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1.
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)  相似文献   

2.
The present work was undertaken to examine the effect of wet suits on the pattern of heat exchange during immersion in cold water. Four Korean women divers wearing wet suits were immersed to the neck in water of critical temperature (Tcw) while resting for 3 h or exercising (2-3 met on a bicycle ergometer) for 2 h. During immersion both rectal (Tre) and skin temperatures and O2 consumption (VO2) were measured, from which heat production (M = 4.83 VO2), skin heat loss (Hsk = 0.92 M +/- heat store change based on delta Tre), and thermal insulation were calculated. The average Tcw of the subjects with wet suits was 16.5 +/- 1.2 degrees C (SE), which was 12.3 degrees C lower than that of the same subjects with swim suits (28.8 +/- 0.4 degrees C). During the 3rd h of immersion, Tre and mean skin temperatures (Tsk) averaged 37.3 +/- 0.1 and 28.0 +/- 0.5 degrees C, and skin heat loss per unit surface area 42.3 +/- 2.66 kcal X m-2 X h. The calculated body insulation [Ibody = Tre - Tsk/Hsk] and the total shell insulation [Itotal = (Tre - TW)/Hsk] were 0.23 +/- 0.02 and 0.5 +/- 0.04 degrees C X kcal-1 X m2 X h, respectively. During immersion exercise, both Itotal and Ibody declined exponentially as the exercise intensity increased. Surprisingly, the insulation due to wet suit (Isuit = Itotal - Ibody) also decreased with exercise intensity, from 0.28 degrees C X kcal-1 X m2 X h at rest to 0.12 degrees C X kcal-1 X m2 X h at exercise levels of 2-3 met.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

3.
Thermal sensation and distribution of skin temperatures in persons exercising at 36.5 W on a bicycle ergometer and resting in a cool environment (10 degrees C) in two different clothings, one with the insulation mainly over the trunk (1.22 clo), and one with well insulated limbs (1.67 clo), were studied. Their general thermal sensations varied from slightly warm to slightly cool. The placing of the insulation had a decisive influence on skin temperature distribution, so that skin temperature was always high in well-insulated areas. When the insulation was placed over the limbs, a greater amount of heat was lost than if a similar insulation was placed on the trunk. Neither Tsk nor skin temperature distribution correlated with general thermal sensation. Instead, mean body temperature seemed to be the determinant of general thermal sensation in these conditions. The best prediction of general thermal sensation was obtained by adding Tre with a weighting factor of 0.8-0.9 and Tsk with a weighting factor of 0.1-0.2.  相似文献   

4.
In vivo thermal conductivity of the human forearm tissues   总被引:1,自引:0,他引:1  
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.  相似文献   

5.
Eight minimally dressed pre- and early pubescent boys (age 11-12 yr) and 11 young adult men (age 19-34 yr) rested for 20 min and exercised on a cycle ergometer for 40 min at approximately 30% of their maximum oxygen consumption (VO2max) at 5 degrees C. To quantify the added increase in metabolic rate because of cold, a separate test was carried out at 21 degrees C at rest and at equal work rates as in the cold. Both groups were similar in subcutaneous fat thickness and VO2max per kilogram body weight. Rectal temperature increased slightly during the exposure to the cold, but no significant difference was observed between the boys and men. In the cold, the boys had lower skin temperatures than the adults in their extremities but not in the trunk. The boys increased their metabolic rates in the cold more than did the men. As a result, the boys maintained their core temperature as effectively as the adults. Similar age-related differences in thermoregulatory responses to cold were observed when two boys and two men with equal body sizes were compared. Our results suggest that there may be maturation-related differences in thermoregulation in the cold between children and adults.  相似文献   

