Document Detail


Female exposure to high G: chronic adaptations of cardiovascular functions.
MedLine Citation:
PMID:  9737759     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
INTRODUCTION: Exposure to microgravity is associated with increased leg venous compliance and reductions in cardiac output, baroreflex functions, and tolerance to orthostatism. However, the effects of chronic exposure to high-G environments are unknown. In addition, there is evidence that females have lower orthostatic tolerance than males, although the underlying mechanisms are unclear. Therefore, we tested the hypotheses that high-G training will enhance baroreflex and orthostatic functions and that females will demonstrate similar adaptations compared with males. METHODS: Calf venous compliance, baroreflex function, and orthostatic performance were measured in six men and seven women before and after repeated exposures on the centrifuge (G-training) for 4 wk, 3 times/wk, with gradual levels of G starting with +3 Gz without G-suit protection during week 1 and advancing to +9 Gz with G-suit protection by the end of week 4. Calf venous compliance was measured by occlusion plethysmography using impedance rheographic recordings of volume change. Baroreflex function was assessed from beat-by-beat changes in heart rate (HR) and mean arterial pressure (MAP) that were measured before, during, and after a Valsalva maneuver strain at 30 mmHg expiratory pressure. The orthostatic performance of reflex responses was assessed from beat-by-beat changes in HR, MAP, stroke volume (SV), cardiac output (Q; by impedance plethysmography), and systemic peripheral resistance during the last 10 cardiac beats of a 4-min squat position and during the initial 10 cardiac beats in a standing position. RESULTS: G-training increased calf compliance in both men and women. SV and Q were increased during the squat-to-stand test in the males, but not in the females, following G-training and provided protection against the development of acute hypotension in the men. CONCLUSIONS: G-training caused adaptations in orthostatic functions opposite to those observed following exposure to microgravity environments. However, adaptations to G-training were limited in females, a finding that may provide a physiological basis for their lower simulated combat tracking performance during simulated aerial combat maneuvers compared with males.
Authors:
V A Convertino; L D Tripp; D A Ludwig; J Duff; T L Chelette
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Aviation, space, and environmental medicine     Volume:  69     ISSN:  0095-6562     ISO Abbreviation:  Aviat Space Environ Med     Publication Date:  1998 Sep 
Date Detail:
Created Date:  1998-11-12     Completed Date:  1998-11-12     Revised Date:  2007-11-15    
Medline Journal Info:
Nlm Unique ID:  7501714     Medline TA:  Aviat Space Environ Med     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  875-82     Citation Subset:  IM; S    
Affiliation:
Clinical Science Division, Armstrong Laboratory, Brooks Air Force Base, TX 78235-5117, USA.
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MeSH Terms
Descriptor/Qualifier:
Adaptation, Physiological / physiology*
Adult
Aerospace Medicine*
Baroreflex / physiology*
Compliance
Female
Hemodynamics / physiology
Humans
Hypergravity / adverse effects*
Hypotension, Orthostatic / etiology,  physiopathology*
Inservice Training
Leg / blood supply*
Male
Military Personnel / education
Plethysmography, Impedance
Sex Characteristics*
Valsalva Maneuver / physiology
Vascular Resistance / physiology*

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


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