Accession Number : ADA338074

Title :   Hypohydration and Thermoregulation in Cold Air.

Corporate Author : ARMY RESEARCH INST OF ENVIRONMENTAL MEDICINE NATICK MA

Personal Author(s) : O'Brien, Catherine ; Young, Andrew J. ; Sawka, Michael N.

PDF Url : ADA338074

Report Date : 1997

Pagination or Media Count : 5

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.

Descriptors :   *LOW TEMPERATURE, *TEMPERATURE CONTROL, *VASOCONSTRICTING, *HEAT STRESS(PHYSIOLOGY), TEMPERATURE, OSMOSIS, EXPOSURE(GENERAL), VOLUNTEERS, REDUCTION, TEMPERATURE GRADIENTS, LOW LEVEL, MALES, MEAN, HEAT, COLD WEATHER, HEAT BALANCE, SKIN(ANATOMY), BODY WEIGHT, BLOOD PLASMA, BLOOD VOLUME, BODY TEMPERATURE, PERSPIRATION, FINGERS.

Subject Categories : Thermodynamics
      Stress Physiology

Distribution Statement : APPROVED FOR PUBLIC RELEASE