Experimental determination of coefficient of evaporative heat loss in still air (author's transl)]

The authors have determined the coefficient of evaporative heat loss of the human body (he) by means of humidity steps in low air movement (Va less than or equal to 0,2 m/s). Such a determination requires a fully wetted skin and this implies therefore some loss of dripping sweat. The collection of this dripping sweat allows the determination of the total evaporation: this evaporation exists on the skin surface and around the drops during their fall from the skin to the oil pan where dripping sweat is collected. An estimation of this dripping sweat evaporation allows to assess the skin evaporation and, consequently, the evaporative coefficient he. In these experimental conditions: E = S - SNE - 0,0005 SNE (PsH2O - PaH2O) where E is the skin evaporative rate (g/h);S = total sweat rate (g/h);SNE = the nonevaporative sweat rate (g/h);PaH2O = the partial pressure of saturated water (at Ts) on skin (mb) and PaH2O the partial pressure of water vapor in ambient air (mb). The coefficient of evaporative heat loss in low air movement thus found, is 5,18 +/- 0,22 W/m2-mb.     

Evaluation of vapor permeation through garments during exercise

Five males [age 28 +/- 8 yr; maximum O2 uptake (VO2max) 50 +/- 6 ml O2 . kg-1 . min-1; body wt 70 +/- 3 kg; DuBois surface area 1.85 +/- 0.02 m2] exercised on a cycle ergometer, placed on a Potter scale, at 31% VO2max for up to 2 h at an ambient temperature (Ta) of 25 degrees C and a dew-point temperature of 15 degrees C. Air movement was varied from still air to 0.4 and 2 m/s. Each subject, in separate runs, wore a track suit (TS ensemble) of 60% polyester-40% cotton (effective clo = 0.5); a Gortex parka (GOR ensemble), covering a sweat shirt and bottom of TS (effective clo = 1.4); or the TS ensemble covered by polyethylene overgarment (POG ensemble). Esophageal, skin temperature (Tsk) at eight sites, and heart rate were continuously recorded. Dew-point sensors recorded temperatures under the garments at ambient and chest (windward site) and midscapular sites. Local skin wettedness (loc w) and ratio of evaporative heat loss (Esk) to maximum evaporative capacity were determined. An observed average effective permeation (Pe, W . m-2 . Torr-1) was calculated as Esk/loc w (Ps,sk - Pw), where w is the average of chest and back loc w and (Ps,sk - Pw) is the gradient of skin saturation vapor pressure at Tsk and Ta. Additionally, the local effective evaporative coefficient was determined for chest and back sites by Esk/(Ps,dpl - Pw). The GOR ensemble produced an almost as high a Pe as the TS ensemble (82-86% of Pe with TS in still air and 0.4- and 2-m/s conditions). Direct dew-point recording offers an easy practical dimension to the study of efficacy of latent heat loss and skin wettedness properties through garments.     

Thermoregulatory responses to intermittent exercise are influenced by knit structure of underwear

The purpose of this study was to evaluate the role of knit structure in underwear on thermoregulatory responses. Underwear manufactured from 100% polypropylene fibres in five different knit structures (1-by-1 rib, fleece, fishnet, interlock, double-layer rib) was evaluated. All five underwear prototypes were tested as part of a prototype clothing system. Measured on a thermal manikin these clothing systems had total thermal resistances of 0.243, 0.268, 0.256, 0.248 and 0.250 m2.K.W-1, respectively (including a value for the thermal resistance of the ambient environment of 0.104 m2.K.W-1). Human testing was done on eight male subjects and took place at ambient temperature (Ta) = 5 degrees C, dew point temperature (Tdp) = -3.5 degrees C and air velocity (Va) = 0.32 m.s-1. The test comprised a repeated bout of 40-min cycle exercise (315 W.m-2; 52%, SD 4.9% maximal oxygen uptake) followed by 20 min of rest (62 W.m-2). The oxygen uptake, heart rate, oesophageal temperature, skin temperature, Ta, Tdp at the skin and in the ambient air, onset of sweating, evaporation rate, non-evaporated sweat accumulated in the clothing and total evaporative loss of mass were measured. Skin wettedness was calculated. The differences in knit structure of the underwear in the clothing systems resulted in significant differences in mean skin temperature, local and average skin wettedness, non-evaporated and evaporated sweat during the course of the intermittent exercise test. No differences were observed over this period in the core temperature measurements.     

Effects of varied air velocity on sweating and evaporative rates during exercise.

