A thermographic study of the effect of body composition and ambient temperature on the accuracy of mean skin temperature calculations

The problem associated with using measurements from a small number of sites to determine mean skin temperature was investigated by studying variations in distributions of skin temperatures of the bare torsos of humans exposed to ambient temperatures of 18, 23, and 28 degrees C. Following a 60 minute equilibration period the temperatures of four regions (chest, abdomen, upper back, and lower back) were measured using both thermistors and an infra-red thermographic system. Regions of the torso usually represented by a single temperature exhibited significant point-to-point temperature variations especially in chilled subjects. Also an earlier finding was confirmed: in that larger variations in skin temperature distributions occur as body fat content increases. Caution must therefore be used in applying the concept of a mean skin temperature derived from a few select sites, especially with nude subjects who are chilled or have a high body fat content.     

Measurement of torso skin temperature under clothing

The influence of clothing on skin temperature distributions of the torso was investigated during and after cold exposure. Volunteers were cooled for one hour at 5 degrees C while wearing clothing designed to have insulation which was intended to be relatively uniformly distributed. Three different thicknesses of clothing were used. Following thermistor measurements of skin temperatures during the cold exposures, clothing was quickly removed from the upper parts of the body to enable thermographic investigations of the temperature distributions of the front of the bare torso. The evolution of temperature distributions were then studied at different ambient temperatures (5 degrees C and 20 degrees C) as a function of the thickness of the insulation which had previously been worn. The patterns of the temperature distributions, and the range and standard deviation of torso temperatures were all found to be relatively constant in spite of the different thicknesses of clothing worn or in the time-variant mean torso temperatures which resulted. The front torso sites normally used for the determination of mean skin temperatures were found to be on portions of the torso which were cooler than the surrounding regions. It was concluded that a site midway between the umbilicus and a nipple yields a more accurate estimate of mean torso temperature in the conditions of the present study.     

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.     

Cutaneous warming promotes sleep onset

Sleep occurs in close relation to changes in body temperature. Both the monophasic sleep period in humans and the polyphasic sleep periods in rodents tend to be initiated when core body temperature is declining. This decline is mainly due to an increase in skin blood flow and consequently skin warming and heat loss. We have proposed that these intrinsically occurring changes in core and skin temperatures could modulate neuronal activity in sleep-regulating brain areas (Van Someren EJW, Chronobiol Int 17: 313-54, 2000). We here provide results compatible with this hypothesis. We obtained 144 sleep-onset latencies while directly manipulating core and skin temperatures within the comfortable range in eight healthy subjects under controlled conditions. The induction of a proximal skin temperature difference of only 0.78 +/- 0.03 degrees C (mean +/- SE) around a mean of 35.13 +/- 0.11 degrees C changed sleep-onset latency by 26%, i.e., by 3.09 minutes [95% confidence interval (CI), 1.91 to 4.28] around a mean of 11.85 min (CI, 9.74 to 14.41), with faster sleep onsets when the proximal skin was warmed. The reduction in sleep-onset latency occurred despite a small but significant decrease in subjective comfort during proximal skin warming. The induction of changes in core temperature (delta = 0.20 +/- 0.02 degrees C) and distal skin temperature (delta = 0.74 +/- 0.05 degrees C) were ineffective. Previous studies have demonstrated correlations between skin temperature and sleep-onset latency. Also, sleep disruption by ambient temperatures that activate thermoregulatory defense mechanisms has been shown. The present study is the first to experimentally demonstrate a causal contribution to sleep-onset latency of skin temperature manipulations within the normal nocturnal fluctuation range. Circadian and sleep-appetitive behavior-induced variations in skin temperature might act as an input signal to sleep-regulating systems.     

Thermoregulatory control of finger blood flow.

