The temperature and temperature gradients distribution in the rabbit body thermophysical model with evaporation of moisture from its surface

On created in laboratory heat-physical model of a rabbit body reflecting basic heat-physical parameters of the body such as: weight, size of a relative surface, heat absorption and heat conduction, heat capacity etc., a change of radial distribution of temperature and size was found across a superficial layer of evaporation of water from its surface, that simulates sweating, with various ratio of environmental temperature and capacity of electrical heater simulating heat production in animal. The experiments have shown that with evaporation of moisture from a surface of model in all investigated cases, there is an increase of superficial layer of body of a temperature gradient and simultaneous decrease of temperature of a model inside and on the surface. It seems that, with evaporation of a moisture from a surface of a body, the size of a temperature gradient in a thin superficial layer dependent in our experiments on capacity for heat production and environmental temperature, is increased and can be used in a live organism for definition of change in general heat content of the body with the purpose of maintenance of its thermal balance with environment.     

Sapflow+: a four-needle heat-pulse sap flow sensor enabling nonempirical sap flux density and water content measurements

? To our knowledge, to date, no nonempirical method exists to measure reverse, low or high sap flux density. Moreover, existing sap flow methods require destructive wood core measurements to determine sapwood water content, necessary to convert heat velocity to sap flux density, not only damaging the tree, but also neglecting seasonal variability in sapwood water content. ? Here, we present a nonempirical heat-pulse-based method and coupled sensor which measure temperature changes around a linear heater in both axial and tangential directions after application of a heat pulse. By fitting the correct heat conduction-convection equation to the measured temperature profiles, the heat velocity and water content of the sapwood can be determined. ? An identifiability analysis and validation tests on artificial and real stem segments of European beech (Fagus sylvatica L.) confirm the applicability of the method, leading to accurate determinations of heat velocity, water content and hence sap flux density. ? The proposed method enables sap flux density measurements to be made across the entire natural occurring sap flux density range of woody plants. Moreover, the water content during low flows can be determined accurately, enabling a correct conversion from heat velocity to sap flux density without destructive core measurements.     

Equations of heat distribution within the body

A vector integral equation describing heat distribution within the body has been derived. The factors considered are heat conduction, forced convection via the circulatory system, environmental exchange, metabolic heat production, and change in heat content. The vector partial differential equation and alternative forms incorporating boundary conditions were also developed. A difference equation based on a first-order approximation to the fundamental equations was derived to form the basis of a model for heat distribution within the body. It has been shown that factors involving conduction and convection must be considered independently unless the temperature of the blood flowing from a region of the body is equal to the average temperature of the tissue in that region. If this relation between tissue and blood temperature does exist, only a single temperature from each eleeent is needed to describe the heat distribution. In this latter case, models which ascribe all heat transfer to “equivalent” conduction or to convection can give valid predictions.     

Body surface temperature distribution in relation to body composition in obese women

Adipose tissue levels and human obesity are known to be associated with increased heat production. At the same time, subcutaneous adipose tissue provides an insulating layer that impedes heat loss. The energy implications of obesity and body thermoregulatory mechanisms remain relatively poorly understood. This study attempted to examine the potential relationship between body composition (subcutaneous and visceral fat) determined by bioimpedance as well as BMI (body mass index), and skin surface temperature distribution recorded at rest.One specific aim of this study was to draw a thermal map of body areas in obese women and compare this with women of normal body mass, and thus to identify body regions within which heat transfer is particularly impeded. As high fat content is a good insulator, it could reduce the body‘s ability to respond effectively to changes in environmental temperature, which would be problematic for thermal homeostasis. Our results showed that core temperature did not differ between obese and normal body mass participants, while skin temperature of most body surfaces was lower in obese subjects.The results of regression analysis showed that the mean body surface temperature (T_mean) decreased with increasing percentage of body fat (PBF) of the abdominal area. The opposite relationship was observed for the front area of the hand (simultaneous increase in T_mean and PBF). We also found a negative correlation between BMI and T_mean of the thigh areas, both the front and the back. From this it could be concluded that the mean body surface temperature is dependent on body fat.     