This study was designed to determine the extent to which changes in the evaporative power of the environment (Emax) affect sweating and evaporative rates. Six male subjects undertook four 60-min bouts of cycle ergometer exercise at 56% maximal O2 uptake (VO2max).Emax was varied by differences in ambient temperature and airflow; two exercise bouts took place at 24 degrees C and two at 35 degrees C, with air velocity at < 0.2 and 3.0 m/s in both. Total sweat production was estimated from body weight loss, whereas whole body evaporative rate was measured continuously from a Potter beam balance. Body core temperature was measured continuously from a thermocouple in the esophagus (T(es)), with mean skin temperature (Tsk) computed each minute from thermocouples at eight sites. Total body sweat loss was significantly greater (P < 0.05) in the 0.2- than in the 3.0-m/s condition at both 24 and 35 degrees C. Tsk was higher (P < 0.05) in the still-air conditions at both temperatures, but final T(es) was significantly higher (P < 0.05) in still air only in the 35 degrees C environment. Thus the reduced Emax in still air caused a greater heat storage, thereby stimulating a greater total sweat loss. However, in part because of reduced skin wettedness, the slope of the sweat rate-to-T(es) relation at 35 degrees C in the 3.0-m/s condition was 118% that at 0.2 m/s (P < 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of menstrual cycle on shivering, skin blood flow, and sweating responses measured at night

In 10 women, external cold and heat exposures were performed both in the middle of luteal phase (L) and in the early follicular phase (F) of the menstrual cycle. Serum progesterone concentrations in L and F averaged 46.0 and 0.9 nmol X l-1, respectively. The experiments took place between 3:00 and 4:30 A.M., when the L-F core temperature difference is maximal. At neutral ambient temperature, esophageal (Tes), tympanic (Tty), rectal (Tre), and mean skin (Tsk) temperatures averaged 0.59 degrees C higher in L than in F. The thresholds for shivering, chest sweating, and cutaneous vasodilation (heat clearance technique) at the thumb and forearm were increased in L by an average of 0.47 degrees C, related to mean body temperature [Tb(es) = 0.87Tes + 0.13 Tsk] and to Tes, Tty, Tre, or Tsk. The above-threshold chest sweat rate and cutaneous heat clearances at the thumb and forearm were also enhanced in L, when related to Tb(es) or time. The metabolic rate, arm blood flow, and heart rate at thermoneutral conditions were increased in L by 5.0%, 1.1 ml X 100 ml-1 X min-1, and 4.6 beats X min-1, respectively. The concomitant increase in threshold temperatures for all autonomic thermoregulatory responses in L supports the concept of a resetting of the set point underlying the basal body temperature elevation in L. The effects of the increased threshold temperatures are counteracted by enhanced heat loss responses.     

Influence of hydrothermal ambient conditions on sweat evaporation efficiency]

Sweat efficiency is defined as the ratio between evaporative and sweat rates. The work was carried out on two resting subjects acclimatised to humid heat. Body sweat rate and rate of sweat loss by dripping were recorded separately by continuous weighing. Evaporation from the skin was obtained by the difference between the two weight loss curves. The subjects were exposed for 75 minutes to increases in humidity levels as constant air temperatures (42, 44, 46, or 48 degrees C). The amplitude of the increases was successively equal to 7.5, 15.0, 22.5 or 50.0 mb of water vapor pressure. During the 75 minutes preceding each increase the water vapor pressure of the air was maintained at 20.0 mb. 1. Sweat efficiency decreases prior to complete wetting of the skin surface. The inter-individual mean value of the wetted skin area threshold over which sweat efficiency is less than 1 is around 60%. 2. Sweat efficiency is linearly related to the reciprocal of the required wetted skin area (see article). These results are compared with those of other authors. The differences observed are explained in terms of physiological or physical variables involved in the sweat rate control or in the evaporative sweat loss. These include wetness of skin, posture, activity of subjects and the velocity of air over the skin surface.     

