A modified,local sweat collector for warm and humid conditions

Summary The purpose of this study was to modify a previously described local sweat collector to facilitate the investigation of sweat rate and composition in a warm (30°C) and humid (relative humidity 80%) environment. The adherence of the collector to the skin was improved and a pouch was appended at the lower end of the collector. The limitations of the closed collector were examined by comparing the local sweat rate and the quantity of electrolyte excreted in sweat with those obtained using a second collector with a wide opening (to permit free evaporation) and by changes in the body mass. Eight subjects performed exercise on a cycle ergometer consisting of four equal periods of 15 min each, at 60% maximal oxygen consumption, with a rest of 5 min between each period. The sweat produced on a local skin area (85 cm², upper posterior thorax region) was collected at the end of each period, before measuring the body mass on a sensitive (±1 g) platform balance. The mean local sweat rate [2.61 (SEM 0.19) Mg-CM^–2. min^-1] was 2.4 times greater than the pro-rated whole body mass loss but the two were strongly correlated (r=0.82,P<0.01). Compared to the open collector, the greater quantity of electrolyte excreted into the closed collector would suggest that the conditions which prevailed in the closed collector, such as a higher local skin temperature, may have affected the function of the sweat gland. This method enabled the efficiency of local sweat evaporation to be assessed by measuring the difference between sweat volume collected in the open and in the closed collectors. Recovery of water volumes at rest indicated that no contamination and no apparent leakage occurred. This improved sweat collector is suitable for obtaining clean local sweat samples of up to 6 ml, and for measuring the sweat composition and also sweat rate during exercise in warm and humid conditions.