Document Detail


Supine cycling plus volume loading prevent cardiovascular deconditioning during bed rest.
MedLine Citation:
PMID:  20223994     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
There are two possible mechanisms contributing to the excessive fall of stroke volume (and its contribution to orthostatic intolerance) in the upright position after bed rest or spaceflight: reduced cardiac filling due to hypovolemia and/or a less distensible heart due to cardiac atrophy. We hypothesized that preservation of cardiac mechanical function by exercise training, plus normalization of cardiac filling with volume infusion, would prevent orthostatic intolerance after bed rest. Eighteen men and three women were assigned to 1) exercise countermeasure (n=14) and 2) no exercise countermeasure (n=7) groups during bed rest. Bed rest occurred in the 6 degrees head-down tilt position for 18 days. The exercise regimen was prescribed to compensate for the estimated cardiac work reduction between bed rest and ambulatory periods. At the end of bed rest, the subjects were further divided into two additional groups for post-bed rest testing: 1) volume loading with intravenous dextran to normalize cardiac filling pressure and 2) no volume loading. Dextran infusion was given to half of the exercise group and all of the sedentary group after bed rest, leading ultimately to three groups: 1) exercise plus volume infusion; 2) exercise alone; and 3) volume infusion alone. Exercise training alone preserved left ventricular mass and distensibility as well as upright exercise capacity, but lower body negative pressure (LBNP) tolerance was still depressed. LBNP tolerance was maintained only when exercise training was accompanied by dextran infusion. Dextran infusion alone following bed rest without exercise maintained neither orthostatic tolerance nor upright exercise capacity. We conclude that daily supine cycle exercise sufficient to prevent cardiac atrophy can prevent orthostatic intolerance after bed rest only when combined with plasma volume restoration. This maintenance of orthostatic tolerance was achieved by neither exercise nor dextran infusion alone. Cardiac atrophy and hypovolemia are likely to contribute independently to orthostatic intolerance after bed rest.
Authors:
Shigeki Shibata; Merja Perhonen; Benjamin D Levine
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Publication Detail:
Type:  Journal Article; Randomized Controlled Trial; Research Support, N.I.H., Extramural; Research Support, U.S. Gov't, Non-P.H.S.     Date:  2010-03-11
Journal Detail:
Title:  Journal of applied physiology (Bethesda, Md. : 1985)     Volume:  108     ISSN:  1522-1601     ISO Abbreviation:  J. Appl. Physiol.     Publication Date:  2010 May 
Date Detail:
Created Date:  2010-05-05     Completed Date:  2010-08-12     Revised Date:  2013-10-24    
Medline Journal Info:
Nlm Unique ID:  8502536     Medline TA:  J Appl Physiol (1985)     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1177-86     Citation Subset:  IM    
Affiliation:
Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, and University of Texas Southwestern Medical Center at Dallas, 7232 Greenville Ave., Suite 435, Dallas, TX 75231, USA.
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MeSH Terms
Descriptor/Qualifier:
Atrophy
Bed Rest / adverse effects*
Bicycling*
Blood Volume
Cardiovascular Deconditioning*
Combined Modality Therapy
Compliance
Dextrans / administration & dosage*
Exercise Test
Exercise Tolerance
Female
Head-Down Tilt / adverse effects*
Hemodynamics
Humans
Hypovolemia / etiology,  physiopathology,  prevention & control
Infusions, Intravenous
Lower Body Negative Pressure
Male
Myocardium / pathology
Orthostatic Intolerance / etiology,  pathology,  physiopathology,  prevention & control*
Plasma Substitutes / administration & dosage*
Supine Position*
Time Factors
Treatment Outcome
Ventricular Function, Left
Ventricular Pressure
Grant Support
ID/Acronym/Agency:
RR-00633/RR/NCRR NIH HHS
Chemical
Reg. No./Substance:
0/Plasma Substitutes; 9004-54-0/Dextrans
Comments/Corrections

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


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