Objectives
This research explored the probability that the disordered arterial baroreflex malfunction documented during weightlessness or after simulated or actual weightlessness is part of, and a contributor to, a broad range of autonomic abnormalities. The objectives of this investigation were: (1) to determine in a definitive way, the adaptive changes in the autonomic nervous system (ANS) during long-term (20 weeks) of space flight and use this information to obtain insights into various mechanisms that underlie the observed integrated autonomic output, (2) to determine the adaptive responses (mediated by the ANS) through which organ perfusion is maintained during space flight, and (3) to examine the consequences immediately following space flight of any adaptation of the ANS that has taken place during space flight, particularly on the various integrated pathways that respond to orthostatic stress in a gravitational field.
Shuttle-Mir Missions Approach
Data were recorded 14 days prior to flight (L-14), on mission day 18 (MD18) and 1 and 15 days after flight (R+1 and R+15) during Mir-23 for one subject. During Mir-25, data were recorded on L-14, MD114, MD148, MD182, R+1 and R+15 for one subject and on L-12, MD120, MD183, and R+15 for another subject.
Results Earth Benefits Publications Principal Investigators Co-Investigators
Mir-23, Mir-25
Principal design features of this project were built around a battery of tests that activated different afferent fibers, evoking different patterns of neural and cardiovascular responses through both separate and common mechanisms. These tests included: Controlled frequency breathing, Valsalva Maneuver, Isometric Exercise (static handgrip), Cold Pressor Test, Graded Lower Body Negative Pressure (LBNP), and Passive Head-up Tilt. EKG, beat-to-beat arterial pressure, cerebral blood flow velocity, and whole-body fluid distribution were successfully recorded during this battery of tests that activated different afferent fibers, evoking different patterns of neural and cardiovascular responses.
Results suggest that long-duration space flight decreases vagal-cardiac neural outflow and vagal baroreflex gain, and that after returning to Earth, the effects of weightlessness may persist beyond two weeks. Although we attempted to document the time-course of autonomic adaptation during flight, directional trends were not apparent, or did not exist. It is not clear whether changes in autonomic cardiovascular regulation progress or stabilize as a function of the duration of exposure to microgravity.
This research should improve understanding of a basic physiological mechanism: human cardiovascular autonomic responses to standing upright. Second, it should improve understanding of pathophysiological mechanisms of enormous public health significance. For example, hypertension, which afflicts over 60 million Americans, is associated with impairment of autonomic cardiovascular control. Another example is acute myocardial infarction and a closely related problem, sudden cardiac death. Sudden cardiac death is the largest cause of death in developed countries; the number of people who die suddenly of catastrophic dysrhythmias dwarfs the number of people who die of other public health problems, including AIDS. In cardiac patients, abnormal autonomic cardiovascular control (as reflected by impairment of baroreceptor-cardiac reflexes and reduced heart rate variability) indicates which patients are at greatest risk for subsequent cardiac events. Therefore, understanding of how autonomic cardiovascular control mechanisms become impaired may be very important. It is the nature of human research that patients with pathologic conditions are not evaluated before they become ill. (Physicians who would study such patients do not know who will become ill.) Therefore, astronauts present a great opportunity. They can be studied before space missions when they are normal, in space as they become abnormal, and after return to Earth as they become normal again. Such longitudinal evaluation of cardiac patients is not possible.
Cooke WH, et al. Nine months in space: the effects on human autonomic cardiovascular regulation. (in preparation)
Dwain L. Eckberg, M.D.
McGuire Research Institute, Inc.
William H. Cooke, Ph.D.
Friedhelm J. Baisch, M.D.
James F. Cox, Ph.D.
Kari U.O. Tahvanainen, M.S.
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Curator:
Julie Oliveaux
Responsible NASA Official: John Uri |
Page last updated: 07/16/1999
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