[Adaptation of the cardiovascular system to negative gravitation stresses during repeated antiorthostatic measures]

The cerebral, pulmonary, liver and peripheral circulation was studied simultaneously in 12 test subjects (aged 24--30) rheographically, photoplethysmographically and rheoplethysmographically; arterial pressure was measured by the Korotkoff method. The measurements were carried out during three antiorthostatic tests at --15degrees for 20 min or --30degrees for 20 min. It was shown that the cardiovascular system can adapt to repeated antiorthostatic exposures. The adaptation includes more significant decrease of the heart rate, increase in the systolic and pulse arterial pressure, fall of the diastolic arterial pressure, more marked reduction of antiorthostatically induced increase of blood filling and congestion of cerebral and pulmonary vessels, lesser decrease of their tone and blood redistribution into the vessels of the liver, upper and lower limbs. From the point of view of the adaptive effect repeated exposures to --15degrees are more effective.