Introduction Lung Clearance Index (LCI) is a measure of lung gas mixing derived from the Multiple Breath Washout (MBW) test. We present LCI, FEV1 and CT data from the Run-In Study, a longitudinal study in preparation for a multi-dose trial of nebulised gene therapy for CF.
Methods MBW, spirometry and low-dose HRCT chest were performed as part of the first Run-In Study visit. LCI was reported as the mean result from at least two technically acceptable sulphur hexafluoride MBW tests performed using a modified Innocor gas analyser. Spirometry was performed to ERS standards. CT scans were assessed by two independent radiologists for extent and severity of bronchiectasis, wall thickening, presence of small and large airway plugs, and gas trapping.
Results 191 patients attended visit 1, mean (range) age 22.6 (10–59.1) years. Validated LCI, FEV1 and CT results were available for 167, 191 and 150 patients, respectively. Mean (SD) FEV1 was 72(19)% predicted. Mean (SD) LCI was 10.7 (2.7), with mean intravisit coefficient of variation of 4.9%. LCI correlated negatively with FEV1 (r=−0.68, p<0.001), but was abnormally elevated in 72% of participants with normal FEV1 (see Abstract S22 Figure 1; triangles indicate FEV1 >80% and LCI >7.5). 95% CI for LCI in normal subjects 5.9 to 7.5. Both FEV1 and LCI correlated with all CT measures (p<0.001), most strongly with extent of bronchiectasis. LCI correlated better than FEV1 with extent of bronchiectasis, r=0.72 (p<0.001) vs r=−0.61 (p<0.001), respectively.
Conclusions Results from this large cohort suggests that LCI is a more sensitive test of early CF lung disease, and correlates better with extent of bronchiectasis seen on CT, than FEV1. Validation of data from subsequent study visits is in progress and will be reported at a future date.