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 (SF6) washout. This work evaluated the repeatability of the lung clearance index (LCI)1/40and LCI1/20among 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 (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 SF6concentration 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 ( FEV1) per cent predicted and LCI1/40thr=−0.311 (p=0.02), and LCI1/20thr=−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 LCI1/40thand a shortened LCI1/20of 0.86 (p<0.01). Conclusions The LCI is repeatable within and between visits. There are weak correlations with measures of spirometry. A shortened LCI1/20thstarting concentration correlates highly with a 1/40th washout, which may encourage clinical use.