP catabolism. This property correlates with thepresence of a specialized component in the inner mito-chondrial membrane named UCP1 (the uncouplingprotein or thermogenin, which establishes a protonshunt bypassing oxidative phosphorylation). The activ-ity of brown adipose tissue is controlled by the sympa-thetic nervous system through release of adrenaline.Note: Chronic exposure to cold (→ nonshivering ther-mogenesis) and to excess food intake (→ diet-inducedthermogenesis) enhance the heat-generating capacityof brown adipose tissue by hypertrophy (including in-crease in UCP1 amount) and hyperplasia. The totalprocess is referred to as recruitment. In accordance withthe sympathetic control of brown adipose tissue, theincrease in metabolic energy transformation of ananimal in a thermoneutral environment after systemicinjection of noradrenaline is considered as an estimateof the thermogenetic capacity of brown adipose tissue.

Brown fat. → Brown adipose tissue.

Calorimetry: The measurement of heat. In thermalphysiology, the measurement of the heat transfer be-tween a tissue, an organ, or an organism and its envi-ronment. (L. calor-heat; Gk. metria-act of measuring)→ calorimetry, direct and calorimetry, indirect.

Calorimetry, direct: The direct physical measurementof heat, usually the rate of transfer of heat (→ heattransfer) between a tissue, an organ, or an organismand its environment.

Calorimetry, indirect: The measurement of the rate oftransfer of a material involved in the transformation ofchemical energy into heat between a tissue, an organ, oran organism and its environment. The process requiresthe calculation of the heat transfer from an empiricallyestablished relation between the material transfer and

the heat transfer.Note: The most common method of indirect calorim-etry is to measure the uptake of oxygen and/or the elim-ination of carbon dioxide, and to convert these values toan equivalent quantity of heat. The calorific equivalentof a litre of oxygen is approximately 20 kJ of heat.

Calorimetry, partitional: The estimation of any singleterm in the body heat balance equation from directmeasurements of all other terms in the equation duringthe steady state. Ref: Winslow, C.E.A., L.P. Herrington,& A.P. Gagge, Am. J. Physiol. 116: 641, 1936.

Cenothermy: The condition of a temperature regula-tor when its core temperature is within +1 SD of therange associated with the normal postabsorptive restingcondition of the species in the thermoneutral zone.(Gk. koinos-common, shared; therme-heat) Synonym:euthermy, normothermy.Note: Ceno (common) seems a more appropriate prefixthan eu (well, good).

Change in heat storage. → Heat storage, change in.

Chemical temperature regulation. → Temperatureregulation, chemical.

Circadian: Relating to the approximate 24-h periodic-ity of a free running biological rhythm, or to the exact24-h periodicity of an environmentally synchronizedbiological rhythm that persists with an approximate24-h periodicity when not environmentally synchro-nized. (L. circa-about, approximately; dies-day)

clo: A unit to express the relative thermal insulationvalues of various clothing assemblies.1 clo = 0.18°C·m2 ·h · kcal–1 = 0.155°C ·m2 ·W–1

Note: The clo is a unit developed to express thermalinsulation (→ thermal resistance) in practical termsand represents the insulation provided by the normalindoor clothing of a sedentary worker in comfortableindoor surroundings (Ref: Gagge, A.P., A.C. Burton, &H.C. Bazett, Science 94: 428, 1941). The term is used inheating and ventilation engineering in the determina-tion of environmental conditions for human comfort.

Cold-blooded: The thermal state of an animal in whichcore temperature remains close to ambient tempera-ture when subjected to a low ambient temperature.Synonym: bradymetabolic, poikilothermic. Ant-onym: warm-blooded.



Note: The existence of only a small temperature gradi-ent between the organism and its environment resultsfrom the low rate of metabolic heat production(bradymetabolism) of cold-blooded animals relativeto the high rate of metabolic heat production (ta-chymetabolism) of warm-blooded animals. Thus, theterms bradymetabolic and tachymetabolic are pre-ferred to the terms cold-blooded and warm-blooded,because the first pair of terms relates to a more basicphysiological distinction and because the second pair ofterms has been used with various meanings not all ofwhich are entirely consistent with the definitions givenhere. Since their core temperatures follow ambienttemperature, all cold-blooded animals are poikilother-mic (i.e., many temperatured). Thus, cold-blooded,poikilothermic, and bradymetabolic are descriptionsof related phenomena. The same cannot be said ofwarm-blooded, homeothermic, and tachymetabolic(→ warm-blooded).

Cold receptor. → Thermoreceptor.

Cold tolerance: The ability to tolerate low ambienttemperatures. This term comprises a variety of physi-ological properties. Certain homeotherms (tachymet-abolic species) are described as cold tolerant, becausethey are able to balance heat production and heat loss inthe state of cenothermy at particularly low ambienttemperatures. This may be due to the development ofinsulation or to the efficiency of metabolic heat pro-duction and is often combined with an improved abil-ity to protect appendages from freezing by effectivevascular control of local heterothermy. In homeo-therms, cold tolerance may also be achieved by gen-eral heterothermy, including hibernation, i.e., bycontrolled forms of hypothermia. Poikilotherms(bradymetabolic species) are characterized as coldtolerant, if they are able to survive low and even sub-freezing body temperatures, either in the state of cryo-thermy, or because intracellular formation of icecrystals is avoided during freezing. All forms of coldtolerance may be subject to adaptation or accli-mat(izat)ion.Note: While some types of what is termed cold toler-ance have already been specified (cryothermy, hiber-nation), further specification and agreement uponadditional definitions seem necessary.

Combined nonevaporative heat transfer coefficient.→ Heat transfer coefficient, combined nonevapora-tive.

Comfort. → Thermal comfort.

Conductance, thermal. → Thermal conductance.

Conductive heat transfer (K): The net rate of heattransfer in a solid material or a non-moving gas orfluid (i.e., by conduction) down a thermal gradient,within an organism, or between an organism and its ex-ternal environment. The latter is usually expressed interms of unit area of the total body surface, i.e. as a heatflux, and is the quantity (K) in the body heat balanceequation in which (–K) = heat gain, and (+K) = heatloss. [W·m–2], [W], [W·m–3], [W·kg–1]

Conductive heat transfer coefficient. → Heat trans-fer coefficient, conductive.

Conductivity, thermal. →Thermal conductivity.

Control: 1. the process by which a physiological vari-able becomes a function of information generated lo-cally or transmitted from remote sources by neural orhormonal signals (feedforward control); 2. the processby which a physiological system stabilizes (“regu-lates”) a variable, generally by means of an informationloop with negative feedback. The control loop com-prises the controlled (passive) system (e.g., the heattransfer processes) and the controlling (active) system,which may be divided into sensor, processor and effec-tor components.Note: With the adoption of definition #2 from the ter-minology of technical control, further terms likeset-point, controlled variable, load-error, nega-tive-feedback, servo-control, etc., have been introducedto describe the various components of the physiologicalprocesses of regulation. Control in the sense of defini-tion #2 and regulation are analogous terms in physiol-ogy. However, the use of the term regulation should begenerally given preference in order to avoid confusionbetween the two definitions of control.

Control, proportional: A control concept with nega-tive feedback, obviously present in thermoregulation,in which the controller activates thermoeffector mech-anisms to an extent dependent on the deviation of thecontrolled variable from its set-point. If the distur-bance (external or internal thermal load) persists, such acontrol concept implies a load error, i.e., a permanentdeviation of the controlled variable. However, such adeviation is much smaller than that which is presentwithout feedback control.



Controlled temperature lability. → Temperature la-bility, controlled.

Convection, circulatory: Flow of blood in the vesselsof the circulatory system. In thermal physiology, con-vective transfer of heat with the blood stream from thethermal core through the thermal shell to the heat dis-sipating surfaces of the body is a thermoeffector of au-tonomic temperature regulation. Its efficiency intransferring heat is a function of flow rate and the tem-perature gradient between core and heat dissipatingsurface, and may be modified by the degree of heat ex-change by conduction between the vessels to and fromthese surfaces (e.g., due to the counter-current arrange-ment of arteries and veins).

Convective heat transfer (C): The net rate of heattransfer in a moving gas or fluid (i.e., by convection)between different parts of an organism, or between anorganism and its external environment; it may developand be amplified by thermal gradients (natural convec-tion) and by forces such as wind, fans, pumps or bodymovement (forced convection) usually expressed interms of unit area of the total body surface (→ Area, to-tal body), i.e., as a heat flux. The quantity (C) in thebody heat balance equation in which (–C) = heat gainand (+C) = heat loss. [W·m–2], [W], [W·m–3], [W·kg–1]

Convective heat transfer coefficient.→ Heat trans-fer coefficient, convective.

Convective mass transfer. → Mass transfer, convec-tive.

Convulsions, febrile: Convulsions (epileptic seizures)occurring before or during fever episodes. Febrile con-vulsions occur mostly in children between the age of 6months and 3 years. They are rare after the age of 8years.Note: Due to its rare occurrence, this term has becomeobsolete in many developed countries.

Core temperature. → Temperature, core.

Core, thermal: Those inner tissues of the body whosetemperatures are not changed in their relationship toeach other by circulatory adjustments and changes inheat dissipation to the environment that affect the ther-mal shell of the body.Note: The term is used mainly to describe the deep bodytissues of homeotherms whose temperatures are repre-sented by the core temperature. The brain is generally

a section of the thermal core: however, in severalmammalian and avian species its temperature may de-viate to some extent from that of the remaining thermalcore due to selective brain cooling.

Crepuscular: Occurring daily during the phases oftwilight. → diurnal. (L. crepusculum-twilight) .

Critical temperature for evaporative heat loss. →Critical temperature, upper.

Critical temperature for heat production.→ Criticaltemperature, lower.

Critical temperature, lower: The ambient tempera-ture below which the rate of metabolic heat produc-tion of a resting thermoregulating tachymetabolicanimal must be increased by shivering and/or nonshiv-ering thermogenesis in order to maintain thermal bal-ance. Synonym: critical temperature for heatproduction. [°C]

Critical temperature, upper: The ambient tempera-ture above which the rate of evaporative heat loss of aresting thermoregulating animal must be increased(e.g., by thermal tachypnea or by thermal sweating)in order to maintain thermal balance. Synonym: criti-cal temperature for evaporative heat loss. [°C]Note: Upper critical temperature has also been usedto define the ambient temperature above which thecapacities of the mechanisms of heat transfer to theenvironment of a resting animal are exceeded, such thatcore temperature is forced to rise and, as a conse-quence, metabolic energy transformation, i.e., the in-ternal heat load, is further increased. This use of theterm should be avoided, however, because it does notaccurately describe the upper temperature survivallimit.

Cryogen: An endogenous or exogenous substance thatlowers the set-point of body temperature and causesanapyrexia. Antonym: pyrogen. (Gk. kruos-cold; <gen-become).

Cryothermy: The thermal status of a supercooled or-ganism (i.e., with the temperature of the body mass be-low the freezing point of the tissue). (Gk. kruos-cold;therme-heat)

Cutaneous evaporative heat loss (CEHL): Rate ofheat dissipated by evaporation from the skin. [W],[W·m–2], [W·m–3], [W·kg–1]. Cutaneous evaporative



heat loss (CEHL) plus respiratory evaporative heatloss (REHL) constitute → evaporative heat loss.

Cutaneous water exchange, passive. → Passive cuta-neous water exchange.

Cutaneous water vapor exchange, passive. → Pas-sive cutaneous water vapor exchange.

Cytokine: A class of immunoregulatory polypeptidesproduced by various cell types, but, at the outset, pri-marily by mononuclear phagocytes activated by vari-ous signals provided by exogenous pyrogens.Cytokines may act as endogenous mediators of fever(endogenous pyrogens). The most prominent amongthe fever producing cytokines are interleukins(IL)-1β and -6, tumor necrosis factor (TNF)-α, andinterferon (IFN)-α.

Deep body temperature. → Temperature, core.

Density (ρ): The ratio of the mass to the volume of asubstance. [kg · m–3]

Dew-point temperature. → Temperature,dew-point.

Diet-induced thermogenesis. → Thermogenesis,diet-induced.

Diffusivity, mass (D): The constant of proportionalityrelating the rate of diffusion of a gas to the gradient ofits concentration in another gas, e.g., water vapor in air.If the rate of diffusion of mass is ·m[kg · s–1] in a direc-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],the rate of flow through an area A is given by the Fick-ian equation, ·m = –DA (∂p/∂y), where D is the massdiffusivity or diffusion coefficient and ∂p/∂y is the ap-propriate concentration gradient. More complex equa-tions are needed to describe diffusion in two or threedirections simultaneously [m2 · s–1]

Diffusivity, thermal (α): The thermal conductivity ofa substance divided by its density (ρ) and specific heatat constant pressure (cp) ·[m2 · s–1]

Direct calorimetry. → Calorimetry, direct.

Directional emissivity. → Emissivity, directional.

Diurnal: 1. Indicates biological processes (e.g., phases

of activity) occurring during the day, as distinct fromthe night. 2. Occurring daily (during each 24-h period).(L. diurnus adj < dies-day).Note: Terms relating to other phases of entrained 24 hperiodicity, i.e., to definition #1, are: nocturnal (duringthe night) and crepuscular (during twilight); nych-themeral corresponds to definition #2.

Dry bulb temperature. → Temperature, dry bulb.

