Publication Abstracts

Plasma Sodium-Osmotic Dissociation and Hormonal Interaction with Drinking-Induced Hypervolemia at 2800 m Altitude

J. E. Greenleaf, Ph.D., H. Hinghofer-Szalkay, M.D., A. Rössler, M.S., P. A. Farrell, Ph.D., J. L. Loomis, M.S., M. J. Fedele, M.S., J. West, M.S., and S. A. Cowell, B.S.
Aviat Space Environ Med 2001; 72:522-8

Abstract

Purpose: To study hormonal factors that may account for the dissociation between beverage -induced plasma sodium p[Na⁺] and osmotic p[Osm] concentrations that appear to refute the high theoretical correlation between p[Na⁺] and p[Osm]. Methods: Ten men (24 ± SD 3 yr of age) sat reclining (head up) for 12 h in a chamber (21-23°C dry bulb, 25-33% relative humidity) at 2800 m (9184 ft, 539 mm Hg) altitude (ALT), and at 321 m (1053 ft, 732 mm Hg) on the ground (GND). During 1000-1030 hours they consumed 3 fluids (12 ml · kg^-1, (Chi macr) = 948 ml · d^-1) with large differences in sodium and osmotic contents: AstroAde (AA) with 185 mEq · L^-1 Na⁺ and 283 mOsm · kg^-1, Performance 1 ™ (Shaklee) (P1) with 22 mEq · L^-1 Na⁺ and 365 mOsm · kg^-1, or H₂O at ALT; and only H₂O on the GND. Results: After drinking: plasma volume (PV) increased at 1200 hours by 8.3% (p < 0.05) with AA but was not significantly (NS) changed in the other sessions ((Chi macr)(Delta) = +0.9%, range -0.9 to 2.8%); p[Na⁺] and p[Osm] were unchanged. Urinary rates and free-water clearances were attenuated with AA and P1 vs. those with H₂O. Correlations between and among p[Na⁺] and p[Osm] suggest that the pNa⁺ ion is more tightly controlled than pOsm; and that there was no clear hormonal response that could account for this dissociation from theoretical considerations. Conclusions: There is significant dissociation between plasma sodium and osmotic concentrations after fluid intake. Induction and maintenance of hypervolemia requires increased (near isotonic) drink Na⁺ osmols rather than increased non-ionic osmols.

Keywords: flight fatigue, fluid intake, flight, stress.

Information on subscribing, and on obtaining copies of an article or of an entire issue.

Table of Contents for Volume 72, Number 6 of the ASME journal.