The validity of shortened multiple breath washout testing using sulphur hexafluoride in the assessment of patients with COPD

Introduction Chronic Obstructive Pulmonary Disease (COPD) affects the small airways and is associated with ventilation heterogeneity. There is little data on the Multiple Breath Washout (MBW) in patients with COPD particularly the variability over eight weeks, using a shortened sulphur hexafluoride (SF6) washout. This work evaluated the repeatability of the LCI1/40 and LCI1/20 among subjects with COPD and compared to spirometry and clinical markers. Methods The MBW was performed on patients with COPD to determine ventilation heterogeneity globally (Lung Clearance Index (LCI)), at conductive (Scond) and acinar (Sacin) levels. The LCI was repeated in triplicate and measured at a traditional 1/40th washout and retrofitted to a shortened 1/20th end tidal SF6 concentration washout. Tests were repeated after 20 min and eight weeks to determine within and between visit repeatability and compared with spirometry. Results 84 subjects were recruited to perform LCI and spirometry with 20 subjects performing the repeatability protocol. There were weak correlations between FEV1 percent predicted and LCI1/40th r=−0.311 (p=0.02), and LCI1/20th r=−0.40 (p Conclusions The LCI is repeatable within and between visits. There are weak correlations with measures of spirometry. A shortened LCI1/20th starting concentration correlates highly with a 1/40th washout which may encourage clinical use.