A Short extension to multiple breath washout provides additional signal of distal airway disease in people with CF: A pilot study.

• MBW with short extension (MBW ShX) is feasible with children from 5 years of age. • LCI ShX is repeatable during clinical stability and has a larger signal around episodes of PEx. • The extent of under/ unventilated lung units cannot be predicted by the baseline LCI 2.5. • Further studies will build on this pilot data to fully establish its utility in monitoring disease status. Adding a slow vital capacity (SVC) to multiple breath washout (MBW) allows quantification of otherwise overlooked signal from under/un-ventilated lung units (UVLU) and may provide a more comprehensive assessment of airway disease than conventional lung clearance index (LCI 2.5). We conducted a pilot study on people undergoing MBW tests: 10 healthy controls (HC) and 43 cystic fibrosis (CF) subjects performed an SVC after the standard end of test. We term the new outcome LCI with Short extension (LCI ShX). We assessed (i) CF/ HC differences, (ii) variability (iii) effect of pulmonary exacerbation (PEx)/treatment and (iv) relationship with CF computed tomography (CFCT) scores. HC/ CF group differences were larger with LCI ShX than LCI 2.5 (P <0.001). Within the CF group UVLU was highly variable and when abnormal it did not correlate with corresponding LCI 2.5. Signal showed little variability during clinical stability (n = 11 CF; 2 visits; median inter-test variability 2.6% LCI ShX, 2.5% LCI 2.5). PEx signal was significantly greater for LCI ShX both for onset and resolution. Both MBW parameters correlated significantly with total lung CT scores and hyperinflation but only LCI ShX correlated with mucus plugging. UVLU captured within the LCI ShX varies between individuals; the lack of relationship with LCI 2.5 demonstrates that new, additional information is being captured. LCI ShX repeatability during clinical stability combined with its larger signal around episodes of PEx may lend it superior sensitivity as an outcome measure. Further studies will build on this pilot data to fully establish its utility in monitoring disease status. [ABSTRACT FROM AUTHOR]