失重对航天员的影响及其对抗措施

Effect of microgravity on astronauts and its countermeasures

目的按航天飞行的持续时间，分析微重力对航天员的影响，并详述对骨骼肌的影响与对抗措施。资料来源与选择国外较新的相关研究论文、综述、美国国家航空航天局（NASA）报告以及专著。资料引用论文与综述22篇，NASA报告3篇，专著4本。资料综合按重要性将微重力对机体的影响进行排序，并归纳以运动为基础的新对抗措施。结论在多种航天异常环境因素中，微重力是惟一不可屏蔽的影响因素。短期微重力可引起航天员体液头向转移与空间运动病，中长期微重力则引起骨质丧失、骨骼肌萎缩、心血管功能紊乱、神经平衡失调与免疫功能降低等适应性改变，其中，骨骼肌萎缩与收缩功能降低机制及其对抗措施是当前研究的热点之一。研究表明：微重力条件下骨骼肌收缩负荷降低是引起其萎缩的主要原因，收缩负荷降低可能通过激活钙蛋白酶（Calpain）导致肌原纤维降解，形成萎缩的上游机制，而三磷酸腺苷泛素与溶酶体的激活则可能为下游机制。除以运动为基础的对抗措施如双负荷跑台与企鹅服外，正在观察其有效性的对抗措施有振动、Galileo空间训练系统与飞轮式自行车功量计等。基于骨骼肌萎缩机制而研制新一代对抗措施，将成为发展趋势。

Objective To sort out the effect of microgravity on astronauts according to spaceflight duration and describe the changes in skeletal muscles and its countermeasures in detail. Literature resource and selection The research papers, reviews, NASA reports and monographs in this field. Literature quotation Twenty-two research papers or reviews, 3 NASA reports and 4 monographs were cited. Literature synthesis The influence of mierogravity on astronauts were prioritized and the exercise-based countermeasurements were summarized. Conclusions Microgravity is a sole factor that can not be shielded with physical methods among abnormally environmental factors in spaceflight. The astronauts suffer from a headward fluid shift and space motion sickness during short-duration spaceflight. The medium- or long-duration microgravity make astronauts to show bone loss, atrophy of antigravity skeletal muscles, dysfunction in cardiovascular system, imbalance of neurovestibular system and depression in immunoreaction. Many of the physiological changes to microgravity are adaptive. Now the mechanisms of skeletal muscle atrophy and their countermeasurements are one of vital researches in space medicine. A lot of researches indicate that the unloading is a main reason induced the atrophy in skeletal muscles during microgravity. The unloading may activate Calpain to degrade myofibrils as a upper stream mechanism inducing atrophy in skeletal muscles, and the activation of ATP-ubiquitin or lysosome maybe located at down stream of degradation. The exercise-based countermeasurement include treadmill, penguin suit and so on. The vibration, Galileo-space training system and fly-wheel ergometer are observing their effectivity in ground-based researches. The new generation of coutermeasures would be constructed by depending on the atrophic mechanisms of skeletal muscle.