Objectives
Adaptation to microgravity causes changes in the autonomic
nervous system that have significant effects on the control of blood flow
and blood pressure. These changes result in orthostatic
intolerance, or the inability to provide sufficient blood flow to body tissues,
particularly to the brain, in the upright body position upon return to Earth.
The objective of this investigation was to provide new physiological data that will improve our understanding of the function of the human heart and blood vessels in space and on return to Earth. Specifically, researchers sought to detect functional abnormalities of the autonomic nervous system pre- and postflight, and furthermore define the effects and time course of adaptation during space flight by applying integrated, clinical tests of autonomic function.
The primary hypothesis to be tested was that adaptation to the unique environment of microgravity causes alterations in the autonomic nervous system that interact with microgravity-induced changes in body fluid distribution, and result in orthostatic intolerance upon return to Earth. It was also hypothesized that this adaptation occurs rapidly and completely within the first few days to weeks of space flight and does not progress with long-term (months) exposure.
Shuttle-Mir Missions Approach By measuring changes in cerebral blood flow velocity non-invasively using
Transcranial
Doppler, changes in cerebral blood flow and resistance could be estimated
and related to changes in systemic flow and resistance in response to metabolic
(hypo-
and hyperventilation)
and hemodynamic
(head-up tilt) provocative
maneuvers.
This experiment was conducted as an integrated cardiovascular experiment based on sessions performed jointly with Dwain L. Eckberg, MD. and William Cooke, Ph.D. of the McGuire Research Institute, University of Virginia, Richmond, Virginia as well as Friedhelm Baisch, M.D. of the German Space Agency (DLR), Cologne, Germany for their investigation Autonomic Mechanisms During Prolonged Weightlessness (E709).
Results Earth Benefits Publications Principal Investigators Co-Investigators
Mir-23/Dara Mir 97E, Mir-24/NASA-6, Mir-25/NASA-7
Principal design features of this investigation were built around a battery
of tests that activated different afferent
nerve fibers, evoking different patterns of neural
and cardiovascular responses. Simple to perform, non-invasive tests--such as
the quantitative Valsalva
maneuver, estimates of heart rate and blood pressure variability, cold
pressor test, and static handgrip exercise--can provide insights into the
adequacy of afferent input, central processing of afferent signals, and sufficiency
of neural and vasomotor
responsiveness. Indirect, non-invasive measures of autonomic balance, including
linear and non-linear variability of heart rate, blood pressure, and cerebral
blood flow were obtained before, during and after flight.
Currently, verification of collected data, and writing of supplemental software to complete the analysis of those data, is in progress. The data analysis is performed jointly with Dr. Eckberg et al. of the McGuire Research Institute.
The experiment provides new data on human cardiovascular control mechanisms
during and after space flights of long duration. Orthostatic
hypotension is a common and important condition in astronauts early after
return from space and is also a common clinical problem. The experiment is likely
to provide new and specific information on pathophysiological
mechanisms that is highly relevant to both general clinical practice and to
flight medicine. The new knowledge is also likely to contribute to the development
of new approaches to the diagnosis and functional evaluation of patients with
orthostatic intolerance.
None available at this time.
C. Gunnar Blomqvist, M.D., Ph.D.
University of Texas Southwestern Medical Center
Benjamin D. Levine, M.D.
Cole A. Giller, Ph.D., M.D.
F. Andrew Gaffney, M.D.
Lynda Denton Lane, M.S., RN
James A. Pawelczyk, Ph.D.
 |
Curator:
Julie Oliveaux
Responsible NASA Official: John Uri |
Page last updated: 07/16/1999
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