Multiple-breath-washout
MBW measurements were performed with a flow, volume and molecular mass measurement analyzer (EXHALYZER D, Ecomedics, Switzerland), according to ERS/ATS Consensus Guidelines 27. A minimum of two satisfactory LCI results were obtained for each patient. Normal cut-off value of LCI was set at 7.81. Scond and Sacin, two MBW test secondary indexes of conductive airways and acinar zone respectively, collected during the measurements, were included in the analysis