【作者】 朱超；

【导师】 孙喜庆； 姚永杰； 张舒；

【作者基本信息】 第四军医大学 ， 航空、航天与航海医学， 2008， 硕士

【摘要】 千百万年来,人类在长期的进化过程中,适应了地球表面的1G重力环境。在航天失重环境下,流体静压消失,体液头向分布,引发机体各生理系统出现一系列的适应性变化,对心血管系统、肌肉骨骼系统、前庭神经系统、血液系统、免疫系统等产生不良影响,严重影响航天员空间工作能力和飞行任务的完成,表现为返回地面后的立位耐力下降、运动能力下降等再适应不良的症状。为了保证航天员的身体健康、安全及工作效率,开展中长期失重对抗措施的研究是非常必要的。微重力暴露后的心血管功能失调与以下因素有关:①体液头向转移以及多尿引起血容量相对不足;②心脏功能减退;③阻力血管对交感刺激的反应性下降;④压力反射功能发生改变。目前的对抗措施主要包括运动、企鹅服、下体负压、水盐补充、抗荷服、营养、药物、肌肉电刺激以及飞行前适应性训练等。但这些措施不足以对抗航天环境给人体带来的不良影响,航天员仍然表现出立位耐力下降和进行性的骨质丢失。采用短臂离心机,可以在空间实现人工重力环境,是一种针对多个生理系统的综合对抗措施,有可能从根本上解决问题,具有较好的应用前景。既往研究表明,有氧运动有助于维持地面模拟失重被试者的血浆容量和运动能力,人工重力锻炼则有利于提高被试者的立位耐力。短臂离心机锻炼可将有氧运动锻炼和人工重力锻炼结合在一起,但是各因素在维持立位耐力中的作用以及以何种方式结合能更好地发挥对抗作用,至今尚无定论。我们改进设计的SAC-Ⅱ型短臂离心机,采用电力驱动方式,并可通过调节阻力矩定量人体运动负荷,有助于分别研究人工重力与运动负荷两种因素的对抗作用。本研究利用SAC-Ⅱ型短臂离心机,观察了短臂离心机不同水平+Gz暴露联合运动负荷时人体的心率和呼吸反应,同时选择一定的方案,观察了间断性人工重力联合运动锻炼对人体心脏功能、自主神经调节功能的影响,旨在为下一步地面模拟失重乃至载人航天飞行选择合适的人工重力对抗方案提供基础。本研究的实验结果及发现如下:1.短臂离心机+Gz暴露联合运动负荷时心率和呼吸的变化本实验应用SAC-Ⅱ型短臂离心机,观察了不同方案离心机+Gz暴露联合运动负荷时人体心率、呼吸的变化。10名健康青年男性间断进行不同G值(1G,2G,3G)+Gz暴露,暴露的同时进行不同负荷(0W,30W,60W)运动锻炼。暴露过程中持续监测心率、呼吸的变化。结果发现:单纯+Gz暴露时心率较基础值显著增加(P<0.05);+2Gz和+3Gz暴露联合30W、60W负荷运动时心率较相同负荷单纯运动时基础值均显著增加(P<0.05);与单纯+Gz暴露相比较,+Gz暴露联合30W运动负荷时心率、呼吸显著增加(P<0.01),联合60W运动负荷时进一步增加(P<0.01),并随着G值的增大而增加。结果提示,+Gz暴露联合运动负荷时心率、呼吸的变化较单纯+Gz暴露更大。2.三周间断性短臂离心机联合运动锻炼对人体心功能的影响本实验利用短臂离心机进行梯度G值联合运动负荷锻炼,观察了间断性人工重力锻炼3周后人体心脏收缩、泵血功能的变化。8名健康青年男性间断进行梯度G值(1G-2G)离心机联合30W运动负荷锻炼,每天30min,持续3周。采用心电机械图法和阻抗法测量锻炼前后心脏的收缩功能与泵血功能。结果发现:锻炼2周后被试者左室射血时间(LVET)及射血分数(EF)较锻炼前显著增加(P<0.05),心率(HR)、射血前期(PEP)与LVET比值(PEP/LVET)显著下降(P<0.05);锻炼3周后,LVET及EF进一步增加(P<0.01),HR及PEP/LVET进一步下降(P<0.05),同时PEP下降达到显著性,每搏量和总外周阻力显著增加(P<0.05)。结果提示3周离心机联合运动负荷锻炼可显著增强心脏收缩与泵血功能。3.间断性短臂离心机联合运动锻炼对心血管自主神经调节功能的影响本实验利用短臂离心机进行梯度G值联合运动负荷锻炼,观察间断性人工重力锻炼3周后人体心血管自主神经调节功能的变化。8名健康青年男性间断进行梯度G值(1G-2G)离心机联合30W运动负荷锻炼,每天30min,持续3周。记录心电图和逐跳连续血压,运用自回归谱分析法得到心率变异性(HRV)与收缩压变异性(SBPV)功率谱。锻炼前后进行头高位倾斜联合下体负压测试,观察立位应激时心血管功能变化。结果发现:在卧位休息时,锻炼3周后被试者HRV的低频与高频比值较锻炼前显著下降(P<0.05),SBPV的低频功率较锻炼前显著增加(P<0.05)。在头高位倾斜联合下体负压试验时,锻炼后被试者心率较锻炼前显著下降(P<0.05),总外周阻力显著增加(P<0.05),每搏量呈增加的趋势。结果提示,离心机联合30W运动锻炼3周可以增加平卧位心脏迷走神经与外周血管交感神经活动水平,增强立位应激时血压调节能力,提高了心血管功能储备。总之,本研究观察了短臂离心机锻炼对人体心血管功能的影响,发现+Gz暴露联合运动负荷时心率、呼吸的变化较单纯+Gz暴露更大,并发现间断性梯度G值(1G-2G)联合30W运动负荷锻炼3周可增强人体心脏收缩与泵血功能,增加平卧位心脏迷走神经与外周血管交感神经活动水平,增强了立位应激时血压的调节能力,提高了心血管功能储备。本工作对下一步地面模拟失重乃至载人航天飞行选择合适的人工重力对抗方案具有一定意义。更多还原

【Abstract】 After evolution for more than 1 million year on earth, human beings are already acclimatized to the 1G environment. Consequently, loss of hydrostatic pressure, lack of gravitation stress and the miss of sense information in individuals exposed to microgravity may result in a series of adaptive changes in cardiovascular system, skeletal musculature, vestibular nervous system, hematological system and immune system, etc. These alterations will not only influence the performance of astronauts, but also result in decrease in orthostatic tolerance and exercise capacity when the astronauts returned to 1 G environment. In order to ensure the health, safety, and working efficiency of astronauts, it is essential to carry out researches on the development of countermeasures against prolonged microgravity.There are four hypotheses for cardiovascular deconditioning after microgravity exposure: 1) hypovolemia due to centralization of