Three men exercised on a bicycle ergometer at 30, 50, asd 70 per cent of maximal aerobic power in ambient temperatures of 15, 25, and 35 degrees C with water vapor pressure less than 18 Torr. Exercies was used to vary internal temperature during as experiment, and different ambient temperatures were used to vary skin temperatures independently of internal temperature. Finger temperature was fixed at about 35.7 degrees C. Espohageal temperature (Tes) was measured with a thermocouple at the level of the left atrium, and mean skin temperature (Tsk) was calcualted from a weighted mean of thermocouple temperatures at eight skin sites. Finger blood flow (BF) was measured by electrocapacitance plethysmography. Although some subjects showed small and equivocal vasomotor effects of exercise, our data are well accounted for by an equation of the form BF equal to alTes + a2Tsk + b, independent of exercise intensity. For these subjects, the ratios a1/a2 (5.9, 8.6, 9.4) were similar to the ratios of the corresponding coefficients recently reported for thermaoregulatory sweating (8.6, 10.4) and for forearm blood flow (9.6).     

Effects of apomorphine on thermoregulatory responses of rats to different ambient temperatures.

Either systemic or central administration of apomorphine produced dose-related decreases in rectal temperature at ambient temperatures (Ta) of 8 and 22 degrees C in rats. At Ta = 8 degrees C, the hypothermia was brought about by a decrease in metabolic rate (M). At Ta = 22 degrees C, the hypothermia was due to an increase in mean skin temperature, an increase in respiratory evaporative heat loss (Eres) and a decrease in M. This increased mean skin temperature was due to increased tail and foot skin temperatures. However, at Ta = 29 degrees C, apomorphine produced increased rectal temperatures due to increased M and decreased Eres. Moreover, the apomorphine-induced hypothermia or hyperthermia was antagonized by either haloperidol or 6-hydroxydopamine, but not by 5,6-dihydroxytryptamine. The data indicate that apomorphine acts on dopamine neurons within brain, with both pre- and post-synaptic sites of action, to influence body temperature.     

Effect of different daytime and night-time temperature regimes on the foliar respiration of Pinus taeda: predicting the effect of variable temperature on acclimation

The objectives of this study were to determine the acclimation of loblolly pine (Pinus taeda L.) foliar respiration to different night-time low temperatures, daytime high temperatures, and daily mean temperatures, and then to use the responses of temperature acclimation to various temperature regimes to predict acclimation under fluctuating temperatures. Experiments were conducted on two-year-old seedlings in growth chambers using different combinations of day and night-time temperatures. The first experiment exposed trees to 22/22, 29/22, 22/15, and 29/15 degrees C day/night (d/n). When measured at a common temperature (15, 22 or 29 degrees C), respiration rates were lower for trees exposed to higher treatment temperatures and acclimation was influenced by both day and night-time temperature. However, the extent of acclimation did not relate to mean temperature, i.e. respiration rates measured at a common temperature ranked as follows for seedlings exposed to different temperature regimes, 22/15>22/22>29/15 congruent with29/22 degrees C d/n. Rather, acclimation of foliar respiration was linearly related to mean daily respiration rate, where mean daily respiration rate is the average of the respiration rates measured at the day and night-time treatment temperatures. The discrepancy between mean daily respiration rate and mean daily temperature occurred because respiration increased exponentially with increasing temperature. In a second experiment, the same seedlings were exposed to 22/22, 15/15, 25.5/18.5, and 25.5/15 degrees C d/n to test the relationship between mean daily respiration rate and acclimation. As in the first experiment, acclimation was linearly related to mean daily respiration rate. The concept of effective acclimation temperature, which is the temperature at which the mean daily respiration rate occurs, was derived from these results as a means to predict the extent that foliar respiration acclimates to treatment temperature.     

