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Sweat loss during heat stress contributes to subsequent reductions in lower-body negative pressure tolerance.
MedLine Citation:
PMID:  22872657     Owner:  NLM     Status:  Publisher    
The contribution of sweating to heat stress-induced reductions in haemorrhagic tolerance is not known. This study tested the hypothesis that fluid loss due to sweating contributes to reductions in simulated haemorrhagic tolerance under heat stress conditions. Eight subjects (35±8 y; 77±5 kg) underwent a normothermic time control and two heat stress trials (randomized). Two heat stress trials were completed: A) with slow intravenous (IV) infusion of Lactated Ringers solution sufficient to offset sweat loss, or B) without intravenous infusion (Dehydration, DEH). Haemorrhage was simulated via progressive lower body negative pressure (LBNP) to pre-syncope after core body (intestinal) temperature was raised ~1.5°C using a water perfused suit or a normothermic time control period. LBNP tolerance was quantified via cumulative stress index. Middle cerebral artery blood velocity (transcranial Doppler) and mean blood pressure (Finometer®) were measured continuously. Relative changes in plasma volume were calculated from haematocrit and haemoglobin. Core body temperature increases and sweat loss (~1.6% body mass deficit) were similar (P>0.05) between heat stress trials. Slow IV infusion (1.2±0.3 L) prevented heat-induced reductions in plasma volume (IV: -0.6±6.1%; DEH: -6.6±5.1%, P=0.01). IV infusion improved LBNP tolerance (632±64 mm Hg x min) by ~20% when compared the DEH trial (407±117 mm Hg x min; P=0.01); yet, tolerance remained 44% lower in the IV trial relative to the time control normothermic trial (1138±183 mm Hg x min, P <0.01). These data indicate that although sweat-induced dehydration impairs simulated haemorrhagic tolerance, this impairment is secondary to the negative impact of heat stress itself.
Rebekah A I Lucas; Matthew S Ganio; James Pearson; Craig G Crandall
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-8-7
Journal Detail:
Title:  Experimental physiology     Volume:  -     ISSN:  1469-445X     ISO Abbreviation:  Exp. Physiol.     Publication Date:  2012 Aug 
Date Detail:
Created Date:  2012-8-8     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9002940     Medline TA:  Exp Physiol     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
1 University of Texas Southwestern Medical Center;
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