Pulmonary function tests (PFTs)
First visit: Children underwent spirometry and DLCO/DLNO measurement (Medisoft, Hyp’Air Compact, Belgium) to calculate the membrane diffusion (Dm) and capillary blood volume (Vc), as recommended (a finite specific conductance in the blood for NO (θNO) was assumed), as previously described.5 The breath-hold time of this DLCO/DLNO measurement was 4 seconds.
Second visit: Children underwent spirometry and DLCO measurement (without DLNO) according to international recommendations. The breath-hold time of this DLCO measurement was 10 seconds.
The predicted values were those of Global Lung Initiative, taking into account ethnicity for spirometry, and those of Caucasians for DLCO. The results of KCO and DLCO are given without and with correction (KCOcorrected, DLCOcorrected) for hemoglobin concentration, as recommended. The changes in DLCO and KCO from visit 1 to visit 2 were calculated as visit 1, % predicted value minus % predicted value of visit 2.