Hypohydration and exercise: effects of heat acclimation, gender, and environment

This study examined the effects of heat acclimation and subject gender on treadmill exercise in comfortable (20 degrees C, 40% rh), hot-dry (49 degrees C, 20% rh), and hot-wet (35 degrees C, 79% rh) environments while subjects were hypo- or euhydrated. Six male and six female subjects, matched for maximal aerobic power and percent body fat, completed two exercise tests in each environment both before and after a 10-day heat acclimation program. One exercise test was completed during euhydration and one during hypohydration (-5.0% from baseline body weight). In general, no significant (P greater than 0.05) differences were noted between men and women at the completion of exercise for rectal temperature (Tre), mean skin temperature (Tsk), or heat rate (HR) during any of the experimental conditions. Hypohydration generally increased Tre and HR values and decreased sweat rate values while not altering Tsk values. In the hypohydration experiments, heat acclimation significantly reduced Tre (0.19 degrees C) and HR (13 beats X min-1) values in the comfortable environment, but only HR values were reduced in hot-dry (21 beats X min-1) and hot-wet (21 beats X min-1) environments. The present findings indicated that men and women respond in a physiologically similar manner to hypohydration during exercise. They also indicated that for hypohydrated subjects heat acclimation decreased thermoregulatory and cardiovascular strain in a comfortable environment, but only cardiovascular strain decreased in hot environments.     

Influence of menstrual cycle on thermoregulatory, metabolic, and heart rate responses to exercise at night

Ten women [mean maximal O2 uptake (VO2max), 2.81 l X min-1] exercised for 15 min on a cycle ergometer in the middle of the luteal phase (L) and in the early follicular phase (F) of the menstrual cycle at the same constant work rates (mean 122 W) and an ambient temperature of 18 degrees C. Serum progesterone averaged 44.7 nmol X l-1 in L and 0.7 nmol X l-1 in F. After a 4-h resting period, exercise was performed between 3 and 4 A.M., when the L-F core temperature difference is maximal. Preexercise esophageal (Tes), tympanic (Tty), and rectal (Tre) temperatures averaged 0.6 degrees C higher in L. During exercise Tes, Tty, and Tre averaged 0.5 degrees C higher. The thresholds for chest sweating and cutaneous vasodilation (heat clearance technique) at the thumb and forearm were elevated in L by an average of 0.47 degrees C, related to mean body temperature (Tb(es) = 0.87Tes + 0.13Tskin), Tes, Tty, or Tre. The above-threshold chest sweat rate and cutaneous heat clearances were also increased in L. The mean exercise heart rate was 170.0 beats X min-1 in L and 163.8 beats X min-1 in F. The mean exercise VO2 in L (2.21 l X min-1) was 5.2% higher than in F (2.10 l X min-1), the metabolic rate was increased in L by 5.6%, but the net efficiency was 5.3% lower. No significant L-F differences in the respiratory exchange ratio and postexercise plasma lactate were demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characteristics of wettedness under constant average skin temperature

1. 1. Experiments were carried out concerning the characteristics of wettedness revealed under constant average skin temperature using sitting-resting nude subjects. From the basic measurements of both environmental parameters and human physiological responses, the conclusions detailed below were proposed regarding the changes of wettedness under constant average skin temperature.

2. 2. There is positive correlation between the wettedness and environmental humidity, and negative correlation between the wettedness and air temperature.

3. 3. There is positive correlation between the evaporative heat loss from the skin surface and air temperature, and negative correlation between the evaporative heat loss and environmental humidity.

4. 4. There is negative correlation between the wettedness and evaporative heat loss.

5. 5. Wettedness is not constant but takes varying values, that is, corresponding to each average skin temperature both the maximum and the minimum wettedness values occur.

6. 6. Deriving from the items mentioned above, the theoretical locus of equal average skin temperature is not a straight line, but is a curved line plotted on the psychrometric chart.

Physiological and metabolic responses to work in heat with graded hypohydration in tropical subjects

Studies were conducted on 25 healthy male volunteers aged 20-25 years drawn randomly from the tropical regions of India. The subjects initially underwent an 8 day heat acclimatization schedule with 2 hours moderate work in a climatic chamber at 45 degrees C DB and 30% RH. These heat acclimatized subjects were then hypohydrated to varying levels of body weight deficits, i.e. 1.3 +/- 0.03, 2.3 +/- 0.04 and 3.3 +/- 0.04%, by a combination of water restriction and moderate exercise inside the hot chamber. After 2 hours rest in a thermoneutral room (25 +/- 1 degree C) the hypohydrated subjects were tested on a bicycle ergometer at a fixed submaximal work rate (40 W, 40 min) in a hot dry condition (45 degrees C DB, 30% RH, 34 degrees C WBGT). Significant increases in exercise heart rate and oral temperature were observed in hypohydrated subjects as compared to euhydration. Sweat rate increased with 1% and 2% hypohydration as compared to euhydration, but a significant decrease was observed with 3% hypohydration. Na+ & K+ concentrations in arm sweat increased with increase in the level of hypohydration. Oxygen consumption increased significantly only when hypohydration was about 2% or more. It appears that the increased physiological strain observed in tropical subjects working in heat with graded hypohydration is not solely due to reduced sweat rates.     