In vivo thermal conductivity of the human forearm tissues

The effective thermal conductivities of the skin + subcutaneous (keff skin + fat) and muscle (keff muscle) tissues of the human forearm at thermal steady state during immersion in water at temperatures (Tw) ranging from 15 to 36 degrees C were determined. Tissue temperature (Tt) was continuously monitored by a calibrated multicouple probe during a 3-h immersion of the resting forearm. Tt was measured every 5 mm from the longitudinal axis of the forearm (determined from computed-tomography scanning) to the skin surface. Skin temperature (Tsk), heat loss (Hsk), and blood flow (Q) of the forearm, as well as rectal temperature (Tre) and arterial blood temperature at the brachial artery (Tbla), were measured during the experiments. When the keff values were calculated from the finite-element (FE) solution of the bioheat equation, keff skin + fat ranged from 0.28 +/- 0.03 to 0.73 +/- 0.14 W.degrees C-1.m-1 and keff muscle varied between 0.56 +/- 0.05 and 1.91 +/- 0.19 W.degrees C-1.m-1 from 15 to 36 degrees C. The values of keff skin + fat and keff muscle, calculated from the FE solution for Tw less than or equal to 30 degrees C, were not different from the average in vitro values obtained from the literature. The keff values of the forearm tissues were linearly related (r = 0.80, P less than 0.001) to Q for Tw greater than or equal to 30 degrees C. It was found that the muscle tissue could account for 92 +/- 1% of the total forearm insulation during immersion in water between 15 and 36 degrees C.     

Thermal insulation and body temperature wearing a thermal swimsuit during water immersion

This study evaluated the effects of a thermal swimsuit on body temperatures, thermoregulatory responses and thermal insulation during 60 min water immersion at rest. Ten healthy male subjects wearing either thermal swimsuits or normal swimsuits were immersed in water (26 degrees C or 29 degrees C). Esophageal temperature, skin temperatures and oxygen consumption were measured during the experiments. Metabolic heat production was calculated from oxygen consumption. Heat loss from skin to the water was calculated from the metabolic heat production and the change in mean body temperature during water immersion. Total insulation and tissue insulation were estimated by dividing the temperature difference between the esophagus and the water or the esophagus and the skin with heat loss from the skin. Esophageal temperature with a thermal swimsuit was higher than that with a normal swimsuit at the end of immersion in both water temperature conditions (p<0.05). Oxygen consumption, metabolic heat production and heat loss from the skin were less with the thermal swimsuit than with a normal swimsuit in both water temperatures (p<0.05). Total insulation with the thermal swimsuit was higher than that with a normal swimsuit due to insulation of the suit at both water temperatures (p<0.05). Tissue insulation was similar in all four conditions, but significantly higher with the thermal swimsuit in both water temperature conditions (p<0.05), perhaps due to of the attenuation of shivering during immersion with a thermal swimsuit. A thermal swimsuit can increase total insulation and reduce heat loss from the skin. Therefore, subjects with thermal swimsuits can maintain higher body temperatures than with a normal swimsuit and reduce shivering thermo-genesis.     

Active cutaneous vasodilation in resting humans during mild heat stress.

The role of skin temperature in reflex control of the active cutaneous vasodilator system was examined in six subjects during mild graded heat stress imposed by perfusing water at 34, 36, 38, and 40 degrees C through a tube-lined garment. Skin sympathetic nerve activity (SSNA) was recorded from the peroneal nerve with microneurography. While monitoring esophageal, mean skin, and local skin temperatures, we recorded skin blood flow at bretylium-treated and untreated skin sites by using laser-Doppler velocimetry and local sweat rate by using capacitance hygrometry on the dorsal foot. Cutaneous vascular conductance (CVC) was calculated by dividing skin blood flow by mean arterial pressure. Mild heat stress increased mean skin temperature by 0.2 or 0.3 degrees C every stage, but esophageal and local skin temperature did not change during the first three stages. CVC at the bretylium tosylate-treated site (CVC(BT)) and sweat expulsion number increased at 38 and 40 degrees C compared with 34 degrees C (P < 0.05); however, CVC at the untreated site did not change. SSNA increased at 40 degrees C (P < 0.05, different from 34 degrees C). However, SSNA burst amplitude increased (P < 0.05), whereas SSNA burst duration decreased (P < 0.05), at the same time as we observed the increase in CVC(BT) and sweat expulsion number. These data support the hypothesis that the active vasodilator system is activated by changes in mean skin temperature, even at normal core temperature, and illustrate the intricate competition between active vasodilator and the vasoconstrictor system for control of skin blood flow during mild heat stress.     

