DOPPLER EVALUATION OF CARDIAC FILLING AND EJECTION PROPERTIES IN HUMANS DURING PARABOLIC FLIGHT

The cardiac filling and ejection properties of seven normal human subj ects were examined during microgravity created on a National Aeronauti cs and Space Administration aircraft during parabolic flight. Doppler echocardiography was used to measure intracardiac velocities in sittin g and supine subjects during three phases of flight: hypergravity (pha se I), early microgravity (phase III), and late microgravity (phase IV ). Heart rate declined 6% (P < 0.001) and right ventricular inflow vel ocities rose (46%, early; 26%, mean; P < 0.01) between phase I and pha ses III or IV in the sitting position only. Peak left ventricular outf low velocities rose 12% and inflow velocities rose (13%, early; 20%, m ean) between phases I and IV while subjects were in the supine positio n (P < 0.05). A 14% rise in early velocities alone was seen between ph ases I and IV while subjects were in the sitting position (P < 0.05). In subjects entering microgravity while sitting, right heart chambers can accept additional venous return. When microgravity was entered whi le subjects were supine, however, venous augmentation was not observed . Left heart filling was more prominently enhanced when microgravity w as entered while subjects were supine, suggesting a shift of fluid wit hin the pulmonary vasculature.