Introduction and objectives Chronic Obstructive Pulmonary Disease (COPD) is a small airway disease associated with ventilation heterogeneity. The Lung Clearance Index (LCI) is a potential early marker of lung damage and has been demonstrated to be repeatable within visit for patients with stable COPD. We sought to evaluate the feasibility and repeatability of the LCI between visits among subjects with stable COPD.

Methods The LCI was measured by performing an inert Multiple Breath Washout using a modified photoacoustic Innocor device with 2% Sulphur Hexafluoride (SF₆) on subjects with stable COPD, GOLD Stage II-IV alongside phase 3 slope analyses. The LCI _SF6 was repeated (in triplicate) at weeks one and eight in accordance to ERS/ATS standards. Repeatability data was analysed using a combination of Intraclass Correlation Coefficients (ICC) and Bland-Altman plots. Phase 3 slopes were analysed using a custom MATLAB algorithm.

Results 20 patients were initially recruited, 18 of which were suitable for analysis (16 male, mean [SD] age 70 [6.5], FEV1%predicted 51 [15.4], LCI 11.104 [2.372]). The between visit repeatability (ICC) was: FRC_LCI 0.919, LCI_SF6 0.881, S_cond 0.517, S_acin 0.801. The Bland Altman plot did not reveal any systematic bias.

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Abstract P231 Figure 1

Difference vs average: LCI_sf6 between visit

Conclusions The LCI_SF6 is feasible and repeatable between visits over an eight week period in patients with stable COPD. This demonstrates high ICC’s in the FRC_LCI, LCI_SF6 and the S_acin. The repeatability of the S_cond was considered moderate.