Simultaneous sulfur hexafluoride and nitrogen multiple-breath washout (MBW) to examine inherent differences in MBW outcomes.

N2 MBW results were higher than SF6 MBW, with some of the largest differences reported to date being observed. The biggest impact was at the end of the washout and this was even the case when gases were washed out simultaneously. N2 and SF6 MBW results are inherently different and should be considered as independent measurements.