Evaluation of SnIII parameters as outcome measures of multiple breath washout (MBW) in preschool children with cystic fibrosis

Scond and Sacin are alternative MBW indices that reflect regional variations in ventilation homogeneity. Verger et al (2020) suggest the use of Scond* and Sacin*, measured from the second breath to 3-TO, in subjects with LCI ≥9 to account for the plateau effect in normalized phase III slopes (SnIII) associated with high ventilation inhomogeneity. Further validation in preschool children with cystic fibrosis (CF) is required. We retrospectively analyzed data collected as part of a longitudinal observational study in preschool age children, where MBW (Exhalyzer® D, EcoMedics AG) was performed at all study visits, to assess SnIII parameters (Scond, Sacin, Scond* and Sacin*). To date, 38 (19 HC; 19 CF) participants have been analyzed (mean age 5 years, SD 0.8). Breath-by-breath quality control was performed per the ERS/ATS consensus statements for inert gas washout (Robinson et al 2013, 2018). Scond and Sacin were acceptable in 79% (30/38) of preschool children, similar to previously reported feasibility. Our results suggest that Scond, Scond*, Sacin and Sacin* differentiate health and disease (p<0.05, paired t test) in early CF disease. Further analysis of this large, longitudinal dataset to determine how these parameters track over time is ongoing. Funded by NHLBI.