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Cardiovascular Deconditioning Countermeasure Assessment (DSO 402)
Principal Investigator
Research Area:
Cardiovascular physiology
Clinical medicine
Species Studied
Scientific Name: Homo sapiens Species: Human

Early in the manned space flight program it was noted that the cardiovascular system undergoes several adaptive changes when subjected to the microgravity environment. Experimentation during NASA's Skylab missions demonstrated that fluid was shifted from the lower extremities to the more central and cephalad portions of the circulation. The results of this redistribution and of other alterations in the controlling mechanisms of the circulation which were not well defined were termed "cardiovascular deconditioning." The term deconditioning was felt to be appropriate because those individuals who were tested during or immediately after space flight demonstrated less orthostatic tolerance when provoked with lower body negative pressure (LBNP), higher submaximal oxygen consumptions at equivalent workloads, and higher resting heart rates when compared to their responses preflight.

With the advent of the Space Shuttle, it was known that astronauts would receive the effects of reentry deceleration in the + Gz axis (head-to-toe), compared to earlier space flights in which these forces were directed + Gx (chest-to-back). The combination of this more stressful acceleration loading with the deconditioned state of the human cardiovascular system following space flights increased efforts directed at developing suitable countermeasures. Most were rejected for actual use in the Space Shuttle due to either complex hardware requirements or objections by flight crews. Even the anti-G suit, considered by many as the only acceptable alternative at the inception of the Shuttle program, was not regarded favorably. Therefore, the development of other, more suitable countermeasures to post-space flight orthostatic intolerance took on greater importance.

Earlier bedrest studies had revealed the usefulness of oral rehydration using normal saline in the more palatable form of bouillon, in providing a degree of protection against the loss of LBNP and acceleration tolerance by expanding the circulating plasma volume. In one study, six male volunteers underwent 15 days of bed rest to "decondition" their cardiovascular systems in a physiological simulation of weightlessness. On each of the last three days of bed rest, each subject was stressed by LBNP at -50 mm Hg in one of three randomly assigned conditions: employing no candidate countermeasures; having ingested 1 L of bouillon alone as a countermeasure; or following ingestion of the bouillon during three hours of LBNP at -30 mm Hg, as a combined countermeasure. The results showed that the combination of oral rehydration and prolonged LBNP provided a more sustained increase in plasma volume and reduction in stressed heart rate response.

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Bungo MW, Charles JB, Johnson PC. Cardiovascular deconditioning during space flight and the use of saline as a countermeasure to orthostatic intolerance. Aviat Space Environ Med. 1985:985-990. []

Bungo MW, Charles JB, Johnson PCJr. Cardiovascular deconditioning during space flight and the use of saline as a countermeasure to orthostatic intolerance. In: Bungo MW, Bagian TM, Bowman MA, Levitan BM, editors. Results of the life sciences DSOs conducted aboard the Space Shuttle 1981-1986. Houston: Space Biomedical Research Institute, NASA Johnson Space Center, 1987:41-7. [NTRS]

Blood pressure
Cardiovascular deconditioning
Fluid shifts
Fluid therapy
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Data Information
Data Availability
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Blood pressure, mean
Cardiovascular Index of deconditioning
Hypotonic solution
Isotonic solution
Orthostatic syncope
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Mission/Study Information
Mission Launch/Start Date Landing/End Date Duration
STS-4 06/27/1982 07/04/1982 7 days
STS-41C 04/06/1984 04/13/1984 7 days
STS-41D 08/30/1984 09/05/1984 6 days
STS-5 11/11/1982 11/16/1982 5 days
STS-6 04/04/1983 04/09/1983 5 days
STS-7 06/18/1983 06/24/1983 6 days
STS-8 08/30/1983 09/05/1983 6 days
STS-9 11/28/1983 12/08/1983 10 days

Additional Information
Managing NASA Center
Johnson Space Center (JSC)
Responsible NASA Representative
Johnson Space Center LSDA Office
Project Manager: Pamela A. Bieri
Institutional Support
National Aeronautics and Space Administration (NASA)
Protocol / Approach
Use of saline as a countermeasure to orthostatic intolerance