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Orthostatic stress is necessary to maintain the dynamic range of cardiovascular control in spaceIn the upright position, gravity fills the low-pressure systems of human circulation with blood and interstitial fluid in the sections below the diaphragm. Without gravity one pressure component in the vessels disappears and the relationship between hydrostatic pressure and oncotic pressure, which regulates fluid passage across the capillary endothelium in the terminal vascular bed, shifts constantly. The visible consequences of this are a puffy face and "bird" legs. The plasma volume shrinks in space and the range of cardiovascular control is reduced. When they stand up for the first time after landing, 30-50% of astronauts suffer from orthostatic intolerance. It remains unclear whether microgravity impairs cardiovascular reflexes, or whether it is the altered volume status that causes the cardiovascular instability following space flight. Lower body negative pressure was used in several space missions to stimulate the cardiovascular reflexes before, during and after a space flight. The results show that cardiovascular reflexes are maintained in microgravity. However, the astronauts' volume status changed in space, towards a volume-retracted state, as measurements of fluid-regulating hormones have shown. It can be hypothesized that the control of circulation and body fluid homeostasis in humans is adapted to their upright posture in the Earth's gravitational field. Autonomic control regulates fluid distribution to maintain the blood pressure in that posture, which most of us have to cope with for two-thirds of the day. A determined amount of interstitial volume is necessary to maintain the dynamic range of cardiovascular control in the upright posture; otherwise orthostatic intolerance may occur more often.
Document ID
20040112558
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Baisch, J. F.
(Institut fur Luft- und Raumfahrtmedizin, Deutsches Zentrum fur Luft- und Raumfahrt, Cologne, Germany)
Wolfram, G.
Beck, L.
Drummer, C.
Stormer, I.
Buckey, J.
Blomqvist, G.
Date Acquired
August 21, 2013
Publication Date
January 1, 2000
Publication Information
Publication: Pflugers Archiv : European journal of physiology
Volume: 441
Issue: 2-3 Suppl
ISSN: 0031-6768
Subject Category
Aerospace Medicine
Distribution Limits
Public
Copyright
Other
Keywords
manned
NASA Discipline Cardiopulmonary
Non-NASA Center
Flight Experiment
STS-90 Shuttle Project
short duration

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