Continuous Heat Exposure Research Articles

ACUTE INTERMITTENT HEAT EXPOSURE WITH MORE FREQUENT AND SHORTER COOLING BREAKS ENHANCES PERFORMANCE AND ELICITS COMPARABLE PHYSIOLOGICAL RESPONSES TO CONTINUOUS HEAT EXPOSURE

INTRODUCTION & AIMS Heat acclimation (HA) is critical to mitigate the adverse effects of heat on exercise performance. While these methods yield physiological adaptations to heat, it also results in greater internal training load. This can potentially compromise training quality and lead to overreaching. Therefore, there is a need for HA protocols that address situations where training quality is crucial, yet the heat stimulus is necessary. The aim of this study was to investigate the influence of shorter, more frequent rest breaks with per-cooling (PerC) as an alternative HA session on physiological, perceptual, and self-paced maximal cycling performance, compared to continuous heat exposure. METHODS Thirteen participants completed one continuous and three intermittent heat exposure (IHE) maximal self-paced cycling protocols matched for total exercise and rest duration, in a random order in heat (36°C, 80% relative humidity): 1 x 60-min exercise (CON), 3 x 20-min exercise with 7.5-min rest between sets (IHE-20), 4 x 15-min exercise with 5-min rest between sets (IHE-15), 6 x 10-min exercise with 3-min rest between sets (IHE-10). Mixed-method PerC (crushed-ice ingestion and cooling vest) was applied during rest periods of all IHE protocols. RESULTS Total distance completed was greater in IHE-10, IHE-15, and IHE-20 compared to CON (+11%, +9%, and +8%, respectively), with no difference observed between IHE protocols. Total time spent above 38.5°C core temperature (Tc) was longer in CON compared to IHE-15 and IHE-20 (+62% and +78%, respectively), but similar to IHE-10 (+5%). Furthermore, a longer time above 38.5°C Tc occurred in IHE-10 versus IHE-15 and IHE-20 (+54% and +69%, respectively). Sweat loss did not differ between conditions. CONCLUSION Intermittent heat exposure with PerC may be a viable alternative HA protocol in situations where training quality takes precedence over thermal stimulus, or when both factors hold equal priority.

Single Session Intermittent Heat Exposure With More Frequent and Shorter Cooling Breaks Facilitates Greater Training Intensity and Elicits Physiological Responses Comparable to Continuous Heat Exposure.

To investigate the influence of shorter, more frequent rest breaks with per-cooling as an alternative heat-acclimation session on physiological, perceptual, and self-paced maximal cycling performance, compared with continuous heat exposure. Thirteen participants completed 1 continuous and 3 intermittent-heat-exposure (IHE) maximal self-paced cycling protocols in a random order in heat (36 °C, 80% relative humidity): 1 × 60-minute exercise (CON), 3 × 20-minute exercise with 7.5-minute rest between sets (IHE-20), 4 × 15-minute exercise with 5-minute rest between sets (IHE-15), and 6 × 10-minute exercise with 3-minute rest between sets (IHE-10). Mixed-method per-cooling (crushed-ice ingestion and cooling vest) was applied during rest periods of all IHE protocols. Total distance completed was greater in IHE-10, IHE-15, and IHE-20 than in CON (+11%, +9%, and +8%, respectively), with no difference observed between IHE protocols. Total time spent above 38.5 °C core temperature was longer in CON compared with IHE-15 and IHE-20 (+62% and +78%, respectively) but similar to IHE-10 (+5%). Furthermore, a longer time above 38.5 °C core temperature occurred in IHE-10 versus IHE-15 and IHE-20 (+54% and +69%, respectively). Sweat loss did not differ between conditions. IHE with per-cooling may be a viable alternative heat-acclimation protocol in situations where training quality takes precedence over thermal stimulus or when both factors hold equal priority.

