Appearance of Ingested H sub 2 (18)O in Plasma and Sweat during Exercise-Heat Exposure

摘要

In an effort to study human water transport and eccrine sweat gland function, this investigation measured the rate of appearance of H2 Oxygen 18 in plasma and sweat. Four healthy males were exposed for 6 h to a hot, wet environment (37.1 C db, 31.3 C wb) and to intermittent cycle ergometer protocols. Baseline plasma (antecubital vein) and scraped sweat samples were collected (-30 to 0 min) prior to administration of 100 g of labelled water (84.7% Oxygen 16 , 15.3% Oxygen 18) via nasogastric tube at 0 min. Samples were analyzed using isotopic ratio mass spectrometry. The isotopic enrichment of baseline sweat samples were slightly greater than that of plasma samples. Peak enrichment (Oxygen 18/Oxygen 16 ratio) in plasma (range: 2.4908 - 2.7206 x .001) occurred at 21 - 28 min postdose and at 21 - 45 min postdose in sweat (range: 2.3089 - 2.6666 x .001). The Oxygen 18/Oxygen 16 ratio in plasma and sweat declined rapidly, then declined slowly for the remaining heat exposure. The appearance of H2 Oxygen 18 in sweat reflected taht of plasma; neither curve was significantly altered by exercise intensity, duration, or frequency. To our knowledge, this is the first stable isotope data to verify that ingested fluid is rapidly assimilated and becomes available for evaporative cooling during work in the heat.