This article reviews recent flight and ground-based studies of cardiovascular adaptation to spaceflight. Prominent features of microgravity exposure include loss of gravitational pressures, relatively low venous pressures, headward fluid shifts, plasma volume loss, and postflight orthostatic intolerance and reduced exercise capacity. Many of these short-term responses to microgravity extend themselves during long-duration microgravity exposure and may be explained by altered pressures (blood and tissue) and fluid balance in local tissues nourished by the cardiovascular system. In this regard, it is particularly noteworthy that tissues of the lower body (e.g., foot) are well adapted to local hypertension on Earth, whereas tissues of the upper body (e.g., head) are not as well adapted to increases in local blood pressure. For these and other reasons, countermeasures for long-duration flight should include reestablishment of higher, Earthlike blood pressures in the lower body.
Submitted for publication February 1995.
Accepted for publication December 1995.
This work was supported by NASA grant 199-14-12-04. The authors thank Karen Hutchinson, Richard Ballard, and Gita Murthy for helpful discussions and technical assistance.
Address for correspondence: Alan R. Hargens, Ph.D., Chief (Acting), Gravitational Research Branch, Life Science Division (239-11), NASA Ames Research Center, Moffett Field, CA 94035-1000.
Life Science Division (239-11), NASA Ames Research Center, Moffett Field, CA 94035-1000