6.
To delineate age- and gender-related differences in physiological responses to cold exposure, men and women between the ages of 20 and 29 yr and 51 and 72 yr, wearing minimal clothing, were exposed at rest for 2 h to 28, 20, 15, and 10 degrees C room temperatures with 40% relative humidity. During the coldest exposure, the rates of increase in metabolic rate (W X m-2 or ml X kg lean body mass-1 X min-1 were similar for all groups. However, older women (n = 7) may have benefited from a larger (P less than 0.05) early metabolic (M) increase (40% within 15 min) than young men (18%) (n = 10), young women (5%) (n = 10), or older men (5%) (n = 10). A similar rapid M response in older women occurred during the 15 degrees C exposure. During all cold exposures, older women maintained constant rectal temperature (Tre) and young women maintained Tre only during the 20 degrees C exposures, whereas Tre of the men declined during all cold exposures (P less than 0.01). Changes in Tre and mean skin temperature (Ts) during cold exposure were largely related to body fat, although age and surface area/mass modified the changes in men. The data suggest that older men are more susceptible to cold ambients than younger people, since they did not prevent a further decline in their initially relatively low Tre. Despite greater insulation from body fat, the older women maintained a constant Tre at greater metabolic cost than men or younger women.  相似文献   

7.
Exercise increases mean body temperature (T(body)) and cytokine concentrations in plasma. Cytokines facilitate PG production via cyclooxygenase (COX) enzymes, and PGE(2) can mediate fever. Therefore, we used a COX-2 inhibitor to test the hypothesis that PG-mediated pyrogenicity may contribute to the raised T(body) in exercising humans. In a double-blind, cross-over design, 10 males [age: 23 yr (SD 5), Vo(2 max): 53 ml x kg(-1) x min(-1) (SD 5)] consumed rofecoxib (50 mg/day; NSAID) or placebo (PLAC) for 6 days, 2 wk apart. Exercising thermoregulation was measured on day 6 during 45-min running ( approximately 75% Vo(2 max)) followed by 45-min cycling and 60-min seated recovery (28 degrees C, 50% relative humidity). Plasma cytokine (TNF-alpha, IL-10) concentrations were measured at rest and 30-min recovery. T(body) was similar at rest in PLAC (35.59 degrees C) and NSAID (35.53 degrees C) and increased similarly during running, but became 0.33 degrees C (SD 0.26) lower in NSAID during cycling (37.39 degrees C vs. 37.07 degrees C; P = 0.03), and remained lower throughout recovery. Sweating was initiated at T(body) of approximately 35.6 degrees C in both conditions but ceased at higher T(body) in PLAC than NSAID during recovery [36.66 degrees C (SD 0.36) vs. 36.39 degrees C (SD 0.27); P = 0.03]. Cardiac frequency averaged 6 x min(-1) higher in PLAC (P < 0.01), whereas exercising metabolic rate was similar (505 vs. 507 W x m(-2); P = 0.56). A modest increase in both cytokines across exercise was similar between conditions. COX-2 specific NSAID lowered exercising heat and cardiovascular strain and the sweating (offset) threshold, independently of heat production, indicating that PGE-mediated inflammatory processes may contribute to exercising heat strain during endurance exercise in humans.  相似文献   

8.
This study was conducted because of the paucity of information concerning gender differences in the cardiovascular and metabolic responses to cold stress. Lightly clad men (n = 8) and women (n = 8) were tested in 21 and 5 degrees C environments during a 20-min rest, followed by 20 min each of 50, 100, and 150 W of exercise. At 21 degrees C there was no gender differences in VO2 or cardiac output. Cold lowered skin temperature more in women than in men, but women demonstrated no differences in heart rate, stroke volume, or VO2 at 5 and 21 degrees C. The women's noradrenaline levels in the cold were higher than comparable 21 degrees C data at rest and 50 W and increased with work intensity in both tests. In contrast, men had a lower heart rate, higher stroke volume, and higher VO2 throughout the 5 degrees C treatment compared with 21 degrees C. The men's noradrenaline response to 5 degrees C was similar to that of women at rest and 50 W, but the level subsequently declined at 100 and 150 W. Thus, the women do not show a heart rate-stroke volume shift in either resting or exercising states in cold environments. Furthermore, the data fail to support that either skin cooling or changes in noradrenaline cause the bradycardia and enhanced stroke volume seen in men.  相似文献   