Effect of biochar on desiccation of marine soils under constant and cyclic temperatures

Biochar has recently been gaining increasing attention as a stable and sustainable soil amendment material. However, the effect of biochar amendment on the desiccation behaviour of coastal soils has not yet been examined. Consequently, the present study primarily investigated the effect of exposing biochar-amended marine soil (BAS) to constant and cyclic temperatures on its swell–shrink, evaporation and desiccation cracking characteristics. Biochar contents of 1%, 2%, 4% and particle size ranges of PS-1 (600 μm < D ≤ 2000 μm), PS-2 (300 μm < D ≤ 600 μm), PS-3 (D ≤ 75 μm) (D: biochar particle diameter) were employed. It was revealed that the absolute volumetric shrinkage of both unamended and biochar-amended specimens increased as the number of thermal cycles increased. Under continuous heat exposure, 4% (PS-3) BAS in compacted state achieved the maximum reduction in volumetric shrinkage which was 42%. Moreover, under continuous heat exposure, 2% (PS-1) BAS in slurry state achieved the highest reduction in desiccation cracking, which was 73%. The present study highlights the importance of identifying the most effective combination of biochar content and particle size required to achieve a desired outcome, in order to gain the maximum benefit of biochar as an amendment material at the lowest possible cost.

Working Productivity Analysis on the Process of Drying Fish Using Solar Dryers

The process of drying fish using solar energy is strongly influenced by weather conditions. Sunlight is needed by household scale workers because it is cheap. On the other hand, sun drying creates additional workload for workers. Workers are exposed to hot sun during drying. Continuous heat exposure results in an increased work pulse. This affects the level of worker productivity. To anticipate this, a solar dryer is used by utilizing a solar collector as an absorber of sunlight and a drying chamber for the drying process of fish. The use of solar dryers has been shown to increase drying temperatures and reduce workers' sun exposure. This decreases the workload of workers, so that it has an impact on increasing productivity. Worker productivity increased by 133.94%.

Changes in Mechanical Properties of Holding Magnet Type LS50 in Liquid Metal Transfer Ladle Due to Repeated Use

Inside a ladle there is one component of the material that often gets damaged, namely the Holding Magnet Type LS50, which has corrosion (damage) on the surface due to temperatures that reaches 1500 °C with a time limit of 150 minutes. Test shows the material contained in the Holding Magnet Type LS50 are steel, copper (CuZn), and magnet. The Steel of Holding Magnet Type LS50 has a chemical composition with the main ingredient of iron (Fe) around 97.961% and other elements such as carbon, silicon, manganese, chromium and other alloy elements. As for the microstructure, CuZn has a microstructure in the form of an α (alpha) phase and a s (betha) phase. The average of Holding Magnet hardness test results shows only CuZn experienced a very drastic decrease in the hardness value due to continuous heat exposure while the temperature for CuZn melting point is only 1084 ° C. Keywords: Chemical Composition, Metallography, Hardness. DOI: 10.7176/CMR/12-7-08 Publication date: October 31st 2020

Using naturalistic incubation temperatures to demonstrate how variation in the timing and continuity of heat wave exposure influences phenotype.

Most organisms are exposed to bouts of warm temperatures during development, yet we know little about how variation in the timing and continuity of heat exposure influences biological processes. If heat waves increase in frequency and duration as predicted, it is necessary to understand how these bouts could affect thermally sensitive species, including reptiles with temperature-dependent sex determination (TSD). In a multi-year study using fluctuating temperatures, we exposed Trachemys scripta embryos to cooler, male-producing temperatures interspersed with warmer, female-producing temperatures (heat waves) that varied in either timing during development or continuity and then analysed resulting sex ratios. We also quantified the expression of genes involved in testis differentiation (Dmrt1) and ovary differentiation (Cyp19A1) to determine how heat wave continuity affects the expression of genes involved in sexual differentiation. Heat waves applied during the middle of development produced significantly more females compared to heat waves that occurred just 7 days before or after this window, and even short gaps in the continuity of a heat wave decreased the production of females. Continuous heat exposure resulted in increased Cyp19A1 expression while discontinuous heat exposure failed to increase expression in either gene over a similar time course. We report that even small differences in the timing and continuity of heat waves can result in drastically different phenotypic outcomes. This strong effect of temperature occurred despite the fact that embryos were exposed to the same number of warm days during a short period of time, which highlights the need to study temperature effects under more ecologically relevant conditions where temperatures may be elevated for only a few days at a time. In the face of a changing climate, the finding that subtle shifts in temperature exposure result in substantial effects on embryonic development becomes even more critical.