Dry heat loss. → Heat loss, nonevaporative.

DuBois area. → Area, DuBois.

Eccritic body temperature. → Preferred body tem-perature.

Ectothermic temperature regulator. → Tempera-ture regulator.

Ectothermy: The pattern of temperature regulationof animals in which body temperature depends mainlyon the behaviorally controlled exchange of heat withthe environment. Autonomic thermoeffectors may betemporarily important in a few ectothermic species(panting in lizards, warming-up of insects). (Gk. ek-tos-outside; therme-heat) Antonym: endothermy.

Effective radiant field. → Radiant flux, effective.

Effective radiant flux. → Radiant flux, effective.

Effective radiating area. → Area, effective radiat-ing.

Effective temperature. → Temperature, effective.

Emissivity (ε): The ratio of the total radiant energyemitted by a body to the energy emitted by a full radi-ator at the same temperature.

Emissivity, directional (ε(θ,φ)): The ratio of the ther-mal radiance (Le,th) of a body in a given direction tothat of a full radiator (Le,(ε=1)) at the same temperature.ε(θ,φ) = Le,th(θ,φ)/Le,(ε=1) in which θ and φare the angularcoordinates defining the given direction.

Emissivity, hemispherical (εh): The ratio of the totalradiant energy emitted by an element of a surface intoa hemisphere to the energy by a similar element on thesurface of a full radiator. The element forms the centerof the equatorial plane of the hemisphere, but it is not



necessary to define its radius.

Emissivity, spectral (ελ): The ratio of the radiant fluxemitted by an element of surface per unit wavelengthinterval to the flux emitted by a full radiator at thesame temperature and in the same waveband.

Emissivity, window (εw): The ratio of the radiant en-ergy emitted by an element of surface between wave-length λ1 and λ2 to the flux emitted by a full radiator atthe same temperature and in the same waveband. Thequantity is a special type of spectral emissivity and isused because some biological materials have a lowemissivity in parts of the infrared or visible spectrum.These parts are known as windows.

Emittance. → Radiant exitance.

Endogenous antipyretic. → Antipyretic, endoge-nous.

Endogenous pyrogen. → Pyrogen, endogenous.

Endothermic temperature regulator. → Tempera-ture regulator.

Endothermy: The pattern of thermoregulation inwhich the body temperature depends on a high (ta-chymetabolic) and controlled rate of heat production.Behavioural responses are often used by endotherms.(Gk. endo-inside; therme-heat) Antonym: ectothermy.Note: The use of endothermy to denote the productionof heat within an organ or organism is etymologicallycorrect but may be found confusing as the same term isused in chemistry to mean the uptake of heat during achemical reaction.

Endotoxin: Heat stable compounds that are intrinsic tothe cell walls of Gram-negative bacteria. The term de-rives from the noxious effects on the infected host; inaddition, endotoxins act as potent exogenous pyrogensand stimulators of the acute-phase response, respec-tively. Endotoxins contain lipopolysaccharides (LPS)of high molecular weight. Other cell wall components,e.g., peptidoglycans, may have partially similar effects.

Energy: Energy may occur either as chemical, electro-magnetic, or mechanical energy. [Ws = J]. Synonymousto mechanical energy (force times length, height or dis-tance) is work, synonymous to thermal energy is heat.Work or heat per unit time (→ work rate or → heatflow) constitute physically → power, and are used as

components in the body heat balance equation.

Energy metabolism. → Metabolism, energy.

Environment. → Total environment.

Estivation: A state of lethargy (often during the sum-mer) with a reduction in body temperature and metab-olism demonstrated by some animals that aretemperature regulators when active. The term is usu-ally, but not exclusively, applied to ectothermic tem-perature regulators. (L. aestivus adj <aestas-summer)

Eurythermy: The tolerance by organisms of a widerange of environmental temperatures, or the accommo-dation to substantial changes in the thermal environ-ment. (Gk. eurus-wide; therme-heat) Antonym:stenothermy.

Euthermy. → Cenothermy.

Evaporative heat gain: → evaporative heat transferfrom the ambiance to the body (i.e., gain of heat en-ergy) due to condensation of vapor on the skin and/orthe surfaces of the respiratory tract, usually expressedin terms of energy per unit time and unit area of totalbody surface. [W], [W · m–2], [W · m–3], [W · kg–1]Note: evaporative heat transfer most frequently oc-curs by vaporization of water from body surfaces and is→ evaporative heat loss.

Evaporative heat loss: → evaporative heat transferfrom the body to the ambiance (i.e., loss of heat energy)by evaporation of water from the skin and the surfacesof the respiratory tract, usually expressed in terms ofheat flow [W] or heat flux [W·m–2] (energy per unittime and unit area of total body surface) or in [W·kg–1]or [W·m–3].Note: Evaporative heat loss comprises passive com-ponents, i.e., water vaporizing from respiratory sur-faces at normal respiration and water diffusing throughthe skin and vaporizing at the surface (→ insensibleperspiration); its thermoregulatory components areestablished by autonomic thermoeffectors, like ther-mal sweating and thermal panting, and behavioralthermoeffectors, like saliva spreading, wallowing,and other modes of behavioral surface wetting.

Evaporative heat loss coefficient. → Heat loss coef-ficient, evaporative.



Evaporative heat loss, respiratory. → Respiratoryevaporative heat loss.Evaporative heat transfer (E): The rate at which heatenergy is transferred by evaporation from or condensa-tion on the skin and the surfaces of the respiratory tract,usually expressed in terms of unit area of total body sur-face. The quantity (E) in the body heat balance equa-tion, evaporation and heat loss from the body areindicated by (+E), condensation and heat gain to thebody by (–E). [W] or [W · m–2].

Exertional heat stroke: An acute syndrome caused byan excessive rise in body temperature as the result ofoverloading or failure of the thermoregulatory systemduring exposure to heat stress while exercising in awarm environment.Note: Exertional heat stroke, in contrast to classicalheat stroke, occurs most commonly in healthy youngor middle-aged adults; cutaneous vasodilatation is re-duced and thermal sweating may decrease but is oftenstill conspicuous.

Exitance. → Radiant exitance.

Exogenous pyrogen. → Pyrogen, exogenous.

Febrile: A term used to describe the state of an organ-ism during a fever. Antonym: afebrile

Febrile convulsions. → Convulsions, febrile.

Fever: A state of elevated core temperature which isoften, but not necessarily, part of the defensive re-sponses of organisms (host) to the invasion by live (mi-croorganisms) or inanimate matter recognized aspathogenic or alien by the host. The rise in core tem-perature is usually designated as due to a change in thethermocontroller characteristics resulting in an eleva-tion of the set-point of body temperature. The highertemperature is actively established and defended by theoperation of heat-producing and heat-conserving ther-moeffectors. Time courses and extent of natural feversare variable, but an upper temperature limit (41°C inhumans) is seldom exceeded, at which level core tem-perature is maintained for some time and eventuallyreduced when the set-point of temperature regulationreturns to its normal level. While any rise in body tem-perature may be due to fever, those rises which are notaccompanied by supportive changes in thermoeffectoractivities, are termed hyperthermia. The humoralmechanisms underlying fever consist of the alterationof the neural control of body temperature by agents

named pyrogens. Endogenous pyrogens (e.g., pros-taglandin E2) are usually the obligatory mediators of fe-ver, but direct actions of exogenous pyrogens are notruled out. Fever can also result as an idiopathic condi-tion of the body. It can also be caused by emotionalstress (→ stress fever). The exact mechanisms of feverinduction are not yet clear.Note: Typical natural fever in response to bacterial in-fection is induced by interleukin-1 (IL-1), IL-6 andother cytokines which are formed as mediators in themultifactorial humoral host-defence response termedacute-phase response. Limited febrile rises in coretemperature are apparently harmless, as long as bodilyfunctions are not compromised by other disturbances orstressful conditions. Fever may contribute to the bene-ficial effects of the humoral host-defence responses toinfection.

Fever, stress. → Stress fever.

Freezing cold injury (FCI): Tissue damage (frostbite)resulting when tissue temperature falls below its freez-ing temperature (ca. –2°C). 90% of FCI’s occur in ex-posed skin and the extremities. The development ofFCI is primarily determined by the ambient tempera-ture, Antonym: Non-freezing cold injury (NFCI).

Full radiator. → Radiator, full.

Genetic adaptation. → Adaptation, genotypic.

Genotypic adaptation. → Adaptation, genotypic.

Globe temperature. → Temperature, globe.

GDP-binding protein. → UCP1.

Gular fluttering: The rapid oscillations of the hyoidapparatus and hence of the gular region of some birds asa characteristic form of thermal panting during expo-sure to high ambient temperature, by which means airis moved across the moist surfaces of the upper respira-tory tract.

Habituation: Reduction of responses to or perceptionof a repeated stimulation.

Heat. → Energy.

Heat balance equation. → Body heat balance equa-tion.



Heat capacity: The product of the mass of an objectand its specific heat. [J ·°C–1]

Heat content, body: The product of the body mass, itsaverage specific heat, and the absolute mean bodytemperature. [J]Note: The actual value of this term is seldom calcu-lated. It is used only in the determination of heat stor-age. → Storage of body heat.

Heat cramps: Painful spasms of skeletal muscles re-lated to prolonged heat stress.Note: Heat cramps are usually strong painful tetaniccontractions of groups of extremity or abdominal mus-cles. They are related to prolonged heat stress, pro-found thermal sweating and water but not salt deficitreplacement.

Heat endurance.→ Heat toleranc.

Heat exhaustion: Muscular weakness, fatigue, anddistress, resulting from prolonged exposure to heat.Core temperature is elevated and thermal sweatingand cutaneous vasodilatation are commonly but not in-variably reduced. This condition is aggravated by mus-cular exertion, dehydration and hyponatremia.Circulatory abnormalities may occur.

Heat flow [H]: The amount of heat transferred perunit time between parts of a body at different tempera-tures, or between a body and its environment when atdifferent temperatures. [W]. Physically it constitutes →power.

Heat flow balance equation.→ Body heat balanceequation.

Heat flux: Heat flow passing through unit area of agiven surface. [W · m–2]

Heat gain. → Heat transfer.

Heat loss. → Heat transfer.

Heat loss coefficient, evaporative. → Heat transfercoefficient, evaporative.

Heat loss, dry: The sum of heat flows or heat fluxesby radiation, convection, and conduction from a bodyto the environment. [W] or [W · m–2] Synonyms: sen-sible heat loss; heat loss, Newtonian.Note: In meteorological literature, sensible heat loss

refers to convection only and does not include otherforms of heat transfer.

Heat loss, evaporative. → Evaporative heat loss.

Heat loss, insensible. → Evaporative heat loss.Note: The term insensible heat loss should be avoidedin favour of evaporative heat loss, because of possibleconfusion with insensible water loss which impliesevaporative heat loss but relates to fluid balance.

Heat loss, Newtonian. → Heat loss, dry.

Heat loss, nonevaporative. → Heat loss, dry.

Heat loss, sensible. → Heat loss, dry.

Heat production, metabolic. → Metabolic heat pro-duction.

Heat production (excess), postprandial: The increasein metabolic heat production, relative to its postab-sorptive resting level, in the hours following food in-take. Its relationship to specific dynamic effect, ordiet-induced thermogenesis is not clear.Note: While the term postprandial heat production iscoming into use, it is recommended to include the spec-ification excess, because the definition means heat pro-duction in excess of resting metabolic rate (RMR).

Heat production, total. → Total heat production.

Heat shock protein (HSP): Intracellular proteinspresent in every species, from bacteria to humans.Among the multiple functions ascribed to these pro-teins they protect nascent proteins, halt proteinsde-folding etc. Their generation may alter the thresholdfor thermal injury.

Heat shock response. → Thermotolerance.

Heat, specific. → Specific heat.

Heat storage, change in: → Storage of body heat.

Heat stroke: An acute syndrome caused by an exces-sive rise in core temperature as the result of overload-ing or failure of the thermoregulatory system duringexposure to heat stress. It is characterized by a large va-riety of pathophysiological alterations of bodily func-tions, including mental disturbances, with a highincidence of permanent or fatal damage.



Note: Classical heat stroke, in contrast to exertionalheat stroke, occurs under sedentary conditions, mostcommonly in very old or very young people; cutaneousvasodilatation is greatly reduced and thermal sweatingis commonly absent.

Heat syncope: Collapse, usually with loss of con-sciousness, during exposure to heat. The symptoms aresimilar to those of the vasovagal syndrome (fainting).

Heat tolerance: The ability to tolerate high ambienttemperatures. This term comprises a variety of physi-ological characteristics. Homeotherms (tachymeta-bolic species) are often characterized as heat tolerant,if they remain comfortable or are able to balance heatproduction and heat loss at particularly high ambienttemperatures. Homeothermic species are also char-acterized as heat tolerant, if they are capable to main-tain normal functions, or to survive, at bodytemperatures exceeding their normal range; this mayinvolve the facility of selective brain cooling. – Poiki-lotherms (bradymetabolic species) may also be spec-ified as heat tolerant, if they are able to survive veryhigh body temperatures. All forms of heat tolerancemay be subject to adaptation or acclimat(izat)ion.Synonym: heat endurance.Note: In the OED the words tolerance and enduranceare almost synonymous. From a physiological point ofview a distinction is sometimes made between heat tol-erance and heat endurance, the former term is some-times used in a more general sense and includes allforms of tolerance, while the latter is sometimes used ina more specific sense as in tolerance with time during asustained stress, e.g., exercise endurance.

