Man in Space: A Survey of the Medical Literature ISABELLE DURAND-ZALESKI Summary The principal effects and modes of action of the space environment on human physiology are discussed with emphasis on the effects of microgravity on the musculoskeletal and cardiovascular system. Our relative level of knowledge about and ability to compensate for the various effects is highlighted. Since the first manned space mission, more than a quarter of a century ago, the physiological effects of exposure to the space environment have been extensively studied. The human factor is critical to the exploration and the exploitation of space as astronauts have increasingly long and complex tasks to perform, be they scientific or mechanical operations. Man did not need to evolve mechanisms to compensate for weightlessness: on the contrary, man had to adapt to live in a strong gravitational field. The musculo-skeletal, cardiovascular and nervous systems have themselves developed in a way that responds to the demands of gravity. How does weightlessness act on the human body, what alterations does the body undergo, what are the stresses resulting from life in space and what possibilities are there to compensate for this and to provide protection for astronauts? The hazards involved in space travel include: • effects of weightlessness, • effects of ionizing radiation, • risks of human error, • life support system variations, • atmospheric variations, and • problems associated with prolonged enclosure. I review these hazards in the light of data provided by actual experiments in space and simulations on the ground. Weightlessness can be simulated by bed rest or water immersion in certain cases. 1. Effects of Microgravity There are three types of structure which weightlessness affects: • static structures, such as bones and collagen; • dynamic structures, related to the circulation of fluids in the body; • mobile structures that play an important role in the orientation of movements and postural balance. Isabelle Durand-Zaleski, 77 bis Avenue de Breteuil, 75015 Paris, France.
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