Ventilation heterogeneity in children with severe asthma.

Small airway disease, characterised by ventilation heterogeneity (VH), is present in a subgroup of patients with asthma. Ventilation heterogeneity can be measured using multiple breath washout testing. Few studies have been reported in children. We studied the relationship between VH, asthma severity, and spirometry in a cross-sectional observational cohort study involving children with stable mild-moderate and severe asthma by GINA classification and a group of healthy controls. Thirty-seven participants aged 5-16 years completed multiple breath nitrogen washout (MBNW) testing (seven controls, seven mild-moderate asthma, 23 severe asthma). The lung clearance index (LCI) was normal in control and mild-moderate asthmatics. LCI was abnormal in 5/23 (21%) of severe asthmatics. The LCI negatively correlated with FEV1 z-score.Conclusion: VH is present in asthmatic children and appears to be more common in severe asthma. The LCI was significantly higher in the cohort of children with severe asthma, despite no difference in FEV1 between the groups. This supports previous evidence that LCI is a more sensitive marker of airway disease than FEV1. MBNW shows potential as a useful tool to assess children with severe asthma and may help inform clinical decisions. What is Known: • Increased ventilation heterogeneity is present in some children with asthma • Spirometry is not sensitive enough to detect small airway involvement in asthma What is New • Lung clearance index is abnormal in a significant subgroup of children with severe asthma but rarely in children with mild-moderate asthma • Our data suggests that LCI monitoring should be considered in children with severe asthma.