Heat transfer: Process of heat flow [W], i.e., the rateat which heat energy is transferred from one part of anorganism to another especially between body core andshell. In this case the heat transfer is a combination ofconduction and convection. A more frequently investi-gated topic of thermal physiology is heat transfer be-tween an organism and its environment, byconduction, convection, radiation, evaporation, or acombination of these. Net transfer from the organism tothe environment is heat loss, and from the ambianceinto the organism is heat gain. → Body heat balanceequation.

Heat transfer coefficient: A parameter (h) [W · m–2

·°C–1] which determines the amount of heat flux (H)due to a temperature difference (∆T): H = h· ∆T. H maybe defined for conduction, convection, radiation (or the

combination of these processes) and for evaporation(see below).

Heat transfer coefficient, combined nonevaporative(hcomb): The ratio of total heat transfer per unit areaby radiation, convection, and conduction to the temper-ature difference between the surface and operativetemperature of the environment.

hcomb = hr + hc + hk [W· m–2 · °C–1]

Heat transfer coefficient, conductive (hk): The netheat transfer by conduction per unit area between asurface and a solid or stationary fluidic medium in con-tact with the surface per unit temperature difference(∆T) between the surface and the substance with whichit is in contact.

hk = K· ∆T–1 [W·m–2 ·°C–1]

Heat transfer coefficient, convective (hc): The netheat transfer per unit area between a surface and amoving fluidic medium per unit temperature difference(∆T) between the surface and the medium.

hc = C· ∆T–1 [W· m–2· °C–1]

Heat transfer coefficient, evaporative (he): The netheat transfer per unit vapor pressure gradient causedby the evaporation of water from a unit area of wet sur-face or by the condensation of water vapor on a unitarea of body surface. The driving force is the vaporpressure gradient from Pws (on the surface) to Pwa (ofthe ambient gas). Thus

he = E(Pws – Pwa)–1· [W· m–2· Pa–1] or [W· m–2 ·Torr–1].

In terms of the latent heat of vaporization (λ or LHV)of water, the gas constant for water vapor (Rw), themean temperature (T) of the medium in °K and themass transfer coefficient (hD)

he = hD·λ·Rw–1·T–1

Note: In most physiological applications the vaporpressure gradient instead of the concentration gradientcan be considered as the driving potential for the evap-orative process since the temperature difference be-tween the evaporating surface and the ambient air issmall in relation to the average temperature of the sur-face-water vapor medium.



Heat transfer coefficient, radiative: The net rate ofheat transfer per unit area by the exchange of thermalradiation between two surfaces, per unit temperaturedifference between the surfaces. [W · m–2 · °C–1]

Heat transfer coefficient, radiative (linear) (hr): Ac-cording to the Stefan-Boltzmann Law, the exchangeof radiation between two black surfaces at temperaturesT1 and T2 [°K] is proportional to σT4, where σ is theStefan-Boltzmann constant. When the ratio (T1 – T2)/Tis small, where T = (T1 + T2)/2,σ(T1

4 – T24) ≈ 4σT3 ·

(T1 + T2) and the term 4σT3 can be treated as a linearheat transfer coefficient. [W · m–2 · °C–1]

Heliothermy: The regulation of the body temperatureof an ectothermic animal by behavioral adjustments ofits exposure to solar radiation. (Gk. helios-the sun;therme-heat)

Hemihidrotic response: Suppression of thermalsweating, due to the skin pressure effect, if one half ofthe body is affected.

Hemispherical emissivity. → Emissivity, hemispher-ical.

Heterothermy: The pattern of temperature regula-tion in a tachymetabolic species in which the variationin core temperature, either nychthemerally or sea-sonally, exceeds that which defines homeothermy.(Gk. hetero-different; therme-heat)Note: This is an arbitrary term in two senses: i) becausehetero = a difference from (i.e., a difference betweentwo) rather than a wide range, and ii) because the dis-tinction that is being made between thermostable andrather less thermally stable species depends on an arbi-trary division. →: 1. poikilothermy (diversified tem-peratures) although etymologically satisfactory hasalready been given a more restricted meaning. 2. steno-thermy (narrow temperature range) and eurythermy(wide temperature range) would have suited the cir-cumstance well, but these terms are already in use todescribe animals that are able to adjust to narrow rangesand wide ranges respectively, of ambient tempera-ture.

Heterothermy, local: The pattern of temperature inthose parts of the body which comprises the thermalshell of homeotherms.

Hibernation: The state of winter (sometimes late fallor early spring) lethargy with a reduction in body tem-

perature and metabolism of some animals that are ho-meothermic temperature regulators when active. (L.hibernare- to pass the winter)Note: Body temperature is regulated in the state of hi-bernation, however, with set-point differing from thatin the state of cenothermy (euthermy).

Hidromeiosis: The swelling of keratinized layers ofthe skin, due to prolonged exposure to water or sweat,which blocks sweat ducts and reduces sweating rate.(Gk. hidros-sweat; meiosis-decrease)

Homeostasis: General term characterizing the relativeconstancy of physico-chemical properties of the inter-nal environment of an organism as being maintained byregulation. (Gk. homoio-similar, resembling; sta-sis-standing)

Homeothermy: The pattern of temperature regula-tion in a tachymetabolic species in which the cyclicvariation in core temperature, either nychthemerallyor seasonally, is maintained within arbitrarily definedlimits despite much larger variations in ambient tem-perature, i.e., homeotherms regulate their body tem-perature within a narrow range. (Gk. homoio-similar,resembling; therme-heat) Synonym: homoiothermy.Note: A number of homeothermic species may tempo-rarily enter states in which their set-range of body tem-perature regulation is not definable or much lowerthan during their normal state of homeothermy (→heterothermy, hibernation, torpor).

Homoiothermy. → Homeothermy.

Humidity, absolute (γ): Mass of water vapor in air perunit volume of air/water vapor mixture. [kg · m–3]

Humidity, relative (φ): The ratio of the mol fraction ofwater vapor present in a volume of air to the mol frac-tion present in saturated air, both at the same tempera-ture and pressure; in thermal physiology, the ratio of thesaturated vapor pressure at the dew point tempera-ture (Ps, dp) of the enclosure to the saturated vaporpressure at its dry bulb temperature (Ps, db) [ND].When the relative humidity is expressed as a percent-age, the symbol is RH.

Hyperpnea, thermal. → Thermal hyperpnea.

Hyperthermia: The condition of a temperature regu-lator when core temperature is above its range speci-fied for the normal active state of the species. (Gk.



hyper-over; therme-heat)Note: Hyperthermia may be regulated (e.g., in feveror during dehydration) or may be forced if total heatproduction exceeds the capacity for heat loss.

Hyperthermia, induced: The state of hyperthermiaproduced purposefully by increase in heat load and/orinactivation of heat dissipation by physical and/or phar-macological means.Note: Induced hyperthermia is used in a few specificconditions as a therapeutical adjuvant. It may also belocally induced (e.g., by microwave irradiation or organperfusion). Induced hyperthermia should be distin-guished from fever induced by administration of pyro-gens, which is an obsolete technique to produceelevations of body temperature in medicine for thera-peutical purposes.

Hyperthermia, malignant: A pharmacogenetic my-opathy characterized by a rapid rise in body tempera-ture in genetically susceptible subjects duringanaesthesia (triggering agents: halothane, succinyl cho-line, etc.). Malignant Hyperthermia stems from im-pairment (genetically originated) in the sarcoplasmicreticulum, leading to alteration in handling of the ex-cess cytosolic Ca++, skeletal muscle rigidity and spas-ticity and, in-turn, increased heat production. Theoften fatal hyperthermia is the result of heat produc-tion in skeletal muscle and supported by the limitationsof active heat dissipation during anaesthesia. It is com-plicated by sympathetic activation, excessive lactateproduction and acidosis, muscle rigidity, myoglobin-aemia, and disturbances of cellular permeability.

Hypothermia: The condition of a temperature regu-lator when core temperature is below its range speci-fied for the normal active state of the species. (Gk.hypo-beneath; therme-heat).Note: Hypothermia may be regulated (e.g., Torpor,Hibernation) or may be forced if heat loss exceeds thecapacity for total heat production.

Hypothermia, accidental: The condition of a temper-ature regulator following an accidental or deliberatedecrease in core temperature below its range specifiedfor the normal active state of the species. The conditionusually occurs in a cold environment and is associatedwith an acute problem, but without primary pathologyof the temperature regulating system.

Hypothermia, induced: The state of hypothermiaproduced purposefully by increasing heat loss from the

body and/or inactivation of heat conservation and heatproduction by physical and/or pharmacological means.Note: Induced hypothermia is employed in surgery toreduce the oxygen demand of tissues that are particu-larly sensitive to circulatory arrest.

Indirect calorimetry. → Calorimetry, indirect.

Induced Hypothermia.→ Hypothermia, induced.

Infrared. → Radiant energy.Note: The infrared wave band is radiant heat.

Insensible heat loss. → Heat loss, insensible.

Insensible perspiration: The mass of water passingthrough the skin by diffusion per unit area in unit time.[kg · m–2 · s–1] Synonym: passive cutaneous water va-por exchange. Insensible perspiration represents afraction of the insensible water loss.Note: Hitherto, rates of insensible perspiration and ofsweating have been expressed most commonly in [g ·m–2 · h–l], but this does not conform with SI conven-tions. The most convenient SI term appears to be [mg ·m–2 · s–1] (3.6 g · m–2 · h–1 = 1 mg · m–2 · s–1).

Insensible water loss: The sum of the water lost by dif-fusion through the skin and water lost in breathing, andexcluding any water excreted (e.g., in sweat, urine, fe-ces). [kg · s–1] or [kg · m–2 · s–1] Loss of water as vaporimplies loss of heat according to the latent heat of va-porization of water.Note: Restricting the term water to its state as a fluid isobsolete, as is the designation of water loss as insensi-ble if it is lost as water vapor. However, the term insen-sible water loss is still used, mainly in the literaturepertaining to farm animals. In thermal physiology itsuse should be avoided because of possible confusionwith insensible heat loss; passive evaporative waterloss should be considered as an alternative term.

Insulation. → Thermal resistance.

Interleukin-1 (IL-1): Heat labile proteins produced by im-mune cells (e.g., mononuclear phagocytes) when activatedby microorganisms or their products. There are two formsof IL-1 (α and β). The production of interleukin-1 (IL-1) iscaused by infection, injury and trauma. It (as well as othercytokines) produces the acute phase response. IL-1 is con-sidered an important endogenous pyrogen, as are interleu-kin-6 (IL-6), tumor necrosis factor α (TNF α), and someother cytokines.



Interthreshold zone. → Thermoeffector thresholdzone.

Irradiance (E): The radiant flow incident on or pass-ing through unit area of a surface. [W · m–2]

Katathermometer: An instrument which measures theheat flow from a surface to a cooler environment.

Latent heat of fusion: The quantity of heat absorbed,or released, in the reversible change of state, melting orfreezing, of unit mass of solid or liquid, without changeof temperature. [J · g–1]Note: The melting of 1 g of ice to water at 0°C absorbs333.15 J.

Latent heat of vaporization (λ or LHV): The quantityof heat absorbed (or released) by a volatile substance(fluid) per unit mass in the process of its reversiblechange of state by evaporation (or condensation) underisobaric and isothermal equilibrium conditions. [J · g–1]Note: For water: λ = 2490.9 – 2.34 T, with T = temper-ature of water in °C, e.g., l g of water, when changingfrom fluid to vapor at T = 34°C, absorbs 2411.3 J.

Least observed metabolic rate. → Metabolic rate,least observed.

Lower critical temperature. → Critical tempera-ture, lower.

Lower temperature survival limit. → Temperaturesurvival limit, lower.

Malignant hyperthermia. → Hyperthermia, malig-nant.

Mass diffusivity. → Diffusivity, mass.

Mass transfer coefficient (diffusion) (hD): The rate ofmass transfer (·m) from a vaporizing liquid (usually wa-ter) to a moving gas (usually air) in contact with it, perunit area (A) of the liquid surface and per unit differ-ence between the vapor density (saturated) at the sur-face (pws) and the vapor density of the ambient gas(pwa), expressed in the equation

hD = ·m · A–1 (pws – pwa)–1 [m · s–1]

→ heat transfer coefficient, evaporative; masstransfer rate.

Mass transfer, convective: The transport by convec-tion of one component of a nonreactive mixture (usu-ally air-water) across an interface caused by aconcentration gradient often accompanied by a trans-formation of phase and by a simultaneous transfer ofheat.

Mass transfer rate ( ·m): The rate of transfer of mass.[kg · s–1]

Maximum metabolic rate. → Metabolic rate, maxi-mum.

Maximum oxygen consumption. → Oxygen con-sumption, maximum.

Mean body temperature. → Temperature, meanbody.

Mean radiant temperature. → Temperature, meanradiant.

Mean skin temperature. → Temperature, meanskin.

Menopausal hot flush (flash): An abrupt heat dissipa-tion response, provoked or unprovoked, occurring inhypoestrogenic women following the decline of ova-rian function. The response typically lasts about 5 min-utes and consists of peripheral vasodilation, sweatingand reports of intense warmth.

