Document Detail

Heart rate and blood pressure responses to +Gz following varied-duration -Gz.
MedLine Citation:
PMID:  10685587     Owner:  NLM     Status:  MEDLINE    
BACKGROUND: The push-pull effect has been defined previously as decreased +Gz tolerance caused by previous baseline zero or -Gz exposure. Earlier work indicates that the delay in BP (BP) recovery during +Gz is a function of time at -G7, and is due to the lengthened time-course of sympathetically mediated peripheral vasoconstriction. HYPOTHESIS: The purpose of this study was to retrospectively determine whether heart rate (HR) varies with BP as duration at preceding -Gz increased. METHODS: Continuous ECG R-R interval data from 15 s of +2.25Gz after preceding 2, 5, 10, or 15 s at 2Gz obtained from previous experiments were analyzed and compared with the previously reported BP data. Repeated measures ANOVA and regression analyses were used to compare +2.25Gz HR responses after the four -Gz conditions and one control +2.25Gz condition. RESULTS: An initial rapid rise in HR was observed for all conditions with a consistent steady-state plateau achieved after the first 7 s of +2.25Gz. However, there were significant differences in mean HR attained during the +2.25Gz plateau for preceding 15 s -2.0 Gz vs. the control, 2, 5, and 10s -Gz conditions (109+/-1.1 vs. 102+/-1.8, 100+/-2.0, 97+/-1.1 and 101+/-1.1, bpm, respectively; p<0.05). CONCLUSIONS: HR, unlike BP, increases briskly across all preceding -Gz time conditions, adapting within the initial baroreflex-compensatory time frame typically expected for +Gz exposures. These results suggest there may be a threshold effect for HR response. Consequently, vasoconstrictor response is a critical adaptive mechanism during +Gz when preceded by long (>10 s) -Gz exposures.
L S Goodman; R D Banks; J D Grissett; P L Saunders
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Aviation, space, and environmental medicine     Volume:  71     ISSN:  0095-6562     ISO Abbreviation:  Aviat Space Environ Med     Publication Date:  2000 Feb 
Date Detail:
Created Date:  2000-03-02     Completed Date:  2000-03-02     Revised Date:  2004-11-17    
Medline Journal Info:
Nlm Unique ID:  7501714     Medline TA:  Aviat Space Environ Med     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  137-41     Citation Subset:  IM; S    
Defence and Civil Institute of Environmental Medicine, Aerospace Life Support Section, Toronto, Ontario, Canada.
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MeSH Terms
Adaptation, Physiological / physiology*
Aerospace Medicine*
Analysis of Variance
Blood Pressure / physiology*
Bradycardia / diagnosis,  etiology*,  physiopathology
Heart Rate / physiology*
Hypergravity / adverse effects*
Hypogravity / adverse effects*
Monitoring, Physiologic
Regression Analysis
Retrospective Studies
Time Factors
Vasoconstriction / physiology*

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

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