Thermoregulatory model for immersion of humans in cold water

The mathematical models of thermoregulation of Stolwijk and Hardy, and Montgomery were used to develop a model suitable for the simulation of human physiological responses to cold-water immersion. Data were obtained from experiments where 13 healthy male volunteers were totally immersed under resting and nude conditions for 1 h in water temperatures of 20 and 28 degrees C. At these temperatures, the mean measured rectal temperature (Tre) fell by approximately 0.9 and 0.5 degrees C, respectively, yet mean measured metabolic rate (M) rose by approximately 275 and 90 W for the low body fat group (n = 7) and 195 and 45 W for the moderate body fat group (n = 6). To predict the observed Tre and M values, the present model 1) included thermal inputs for shivering from the skin independent of their inclusion with the central temperature to account for the observed initial rapid rise in M, 2) determined a thermally neutral body temperature profile such that the measured and predicted initial values of Tre and M were matched, 3) confined the initial shivering to the trunk region to avoid an overly large predicted initial rate of rectal cooling, and 4) calculated the steady-state convective heat loss by assuming a zero heat storage in the skin compartment to circumvent the acute sensitivity to the small skin-water temperature difference when using conventional methods. The last three modifications are unique to thermoregulatory modeling.     

Insulative power of body fat on deep muscle temperatures and isometric endurance.

Four male subjects were examined to assess the relationship of body fat content to deep muscle temperature and the endurance of a fatiguing isometric handgrip contraction at a tension set at 40% MVC. Muscle temperature was altered by the immersion of the forearm in water at temperatures varying from 7.5 to 40 degrees C. In all subjects, there was a water bath temperature above and below which isometric endurance decreased markedly; the difference among individuals was solely accounted for by the individual's body fat content. Thus, subjects with higher body fat content required lower bath temperatures to cool the forearm musculature to its optimum temperature, which we found to always be approximately 27 degrees C measured 2 cm perpendicularly to the skin in the belly of the brachioradialis muscle. Further, in one subject, we found that a reduction in this subject's body fat content resulted in a corresponding increase in the water bath temperature necessary to cool his muscles to their optimum isometric performance. The data demonstrate the striking insulative power of the thin layer of fat around the forearm in man in protecting shell tissues from cold exposure.     

Prediction of the thermoregulatory response for clothed immersion in cold water

A multi-compartmental thermoregulatory model was applied to data of ten resting clothed males immersed for 3 h in water at 10 and 15 degrees C. Clothing consisted of a dry suit and either a light or heavy undergarment, representing a total insulation of 0.15 (0.95) or 0.20 m2 degrees CW-1 (1.28 clo), respectively. Data were grouped according to low (less than 14%) and high (14 to 24%) body fat individuals. Mean decreases in rectal temperature ranged from 0.79 to 1.38 degrees C, mean decreases in the mean weighted skin temperature ranged from 6.3 to 10.2 degrees C, and mean increases in the metabolic rate ranged from 33.9 to 80.8 W. The model consists of eight segments, each representing a specific region of the body. Each segment is comprised of compartments representing the core, muscle, fat, skin, and clothing. Each compartment is assigned thermophysical values of heat conduction and heat capacitance, and with the exception of clothing, physiological values of blood flow and metabolic heat production. During cold exposure, responses are directed towards increased heat production in the form of shivering and heat conservation in the form of vasoconstriction and convective heat exchange at the vascular level. Agreement between the model predictions and the experimental observations was obtained by adjusting the parameters governing these responses.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thermal responses of unclothed men exposed to both cold temperatures and high altitudes.