Met: An assigned unit of measurement to designate"sitting-resting" metabolic rate of man.

1 met = 58.15 W · m–2 = 50 kcal · h–1 · m–2

It is an empirical unit of measurement to express themetabolic rate (M or MR) of a man whose clothing hasan insulative value of 1 clo when he is sitting at rest incomfortable indoor surroundings (21°C).

Metabolic body size: The function of an animal's bodysize to which standard metabolic rate (SMR) (orbasal metabolic rate (BMR)) is directly proportional.Synonym: metabolically effective body mass.Note: Metabolic body size is often calculated usingbody mass raised to a power (Wb) as in the expressionM = aWb. That the resting metabolic rate (RMR) ofadult animals (both tachymetabolic and bradymeta-bolic) changes in proportion to the 3/4 power of bodymass is an empirically established fact, and the use of



W3/4 as the metabolic body size permits comparisonsto be made between the metabolic levels of differentanimals. When W2/3 is used, this implies proportional-ity of metabolic body size to the animal's surface area(→ surface rule). The relation between metabolic rate(M or MR) and body size (M = aW3/4) is a particularcase of the general allometric equation (y = axb) whichsays that plotting a biological variable, y, against an-other biological variable, x, after logarithmic transfor-mation (i.e., log y = log a + b · log x) will result in astraight line with slope b. Ref: von Bertalanffy, L., Hel-goländer Wiss. Meeresuntersuch. 9: 5, 1964.

Metabolic energy production. → Metabolic energytransformation.

Metabolic energy transformation (M). → Metabolicrate.

Metabolic heat production (H): Rate of transforma-tion of chemical energy into heat in an organism, usu-ally expressed in terms of unit area of the total bodysurface (→ total body area). H is equal to M – (W) inthe body heat balance equation. [W · m–2], [W · kg–1]or [W]Note: During positive work rate (+W) or in the ab-sence of work (W = 0) metabolic heat production (H =M – (+W)), i.e. positive work rate subtracted from therate of metabolic energy transformation (=meta-bolic rate), equals total heat production. When workis being done on the body by an external source (nega-tive work), total heat production is the sum of meta-bolic rate (M or MR) (which is equal to metabolic heatproduction in this condition) and the heat liberatedwithin the body due to negative work (M – (– W)).

Metabolic level: The metabolic heat productionmeasured under standard conditions (→ metabolicrate, standard (SMR)) during a 24-h period divided bythe metabolic body size. [kJ · kg–3/4· (24 h)–1]*Note: *1 kJ . kg–3/4 · (24 h)–l = 0.2388 kcal · kg–3/4 ·(24h)–l. Metabolic levels are approximately constantwithin phylogenetic groups but may vary betweengroups. For example, mammalian and avian species(tachymetabolism) have higher metabolic levels thanother species (bradymetabolism), while the metaboliclevels of birds are apparently higher than those of mam-mals, and those of prototherian (monotreme) and met-atherian (marsupial) mammals are lower than those ofeutherian (placental) mammals.(Poczopko, 1971). Ref: Poczopko, P., Acta Theriolog-ica 16: 1, 1971.

Metabolic rate (M or MR): = metabolic energytransformation. [W], [W·m–2], [W·m–3], [W·kg–l],[W·kg–3/4] The rate of transformation of chemical en-ergy into heat and mechanical work by aerobic andanaerobic metabolic activities within an organism, usu-ally expressed in terms of unit area of the total bodysurface, i.e., as a heat flux. The quantity M in the bodyheat balance equation.Note: Metabolic energy transformation may not allresult from aerobic metabolic activities and may there-fore exceed that indicated by the rate of oxygen con-sumption. Part of the metabolic energytransformation may be used to do work on an externalsystem, and therefore the rate of heat production maybe less than the metabolic energy transformation.Terms in the body heat balance equation are often ex-pressed as quantities of energy per unit surface areaand per unit time [W · m–2], because heat exchange is afunction of area. Metabolic rate (M or MR) is given asthe total energy production in the organism in unit time[W] or often as the energy production per unit mass oftissue in unit time [W · kg–1]. For comparison of meta-bolic rates of animals of different body sizes, meta-bolic rate (M or MR) is usually related to (bodymass)3/4 (→ metabolic body size).

Metabolic rate, basal (BMR): metabolic energytransformation calculated from measurements of heatproduction or oxygen consumption in an organism in arested, awake, fasting* sufficiently long to be inpost-absorptive state, and thermoneutral zone (a par-ticular case of standard metabolic rate (SMR)).[W],[W · m–2], [W · m–3], [W · kg–1], [W · kg–3/4]Note: In these conditions, when the amount of work be-ing done on an external system is negligible, the rate ofheat production is equal to the rate of metabolism(metabolic energy production).* The period of fast-ing needs to be specified as this may be for days in largeanimals, and for much shorter periods for very smallmammals and birds.

Metabolic rate, lowest observed (LOMR): The lowestobserved rate of metabolism during specified periodsof minimum activity. [W], [W · m–2], [W · kg–1], [W ·kg–3/4] → metabolic rate, minimum observed(MOMR). The rationale and objective of lowest ob-served metabolic rate (LOMR) and minimum ob-served metabolic rate (MOMR) are identical: tomeasure the metabolic rates of small and wild animalsduring periods of minimal activity as the nearest thatcan be made to a measurement of a standard meta-bolic rate (SMR).



Note: There are small but significant differences intechnique: Minimum observed metabolic rate(MOMR) is the average metabolic rate (M or MR)during periods of minimum activity; lowest observedmetabolic rate (LOMR) is the lowest recorded meta-bolic rate (M or MR) during periods of minimum ac-tivity. Such brief low values may be influenced byphysical characteristics of the system of measurement.Note: lowest observed metabolic rate (LOMR) maybe lower than basal metabolic rate (BMR) (e.g., dur-ing some stages of sleep).

Metabolic rate, maximum (MMR): The highest met-abolic rate (M or MR) during a specified period ofwork compatible with sustained aerobic metabolism(i.e., when there is no progressive accumulation of lac-tic acid in the blood). [W], [W · m–2], [W · m–3], [W ·kg–1],[W · kg–3/4]Note: There may be some confusion between maxi-mum and peak metabolic rates (PMR). Both terms in-dicate maximum rates. The distinction is in usage:maximum relates to work, peak relates to cold expo-sure. The terms should also be distinguished from max-imum oxygen consumption.

Metabolic rate, minimum observed (MOMR): Aver-aged metabolic rate during specified periods of mini-mum activity. [W], [W · m–2], [W · m–3], [W · kg–l], [W· kg–3/4]Note: The metabolic rate (M or MR) of small animalsin particular, but also of larger wild animals, cannot bemeasured under basal or other standard conditions (→metabolic rate, basal (BMR), and metabolic rate,standard (SMR)). A practical solution to the problemis to measure metabolic rate (M or MR) continuouslyand accept the average metabolic rate (M or MR) dur-ing periods of minimum activity as the best possible es-timate of standard metabolic rate (SMR).

Metabolic rate, peak (PMR): The highest metabolicrate (M or MR) that can be induced in a resting animalby any cold environment. [W], [W · m–2], [W · m–3],[W · kg–l], [W · kg–3/4] Synonym: summit metabolicrate. → Metabolic rate, maximum (MMR).Note: Although summit metabolic rate (SMR) is now anaccepted term, peak metabolic rate (PMR) is prefera-ble because the abbreviation SMR is indistinguishablefrom that for standard metabolic rate (SMR).

Metabolic rate, resting (RMR): The metabolic rate(M or MR) of an animal that is resting in a thermoneu-tral environment but not in the postabsorptive state.

[W], [W· m–2], [W · m–3], [W · kg–1], [W · kg –3/4]Note: A particular case of standard metabolic rate(SMR) used when the subject cannot be brought to afasting condition, e.g., ruminant animals. The period offood deprivation should be stated.

Metabolic rate, standard (SMR): metabolic energytransformation calculated from measurements of heatproduction or oxygen consumption in an organism un-der specified standard conditions*. [W], [W · m–2], [W· m–3], [W · kg–1], [W · kg–3/4]Note: The conditions are usually such that the amountof work being done on an external system is negligible.The rate of heat production is then an acceptable indexof the rate of metabolism. * The specified standard con-ditions are usually that the organism is rested (or as nearto rested as is possible), fasting (if possible), awake,and in a thermoneutral environment. The extent towhich standard conditions can be achieved varies withspecies. → Metabolic rate, minimum observed(MOMR).

Metabolic rate, summit. → Metabolic rate, peak.

Metabolic scope. → Scope, metabolic.

Metabolically effective body mass: → metabolicbody size (preferred synonym).Note: The term metabolically effective body massmay be wrongly understood to be that part of the bodymass which is metabolically active in contrast to a partthat is metabolically inert. Its use should be avoided.

Metabolism. → Metabolism, energy. (Gk. metab-ole-change)Note: Metabolism is a general term which relates tochemical and physical changes occurring in living or-ganisms. In thermal physiology metabolism invariablyrelates to the transformation of chemical energy intowork and heat. In other divisions of physiology theterm is used in relation to other changes in state ofchemical energy (e.g., from storage compounds toreadily available compounds, including the energytransferring polyphosphates, and vice versa), or to turn-over of material between different states (e.g., calciumsalts from ionized to solid, and vice versa).

Metabolism, anaerobic: Transformation of matter andenergy without uptake of oxygen.

Metabolism, energy: The sum of the chemicalchanges in living matter in which energy is trans-



formed. (Gk. metabole-change) → metabolism.

Microwave: Part of the electromagnetic spectrum withwavelength from 1 to 100 mm. Microwaves are ab-sorbed by metal and water and thus permit deep heatingof aqueous or metallic bodies exposed to them (→ ra-diant energy).

Minimum observed metabolic rate. → Metabolicrate, minimum observed.

Natural convection. → Convective heat transfer.

Negative work. → Work rate, negative.

Neuroleptic malignant syndrome: The developmentof severe muscle rigidity, elevated core temperature,and a disturbance of mental status associated with theuse of neuroleptic medication.

Nocturnal: Occurring during the nighttime, as distinctfrom daytime. (L. nocturnus adj < nox-night) Antonym:diurnal.

Nonevaporative heat loss. → Heat loss, nonevapora-tive.

Non-freezing cold injury (NFCI): Tissue damage re-sulting from prolonged exposure to ambient tempera-tures between 15°C down to –0.5°C. In NFCI thenormal thermoregulatory responses of the injured bodyare disturbed. All types of tissue may be damaged bysustained cooling, but the most serious effects occur inthe nerves and blood vessels. Antonym: Freezing coldinjury (FCI).

Nongenetic adaptation. → Adaptation, phenotypic.

Nonshivering thermogenesis. → Thermogenesis,nonshivering.

Nonthermal sweating. → Sweating, nonthermal.

Normothermy. → Cenothermy.

Nychthemeral: Relating to an exact period of 24 h.(Gk. nux-night; hemera-day).

Nychthemeron: A period of 24 h, consisting of a dayand a night (SOED).

Obligatory nonshivering thermogenesis. → Ther-

mogenesis, nonshivering (obligatory).

Operative temperature. → Temperature, operative.

Optimal body temperature range: The range of bodytemperatures in which a species carries out its normaldaily activity.Note: This “ecological optimum” integrates internaland external forces acting on a species; it appliesmostly to ectotherms.

Oxygen consumption, maximum ( ·VO2max): Themaximum rate at which an organism can take up oxy-gen. [ml · s–1], conventionally [ml · min–1], [l · min–1]Note: Determination of this parameter requires veryhigh motivation of the subject and can probably bedone only on humans. Criteria used to show that a hu-man subject has reached the ·VO2max although not as yetagreed upon, include an indication of no further in-crease in oxygen uptake during further increase in workload.

P 32000 polypeptide. → UCP1

Panting, thermal. → Thermal panting.

Partitional calorimetry. → Calorimetry, partitional.

Passive cutaneous water exchange: The passagethrough the skin in either direction of water down an os-motic gradient per unit area in unit time. [kg . m–2 · s–1],also [mg · m–2 · s–1]Note: Passive cutaneous water exchange occurs onlywhen the skin is covered with water or an aqueous so-lution.

Passive cutaneous water vapor exchange: The pas-sage through the skin in either direction of water vapordown a water vapor pressure gradient per unit area inunit time. [kg · m–2 · s–1], also [mg · m–2 · s–1]. Syn-onym: insensible perspiration.

Passive temperature lability. → Temperature labil-ity, passive.

Peak metabolic rate. → Metabolic rate, peak.

Phenotypic adaptation. → Adaptation, phenotypic.

Physical temperature regulation. → Temperatureregulation, physical.



Physical thermoregulation. → Temperature regula-tion, physical.

Physiological temperature regulation. → Tempera-ture regulation, physiological.

Physiological thermoregulation. → Temperatureregulation, physiological.

Piloerection: Involuntary bristling of hairs or rufflingof feathers; in thermal physiology an autonomic ther-moeffector response often associated with behavioral(e.g., postural) adjustments.

