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Drug effects on orthostatic intolerance induced by bedrest
J Vernikos1, M F Dallman, G Van Loon
1Life Science Division, Ames Research Center, NASA, Moffett Field, CA 94035.
Journal of Clinical Pharmacology
|October 1, 1991
Summary
Fludrocortisone effectively expanded plasma volume, aiding four subjects in tolerating a 1-hour stand test post-bedrest. This study explored pharmacological countermeasures for orthostatic intolerance.
Area of Science:
- Space Medicine
- Human Physiology
- Pharmacology
Background:
- Postflight orthostatic intolerance is a significant challenge for astronauts.
- Current countermeasures like salt and fluid loading have proven benefits.
- Alternative pharmacological approaches are needed for effective prevention.
Purpose of the Study:
- To evaluate fludrocortisone, dextroamphetamine, and atropine as countermeasures for post-bedrest orthostatic intolerance.
- To assess the effects of these agents on plasma volume and physiological responses during orthostatic stress.
Main Methods:
- Seven subjects with orthostatic intolerance underwent a 7-day head-down bedrest study.
- Fludrocortisone was administered to expand plasma volume and promote sodium retention.
- Dextroamphetamine and atropine were given before a 1-hour stand test.
Main Results:
- Fludrocortisone expanded plasma volume by 16% and induced sodium retention.
- Four of seven subjects successfully completed the 1-hour stand test.
- Enhanced and sustained heart rate, plasma norepinephrine, and PRA responses were observed.
Conclusions:
- Pharmacological countermeasures including fludrocortisone, dextroamphetamine, and atropine show promise in preventing post-bedrest orthostatic intolerance.
- Vasoconstriction and sustained heart rate appear to be key mechanisms for overcoming orthostatic stress.
- These findings support the development of targeted pharmacologic strategies for spaceflight and bedrest scenarios.