Combined Effects of Metabolic Heat Production and High AmbientTemperature on Rectal Temperature during Work and at Rest

Abstract

Eight healthy male Japanese were exposed to different heat stress, i.e., metabolic heai production during work, high ambient temperature and both of them. After resting on a chair for 30 min. at 28°C with 50% R.H., subjects were examined for 61 min. at following conditions: bicycle ergometer work at 28°C with 50% R.H., rest on a chair at 45°C with 50% R.H. and bicycle ergometer work at 45°C with 50% R.H.. The work load of bicycle ergometer was 450 kgrn/min, and the pedalling frequency was kept at 50 rpm. At the condition of work at 45°C, exposure was stopped due to rise in rectal temperature to 39.0°C, subjective impossibility to continue the work and objective observation. All of the eight subjects could not complete the work for 61 min. at 45°C because of some of the criteria descrived above. The mean value of duration of work at 45°C was 39.4 min.. At the end of the resting period at 28°C, rectal and skin temperature measurements and expired gas collection for 3 min. were made. During exposure period, rectal and skin temperature were measured at every 2 and I min., respectively. Expired gas was collected at 8-11, 28-31 and 58-61 min, during exposure period. The sites of skin temperature measurement were chest. upper arm, thigh and leg. Oxygen uptake was used to calculate the heat production. Body heat content was calculated by rectal temperature and skin temperature, and heat dissipation by heat production and increase in body heat content. During work at 45°C, rectal temperature rised rapidly and there was remarkable heat storage because high ambient temperature disturbed heat dissipation from body to environment. During work at 28°C, there was no significant heat storage though rectal temperature rised. At rest at 45°C, rectal temperature rised due to heat invation from environment to body, and there was significant heat storage.