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Adaptation to repeated presyncopal lower body negative pressure exposures
J T Lightfoot1, S Febles, S M Fortney
1Department of Physical Education and Dance, University of Tennessee, Knoxville.
Aviation, Space, and Environmental Medicine
|January 1, 1989
Summary
The body can adapt to repeated central hypovolemia, a simulated blood volume loss. Daily exposure to lower body negative pressure (LBNP) increased tolerance, indicating adaptation to this stressor.
Area of Science:
- Physiology
- Human Adaptation
- Cardiovascular Regulation
Background:
- Chronic stressors like exercise and heat exposure induce physiological adaptations.
- The body's ability to adapt to repeated central hypovolemia remains largely unexplored.
- Central hypovolemia can be simulated using lower body negative pressure (LBNP).
Purpose of the Study:
- To investigate whether repeated exposure to a central hypovolemic stressor alters tolerance.
- To determine if daily presyncopal symptom-limited lower body negative pressure (PSL-LBNP) exposures enhance LBNP tolerance.
Main Methods:
- Six subjects underwent daily PSL-LBNP exposures for nine consecutive days, with a two-day break.
- Tolerance was assessed using a cumulative stress index (CSI) and LBNP levels.
- Cardiovascular responses, including mean arterial pressure, heart rate, and rate-pressure product, were monitored.
Main Results:
- LBNP tolerance significantly increased by 47% by the fifth PSL-LBNP exposure.
- No further significant improvements in tolerance were observed after the fifth exposure.
- Maximum heart rates and rate-pressure product increased significantly from Day 1 after repeated exposures, while mean arterial pressure remained unchanged.
Conclusions:
- The human body demonstrates adaptation to repeated central hypovolemia simulated by PSL-LBNP.
- Adaptation may involve enhanced compensatory mechanisms or a reset of the presyncopal threshold.
- These findings highlight the plasticity of cardiovascular regulation in response to hypovolemic stress.