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

INTRODUCTION: COPD affects the small airways and is associated with ventilation heterogeneity. There are little data on the multiple-breath washout (MBW) in patients with COPD, particularly the variability over 8 weeks, using a shortened sulfur hexafluoride (SF(6)) washout. This work evaluated the repeatability of the lung clearance index (LCI)(1/40) and LCI(1/20) 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 (LCI), at conductive (S(cond)) and acinar (S(acin)) levels. The LCI was repeated in triplicate and measured at a traditional 1/40th washout and retrofitted to a shortened 1/20th end tidal SF(6) concentration washout. Tests were repeated after 20 min and 8 weeks to determine within and between visit repeatability and compared with spirometry. RESULTS: Eighty-four subjects were recruited to perform LCI and spirometry with 20 subjects performing the repeatability protocol. There were weak correlations between forced expiratory volume in 1 s ( FEV(1)) per cent predicted and LCI(1/40th) r=−0.311 (p=0.02), and LCI(1/20th) r=−0.40 (p<0.01). The LCI demonstrated excellent within and good between visit repeatability for both a 1/40th and 1/20th washout (intraclass correlation coefficient (ICC)≥0.80). There was a statistically significant strong correlation between LCI(1/40th) and a shortened LCI(1/20) of 0.86 (p<0.01). CONCLUSIONS: The LCI is repeatable within and between visits. There are weak correlations with measures of spirometry. A shortened LCI(1/20th) starting concentration correlates highly with a 1/40th washout, which may encourage clinical use.