[Preliminary results of medical research completed during the flight of the second expedition of orbital station "Salyut-4"].

The 63-day flight of cosmonauts P. I. Klimuk and V. I. Sevastyanov onboard the orbital station Salyut-4 has shown that man can well adapt to weightlessness and carry out diverse and intensive activities in the weightless state. Weightlessness effects on the human body may be both direct and indirect. The direct effects include reversal of deformations and mechanical tensions in tissue structures, change in the afferent impulsation from receptor zones reacting to the gravity effect, blood redistribution, disturbance in the function of sensory system. The indirect effects of weightlessness are associated with an unusual environment and unusual conditions of work rest, food and water consumption, etc. In the course of flight the human body adapts itself to the new environment; this is assured by self-regulation of physiological functions aimed at the maintenance of a constant level of vitally important parameters. Human adaptation to the weightless state can be subdivided into two periods: 1) period of adaptive rearrangement and 2) period of relative stabilization. The first period includes a rearrangement of functions and regulatory systems of the body. The second period can be defined as attainment of an intersystem homeostasis in the human body and a relatively stable equilibrium of the body with the environment. Incomplete adaptive reactions in shorter flights, e. g. during the first expedition of the orbital station Salyut-4 (G. M. Grechko, A. A. Gubarev), may be one of the factors responsible for a less favourable development of postflight readaptation. Thus, the most important purpose of the medical monitoring and prediction in prolonged space missions is to determine how complete or incomplete these adaptive reactions are. Relative stabilization can be reached, as a rule, after a 1.5 month exposure to weightlessness. However, this time period is rather relative since it depends on the characteristic features of the human body. The results of medical investigations carried out during and after the 63-day flight demonstrated no changes that could prevent from a further increase in the duration of future space missions.