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Human muscle sympathetic nerve activity and plasma noradrenaline kinetics in spaceAstronauts returning from space have reduced red blood cell masses, hypovolaemia and orthostatic intolerance, marked by greater cardio-acceleration during standing than before spaceflight, and in some, orthostatic hypotension and presyncope. Adaptation of the sympathetic nervous system occurring during spaceflight may be responsible for these postflight alterations. We tested the hypotheses that exposure to microgravity reduces sympathetic neural outflow and impairs sympathetic neural responses to orthostatic stress. We measured heart rate, photoplethysmographic finger arterial pressure, peroneal nerve muscle sympathetic activity and plasma noradrenaline spillover and clearance, in male astronauts before, during (flight day 12 or 13) and after the 16 day Neurolab space shuttle mission. Measurements were made during supine rest and orthostatic stress, as simulated on Earth and in space by 7 min periods of 15 and 30 mmHg lower body suction. Mean (+/- S.E.M.) heart rates before lower body suction were similar pre-flight and in flight. Heart rate responses to -30 mmHg were greater in flight (from 56 +/- 4 to 72 +/- 4 beats min(-1)) than pre-flight (from 56 +/- 4 at rest to 62 +/- 4 beats min(-1), P < 0.05). Noradrenaline spillover and clearance were increased from pre-flight levels during baseline periods and during lower body suction, both in flight (n = 3) and on post-flight days 1 or 2 (n = 5, P < 0.05). In-flight baseline sympathetic nerve activity was increased above pre-flight levels (by 10-33 %) in the same three subjects in whom noradrenaline spillover and clearance were increased. The sympathetic response to 30 mmHg lower body suction was at pre-flight levels or higher in each subject (35 pre-flight vs. 40 bursts min(-1) in flight). No astronaut experienced presyncope during lower body suction in space (or during upright tilt following the Neurolab mission). We conclude that in space, baseline sympathetic neural outflow is increased moderately and sympathetic responses to lower body suction are exaggerated. Therefore, notwithstanding hypovolaemia, astronauts respond normally to simulated orthostatic stress and are able to maintain their arterial pressures at normal levels.
Document ID
20040088546
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Ertl, Andrew C.
(Vanderbilt University Medical Center Nashville, TN, United States)
Diedrich, Andre
Biaggioni, Italo
Levine, Benjamin D.
Robertson, Rose Marie
Cox, James F.
Zuckerman, Julie H.
Pawelczyk, James A.
Ray, Chester A.
Buckey, Jay C Jr
Lane, Lynda D.
Shiavi, Richard
Gaffney, F. Andrew
Costa, Fernando
Holt, Carol
Blomqvist, C. Gunnar
Eckberg, Dwain L.
Baisch, Friedhelm J.
Robertson, David
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
Funding Number(s)
CONTRACT_GRANT: 5P01 HL56693
CONTRACT_GRANT: 1U01HL53206
CONTRACT_GRANT: 1U01NS33460
CONTRACT_GRANT: M01 RR00095
Distribution Limits
Public
Copyright
Other
Keywords
STS-90 Shuttle Project
manned
NASA Discipline Cardiopulmonary
Non-NASA Center
short duration
Flight Experiment

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