Introduction Lung clearance index (LCI) is a measure of ventilation in homogeneity derived from multiple breath washout (MBW). Although FEV1 is commonly used to assess severity of airway disease and response to therapy, it is insensitive to small airways disease and is often within normal range in bronchiectasis (BE) not caused by Cystic Fibrosis (CF) until disease is well established. In CF, LCI is more sensitive than FEV1 in detecting airways abnormalities and is currently used as an outcome measure in clinical trials. In BE, there is a need to find a sensitive outcome measure that is responsive to interventions, particularly in those with mild disease.
Objective To assess within and between visit repeatability of LCI and determine the relationship between FEV1 and LCI in stable BE.
Methods Inclusion criteria: HRCT diagnosis of BE within the last 5 years; clinically stable (no infective symptoms for >4 weeks); no genetic or clinical features of CF. Participants attended for two visits, 2 weeks apart. At each visit they performed MBW in triplicate, using 0.2% sulphur hexafluoride and a modified Innocor device. LCI was derived from the mean of at least 2 acceptable washouts. Spirometry was performed to ATS/ERS standards.
Results 14 patients (8M/6F) attended for two visits. The mean (SD) age was 60.5 (15.4) yrs. Mean (SD) FEV1 % predicted was 87.1 (18.6), range (44–117). Mean (SD) LCI was 9.4 (2.0) on visit 1 and 9.4 (1.9) on visit 2 (normal <7.5). The intra-visit coefficient of variation (CV) was 4.7 % (3 measures). Between visit repeatability of LCI was 0.54 (SD of variance between visits). LCI negatively correlated with FEV1 (r=−0.69, p<0.001). Sensitivity of LCI and FEV1 for the diagnosis of bronchiectasis by CT was 71% and 29% respectively.
Conclusions This is the first report of LCI in non-CF BE. LCI is a more sensitive test of lung function than FEV1 and is abnormal in the majority of people with BE who have a normal FEV1. LCI has good intra-visit and between visit repeatability. Across a range of FEV1 there is a strong relationship between LCI and FEV1.