Calculation of Scond between 0 and 3 lung turn over (Scond*) in mild to moderate chronic lung disease

Abstract

Background: Nitrogen multiple breath washout (MBW) is an established method to detect ventilation inhomogeneity (VI) in cystic fibrosis (CF) and primary ciliary dyskinesia (PCD). A specific marker for convection-dependent inhomogeneity (CDI) is Scond. In adults with severe lung disease (FEV 1 below -1.64 z-scores), phase III slope fitting became distorted and lead to a ceiling effect of Scond. Therefore Scond*, calculated from an abbreviated MBW protocol, was proposed. We determined if the ceiling effect also occurs in younger patients with less severe lung disease, and if Scond* could also be used in these patients, with the additional benefit of shorter measurement duration. Method: In a prospective cross-sectional study, we applied MBW in 132 children and adults with CF (n= 92) or PCD (n=40). Patients showed mild to moderate lung disease with mean FEV 1 of -1.1 z-scores. We calculated lung clearance index (LCI), Scond/Scond* and Sacin/Sacin*. The (*) indices were derived between 0-3 lung turn over. Abnormal ventilation heterogeneity was defined as >1.64 z-scores from our control group measured with the same settings. Primary endpoints were prevalence of abnormal ventilation heterogeneity for Scond* and the agreement with Scond and LCI. Results: Mean (SD) age was 12.4 (4.4) years. In the whole population, LCI was abnormal in 106 (80 %), Scond in 105 (80%), Scond* in 34 (26%), Sacin in 14 (11%), and Sacin* in 14 (11%). Agreement between VI estimated by Scond* was poor compared with Scond and LCI in CF and PCD. Conclusion: Scond* does not reliably capture CDI in CF or PCD patients with mild to moderate lung disease.