Exercise Tolerance and Cardiorespiratory Response to Exercise Before and After the Fontan Operation

To determine the effect of the Fontan operation on exercise tolerance and cardiorespiratory response to exercise, we compared the preoperative and postoperative responses to graded exercise to maximal effort in 20 patients who underwent a modified Fontan procedure. The mean interval between preoperative and postoperative exercise testing was 1.8 years. Postoperatively, total work performed, duration of exercise, and maximal oxygen uptake were significantly increased. Although cardiac output increased during exercise, the response was subnormal, and stroke volume was unchanged. The heart rate and systolic blood pressure during maximal exercise were not significantly changed from preoperative values, but the diastolic blood pressures during rest and maximal exercise were significantly increased postoperatively. Systemic arterial blood oxygen saturation increased after the modified Fontan operation, but during exercise, a mild but significant desaturation occurred (93% compared with 90%). The ventilatory equivalent for oxygen decreased toward normal during exercise. The respiratory rate and oxygen consumption during resting remained unchanged from preoperative values. For this subset of patients, these data indicate that exercise tolerance improves, cardiac output and stroke volume responses to exercise are subnormal, and ventilatory response to exercise decreases toward normal after the modified Fontan operation.