Poikilothermy: Large variability of body temperatureas a function of ambient temperature in organismswithout effective autonomic temperature regulation.As a rule, bradymetabolism implies poikilothermywith only temporary exceptions in some species (e.g.,active warming-up of insects before flight). Synonym:Temperature conformer. Tachymetabolism excludespoikilothermy, except in pathological conditions (im-pairment of temperature regulation), but permits het-erothermy or torpor to occur in a number of species.(Gk. poikilos-changeful, diversified; therme-heat) Ant-onym: homeothermy.Note: For ectothermic organisms without effectivethermoregulatory behavior, poikilothermy is synon-ymous with temperature conformity. Poikilo- is in-consistent with other uses of this root in biology; itshould, perhaps, be poecilo- or pecilo-; cf. poeciloblast,poecilocyte (OED).

Polypnea, thermal. → Thermal polypnea.

Positive work. → Work, positive.

Postprandial (excess) heat production. → Heat pro-duction (excess), postprandial.

Potohidrotic response: The instantaneous intensesweating appearing when hyperthermic dehydratedhumans drink. (Gk. poto-drink; hidro-sweat).

Power (W): Physically power [W] is energy per timeunit. In the case of mechanical energy per time unit it iscalled mechanical power or, particularly in thermal,sports and occupational physiology, work rate and at-tributed the letter W.Note: W, e.g., in the heat balance equation, is workrate in [W] and not work in [Ws = J]. In the case of ther-mal energy (heat) per time unit it is called heat flow and

attributed the letter H [W].Note: All quantities in the so-called body heat balanceequation constitute power (either heat flow or workrate). For convenience, they may be expressed in [W],in [W · m–2], in [W · m–3], or in [W · kg–1].

Preferred ambient temperature: The range of ambi-ent temperature, associated with specified radiationintensity, humidity, and air movement, from which anunrestrained human or animal does not seek to move toa warmer or colder environment. [°C]

Preferred body temperature: The range of core tem-perature within which an ectothermic animal seeks tomaintain itself by behavioral means. [°C]

Pressure (P): The force exerted per unit area. [Pa, bar,Torr] A liquid or gas enclosed in a container will exertan uniform pressure on its walls, if the influence ofgravitational forces is excluded or of little importanceas in case of gases.Note: The SI-derived unit of pressure is the Pascal (Pa),which is defined as a newton per square meter (N·m–2).An alternate SI-derived unit of pressure is the bar (bar)defined as 105 Pa. The unit of pressure currently ap-proved by the International Commission of the IUPSfor Respiratory Physiology is the Pascal [Pa] which issynonymous with the pressure unit mmHg (an obsoles-cent unit). One Torr is equal to 1.33322 millibars or133.322 Pa.

Pressure, atmospheric (P): The pressure due to theweight of the atmosphere as indicated by a barometer.Standard atmospheric pressure is the pressure101.325 kilopascals (kPa) (or the weight of a 760 mmcolumn of mercury at 0°C with density 13.5951 × 103

kg · m–3 under standard gravity of 9.80665 m · s–2) andis equivalent to 1,013.25 millibars or to 760 Torr.

Pressure, water vapor (Pw): The pressure exerted bywater vapor. If water vapor is confined over its liquid sothat the vapor comes into equilibrium with the liquid,and the ambient temperature Ta of the medium is heldconstant, the vapor pressure approaches a maximumvalue called the saturated vapor pressure (Ps,Ta) or(Psa). The term vapor pressure (water) is always syn-onymous with a saturated vapor pressure at a temper-ature T. [Pa, millibar, Torr]Note: The water vapor pressure (→ vapor pressure(water)) of an enclosure may be calculated from theobserved wet bulb and dry bulb temperatures and theatmospheric pressure, by using standard steam or mete-



orological tables and formulas (Ref: Chambers, A.B., Apsychrometric chart for physiological research, J. Appl.Physiol. 29: 406–412, 1970). The water vapor pressurein an enclosure is equal to the saturated vapor pres-sure at its dew-point temperature (Ps,Tdp) or to theproduct of the relative humidity (N) and the saturatedvapor pressure at its dry bulb temperature (NPs,Tdp).

Projected area. → Area, projected.

Pyrexia: The condition of being febrile.Note: Pyrogen: The generic term for any substancewhether exogenous or endogenous that causes feverwhen introduced into or released in the body. (Gk.pur-fire; <gen-become).

Pyrogen, bacterial: Any pyrogen derived from bacte-ria.Note: All endotoxins are bacterial pyrogens.

Pyrogens, endogenous: Heat labile proteins, and lipidsthat cause fever. Their production is often stimulatedby exogenous pyrogens (microorganisms and theirproducts, e.g., antigens), but also by injury, trauma andstress. The best identified endogenous pyrogen is in-terleukin-1β (IL-1β). It is thought that this cytokineinduces fever via the production of another cytokine,IL-6. Other endogenous pyrogens include inter-feron-α and tumor necrosis factor-α. The final com-mon pathway for cytokine-mediated fever is generallythought to be the production of prostaglandins of the Eseries in or near the anterior hypothalamus.

Pyrogen, exogenous: A substance which, when enter-ing the inner environment of a multicellular organism(host) will cause fever. Stimulation of the productionand/or release of endogenous pyrogens is, at least inmost instances, the humoral effect from which fever ul-timately results.Note: The most potent exogenous pyrogens areheat-stable lipopolysaccharides intrinsic to the cellwalls of gram-negative bacteria (→ endotoxin). Manyexogenous pyrogens of different molecular composi-tion exist; they comprise compounds intrinsic to bacte-ria, viruses, fungi, mycobacteria, and some protozoa, aswell as foreign proteins and some steroids.

Q10: The ratio of the rate of a physiological process ata particular temperature to the rate at a temperature10°C lower, when the logarithm of the rate is an ap-proximately linear function of temperature (Ref. Pre-cht, H., J. Christophersen, H. Hensel, & W. Larcher.

Temperature and Life, Berlin-Heidelberg-New York,Springer, 1973, p. 17 ff.).

Radiance (Le): Radiance at a surface element (dA) ofa source or receiver is the radiant intensity (dI) fromdirection θ divided by the orthogonal projection of thissurface element (dA ·cosθ) on a plane perpendicular tothe direction θ. θ is the angle between the normal to theelement (dA) of the source or receiver and the directionof the observation. [W · sr–1 · m–2]

Radiance thermal (Le,th): radiance due to thermal ra-diation. [W · sr–1 · m–2]

Radiant absorptance, total (α): The ratio of total ra-diant flux absorbed by a body to the total incident flux.

Radiant emittance. → Radiant exitance.

Radiant energy (Q): Energy travelling in the form ofelectromagnetic waves. [J]Note: This term should be distinguished from the radi-ant heat exchange (R) of the environment with thebody. That part of the electromagnetic spectrum of sig-nificance in thermal physiology is divided for conve-nience into the wavebands:

Radiant energy, spectral (Qλ): The radiant energyper unit wave length interval at wavelength λ. [J · nm–1]

Radiant exitance (Me): The radiant flux leaving anelement of a surface. This quantity includes radiationemitted, reflected, and transmitted by the surface.

Me = dφe/dA = ∫ Le · cos θ · dΩ[W · m–2]

Note: The name radiant emittance previously given tothis quantity is abandoned because it has given rise toconfusion. Thus, the term emittance is used to desig-nate either the flux leaving a surface whatever the ori-gin (emitted, reflected, or transmitted), or the fluxemitted by a surface (originating in the surface), or aquantity without dimensions similar to emissivity butapplicable only to a specimen.

Ultraviolet 0.25–0.38 µm

Visible 0.38–0.78 µm

Infrared 0.78–100 µm

Microwave 1–100 mm



Radiant exitance, self (Me,s): The radiant flux emit-ted by a surface. The flux considered does not includereflected or transmitted flux. [W · m–2]

Radiant exitance, thermal (Me,th): The radiant fluxemitted as thermal radiation by a surface.Note: In the case of a full radiator, the radiance (Le) isuniform in all directions. In consequence, when thesolid angle is measured in steradians, the radiant exi-tance has the numerical value Me = 4πLe.

Radiant field, effective. → Radiant flux, effective.

Radiant flow (φ): The amount of radiant energy perunit of time. [W]

Radiant flow spectral (φλ): The radiant flow per unitwavelength interval at wavelength λ. [W · nm–1]

Radiant fIux (dφ/dA): The radiant flow per unit area.[W · m–2]Note: The radiant flux emitted by a surface is the ther-mal radiant exitance. The radiant flux incident on orpassing through an area is the irradiance.

Radiant flux, effective (Hr): The net radiant flux ex-changed with all enclosing surfaces and with any in-tense directional sources and sinks for exchange ofradiant heat by a human or human-shaped object whosesurface temperature is hypothetically at ambient airtemperature. [W · m–2]Note: If the same object, with surface temperature atambient air temperature, is assumed to exchange ra-diant heat at a given effective radiant flux with a hy-pothetical black surface enclosure of correspondingwall temperature, then this condition defines the effec-tive radiant field transferring the amount of heat perunit time and per unit surface of the object which isquantified by the effective radiant flux. In this sense,effective radiant field and effective radiant flux aresynonymous terms.

Radiant heat exchange (R): The net rate of heat ex-change by radiation between an organism and its envi-ronment, usually expressed in terms of unit area of thetotal body surface, i.e., as a heat flux. The quantity (R)in the body heat balance equation where (–R) = heatgain and (+R) = heat loss. [W] or [W · m–2]

Radiant intensity (I): The radiant flow proceedingfrom a source per unit solid angle in the direction con-sidered. [W · sr–1]

Radiant intensity, spectral (Iλ): The radiant inten-sity per unit wave length interval. [W · sr–1 · nm–1]

Radiation reflectance. → Reflectance, radiation.

Radiation shape factor (Fij): A dimensionless quan-tity expressing the fraction of the diffuse energy emit-ted by a surface (or a source), denoted by the subscripti, that is received by another surface, denoted by thesubscript j, visible by it and in known geometric rela-tion with it. Synonym: radiation view factor.

Radiation transmittance. → Transmittance, radia-tion.

Radiation view factor. → Radiation shape factor.

Radiative heat transfer coefficient. → Heat transfercoefficient, radiative.

Radiative (linear) heat transfer coefficient. → Heattransfer coefficient, radiative (linear).

Radiator: An emitter of radiant energy.

Radiator, full: A radiator of uniform surface temper-ature whose radiant exitance in all parts of the spec-trum is the maximum obtainable. The emissivity of afull radiator is unity for all wavelengths. Synonym:blackbody.

Radiator, graybody: A radiator whose spectralemissivity is less than unity, at least in the wavebandfor thermal radiation (3–30 µm), but is the same at allwavelengths.

Radiator, selective: A radiator with a spectral emis-sivity less than unity which varies with wavelength.Note: Human and animal skins have high emissivitiesin the waveband 3–30 µm but not between 0.7 and 3µm.

Reflectance, radiation (p): The ratio of the radiantflux reflected by a surface or medium to the incidentflux.Note: Measured values of reflectance depend upon theangles of incidence and view and the spectral characterof the incident flux; these factors should be specified.

Regulation: The processes by which a biological sys-tem stabilizes variables, generally by information loops(negative feedback control). The regulated (controlled)



physiological variables can usually be described as afunction of physical variables. In the case of changes ofa regulated variable due to external or internal interfer-ence, the processes of regulation will alter certainbodily functions, the effectors in the regulatory process,which act to minimize the deviations of the regulatedvariable from its set-point.Note: In thermal physiology, core temperature is oftenconsidered as the regulated variable in homeothermicspecies, because its changes are most effective in acti-vating the thermoeffectors of heat production, heatconservation, or heat loss in such a way that deviationsof core temperature are minimized. Mean body tem-perature, if representing the weighted contributions ofcore and shell temperatures to the entire thermal infor-mation, may be a better estimate of the regulated vari-able.

Relative humidity. → Humidity, relative.

Resistance, thermal. → Thermal resistance.

Respiratory evaporative heat loss (REHL): Rate ofheat dissipated by exhalation of air saturated with watervapor, [W], [W·m–2], [W·m–3], [W·kg–1].Note: Respiratory evaporative heat loss (REHL)comprises a passive (obligatory) fraction associatedwith normal breathing and, in many animals, a regula-tory fraction which depends on the rate at which the wa-ter vapor dissipating respiratory surfaces are ventilated(e.g., during thermal tachypnea), and on surface tem-perature depending on circulatory convection (→convection, circulatory) transferring heat to these sur-faces. Net dissipation of evaporated water and, conse-quently, of heat with the exhaled air is possible only aslong as the inhaled air is not saturated with water vaporat the temperature of the moist respiratory surfaces.

Resting metabolic rate. → Metabolic rate, resting.

Saliva spreading: The spreading of saliva on the bodysurface, often a deliberate (behavioral) thermoeffectoraction to cool the surface by evaporation. Sometimesinaccurately termed grooming.

Saturated vapor pressure. →Pressure, water vapor.

Scope, metabolic: Metabolic rate (M or MR) at max-imum oxygen consumption divided by least observedmetabolic rate (LOMR).

Second phase panting. → Thermal hyperpnea.

Selective brain cooling: Lowering of brain tempera-ture, either locally or as a whole, below aortic (arterialblood) temperature. Cool venous blood returning fromcephalic heat dissipating surfaces acts as a heat sink, ei-ther for brain tissue directly or for arterial blood supply-ing brain tissue. Special vascular arrangements, e.g.,the ophthalmic or carotid retia mirabilia, support arte-rio-venous heat exchange underlying selective braincooling. Its existence in many species has been proven,but the situation in humans is still debated.