Steam Burn Injury Model of Firefighter’s Personal Protective Clothing

Burn injury is one of the most common injury among firefighters. Moisture comes from perspiration or hose spray absorbed in the personal protective clothing and steam burn injury occur with continuous heat exposure. The heat transfer from the heat flux is enhanced due to transformation material properties that holds high thermal conductivity and heat conductivity. Finite element method is used to predict steam burn injury among firefighters. The model is developed in 1dimensional cylinderical quarter geometry representing the human limb. It is discovered the skin temperature 10°C increases with wet material than dry material. The pain threshold at the lower arm of wet material condition is formed 40second rapidly compare to dry material condition. The first degree burn occur at t=9.5second sooner than the dry condition t=25second. The skin temperature increases with the wet material resulting severe skin burn. It is found that the wet personal protective clothing had compromised its thermal protection. Therefore, firefighters will experience high risk of thermal hazard.

Early posthatch thermal stress affects breast muscle development and satellite cell growth and characteristics in broilers

Heat or cold stress, can disrupt well-being and physiological responses in birds. This study aimed to elucidate the effects of continuous heat exposure in the first 2 wk of age on muscle development in broilers, with an emphasis on the pectoralis muscle satellite cell population. Chicks were reared for 13 d under either commercial conditions or a temperature regime that was 5°C higher. Body and muscle weights, as well as absolute muscle growth were lower in heat-exposed chicks from d 6 onward. The number of satellite cells derived from the experimental chicks was higher in the heat-treated group on d 3 but lower on d 8 and 13 compared to controls. This was reflected in a lower number of myonuclei expressing proliferating nuclear cell antigen in cross sections of pectoralis major muscle sampled on d 8. However, a TUNEL assay revealed similar cell survival in both groups. Mean myofiber diameter and distribution were lower in muscle sections sampled on d 8 and 13 in heat-treated versus control group, suggesting that the lower muscle growth is due to changes in muscle hypertrophy. Oil-Red O staining showed a higher number of satellite cells with lipids in the heat-treated compared to the control group on these days. Moreover, lipid deposition was observed in pectoralis muscle cross sections derived from the heat-treated chicks on d 13, whereas the controls barely exhibited any lipid staining. The gene and protein expression levels of CCAAT/enhancer binding protein β in pectoralis muscle from the heat-treated group were significantly higher on d 13 than in controls, while myogenin levels were similar. The results suggest high sensitivity of muscle progenitor cells in the early posthatch period at a time when they are highly active, to chronic heat exposure, leading to impaired myogenicity of the satellite cells and increased fat deposition.

Use of thermobalancing therapy in ageing male with benign prostatic hyperplasia with a focus on etiology and pathophysiology

Introduction: We investigated if “thermobalancing” therapy (TT), using Dr Allen’s therapeutic device (DATD) in men with benign prostatic hyperplasia (BPH), can aid in understanding the etiology and pathophysiology of BPH.Methods: We compared urinary and other parameters of BPH patients who received TT over 6 months (treatment group) with those of healthy volunteers who had not received the treatment (control group). Dynamics of symptoms and indicators in each group were evaluated in comparison with their data at the beginning and end of the study. Parameters were the International Prostate Symptom Score (IPSS) for urinary symptoms and quality of life (QoL), ultrasound measurement of prostate volume (PV) and uroflowmetry (maximum flow rate, Qmax). TT effectiveness was examined in 124 men with BPH and PV <60 mL. We also investigated the data of five patients with BPH and PV >60 mL.Results: TT decreased urinary symptoms and PV, increased Qmax and improved QoL in men with BPH, PV <60 mL, and in men with BPH, PV >60 mL.Conclusions: The present study demonstrated that TT is effective for BPH, suggesting that blood circulation plays a crucial role in its cause. The continuous heat exposure that does not exceed the normal body temperature terminates the trigger of BPH development, “micro-focus” of hypothermia, and the following spontaneous expansion of capillaries. TT could be considered to be a useful tool in BPH treatment.