9.
Trunk (HT), limb (HL), and whole-body (HDIR = HT + HL + Hforehead) skin-to-water heat flows were measured by heat flow transducers on nine men immersed head out in water at critical temperature (TCW = 30 +/- 2 degrees C) and below [overall water temperature (TW) range = 22-32 degrees C] after up to 3 h at rest and exercise. Body heat flow was also determined indirectly (HM) from metabolic rate corrected for changes in heat stores. At rest at TCW [O2 uptake (VO2) = 0.33 +/- 0.07 l/min, n = 7], HT = 52.3 +/- 14.2 (SD) W, HL = 56.4 +/- 14.6 W, HDIR = 120 +/- 27 W, and HM = 111 +/- 29 W (significantly different from HDIR). TW markedly affected HDIR but only slightly affected HM (n = 22 experiments at TW different from TCW plus 7 experiments at TCW). During light exercise (3 MET) at TCW (VO2 = 1.06 +/- 0.26 l/min, n = 9), HT = 122 +/- 43 W, HL = 130 +/- 27 W, HDIR = 285 +/- 69 W, and HM = 260 +/- 60 W. During severe exercise (7 MET) at TCW (VO2 = 2.27 +/- 0.50 l/min, n = 4), HT = 226 +/- 100 W, HL = 262 +/- 61 W, HDIR = 517 +/- 148 W, and HM = 496 +/- 98 W. Lowering TW at 7-MET exercise (n = 9, plus 4 at TCW) had no effect on HDIR and HM. In conclusion, resting HL and HT are equal. At TW less than TCW at rest, HDIR greater than HM, showing that unexpectedly the shell was still cooling. During exercise, HL increases more than HT but less than expected from the heat production of the working limbs. Therefore some heat produced by the limbs is probably transported by blood to the trunk. During heavy exercise, HDIR is constant at all considered TW; apparently it is regulated by some thermally dependent mechanism, such as a progressive cutaneous vasodilation occurring as TW increases.  相似文献   

10.
This study compared glycogen depletion in active skeletal muscle after light and moderate exercise in both cold and comfortable ambient conditions. Twelve male subjects (Ss) were divided into two groups equally matched for the submaximal exercise intensity corresponding to a blood lactate concentration of 4 mM (W4) during cycle exercise. On two separate days Ss rested for 30 min at ambient temperatures of either 9 degrees C or 21 degrees C, with the order of temperature exposure being counter-balanced among Ss. Following rest a tissue specimen was obtained from the m. vastus lateralis with the needle biopsy technique. Six Ss then exercised on a cycle ergometer for 30 min at 30% W4 (range = 50 - 65 W) while the remaining group exercised at 60% W4 (range = 85 - 120 W). Another biopsy was taken immediately after exercise and both samples were assayed for glycogen content. Identical procedures were repeated for the second environmental exposure. No significant glycogen depletion was observed in the Ss exercising at 30% W4 in 21 degrees C, but a 23% decrease (p = 0.04) was observed when the same exercise was performed at 9 degrees C. A 22% decrease (p = 0.002) in glycogen occurred in the 60% W4 group at 21 degrees C, which was not significantly different from that observed during the same exercise at 9 degrees C. The results suggest that muscle substrate utilization is increased during light exercise in a cold environment as compared to similar exercise at a comfortable temperature, probably due to shivering thermogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

11.
Eight healthy and physically well-trained male students exercised on a treadmill for 60 min while being immersed in water to the middle of the chest in a laboratory flowmill. The water velocity was adjusted so that the intensity of exercise correspond to 50% maximal oxygen uptake of each subject, and experiments were performed once at each of three water temperatures: 25, 30, 35°C, following a 30-min control period in air at 25°C, and on a treadmill in air at an ambient temperature of 25°C. Thermal states during rest and exercise were determined by measuring rectal and skin temperatures at various points, and mean skin temperatures were calculated. The intensity of exercise was monitored by measuring oxygen consumption, and heart rate was monitored as an indicator for cardiovascular function. At each water temperature, identical oxygen consumption levels were attained during exercise, indicating that no extra heat was produced by shivering at the lowest water temperature. The slight rise in rectal temperature during exercise was not influenced by the water temperature. The temperatures of skin exposed to air rose slightly during exercise at 25°C and 30°C water temperature and markedly at 35°C. The loss of body mass increased with water temperature indicating that both skin blood flow and sweating during exercise increased with the rise in water temperature. The rise in body temperature provided the thermoregulatory drive for the loss of the heat generated during exercise. Heart rate increased most during exercise in water at 35°C, most likely due to enhanced requirements for skin blood flow. Although such requirements were certainly smallest at 25°C water temperature, heart rate at this temperature was slightly higher than at 30°C suggesting reflex activation of sympathetic control by cold signals from the skin. There was a significantly greater increase in mean skin and rectal temperatures in subjects exercising on the treadmill in air, compared to those exercising in water at 25°C. Accepted: 22 May 1998  相似文献   

