Methods
The study was approved by both hospital IRB-committees and informed consent was obtained from the patients or parents/caregivers. The study was conducted between 2015 – 2018. Patients above the age of 4 years with a confirmed diagnosis of CF10, FEV1 ≄80% predicted, clinically stable, and with no pulmonary exacerbations (PEx) in the four weeks prior to the study, were recruited from two CF Centers, the Hadassah Medical Center in Jerusalem, Israel, and the Vall d’ Hebron Hospital in Barcelona, Spain.
Demographic data e.g., age, gender, CFTR-mutations, body mass index (BMI), pancreatic status [pancreatic insufficiency (PI) or sufficiency (PS)] and the presence of CF-related diabetes (CFRD), were obtained from patient files. Spirometry was measured according to ATS/ERS guidelines11. FEV1 results were transformed into Z-scores using the Global Lung Function Initiative calculator (version 3.3.1). Multiple breath washout (MBW) test was performed using the Exhalyzer D (EcoMedics AG, Duernten, Switzerland), according to ERS/ATS Consensus Guidelines12, and was carried out on the same visit day of the spirometry in order to correlate the results. Mean LCI calculated from a minimum of two technically valid and repeatable tests was reported. Analysis of MBW data was performed using the nitrogen washout FRC/LCI software (Spiroware).
All chest high resolution computed tomography (HRCT) scans performed during the study period (up to one year before or after spirometry and LCI tests) were examined by an experienced radiologist or by a specifically trained pediatric pulmonologist. HRCT scans were analyzed based on the modified Brody score; hyperaeration of the lungs was assessed instead of air trapping as expiratory images were not available for all patients13. Subscores for the presence and severity of bronchiectasis, mucous plugging, bronchial wall thickening, parenchyma, and focal hyperaeration in each lobe were calculated. Parenchymal findings of ground glass opacities, consolidations, and cysts or bullae were considered in determining a single parenchymal subscore. The sum of subscores comprised the lung Total Brody Score (TBS) for each patient, ranging from 0 to 207. Pulmonary exacerbations (PEx) were defined as acute clinical deterioration, including malaise, anorexia, dyspnea, fever, increased cough, change in sputum quantity/quality, worsening in nutritional status and/or decline in pulmonary function, requiring addition or change of oral (PO) or intravenous (IV) antibiotics (Abx). Pulmonary exacerbations were subdivided into minor exacerbations, requiring PO antibiotics andmajor exacerbations, if IV Abx had to be initiated. Expectorated or induced sputum samples for microbiologic analysis are routinely collected from CF patients at each visit to the CF Center. Respective data were retrieved from patient files and/or electronic medical records. Chronic P. aeruginosa (PA) infection was defined by the Leeds criteria, i.e. >50% of the sputum samples over the preceding 12 months were positive14. Chronic PA infection, the number and type of PEx and duration of Abx treatment in days, during the previous year, were evaluated for each spirometry, LCI and HRCT test time point performed by each patient. A six-minute walk test (6MWT) was performed according to ATS guidelines15. The 6MWT results (i.e. six-minute walk distance [6MWD]) were transformed into Z-scores based on reference data16,17 using the following formula: {value found āˆ’ normal value / standard deviation}.