Document Detail


Hypotensive effect of push-pull gravitational stress occurs after autonomic blockade.
MedLine Citation:
PMID:  12794095     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
The "push-pull" effect denotes the reduced tolerance to +Gz (hypergravity) when +Gz stress is preceded by exposure to hypogravity, i.e., fractional, zero, or negative Gz. Previous studies have implicated autonomic reflexes as a mechanism contributing to the push-pull effect. The purpose of this study was to test the hypothesis that nonautonomic mechanisms can cause a push-pull effect, by using eye-level blood pressure as a measure of G tolerance. The approach was to impose control (30 s of 30 degrees head-up tilt) and push-pull (30 s of 30 degrees head-up tilt immediately preceded by 10 s of -15 degrees headdown tilt) gravitational stress after administration of hexamethonium (10 mg/kg) to inhibit autonomic ganglionic neurotransmission in four dogs. The animals were chronically instrumented with arterial and venous catheters, an ascending aortic blood flow transducer, ventricular pacing electrodes, and atrioventicular block. The animals were paced at 75 beats/min throughout the experiment. The animals were sedated with acepromazine and lightly restrained in lateral recumbency on a tilt table. After the onset of head-up tilt, the magnitude of the fall in eye-level blood pressure from baseline was -27.6 +/- 2.3 and -37.9 +/- 2.7 mmHg for the control and push-pull trials, respectively (P < 0.05). Cardiac output fell similarly in both conditions. Thus a push-pull effect attributable to a rise in total vascular conductance occurs when autonomic function is inhibited.
Authors:
Don D Sheriff
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Journal of applied physiology (Bethesda, Md. : 1985)     Volume:  95     ISSN:  8750-7587     ISO Abbreviation:  J. Appl. Physiol.     Publication Date:  2003 Jul 
Date Detail:
Created Date:  2003-06-09     Completed Date:  2004-02-02     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:  167-71     Citation Subset:  IM; S    
Affiliation:
Department of Exercise Science, The University of Iowa, Iowa City, Iowa 52242, USA.
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MeSH Terms
Descriptor/Qualifier:
Animals
Aorta / physiology
Autonomic Agents / pharmacology*
Blood Pressure / drug effects*,  physiology*
Cardiac Output / drug effects,  physiology
Cardiac Pacing, Artificial
Dogs
Ganglionic Blockers / pharmacology*
Hexamethonium / pharmacology*
Hypergravity*
Hypogravity*
Posture / physiology
Regional Blood Flow / physiology
Vascular Resistance / drug effects,  physiology
Ventricular Function
Grant Support
ID/Acronym/Agency:
HL-46314/HL/NHLBI NIH HHS
Chemical
Reg. No./Substance:
0/Autonomic Agents; 0/Ganglionic Blockers; 60-26-4/Hexamethonium

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


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