Sensible heat loss. → Heat loss, dry.

Set-point: The value of a regulated variable which ahealthy organism tends to stabilize by the processes ofregulation. It is found in the condition when the effec-tor activities tending to counteract alterations of theregulated variable are minimal. With thermal loadpresent, the regulated variable, due to proportional con-trol, does not stabilize at, but near the set-point. In hy-per- or hypothermia, body temperature deviatessubstantially from the set-point, mostly because of in-sufficient effector capacity and thereby lack of stabili-zation. In biological systems, the apparent set-points ofmany regulated variables may change with time, eitherperiodically or temporarily (e.g., nychthemerally, an-nually, with the ovulatory cycle, or in connection withother physiological events). In temperature regula-tion the set-point may change temporarily, due to inter-ference with the regulations of nonthermal variables(e.g., in states of dehydration and starvation, etc.), ordue to pathological, nonthermal influences (e.g., in fe-ver or anapyrexia). Also, the processes of accli-mat(izat)ion and adaptation may change the set-pointof temperature regulation. Hibernation is a specialcondition in which the set-point differs distinctly fromthat existing in the same animal in the state of ceno-thermy. The change of set-point in these processes isthought to be due to changes in the thermal controllercharacteristics, particularly changes of thresholds (→thermoeffector threshold temperature) and/orchanges of thermoeffector gain, which obviously haveneuronal correlates, too.Note: The term set-point has evoked much confusion,as it has been used for different phenomena: (1) forsteady state of body temperatures (which can be verydifferent in the thermoregulatory system depending onenvironmental and internal conditions). (2) for a centralreference signal (which obviously does not exist explic-itly in the thermoregulatory system). (3) for thermoef-fector threshold zone of (mean) body temperature,which is correct only in the non-acclimated and afe-



brile state. In fever (also in acclimat(izat)ion andother adaptational or periodical processes) the thermo-controller characteristics change (particularly effectorthreshold), and by this the set-point, which then doesnot fall into the interthreshold zone. With non-exces-sive additional thermal load, body temperature stabi-lizes near this febrile set-point.

Shape factor, radiation. → Radiation shape factor.

Shell, thermal: The skin and mucosal surfaces of thebody engaged directly in heat exchange with the envi-ronment and, in addition, those tissues under these sur-faces whose temperatures may deviate from coretemperature, due to heat exchange with the environ-ment and to changes in circulatory convection (→convection, circulatory) of heat from the core to theheat exchanging surfaces. Antonym: thermal core.Note: The temperature of the shell of temperature reg-ulators depends on ambient temperature, heat loss tothe environment, and on rate and geometry of bloodflow to and from the skin.

Shivering: Involuntary tremor of skeletal muscles as athermoeffector activity for increasing metabolic heatproduction (→ thermogenesis, shivering). Its elec-tromyographically distinct pattern of motor unit dis-charges may be quantified as the integrated voltage (V)deflections per unit time (t): Σ(∆V·∆t)·t–1·[V].(→ ther-moregulatory muscle tone).

Sickness behavior: A group of signs or symptomswhich accompany cytokine-producing events (e.g., in-fection), usually with the elevation of body tempera-ture. The behaviours include, among others, loss ofappetite, lethargy, depression and decreased motor ac-tivity, and are thought to be mediated by the action ofcytokines, not necessarily those which mediate the risein body temperature, as a result of the infection.

Skin pressure effect on sweating: The inhibition ofsweating in the dermatomal area of skin when mechan-ical pressure is locally applied (→ hemihidrotic re-sponse).

Skin wettedness. → Wettedness, skin.

Solar radiation area. → Area, solar radiation.Specific dynamic action. → Specific dynamic effect.

Specific dynamic effect: Temporary increase in meta-bolic energy transformation following food intake.

Originally described as “spezifisch-dynamischeWirkung” by Rubner, the term “Wirkung” has beentranslated as “action” as well as “effect”. The phenom-enon is assumed to be related to the catabolism of foodstuffs, particularly proteins. (Kleiber, M. The Fire oflife, Huntington, N.Y., R.E. Krieger Publ. Co., 1976).Note: The term is becoming obsolete, because it cannotbe distinguished precisely from other factors that stim-ulate metabolic energy transformation in the hours fol-lowing food intake and, with the inclusion of thespecific dynamic effect, account for postprandial (ex-cess) heat production. Synonyms: specific dynamicaction; diet-induced thermogenesis.

Specific heat (c): The quantity of heat required to raisethe temperature of unit mass of a substance by one de-gree Celsius. [J · kg–1 · °C–l]Note: For gases, it is necessary to specify whether thepressure (cp) or the volume (cv) is held constant duringits determination. The specific heat of body tissue isusually taken to be 3.48 kJ · kg–1 · °C–1 (i.e., 0.83 kcal· kg–1 · °C–1). Ref: Schafer, E.A., Textbook of Physiol-ogy, London: Hodder & Stoughton, 1898, vol. I, p. 838.

Specific heat, volumetric: The product of the densityρ of a material and its specific heat. [J · °C–1 · m–3]

Spectral emissivity. → Emissivity, spectral.

Spectral radiant energy. → Radiant energy, spec-tral.

Spectral radiant flow. → Radiant flow, spectral.

Standard atmospheric pressure. → Pressure, atmo-spheric.

Standard metabolic rate. → Metabolic rate, stan-dard.

Steady state: The state of body heat balance in whichthere is no positive or negative heat storage when heatgain and heat loss between the body and the environ-ment are equivalent. The body temperatures reached ina steady state depend on the extent of external or inter-nal thermal load. If the thermoeffector capacities areexceeded due to excessive load or pathological pro-cesses, a steady state will not be reached, leading tohypo- or hyperthermia.

Stefan-Boltzmann law: The thermal radiant exi-tance of a full radiator is proportional to the fourth



power of its absolute temperature, Me,th = σT4. The cur-rently recommended value of the Stefan-Boltzmannconstant (σ) is 5.6696 × 10–8 [W · m–2 · K–4].

Stenothermy: Descriptive of organisms, which occurnaturally in a narrow range of environmental tempera-tures and which, singly or collectively, are intolerant ofor accommodate ineffectually to wide changes in theirthermal environment. (Gk. stenos-narrow; therme-heat) Antonym: eurythermy.

Storage of body heat (S): The rate of increase (+) ordecrease (–) in the heat content [Ws = J] of the bodycaused by an imbalance between heat production (met-abolic heat transformation) and heat loss, usually ex-pressed in terms of unit area of total body surface (→Area, total body). The quantity S in the body heat bal-ance equation. [W], [W · m–2], [W · m–3] or [W · kg–1]:

Stress fever: A rise in body temperature due to expo-sure of a person or an animal to a psychological stres-sor. Synonym: Stress hyperthermia.

Stress hyperthermia. → Stress fever.

Sunstroke: An acute and dangerous reaction to heatexposure caused by a failure of the heat regulatingmechanisms of the body. It is characterized by highcore temperature, usually above 40.6°C, cessation ofthermal sweating; headache, numbness, tingling andconfusion prior to sudden delirium or coma, fast pulse,rapid respiratory rate and elevated blood pressure.

Surface area. → Area, total body, and area DuBois(for humans only).

Surface rule: A statement that the basal metabolicrate (BMR) is proportional to the 2/3 power of bodymass.Note: The rule is based on the proposition that basalmetabolic rate (BMR) is related to surface area andthat surface area varies with the 2/3 power of bodymass. However, this is not experimentally verifiable,for when basal metabolic rate (BMR) is expressed per2/3 power of body mass it increases systematically withbody size (Kleiber, 1947). Basal metabolic rate(BMR) is more nearly proportional to the 3/4 power ofbody mass (→ metabolic body size). Ref: Kleiber, M.,Physiol. Rev. 27: 411, 1947.

Sweating, nonthermal: A response of the sweatglands to a nonthermal stimulus.

Sweating, thermal: A response of the sweat glands toa thermal stimulus. Rate [mg · m–2 · s–1]Note: 1 mg · m–2 · s–1 = 3.6 g · m–2 · h–1.

Sweating topography, thermal: The sequence of theonset of thermal sweating and the differences in sweatrate observed between different skin regions.

Tachymetabolism: The high level of basal metabo-lism of birds and mammals relative to those of reptilesand other nonavian and nonmammalian animals of thesame body mass and at the same tissue temperatures.(Gk. takhus-fast; metabole-change) Synonym:warm-blooded. Antonym: bradymetabolism,cold-blooded.Note: This relatively high level of basal metabolism inmammals and birds is a precondition for the relativestability of core temperature during exposure to cold(warm-blooded) and of endothermic homeothermyand heterothermy.

Tachypnea, thermal. → Thermal tachypnea.

Temperature: A measure of the mean kinetic energy ofthe molecules in a volume.

Temperature, ambient (Ta): The average temperatureof a gaseous or liquid environment (usually air or wa-ter) surrounding a body, as measured outside the ther-mal and hydrodynamic boundary layers that overlay thebody. [°C] Synonym: temperature, dry bulb (in a gas-eous environment).

Temperature coefficient: The ratio between thechange in any temperature dependant activity and thedefined temperature range within which this change oc-curs.

Temperature conformer: An organism, the core tem-perature of which varies as a proportional function ofambient temperature; an animal without effectivetemperature regulation by autonomic or behavioralmeans. Synonym: poikilothermy. Antonym: tempera-ture regulator.

Temperature conformity: The thermal relation be-tween the environment and an organism, the core tem-perature of which varies as a proportional function ofambient temperature, i.e., an absence of effectivetemperature regulation by autonomic or behavioralmeans.



Temperature, core: Ideally, the mean temperature ofthe thermal core. In practice it is represented by aspecified core temperature, usually rectal or (in hu-mans) sublingual temperature. More reliable in condi-tions of changing core temperature are esophageal (atthe cardia) or aortic (arterial blood) temperature.Note: Brain temperatures are core temperatures. Theymay differ regionally within the brain or from othercore temperatures outside of the brain, due to selec-tive brain cooling, which directly influences braintemperature, locally or as a whole, in a number of spe-cies.

Temperature, deep body. → Temperature, core (pre-ferred synonym).

Temperature dependence: The influence of the localtemperature upon the rate of all molecular transforma-tions and thereby upon practically all cellular and phys-iological processes. → Q10.

Temperature, dew-point (Tdp): The temperature atwhich condensation first occurs when an air-water va-por mixture is cooled at constant pressure. [°C]

Temperature, dry bulb (Tdb): The temperature of agas or mixture of gases indicated by a thermometershielded from radiation. [°C] Synonym: temperature,ambient.

Temperature, effective (Teff): An arbitrary indexwhich combines in a single value the effect of temper-ature, humidity, and air movement on the sensation ofwarmth or cold felt by human subjects. The numericalvalue is that of the temperature of “still” air saturatedwith water vapor which would induce an identical sen-sation. [°C]

Temperature, globe (Tg): The temperature of a black-ened hollow sphere of thin copper (usually 0.15 m di-ameter) as measured by a thermometer at its center; Tgapproximately equals temperature, operative. [°C]

Temperature lability, controlled: An expression ofthe extent of the daily and seasonal variations in thelevel at which core temperature is being regulated.Synonym: thermolability, controlled.Temperature lability, passive: An expression of theextent to which core temperature fluctuates passively(i.e., without the recruitment of thermoeffector activi-ties) when either the rate of heat production or of heatexchange with the environment is varied. Synonym:

thermolability, passive.

Temperature, mean body (Tb): (1) Ideally, the sum ofthe products of the heat capacities (ci · mi) and temper-ature (Ti) of all tissues of the body divided by the totalheat capacity of the organism:

Tb = Σ(ci · mi · Ti)/Σ(ci · mi).

(2) The total temperature signal generated by all ther-mosensors distributed in the core and shell. (2) shouldbe different from (1). For discussion, see Minard, D.,In: Physiological and Behavioral Temperatuve Regula-tion, edited by J.D. Hardy, A.P. Gagge, & J.A.J. Stol-wijk, Springfield, I11., Thomas, 1970, p. 345.Mean body temperature often is estimated approxi-mately from measurements of a representative coretemperature (Tc) and mean skin temperature (Tsk)according to:

Tb = al · Tc + a2 · Tsk, with al + a2 = 1,

in which the factors al and a2 represent the empiricallydetermined contributions of thermal core and shell tomean body temperature.

Temperature, mean radiant (Tr): The temperature ofan imaginary isothermal "black" enclosure in which asolid body or occupant would exchange the sameamount of heat by radiation as in the actual nonuniformenclosure. [°C]

Temperature, mean skin (Tsk): The sum of the prod-ucts of the area of each regional surface element (Ai)and its mean temperature (Ti) divided by the total body(surface) area.

Tsk = Σ(Ai · Ti)/Ab [°C]

Note: Mean skin temperature can be used as a physi-cal variable in the calculation of heat balance or of heatcontent of the body. It is, however, not necessarily agood estimate of what might be sensed as a mean skintemperature according to the integrated neural inputof the cutaneous thermoreceptors, because differentsurface regions may differ in their importance as ther-mosensor sites.Temperature, operative (To): The temperature of auniform (isothermal) “black” enclosure in which a solidbody or occupant would exchange the same amount ofheat by radiation and convection as in the actual non-uniform environment. [°C]



Temperature receptor. → Thermoreceptor.

