Basic Research Of Short Arm Centrifuge For Application

The biggest problem for space missions of several years in duration is the harmful effects of microgravity on the human body. When individuals expose to microgravity, the loss of gravitation stress and the sense information could result in a series of physiological changes, such as bone loss, muscle weakness, vestibular readjustment, cardiovascular deconditioning, metabolic and endocrine alterations, and altered sensory motor performance. Such reactions by the body might be appropriate for zero-gravity flight but are inappropriate for return to the surface of our planet or another planet. For the next generation of human exploratory missions, the key to mission success lies in overcoming the physiological limitations of prolonged exposure to microgravity by means of effective countermeasures to ensure the long-term health maintenance of the astronauts.Over the 50 years of human space flight experience, a variety of countermeasures have been developed, including saline loading, intermittent venous pooling (using lower body negative pressure, LBNP), pharmacological manipulations and resistance training, but all have had only limited success. Indeed, despite extensive in-flight exercise, most astronauts experience problems with balance and orientation, fainting, and risk of muscle tears and bone fractures for the first few days after landing. Because of its profound effects on various physiological systems, artificial gravity, generated by short-arm centrifuge (SAC), is consided as a promising countermeasure.Ground based researches have shown that AG could enhance subjects'orthostatic tolerance after head-down bed rest, however, purely AG training could not maintain the exercise capacity. But, studies found that volume and work capacity could be maintained by aerobic exercise training during bed rest. Therefore, centrifuge training includes an aerobic exercise component as well as an artificial gravity component may be a more efficient countermeasure to microgravity. Unfortunately, we still unkown how much gravity and work losd are neededThis study was designed to investigate the changes of cardiovascular and vestibular function when exposed to artificial gravity generated by short-arm centrifuge with different body positions. Furthermore, the Changes of cardiovascular function after short-arm centrifuge or aerobic exercise or short-arm centrifuge combined with aerobic exercise training were observed. Finally, we choose the most efficient countermeasure to test its effects during 4-day head down bed rest.The main results and findings of this study were as follows:1. Effects of artificial gravity exposed at different body positions on human cardiovascular and vestibular system. We observed and compared the changes of cardiovascular and vestibular function when exposed to artificial gravity generated by short-arm centrifuge with different body positions. Ten healthy male volunteers were exposed to artificial gravity at three different body positions: 75°, 45°and 15°. Each position underwent short-arm centrifuge with two sessions at rotary speed of 31r/min (2G) or 39r/min (3G) respectively. Beat-by-beat arterial blood pressure were measured during the exercise by means of a Portapres. Meanwhile, vestibular sensations of discomfort were recorded. The results showed that no significant changes of blood pressure, heart rate, cardiac output, stroke volume and total peripheral resistant were observed in the 45°position as compared with the body position of 75°, When compared with that in the 31r/min session, heart rate increased significantly when at the rotary speed of 39r/min (P<0.05). As compared the baseline, blood pressure, heart rate and total peripheral increased significantly (P<0.05), and stroke volume decreased significantly (P<0.05). As compared with that in the position of 15°, the stimulus of vestibular system increased significantly (P<0.05) in the position of 45°or 75°. It was concluded that the body position of 75°may be the best model with artificial gravity exposure.2. Changes of cardiovascular function after short-arm centrifuge or aerobic exercise or short-arm centrifuge combined with aerobic exercise training. We observed and compared the changes of cardiovascular function and cardiovascular autonomic nervous regulation after short-arm centrifuge(SAC), aerobic exercise(EX) or a combination of the joint training(SAC+EX). 24 healthy male subjects were randomly divided into three groups, respectively, and executed short arm centrifuge, or aerobic exercise (40W) or a combination of a joint exercise for 1 week. Heart rate variability, systolic blood pressure variability, cardiac puming function, and systolic function were analyzed before and after training. The results showed that 1 week of SAC training with aerobic exercise improved cardiac pumping function and enhance cardiovascular autonomic nervous modulation, which associated with a decrease in heart rate and increase in stroke volume(SV), left ventricular ejection time and low frequency of arterial pressure spectral power (P<0.05). While other two groups appeared no marked changes in above parameters. Our results suggested that 1 week of AG generated by short-arm centrifuge combined with aerobic exercise training could significantly improve cardiac pumping function, cardiac vagal nerve modulation and peripheral smooth muscle vascular tone. However, alternative in AG or aerobic exercise training was not sufficiently enough to induce similar alterations. It implied that short-arm centrifuge and aerobic exercise were necessary conditions to improve cardiac function and cardiovascular autonomic nerve modulation in 1 week of training time.3. Artificial Gravity With Ergometric Exercise During 4-Day Head-Down Bed Rest Preserves Cardiovascular Function and Venous Compliance . This study was designed to elucidate the effect of short arm centrifuge-induced artificial gravity with exercise training during ground-based simulated spaceflight, head-down bed rest, on cardiovascular function, compliance compliance and cerebral vascular function. Twelve healthy male volunteers were exposed to simulated microgravity for 4 days of head-down bed rest. Six subjects were randomly loaded 1.0~2.0 G intermittent artificial gravity with 40W of ergometric workload every day (CM group). The six others served as the control (CON group). Heart rate variability and systolic blood pressure variability were analyzed using auto regression method. Orthostatic tolerance were evaluated by orthostatic stress induced by head up tilt test. A Monark cycle ergometer (Monark, Sweden) was used to assess physical working capacity (PWC170). The strain gauge venous occlusion plethysmography was used to assess limb venous vascular characteristics. Cross-sectional area of the popliteal vein at the different cuff pressures was measured with an ultrasound device. The cerebral blood flow velocities in the right middle cerebral artery were measured by a transcranial Doppler flowmeter. The results showed that the heart rate and compliance of popliteal vein increased significantly, while SV, CO,PWC170,VaO2, HFRR decreased significantly after 4-day head-down bed rest in the CON group (P<0.05). However, these parameters showed no changes in the AG group. All subjects led to similar changes on cerebral vascular function. Our results suggested that a four-day simulated weightlessness leads to cardiovascular deconditioning, reduction of exercise capacity and increase of popliteal venous compliance; intermittent(1-2G) artificial gravity with 40w work load exercise can successfully prevent these changes; however, it could not prevent the changes of cerebral vascular function.In conclusion, we found that the body position of 75°may be the best model with artificial gravity exposure. Additionally, short-arm centrifuge and aerobic exercise were necessary conditions to improve cardiac function and cardiovascular autonomic nerve modulation. Finally, intermittent(1-2G) artificial gravity with 40w work load exercise can eliminate the changes in cardiovascular function, exercise capacity and the compliance of popliteal vein.