INFLUENCE OF GRAVITY ON CARDIAC-PERFORMANCE

Results obtained by the investigators in ground-based experiments and in two parabolic flight series of tests aboard the NASA KC-135 aircraf t with a hydraulic simulator of the human systemic circulation have co nfirmed that a simple lack of hydrostatic pressure within an artificia l ventricle causes a decrease in stroke volume of 20%-50%. A correspon ding drop in stroke volume (SV) and cardiac output (CO) was observed o ver a range of atrial pressures (AP), representing a rightward shift o f the classic CO versus AP cardiac function curve. These results are i n agreement with echocardiographic experiments performed on space shut tle flights, where an average decrease in SV of 15% was measured follo wing a three-day period of adaptation to weightlessness. The similarit y of behavior of the hydraulic model to the human system suggests that the simple physical effects of the lack of hydrostatic pressure may b e an important mechanism for the observed changes in cardiac performan ce in astronauts during the weightlessness of space flight. (C) 1998 B iomedical Engineering Society. [S0090-6964(98)00806-6].