Temperature regulation: The maintenance of the tem-perature or temperatures of a body within a restrictedrange under conditions involving variable internaland/or external heat loads. Biologically, the existenceof body temperature regulation to some extent by au-tonomic or behavioral means. Antonym: temperatureconformity.

Temperature regulation, autonomic: The regulationof body temperature by autonomic (i.e., involuntary)thermoeffector responses to heat and cold which mod-ify the rates of heat production and heat loss (i.e., bysweating, thermal tachypnea, shivering, nonshiver-ing thermogenesis, and adjustments of circulatoryconvection of heat to the surfaces of the body). (Gk.autos-self; nomos-law, i.e., self-governing, SOED).Note: In this definition the term autonomic is used in itsmore general sense and does not imply that all re-sponses are controlled by the Autonomic Nervous Sys-tem (sympathetic and parasympathetic efferents).Autonomic temperature regulation is frequently de-scribed as physiological temperature regulation, aterm which should be used for both autonomic and be-havioral thermoregulatory processes.

Temperature regulation, behavioral: Any coordi-nated movement of an organism ultimately tending toestablish a thermal environment that represents a pre-ferred condition for heat exchange (heat gain, heatloss, or heat balance) of the organism with its environ-ment. The distinction between thermoregulatory be-havior and thermotropism is ill-defined. A plant mayexhibit thermotropism but is not considered to be ther-moregulating. Some aquatic unicellular organismsmove to a preferred ambient temperature, however,whether this is thermotropism or thermoregulatorybehavior may be disputed. For these reasons the termis usually restricted in thermal physiology to patterns ofbehavior controlled by a nervous system. The complexpatterns of somato-motor activities that serve as behav-ioral thermoeffector responses to heat and cold oftemperature regulators in modifying their conditionsof heat exchange with the environment, involve a widevariety of performances (e.g., moving to a differentthermal ambiance, changes in posture, wetting of bodysurfaces, change of microclimate by nest building, pa-rental behavior, huddling) and, in humans, also includevoluntary exercise and cultural achievements (clothing,housing, air-conditioning etc.). In endothermic tem-perature regulators, the reduced demand for auto-

nomic temperature regulation is a potential result ofbehavioral temperature regulation which, however,competes with other, nonthermal, behavioral drives(e.g., search for food).Note: Behavioral temperature regulation is charac-terized as operant, if it is acquired in an experimentalcondition only after training guided by an experi-menter. Otherwise, it is defined as natural, but thismay also involve learning. In humans the distinctionbetween natural and operant behavioral temperatureregulation becomes arbitrary in many instances.

Temperature regulation, chemical (obsolete): Bodytemperature regulation involving changes in heatproduction.Note: This can be due to: 1. voluntary muscle move-ments; 2. involuntary muscle movements (e.g., shiver-ing); 3. nonshivering thermogenesis; 4. increase ordecrease in basal metabolic rate (BMR).

Temperature regulation, physical (obsolete): Bodytemperature regulation involving control of the rateof heat flow into or out of an organism.Note: The responses involved in such regulation consistof those autonomic and behavioral responses that varythe thermal conductance of peripheral tissues, but notof those behavioral responses which involve alterationof the local environment. For example: 1. changes inperipheral vasomotor tone; 2. piloerection; 3. evapora-tion of water from skin (following sweating, salivaspreading, wallowing) and from respiratory tract sur-faces; 4. changes in body conformation.

Temperature regulation, physiological: 1) Both auto-nomic and behavioral temperature regulation (pre-ferred). 2) Obsolete synonym for autonomictemperature regulation.Note: Traditionally, mammalian thermoregulatoryphysiology has been concerned with those responses toheat or cold which do not depend on behavior. These re-ponses are autonomic (SOED self-governing; Gk. au-tos-self, independently; nomos-law). Autonomicresponses are generally referred to as physiological re-sponses, but behavioral responses are also physiologi-cal (Physiology = the science of the normal functionsand phenomena of living things, SOED). Thus, physio-logical thermoregulatory responses properly consist ofboth autonomic and behavioral responses.

Temperature regulator: An organism which regulatesits body temperature to some extent by autonomicand/or behavioral processes. Antonym: temperature



conformer.Note: Tachymetabolism is the property of endother-mic temperature regulators in which core temperatureappears as the controlled variable, with arbitrarily de-fined degrees of thermostability (homeothermy, het-erothermy). Bradymetabolism does not exclude thatsuch species may be ectothermic temperature regula-tors, although mainly by means of behavioral temper-ature regulation, because thermoeffectors ofautonomic temperature regulation are vestigial orabsent.

Temperature responsive. → Thermoresponsive.

Temperature sensitive. → Thermosensitive.

Temperature sensor. → Thermosensor.

Temperature survival limit, lower: The environmen-tal temperature below which thermal balance cannot bemaintained for a long period and animals become pro-gressively hypothermic. At this temperature → basalmetabolic rate (BMR) can be measured.

Temperature survival limit, upper: The environmen-tal temperature above which thermal balance cannot bemaintained for a long period and animals become pro-gressively hyperthermic.

Temperature, tolerated ambient range. → Toleratedambient temperature range.

Temperature, tympanic (Tty): The temperature of thetympanic membrane.

Temperature, wet bulb (Twb): The thermodynamicwet bulb temperature of a sample of air is the lowesttemperature to which it can be cooled by evaporatingwater adiabatically. This measurement is compared tothat read by an ordinary thermometer, or dry bulb ther-mometer, to estimate the ambient humidity. [°C]Note: The term is usually applied to the temperature re-corded by an aspirated thermometer covered with a wetsleeve that is approximately equal to the thermody-namic wet bulb temperature when the bulb is shieldedfrom radiation.Thermal comfort: Subjective indifference to the ther-mal environment.

Thermal comfort, zone of: The range of ambienttemperatures, associated with specified mean radianttemperature, humidity, and air movement, within

which a human in specified clothing expresses indiffer-ence to the thermal environment for an indefinite pe-riod. [°C]

Thermal conductance (k): The rate at which heat istransferred between unit area of two parallel surfaces ina medium when unit temperature difference is main-tained between them, or the rate of heat transfer dur-ing steady state when a temperature difference of 1 °Cis maintained across a layer of tissue, either expressedper unit area [W · m–2 · °C–1] or in absolute terms [W ·°C–1].Note: This term relates to the total heat transfer (nomatter which physical processes are involved) down atemperature gradient from any tissue to its immediateenvironment, e.g., from a tissue to circulating blood, aswell as from the body core through peripheral tissues tothe body surface (due to conductive as well as convec-tive processes). In practice tissue thermal conduc-tance of living tissues within the organism is notamenable to direct measurement. Calculated values areusually based on several assumptions, e.g., mean tissuetemperature, mean blood temperature, and the surfaceareas of blood vessel walls.

Thermal conductivity (λ): A property of a materialdefined by the flow of heat by conduction through unitthickness of the material per unit area and per unit tem-perature difference maintained at right angles to the di-rection of heat flow. [W · m –1 · °C–1]

Thermal contact coefficient. → Thermal inertia forradiant heat.

Thermal core. → Core, thermal.

Thermal diffusivity. → Diffusivity, thermal.

Thermal expansion coefficient of volume (β): Thechange in volume (V) at constant pressure of a sub-stance (solid or fluid) per unit volume, per degreechange in temperature (T; degree Kelvin).β = V–1 · dV/dT (gases only) [K–1]

Thermal hyperpnea: An increase in tidal volume associ-ated with an increase in alveolar ventilation occurring dur-ing severe heat stress which has caused a large rise in coretemperature. In animals capable of thermal panting thephase of thermal hyperpnea with its slower, deeperbreathing is also named second phase panting, since it isusually preceded by a phase of typical panting (rapid, shal-low breathing). (Gk. hyper-above, over; pnoia-breath)



Thermal indifference, zone of: The range of ambienttemperatures, associated with specified water vaporpressure, air velocity, and radiant exchange, withinwhich 80% of active people do not complain of thethermal environment. [°C] Cf. thermoneutral zone.

Thermal inertia for radiant heat (√kpc ): One of theproperties of a material which determines the rate of in-crease of surface temperature during an exposure to ir-radiance (E). For nonpenetrating radiation incidentupon a semi-infinite solid with uniform properties, thevalue of the thermal inertia for the surface can be deter-mined in appropriate units by √kpc = 2π–1/2 · t1/2 · E ·∆T–1 in which ∆T is the rise in surface temperature attime, t.

Thermal insulation. → Thermal resistance.

Thermal insulation, clothing (Icl): The intrinsic insu-lation of a clothing assembly. The effective insulationof clothing is (Icl + Ia) where Ia is the reciprocal of thethermal conductance of the ambient environment. (Icl +Ia) is usually measured as the temperature gradientfrom the surface of a heated man-sized manikin to theambient air divided by the heat production per unit areaof manikin surface. [°C · m2 · W–1] The value is some-times expressed in clo units.

Thermal panting: Increased respiratory evaporativeheat loss (REHL) due to increased respiratory minutevolume.Note: Thermal panting in animals can occur both witha closed and open mouth.

Thermal polypnea. → Thermal tachypnea.Note: Although polypnea is more commonly used, ta-chypnea is etymologically more correct.

Thermal radiance. → Radiance, thermal.

Thermal radiant exitance. → Radiant exitance,thermal.

Thermal resistance (R): The reciprocal of thermalconductance. [°C · m–2 · W–1] or [°C · W–1] Synonym:thermal insulation.

Thermal shell. → Shell, thermal.

Thermal strain: In temperature regulators: 1. Anydeviation of body temperature induced by sustainedthermal stress that cannot be fully compensated by

temperature regulation; 2. Any activation of thermo-effector activities in response to thermal stress thatcause sustained changes in the state of other, nonther-mal, regulatory systems.

Thermal stress: Any change in the thermal relation be-tween a temperature regulator and its environmentwhich, if uncompensated by temperature regulation,would result in hyper- or hypothermia.

Thermal sweating. → Sweating, thermal.

Thermal tachypnea: A rapid respiratory frequency ac-companied by an increase in respiratory minute volumeand, commonly, a decrease in tidal volume, in responseto a thermoregulatory need to dissipate heat. (Gk. ta-khus-swift; pnoia-breath) Synonym: thermal polyp-nea.

Thermoeffector: An organ system and its action, re-spectively, that affect heat balance in a controlledmanner as part of the processes of temperature regu-lation.Note: A multitude of thermoeffectors is involved inboth autonomic and behavioral temperature regula-tion.

Thermoeffector gain: The derivative of the thermoef-fector output with respect to body temperature devia-tion from the set-point.Note:The gain may change due to fever, adaptationand other processes. In combination with thermoeffec-tor threshold temperature, thermoeffector gain is animportant characteristic of thermoeffectors.

Thermoeffector threshold: The level of activity of apotential thermoeffector that is transgressed when itbecomes actively involved in temperature regulation.Note: For some of the thermoeffectors, thresholds canbe precisely determined, e.g., as the level of basal met-abolic rate (BMR) or resting metabolic rate (RMR)of a tachymetabolic animal above which metabolicheat production (H) will increase in response to a suf-ficiently strong cold exposure. The thresholds of otherthermoeffectors are arbitrarily defined, or agreed uponby convention, because basal or resting levels are diffi-cult to define, e.g., in case of circulatory convection ofheat to the skin and the underlying cutaneous vasomo-tor tone.

Thermoeffector threshold temperature: Describesthe level of a specified body temperature (e.g., core



temperature or mean body temperature) the trans-gression of which in one direction, either upward ordownward, will activate a certain thermoeffector. As arule, the threshold core temperature determined for agiven effector will be a function of skin temperature,and vice versa; similar interdependencies exist with andamong the threshold temperatures determined for spec-ified thermosensor regions in the body core (e.g., hy-pothalamus, spinal cord). Evaluation of mean bodytemperature threshold values tries to account for theentire thermal input from the body. Specified thresholdtemperatures for certain thermoeffectors may changeduring the processes of fever, acclimat(izat)ion andadaptation. Threshold temperature and thermoeffec-tor gain are the dominant parameters describing thethermoeffector output as a function of body tempera-ture, thus, they constitute essential characteristics of thethermal controller.

Thermoeffector threshold zone (Interthresholdzone): The temperature range between two threshold(body) temperatures, for activation of any thermoef-fector responses, particularly of metabolic heat pro-duction (H) and of evaporative heat loss when nothermal load is present. This special steady-state maybe called set-point. Thermoeffector threshold zoneshould be distinguished from thermoneutral zone(TNZ).

Thermogenesis, diet-induced: Increase of obligatorynonshivering thermogenesis occurring especially inrodents when transferred from standard food to a highlypalatable cafeteria diet, of which the animals consumemore but dissipate part of the surplus caloric intake byenhanced heat production. The brown adipose tissue(BAT) is considered as the main effector organ ofdiet-induced thermogenesis.Note: The relationship between postprandial (excess)heat production and diet-induced thermogenesis is notpresently clarified.Thermogenesis, nonshivering (NST): Heat produc-tion due to metabolic energy transformation by pro-cesses that do not involve contractions of skeletalmuscles, i.e., tone, microvibrations, tremor (→ shiver-ing), or tonic or voluntary contractions. In thermalphysiology this term is conventionally used to indicatethermoregulatory (cold-induced) nonshivering ther-mogenesis (NST). [W], [W · m–2], [W · kg–1]Note: While all organs contribute to obligatory non-shivering thermogenesis according to their rates ofresting metabolism, the principal effector organ re-sponsible for the short-term or adaptive activation of

nonshivering thermogenesis (NST), observed partic-ularly in small mammals, is the brown adipose tissue(BAT).