How heat stress (continuous or cyclical) interferes with nutrient digestibility, energy and nitrogen balances and performance in broilers

The effect of continuous and cyclical heat stress on broiler growth performance, nutrient digestibility, energy and nitrogen balances was investigated. Four hundred and fifty, 21-day-old, Cobb male broilers were raised in battery cages in five treatments: 22C/AL (continuous 22°C, ad libitum feed consumption); 32C/AL (continuous 32°C, ad libitum feed consumption); 22C/PF32C (continuous 22°C, pair-fed on the daily feed intake of 32C/AL); CY/AL (cyclical – 32°C for 8h and 25°C for 12h, ad libitum feed consumption); 22C/PFCY (continuous 22°C, pair-fed on the daily feed intake of CY/AL). Between 39 and 42 days of age, dry matter, crude protein, crude fat and AMEn were analyzed in the diets and excreta to determine nutrient digestibility. Energy and nitrogen balances were evaluated through comparative slaughter (21 and 42 days of age). Growth performance was significantly lower in broilers exposed to either continuous or cyclical heat stress. However, the cyclical heat stress had a lower effect on feed intake and weight gain and no effect on the feed conversion rate. Nutrient digestibility was only influenced by continuous heat exposure, decreasing dry matter (3.9%) and protein digestibility (9.7%) in comparison to control birds. Broilers exposed to continuous heat stress increased metabolizable energy intake (20.3%) and heat production (35.5%), and decreased energy retention (20.9%) and energy efficiency (32.4%) in relation to control ones. Nitrogen intake and nitrogen retention were reduced by both forms of heat exposure, in comparison to control, but more strongly under continuous heat. Nitrogen retention was reduced by 50.4% and 20.4%, for continuous or cyclical heat stress, respectively. Nitrogen efficiency was reduced only by the continuous heat exposure (33.1%). These results revealed important differences between the effects of a continuous or a cyclical heat exposure in broiler chickens for digestibility, performance and energy and nitrogen balances.

Occurrence and behaviour of Mo containing precipitates in nodular cast iron at high temperatures

In nodular cast iron, molybdenum is alloyed in the range of 0.5 to 1.5 wt.-% to increase the mechanical properties for high temperature application, especially for thick walled castings like housings of gas or steam turbines. The behaviour of Mo precipitates in the as cast state as well as under long exposure to heat was the object of this investigation. In the as cast state, Mo forms metastable carbidic grain boundary precipitates with iron, silicon and carbon. These transform into stable MoC precipitates during sustained temperature influence. Furthermore, there are finely dispersed Mo containing precipitates found in the matrix. These increase the high temperature strength of Mo alloyed cast iron due to the Orowan mechanism and the occurrence of additional grain boundaries. However, it has been shown that these Mo containing precipitates underlie Ostwald ripening under continuous heat exposure, and a precipitate free area occurs along the ferritic grain boundary.

Heat and PAHs Emissions in Indoor Kitchen Air and Its Impact on Kidney Dysfunctions among Kitchen Workers in Lucknow, North India.

Indoor air quality and heat exposure have become an important occupational health and safety concern in several workplaces including kitchens of hotels. This study investigated the heat, particulate matter (PM), total volatile organic compounds (TVOCs) and polycyclic aromatic hydrocarbons (PAHs) emissions in indoor air of commercial kitchen and its association with kidney dysfunctions among kitchen workers. A cross sectional study was conducted on 94 kitchen workers employed at commercial kitchen in Lucknow city, North India. A questionnaire-based survey was conducted to collect the personal and occupational history of the kitchen workers. The urine analysis for specific gravity and microalbuminuria was conducted among the study subjects. Indoor air temperature, humidity, wet/ dry bulb temperature and humidex heat stress was monitored during cooking activities at the kitchen. Particulate matter (PM) for 1 and 2.5 microns were monitored in kitchen during working hours using Hazdust. PAHS in indoor air was analysed using UHPLC. Urinary hydroxy-PAHs in kitchen workers were measured using GC/MS-MS. Higher indoor air temperature, relative humidity, PM1 and PM2.5 (p<0.001) was observed in the kitchen due to cooking process. Indoor air PAHs identified are Napthalene, fluorine, acenaphthene, phenanthrene, pyrene, chrysene and indeno [1,2,3-cd) pyrene. Concentrations of all PAHs identified in kitchen were above the permissible OSHA norms for indoor air. Specific gravity of urine was significantly higher among the kitchen workers (p<0.001) as compared to the control group. Also, the prevalence of microalbuminuria was higher (p<0.001) among kitchen workers. Urinary PAH metabolites detected among kitchen workers were 1-NAP, 9-HF, 3-HF, 9-PHN and 1-OHP. Continuous heat exposure in kitchens due to cooking can alter kidney functions viz., high specific gravity of urine in kitchen workers. Exposure to PM, VOCs and PAHs in indoor air and presence of urinary PAHs metabolites may lead to inflammation, which can cause microalbuminuria in kitchen workers, as observed in the present study.

