Background Lung clearance index (LCI) is a measure of gas mixing inhomogeneity derived from multi-breath wash (MBW) out techniques, which has been shown to be more sensitive than conventional spirometry/ FEV1. The potentiator, Ivacaftor, led to improvement in LCI in patients with mild cystic fibrosis (CF) lung disease however its utility as an outcome measure in more severe disease requires further investigation. Whilst LCI reflects overall ventilation heterogeneity, analysis of the phase III slopes of successive breaths in the MBW; known as Sacin and Scond; are thought to reflect the ventilation heterogeneity generated at branch points in the acinar and conductive lung zones respectively. This study aimed to explore changes in the indices derived from analysis of MBW following a year of treatment with Ivacaftor.
Method A prospective study was performed between March 2013 and April 2014 on patients with the G551D mutation and eligible for clinically prescribed Ivacaftor. MBW (Innocor SF6 technique) and spirometry were performed immediately prior to commencing Ivacaftor, and at a clinic visit following 9–12 months therapy. FEV1 is calculated using Stanojevic references and all data are expressed as mean (SD). Paired data were analysed with a Wilcoxon rank sum test and correlations with Spearman’s rank correlation. The null hypothesis was rejected at p < 0.05.
Results 8 patients were enrolled with ages ranging from 6–27 years. FEV1 increased from 68.7 (17.2)% before treatment to 80.1 (16.3)% after 9–12 months (p1 and LCI did not correlate with each other.
Discussion Patients prescribed Ivacaftor demonstrated improvements in both conventional FEV1 and the newer measure of LCI; improvement was not limited to patients with milder disease and was seen throughout the group. In this study, the phase III slope measures did not appear to add further value to the LCI. It is possible that this reflects under powering in this small group; further data will be obtained.
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