Effect of a vapor barrier on rates of excretion of sweat solutes

¹ Physiology Branch, Environmental Protection Research Division, Quartermaster Research and Engineering Command, U.S. Army, Quartermaster Research and Engineering Center, Natick, Massachusetts

The effects of a vapor-impermeable barrier on rates of excretion of Na, Cl, K, true creatinine and ‘apparent’ creatinine from the arms of men during thermal sweating were determined by collecting sweat solutes simultaneously from both arms, one of which was enclosed in a polyethylene bag. The separate effects on rates of excretion of the higher local skin temperature (T_s) and relative humidity (RH) imposed by a vapor barrier were assessed by means of a thermoregulated arm-chamber. Wearing a vapor barrier resulted in a significantly decreased rate of excretion of K and an increased rate for both true and ‘apparent’ creatinine. The effect on ‘apparent’ creatinine was attributable entirely to the increased excretion of the fraction represented by true creatinine. Rates of excretion of Na and Cl were not significantly affected by the vapor barrier. Increased T_s, per se, resulted in higher excretion rates of Na, Cl, K, true creatinine and urea. Increased RH, per se, led to decreased excretion of Na, Cl, K and urea, but no effect on rate of excretion of true creatinine. The observed effect of a vapor barrier on excretion rates of these sweat solutes was therefore the net result of T_s and RH operating in opposite directions.