body fluid and diuresis, 2) cardiac hypofunction, 3) reduced responsiveness of resistant vessels to sympathetic stimulation due to lack of shear stress, 4) alterations in the baroreflex. Present countermeasures include: exercise, penguin suits, lower body negative pressure, saline loading, anti-G suits, nutrition, drugs, muscle stimulation and adaptive training in pre-flight, etc. Despite the wide range of countermeasures used, orthostatic intolerance upon return to Earth’s gravity environment and bone calcium metabolism are still unsolved problems faced by many astronauts. Artificial gravity (AG) training on short-arm centrifuge (SAC) may be a promising countermeasure due to its profound effects on various physiological systems.Previous studies have shown that aerobic exercise training helped maintain plasma volume and work capacity during bed rest. On the other hand, AG training improved orthostatic tolerance following simulated microgravity. Human-powered centrifuge training includes an aerobic exercise component as well as an AG component. However, up to now, no definite results are established regarding to the effects of the combination of these two countermeasures and the contribution of each component to the maintenance of orthostatic tolerance. With adjustable resistance trig, subjects can be trained with fixed work loads on an electrically driven SAC designed by our research group. This SAC device is especially developed to carry out researches to understand the contribution of two different countermeasures and the effects of their combination.This study was designed to elucidate heart rate (HR) and respiratory responses when human subjects performed different training protocols including AG and exercise training. Furthermore, the effects of intermittent AG combined with exercise training on cardiovascular function as well as autonomic regulation function were analytically evaluated. We hope that present results would provide support for further studies on AG regimen selection.The main results and findings of this study are as follows:1. Heart Rate and Respiratory Responses When Exposed to Short Arm Centrifuge with Exercise. We observed and compared HR and respiratory responses when human subjects performed different protocols of SAC induced AG with exercise training. Ten healthy male subjects were exposed to different +Gz (1G, 2G, 3G) with work loads (0W, 30W, 60W) intermittently, and HR and respiratory rate (RR) were monitored continually and analyzed subsequently. The results showed that HR increased significantly when exposed to +Gz acceleration compared with supine baseline. 2G or 3G exposure combined with 30W or 60W work load exercise induced significant increase of HR (P<0.05), compared with the same work load exercise. As compared with simple +Gz acceleration exposure, HR and RR increased significantly when centrifuging combined with 30W work load exercise, and reached to higher level with 60W work load exercise. Under the condition of 30W or 60W work load, HR and RR increased with G levels. It was concluded that AG via SAC with exercise training could induce higher HR and respiratory response compared to simple +Gz exposure.2. Effects of 