THE EFFECT OF ARTIFICIAL GRAVITY DURING SHORT-TERM EXPOSURE TO SIMULATED MICROGRAVITY ON CARDIOVASCULAR RESPONSES TO ORTHOSTATIC STRESS

摘要

Human centrifuge has been proposed as a countermeasure to limit physiological deconditioning during prolongedexposure to microgravity. However, few studies have compared the cardiovascular benefits of continuous vs.intermittent centrifuge exposure.Purpose: This study investigated the response to an orthostatic stress following 5 days of 6-degrees head-downbedrest (HDBR)with and without daily exposure of a 1 G load for both continuous and intermittent conditions.Methodology: A supine to 80-degrees upright tilt, in combination with lower body negative pressure, was used as anorthostatic stress pre- and post-bedrest for each condition. The three conditions used in this study were a control,continuous centrifugation for 30 minutes and an intermittent centrifugation which involved being rotated for 5minutes before the centrifuge came to a complete stop and this was repeated 6 times in one session. Each participantserved as his own control, performing all three conditions in a randomized order with 3 weeks separating trials.Results: Heart rate (HR), cardiac output, stroke volume, mean arterial pressure (MAP), total peripheral resistance(TPR) and tolerance times were observed for 12 men (aged 34.9 ± 5.1 years, BMI 23.6 ± 2.0). Due to the high rateof orthostatic intolerance post-HDBR in the control condition there was a lack of power to test for statisticallysignificant results past the 15 minute mark during the tilt test. However, when evaluating a typical subject's values,trends indicate that the countermeasures were beneficial in preserving HR, Q, TPR and MAP post-HDBR whencompared to the control condition. Tilt tolerance times were also better maintained post-HDBR in thecountermeasure groups versus the control group. After 20 minutes of tilt, the number of surviving participants in thepre-HDBR was n≥8; post-HDBR, only 3 members of the control group survived to 20 minutes while in bothcentrifuge protocols there were 6 survivors. These results suggested an improved orthostatic tolerance for bothcountermeasure groups.Conclusions: These results suggest that daily exposure to a 1 G load (continuous or intermittent) for 30 minutes mayimprove orthostatic tolerance when in a simulated weightless environment. Furthermore, it may provide protectiveeffects on HR and TPR, and thus MAP when compared to a control protocol. Supported by the Canadian SpaceAgency.