Measuring the effects of heat wave episodes on the human body’s thermal balance

During the peak of an extensive heat wave episode on 23–25 July 2007, simultaneous thermophysiological measurements were made in two non-acclimated healthy adults of different sex in a suburban area of Greater Athens, Greece. Based on experimental measurements of mean skin temperature and metabolic heat production, heat fluxes to and from the human body were calculated, and the biometeorological index heat load (HL) produced was determined according to the heat balance equation. Comparing experimental values with those derived from theoretical estimates revealed a great heat stress for both individuals, especially the male, while theoretical values underestimated heat stress. The study also revealed that thermophysiological factors, such as mean skin temperature and metabolic heat production, play an important role in determining heat fluxes patterns in the heat balance equation. The theoretical values of mean skin temperature as derived from an empirical equation may not be appropriate to describe the changes that take place in a non-acclimated individual. Furthermore, the changes in metabolic heat production were significant even for standard activity.     

Heat balance precedes stabilization of body temperatures during cold water immersion.

Certain previous studies suggest, as hypothesized herein, that heat balance (i.e., when heat loss is matched by heat production) is attained before stabilization of body temperatures during cold exposure. This phenomenon is explained through a theoretical analysis of heat distribution in the body applied to an experiment involving cold water immersion. Six healthy and fit men (mean +/- SD of age = 37.5 +/- 6.5 yr, height = 1.79 +/- 0.07 m, mass = 81.8 +/- 9.5 kg, body fat = 17.3 +/- 4.2%, maximal O2 uptake = 46.9 +/- 5.5 l/min) were immersed in water ranging from 16.4 to 24.1 degrees C for up to 10 h. Core temperature (Tco) underwent an insignificant transient rise during the first hour of immersion, then declined steadily for several hours, although no subject's Tco reached 35 degrees C. Despite the continued decrease in Tco, shivering had reached a steady state of approximately 2 x resting metabolism. Heat debt peaked at 932 +/- 334 kJ after 2 h of immersion, indicating the attainment of heat balance, but unexpectedly proceeded to decline at approximately 48 kJ/h, indicating a recovery of mean body temperature. These observations were rationalized by introducing a third compartment of the body, comprising fat, connective tissue, muscle, and bone, between the core (viscera and vessels) and skin. Temperature change in this "mid region" can account for the incongruity between the body's heat debt and the changes in only the core and skin temperatures. The mid region temperature decreased by 3.7 +/- 1.1 degrees C at maximal heat debt and increased slowly thereafter. The reversal in heat debt might help explain why shivering drive failed to respond to a continued decrease in Tco, as shivering drive might be modulated by changes in body heat content.     

Rattlesnake denning: theoretical considerations on winter temperatures

Aggregations of over-wintering rattlesnakes are considered as a hypothetical metabolic unit. Estimates of fat consumption are utilized to predict heat production during the denning season. Previously determined temperature heat production curves allow prediction of a mean body temperature for the winter season which is around 15°C above the ambient den site temperature. An estimate from the previously derived relationship between heat production per unit surface area and body temperature predicts a reduction in aggregate effective surface area of 40 % of the summed surface areas of the individual animals constituting the hypothetical aggregation.     

Ambient temperature correlates with geographic variation in body size of least horseshoe bats

Geographic variation in body size is common within many animal species. The causes of this pattern, however, remain largely unexplored in most vertebrate groups. Bats are widely distributed globally owing to their ability of powered flight. Most bat species encounter a variety of climatic conditions across their distribution range, making them an ideal taxon for the study of ecogeographic patterns in body size. Here, we used adult least horseshoe bats, Rhinolophus pusillus, to test whether geographic variation in body size was determined by heat conservation, heat dissipation, climatic seasonality, or primary productivity. We measured body mass and head-body length for 246 adult bats from 12 allopatric colonies in China. We quantified the ecological conditions inhabited by each colony, including mean maximum temperature of the warmest month, mean minimum temperature of the coldest month, temperature seasonality, precipitation seasonality, and annual net primary productivity (ANPP). Body mass and head-body length, 2 of the most reliable indicators of body size, exhibited marked differences between colonies. After controlling for spatial autocorrelation, the mean minimum temperature of the coldest month explained most of the variation in body size among colonies, regardless of sex. The mean maximum temperature, climatic seasonality, and ANPP had limited power in predicting body size of males or females in comparison with mean minimum temperature. These results support the heat conservation hypothesis and suggest adaptive responses of body size to cold climates in cave-dwelling bats.     

