Increased tolerance of orthostatic stress in patients with heart failure was studied. Responses of heart rate and blood pressure to passive 70 ° upright tilt were measured in 6 healthy subjects and 33 patients with heart disease and analyzed in relation to hemodynamic data in the supine position. The responses of heart rate and diastolic blood pressure correlated negatively with the level of right and left ventricular filling pressures and pulmonary arterial pressure. The response of heart rate correlated positively with cardiac index and negatively with arteriovenous oxygen difference and peripheral resistance. Thus, hemodynamic abnormalities characteristic of heart failure were associated with increased orthostatic tolerance. In 5 healthy subjects the effect of expansion of intravascular volume upon the response to tilt was studied. After expansion heart rate and diastolic blood pressure increased less in response to orthostatic stress. In contrast, 5 individuals studied after volume reduction by diuresis exhibited a vasodepressor response, accompanied by significant tachycardia. Improved tolerance of orthostatic stress by cardiac patients may thus be related to increased intravascular volume, increased peripheral resistance and increased ventricular filling pressures. © 1969.
