Document Detail

Muscle blood flow is reduced with dehydration during prolonged exercise in humans.
MedLine Citation:
PMID:  9824726     Owner:  NLM     Status:  MEDLINE    
1. The present study examined whether the blood flow to exercising muscles becomes reduced when cardiac output and systemic vascular conductance decline with dehydration during prolonged exercise in the heat. A secondary aim was to determine whether the upward drift in oxygen consumption (VO2) during prolonged exercise is confined to the active muscles. 2. Seven euhydrated, endurance-trained cyclists performed two bicycle exercise trials in the heat (35 C; 40-50 % relative humidity; 61 +/- 2 % of maximal VO2), separated by 1 week. During the first trial (dehydration trial, DE), they bicycled until volitional exhaustion (135 +/- 4 min, mean +/- s.e.m.), while developing progressive dehydration and hyperthermia (3.9 +/- 0.3 % body weight loss; 39.7 +/- 0.2 C oesophageal temperature, Toes). In the second trial (control trial), they bicycled for the same period of time while maintaining euhydration by ingesting fluids and stabilizing Toes at 38.2 +/- 0.1 C after 30 min exercise. 3. In both trials, cardiac output, leg blood flow (LBF), vascular conductance and VO2 were similar after 20 min exercise. During the 20 min-exhaustion period of DE, cardiac output, LBF and systemic vascular conductance declined significantly (8-14 %; P < 0.05) yet muscle vascular conductance was unaltered. In contrast, during the same period of control, all these cardiovascular variables tended to increase. After 135 +/- 4 min of DE, the 2.0 +/- 0.6 l min-1 lower blood flow to the exercising legs accounted for approximately two-thirds of the reduction in cardiac output. Blood flow to the skin also declined markedly as forearm blood flow was 39 +/- 8 % (P < 0.05) lower in DE vs. control after 135 +/- 4 min. 4. In both trials, whole body VO2 and leg VO2 increased in parallel and were similar throughout exercise. The reduced leg blood flow in DE was accompanied by an even greater increase in femoral arterial-venous O2 (a-vO2) difference. 5. It is concluded that blood flow to the exercising muscles declines significantly with dehydration, due to a lowering in perfusion pressure and systemic blood flow rather than increased vasoconstriction. Furthermore, the progressive increase in oxygen consumption during exercise is confined to the exercising skeletal muscles.
J González-Alonso; J A Calbet; B Nielsen
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Publication Detail:
Type:  Clinical Trial; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  The Journal of physiology     Volume:  513 ( Pt 3)     ISSN:  0022-3751     ISO Abbreviation:  J. Physiol. (Lond.)     Publication Date:  1998 Dec 
Date Detail:
Created Date:  1999-03-03     Completed Date:  1999-03-03     Revised Date:  2013-06-11    
Medline Journal Info:
Nlm Unique ID:  0266262     Medline TA:  J Physiol     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  895-905     Citation Subset:  IM; S    
Human Physiology Department, August Krogh Institute, University of Copenhagen, DK-2100 Copenhagen O,
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MeSH Terms
Blood Pressure / physiology
Body Temperature / physiology
Cardiac Output / physiology
Dehydration / physiopathology*
Exercise / physiology*
Forearm / blood supply
Leg / blood supply
Muscle, Skeletal / blood supply*
Oxygen Consumption / physiology
Regional Blood Flow / physiology
Vascular Resistance / physiology

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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