Effects of humid heat exposure in later sleep segments on sleep stages and body temperature in humans

This study sought to investigate the effects of humid heat exposure in later sleep segments on sleep stages and body temperature in humans. The subjects were eight healthy males, from whom informed consent had been obtained. The experiments were carried out under three different sets of conditions: a control climate [air temperature (Ta)=26°C, relative humidity (RH)=50%] (C); a humid heat climate (Ta=32°C, RH=80%) (H); and a humid heat exposure in later sleep segments (C for the first 3 h 45 min, followed by a 30-min transition to H, which was then maintained for the last 3 h 45 min) (C–H). Electroencephalogram, EOG, and mental electromyogram, rectal temperature (Tre), and skin temperature (Tsk) were continuously measured. The total amount of wakefulness was significantly increased in H compared to C–H or C. Compared to C, wakefulness in C–H and H was significantly increased during later sleep segments. Tre and mean Tsk were significantly higher in H than in C–H or C. In C–H, Tsk and Tre increased to levels equal to those observed in H after Ta and RH increase. Whole body sweat loss was significantly lower in C–H and C than in H. These results suggest that humid heat exposure in the later sleep segment reduces thermal load as compared to full-night humid heat exposure. In daily life, the use of air conditioning in the initial sleep hours can protect sleep and thermoregulation.     

Influence of lysine on urea cycle activity and orotate formation in the isolated perfused rat liver

There was a reversible inhibition of urea formation in the perfused rat liver caused by 2.25-27 mM lysine acting with a Ki of 10.8 mM in competition with ornithine. Urea formation in the presence of inhibitory concentrations of lysine ranged between 2.3 and 2.9 mumol X min-1 X (g, liver wet)-1 after addition of 1 mM of citrulline, argininosuccinate or arginine, whereas it amounted to 0.5 mumol X min-1 X (g, liver wet)-1 after addition of ornithine, showing that lysine inhibited the urea cycle between ornithine and citrulline. There was a rise of basal orotate formation of 0.03 +/- 0.02 mumol X h-1 X (g, liver wet)-1 towards a maximum of 0.6 +/- 0.04 mumol X h-1 X (g, liver wet)-1 after addition of 13.5 mM lysine, provided orotate utilization was blocked with allopurinol. Maximal rates of orotate formation were reached when ammonium concentrations exceeded 1 mM. We conclude that an inhibition of urea synthesis and a rise of orotate formation are caused by lysine in the isolated liver in vitro at rates observed in vivo. Hence, these metabolic alterations observed in the whole animal are most probably due to changes of liver metabolism.     

Thermoregulatory adjustments during continuous heat exposure

Body temperature regulation was studied in 6 male subjects during an acclimation procedure involving uninterrupted heat exposure for 5 successive days and nights in a hot dry environment (ambient temperature = 35 degrees C, dew-point temperature = 7 degrees C; air velocity = 0.2 m.s-1). Data were obtained at rest and during exercise (relative mechanical workload = 35% VO2max). At rest, hourly measurements were made of oesophageal and 4 local skin temperatures, to allow the calculation of mean skin temperature, and of body motility and heart rate. During the working periods these measurements were made at 5 min intervals. Hourly whole-body weight loss was measured at rest on a sensitive platform scale while in the working condition just before starting and immediately after completing the bicycle exercise. The results show that, in both exercise and at rest, the successive heat exposures increased the sweat gland output during the first 3 days. Afterwards, sweat rate decreased without any corresponding change in body temperature. For the fixed workload, the sweat rate decline was associated with a decrease in circulatory strain. Adjustments in both sweating and circulatory mechanisms occur in the first 3 days of continuous heat exposure. The overall sweat rate decline could involve a redistribution of the regional sweating rates which enhances the sweat gland activities of skin areas with maximal evaporative efficiencies.     

