Modulation of central sudomotor control by short-term heat acclimation as evidenced by frequency of sweat expulsions

Abstract

The purpose of this study was to examine changes in the control of sweating by heat acclimation by using frequency of sweat expulsion (Fsw), an index of central sudomotor activity. Eight healthy young volunteers underwent a six-day heat acclimation program [a total of 80-min exercise at 50% peak rate of oxygen consumption in the heat (36°C)]. In the days before and after the heat acclimation program, we examined the local sweating rate (SR) at the chest and forearm, Fsw and esophageal temperature (Tes) during whole body heating using a water-perfused suit. Heat acclimation decreased (P<0.01)the Tes thresholds for initiation of chest and forearm sweating. Heat acclimation did not change the slopes of the SR at either site or Fsw versus Tes during heating, but shifted the slopes to a lower Tes. Heat acclimation did not change the slopes of the SR at either site versus Fsw, and the SR values at a given Fsw were similar between before and after heat acclimation. These findings suggest that short-term heat acclimation modulates central sudomotor mechanisms, decreasing the temperature threshold for sweating. We did not find a significant change in the peripheral mechanism for sweating by the heat acclimation program.