12.
Accommodating weanling horses in loose housing (sleeping hall with deep-litter bed and paddock) environments in winter at northern latitudes exposes the nonhuman animals to low ambient temperatures. We determined the heat loss of nine weanling horses in a cold environment by infrared thermography to assess their thermoregulatory capacity. The rate of heat loss was 73.5 to 98.7 W/m2 from the neck and 69.9 to 94.3 W/m2 from the trunk. The heat loss was higher at -16 degrees C than at 0 degrees C and -9 degrees C (p相似文献   

13.
To study the influence of the menstrual cycle on whole body thermal balance and on thermoregulatory mechanisms, metabolic heat production (M) was measured by indirect calorimetry and total heat losses (H) were measured by direct calorimetry in nine women during the follicular (F) and the luteal (L) phases of the menstrual cycle. The subjects were studied while exposed for 90 min to neutral environmental conditions (ambient temperature 28 degrees C, relative humidity 40%) in a direct calorimeter. The values of M and H were not modified by the phase of the menstrual cycle. Furthermore, in both phases the subjects were in thermal equilibrium because M was similar to H (69.7 +/- 1.8 and 72.1 +/- 1.8 W in F and 70.4 +/- 1.9 and 71.4 +/- 1.7 W in L phases, respectively). Tympanic temperature (Tty) was 0.24 +/- 0.07 degrees C higher in the L than in the F phase (P less than 0.05), whereas mean skin temperature (Tsk) was unchanged. Calculated skin thermal conductance (Ksk) was lower in the L (17.9 +/- 0.6 W.m-2.degrees C-1) than in the F phase (20.1 +/- 1.1 W.m-2.degrees C-1; P less than 0.05). Calculated skin blood flow (Fsk) was also lower in the L (0.101 +/- 0.008 l.min-1.m-2) than in the F phase (0.131 +/- 0.015 l.min-1.m-2; P less than 0.05). Differences in Tty, Ksk, and Fsk were not correlated with changes in plasma progesterone concentration. It is concluded that, during the L phase, a decreased thermal conductance in women exposed to a neutral environment allows the maintenance of a higher internal temperature.  相似文献   

14.
The rate of sensible heat loss from a Clun Forest ewe was studied at several fleece depths in a temperature-controlled chamber. A simple resistance analogue was used to describe the heat flow from different body regions. Heat loss from the trunk depends largely on the mean fleece depth l. The fleece resistance was about 1.5 s cm-1 per centimetre depth. Heat transfer through the fleece was accounted for by molecular conduction, thermal radiation and free convection. The fleece conductivity -kb attributed to free convection depends on the mean temperature difference (-Tst---Tct) across the fleece according to the relation -kb = 8.0 (-Tst---Tct)0.53. Estimates of the sensible heat flux from the trunk at environmental temperatures, Ta, between 0 and 30 degrees C range from about 8 W (l = 7.0 cm, Ta = 30 degrees C) to about 160 W (l = 0.1 cm, Ta = 0 degrees C). In contrast, the sensible heat loss from the legs depends mainly on the local tissue resistance. For environmental temperatures between 0 and 30 degrees C, the calculated tissue resistance for this region of the body varied from about 8 to 1 s cm-1. The corresponding heat loss from the legs was between 10 and 20 W, compared with between 3 and 7 W from the head. The fastest heat loss from the legs occurred at an environmental temperature of about 12 degrees C. Although the proportion of the heat loss from the extremities depends on environmental temperature, the total heat loss (sensible or latent) was closely related to the mean skin temperature of the trunk.  相似文献   

