Characteristics of central sudomotor mechanism estimated by frequency of sweat expulsions.

Each of six male subjects was exposed during rest to at least ten different thermal environments (Ta, 22-44 degrees C; rh, 40%). Local sweat rates from both forearms were continuously recorded in a steady state of each exposure, using capacitance hygrometry. In the absence of spontaneous sweating, localized sweating was induced by intradermal administration of pilocarpine. Sweat expulsions synchronous at the two test areas were counted and their frequency (Fsw) was calculated. For each of additive and multiplicative combinations of Tcore (Tre, Tty) and Ts, the best combination for estimation of thermal input to the sudomotor center was determined using multiple regression analysis. Approximately 0.75Tre + 0.25Ts or 0.85Tty + 0.15Ts, and (Tre-36.33) (Ts-33.13) or (Tty-36.42) (Ts-32.24) were obtained for the additive and multiplicative combinations, respectively. The correlation coefficient (r) for the relationship of Fsw to the obtained best combination, either additive or multiplicative, and that of Fsw to Tb were almost comparable to each other. It is considered that Tb can be used as an approximation of thermal input and that the characteristics of frequency of sweat expulsion is a useful index for determining whether and how much the central sudomotor mechanism is involved in the change of sweat rate in response to various thermal and non-thermal stresses.