RESUMO
BACKGROUND: 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 (LCI2.5). METHODS: 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 (LCIShX). We assessed (i) CF/ HC differences, (ii) variability (iii) effect of pulmonary exacerbation (PEx)/treatment and (iv) relationship with CF computed tomography (CFCT) scores. RESULTS: HC/ CF group differences were larger with LCIShX than LCI2.5 (P<0.001). Within the CF group UVLU was highly variable and when abnormal it did not correlate with corresponding LCI2.5. Signal showed little variability during clinical stability (n = 11 CF; 2 visits; median inter-test variability 2.6% LCIShX, 2.5% LCI2.5). PEx signal was significantly greater for LCIShX both for onset and resolution. Both MBW parameters correlated significantly with total lung CT scores and hyperinflation but only LCIShX correlated with mucus plugging. CONCLUSIONS: UVLU captured within the LCIShX varies between individuals; the lack of relationship with LCI2.5 demonstrates that new, additional information is being captured. LCIShX 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.