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Recent bed rest results and countermeasure development at NASABedrest studies of normal subjects provide opportunities to understand physiologic responses to supine posture and inactivity. Furthermore, head-down tilt has been a valuable procedure to investigate adaptation to microgravity and development of countermeasures to maintain the health and well-being of humans during space-flight. Recent bedrest experiments at NASA have ranged in duration from a few hours to 17 weeks. Acute studies of 6 degrees head-down tilt indicate that elevation of capillary blood pressure from 28 to 34 mm Hg and increased capillary perfusion in tissues of the head cause facial and intracranial edema. Intracranial pressure increases from 2 to 17 mm Hg going from upright posture to 6 degrees head-down tilt. Microvessels of the head have a low capacity to constrict and diminish local perfusion. Elevation of blood and tissue fluid pressures/flow in the head may also explain the higher headward bone density associated with long-term head-down tilt. These mechanistic studies of head-down tilt, along with a better understanding of the relative stresses involved with upright posture and lower body negative pressure, have facilitated development of suitable physiologic countermeasures to maintain astronaut health during microgravity. Presently no exercise hardware is available to provide a blood pressure gradient from head to feet in space. However, recent studies in our laboratory suggest that treadmill exercise using a graded lower-body compression suit and 100 mmHg lower body negative pressure provides equivalent or greater physiologic stress than similar upright exercise on Earth. Therefore, exercise within a lower body negative pressure chamber may provide a cost-effective and simple countermeasure to maintain the cardiovascular and neuro-musculoskeletal systems of astronauts during long-duration flight.
Document ID
20050000394
Acquisition Source
Ames Research Center
Document Type
Reprint (Version printed in journal)
Authors
Hargens, A. R.
(NASA Ames Research Center Moffett Field, CA United States)
Date Acquired
August 22, 2013
Publication Date
January 1, 1994
Publication Information
Publication: Acta physiologica Scandinavica. Supplementum
Volume: 616
ISSN: 0302-2994
Subject Category
Life Sciences (General)
Distribution Limits
Public
Copyright
Other
Keywords
manned
short duration
Flight Experiment
NASA Center ARC
NASA Discipline Cardiopulmonary
NASA Discipline Musculoskeletal
Review, Tutorial
Review
STS Shuttle Project

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