3 weeks of Intermittent Centrifuge Training with Exercise on Cardiac Function in humans. We observed and compared the changes of human cardiac systolic and pumping function during 3 weeks of intermittent graded G centrifuge training with exercise. During 3 weeks experiment, 8 healthy ambulatory men were exposed to graded G centrifugation with 30W exercise for 30min everyday. Cardiac systolic and pumping function was measured using electromechanical cardiograph and impedance rheogram. The results showed that as compared with baseline, left ventricular ejection time (LVET) and ejection fraction (EF) increased significantly after 2 weeks training, while HR and the ratio of pre-ejection period (PEP) to LVET (PEP/LVET) decreased significantly. LVET, EF, HR and PEP/LVET changed further after 3 weeks training. At the same time, PEP declined significantly compared with baseline. Stroke volume (SV) and total peripheral resistance (TPR) increased significantly only after 3 weeks training. Our results suggested that three weeks centrifuge training with exercise could improve human cardiac systolic and pumping function.3. Changes of Cardiovascular Autonomic Regulation Function after Intermittent Centrifuge Training with Exercise. In this study we evaluated the changes of cardiovascular autonomic regulation function during 3 weeks of intermittent SAC training with exercise. During 3 weeks experiment, 8 healthy ambulatory men were exposed to graded G centrifugation with 30W exercise for 30min everyday. The ECG and beat by beat blood pressure were non-invasively recorded. Heart rate variability and systolic blood pressure variability were analyzed using auto regression method. A combination of head up tilt test (HUT) and lower body negative pressure (LBNP) was used as an orthostatic stress to evaluate cardiovascular function. During supine position, heart rate spectral analysis showed that the power ratio of low to high frequency components was significantly declined after 3 weeks training, while systolic blood pressure variability analysis showed that the low frequency components increased significantly. During HUT and LBNP, HR after training decreased significantly while TPR increased, when compared with those of before training. SV had a tendency to increase. The results of the present study suggest that three weeks centrifuge training with 30W exercise might induce an increase in cardiac vagal modulation and vascular sympathetic responsiveness, and enhance blood pressure regulation capacity and improve the potential of cardiac function during orthostatic stress.In conclusion, we observed HR and respiratory responses when human subjects were exposed to different G protocols with exercise on SAC. It is concluded that AG via SAC with exercise training could induce higher HR and respiratory response compared to simple +Gz exposure. Additionally, present results have shown that three weeks of graded G load centrifuge training with 30W exercise might induce an increase in cardiac function, cardiac vagal modulation and vascular sympathetic responsiveness, enhance blood pressure regulation capacity and improve the potential of cardiac function during orthostatic stress.更多还原