Cardiovascular changes in prolonged space flights

In prolonged manned space flights, the cardiovascular function was examined at rest and during provocative tests. As compared to the preflight data the following changes were seen: higher heart rate at rest and during LBNP tests, decrease of stroke volume at rest and during LBNP test and a less marked increase (or decrease) during exercise tests, symptoms of a greater heart load which transformed to the syndrome of myocardial hypodynamics (preload) during LBNP tests or to the syndrome of myocardial hyperdynamics (afterload) during exercise tests (with other than preflight ratios of systolic and diastolic time intervals). The above cardiovascular changes did not, as a rule, aggravate with flight time and can be viewed as adaptive reactions to microgravity. The above cardiovascular changes were primarily produced by fluid redistribution in the cranial direction, diminished participation of the muscle system in circulation, and involvement of unloading reflexes from the cardiopulmonary receptor zones.