Characterization of the Circulatory Response to Maximal Upright Exercise in Normal Subjects and Patients with Heart Disease

The circulatory responses to mild and maximal upright exercise were studied in six normal subjects and 21 patients with various types of cardiac disease. It was found that the usual hemodynamic indices employed to evaluate cardiac performance during exertion were unreliable in separating patients from normal persons. In contrast, the cardiac index achieved at a pulmonary arterial (PA) O2 saturation of 30% was found to be highly reliable and sensitive for distinguishing the normal from the abnormal response to exercise. At a level of exercise that lowers PA O2 saturation to 30%, all normal subjects achieved a cardiac index greater than 7.0 L/minm2 while no patient exceeded 4.8 L/min/m.2 In addition, the maximal capacity to extract O2 was greater in patients than in normal subjects; thus, during maximal exercise it was not unusual for patients to achieve PA O2 saturations of 15% or less, while the lowest value achieved in normal subjects was 23%.