The Lung Clearance Index detects incomplete lung function recovery with acute respiratory events in school-age children with cystic fibrosis

Background: We previously demonstrated that the lung clearance index (LCI) worsens with acute respiratory events (ARE) in preschool children with cystic fibrosis (CF) (Rayment, Thorax 2018). We are now describing the functional consequences of ARE in school-age children. Methods: We extended this multisite prospective observational study into the school-age years. LCI and FEV1 were measured quarterly and during ARE over a 2-year period. We included pulmonary exacerbations (PEx), defined as ARE treated with antibiotics, and untreated increased cough events (UIC). A linear regression within a generalized estimating equation model, accounting for repeated events, was used to compare changes from a recent stable visit. Results: We enrolled 103 subjects with a mean (range) age of 9.8 (5-16.8) years. 360 stable visits, 83 PEx and 50 UIC were analyzed. Mean (range) LCI and FEV1 at enrolment were 9.5 units (5.9-17.2) and 93% predicted (39-125), respectively. LCI and FEV1 worsened with both PEx and UIC and did not recover at the next consecutive follow-up visit. At the first stable visit after follow-up, neither LCI or FEV1 recovered to baseline for the PEx group, and, for the UIC group, only FEV1 recovered. Conclusion: In school-age children with CF, lung function does not recover to baseline after PEx and, as detected by LCI, recovery is also incomplete after UIC.