Predictors of sweat loss in man during prolonged exercise

Nineteen healthy male subjects, differing in training status and Vo2max (52 +/- 1 ml.min-1.kg-1, mean +/- SEM; 43-64 ml.min-1.kg-1, range), exercised for 1 h at an absolute workload of 192 +/- 8 W (140-265 W); this was equivalent to 70 +/- 1% Vo2max (66-74%). Each exercise test was performed on an electrically braked cycle ergometer at a constant ambient temperature (22.5 +/- 0.0 degrees C) and relative humidity (85 +/- 0%). Nude body weight was recorded prior to and after each exercise test. Absolute sweat loss (body weight loss corrected for respiratory weight loss) during each test was 910 +/- 82 g (426-1665 g); this was equivalent to 1.3 +/- 0.1% (0.7-2.2%) of pre-exercise body weight (relative sweat loss). Weighted mean skin temperature and rectal temperature increased after 5 min of exercise from 30.5 +/- 0.3 degrees C and 37.2 +/- 0.1 degrees C respectively to 32.5 +/- 0.2 degrees C and 38.8 +/- 0.1 degrees C respectively, recorded immediately prior to the end of exercise. Bivariate linear regression and Pearson's correlation demonstrated absolute sweat loss was related to Vo2max (r = 0.72, p less than 0.001), absolute exercise workload (r = 0.66, p less than 0.01), body surface area (r = 0.62, p less than 0.01), weight (r = 0.60, p less than 0.01) and height (r = 0.53, p less than 0.05). Relative sweat loss was related to VO2max (r = 0.77, P less than 0.001) and absolute exercise workload (R = 0.59, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Exercise-rest cycles do not alter local and whole body heat loss responses

Previous studies have suggested that greater core temperatures during intermittent exercise (Ex) are due to attenuated sweating [upper back sweat rate (SR)] and skin blood flow (SkBF) responses. We evaluated the hypothesis that heat loss is not altered during exercise-rest cycles (ER). Ten male participants randomly performed four 120-min trials: 1) 60-min Ex and 60-min recovery (60ER); 2) 3 × 20-min Ex separated by 20-min recoveries (20ER); 3) 6 × 10-min Ex separated by 10-min recoveries (10ER), or 4) 12 × 5-min Ex separated by 5-min recoveries (5ER). Exercise was performed at a workload of 130 W at 35°C. Whole body heat exchange was determined by direct calorimetry. Core temperature, SR (by ventilated capsule), and SkBF (by laser-doppler) were measured continuously. Evaporative heat loss (EHL) progressively increased with each ER, such that it was significantly greater (P ≤ 0.05) at the end of the last compared with the first Ex for 5ER (299 ± 39 vs. 440 ± 41 W), 10ER (425 ± 51 vs. 519 ± 45 W), and 20ER (515 ± 63 vs. 575 ± 74 W). The slope of the EHL response against esophageal temperature significantly increased from the first to the last Ex within the 10ER (376 ± 56 vs. 445 ± 89 W/°C, P ≤ 0.05) and 20ER (535 ± 85 vs. 588 ± 28 W/°C, P ≤ 0.05) conditions, but not during 5ER (296 ± 96 W/°C vs. 278 ± 95 W/°C, P = 0.237). In contrast, the slope of the SkBF response against esophageal temperature did not significantly change from the first to the last Ex (5ER: 51 ± 23 vs. 54 ± 19%/°C, P = 0.848; 10ER: 53 ± 8 vs. 56 ± 21%/°C, P = 0.786; 20ER: 44 ± 20 vs. 50 ± 27%/°C, P = 0.432). Overall, no differences in body heat content and core temperature were observed. These results suggest that altered local and whole body heat loss responses do not explain the previously observed greater core temperatures during intermittent exercise.     

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)     

Thermoregulation during prolonged actual and laboratory-simulated bicycling

Thermoregulatory and cardiorespiratory responses to bicycling 55 km (mean speed 9.7 m X s-1) outdoors (15 degrees C DB) were compared to equivalent cycle ergometry (90 min at 65% VO2max) in the laboratory (20-23 degrees C DB, 50% RH) in 7 trained cyclists. Outdoor environmental conditions were simulated with fans and lamps, and were contrasted with standard no-wind, no-sun laboratory conditions. Sweating rate was similar during outdoor and laboratory simulated outdoor cycling (0.90 and 0.87 to 0.94 1 X h-1 respectively). During outdoor bicycling, mean heart rate (161 bt X min-1) was 7-13% higher (p less than .05) than under laboratory conditions, suggesting a greater strain for a similar external work rate. The increase in rectal temperature (0.8 degrees C) was 33-50% less (p less than 0.05) at the cooler outdoor ambient temperature than in the laboratory. Thermoregulatory stress was greater under the no-fan, no-lamp laboratory condition than during simulated outdoor conditions (36-38% greater (p less than 0.05) sweating rate, 15-18% greater (p less than 0.01) mean skin temperature, 6.4 to 7.8 fold greater (p less than 0.01) amount of clothing-retrained sweat). The cooling wind encountered in actual road bicycling apparently reduces thermoregulatory and circulatory demands compared with stationary cycle ergometry indoors. Failure to account for this enhanced cooling may result in overestimation of the physiological stress of actual road cycling.(ABSTRACT TRUNCATED AT 250 WORDS)     

