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Acute hemodynamic responses to weightlessness during parabolic flight
C N Mukai1, C M Lathers, J B Charles
1NASA/Johnson Space Center, Houston, Texas 77058.
Journal of Clinical Pharmacology
|October 1, 1991
Summary
Pilots and astronauts experience cardiovascular changes in variable gravity. This study monitored fluid shifts and autonomic nervous system responses during parabolic flight, revealing significant heart rate and cardiac output alterations.
Area of Science:
- Cardiovascular Physiology
- Aerospace Medicine
- Autonomic Nervous System Function
Background:
- Spaceflight and aviation expose individuals to microgravity and hypergravity, causing significant fluid shifts.
- Understanding the cardiovascular and autonomic responses to these shifts is crucial for crew health and performance.
Purpose of the Study:
- To investigate the acute cardiovascular effects of fluid shifts during parabolic flight.
- To assess the role of the autonomic nervous system in regulating these responses.
Main Methods:
- Utilized NASA's KC-135 aircraft for parabolic flight to simulate variable gravity (0-G, 1.3-G, 1.7-G, 1.9-G).
- Measured R-R interval variability (cardiac neural activity), thoracic fluid index (TFI), heart rate (HR), and cardiac output (CO) in various postures.
- Employed a noninvasive continuous cardiac output monitor (NCCOM 3) and recorded data on a laptop computer.
Main Results:
- In the standing posture during 0-G, TFI decreased by 2.5 ohms, HR by 22 bpm, and CO increased by 1 L/min compared to pre-0-G values.
- In the sitting posture during 0-G, TFI decreased by 1.25 ohms, HR by 10 bpm, and CO increased by 0.5 L/min.
- R-R interval variability indicated autonomic nervous system involvement in regulating acute fluid shifts.
Conclusions:
- Parabolic flight effectively simulates microgravity-induced fluid shifts and their cardiovascular consequences.
- The autonomic nervous system plays a significant role in adapting to acute fluid shifts during transitions in gravitational load.