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Background: Multiple breath washout (MBW) is a lung function test that allows measurement of functional residual capacity (FRC) and lung clearance index (LCI), a marker of ventilation heterogeneity. It has previously been described that N 2 washout results in higher values for FRC and LCI compared to SF 6 using the Mass Spectrometer but this has not been assessed with the Innocor TM device. The aim of study was to compare the MBW N2 with the SF 6 Innocor TM for a) FRC, b) LCI, c) intra-test variability. Methods: 21CF (14F, median 16(range6-63)yrs)) and 10non-CF (8F, median 29(10-44)yrs) completed MBW trials with N 2 (Exhalyzer D, Ecomedics AG, Switzerland) and SF 6 (Innovision, Denmark) in random order on the same visit; methods previously described (Horsley et al. 2008, Thorax; 63,2,135-140, Jensen et al. 2013, PloS One; 8,2,e56868). Results: FRC and LCI were significantly higher with N 2 than with SF 6 in both CF (2.44L vs. 1.91L; p= 2 and SF 6 (FRCCV 2.90 vs. 2.53%,ns; LCICV 3.57 vs 3.78%,ns). CV did not relate to underlying severity: separating the results below and above the median, LCI and FRC CV were not significantly different. Conclusions: FRC and LCI values cannot be used interchangeably between the Innocor TM and Exhalyzer D. In non CF, there was a statistically significant difference in both, with higher values for N 2 . The difference was greater in CF and increased as LCI did, magnitude of the LCI did not affect the CV between tests. Both machines have similar discriminative power. Sponsored by a non-restricted grant from Novartis. |
