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Aerobic Fitness Does Not Contribute to Prediction of Orthostatic IntoleranceSeveral investigations have suggested that orthostatic tolerance may be inversely related to aerobic fitness (VO (sub 2max)). To test this hypothesis, 18 males (age 29 to 51 yr) underwent both treadmill VO(sub 2max) determination and graded lower body negative pressures (LBNP) exposure to tolerance. VO(2max) was measured during the last minute of a Bruce treadmill protocol. LBNP was terminated based on pre-syncopal symptoms and LBNP tolerance (peak LBNP) was expressed as the cumulative product of LBNP and time (torr-min). Changes in heart rate, stroke volume cardiac output, blood pressure and impedance rheographic indices of mid-thigh-leg initial accumulation were measured at rest and during the final minute of LBNP. For all 18 subjects, mean (plus or minus SE) fluid accumulation index and leg venous compliance index at peak LBNP were 139 plus or minus 3.9 plus or minus 0.4 ml-torr-min(exp -2) x 10(exp 3), respectively. Pearson product-moment correlations and step-wise linear regression were used to investigate relationships with peak LBNP. Variables associated with endurance training, such as VO(sub 2max) and percent body fat were not found to correlate significantly (P is less than 0.05) with peak LBNP and did not add sufficiently to the prediction of peak LBNP to be included in the step-wise regression model. The step-wise regression model included only fluid accumulation index leg venous compliance index, and blood volume and resulted in a squared multiple correlation coefficient of 0.978. These data do not support the hypothesis that orthostatic tolerance as measured by LBNP is lower in individuals with high aerobic fitness.
Document ID
19970028935
Acquisition Source
Ames Research Center
Document Type
Reprint (Version printed in journal)
Authors
Convertino, Victor A.
(Bionetics Corp. Moffett Field, CA United States)
Sather, Tom M.
(Bionetics Corp. Moffett Field, CA United States)
Goldwater, Danielle J.
(Bionetics Corp. Cocoa Beach, FL United States)
Alford, William R.
(Bionetics Corp. Cocoa Beach, FL United States)
Date Acquired
August 17, 2013
Publication Date
January 1, 1986
Publication Information
Publication: Medicine and Science in Sports and Exercise
Publisher: American College of Sports Medicine
Volume: 18
Issue: 5
ISSN: 0195-9131
Subject Category
Man/System Technology And Life Support
Report/Patent Number
NAS 1.26:204456
NASA-CR-204456
Accession Number
97N72331
Funding Number(s)
CONTRACT_GRANT: NCA2-OR745-911
CONTRACT_GRANT: NGT-03-002-802
Distribution Limits
Public
Copyright
Public Use Permitted.
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