A study of water relations in neem (Azadirachta indica) seed that is characterized by complex storage behaviour

Neem (Azadirachta indica) seed is reputed to have limited tolerance to desiccation, to be sensitive to chilling and imbibitional stress, and to display intermediate storage behaviour. To understand this behaviour the properties of water in seed tissues were studied. Water sorption isotherms showed that at similar relative humidity (RH), the water content was consistently higher in axes than in cotyledons, mainly due to the elevated lipid content (51%) in the cotyledons. Using differential scanning calorimetry, melting transitions of water were observed at water contents higher than 0.14 g H2O g-1 DW in the cotyledons and 0.23 g H2O g-1 DW in the axes. Beside melting transitions of lipid, as verified by infrared spectroscopy, changes in heat capacity were observed which shifted with water content, indicative of glass-to-liquid transitions. State diagrams are given on the basis of the water content of seed tissues, and also on the basis of the RH at 20 degrees C. Longevity was considerably improved, and the sensitivity to chilling/subzero temperatures was reduced when axis and cotyledons were dehydrated to moisture contents < or = of approximately 0.05 g H2O g-1 DW. However, longevity during storage at very low water contents was limited. A possible mechanism for the loss of sensitivity to chilling/subzero temperatures at low water contents is discussed. The results suggest that dry neem seeds in the glassy state have great potential for extended storability, also at subzero temperatures.     

Control of sweating in man after work-induced thermal load and symmetrically applied cooling

To examine the compensatory effects of work-induced thermal load and symmetrically applied local cooling on local sweat rates, two kinds of experiment were carried out on eight male subjects in a climatic chamber: 1) Experiments at 36 degrees C ambient temperature with a work load of about 25 W by the right leg. 2) Experiments at 36 degrees C ambient temperature with a work load of about 25 W by the right leg as in 1., but with additional compensatory cooling of the left leg controlled throughout by heat balance calculations at 75-85 W, equal to the heat produced in the working leg, the necessary air temperature being dependent on local sweat rate. Work load without cooling brought about a significant increase in core temperatures, metabolism, heart rate and local sweat rates. With unchanged local skin temperatures local sweat rate increase was higher in the working leg. Therefore the existence of muscle thermoreceptors should be assumed, the afferent information from which is processed and weighted in a different way to that provided by skin receptors. Work load combined with additional cooling reduced local and mean skin temperatures and heart rate, but had no significant influence on core temperature or metabolism. However, local sweat rate was generally lower in both thighs, with a major reduction in the cooled leg confirming control of local sweat rate by local temperature.(ABSTRACT TRUNCATED AT 250 WORDS)     

Water loss distribution in exercising men under hot conditions

Dynamics of sweating and water loss distribution were studied in 7 exercising men under thermoneutral conditions (Ta, 25 degrees C; Tw, 24 degrees C and RH, 54%) and during moderate heat exposure (Ta, 30 degrees C; Tw, 30 degrees C; RH, 54%). The subjects performed bicycle exercise at intensity of 50% V O2 max. Dynamics of sweating was greater after heat exposure (delay in onset of sweating 3.6 and 1.4 min, p less than 0.05; time constant 10.1 and 7.3 min, p less than 0.02). The dynamics of sweating was related to the net body heat load (r = -0.80, p less than 0.001). Sweat evaporation from the skin (Esk) was significantly higher in heat exposed exercising subjects while dripping sweat (mdrip) did not differ significantly. Water loss distribution in relation to total water loss during control exercise was as follows: (Ediff + Eres) 14.8% (Esk) 59.6%; and (mdrip) 25.6%. During exercise under heat exposure (Ediff + Eres) was 12.1%; (Esk) was 67.5%; and (mdrip) was 20.4%. It is concluded that moderate heat exposure accelerate sweating reaction but does not change significantly water loss distribution in exercising subjects. Dripping sweat seems to be an attribute of sweating not only in hot humid conditions but also under temperate temperature and air humidity.