Reanalysis of N-lung clearance index and the comparison to SF-lung clearance index and magnetic resonance imaging.

Since the finding and correction of an error in previous spiroware software versions commonly used with the Exhalyzer D for multiple-breath washout (MBW) analysis, there has been an ongoing discussion about its impact on MBW results. In this study, we reanalyzed previously published findings with the corrected spiroware version 3.3.1. In total, 31 infants and preschool children with cystic fibrosis (CF) (mean age 2.3 ± 0.8 years) and 20 healthy controls (mean age 2.3 ± 1.1 years) underwent consecutive sulfure hexafluoride (SF)- and nitrogen (N)-MBW. In addition, children with CF underwent chest magnetic resonance imaging (MRI) on the same day. After reanalysis of MBW data, the corrected N-lung clearance index (LCI) decreased by 10-15% in both groups (P = 0.001) but remained significantly higher than the SF-LCI (P<0.01). Diagnostic agreement between the MBW results remained moderate with a persistent correlation between SF- and N-MBW. The corrected upper limit of normal of the N-LCI changed classification of nine children with CF, eight of which were within the normal range after correction. The correlation between the different LCI values and the chest MRI scores remained significant with strongest correlation with the MRI perfusion score. Consequently, the corrected N-LCI is significantly lower than the previous N-LCI, but key results published before are not affected by the reanalysis.