Penetration of external thermal perturbations into homeothermic organisms, part I (author's transl)

The general importance of the mean surface curvature for heat conduction problems is explained and a special symmetry with constant mean curvature on the isothermal surfaces is defined. The applicability for the body shapes of homeothermic organisms is demonstrated and the partial differential equation of heat conduction for this case is derived. The definition: heat release = real heat production + convective pseudoproduction eliminates the term of convective heat transfer through the blood stream and allows the reduction to a mere heat conduction problem. Formulas for the heat loss to the environment and for steady state temperature profiles are given. In case of sudden change of heat loss the partial differential equation is solved and a formula is derived, using dimensionless coordinates of time and distance. The mean surface curvature has strongest influence to the interior temperature field. The solution shows clearly the importance of thermal inertia of the homeothermic organism, for the external temperature wave penetrates into the body with a long phase displacement in time.     

Behavioral and Physiological Thermoregulation of Crocodilians

Crocodilians, like other reptiles, regulate their body temperaturesby a combination of behavioral and physiological mechanisms.Behaviorally, they seek warm surface water or bask when cooland avoid overheating by the evaporation of water from theirdorsum, evaporation of water by gaping or by retreating to deep,cool water. Physiologically, crocodilians increase cutaneousthermal conductance by increasing blood flow to the skin (andsubdermal musculature) during warming. This hastens the warmingprocess. Cutaneous blood flow is reduced during general coolingand locally if the body temperature exceeds skin temperature.This enables crocodilians to increase body temperature significantlywhile basking in cool shallow water. Large crocodilians appearto be able to alter their rates of heat exchange to a largerextent than small ones and they can do so with less cardiovascularinvolvement. Large crocodilians, with their lower surface/volumeratio, are capable of producing sufficient metabolic heat toelevate their body temperature above water temperature.     

An infrared thermographic study of surface temperature in the euthermic woodchuck (Marmota monax).

Surface temperatures were measured in euthermic woodchucks (Marmota monax) using infrared thermography across a range of ambient temperatures from -10 degrees C to 32 degrees C. The woodchuck keeps surface temperature of the peripalpebral region uniformly high, while head and body surfaces change proportionally with ambient temperature. When ambient temperature was below 0 degrees C, all surface temperatures increased which prevents freezing. At no point did the animals appear to be unable to regulate heat exchange. This species appears to be especially well adapted to the higher temperatures it encounters in its range. Vasomotion in the feet and to a lesser extent in the pinnae was used to regulate heat loss. At ambient temperature of 32 degrees C, mean temperatures of nose surfaces were 0.2 degrees C and 0.3 degrees C less than ambient temperature suggesting a type of counter current cooling mechanism may be present.     

Static response in body temperature regulation of the euthermic warm-acclimated golden hamster (Mesocricetus auratus)

A characteristic feature of the body temperature regulation of euthermic golden hamsters is a great individual variability of body temperature in the thermoneutral zone. Resting values of the total metabolic rate (M) at ambient temperature 30-34 degrees C vary from 5.3 to 8.8 W.kg-1 between individuals, body temperature reaching 33.5-37.7 degrees C (subcutaneous temperature, Ts) and 35.4-39.0 degrees C (hypothalamic temperature, Th). The dependence of metabolic heat production on steady deviations of peripheral and central body temperature from the resting values in nonlinear in general, but the unknown functional relationship delta M = f (delta Th, delta Ts) can be replaced by a single linear regression function of Ts by neglecting the change of central body temperature: delta M = 2.14-2.00. delta Ts. Total body thermosensitivity of the golden hamster determined from steady changes of rectal temperature and metabolic rate after external cooling is -6.8 +/- 1.3 W.kg-1. degrees C-1.     

