The clinical thermoregulatory sweat test induces maximal sweating

Although thermoregulatory sweat testing is commonly used to assess the autonomic nervous system, the power of this stimulus to induce sweating has not been studied. In 8 healthy male subjects, the authors quantitated sweat rates, core temperature, heart rate, and blood pressure during clinical thermoregulatory sweat testing, a separate exercise protocol, and with exercise added to thermal conditions. The authors found that (1) the addition of exercise to the thermal environment produced no further increase in sweat rate (3,841+/-948 versus 3,888+/-866 nl/mn - cm2); (2) maximum sweat rates closely corresponded to the theoretical maximum (6,000 nl/mn - cm2) derived from single gland studies; (3) sweat rates vary across subjects, but are similar across sites in any one individual; (4) core temperature rise is a major determinant of cardiovascular load in both thermal and exercise settings; (5) blood pressure decreased 28/11 mm Hg during thermal load, but increased 26/10 mm Hg with exercise, in agreement with current understanding of muscle and skin vascular physiology. The authors conclude that clinical thermoregulatory testing conditions produce maximum sweat rates in humans.