Alterations of circulatory responses to upright tilt in cardiac patients.

Circulatory responses to the upright tilt were studied in 20 normal subjects and 27 cardiac patients with ischemic heart disease or idiopathic cardiomyopathy. In normal subjects, the upright tilt caused obvious increases in heart rate and diastolic pressure, a slight decrease in systolic pressure and marked decreases in cardiac output and stroke volume. The circulatory changes during the tilt were less pronounced in the cardiac patients as compared with the normal subjects. The reductions of cardiac output and stroke volume and the increase in total peripheral resistance were all significantly diminished. A paradoxical increase in cardiac output during the tilt, an observation hitherto not well recognized, was observed in 5 cases with low cardiac index during the control period. Although several possibilities can be considered for the explanation of the diminished, sometimes paradoxical, circulatory responses to the tilt in cardiac patients, the improvement of the function of the diseased heart by preload reduction was proposed as an important factor. There was a significant negative correlation between the per cent changes of cardiac output and the per cent changes of PEP/LVET. It was suggested that the measurements of systolic time intervals during the tilt might be useful for evaluating the severity of the hemodynamic derangement in cardiac patients.