The use of a shortened Multiple Breath Washout in the assessment of airway clearance in patients with COPD

Background: The Lung Clearance Index (LCI) measured by Multiple Breath Washout (MBW) may offer value in assessing airway clearance devices in COPD however the standardised 1/40th washout is time consuming. This study aims to assess the use of a shortened 1/20th washout in response to an airway clearance device. Methods: This is a sub-analysis of a randomised, double blind, sham controlled trial using High Frequency Airway Oscillations (HFAO) vs sham for eight weeks. The MBW adhered to ERS/ATS standards using an open circuit Innocor device using 0.2% SF6 and performed pre- and post intervention. Tests were analysed using a custom MatLab algorithm and accessed performance characteristics of an earlier 1/20th cut off. Results: 63 participants with COPD were recruited (mean[SD] age 70.02[7.62], FEV1 46.45%[18.03]). Post intervention the LCI1/40 increased in the HFAO and sham groups (0.757[1.233], 0.426[1.463] respectively) and in the LCI1/20 (0.343[0.173], 0.071[0.731] respectively) however this was not significant. The ratio of change between the LCI1/40 and LCI1/20 was 0.453 in the HFAO group and 0.167 in the sham (p=0.29). The average washout time was 204[93]secs (LCI1/40) and 140[61]secs (LCI1/20) per test with a time saving of 35%. Conclusion: The ratio of change following an intervention for the LCI1/20 and LCI1/40 differs between groups. The use of the LCI1/20 may overestimate between group differences.