Thermogenesis, nonshivering (obligatory)(NST(O)): That component of nonshivering thermo-genesis (NST) (i.e., heat production unrelated to thecontractions of voluntary muscles) that is independentof short-term changes in ambient temperature (Ta).Note: NST(O) corresponds to basal metabolic rate(BMR) or standard metabolic rate (SMR). AlthoughNST(O) is unaffected by short-term exposure to cold, itmay be changed by processes of acclimat(izat)ion tosustained cold or heat stress or feeding conditions.

Thermogenesis, nonshivering, (thermoregulatory)(NST(T)): The increase in nonshivering thermogene-sis (NST) in response to acute cold exposure. The prin-cipal effector organ is the brown adipose tissue(BAT). which may adaptively increase its capacity forheat production in the course of acclimat(izat)ion andadaptation to cold stress.Note: The term nonshivering thermogenesis (NST)usually refers to NST(T).

Thermogenesis, shivering: An increase in the rate ofheat production during cold exposure due to increasedcontractile activity of skeletal muscles not involvingvoluntary movements and external work. [W], [W·kg–1], [W · m–2] or [W · m–3]Note: Shivering thermogenesis progresses, as its in-tensity increases, from thermoregulatory muscletone, to micro-vibrations, to clonic contractions of bothflexor and extensor muscles. All shivering thermo-genesis is blocked by curare.

Thermogenin. → P 32000 Polypeptide.

Thermography, infra-red: The recording of the tem-perature distribution of a body from the infra-red radi-ation emitted by the surface.

Thermolability, controlled. → Temperature lability,controlled.Thermolability, passive. → Temperature lability,passive.

Thermoneutral zone (TNZ): The range of ambienttemperature at which temperature regulation isachieved only by control of sensible heat loss, i.e.,without regulatory changes in metabolic heat produc-tion (H) or evaporative heat loss. The thermoneutral



zone (TNZ) will therefore be different when insulation,posture or basal metabolic rate (BMR) vary. The termthermoneutral zone (TNZ) does not apply to ecto-therms. The thermoneutral zone (TNZ) should bedistinguished from thermoeffector threshold zone.

Thermopreferendum: The thermal conditions that anindividual organism or a species selects for its ambientenvironment in natural or experimental circumstances.

Thermoreactive: Descriptive of neural elementswhose activity changes with the temperature of a re-mote region of the body, due to synaptic input from thisregion.Note: A central nervous neuron may be both thermore-active and thermoresponsive (thermosensitive).

Thermoreceptor: Thermosensitive neural elementfor which both its afferent function and its responsecharacteristics are electrophysiologically identified (→thermosensor). Synonym: temperature receptor.Note: Thermoreceptors have been unequivocallyidentified, so far, only in the skin and mucous surfacesas cold receptors, warm receptors, and infrared re-ceptors.

Thermoregulation. → Temperature regulation.

Thermoregulatory behavior. → Temperature regu-lation, behavioral.

Thermoregulatory behavior, natural: → Tempera-ture regulation, behavioral.

Thermoregulatory behavior, operant. → Tempera-ture regulation, behavioral.

Thermoregulatory conditioned reflex: The physio-logical (autonomic and behavioral) responses of anorganism to changes in its thermal environment, whichcan also be elicited by a conditioned stimulus.

Thermoregulatory muscle tone: The increase in theelectrical activity of the skeletal musculature of a rest-ing tachymetabolic temperature regulator duringmoderate cooling. During more intensive cooling,thermoregulatory muscle tone will be superimposedby microvibrations and eventually shivering tremor.The corresponding electrical activities can be deter-mined qualitatively and quantitatively by means ofelectromyographical recording (→ shivering).

Thermoregulatory nonshivering thermogenesis. →Nonshivering thermogenesis (thermoregulatory).

Thermoresponsive: Neural element which changes itsactivity in response to changes of its own temperature.Synonyms: temperature responsive, thermosensi-tive.Note: In comparison to the more general term temper-ature dependence, neuronal thermoresponsivenessimplies at least the possibility of generation or modula-tion of information by temperature, either non-specificor as a specific temperature signal. The synonymousterm thermosensitive implies the specificity of thethermoresponsive neural element as a temperature sig-nal generator.

Thermosensitive: Descriptive of thermoresponsiveneural structures with the implication that the neural el-ements involved provide specific temperature signals.Synonym: temperature sensitive.

Thermosensor: Neural element or circuitry of neuralelements for which it is established by psychophysicalcriteria or analysis of thermoeffector responses orchanges of core temperature that they transduce tem-perature in such a way that thermal sensation is elicitedand/or temperature regulation is adequately stimu-lated.Note: Thermosensors may not (yet) be accessible toelectrophysiological identification, but their function isequivalent to that of thermoreceptors which are elec-trophysiologically identified thermosensors.

Thermotolerance: A rapid, short acting molecularprocess associated with the synthesis of several fami-lies of heat shock proteins (HSP) of different molecu-lar weights elicited as a result of acute short sublethalheat injury. It is thought to protect cells from noxiousstimuli as well as to accelerate their repair. It is also de-fined as heat shock response (HSR). The time courseof heat shock proteins (HSP) vary in different cellsbut, on the average, heat shock proteins (HSP) in theintact body seem to operate several hours following thestress and retains its activity for a few days. The re-sponse is not heat-specific and can be elicited subse-quent to subjection to several other stressors (e.g.,ischemia, some chemicals, etc.). Synonym: heat shockresponse (HSR).

Thermotropism: The turning or movement of a plantor animal in response to a temperature stimulus. (Gk.therme-heat; trope-turn)



Thigmothermy: The dependence of the core temper-ature of an ectothermic animal on the conductive ex-change of heat with its immediate environment, e.g.,water, air, soil. (Gk. thigma-touch; therme-heat)

Threshold temperature. → Thermoeffector thresh-old temperature.

Threshold, thermoeffector. → Thermoeffectorthreshold.

Tissue thermal conductance. → Thermal conduc-tance, tissue.

Tolerated ambient temperature range: The range ofambient temperature (Ta) within which the body coretemperature can be kept, by means of autonomicthermoregulatory processes, within certain limits typ-ical for the species or the individual under consider-ation. [°C]

Torpor: A state of inactivity and reduced responsive-ness to stimuli (e.g., during hibernation, hypother-mia, or estivation).

Total body area (Ab). → Area, total body.

Total environment: All environmental factors that ex-ert an influence on an organism and to which an organ-ism must be adequately adapted in order to survive (i.e.,competitors for food sources and predators as well asthe many components of the physical environment andthe climate).

Total heat production: The rate of transformation ofchemical energy into heat in an organism (metabolicheat production (H)) plus any heat flow liberatedwithin the body resulting from work done on the or-ganism by an external force (negative work rate).[W], [W · m–2], [W · m–3], [W · kg–1]Note: During positive work and when no work is beingdone on or by the organism, total heat productionequals metabolic heat production (H).Total radiant absorptance. → Radiant absorptance,total.

Transmittance, radiation (τ): The ratio of the radiantenergy transmitted through a body to the total radiationincident on it.

Tumor necrosis factor-α (TNF-α): Heat labile pro-teins produced by immune cells (e.g., mononuclear ph-

agocytes) when activated by microorganisms or theirproducts. The production of tumor necrosis factor(TNF-α) is caused by infection, injury and trauma. It(as well as other cytokines) produces the acute phaseresponse. Tumor necrosis factor-α (TNF-α) is con-sidered an important endogenous pyrogen, as are inter-leukin-1 (IL-1), interleukin-6 (IL-6), and some othercytokines.

UCP1: Specialized protein with a subunit Mr 32000 ofthe mitochondrial inner membrane of brown adiposetissue (BAT); collapses the electro-chemical protongradient generated by respiration and thus, preventsATP synthesis; the amount of this mitochondrial com-ponent is increased when brown adipose tissue (BAT)is in a recruited state. Synonym: thermogenin, uncou-pling protein, P 32000 polypeptide.

UCP2, UCP3: Proteins of similar amino acid sequenceto UCP1, but found in tissues other than brown adi-pose tissue (BAT), discussed as being involved in ther-mogenesis

Ultraviolet. → Radiant energy.

Uncoupling protein. → P 32000 Polypeptide.

Upper critical temperature. → Critical tempera-ture, upper.

Upper temperature survival limit. → Temperaturesurvival limit, upper.

Useful work accomplished. → Work, positive.

Vapor pressure (water). → Pressure, water vapor.

Volume, thermal expansion coefficient of. → Ther-mal expansion coefficient of volume.

Volumetric specific heat. → Specific heat, volumet-ric.

Wallowing: The thermoregulatory increase in evapora-tive heat loss by spreading an aqueous fluid (e.g., water,mud, urine) on the body surface.

Warm-blooded: The thermal state of an animal thatmaintains its core temperature considerably higherthan that of the environment when subjected to a lowambient temperature (Ta). Synonym: tachymeta-bolic (preferred). Antonym: cold-blooded.



Note: This maintained temperature gradient betweenthe organism and its environment is dependent on therelatively high rate of metabolic heat production (H)(tachymetabolism) of warm-blooded animals com-pared with the low rate of heat production (bradyme-tabolism) of cold-blooded animals. Thus, the termstachymetabolic and bradymetabolic are preferred tothe terms warm-blooded and cold-blooded becausethe first pair of terms relates to a more basic physiolog-ical distinction and because the second pair of terms hasbeen used with various meanings not all of which areconsistent with the definitions given here.Warm-blooded is not a synonym of homeothermic,because the definition of warm-blooded does not spec-ify the degree of temperature stability consistent withhomeothermy: the core temperatures of somewarm-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 bodyarea (Ab) that is covered by sweat (the wetted area(Aw)), i.e., Aw/Ab.Note: For man the total skin area would usually betaken to be the DuBois area (AD).

Window emissivity. → Emissivity, window.

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

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

chanical energy, work production, useful work ac-complished. Antonym: workrate, negative.

Work production. → Work rate, positive.

Zone of thermal comfort. → Thermal comfort, zoneof.

Zone of thermal indifference. → Thermal indiffer-ence, zone of.

Zone of thermoneutrality. → Thermoneutral zone.



APPENDIX 1. Système Internationale (SI) Units Used in the Glossary

Quantity Symbol forQuantity

SI Units Abbreviations

Basic electric current I ampere A

temperature T degree Kelvin K

mass m kilogram kg

length l meter m

time t second s

Supplementary plane angle θ radian rad

solid angle Ω steradian sr

Derived temperature T degree Celsius (0 °C = 273.15 K) °C

energy E joule (kg · m2 · s–2) J

force F newton (J · m–1) N

electric potentialdifference

V volt (J · A–1 · s–1) V

power W watt (J · s–1) W

pressure P pascal (kg · m–1 · s–2) (= N · m–2)or bar (= 105 Pa)

Pabar

or torr (= 133.3 Pa) Torr

APPENDIX 2. Symbols Used in the Glossary

Symbol orAbbreviation

Term SI Units (Abbreviations)(ND = No Dimensions)

Ab area, total body m2

AD area, DuBois m2

Ap area, projected m2

Ar area, effective radiating m2

As area, solar radiation m2

Aw area, wetted m2

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



Hr radiant flux, effective W · m–2

I radiant intensity W · sr–1

Iλ radiant intensity, spectral W · sr–1 · nm–1

Icl thermal insulation, clothing m2 · °C · W–1

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

Le radiance W · sr–1 · m–2

Le,th radiance, thermal W · sr–1 · m–2

LOMR metabolic rate, lowest observed W, W · m–2, W · m–3, W · kg–1, W · kg–3/4

Me radiant exitance W · m–2

Me,s radiant exitance, self W · m–2

Me,th radiant exitance, thermal W · m–2

M, MR metabolic rate (metabolic energytransformation)

W, W · m–2, W · m–3, W · kg–1, W · kg–3/4

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(obligatory)

W, W · m–2, W · m–3, W · kg–1, W · kg–3/4

NST(T) thermogenesis, nonshivering(thermoregulatory)

W, W · m–2, W · m–3, W · kg–1, W · kg–3/4

P pressure Pa, bar, Torr

Ps,T pressure, vapor (saturated) attemperature T

Pa, bar, Torr

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

Qλ radiant energy, spectral J · nm–1

Rw gas constant (water vapor) 3.47 m3 · Torr · kg–1 · K–1

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




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

V· O2max rate of oxygen consumption, maximum ml · s–1, l · min–1

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

hcomb.,h heat transfer coefficient, combinednonevaporative

W · m–2 · °C–1

hc heat transfer coefficient, convective W · m–2 · °C–1

hD mass transfer coefficient (diffusion) m · s–1

he heat transfer coefficient, evaporative W · m–2 · kPa–1, W · m–2 · Torr–1

hk heat transfer coefficient, conductive W · m–2 · °C–1

hr heat transfer coefficient, radiative(linear)

W · m–2 · °C–1

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

εh emissivity, hemispherical ND

εw 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




φ humidity, relative ND

φ radiant flow W

φλ radiant flow, spectral W · nm–1

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. (Max Planck 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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