CARDIOVASCULAR-RESPONSES TO REPETITIVE EXPOSURE TO HYPERGRAVITY AND HYPOGRAVITY STATES PRODUCED BY PARABOLIC FLIGHT

Physiologic changes to repetitive hyper- and hypogravity stresses occu rring during eight to ten parabolas on NASA's KC-135 aircraft were stu died. Hemodynamic responses in 11 subjects in 4 different postures (su pine, standing, sitting, and semisupine Space Shuttle launch position) were determined using noninvasive impedance cardiography. Five second s of heart rate, cardiac index, thoracic fluid index, stroke index, ej ection velocity index, and ventricular ejection time data were average d during four different gravity (g) states: 1.3g (before parabola onse t); 1.9g (parabola entry); Og (parabola peak); and 1.7g (parabola exit ) for each subject. The standing position was associated with the larg est changes in the cardiovascular response to hypo- and hypergravity. The thoracic fluid index did not indicate a headward redistribution du ring transition from a simulated launch position to weightlessness. An alysis of the eight to ten parabolas revealed that, in general, values obtained at 1.8g differed from 1.6g, Og differed from 1.6 and 1.3g, a nd 1.6g differed from 1.3g. The factors of gravity, thoracic fluid ind ex, and cardiac index exhibited significant differences that were most likely to occur between parabola 1 versus parabolas 6, 7, and 8, and parabola 2 versus parabolas 4 through 8. Only the parameter of thoraci c fluid index exhibited significance for parabolas 3 versus parabolas 6 and 7.