Mean body temperature does not modulate eccrine sweat rate during upright tilt.

Conflicting reports exist about the role of baroreflexes in efferent control of eccrine sweat rate. These conflicting reports may be due to differing mean body temperatures between studies. The purpose of this project was to test the hypothesis that mean body temperature modulates the effect of head-up tilt on sweat rate and skin sympathetic nerve activity (SSNA). To address this question, mean body temperature (0.9.internal temperature + 0.1.mean skin temperature), SSNA (microneurography of peroneal nerve, n = 8), and sweat rate (from an area innervated by the peroneal nerve and from two forearm sites, one perfused with neostigmine to augment sweating at lower mean body temperatures and the second with the vehicle, n = 12) were measured in 13 subjects during multiple 30 degrees head-up tilts during whole body heating. At the end of the heat stress, mean body temperature (36.8 +/- 0.1 to 38.0 +/- 0.1 degrees C) and sweat rate at all sites were significantly elevated. No significant correlations were observed between mean body temperature and the change in SSNA during head-up tilt (r = 0.07; P = 0.62), sweating within the innervated area (r = 0.06; P = 0.56), sweating at the neostigmine treated site (r = 0.04; P = 0.69), or sweating at the control site (r = 0.01; P = 0.94). Also, for each tilt throughout the heat stress, there were no significant differences in sweat rate (final tilt sweat rates were 0.69 +/- 0.11 and 0.68 +/- 0.11 mg.cm(-2).min(-1) within the innervated area; 1.04 +/- 0.16 and 1.06 +/- 0.16 mg.cm(-2).min(-1) at the neostigmine-treated site; and 0.85 +/- 0.15 and 0.85 +/- 0.15 mg.cm(-2).min(-1) at the control site, for supine and tilt, respectively). Hence, these data indicate that mean body temperature does not modulate eccrine sweat rate during baroreceptor unloading induced via 30 degrees head-up tilt.     

季节性干旱对中亚热带人工林显热和潜热通量日变化的影响

植被与大气间的显热和潜热通量的日变化是大气过程和植被生理过程的显著标志。本研究利用ChinaFLUX千烟洲站典型的夏季雨热不同季的季节性干旱的试验条件,探讨了2003年季节性干旱对该生态系统显热和潜热通量日变化变异幅度和峰值时间的影响。研究表明：显热通量的日变化变异幅度年平均值为176 W/m2。潜热通量的日变化变异幅度年平均值为171 W/m2。显热通量到达日变化峰值的时间平均为11:57。全年潜热通量的日变化都在午后达到峰值,平均值为12:33。季节性干旱造成显热通量的日变异幅度明显增大,从144W m-2增加到321 W m-2。而潜热通量的日变异幅度明显降低,从324 W/m2减小到198 W/m2。,显热和潜热通量日变异幅度的相对变化明显增大,从-165 W/m2增加到76 W/m2,气温和饱和水汽压差是影响显热和显热日变异幅度及其相对变化的主要控制因素。干旱胁迫期,深层水对显热通量日变化变异幅度及其与潜热通量日变化变异幅度的相对变化的作用更显著,而潜热通量日变化变异幅度与气象要素关系不显著。季节性干旱造成显热通量日变化的峰值时间和显热和潜热通量日变化峰值时间的相对变化明显向下午偏移,显热通量日变化的峰值从上午11:31到中午12:17,相对变化从1小时到1小时20分钟。季节性干旱对潜热通量日变化峰值时间没有显著的影响。非干旱胁迫期,显热通量日变化峰值时间和显热及潜热通量日变化峰值时间的相对变化均与气温负相关,而干旱胁迫期,则与气温正相关。潜热通量日变化峰值时间与气象要素关系均不显著。该生态系统显热和潜热通量日变化峰值的相对变化主要受降水量的季节分配控制,在干旱胁迫期降水的作用更加明显。潜热和显热通量日变化峰值时间的相对变化总体上都受植被与大气间的耦合程度控制。     

