Abstract
AimsExposure to artificial gravity (AG) at different G loads and durations on human centrifuges has been shown to improve orthostatic tolerance in men. However, the effects on women and of an individual-specific AG training protocol on tolerance are not known.MethodsWe examined the effects of 90 minutes of AG vs. 90 minutes of supine rest on the orthostatic tolerance limit (OTL), using head up tilt and lower body negative pressure until presyncope of 7 men and 5 women. Subjects were placed in the centrifuge nacelle while instrumented and after one-hour they underwent either: 1) AG exposure (90 minutes) in supine position [protocol 1, artificial gravity exposure], or 2) lay supine on the centrifuge for 90 minutes in supine position without AG exposure [protocol 2, control]. The AG training protocol was individualized, by first determining each subject’s maximum tolerable G load, and then exposing them to 45 minutes of ramp training at sub-presyncopal levels.ResultsBoth sexes had improved OTL (14 minutes vs 11 minutes, p < 0.0019) following AG exposure. When cardiovascular (CV) variables at presyncope in the control test were compared with the CV variables at the same tilt-test time (isotime) during post-centrifuge, higher blood pressure, stroke volume and cardiac output and similar heart rates and peripheral resistance were found post-centrifuge.ConclusionsThese data suggest a better-maintained central circulating blood volume post-centrifugation across gender and provide an integrated insight into mechanisms of blood pressure regulation and the possible implementation of in-flight AG countermeasure profiles during spaceflights.
Highlights
Post-spaceflight orthostatic intolerance is a common phenomenon in both male and female astronauts
We examined the effects of 90 minutes of artificial gravity (AG) vs. 90 minutes of supine rest on the orthostatic tolerance limit (OTL), using head up tilt and lower body negative pressure until presyncope of 7 men and 5 women
When cardiovascular (CV) variables at presyncope in the control test were compared with the CV variables at the same tilt-test time during post-centrifuge, higher blood pressure, stroke volume and cardiac output and similar heart rates and peripheral resistance were found post-centrifuge
Summary
Post-spaceflight orthostatic intolerance is a common phenomenon in both male and female astronauts. Artificial gravity (AG) administered during spaceflight may prevent the development of orthostatic intolerance upon return to Earth. Ground-based studies observed that AG: a) improved orthostatic tolerance in ambulatory men [1,2]; and b) maintained orthostatic tolerance in bed rested men [3]. In these studies different gravity (G) exposures were administered and for different durations. The beneficial effects of AG exposure for women are, not clear. To our knowledge only two studies have previously examined the effects of AG exposure across gender [4,5]. Stenger et al concluded that three weeks of daily AG training was more effective in men than women with a greater response from subjects who exercised during AG sessions than in those who passively rode the centrifuge [5]
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