Erythema ab igne bei einer Patientin mit Bulimia nervosa

Erythema ab igne (EAI) is a skin lesion, which is characterized by a localized netlike erythema. For the occurrence of the dermatosis a continuous or regular heat exposure and infrared radiation to a skin area is necessary. The reticulated maculae could fade after stopping the heat exposure, persist as hyperpigmentation and in single cases a malignant transformation is possible. We present a patient with bulimia nervosa (BN), who developed an EAI after consequent use of a hot-water bottle. In the context of the eating disorder the patient reported a general feeling of cold. She avoided the contact with the abdomen to prevent a stimulation of the digestion. Therefore the EAI was located predominantly on the medial thighs. After stopping the heat application the EAI faded slightly in the periphery und turned browner.

Effects of Work and Environmental Measurement Protocols in High Temperature Exposure

Nonoptimal environments often result in worker discomfort and loss of productivity in the workplace. The temperature in a workplace can strongly influence efficiency of task. Hot, humid conditions added to the demands of moderately heavy to heavy physical work may cause excessive stress and potential health risks by reducing a person's work capacity. Discomfort produced by exposure to conditions outside the comfort zone can distract a person from the task at hand and may increase the potential for unsafe act. Various factors affecting the feeling of comfort are temperature, humidity, air velocity, work load, clothing and radiant heat loss. By altering environmental protocols one can improve comfort within the discomfort zone. An attempt is made to investigate factors like temperature, humidity and determining continuous heat exposure for workers working in a hot environment. By altering environmental protocols one can prevent heat injuries like heat stroke, fatigue, irritation, discomfort, giddiness; disorientation at work. This paper discusses the effect of temperature and humidity for an industrial worker working in a hot environment.

Effect of continuous heat exposure on sleep during partial sleep deprivation.

This study examined the effects of continuous heat exposure on sleep structure during a partial sleep-deprivation regime. The experimental protocol was divided into three periods. After a baseline period (5 days and nights at 20 degrees C), the sleep of the subjects was restricted to the second half of the night (3 a.m.-7 a.m.) for four consecutive nights. The restricted-sleep period was followed by two recovery days and nights. During the deprivation and recovery periods, the ambient temperature was 20 degrees C for six of the 12 subjects and 35 degrees C for the others. Sleep, esophageal and mean skin temperatures were continuously recorded. At 20 degrees C, the expected effect of sleep debt was apparent. There were significant reductions in time spent awake and in latencies for sleep and stage 4 sleep. The duration of stage 4 sleep significantly increased during the four successive restricted-sleep nights, whereas esophageal temperature significantly decreased over the successive days. When heat was added, esophageal temperature decrease was weakened, and the significant increase in stage 4 duration seen at 20 degrees C was not found. The findings suggest that the heat load imposed in our experimental condition has a suppressive effect on sleep stage 4 increase, which is induced by sleep restriction. The hypothesis that an increase in this sleep stage serves as a mechanism for energy conservation should be also considered.

Nocturnal pituitary hormone and renin profiles during chronic heat exposure.

To establish the principal endocrine systems involved in the initial adaptation to chronic passive heat exposure, responses of the hydromineral and pituitary systems were compared. Nocturnal plasma profiles of growth hormone, prolactin, thyrotropin, and plasma renin activity were determined during a period of prolonged heat exposure designed to simulate a hot climate. Two groups of six male subjects (G1 and G2) were kept for 11 days in a climatically controlled apartment. The G1 group was exposed to 20 degrees C throughout the study, and the G2 group was exposed to 20 degrees C for 5 days and to 35 degrees C for the following 6 days. Blood was collected continuously during the 1st and 10th nights from 2300 to 0700 h and was sampled in 10-min aliquots for hormone analysis. Heat exposure increased the nocturnal mean core temperature (P < 0.02) and stimulated plasma renin activity (P < 0.01) but had little effect on the pituitary hormones except for a small increase in prolactin (P < 0.05). For the G1 group there was no change in hormone profiles. These results demonstrate that the principal initial endocrine system involved in acclimatization to passive heat exposure is the renin-angiotensin system, reflecting counteractive measures against salt and water losses. In contrast, 5 days of continuous heat exposure does not provoke metabolic changes, indicated by the small effect on pituitary hormone profiles.

