Pulmonary gas exchange during exercise in Fontan patients at a long-term follow-up

Desaturation during exercise in the Fontan type of circulation may be due to known right-to-left shunts in some patients, while in others there are no obvious signs of shunts. Aim: To evaluate the gas exchange and exercise capacity in patients with Fontan circulation. Material and methods: Twenty patients with the Fontan type of circulation, median age at operation 7.5 years (3.0-35 years), follow-up time 12.1 years (8.3-20.4 years), were included. The intrapulmonary gas mixing (N-2-slope) and diffusion capacity for carbon monoxide (D-LCO) was evaluated and determination of cardiac output was performed at rest and during exercise with measurements of ventilation, oxygen uptake, respiratory rate, carbon dioxide production and heart rate. Samples for blood gases (PaO2, SaO2) were obtained at rest and at the end of each work load. Results: The median exercise capacity was 1.47 l min(-1). During exercise, all the patients had an alveolar-arterial oxygen partial pressure difference (PA-aO2) above 2 SD. Patients with known right-to-left shunts had lower PaO2 and SaO2 values and higher PA-aO2 values both at rest, median 7.5 kPa, 90%, and 7.2 kPa, respectively, and during exercise, median 5.8 kPa, 77% and 10.1 kPa, compared with those with no shunts, median 11.2 kPa, 97% and 4.1, respectively, at rest and 9.7 kPa, 94%, and 6.3 during exercise (P<0.01). No correlation was found between cardiac index, the N-2-slope or the D-LCO at rest and the PaO2 and SaO2 at rest or during exercise. Conclusion: In patients with the Fontan type of circulation, right-to-left shunts are the major cause of desaturation during exercise.