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Microgravity and orthostatic intolerance: carotid hemodynamics and peripheral responses
P J Lacolley1, B M Pannier, J L Cuche
1Department of Internal Medicine, Hôpital Broussais, Paris, France.
The American Journal of Physiology
|February 1, 1993
Summary
Twenty-four hours of head-down tilt bed rest caused cardiovascular deconditioning, increasing blood pressure and total peripheral resistance. This response was blunted after lower body negative pressure, indicating altered cardiovascular regulation.
Area of Science:
- Cardiovascular Physiology
- Space Medicine
- Human Physiology
Background:
- Orthostatic intolerance is common after weightlessness.
- Head-down tilt bed rest simulates microgravity effects.
- Understanding cardiovascular deconditioning is crucial for spaceflight.
Purpose of the Study:
- To investigate cardiovascular deconditioning from 24-hour head-down tilt bed rest.
- To analyze the impact on orthostatic tolerance using lower body negative pressure.
- To identify changes in blood pressure, cardiac output, and vascular resistance.
Main Methods:
- Utilized a 24-hour ground-based model of bed rest with head-down tilt.
- Applied -40 mmHg lower body negative pressure to challenge cardiovascular homeostasis.
- Measured mean blood pressure, total peripheral resistance, cardiac output, heart rate, and plasma catecholamines.
Main Results:
- Bed rest increased mean blood pressure and total peripheral resistance.
- Plasma dopamine levels significantly increased post-bed rest.
- Lower body negative pressure revealed a blunted increase in total peripheral resistance after bed rest, unlike pre-bed rest responses.
Conclusions:
- 24-hour head-down tilt bed rest induces cardiovascular deconditioning.
- The ability to increase total peripheral resistance during orthostatic stress is impaired after bed rest.
- Further research is needed to explain the altered vascular response to deconditioning.