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Drug effects on orthostatic intolerance induced by bedrestEffective and practical preventive procedures for postflight orthostatic intolerance are highly desirable. The current practice of attempts to expand plasma volume by ingestion of salt and fluids before reentry has proven benefits. This study evaluated alternative options using fludrocortisone (F) to expand plasma volume (PV), dextroamphetamine (Dex) to enhance norepinephrine (NE) release, and atropine (A) to reduce the effects of vagal stimulation. Seven subjects with proven post-bedrest orthostatic intolerance returned for a 7-day 6-deg head-down bedrest study. F (0.2 mg) was given at 8:00 AM and 8:00 PM the day before and 8:00 AM the day the subjects got out of bed (2 hours before standing). PV was measured before and 1 hour after the last dose of F. Dex (5 mg) and A (0.8 mg) were then taken orally 1 hour before the stand test. F expanded PV by 16 percent and caused sodium retention. Four of the 7 subjects stood for 1 hour post-bedrest and heart rate, plasma NE and plasma renin responses to standing were greatly enhanced and sustained. Although there was a narrowing of pulse pressure, the ability to overcome orthostatic intolerance with these countermeasures was largely due to vasoconstriction and sustained high heart rate.
Document ID
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Vernikos, J.
(NASA Ames Research Center Moffett Field, CA, United States)
Dallman, M. F.
(California Univ. San Francisco, United States)
Van Loon, G.
(Billings Clinic MN, United States)
Keil, L. C.
(NASA Ames Research Center Moffett Field, CA, United States)
Date Acquired
August 15, 2013
Publication Date
October 1, 1991
Publication Information
Publication: Journal of Clinical Pharmacology
Volume: 31
Issue: 10
ISSN: 0091-2700
Subject Category
Aerospace Medicine
Accession Number
Distribution Limits

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