Double gas transfer factors (DLCO-DLNO) at rest in patients with congenital heart diseases correlates with their ventilatory response during maximal exercise

Aim: Exercise capacity is altered in congenital heart diseases (CHD) with potentially impaired pulmonary perfusion adaptation during exercise, such as in single ventricle or in significant pulmonary regurgitation. This study aimed to evaluate the value of double gas transfer factor analysis, at rest in conjunction with postural manoeuvres, to explore the various components of pulmonary gas transfer and its association with exercise capacity.

Methods: A total of 40 subjects (24 CHD, 16 controls) underwent a combined measurement of lung diffusing capacity for carbon monoxide and nitric oxide (DLCO-DLNO) to determine pulmonary membrane diffusion (Dm) and Vcap, in sitting then supine position. CHD patients performed a maximal cardiopulmonary exercise test.

Results: Compared to normal controls, the CHD group's DLNO, DLCO, Vcap, and alveolar volume (AV) at rest, in the sitting position were depressed, whereas the DLCO/AV and DLNO/AV were similar. The magnitude of Dm and Vcap adaptation induced by postural change was similar in both groups, indicating a preserved pulmonary capillary recruitment capacity in CHD. In the CHD group, at rest, for each ml of postural-induced increase in Vcap we observed during exercise a VE/VCO2 slope decrease of 0.46 (95% CI[0.83; 0.098]), indicating a better ventilatory response to exercise.

Conclusion: CHD patients with impaired pulmonary circulation have a reduced Dm and Vcap mainly due to decreased pulmonary volume but maintain a normal capacity to adapt these parameters through a simple recruitment manoeuver. Vcap adaptation evaluated at rest predicts the level of ventilatory efficiency during exercise, which represents a main limiting factor in these CHD patients.