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Publication AbstractsEffect of 6° Head-Down Tilt on Cardiopulmonary Function: Comparison with MicrogravityG. Kim Prisk, Janelle M. Fine, Ann R. Elliott, and John B. WestAviat Space Environ Med 2002; 73:8-16 AbstractBackground: Head-down tilt (HDT) of 6° is a commonly used model of weightlessness, but there are few comparisons with actual microgravity. Hypothesis: Our study was designed to prove that the changes in cardiopulmonary function seen in HDT would be similar to those seen in microgravity. Methods: We compared measurements of cardiovascular and pulmonary function from three separate spaceflights of 14 to 17 d duration, with data collected during a 17-d period of HDT. Results: HDT proved a good model of the cardiovascular response to microgravity, resulting in increases in cardiac output and stroke volume of a similar magnitude to those seen in microgravity, with a concomitant reduction in heart rate. By contrast, HDT was a poor model of the effects of microgravity on pulmonary ventilation and gas exchange. Conclusion: Pulmonary function in HDT approximated the changes seen in the 1-G supine posture, while in microgravity this was much closer to that seen in the 1-G upright position. The differences probably reflect the fact that changes in cardiovascular function result primarily from fluid shifts within the entire body, whereas changes in pulmonary ventilation are primarily a result of mechanical influences on the lung and chest and abdominal wall.Keywords: supine, cardiac output, pulmonary gas exchange, gravity, weightlessness. Information on subscribing, and on obtaining copies of an article or of an entire issue. Table of Contents for Volume 73, Number 1 of the ASME journal.
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