[Orthostatic stability in cosmonauts following 30- and 63-day flights in orbital station "Salyut-4"].

Reactions of the circulation system of cosmonauts to the up and down body movements were studied after 30-day and 63-day flights. All the four cosmonauts showed a decline in the orthostatic tolerance. An improved system of countermeasures against unfavourable effects of weightlessness used in the 63-day flight helped to maintain a better orthostatic tolerance of the crewmembers than that of the 30-day cosmonauts. It is assumed that a rapid increase of orthostaic tolerance postflight indicates an adequate maintenance of functional capabilities of circulation and suggests possible stimulation of its antigravity mechanisms prior to reentry in order to prevent postflight orthostatic disorders. An exposure to weightlessness increased the capacity of circulation to counteract the blood redistribution in the cranial direction in the head-down position. This capacity became more pronounced and stable with an increase in the flight time.