Thermoregulation during hibernation: Application of Newton's law of cooling

Henshaw, Robert E.

doi:10.1016/0022-5193(68)90093-3

Cited by 33 publications

(13 citation statements)

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“…It would be interesting to investigate how blood flow during this phase is altered, and whether the increased peripheral resistance and restriction of circulation is partially withdrawn. Our results show that in thermoregulating torpid bats, thermal conductance is similar to that in resting bats, as reported for other heterotherms (Henshaw, 1968;Geiser, 2004), and this may be the result of such changes in blood flow. We have previously suggested that this may be the case in bats during passive rewarming (Currie et al, 2015), and it may be that changes in blood flow influence the relationship between metabolism and heart rate when animals are thermoregulating during torpor.…”

Section: Discussionsupporting

confidence: 87%

Cold-hearted bats: uncoupling of heart rate and metabolism during torpor at subzero temperatures

Currie

Stawski

Geiser

2017

Journal of Experimental Biology

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Many hibernating animals thermoregulate during torpor and defend their body temperature () near 0°C by an increase in metabolic rate. Above a critical temperature (), animals usually thermoconform. We investigated the physiological responses above and below for a small tree-dwelling bat (, ∼14 g) that is often exposed to sub-zero temperatures during winter. Through simultaneous measurement of heart rate () and oxygen consumption ( ), we show that the relationship between oxygen transport and cardiac function is substantially altered in thermoregulating torpid bats between 1 and -2°C, compared with thermoconforming torpid bats at mild ambient temperatures ( 5-20°C). for this species was at a of 0.7±0.4°C, with a corresponding of 1.8±1.2°C. Below, animals began to thermoregulate, as indicated by a considerable but disproportionate increase in both and The maximum increase in was only 4-fold greater than the average thermoconforming minimum, compared with a 46-fold increase in The differential response of and to low was reflected in a 15-fold increase in oxygen delivery per heart beat (cardiac oxygen pulse). During torpor at low, thermoregulating bats maintained a relatively slow and compensated for increased metabolic demands by significantly increasing stroke volume and tissue oxygen extraction. Our study provides new information on the relationship between metabolism and in an unstudied physiological state that may occur frequently in the wild and can be extremely costly for heterothermic animals.

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Section: Discussionsupporting

confidence: 87%

Cold-hearted bats: uncoupling of heart rate and metabolism during torpor at subzero temperatures

Currie

Stawski

Geiser

2017

Journal of Experimental Biology

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“…In the T a range where torpid heterotherms are thermo-conforming, the T b -T a differential is often constant or changes little, although TMR declines significantly (13,51,74,79,142,159). These observations indicate that the T b -T a differential does not determine TMR above the T set as has been suggested (68).…”

Section: Tmr and The T B -T A Differentialmentioning

confidence: 81%

“…Obviously, regulation of T b , even during torpor, will result in a proportional heat loss as occurs during normothermia, which must be compensated for by an increase in heat production. Whereas the T b -T a differential determines TMR in thermo-regulating torpid individuals, it has been suggested that the slope of TMR versus T a during torpor may be shallower than that for RMR versus T a during normothermia, perhaps because of a decrease in C at low T b (74,143). Although this interpretation may appear plausible, it is not supported by the empirical evidence from most species.…”

Section: Tmr and The T B -T A Differentialmentioning

confidence: 99%

Metabolic Rate and Body Temperature Reduction During Hibernation and Daily Torpor

Geiser

2004

Annu. Rev. Physiol.

