The maintenance of physiological function in humans during spaceflight.

Objective: There are a number of physiological changes which occur in astronauts in both short- and long-duration space missions, including nausea and spatial disorientation, orthostatic hypotension, muscle atrophy, bone loss, increased cancer risk from space radiation, and many others. This review examines the procedures and methods, also called countermeasures, used to moderate these changes. Data sources: The information in this paper is taken from a review of articles and book chapters (Source: PubMed and MEDLINE, years covered 1995-2005). Conclusions: The countermeasures currently adopted to counteract the effects of microgravity conditions on board space missions aim at stimulating a particular physiological system: the treadmill, the cycle ergometer and the interim resistive exercise device primarily for muscles and bones, intermittent venous pooling and fluid loading for cardiovascular responses, and pharmacological manipulations for space motion sickness. However, all have only limited success. Indeed, despite extensive in-flight exercise, most astronauts experience difficulties in standing, walking and getting oriented for several days after landing. This poses a serious problem in case of an emergency landing on Earth or a landing on Mars after a long-duration spaceflight. Studies are being conducted for the search of more effective countermeasures that address all physiological systems across the board, such as artificial gravity generated by short-arm centrifugation. [ABSTRACT FROM AUTHOR]