Document Detail


Head-down bed rest impairs vagal baroreflex responses and provokes orthostatic hypotension.
MedLine Citation:
PMID:  2347788     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
We studied vagally mediated carotid baroreceptor-cardiac reflexes in 11 healthy men before, during, and after 30 days of 6 degrees head-down bed rest to test the hypothesis that baroreflex malfunction contributes to orthostatic hypotension in this model of simulated microgravity. Sigmoidal baroreflex response relationships were provoked with ramped neck pressure-suction sequences comprising pressure elevations to 40 mmHg followed by serial R-wave-triggered 15-mmHg reductions to -65 mmHg. Each R-R interval was plotted as a function of systolic pressure minus the neck chamber pressure applied during the interval. Compared with control measurements, base-line R-R intervals and the minimum, maximum, range, and maximum slope of the R-R interval-carotid pressure relationships were reduced (P less than 0.05) from bed rest day 12 through recovery day 5. Baroreflex slopes were reduced more in four subjects who fainted during standing after bed rest than in six subjects who did not faint (-1.8 +/- 0.7 vs. -0.3 +/- 0.3 ms/mmHg, P less than 0.05). There was a significant linear correlation (r = 0.70, P less than 0.05) between changes of baroreflex slopes from before bed rest to bed rest day 25 and changes of systolic blood pressure during standing after bed rest. Although plasma volume declined by approximately 15% (P less than 0.05), there was no significant correlation between reductions of plasma volume and changes of baroreflex responses. There were no significant changes of before and after plasma norepinephrine or epinephrine levels before and after bed rest during supine rest or sitting.(ABSTRACT TRUNCATED AT 250 WORDS)
Authors:
V A Convertino; D F Doerr; D L Eckberg; J M Fritsch; J Vernikos-Danellis
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Journal of applied physiology (Bethesda, Md. : 1985)     Volume:  68     ISSN:  8750-7587     ISO Abbreviation:  J. Appl. Physiol.     Publication Date:  1990 Apr 
Date Detail:
Created Date:  1990-07-11     Completed Date:  1990-07-11     Revised Date:  2013-09-26    
Medline Journal Info:
Nlm Unique ID:  8502536     Medline TA:  J Appl Physiol (1985)     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  1458-64     Citation Subset:  IM; S    
Affiliation:
National Aeronautics and Space Administration, Space Center, Florida 32899.
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MeSH Terms
Descriptor/Qualifier:
Adult
Bed Rest / adverse effects*
Blood Pressure
Epinephrine / blood
Head
Heart Rate
Humans
Hypotension, Orthostatic / etiology*,  physiopathology
Male
Norepinephrine / blood
Plasma Volume
Posture*
Pressoreceptors / physiopathology*
Reflex
Vagus Nerve / physiopathology*
Grant Support
ID/Acronym/Agency:
HL-22296/HL/NHLBI NIH HHS
Chemical
Reg. No./Substance:
51-41-2/Norepinephrine; 51-43-4/Epinephrine

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


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