Hypohydration and Thermoregulation in Cold Air.
Abstract
Hypohydration and thermoregulation in cold air. J. App 1. Physiol. 84(1): 185-189, 1998.This study examined the effects of hypohydration on thermoregulation during cold exposure. In addition, the independent influences of hypohydration-associated hypertonicity and hypovolemia were investigated. Nine male volunteers were monitored for 30 min at 250C, then for 120 min at 70C, under three counterbalanced conditions: euhydration (Eu), hypertonic hypohydration (HH), and isotonic hypohydration (IH). Hypohydration was achieved 12 h before cold exposure by inducing sweating (HH) or by ingestion of flirosemide (IH). Body weight decrease (4.1 _ 0.2%) caused by hypohydration was similar for HH and IH, but differences (P < 0.05) were found between HH and IH in plasma osmolality (292 t 1 vs. 284 % 1 mosmol/kgH2O) and plasma volume reduction (-8 % 2 vs. -1813%). Heat debt (349 1 14 among) did not differ (P> 0.05) among trials. Mean skin temperature decreased throughout cold exposure during Eu but plateaued alter 90 min during HH and IH. Forearm- finger temperature gradient tended (P = 0.06) to be greater during Eu (10.0 1 0.70C) than during HH or III (8.9 1 0.70C). This suggests weaker vasoconstrictor tone during hypohydra- tion than during Eu. Final mean skin temperature was higher for HH than for Eu or IH (23.5 1 0.3, 22 6 _ 0 4 and 22.9 1 0.30C, respectively), and insulation was lower on HH than on IH (0.13 1 0.01 vs. 0.15 1 0.01C.W-1.m-2 respec tively), but not with Eu (0.H 1 0.010C.W-'.m-2). This provides some evidence that hypertonicity impairs the vasoconstrictor response to cold. Although mild hypohydration did not affect body heat balance during 2-h whole body exposure to moderate cold, hypohydration-associated hypertonicity may have subtle effects on vasoconstriction that could become important during a more severe cold exposure.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1997
- Accession Number
- ADA338074
Entities
People
- Andrew J Young
- Catherine O'brien
- Michael N. Sawka
Organizations
- United States Army Research Institute of Environmental Medicine