Six resting men were exposed to three temperatures (15.5, 21, 26.5 degrees C) for 120 min at three altitudes (sea level, 2,500 m, 5,000 m). A 60-min sea-level control at the scheduled temperature preceded the nine altitude episodes. Comparison of the base-line results at any one temperature showed no differences between rectal temperatures (Tre) or mean weighted skin temperatures (Tsk). After 120 min, Tre and Tsk not only depended on ambient temperature but also altitude. The initial rate of fall in Tre increased with altitude and equilibrium occurred earlier. At 15.5 degrees C, Tre was 0.3 degrees C lower at 5,000 m and 0.2 degrees C lower at 2,500 m than at sea level. Tsk was almost 2 degrees C higher at 15.5 degrees C at 5,000 m and 1 degrees C higher at 2,500 m than at sea level. Similar, smaller differences were observed at 21 degrees C. Mean weighted body temperature showed no change with altitude, but, since the gradient between core and shell was reduced, a shift of blood toward the periphery is implied.     

Effects of high temperature on body temperature and hormonal adjustments in piglets

Effects of a high (33 degrees C) or thermoneutral (23 degrees C) temperature on body temperature and endocrine parameters were studied in weaned piglets. Rectal and skin temperatures were measured in four ad libitum fed animals per temperature during three weeks. After this acclimation period, 11 blood samples were withdrawn on a 24-h period. Over the acclimation period, rectal and skin temperatures were 0.6 and 2.9 degrees C higher, respectively, at 33 degrees C than at 23 degrees C (P < 0.01), this change occurring from the 1st day at 23 or 33 degrees C. A tendency of serum leptin concentrations to be lower after meals at 33 degrees C than at 23 degrees C was also displayed (P = 0.09). Plasmatic concentrations in Insulin-like growth factor I and thyroxine were decreased at 33 degrees C relative to 23 degrees C (P < 0.01 and P < 0.06, respectively), and triiodothyronine concentrations tended to be lower at 33 degrees C than at 23 degrees C (P = 0.1), which could account for the lower heat production and growth observed in pigs exposed to high temperatures.     

Influence of white light on production of aflatoxins and anthraquinones in Aspergillus parasiticus.

The effect of continuous light and continuous darkness on the growth of Aspergillus parasiticus and on the production of aflatoxin, averufin, versicolorin A, and versicolorin C by Aspergillus parasiticus were determined at six different temperatures with six replicates for each experiment. No growth was observed at 15 degrees C in the light, although slight growth was observed at this temperature in the dark. No aflatoxins or anthraquinones were produced in the light or dark at 35 and 40 degrees C, although growth was good at these temperatures. Differences in aflatoxins and anthraquinones for cultures grown in light and in dark were consistent at each temperature. Higher mean quantities of these secondary metabolites were produced in the light at 20 and 25 degrees C; lower mean quantities were produced in the light at 30 degrees C. The ranges of values overlapped considerably, but in all cases the differences between temperatures were significant.     

Phenotypic responses of hatchlings to constant versus fluctuating incubation temperatures in the multi-banded krait, Bungarus multicintus (Elapidae)

Most studies on egg incubation in reptiles have relied on constant temperature incubation in the laboratory rather than on simulations of thermal regimes in natural nests. The thermal effects on embryos in constant-temperature studies often do not realistically reflect what occurs in nature. Recent studies have increasingly recognized the importance of simulating natural nest temperatures rather than applying constant-temperature regimes. We incubated Bungarus multicintus eggs under three constant and one fluctuating-temperature regimes to evaluate the effects of constant versus fluctuating incubation temperatures on hatching success and hatchling phenotypes. Hatching success did not differ among the four treatments, and incubation temperature did not affect the sexual phenotype of hatchlings. Incubation length decreased as incubation temperature increased, but eggs incubated at fluctuating temperatures did not differ from eggs incubated at constant temperatures with approximately the same mean in incubation length. Of the hatchling phenotypes examined, residual yolk, fat bodies and locomotor performance were more likely affected by incubation temperature. The maximal locomotor speed was fastest in the fluctuating-temperature and 30 degrees C treatments and slowest in the 24 degrees C treatment, with the 27 degrees C treatment in between. The maximal locomotor length was longest in the fluctuating-temperature treatment and shortest in the 24 degrees C and 27 degrees C treatments, with the 30 degrees C treatment in between. Our results show that fluctuating incubation temperatures do not influence hatching success and hatchling size and morphology any differently than constant temperatures with approximately the same mean, but have a positive effect on locomotor performance of hatchlings.     

