Closing volume by forced oscillations and severity of lung disease in young CF patients

<bold>Background:</bold> Data on small airway collapse in young patients with cystic fibrosis (CF) are scarce, mainly due to the complexity of the relevant measurements. Recently, a simpler method based on oscillatory dynamics has been introduced to detect airway closure. <bold>Objectives:</bold> To determine the airway closing volume by the forced oscillations technique (CV_FOT) in children and young adults with CF and relate it to the severity of lung disease. <bold>Methods:</bold> Twenty young patients with CF (age 15.9 ± 5.6 years, range 7-27 years) underwent spirometry, FOT at 5Hz, and nitrogen multiple-breath washout measurements. CV_FOT was defined as the volume at which the respiratory reactance drops suddenly during a slow expiration from total lung capacity to residual volume (RV). CV_FOT was expressed as % of vital capacity and related to patients' age, spirometric parameters (FEV1 and FVC), and lung clearance index (LCI). <bold>Results:</bold> The CV_FOT in our cohort was 21.6 ± 6.9% (range 10.6-32.8%). There was a positive but not significant correlation between CV_FOT and age (r 0.378; P=0.101), a negative correlation between CV_FOT and FEV1 z-score (r –0.743; P<0.001) and between CV_FOT and FVC z-score (r –0.800; P<0.001), and a positive correlation between CV_FOT and LCI (r 0.688; P<0.001). We also observed a positive correlation between CV_FOT and RV z-score (r 0.545; P=0.013). In a linear regression model (R2 0.582), CV_FOT emerged as the only significant predictor of LCI (beta 0.611; P=0.023), independently of patients’ age and FEV1 z-score. <bold>Conclusion:</bold> CVFOT relates closely to the progression and severity of lung disease in young CF patients. This novel and easy-to-obtain FOT parameter holds promise as a simpler tool for CF monitoring.