Individual Difference in Transient Thermophysiological Responses to Stepwise Change in Air Temperature: A Study Based on Experiments for Sedentary Young Male Subjects

摘要

In order to quantitatively assess the individual differences in the thermophysiological responses, human subjects were exposed to a series of stepwise air temperature changes, and the rectal and skin temperatures and weight change were measured. The differences between subject responses were evaluated not only for steady state but also for a transient state. Ten young males were used as subjects and were monitored in a sedentary state. From the results of the transient exposure to cold and hot environments for 150 min. (29 ℃, 30 min. – 20 ℃, 20 min. – 29 ℃, 60 min. – 38 ℃, 20 min. – 29 ℃, 20 min.), it was shown that the individual differences in rectal temperatures amounted to a standard deviation of 0.3 K, and that for mean skin temperature the standard deviation was 0.5 K for both steady and transient states. Local skin temperatures, measured at seven points to represent each body segment, showed larger individual differences than those for mean skin temperature, which suggests the existence of individual differences in skin temperature distributions. In addition, the skin temperature time derivative at the beginning of a step change in air temperature and body weight change were studied from the viewpoint of the individual difference. It was shown that the individual differences in rectal temperature, skin temperature distribution, and sweat rate were significant, and that the difference between individuals for skin temperature change during the transient state was almost the same as that for the thermally neutral and steady state. Furthermore, correlations between the responses and basic body parameters (the body weight, body surface area, and body fat percentage of the subjects) were studied using correlation analysis. As the results indicated, body fat percentage had greater influence on thermophysiological responses than height, body weight and surface area, and the correlation coefficients were fairly high for each of the thermophysiological responses measured in this study. For the thermally neutral and steady state data, rectal temperature showed a positive correlation with body fat percentage, while mean skin temperature showed a negative correlation with body fat percentage. These findings suggest that body fat percentage might be a promising parameter for explaining individual differences in thermophysiological responses.