Accumulation of 2H2O in plasma and eccrine sweat during exercise-heat stress

Abstract

The purpose of this research was to characterize the movement of ingested water through body fluids, during exercise-heat stress. Deuterium oxide ((2)H(2)O) accumulation in plasma and eccrine sweat was measured at two sites (back and forehead). The exercise of 14 males was controlled via cycle ergometry in a warm environment (60 min; 28.7 degrees C, 51%rh). Subjects consumed (2)H(2)O (0.15 mg kg(-1), 99.9% purity) mixed in flavored, non-caloric, colored water before exercise, then consumed 3.0 ml kg(-1) containing no (2)H(2)O every 15 min during exercise. We hypothesized that water transit from mouth to skin would occur before 15 min. (2)H(2)O appeared rapidly in both plasma and sweat (P < 0.05), within 10 min of water consumption. The ratio (2)H(2)O/H(2)O (D:H) was 47.3-55.0 times greater in plasma than in back sweat at minutes 10, 20, and 30 (DeltaD:H relative to baseline). At elapsed minute 20, the mean rate of deuterium accumulation (DeltaD:H min(-1)) in plasma was 14.9 and 23.7 times greater than in forehead and back sweat samples, respectively. Mean (+/-SE) whole-body sweat rate was 1.04 +/- 0.05 L h(-1) and subjects with the greatest whole-body sweat rate exhibited the greatest peak deuterium enrichment in sweat (r(2) = 0.87, exponential function); the peak (2)H(2)O enrichment in sweat was not proportional (P > 0.05) to body mass, volume of the deuterium dose, or total volume of fluid consumed. These findings clarify the time course of fluid movement from mouth to eccrine sweat glands, and demonstrate considerable differences of (2)H(2)O enrichment in plasma versus sweat.

Appearance of D2O in Sweat after Oral and Oral-Intravenous Rehydration in Men

“…Because the eccrine sweat gland draws fluid from the interstitial compartment, perhaps the appearance of D 2 O in the plasma or serum may be used as an index of fluid bioavailability to the eccrine sweat gland when a person is not actively sweating. Although the fluid would be transported from the duct to the secretory coil before it is secreted onto the skin, it appears that this process may occur within a few minutes (3).…”

“…Armstrong et al (3) found that water ingested orally during exercise appears in sweat in as early as 10 minutes. We hypothesize that D 2 O will not appear in the sweat as quickly when an athlete is dehydrated and at rest during recovery from exercise in the heat but may be apparent within the first 20 minutes.…”

Transition duration of ingested deuterium oxide to eccrine sweat during exercise in the heat

“…Using previously published time estimates for fluid movement through various tissues in the body, we estimated that the minimum time duration required for ingested fluid to appear as sweat to be approximately three minutes. This is considerably less than the 10 min period currently reported in the literature (Armstrong, et al, 2010). Therefore, the purpose of this study was to test our theorized time estimate for water movement by identifying the initial enrichment of D 2 O in eccrine sweat following fluid ingestion during continuous exercise in the heat.…”

“…Only three studies (Armstrong, et al, 2010;Davis et al, 1985;Koulmann, et al, 1997) in the scientific literature have addressed this topic, and none were specifically designed to determine how rapidly ingested water starts to appear as sweat. For example, the seminal study by Armstrong et al (2010) determined fluid kinetics from ingestion to sweat secretion using deuterium oxide (D 2 O) enrichment during an hour of exercise in the heat.…”

“…For example, the seminal study by Armstrong et al (2010) determined fluid kinetics from ingestion to sweat secretion using deuterium oxide (D 2 O) enrichment during an hour of exercise in the heat. Their protocol limited sampling resolution to 10 min intervals and thus could not identify initial D 2 O enrichment in sweat as significant appearance was already apparent in the first sample at 10 min following ingestion.…”