Total Evaporative Heat Loss Research Articles

Phenotypic flexibility in heat production and heat loss in response to thermal and hydric acclimation in the zebra finch, a small arid-zone passerine

To maintain constant body temperature (Tb) over a wide range of ambient temperatures (Ta) endothermic animals require large amounts of energy and water. In hot environments, the main threat to endothermic homeotherms is insufficient water to supply that necessary for thermoregulation. We investigated flexible adjustment of traits related to thermoregulation and water conservation during acclimation to hot conditions or restricted water availability, or both, in the zebra finch, Taeniopygia guttata a small arid-zone passerine. Using indirect calorimetry, we measured changes in whole animal metabolic rate (MR), evaporative heat loss (EHL) and Tb before and after acclimation to 23 or 40 °C, with different availability of water. Additionally, we quantified changes in partitioning of EHL into respiratory and cutaneous avenues in birds exposed to 25 and 40 °C. In response to heat and water restriction zebra finches decreased MR, which together with unchanged EHL resulted in increased efficiency of evaporative heat loss. This facilitated more precise Tb regulation in heat-acclimated birds. Acclimation temperature and water availability had no effect on the partitioning of EHL into cutaneous or respiratory avenues. At 25 °C, cutaneous EHL accounted for ~ 60% of total EHL, while at 40 °C, its contribution decreased to ~ 20%. Consistent among-individual differences in MR and EHL suggest that these traits, provided that they are heritable, may be a subject to natural selection. We conclude that phenotypic flexibility in metabolic heat production associated with acclimation to hot, water-scarce conditions is crucial in response to changing environmental conditions, especially in the face of current and predicted climate change.

Análise de algumas variáveis fisiológicas para avaliação do grau de adaptação de ovinos submetidos ao estresse por calor

Investigaram-se a temperatura retal, a freqüência respiratória e a taxa de evaporação total de ovinos Corriedale sob três temperaturas ambientes, visando uma melhor compreensão dos mecanismos de termorregulação desses animais. Inicialmente, 21 animais adultos foram alojados em câmara climática à temperatura de 45ºC, e pressão parcial de vapor (PV) variável, registrando-se a freqüência respiratória (FR) e a temperatura retal (TR). Baseando-se na FR e TR, foram selecionados 10 animais, cinco com os valores mais baixos, assumindo-os como mais adaptados ao calor (grupo 1) e cinco com valores mais altos, assumindo-os como menos adaptados (grupo 2). Os animais selecionados foram mantidos em câmara climática, onde mediram-se novamente TR, FR e taxa de evaporacão total (TET), sob 20, 30 e 40ºC de temperatura do ar e PV variável. Não houve diferença estatística entre os grupos classificados, para todas as variáveis medidas. Concluiu-se que a utilização das variáveis fisiológicas TR e FR como parâmetros únicos para a seleção destes animais não é suficiente para avaliar o grau de adaptação a temperaturas elevadas.

Implications of the large surface area to body mass ratio on the heat balance of the greater glider (Petauroides volans: Marsupialia)

1. In a study of thermoregulation in the greater glider, a small arboreal marsupial with large gliding membranes, metabolic rate (MR), skin and deep body temperature (Tsk,Tb), and respiratory and total evaporative heat loss (Eex,Etot) were measured in relation to ambient temperature (Ta). 2. Although the surface area is twice that of marsupials of similar body weight, MR was not significantly different from the average marsupial metabolic rate. This must be attributed to an excellent thermal insulation and behavioural factors. 3. AtTa above the thermoneutral point, at 20°C, the greater glider became hyperthermic.Tb increased from 35.4°C at 20°CTa to 39.1°C at 40°C. At 30°C, 55% of MR was dissipated by evaporation. This proportion increased to 105% at 35°C and 132% of MR at 40°C. The increase inEtot was accompanied by intense licking of extremities and the ventral body surface.Eex dissipated only 12% of MR at 40°C irrespective of an 8-fold increase in respiratory frequency from a basal value of 18 breaths·min−1. 4. It is concluded that the greater glider can utilize its gliding membranes to reduce heat losses by increasing the insulative layer around the body surface. At highTa, a clear contrast between the inefficient use of water for evaporative thermolytic processes, mainly salivation, and the limited availability of water in its arboreal habitat becomes evident.

Thermal balance in ketamine-anesthetized rhesus monkey Macaca mulatta

A partitional calorimetry study compared thermoregulatory responses of unanesthetized adult rhesus monkeys (4 female, 1 male) to those anesthetized with ketamine HCl and exposed to ambient temperature (Ta) of 18, 29, 38 degrees C. Steady-state metabolic heat production (M), mean skin temperature (Tsk), rectal temperature (Tre), respiratory evaporative heat loss (Eres), and total evaporative heat loss (Etot) were measured at each Ta. Average Tre of anesthetized animals was reduced by approximately 1 degree C at Ta 18 degrees C, but thermal balance in anesthetized and control animals was maintained by reflexly decreased tissue conductance and shivering. For anesthetized animals, the average M increased 1.8 times over the lowest value of 40.13 W/m2 at Ta 29 degrees C, compared to a 1.5-fold increase for controls. Responses for both groups were not different at Ta 29 degrees C, both groups regulated body temperatures by vasodilation and increased sweating, but with ketamine sweating was reduced (35%). Effective tissue thermal conductance (K) was lowest at Ta 18 (10.8 W/m2 . degrees C) and increased to 39.4 W/m2 . degrees C at Ta 38 degrees C. No significant difference in K was found between ketamine and control groups at other Ta's.

