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

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)_1/40 and LCI_1/20 among subjects with COPD and compared to spirometry and clinical markers.

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 SF₆ concentration washout. Tests were repeated after 20 min and 8  weeks to determine within and between visit repeatability and compared with spirometry.

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 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).

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.