VENTILATORY RESPONSES TO EXERCISE IN ADULTS AFTER REPAIR OF TETRALOGYOF FALLOT

Background-Adult patients with total correction of tetralogy of Fallot may have poor exercise capacity associated with impaired right heart function and in particular pulmonary regurgitation. The ventilatory re sponses to exercise were studied in a group of such patients to assess relations between ventilation, exercise capacity, and right ventricul ar function. Methods-30 patients (7 female) (aged 27.8 (6.0) years) an d 30 (7 female) controls of a similar age range were studied prospecti vely. All underwent exercise testing with metabolic gas exchange to de termine peak oxygen consumption (peak VO2), and (as indices of the ven tilatory response) the slope of the relation between both respiratory rate (RR) and ventilation (VE) against carbon dioxide production (VCO2 ). Patients were studied with pulsed wave Doppler echocardiography to determine pulmonary arterial systolic and diastolic flow characteristi cs. Patients were defined as having restrictive right ventricular func tion where diastolic pulmonary forward flow was seen coincident with a trial systole. Results-in the group With tetralogy of Fallot mean (SD) peak VO2 was 35.3 (7.5) ml/kg/min (93.6 (15.3) % of expected for age, weight, height and sex). The RR/VCO2 slope was steeper in the Fallot group (6.8 (2.6) v 9.6 (4.7), P < 0.02). Those with restrictive right ventricles achieved a higher peak Vo, than those without (82.5 (10.1)% v 100.9 (13.8), P < 0.001). In the Fallot group alone, there was an i nverse relation between ventilatory response and peak VO2 (RR/VCO2 v p eak VO2; r = - 0.63, P = 0.003: VE/VCO2 v peak VO2; r = - 0.62, P < 0. 001). Conclusions-Many of these patients with repaired tetralogy of Fa llot had near normal exercise capacity, but as exercise capacity decre ased, the ventilatory response to exercise increased. This was not due to alterations in pulmonary function tests or to the effects of cardi ac size causing decreased lung volume. It may be that the increased ve ntilatory rate at a given level of carbon dioxide production acts as a respiratory pump aiding right ventricular function.