15.
The onset and intensity of shivering of various muscles during cold air exposure are quantified and related to increases in metabolic rate and convective heat loss. Thirteen male subjects resting in a supine position and wearing only shorts were exposed to 10 degrees C air (42% relative humidity and less than 0.4 m/s airflow) for 2 h. Measurements included surface electromyogram recordings at six muscle sites representing the trunk and limb regions of one side of the body, temperatures and heat fluxes at the same contralateral sites, and metabolic rate. The subjects were grouped according to lean (LEAN, n = 6) and average body fat (NORM, n = 7) content. While the rectal temperatures fluctuated slightly but not significantly during exposure, the skin temperature decreased greatly, more at the limb sites than at the trunk sites. Muscles of the trunk region began to shiver sooner and at a higher intensity than those of the limbs. The intensity of shivering and its increase over time of exposure were consistent with the increase in the convective heat transfer coefficient calculated from skin temperatures and heat fluxes. Both the onset of shivering and the magnitude of the increase in metabolic rate due to shivering were higher for the LEAN group than for the NORM group. A regression analysis indicates that, for a given decrease in mean skin temperature, the increase in metabolic rate due to shivering is attenuated by the square root of percent body fat. Thus the LEAN group shivered at higher intensity, resulting in higher increases in metabolic heat production and convective heat loss during cold air exposure than did the NORM group.  相似文献   

16.
Core temperature "null zone".   总被引:1,自引:0,他引:1  
An experimental protocol was designed to investigate whether human core temperature is regulated at a "set point" or whether there is a neutral zone between the core thresholds for shivering thermogenesis and sweating. Nine male subjects exercised on an underwater cycle ergometer at a work rate equivalent to 50% of their maximum work rate. Throughout an initial 2-min rest period, the 20-min exercise protocol, and the 100-min recovery period, subjects remained immersed to the chin in water maintained at 28 degrees C. On completion of the exercise, the rate of forehead sweating (Esw) decayed from a mean peak value of 7.7 +/- 4.2 (SD) to 0.6 +/- 0.3 g.m-2.min-1, which corresponds to the rate of passive transpiration, at core temperatures of 37.42 +/- 0.29 and 37.39 +/- 0.48 degrees C, as measured in the esophagus (Tes) and rectum (Tre), respectively. Oxygen uptake (VO2) decreased rapidly from an exercising level of 2.11 +/- 0.25 to 0.46 +/- 0.09 l/min within 4 min of the recovery period. Thereafter, VO2 remained stable for approximately 20 min, eventually increased with progressive cooling of the core region, and was elevated above the median resting values determined between 15 and 20 min at Tes = 36.84 +/- 0.38 degrees C and Tre = 36.80 +/- 0.39 degrees C. These results indicate that the core temperatures at which sweating ceases and shivering commences are significantly different (P less than 0.001) regardless of whether core temperature is measured within the esophagus or rectum.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

17.
It is necessary to consider breed and cold tolerance in the housing and caring of horses. This study demonstrates differences in heat loss between horse types at low temperatures and examines rate of loss in different types during different seasons. Eighteen horses participated. Groups by type were light (L), warmblood (W), coldblood (C), and pony (P). A camera filmed thermographic images at 15 degrees C, 2 degrees C (all types), -8 degrees C (L, W, C), and -12 degrees C (P). The study calculated loss from the neck, trunk, and inner surfaces of front and hind legs. Loss was similar in all types at 15 degrees C. L, W, and C dissipated more heat at 2 degrees C than at 15 degrees C (p < .001) and from neck and trunk at -8 degrees C than at 2 degrees C (p < .05). P dissipated heat similarly at 2 degrees C and -12 degrees C. At 2 degrees C, loss was less from neck and trunk in C and P compared with L (p < .05). At -8 degrees C, loss in L and W was greater than in C (p < .05).  相似文献   

