Relationship between impulse oscillometry and spirometric indices in cystic fibrosis children

Background: The aim of our retrospective study was to determine the relationship between impulse oscillometry (IOS) data and spirometric tests in cystic fibrosis (CF) children. Methods: Thirty CF children aged 4–19 years have performed lung function tests (LFT). A subset of 15 patients repeated LFT on five separate occasions. IOS parameters were respiratory resistance (Rrs), reactance (Xrs) and impedance at 5 Hz (R5, X5, Zr) and the resonant frequency (Fres). Spirometry indices (SI) included forced expiratory volume in 1 sec (FEV1), forced expiratory flow during the middle half of FVC (FEF25–75) and forced vital capacity (FVC). Results: An inverse relationship was observed between raw values of R5, Zr, Fres and SI respectively, and X5 correlated positively with SI. Although significant, these correlations were poor. Receiver operating characteristic curves (ROC) were constructed to identify cutoff points for IOS parameters to discriminate between children according to predefined FEV1 thresholds (percent predicted), generally used to categorize the level of lung function impairment. No acceptable cutoff points can be found for IOS parameters. Trends analyses in the subgroup of 15 patients showed a significant decline of FEV1 between the first and the fifth evaluation. None of the IOS indices demonstrated a consistent tendency, apart from a slight decrease of Fres. Conclusion: IOS measurements presented an insufficient sensitivity to detect and follow bronchial obstruction in CF patients.