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The hemodynamic effects of repeated bed rest exposure
H Sandler1, R L Popp, D C Harrison
1National Aeronautics and Space Administration, Cardiovascular Research Office, Ames Research Center, Moffett Field, CA.
Aviation, Space, and Environmental Medicine
|November 1, 1988
Summary
Cardiovascular deconditioning in active individuals after bed rest takes longer than three weeks to recover from, even with exercise. Mild exercise and ambulation do not prevent or accelerate recovery from bed rest-induced deconditioning.
Area of Science:
- Cardiovascular Physiology
- Human Physiology
- Exercise Physiology
Background:
- Bed rest leads to cardiovascular deconditioning, affecting hemodynamic responses.
- The recovery time and effectiveness of exercise interventions for deconditioning are not fully understood.
- Physically active individuals may experience unique deconditioning patterns.
Purpose of the Study:
- To investigate hemodynamic changes during lower-body negative pressure (LBNP) in physically active subjects before and after bed rest.
- To assess the efficacy of dynamic and isometric exercise during bed rest and reambulation in preventing or accelerating recovery.
- To determine the time course of cardiovascular recovery after bed rest.
Main Methods:
- Seven physically active subjects underwent stepwise LBNP (-20, -30, -40 mm Hg) before and after three 2-week bed rest periods.
- Bed rest periods were interspersed with 3-week ambulatory recovery intervals.
- Subjects performed daily dynamic (68% max O2) and isometric (21% max leg extension) exercises during bed rest and recovery.
Main Results:
- Heart rate (HR) and end-diastolic volume index (EDVI) showed the most significant changes during LBNP.
- HR increases during -40 mm Hg LBNP were substantially higher after bed rest (57.8%-75.5%) compared to pre-bed rest (13.3%-51.0%).
- Incomplete recovery was indicated by elevated HR responses even in pre-bed rest control periods; recovery took at least 3 weeks.
Conclusions:
- Cardiovascular deconditioning involves factors beyond plasma volume loss in active individuals.
- Full recovery to pre-bed rest cardiovascular state requires at least three weeks.
- The exercise protocols used did not counteract bed rest-induced deconditioning or accelerate recovery.