Single-breath washout and association with structural lung changes in children with cystic fibrosis

Abstract

Background In school-aged children with cystic fibrosis (CF) outcomes of ventilation distribution from multiple-breath washout (MBW) strongly correlate with structural lung disease. Data for the recently validated single-breath washout (SBW) are lacking. Objectives To assess whether SBW measurements using a double-tracer gas reflects structural lung damage assessed by chest computed tomography (CT) in children with CF. Methods Children with CF completed at least two nitrogen-MBW and SBW tests and underwent chest CT. Primary outcomes were LCI, volume corrected S cond and S acin from MBW, and volume corrected phase III slope of SBW (SIII). Extent of bronchiectasis and air trapping was scored on CT. Relationships between washout outcomes and CT scores were explored with Spearman correlations. Results Of 32 children studied, acceptable MBW was obtained in 27, SBW in 26 and CT in 26 respectively. Median (range) age was 8.2 (5.2 – 16.3) years. Mean (SD) LCI was 8.4 (1.3), S cond 0.049 (0.025), S acin 0.071 (0.043), and SIII -150.7 (90.1) mg/mol. Twenty children (77%) had bronchiectasis and 24 (92%) air trapping. We found no association between SIII and either the MBW outcomes or CT scores. LCI and S cond were associated with bronchiectasis extent (r = 0.59, p = 0.003; r = 0.44, p = 0.023, respectively). Conclusions Structural lung disease on CT scans in children with CF were not reflected by impaired acinar ventilation measured by SBW and S acin ,(from MBW) but were associated with changes in LCI and S cond . Structural disease in acinar regions may not be detected on CT or may be too mild to be detected using inert gas washout tests at this age. SBW added no benefit to indices measured by MBW.