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Influence of Microgravity on Arterial Baroreflex Responses Triggered by Valsalva's ManeuverWhen astronauts return to Earth and stand upright, their heart rates may speed inordinately, their blood pressures may fall, and some returning astronauts may even faint. Since physiological adjustments to standing are mediated importantly by pressure-regulating reflexes (baroreflexes), we studied involuntary (or autonomic) nerve and blood pressure responses of astronauts to four, 15-second periods of 15- and 30-mmHg straining (Valsalva'.~ maneuver). We measured the electrocardiogram, finger blood pressure, respiration, and muscle sympathetic nerve activity in four healthy male astronauts before and during the 16-day Neurolab Space Shuttle mission. We found that although microgravity provoked major autonomic changes, no astronaut experienced fainting symptoms after the mission. Blood pressure fell more during straining in space than on Earth (the average reduction of systolic pressure with 30-mmHg straining was 49 mmHg during and 27 mmHg before the mission). However, the increases of muscle sympathetic nerve activity that were triggered by straining were also larger in space than on Earth. As a result, the gain of the sympathetic baroreflex, taken as the total sympathetic nerve response divided by the maximum pressure reduction during straining, was the same in space as on Earth. In contrast, heart rate changes, which are mediated by changes of vagus nerve activity, were smaller in space. This and earlier research suggest that exposure to microgravity augments blood pressure and sympathetic adjustments to Valsalva straining and differentially reduces vagal, but not sympathetic baroreflex responsiveness. The changes that we documented can be explained economically as a consequence of the blood volume reduction that occurs in space.
Document ID
20030068220
Document Type
Other
Authors
Eckberg, Dwain L. (Medical Coll. of Virginia Richmond, VA, United States)
Cox, James F. (Medical Coll. of Virginia Richmond, VA, United States)
Tahvanainen, Kari U. O. (Kuopio Univ. Finland)
Kuusela, Tom A. (Turku Univ. Finland)
Cooke, William H. (Michigan Technological Univ. Houghton, MI, United States)
Ames, Jimey E. (Medical Coll. of Virginia Richmond, VA, United States)
Date Acquired
September 7, 2013
Publication Date
January 1, 2003
Publication Information
Publication: The Neurolab Spacelab Mission: Neuroscience Research in Space: Results from the STS-90, Neurolab Spacelab Mission
Subject Category
Aerospace Medicine
Funding Number(s)
CONTRACT_GRANT: NAS2-19541
CONTRACT_GRANT: NAG2-48
CONTRACT_GRANT: UOIHL-56417
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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IDRelationTitle20030068190Analytic PrimaryThe Neurolab Spacelab Mission: Neuroscience Research in Space: Results from the STS-90, Neurolab Spacelab Mission