Effects of color temperature of fluorescent lamps on body temperature regulation in a moderately cold environment

A study on the effects of different color temperatures of fluorescent lamps on skin and rectal temperatures in a moderately cold environment involving (i) changes in skin temperature of 7 male subjects exposed to an ambient temperature ranging from 28 degrees C to 18 degrees C (experiment I) and (ii) changes in skin and rectal temperatures and metabolic heat production of 11 male subjects exposed to ambient temperature of 15 degrees C for 90 min (Experiment II) was conducted. In Experiment I, the reduction of mean skin temperature from the control value was significantly greater under 3000 K than under 5000 K or 7500 K lighting. In Experiment II, the reductions in mean skin temperature and rectal temperature were respectively greater and smaller under 3000 K than those under 5000 K or 7500 K lighting. However, metabolic heat production was not affected by color temperature conditions. The relationships between morphological and physiological parameters revealed that no significant relation of rectal temperature to body surface area per unit body weight was found only under 3000 K. Furthermore, while the mean skin temperature was independent on the mean skinfold thickness under 3000 K, a significant negative correlation between the rectal and mean skin temperatures was observed. Therefore, body heat loss might be suppressed effectively by increasing the vasoconstrictor tone under a color temperature of 3000 K, and the body shell was dependent only on morphological factors under 5000 K and 7500 K lighting.     

Influence of body heat content on hand function during prolonged cold exposures.

We examined the influence of 1) prior increase [preheating (PHT)], 2) increase throughout [heating (HT)], and 3) no increase [control (Con)] of body heat content (H(b)) on neuromuscular function and manual dexterity of the hands during a 130-min exposure to -20 degrees C (coldEx). Ten volunteers randomly underwent three passive coldEx, incorporating a 10-min moderate-exercise period at the 65th min while wearing a liquid conditioning garment (LCG) and military arctic clothing. In PHT, 50 degrees C water was circulated in the LCG before coldEx until core temperature was increased by 0.5 degrees C. In HT, participants regulated the inlet LCG water temperature throughout coldEx to subjective comfort, while the LCG was not operating in Con. Thermal comfort, rectal temperature, mean skin temperature, mean finger temperature (T(fing)), change in H(b) (DeltaH(b)), rate of body heat storage, Purdue pegboard test, finger tapping, handgrip, maximum voluntary contraction, and evoked twitch force of the first dorsal interosseus muscle were recorded. Results demonstrated that, unlike in HT and PHT, thermal comfort, rectal temperature, mean skin temperature, twitch force, maximum voluntary contraction, and finger tapping declined significantly in Con. In contrast, T(fing) and Purdue pegboard test remained constant only in HT. Generalized estimating equations demonstrated that DeltaH(b) and T(fing) were associated over time with hand function, whereas no significant association was detected for rate of body heat storage. It is concluded that increasing H(b) not only throughout but also before a coldEx is effective in maintaining hand function. In addition, we found that the best indicator of hand function is DeltaH(b) followed by T(fing).     

Heat debt as an index for cold adaptation in men

Several types of cold adaptation in men have been described in the literature (metabolic, insulative, hypothermic). The aim of this study is to show that the decrease of heat debt can be considered as a new index for cold adaptation. Ten male subjects were acclimated by water immersions (temperature 10-15 degrees C, 4 immersions/wk over 2 mo). Thermoregulatory responses before and after acclimation were tested by a standard cold test in a climatic chamber for 2 h at rest [dry bulb temperature (Tdb): 10 degrees C; relative humidity (rh): 25%]. After adaptation, four thermoregulatory modifications were observed: an increase in the delay for the onset of shivering (32.7 +/- 7.99 instead of 14.1 +/- 5.25 min); a decrease of body temperature levels for the onset of shivering [rectal temperature (Tre): 37.06 +/- 0.08 instead of 37.31 +/- 0.06 degrees C; mean skin temperature (Tsk): 24.83 +/- 0.56 instead of 26.86 +/- 0.46 degrees C; mean body temperature (Tb): 33.03 +/- 0.20 instead of 34.16 +/- 0.37 degrees C); a lower level of body temperatures in thermoneutrality (Tre = 37.16 +/- 0.08 instead of 37.39 +/- 0.06 degrees C; Tsk = 31.29 +/- 0.21 instead of 32.01 +/- 0.22 degrees C; Tb = 35.92 +/- 0.08 instead of 36.22 +/- 0.05 degrees C); a decrease of heat debt calculated from the difference between heat gains and heat losses (5.66 +/- 0.08 instead of 8.33 +/- 0.38 kJ/kg). The different types of cold adaptation observed are related to the physical characteristics of the subjects (percent body fat content) and the level of physical fitness (VO2max).(ABSTRACT TRUNCATED AT 250 WORDS)     

