Development of biological monitoring methods of heat strain for preventing a heat stroke.

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We investigate the biological monitoring methods of heat strain for preventing a heat stroke among workers working in the hot environment. We choose an auditory canal to measure a core temperature. The auditory canal was insulated with an ear plug to reduce external climate effects. In the artificial climate chamber controlled at 25, 30, 35゜C and humidity 60%, six male volunteers were asked to perform three repeats of 20 min of 75 W exercise and 15 min rest on the bicycle ergometer. Auditory canal temperature was measured using an ear plug type thermo-sensor. Rectal temperature had a correlation with auditory canal temperature under stable environmental temperature condition. However, environmental temperature changes to hot or cold direction, auditory canal temperature also changes to hot or cold point depending on the environmental temperature. From 25゜C to 35゜C in environmental condition, the difference of rectal temperature and auditory canal temperature was within 0.6゜C. Then we measured the auditory canal temperature among workers using a mini thermo data logger. Twenty-seven workers in the four workshops wore the ear plug with thermo sensor connected to the mini data logger, worked in the hot environment. We also asked the questionnaire to the workers about heat sensation and tiredness by visual analog scale (VAS) before and after the job. Peak and mean value of the auditory canal temperature had correlation with sum of the heat sensation and tiredness VAS value. We think that the peak value of the auditory canal temperature shows the exposure limit of heat strain and the mean value of the auditory canal temperature shows the exposure dose of the heat strain. It is possible that the peak and mean value of the auditory canal temperature might be the effective indexes for preventing a heat stroke.