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Influence of microgravity on astronauts' sympathetic and vagal responses to Valsalva's manoeuvreWhen astronauts return to Earth and stand, their heart rates may speed inordinately, their blood pressures may fall, and some may experience frank syncope. We studied brief autonomic and haemodynamic transients provoked by graded Valsalva manoeuvres in astronauts on Earth and in space, and tested the hypothesis that exposure to microgravity impairs sympathetic as well as vagal baroreflex responses. We recorded the electrocardiogram, finger photoplethysmographic arterial pressure, respiration and peroneal nerve muscle sympathetic activity in four healthy male astronauts (aged 38-44 years) before, during and after the 16 day Neurolab space shuttle mission. Astronauts performed two 15 s Valsalva manoeuvres at each pressure, 15 and 30 mmHg, in random order. Although no astronaut experienced presyncope after the mission, microgravity provoked major changes. For example, the average systolic pressure reduction during 30 mmHg straining was 27 mmHg pre-flight and 49 mmHg in flight. Increases in muscle sympathetic nerve activity during straining were also much greater in space than on Earth. For example, mean normalized sympathetic activity increased 445% during 30 mmHg straining on earth and 792% in space. However, sympathetic baroreflex gain, taken as the integrated sympathetic response divided by the maximum diastolic pressure reduction during straining, was the same in space and on Earth. In contrast, vagal baroreflex gain, particularly during arterial pressure reductions, was diminished in space. This and earlier research suggest that exposure of healthy humans to microgravity augments arterial pressure and sympathetic responses to Valsalva straining and differentially reduces vagal, but not sympathetic baroreflex gain.
Document ID
20040088547
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Cox, James F.
(Hunter Holmes McGuire Veterans Affairs Medical Center and Medical College of Virginia at Virginia Commonwealth University Richmond, Virginia, USA 23249)
Tahvanainen, Kari U O.
Kuusela, Tom A.
Levine, Benjamin D.
Cooke, William H.
Mano, Tadaaki
Iwase, Satoshi
Saito, Mitsuru
Sugiyama, Yoshiki
Ertl, Andrew C.
Biaggioni, Italo
Diedrich, Andre
Robertson, Rose Marie
Zuckerman, Julie H.
Lane, Lynda D.
Ray, Chester A.
White, Ronald J.
Pawelczyk, James A.
Buckey, Jay C Jr
Baisch, Friedhelm J.
Blomqvist, C. Gunnar
Robertson, David
Eckberg, Dwain L.
Roberton, D.
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: UO1HL-56417
Distribution Limits
Public
Copyright
Other
Keywords
Non-NASA Center
Flight Experiment
NASA Discipline Cardiopulmonary
short duration
manned
STS-90 Shuttle Project

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