986

870

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Although it is well established that during periods of torpor heterothermic mammals and birds can reduce metabolic rates (MR) substantially, the mechanisms causing the reduction of MR remain a controversial subject. The comparative analysis provided here suggests that MR reduction depends on patterns of torpor used, the state of torpor, and body mass. Daily heterotherms, which are species that enter daily torpor exclusively, appear to rely mostly on the fall of body temperature (Tb) for MR reduction, perhaps with the exception of very small species and at high torpor Tb, where some metabolic inhibition may be used. In contrast, hibernators (species capable of prolonged torpor bouts) rely extensively on metabolic inhibition, in addition to Tb effects, to reduce MR to a fraction of that observed in daily heterotherms. In small hibernators, metabolic inhibition and the large fall of Tb are employed to maximize energy conservation, whereas in large hibernators, metabolic inhibition appears to be employed to facilitate MR and Tb reduction at torpor onset. Over the ambient temperature (Ta) range where torpid heterotherms are thermo-conforming, the Tb-Ta differential is more or less constant despite a decline of MR with Ta; however, in thermo-regulating torpid individuals, the Tb-Ta differential is maintained by a proportional increase of MR as during normothermia, albeit at a lower Tb. Thermal conductance in most torpid thermo-regulating individuals is similar to that in normothermic individuals despite the substantially lower MR in the former. However, conductance is low when deeply torpid animals are thermo-conforming probably because of peripheral vasoconstriction.

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“…3). Accordingly, it has been employed to study thermoregulation and energy balance during torpor and hibernation (Hensaw 1968;Humphries et al 2002), and to quantify the effects of reduced metabolic costs to maintain the thermal gradient T b − T a in conjunction with passive Q 10 effects of lowered T b on enzyme kinetics (Heldmaier and Ruf 1992). More specifically, Humphries et al (2002) developed a bioenergetic model to compare the energy requirements to hibernate during the length of the winter against fat store estimates (Fig.…”

Section: Box 1: Thermoregulatory Polygons In a Nutshellmentioning

confidence: 99%

Thermoregulation in endotherms: physiological principles and ecological consequences

Rezende

Bacigalupe

2015

J Comp Physiol B

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In a seminal study published nearly 70 years ago, Scholander et al. (Biol Bull 99:259-271, 1950) employed Newton's law of cooling to describe how metabolic rates (MR) in birds and mammals vary predictably with ambient temperature (T a). Here, we explore the theoretical consequences of Newton's law of cooling and show that a thermoregulatory polygon provides an intuitively simple and yet useful description of thermoregulatory responses in endothermic organisms. This polygon encapsulates the region in which heat production and dissipation are in equilibrium and, therefore, the range of conditions in which thermoregulation is possible. Whereas the typical U-shaped curve describes the relationship between T a and MR at rest, thermoregulatory polygons expand this framework to incorporate the impact of activity, other behaviors and environmental conditions on thermoregulation and energy balance. We discuss how this framework can be employed to study the limits to effective thermoregulation and their ecological repercussions, allometric effects and residual variation in MR and thermal insulation, and how thermoregulatory requirements might constrain locomotor or reproductive performance (as proposed, for instance, by the heat dissipation limit theory). In many systems the limited empirical knowledge on how organismal traits may respond to environmental changes prevents physiological ecology from becoming a fully developed predictive science. In endotherms, however, we contend that the lack of theoretical developments that translate current physiological understanding into formal mechanistic models remains the main impediment to study the ecological and evolutionary repercussions of thermoregulation. In spite of the inherent limitations of Newton's law of cooling as an oversimplified description of the mechanics of heat transfer, we argue that understanding how systems that obey this approximation work can be enlightening on conceptual grounds and relevant as an analytical and predictive tool to study ecological phenomena. As such, the proposed approach may constitute a powerful tool to study the impact of thermoregulatory constraints on variables related to fitness, such as survival and reproductive output, and help elucidating how species will be affected by ongoing climate change.

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Thermoregulation during hibernation: Application of Newton's law of cooling

Cited by 33 publications

References 13 publications

Cold-hearted bats: uncoupling of heart rate and metabolism during torpor at subzero temperatures

Cold-hearted bats: uncoupling of heart rate and metabolism during torpor at subzero temperatures

Metabolic Rate and Body Temperature Reduction During Hibernation and Daily Torpor

Thermoregulation in endotherms: physiological principles and ecological consequences

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