Effects of Dehydration, Hypohydration, and Hyperhydration on Tolerance During Uncompensable Heat Stress

The present study examined the effects of dehydration from prior exercise on subsequent exercise tolerance time (TT) that involved wearing nuclear, biological, and chemical (NBC) protective clothing. It was hypothesised that TT would be reduced in the dehydrated state. Ten men undertook continuous treadmill walking at 4.8 km • h−1 at 35 °C and 50% relative humidity, wearing NBC clothing while euhydrated (EU) or dehydrated (D) by 2.3% of body weight. Hydration status had no impact on thermoregulatory or cardiovascular responses during exercise. Also rectal temperature at exhaustion did not differ between EU (38.52 ± 0.39 °C) and D (38.43 ± 0.45 °C). Exercise TT during this uncompensable heat stress was reduced significantly for D (47.7 ± 15.3 min) compared with EU (59.0 ± 13.6 min). It was concluded that prior exercise leading to levels of dehydration to 2.3% of body weight, together with subsequent fluid restriction during exposure to uncompensable heat stress, impaired TT while wearing the NBC protective clothing. The integration of these findings together with other comparable studies that have examined the influence of hypo- and hyperhydration on TT while wearing NBC protective clothing revealed that hydration status has less effect on TT as the severity of uncompensable heat stress increases. Key words: thermoregulation, protective clothing, heat tolerance, rectal temperature

Heat Strain in the Canadian Forces Chemical Defence Clothing: Problems and Solutions

The Canadian Forces chemical defence protective clothing can induce an overwhelming strain on one's ability to regulate body temperature. Recently a number of investigations have been completed at the Defence and Civil Institute of Environmental Medicine that focused initially on understanding the interaction of metabolic rate, ambient temperature, and ambient vapour pressure on the severity of heat strain associated with wearing the protective clothing. This paper presents a summary of these initial studies together with an overview of different attempts to reduce heat strain during exercise in a hot environment. Factors such as improved aerobic fitness or a period of dry heat acclimation have little if any benefit on tolerance time while wearing the clothing during light or moderate exercise. The best solution to the problem of heat strain remains the use of microclimate conditioning (personal cooling), and these techniques have been successful for Naval and Air Force personnel. For our Land Forces, however, microclimate conditioning is not feasible until a lightweight high-energy power source is developed. Key words: thermoregulation, endurance training, heat acclimation, microclimate conditioning

Thermoregulation through Skin at Low Atmospheric Temperatures

The metabolic heat generation decreases exponentially if the persistence of cooling in human body is sustained. This phenomena is under consideration in dermis and subcutaneous tissue to study the exact solution of temperature distribution in dermal layers at low atmospheric temperatures. Other suitable variable physiological conditions are taken and the solution has been obtained using laplace tranform in one dimensional case. Key words: Thermoregulation; Human dermal part; Laplace transform. 2000 Mathematics Subject Classification: 92 C 35. DOI: 10.3126/kuset.v5i1.2843 Kathmandu University Journal of Science, Engineering and Technology Vol.5, No.1, January 2009, pp 14-22