Abbreviation Modalities of Nitrogen Multiple-Breath Washout Tests in School Children With Obstructed Lung Disease

Rationale: Nitrogen multiple-breath washout (N-2 MBW) is a promising tool for assessing early lung damage in children with chronic obstructive pulmonary disease, but it can be a time-consuming procedure. We compared alternative test-shortening endpoints with the most commonly reported N-2 MBW outcome, the lung clearance index, calculated as lung volume turnovers required to reach 2.5% of the starting N-2 concentration (LCI2.5). Methods: Cross-sectional study of triplicate N-2 MBWmeasurements obtained in cystic fibrosis (CF) patients (N = 60), primary ciliary dyskinesia (PCD) patients (N = 28), and matched healthy controls (N = 48) aged 5-18 years. Bland-Altman analysis was used to compare LCI2.5 with earlier LCI endpoints (3%, 4%, 5%, 7%, and 9% of starting N-2 concentration), Cn@TO6 (defined as % of N-2 starting concentration when reaching six lung volume turnovers), and LCI derived from only two N-2 MBW runs in each session. N2 MBW endpoints were analyzed as z-scores calculated from healthy controls. Results: In PCD, Cn@TO6 and LCI2.5 exhibited similar values (mean [95% CI] difference: 0.33 [-0.24; 0.90] z-scores), reducing the test duration by one-third (5.4 min; 95% CI: 4.0; 6.8). All other tested alternative endpoints exhibited increasing disagreement with increasing LCI2.5. With an average reduction in test duration of 40%, LCI2.5 derived from two runs exhibited good agreement in all children. Conclusions: Cn@TO6 may be suggested as a potential test-shortening endpoint in school children with PCD. In CF, early test termination may reduce measurement power with advancing pulmonary disease, suggesting differences in underlying pathophysiology. Two technically acceptable N-2 MBW runs may be sufficient in school children irrespective of diagnosis with CF or PCD. (C) 2015 Wiley Periodicals, Inc.