Pulmonary Function
All patients underwent spirometry with bronchodilator testing. Forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), FEV1/FVC ratio, and forced expiratory flow at 25–75% of FVC (FEF25–75) were calculated. A positive bronchodilator response was defined as an increase in the FEV1 of ≥ 12% from baseline (15 minutes after inhalation of 400 mcg of salbutamol by metered-dose inhaler plus spacer). Where available, total body plethysmography and lung diffusion by the single breath diffusion method were performed, and the following parameters were collected: total lung capacity (TLC), functional residual capacity, residual volume (RV), RV/TLC ratio, diffusing capacity of the lung for carbon monoxide (DLCO), and DLCOadjusted for alveolar volume (KCO). All parameters were expressed as a percentage of the predicted value (%pred) and as a z-score, except for the RV/TLC ratio, which was only expressed as a percentage. The FEV1/FVC and RV/TLC ratios were also expressed as actual values (percentages). The Global Lung Function Initiative equations12,13 were used as references for spirometry and diffusion, while equations from Rosenthal et al14. were used for plethysmography. All measurements were performed according to American Thoracic Society/European Respiratory Society guidelines15-17.