Prediction of mean skin temperature in warm environments

The data collected by the authors in four experimental series have been analysed together with data from the literature, to study the relationship between mean skin temperature and climatic parameters, subject metabolic rate and clothing insulation. The subjects involved in the various studies were young male subjects, unacclimatized to heat. The range of conditions examined involved mean skin temperatures between 33 degrees C and 38 degrees C, air temperatures (Ta) between 23 degrees C and 50 degrees C, ambient water vapour pressures (Pa) between 1 and 4.8 kPa, air velocities (Va) between 0.2 and 0.9 m.s-1, metabolic rates (M) between 50 and 270 W.m-2, and Clo values between 0.1 and 0.6. In 95% of the data, mean radiant temperature was within +/- 3 degrees C of air temperature. Based on 190 data averaged over individual values, the following equation was derived by a multiple linear regression technique: Tsk = 30.0 + 0.138 Ta + 0.254 Pa-0.57 Va + 1.28.10(-3) M-0.553 Clo. This equation was used to predict mean skin temperature from 629 individual data. The difference between observed and predicted values was within +/- 0.6 degrees C in 70% of the cases and within +/- 1 degrees C in 90% of the cases. It is concluded that the proposed formula may be used to predict mean skin temperature with satisfactory accuracy in nude to lightly clad subjects exposed to warm ambient conditions with no significant radiant heat load.     

Effect of skin surface temperature on localization error and two-point threshold

The average localization error and two-point threshold were determined from 9 subjects at 5 skin temperatures on the volar forearm. The temperatures were physiological zero (31 degrees--32 degrees C), 19 degrees C, 25 degrees C, 38 degrees C, and 44 degrees C. Localization error was not significantly affected by skin surface temperature. This was verified on palm and forehead locations. The two-point threshold was increased by skin surface temperatures above physiological zero and decreased by skin surface temperatures below physiological zero. These results are consistent with a previous report of similar changes in punctate pressure sensitivity with varied skin surface temperatures. Such cross-model effects are considered in terms of cutaneous sensory mechanisms combining broad receptor specificity and subsequent coding of information by patterns of neural impulses.     

Conductive and convective heat flows of exercising humans in cold water

The apparent conductance (Kss, in W.m-2.degrees C-1) of a given region of superficial shell (on the thigh, fat + skin) was determined on four nonsweating and nonshivering subjects, resting and exercising (200 W) in water [water temperature (Tw) 22-23 degrees C] Kss = Hss/(Tsf-Tsk) where Hss is the skin-to-water heat flow directly measured by heat flow transducers and Tsf and Tsk are the temperatures of the subcutaneous fat at a known depth below the skin surface and of the skin surface, respectively. The convective heat flow (qc) through the superficial shell was then estimated as qc = (Tsf - Tsk).(Kss - Kss,min), assuming that at rest Kss was minimal (Kss,min) and resting qc = 0. The duration of immersion was set to allow rectal temperature (Tre) to reach approximately 37 degrees C at the end of rest and approximately 38 degrees C at the end of exercise. Except at the highest Tw used, Kss at the start of exercise was always Kss,min and averaged 51 W.m-2.degrees C-1 (range 33-57 W.m-2.degrees C-1) across subjects, and qc was zero. At the end of exercise at the highest Tw used for each subject, Kss averaged 97 W.m-2.degrees C-1 (range 77-108 W.m-2.degrees C-1) and qc averaged 53% (range 48-61%) of Hss (mean Hss = 233 W.m-2).(ABSTRACT TRUNCATED AT 250 WORDS)