Abnormal Lung Clearance Index in Cystic Fibrosis Children with Normal FEV1 and Single-Breath Nitrogen Washout Test.

Single- and multiple-breath washout tests (SBW and MBW) measure ventilation inhomogeneity, but the relationship between them is unclear. Forty-three subjects with cystic fibrosis (CF) and healthy controls (HC) 8-21 years of age were recruited (CF = 30 and HC = 13) and performed nitrogen MBW, vital capacity SBW, spirometry, and plethysmography. Mean phase III slope from SBW (SIII) and lung clearance index (LCI) were significantly different between CF and HC (p = 0.017 and p < 0.0001, respectively). Based on Pearson correlation, SIII and LCI showed strong correlation (ρ = 0.81, p < 0.0001). Both SIII and LCI significantly correlated with spirometry (all p < 0.05). Among CF subjects with normal FEV1 (≥ 80%; n = 17), 76% (n = 13) had normal SIII but abnormal LCI. We conclude that LCI can be abnormal despite normal SIII and FEV1 in CF children. Although LCI and SIII showed strong correlation, our results suggest that LCI is a better test to detect ventilation inhomogeneity in CF children with normal FEV1.