Document Detail

Ventilatory responses to exercise and hypercapnia following 18 days of head-down rest.
MedLine Citation:
PMID:  19378912     Owner:  NLM     Status:  MEDLINE    
INTRODUCTION: The effects of head-down rest (HDR) and microgravity on cardiovascular control have been widely studied; however, their effects on ventilatory control are less clear. An increased ventilatory response to exercise and/or to hypercapnia (HCVR) could cause significantly increased ventilatory demand and/or dyspnea, and thus limit the ability of flight crew to perform high-intensity exercise during or after spaceflight. Based on limited previous studies, we hypothesized that the ventilatory response to exercise would be increased, while the HCVR would be decreased after HDR. METHODS: In 21 healthy subjects, ventilatory responses to submaximal exercise and to hypercapnia were tested before and immediately after 18 d of HDR. Subjects were randomly assigned to either daily supine cycle exercise (Exercise group; N = 14, 2 women) or no exercise (Rest group; N = 7, 1 woman) during HDR. RESULTS: The exercise ventilatory response (DeltaV(E)/DeltaV(CO2)) and the HCVR were unchanged following HDR in both groups. However, ventilation was significantly elevated after HDR at rest, during submaximal exercise, and while breathing 6% CO2. End-tidal P(CO2) was significantly reduced at rest, during submaximal exercise, and while breathing 3% CO2, indicating a decrease in the CO2 set point. DISCUSSION: Although HDR had no effect on the ventilatory responses to exercise and hypercapnia, the CO2 set point appeared to be reduced, suggesting an increase in drive to breathe that occurred regardless of whether or not subjects undertook exercise during HDR. These preliminary results indicate that further study of the effects of HDR on ventilatory control is warranted.
Helen E Wood; Benjamin D Levine; Tony G Babb
Publication Detail:
Type:  Journal Article; Randomized Controlled Trial; Research Support, N.I.H., Extramural; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Aviation, space, and environmental medicine     Volume:  80     ISSN:  0095-6562     ISO Abbreviation:  Aviat Space Environ Med     Publication Date:  2009 Apr 
Date Detail:
Created Date:  2009-04-21     Completed Date:  2009-06-02     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  7501714     Medline TA:  Aviat Space Environ Med     Country:  United States    
Other Details:
Languages:  eng     Pagination:  395-9     Citation Subset:  IM; S    
Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, University of Texas Southwestern Medical Center-Dallas, Dallas, TX 75231, USA.
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MeSH Terms
Carbon Dioxide / metabolism
Exercise / physiology*
Exercise Test
Head-Down Tilt / physiology*
Hypercapnia / physiopathology
Pulmonary Ventilation / physiology*
Space Flight
Weightlessness Simulation
Grant Support
Reg. No./Substance:
124-38-9/Carbon Dioxide

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

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