Thermoregulatory responses to acute body heating in rats acclimated to continuous heat exposure

Thermoregulatory responses to an acute heat load with intraperitoneal heating (IH) or indirect external warming (EW) by increasing ambient temperature (Ta) were investigated with direct and indirect calorimetry in rats acclimated to environments of 24.0 degrees C (Cn), 29.4 degrees C (H1), and 32.8 degrees C (H2) for greater than 15 days. The rats were placed in a direct calorimeter where the air temperature was maintained at 24 degrees C for the initial 3 h. IH was then made for 30 min through an electric heater implanted chronically (6.5 W.kg-1) in the peritoneal cavity, and EW was performed by raising the jacket water temperature surrounding the calorimeter from 24 to 39 degrees C (0.19 degrees C.min-1). Hypothalamic (Thy) and colonic temperature immediately before the start of the heat load tended to be higher as the acclimation temperature increased. During IH, the threshold Thy for the tail skin vasodilation (Tth) was significantly higher in H2 than in Cn rats. During EW, however, there was no difference in Tth between the groups. Metabolic heat production (M) was slightly suppressed during IH and significantly depressed only in H2 rats. During EW, M was suppressed in all the groups. The magnitude and duration of suppression were greater in H2 rats than in the other two groups. The responses in nonevaporative heat loss and thermal conductance (C) to the rise in Thy did not differ among the three groups during IH. According to the rise in Thy, however, there was a greater C increase in H2 than in Cn and H1 rats during EW.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma corticosterone response in continuous versus discontinuous chronic heat exposure in rat

Effects of chronic exposure (25 days) to continuous (CHE) or discontinuous (DHE) hot environment (34°C) on growth rate, food intake and cortico-adrenal function were studied in adult male rats. Growth rate and food intake were 40 and 31% less respectively in CHE and 7 and 9% less respectively in DHE than in control (CE) animals. The adrenal response to heat (40°C) was reduced by 54 and 82% in CHE and DHE rats respectively but the plasma corticosterone (B) response to exogenous ACTH and ether stress was not altered by chronic heat. The plasma B rhythm was altered only in CHE rats which exhibited a 40% decrease in amplitude and a delayed nocturnal recession of plasma B values. These results indicate that 1) CHE induced major alterations of behavior specially during the nocturnal period of the L-D cycle, 2) that the altered circadian B rhythm of CHE rats could be linked to changes in feeding behavior and to reduced metabolic activity, 3) and that CHE induced a poorer adaptation than DHE.

Amplification of nocturnal oscillations in PRA and aldosterone during continuous heat exposure

To assess the effect of continuous heat exposure on the nocturnal patterns of renin, aldosterone, adrenocorticotropic hormone (ACTH), and cortisol, six young men were exposed to thermoneutral environment for 5 days, followed by a 5-day acclimation period in a hot dry environment (35 degrees C). Blood was collected at 10-min intervals during the second night at thermoneutrality (N0) and during the first (N1) and the last (N5) nights of heat exposure. Polygraphic recordings of sleep were scored according to established criteria. Continuous heat exposure led to progressive decreases in the 24-h urinary volume and in Na excretion, whereas urinary osmolality increased. After 5 days of uninterrupted heat, significant increases were found in plasma volume (P less than 0.05), osmolality (P less than 0.01), plasma Na (P less than 0.01), and protein levels (P less than 0.05). Sweat gland output increased during the first 3 days and then declined without any concomitant increases in body temperature. Compared with N0, there were no differences in plasma renin activity (PRA) and aldosterone (PA) profiles during N1 at 35 degrees C. However, during N5 the mean PRA and PA levels were significantly (P less than 0.05) enhanced, and their nocturnal oscillations were amplified (P less than 0.05). This amplification occurred mainly in the second part of the night when regular rapid-eye-movement and non-rapid-eye-movement sleep cycles were observed, leading to a general upward trend in the nocturnal profiles. The relationship between the nocturnal PRA oscillations and the sleep cycles was not modified. ACTH and cortisol patterns were not affected by continuous heat exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

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.