P230 The lung clearance index in adults with connective tissue disease – a pilot study in rheumatoid arthritis

Introduction and objectives Initial manifestations of lung disease in rheumatoid arthritis often occur in the small airways which can be challenging to measure using traditional lung function tests. The lung clearance index (LCI), measured by the nitrogen multiple breath washout (MBW) is a non-invasive measure of ventilation inhomogeneity and has been shown to be elevated in patients with primary lung disease. This study aimed to assess whether LCI, Scond (convection-dependent ventilation inhomogeneity) and Sacin (diffusion-convection dependent inhomogeneity) were elevated in patients with rheumatoid arthritis related lung disease and to assess whether MBW is feasible in this patient population. Methods 19 patients with rheumatoid arthritis (5 without lung disease and 14 with associated lung disease) were recruited from the respiratory and rheumatology clinics at North Bristol NHS Trust. Each patient participant completed spirometry, MBW and health-related quality of life (HRQoL) questionnaires at a single study visit. A separate group of 8 healthy controls also completed spirometry and MBW at a single visit. MBW was completed using the EasyOne proLAB™ (ndd Medizntechnik AG, Zurich, Switzerland). Results The mean time to perform a single test was 214 s and the mean number of tests required to achieve 3 acceptable efforts was 3.5 tests. All MBW parameters were repeatable (intra-class correlation coefficient >0.8). LCI and Sacin were significantly increased in patients with associated lung disease compared to healthy controls (p=0.008, p=0.004). No significant difference was seen in LCI and Sacin between patients without lung disease and healthy controls (p=0.171, p=0.083). There was no significant difference in spirometry z-scores. There was a significant correlation between LCI and HRQoL as measured by K-BILD and SGRQ. Conclusion MBW is a repeatable and feasible technique in patients with rheumatoid arthritis. The data from this pilot study suggests that N2 MBW may be a promising technique in the assessment of lung disease in patients with rheumatoid arthritis, with LCI and Sacin appearing to be the most useful parameters. The findings support the further investigation of MBW in patients with rheumatoid arthritis in a longitudinal cohort study to assess the variability over time and the relationship with HRQoL.