18.
Energetic adaptation to fasting in the cold has been investigated in a nocturnal raptor, the barn owl (Tyto alba), during winter. Metabolic rate and body temperature (Tb) were monitored in captive birds, (1) after acute exposure to different ambient temperatures (Ta), and (2) during a prolonged fast in the cold (4 degrees C), to take into account the three characteristic phases of body fuel utilization that occur during a long-term but reversible fast. In postabsorptive birds, metabolic rate in the thermoneutral zone was 4. 1+/-0.1 W kg-1 and increased linearly below a lower critical temperature of 23 degrees C. Metabolic rate was 70% above basal at +4 degrees C Ta. Wet thermal conductance was 0.22 W kg-1 degrees C-1. During fasting in the cold, the mass-specific resting metabolic rate decreased by 16% during the first day (phase I) and remained constant thereafter. The amplitude of the daily rhythm in Tb was only moderately increased during phase II, with a slight lowering (0. 6 degrees C) in minimal diurnal Tb, but rose markedly in phase III with a larger drop (1.4 degrees C) in minimal diurnal Tb. Refeeding the birds ended phase III and reversed the observed changes. These results indicate that diurnal hypothermia may be used in long-term fasting barn owls and could be triggered by a threshold of body lipid depletion, according to the shift from lipid to protein fuel metabolism occurring at the phase II/phase III transition. The high cost of regulatory thermogenesis and the limited use of hypothermia during fasting may contribute to the high mortality of barn owls during winter.  相似文献   

19.
Ten male volunteers were divided into two groups based on body morphology and mass. The large-body mass (LM) group (n = 5) was 16.3 kg heavier and 0.22 cm2 X kg-1 X 10(-2) smaller in surface area-to-mass ratio (AD X wt-1) (P less than 0.05) than the small-body mass (SM) group (n = 5). Both groups were similar in total body fat and skinfold thicknesses (P greater than 0.05). All individuals were immersed for 1 h in stirred water at 26 degrees C during both rest and one intensity of exercise (metabolic rate approximately 550 W). During resting exposures metabolic rate (M) and rectal temperature (Tre) were not different (P greater than 0.05) between the LM and SM groups at min 60. Esophageal temperature (Tes) was higher (P less than 0.05) for the SM group at min 60, although the change in Tes during the 60 min between groups was similar (LM, -0.4 degrees C; SM, -0.2 degrees C). Tissue insulation (I) was lower (P less than 0.05) for SM (0.061 degrees C X m-2 X W-1) compared with the LM group (0.098 degrees C X m-2 X W-1). During exercise M, Tre, Tes, and I were not different (P greater than 0.05) between groups at min 60. These data illustrate that a greater body mass between individuals increases the overall tissue insulation during rest, most likely as a result of a greater volume of muscle tissue to provide insulation.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

20.
Hybrid male mice were exposed to 2.45 GHz microwaves for 30 min/day, 6 days a week for two consecutive weeks at power densities of 1.0, 100 or 400 W m-2, with sham-exposed controls. Rectal temperatures before and after exposure were measured on days 1, 6 and 12. Measurements made on day 1 were treated with caution because of heterogeneity in rectal temperatures taken before exposure between the groups of mice given different treatments. On days 6 and 12, rectal temperatures rose by approximately 1 degree C in mice sham exposed, or exposed to 1 W m-2 or 100 W m-2. Only in the group of mice exposed to 400 W m-2 was the mean rise in rectal temperature during exposure (about 3 degrees C) significantly increased above the sham value. In groups killed 2-3 days after treatment (mainly meiotic exposure) frequencies of chromosome aberrations in spermatocytes showed no significant heterogeneity although the highest frequency of 1.5 per cent was at the highest (400 W m-2) power density. Another group killed 30 days after 100 W m-2 exposures (spermatogonial sampling) showed no significant increase over controls in chromosome aberration frequency. There was a small but significant increase in sperm count with increasing power density in mice killed 12-13 days after exposure, but a non-significant one in those exposed as spermatogonia (killed 41 days later). Thus effects were markedly less severe than those reported previously by Manikowska-Czerska et al. (1985) with a very similar radiation regime and were probably caused by the temperature enhancement.  相似文献   

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