Pulmonary arterial oxygen saturation during treadmill exercise. A discriminative index of functional class

Six patients in functional class II and 11 in functional class III underwent graded treadmill exercise, with severe fatigue as their limiting symptom. During exercise, none of the patients developed chest pain, or significant arrhythmia. Our data suggest that at a treadmill workload of 2 mph and 7 per cent slope, with an oxygen consumption four times that at rest, measurement of the pulmonary arterial oxygen saturation permits clear separation of functional class II from functional class III. Although there was a significant difference in the heart rate response, mean pulmonary arterial pressure, and percentage change in pulmonary arterial end-diastolic pressure, considerable overlap occurred. The use of pulmonary arterial oxygen saturation may prove to be of value in instances in which the functional cardiac status is not reasonably clear from the clinical interview or routine exercise testing. It requires less than maximal effort on the part of the patient, and provides an objective end point to distinguish between two important groups of patients.