Thermally mediated body temperature, water content and aggregation behaviour in the intertidal gastropod Nerita atramentosa

Intertidal organisms are vulnerable to global warming as they already live at, or near to, the upper limit of their thermal tolerance window. The behaviour of ectotherms could, however, dampen their limited physiological abilities to respond to climate change (e.g. drier and warmer environmental conditions) which could substantially increase their survival rates. The behaviour of ectotherms is still mostly overlooked in climate change studies. Here, we investigate the potential of aggregation behaviour to compensate for climate change in an intertidal gastropod species (Nerita atramentosa) in South Australia. We used thermal imaging to investigate (1) the heterogeneity in individual snail water content and body temperature and surrounding substratum temperature on two topographically different habitats (i.e. rock platform and boulders) separated by 250 m at both day- and night-times, (2) the potential relationship between environment temperature (air and substratum) and snail water content and body temperature, and (3) the potential buffering effect of aggregation behaviour on snail water content and body temperature. Both substratum and snail temperature were more heterogeneous at small spatial scales (a few centimetres to a few metres) than between habitats. This reinforces the evidence that mobile intertidal ectotherms could survive locally under warmer conditions if they can locate and move behaviourally in local thermal refuges. N. atramentosa behaviour, water content and body temperature during emersion seem to be related to the thermal stability and local conditions of the habitat occupied. Aggregation behaviour reduces both desiccation and heat stresses but only on the boulder field. Further investigations are required to identify the different behavioural strategies used by ectothermic species to adapt to heat and dehydrating conditions at the habitat level. Ultimately, this information constitutes a fundamental prerequisite to implement conservation management plans for ectothermic species identified as vulnerable in the warming climate.     

Human heat balance during postexercise recovery: separating metabolic and nonthermal effects

Previous studies report greater postexercise heat loss responses during active recovery relative to inactive recovery despite similar core temperatures between conditions. Differences have been ascribed to nonthermal factors influencing heat loss response control since elevations in metabolism during active recovery are assumed to be insufficient to change core temperature and modify heat loss responses. However, from a heat balance perspective, different rates of total heat loss with corresponding rates of metabolism are possible at any core temperature. Seven male volunteers cycled at 75% of Vo(2peak) in the Snellen whole body air calorimeter regulated at 25.0 degrees C, 30% relative humidity (RH), for 15 min followed by 30 min of active (AR) or inactive (IR) recovery. Relative to IR, a greater rate of metabolic heat production (M - W) during AR was paralleled by a greater rate of total heat loss (H(L)) and a greater local sweat rate, despite similar esophageal temperatures between conditions. At end-recovery, rate of body heat storage, that is, [(M - W) - H(L)] approached zero similarly in both conditions, with M - W and H(L) elevated during AR by 91 +/- 26 W and 93 +/- 25 W, respectively. Despite a higher M - W during AR, change in body heat content from calorimetry was similar between conditions due to a slower relative decrease in H(L) during AR, suggesting an influence of nonthermal factors. In conclusion, different levels of heat loss are possible at similar core temperatures during recovery modes of different metabolic rates. Evidence for nonthermal influences upon heat loss responses must therefore be sought after accounting for differences in heat production.