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Human muscle sympathetic neural and haemodynamic responses to tilt following spaceflightOrthostatic intolerance is common when astronauts return to Earth: after brief spaceflight, up to two-thirds are unable to remain standing for 10 min. Previous research suggests that susceptible individuals are unable to increase their systemic vascular resistance and plasma noradrenaline concentrations above pre-flight upright levels. In this study, we tested the hypothesis that adaptation to the microgravity of space impairs sympathetic neural responses to upright posture on Earth. We studied six astronauts approximately 72 and 23 days before and on landing day after the 16 day Neurolab space shuttle mission. We measured heart rate, arterial pressure and cardiac output, and calculated stroke volume and total peripheral resistance, during supine rest and 10 min of 60 deg upright tilt. Muscle sympathetic nerve activity was recorded in five subjects, as a direct measure of sympathetic nervous system responses. As in previous studies, mean (+/- S.E.M.) stroke volume was lower (46 +/- 5 vs. 76 +/- 3 ml, P = 0.017) and heart rate was higher (93 +/- 1 vs. 74 +/- 4 beats min(-1), P = 0.002) during tilt after spaceflight than before spaceflight. Total peripheral resistance during tilt post flight was higher in some, but not all astronauts (1674 +/- 256 vs. 1372 +/- 62 dynes s cm(-5), P = 0.32). No crew member exhibited orthostatic hypotension or presyncopal symptoms during the 10 min of postflight tilting. Muscle sympathetic nerve activity was higher post flight in all subjects, in supine (27 +/- 4 vs. 17 +/- 2 bursts min(-1), P = 0.04) and tilted (46 +/- 4 vs. 38 +/- 3 bursts min(-1), P = 0.01) positions. A strong (r(2) = 0.91-1.00) linear correlation between left ventricular stroke volume and muscle sympathetic nerve activity suggested that sympathetic responses were appropriate for the haemodynamic challenge of upright tilt and were unaffected by spaceflight. We conclude that after 16 days of spaceflight, muscle sympathetic nerve responses to upright tilt are normal.
Document ID
20040088545
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Levine, Benjamin D.
(Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas and the University of Texas Southwestern Medical Center at Dallas Dallas, TX 75231, United States)
Pawelczyk, James A.
Ertl, Andrew C.
Cox, James F.
Zuckerman, Julie H.
Diedrich, Andre
Biaggioni, Italo
Ray, Chester A.
Smith, Michael L.
Iwase, Satoshi
Saito, Mitsuru
Sugiyama, Yoshiki
Mano, Tadaaki
Zhang, Rong
Iwasaki, Kenichi
Lane, Lynda D.
Buckey, Jay C Jr
Cooke, William H.
Baisch, Friedhelm J.
Eckberg, Dwain L.
Blomqvist, C. Gunnar
Date Acquired
August 21, 2013
Publication Date
January 1, 2002
Publication Information
Publication: The Journal of physiology
Volume: 538
Issue: Pt 1
ISSN: 0022-3751
Subject Category
Aerospace Medicine
Distribution Limits
Public
Copyright
Other
Keywords
Non-NASA Center
STS-90 Shuttle Project
short duration
Flight Experiment
NASA Discipline Cardiopulmonary
manned

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