[Factors limiting adaptation to exercise after the Fontan operation: role of altered pulmonary function]

The abnormal adaptation to exercise after Fontan operation, is primarily due to a suboptimal increase in cardiac output. We postulated that abnormal pulmonary function could cooperate in reducing effort tolerance of these patients (pts).

We have evaluated 10 pts, mean age 15 +/- 8 yrs, with a mean postoperative follow-up of 6 +/- 2 yrs. Seven pts were asymptomatic while 3 had mildly decreased effort tolerance. These pts were evaluated with echocardiogram, cycle ergometer stress test, basal and effort spirometry and perfusion lungs scanning.

Basal ejection fraction was normal in 9 pts and mildly depressed in 1 pt. Basal cardiac index was 1.8 + 2.2 l/min/m2 and increased to 4.8 + 5 l/min/m2 during exercise. Effort tolerance was 73% +/- 21% of predicted values, with maximal O2 consumption of 60% +/- 13% of predicted. Basal spirometry showed a mild restrictive pattern in 7 pts with a decrease in total pulmonary capacity and in forced vital capacity (mean values respectively 79% +/- 14% and 75% +/- 18% of predicted), otherwise respiratory reserve resulted normal in all pts. Carbon monoxide diffusion was impaired in all pts with a mean value of 49% +/- 10% of predicted. O2 saturation near normal in basal condition decrease during exercise (mean value 96% +/- 2% and 91% +/- 7%). The VE/VO2 and Vd/Vt ratio were both abnormally increased (respectively 111% +/- 28% and 186% +/- 39% of predicted). Lung scanning was abnormal in 6 pts with defects of perfusion localized prevalently in left lung (5/6) especially in upper lobe (4/6).

After Fontan operation exercise tolerance is reduced as consequence of 1) a suboptimal increase in cardiac output and 2) abnormal gas diffusion probably due to a damage of alveolo-capillary membrane and/or to a ventilation/perfusion mismatch as showed by abnormalities in lungs perfusion and by increase Vd/Vt ratio.