SPACE RESEARCH ACTIVITIES DURING MISSIONS OF THE PAST

For over 30 yr, men and women have lived for various periods of time i n a weightless (or free-fall) environment while orbiting the Earth. Du ring these years, we have learned that humans function quite well for short periods of weightlessness, that is, for up to a little more than a year. Some space flight missions have provided physiologic data, in cluding cardiovascular data, from the spacefarers. In fact, some missi ons have provided laboratories for systematic study of cardiovascular responses and adaptation to space flight. However, the opportunity to obtain physiologic data from people in space is a rarity. It is import ant to remember that the population sample sizes are small, other stre sses may confound the effects of weightlessness, and in some situation s the crewmembers are subjects for several experiments at the same tim e. Furthermore, comparison of cardiovascular data from space flight to data obtained on the ground is sometimes difficult because the subjec t's posture on the ground is not always reported; in a gravity environ ment, posture influences the hydrostatic gradient. This overview descr ibes what we have learned about cardiovascular functions during flight and after return to Earth.