Comparison of lung clearance index measured during helium washin and washout in children with cystic fibrosis

AIM: Lung clearance index (LCI) is a sensitive marker of early lung disease in cystic fibrosis (CF). This preliminary study compares results obtained from the washin and the washout phase of the multiple breath washout in CF children and healthy controls using an early commercially available device. METHODS: LCI was measured using a device measuring flow and mainstream molar mass with helium as the inert gas. Sixty-five healthy controls and 65 CF children (age range 4.6-17.9 years) were included. RESULTS: LCI measured on the washout (LCIWO ) and on the washin (LCIWI ) were correlated in CF children (R = 0.440, P < 0.001, n = 185). LCIWO was higher than LCIWI with a mean difference of 1.08 (95% limits of agreement -2.11 to 4.27, n = 185) in CF children and 0.26 (95% LA -3.2 to 3.72, n = 185) in controls. Within-test repeatability criteria were met in 107/130 WO and 93/130 WI (P = 0.034), In 81 children, LCIWI and LCIWO were obtained. LCIWI was higher in CF patients than in controls (7.72 vs. 6.55, P < 0.001), as was LCIWO (8.49 vs. 7.13, P < 0.001). In 34 CF patients with normal FEV1 , LCIWI only was abnormal in five, LCIWO only in five and both were abnormal in three. One of seven CF patients with abnormal FEV1 had normal LCIWI and LCIWO . CONCLUSION: In CF patients, discordances between abnormal LCIWI and LCIWO were observed. LCIWI and LCIWO were only weakly correlated. This likely resulted from technical factors as the use of mainstream molar mass signal, a temperature model validated for infants only and absence of CO2 correction.