Abstract
In healthy male subjects, skin temperature, sweat rate, and skin blood flow of the face were measured in a warm climate of 40°C-50% (rh) . The subjects sat on a chair fixed on a tilting table. Twenty min after their esophageal (Tes) and tympanic (Tty) temperatures reached steady states, the subjects were tilted to a supine sitting position and maintained for 20 min. After this period, they were returned to the former upright sitting position for another 20 min. In the supine sitting position, Tes, Tty and heart rate decreased but blood pressure did not change. Forehead skin temperature and skin blood flow, measured by laser-Doppler flowmetry, increased but sweat rate of the forehead decreased in the supine sitting position. After the body posture was returned to the upright sitting position, all these parameters returned to the previous levels. The reduction of sweat rate of the face may be explained by an inhibition of sweat gland activity by the so-called skin pressure reflex, which may contribute to the reduction of efficiency of the selective brain cooling in supine subjects.