Effect of water restriction on oxygen uptake, evaporative water loss and body temperature of the rock hyrax

1. Evaporative water loss, O2-consumption and body temperature were measured in three rock hyraxes under control and restricted water intake conditions. 2. Water turnover rate was 61±6 ml·kg−0.82· 24 h−1 during control experiments and 37±6 ml· kg−0.82·24 h−1 during water restriction. 3. Water restriction reduced O2-consumption below ambient temperatures (Ta) of 28 and above 33°C; there was no effect within the thermoneutral zone. Between 12 and 27°C total evaporative heat loss decreased from 0.41±0.05 W·kg−1 during control experiments to 0.34±0.04 W·kg−1 during water restriction. Between 39 and 41°C evaporative heat loss increased to 1.61 W·kg−1 during ad libitum and 0.72 W·kg−1 during restricted water availability. 4. During control experiments body temperature ranged between 37 and 40°C asTa was changed between 12 and 38°C. During water restriction the animals became hypothermic below and hyperthermic above aTa of 27°C.

Thermal sweating in different body regions of sheep

Although sheep combat thermal stress mainly by panting, a sizeable amount (40%) of total evaporative heat loss, is from sources other than panting (Hales & Brown, 1974). The frequency of sporadic discharge of sweat glands increases with increase in ambient temperature and is accompanied by a decline in respiration rate (Bligh, 1961). The wool coat can reduce evaporative cooling but sweating may have cooling value in sheep breeds with open fleeces (Rai, Singh & More, 1978). In sheep, the number and size of the sweat glands (Waites & Voglmayr, 1962) and the quantum of sweat production in a particular time period (Ghoshal et al. 1977) varies in different body regions. In view of the possible significance of surface evaporative cooling, thermal sweating in different body regions of sheep was investigated.

Temperature regulation in the smallest ungulate, the lesser mouse deer ( Tragulus javanicus)

1. 1. The rectal temperature, oxygen consumption, respiratory frequency, and total evaporative water loss were measured in the Lesser Mouse deer ( Tragulus javanicus) at air temperatures of 10–40°C. 2. 2. The rectal temperature (mean, 38.4°C) was similar to that of other ungulates. It was relatively constant between air temperatures of 15–30°C, but the mouse deer became hyperthermic at air temperatures >30°C. 3. 3. The oxygen consumption was minimal (mean, 0.539ml O 2/g/hr.) at air temperatures between 26.6 and 29.0°C. The oxygen consumption was close to the value predicted for placental mammals, from their body wt. At lower air temperatures, the animals shivered and their oxygen consumption increased. 4. 4. Respiratory frequency increased at high air temperatures but, under the conditions of the experiments, total evaporative heat loss did not account for >54% of the metabolic heat production. 5. 5. It was concluded that the mouse deer is not particularly well adapted to heat or cold. This conclusion conforms with its behavior, habitat and distribution.

Temperature regulation in the small Indian mongoose ( Herpestes auropunctatus)

Abstract o 1. Small Indian Mongooses were exposed to air temperatures between 5°C and 45°C. 2. Within the thermoneutral zone of ambient temperature (28–38°C), the mean rectal temperature of the animals was 39.76°C ± 0.50 (S.E.) and the oxygen consumption was 0.66 ml. O2/g. hr. ± 0.18 (S.E.). 3. The mongooses responded to cold (5°C) with a threefold increase in oxygen consumption, but their thermal conductance and rectal temperature did not decrease. 4. In a hot environment, the respiratory frequency increased and total evaporative heat loss exceeded metabolic heat production. 5. It was concluded that the mongoose has effective physiological mechanisms for dealing with hot and moderately cold environments, which may help to explain its establishment in a wide range of habitats.

Evaporative heat loss in the California Sea Lion and Harbor Seal

1. 1. Total evaporative heat loss was measured in four California Sea Lions and one Harbor Seal at air temperatures between 13 and 30°C. The total heat loss was partitioned into respiratory and cutaneous components. 2. 2. Thermal polypnea was not observed to occur in any of the animals and respiratory evaporative heat loss was estimated to represent less than 3 per cent of the heat production when the animals were hyperthermic in a hot environment (31°C). 3. 3. Active sweating was noted on the bare skin of the flippers of the sea lions but not on the haired surface of the torso. The total cutaneous evaporative heat loss accounted for approximately 16 per cent of the heat produced by metabolism, in a hot environment. 4. 4. It was concluded that evaporative heat loss mechanisms were relatively ineffective in California Sea Lions and in the Harbor Seal also.

Influence of air humidity on the partition of heat exchanges of cattle

SUMMARYThe balance between heat production and heat loss and the partition of heat exchanges of cattle in relation to air humidity has been studied at two different air temperatures using a direct (gradient-layer) calorimeter.Increasing humidity at 35 °C air temperature caused no significant change in heat production or in the level of total heat loss finally attained, but body temperature and respiratory activity were both increased.Increasing humidity at 15 °C air temperature caused a small reduction in heat loss by evaporation but had no effect on sensible heat loss, body temperature or respiratory frequency.Heat loss by evaporation amounted to 18% of the total heat loss at 15 °C and to 84% at 35 °C.Heat loss by respiratory evaporation amounted to 54% of the total evaporative heat loss at 15 °C and to 38% at 35 °C.