Sweating responses and body temperatures during nocturnal sleep in humans

The changes in the central control of sweating were investigated in five sleeping subjects under neutral and warm conditions [operative temperature (To) = 30, 33, and 34 degrees C; dew-point temperature = 10 degrees C]. Esophageal (Tes) and mean skin (Tsk) temperatures, chest sweat rate (msw,1), and concomitant electroencephalographic data were recorded. Throughout the night, msw,1 was measured under a local thermal clamp of 38 degrees C. Results showed that the thermal environment exerted a strong influence on both the levels and the time patterns of body temperatures. Moreover, local sweating rate correlated positively with Tes, and this relationship varied according to sleep stages. For a given Tes level, there was a sleep stage-related gradation in msw,1 that was higher in slow-wave sleep (SWS) than in stage 1-2 and the lowest in rapid-eye-movement (REM) sleep. This is explained by a change in the excitability or the sensitivity of the thermoregulatory system. The msw,1 differences between stage 1-2 and SWS are accounted for by a decrease in the Tes threshold (Tset) for sweating while the slope of the msw,1-Tes relation remains unchanged. The lower msw,1 in REM sleep is explained by a lesser slope for the msw,1-Tes relation without any Tset change from stage 1-2.