During upright exercise lowering pulmonary arterial O2 saturation to 30%, normal subjects achieved a cardiac index >7.0 L/min/m2, while no patient with heart disease exceeded 4.8 L/min/m2.
Observational (n=27)
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) O 2 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 O 2 saturation to 30%, all normal subjects achieved a cardiac index greater than 7.0 L/minm 2 while no patient exceeded 4.8 L/min/m. 2 In addition, the maximal capacity to extract O 2 was greater in patients than in normal subjects; thus, during maximal exercise it was not unusual for patients to achieve PA O 2 saturations of 15% or less, while the lowest value achieved in normal subjects was 23%.
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Circulation
National Heart Lung and Blood Institute
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Epstein et al. (Thu,) conducted a observational in Heart disease (n=27). Mild and maximal upright exercise vs. Normal subjects was evaluated on Cardiac index achieved at a pulmonary arterial O2 saturation of 30%. During upright exercise lowering pulmonary arterial O2 saturation to 30%, normal subjects achieved a cardiac index >7.0 L/min/m2, while no patient with heart disease exceeded 4.8 L/min/m2.