Within-breath changes in respiratory system impedance in children with cystic fibrosis

Background: The aim of this study was to assess within-breath respiratory system impedance by the forced oscillation technique (FOT) in children with cystic fibrosis (CF) and relate it to the underlying lung disease. Methods: Thirty-three children with CF (median [range] age 12.0 [6-17] years) underwent FOT at 8 Hz during tidal breathing, multiple breath nitrogen washout (LCI), spirometry (FEV1), body plethysmography (RV/TLC), and magnetic resonance imaging (MRI). FOT outcomes included: mean inspiratory, expiratory, and whole breath resistance (R8_INSP, R8_EXP, R8_TOT) and reactance (X8_INSP, X8_EXP, X8_TOT), and the differences between X8_INSP and X8_EXP (ΔX8). Morphological changes were evaluated by MRI using CF-specific morphological scores. Spearman correlation was performed to examine the correlation between FOT indices and other parameters. Results: FEV1 was negatively correlated with R8_EXP (r = −0.52, P = 0.002) and ΔX8 (r = −0.55, P = 0.001), and positively correlated with and X8_EXP (r = 0.56, P < 0.001). RV/TLC was positively correlated with R8_EXP (r = 0.43, P = 0.013), and ΔX8 (r = 0.54, P = 0.001) and negatively correlated with X8_EXP (r = −0.54, P = 0.001). We found poor correlation between FOT parameters and LCI and no correlation between FOT parameters and MRI scores. Conclusion: In children with CF, changes in within-breath FOT parameters are consistent with peripheral obstruction and dynamic airway compression, while they are not associated with ventilation heterogeneities and morphological alterations.