Body posture affects the sudomotor outflow via high central mechanism for thermoregulation

Abstract

Skin pressure affects sweating activity via spinal reflex. It is also observed that the change in body posture may alter sweating function. However, this alteration is explained largely by the spinal mechanism. In the present study, we tested the hypothesis that change in body posture may also affect the higher central mechanism for thermoregulation. Each of 10 young healthy subjects assumed an upright sitting or a supine position for 60 min under a hot environment of ambient temperature at 40°C and relative humidity at 40%. Local sweat rates, tympanic temperature, skin temperatures were recorded. Local sweat rate was measured on forearm, chest and thigh using a ventilated capsule method. Sweat expulsions were identified on the sweat rate curves, and their rate was analyzed for measuring central sudomotor outflow. Mean body temperature was calculated as an index of thermal input to central integrating mechanism. The relationship of the rate of sweat expulsions to mean body temperature indicated that the slope of the regression line was significantly increased following the change of posture from the sitting to the supine position. Meanwhile, the intercept of the regression line for the abscissa was not significantly different. The results suggest that the gain of central integrating mechanism for thermal sweating was altered by the change in body posture. It is assumed that the signals arising from circulatory system or from vestibular system modified the activity of central integrating mechanism. [J Physiol Sci. 2007;57 Suppl:S179]