Age and sex difference in response to short exposure to extreme dry heat.

Sixty volunteers, 33 males and 27 females (18-63 yr), were divided according to age and sex. They were exposed for 10 min to extreme dry heat: 80-90 degrees C dry bulb temperature and 3-4% relative humidity. Their rectal temperature, skin temperature at eight different points, weight, and heart rate were recorded prior to and immediately following the exposure. A mean rise of only 0.5 degrees C in rectal temperature was recorded following exposure as compared to a mean rise of 5.2 degrees C in mean weighted skin temperature (MWST). Female subjects showed a significantly higher rise in MWST than the male subjects. Similarly, a significantly higher rise in MWST was observed in elderly male subjects as compared to the youngest male group (P less than 0.05). The differences in MWST possibly resulted from differences in mean skin blood flow causing differences in skin conductance. Large individual variation in heat response was recorded in rectal temperature, as well as in weighted skin temperatures. The increase in skin temperature during the first 10 min of exposure to extreme dry heat may serve as an indicator for heat tolerance time, and may help predicting heatstroke susceptible individuals.