THE EFFECT OF AN IMPERMEABLE VAPOR BARRIER ON ELECTROLYTE AND NITROGEN CONCENTRATIONS IN SWEAT1

When environmental temperatures are high, 80 to 90 per cent of the total water, sodium, and chloride, and 25 to 50 per cent of the losses of potassium, calcium, magnesium, and nitrogen may occur in the sweat (1, 2). Failure to measure these losses may lead to serious errors in balance studies. Although dermal water loss can ' be quite accurately measured in both acute and prolonged studies, this is not true of sweat electrolytes and nitrogen. Even in metabolic balance studies where the subject's daily activities are rigidly controlled, the accurate collection of all body sweat solutes by repeated body washings presents obvious difficul-ties. Conn and Louis (3) and Johnson, Pitts, and Consolazio (4) have assumed that the dermal losses are equal to the intake-(urine plus fecal losses). This method, however, disregards any daily posi-tive or negative balances of these substances which may occur. The simplest method involves the collection of a local sweat sample, measure-ment of the solute concentration, and determination of the total solute content from the concentration and the totali sweat loss. This method assumes that the local sample is representative of the total body sweat and that the technique of collection does not alter the true solute concentrations. Pre-vious investigations (5, 6, 7, 8) and data from this Laboratory (7) indicate that neither of these as-sumptions is correct. In general, previous studies (5, 6, 7, 8, 9) indicate that the chloride, nitrogen, and lactic acid concentrations of arm sweat col-lected under an impermeable barrier, are higher than the concentrations of these solutes in total body sweat. Mickelsen and Keys (6) have shown that the concentrations of chloride ion, urea, an