P89 Ventilation heterogeneity is a feature of children with severe asthma and normal spirometry

Introduction Ventilation heterogeneity (VH) is a feature of a subgroup of adults with asthma (Verbanck et al. AJRCCM 1999; 159.5:1545–1550), however less is known regarding VH in childhood asthma. Previous data indicates VH is raised in asthmatic children compared with controls, and may be particularly high in those with severeor poorly controlled asthma. This may be important as many children report poor symptom control, despite normal spirometry. Objectives We aimed to study the relationship between ventilation heterogeneity, disease severity, and symptom control in children with asthma. Methods Stable asthmatic children were recruited from the Difficult Asthma Clinic, with controls recruited from diabetes clinic patients and their siblings. Asthma severitywas classified in accordance with GINA guidelines (Step 1–3=Mild Moderate, Step 4–5= Severe). Asthmatics completed C-ACT/ACT to assess symptom control (score ≤19 = uncontrolled). All children performed Spirometry. Ventilation heterogeneity was assessed using Multiple-Breath Nitrogen Washout(MBNW) (Exhalyzer-D, Ecomedics). MBNW was performed in triplicate, with Lung Clearance Index (LCI) and indices of ventilatory heterogeneity in conductive and acinar airways (S cond and S acin , respectively) calculated. Results 35 participants aged 7–16 completed testing (7 controls, 7 mild-moderate asthma, 21 severeasthma). Results for MBNW displayed in Table 1. All MBNW parameters were normal in control subjects. Only the severeasthmatics had MBNW Results significantly higher than controls (LCI p = 0.006 , S cond p = 0.021 , S acin p = 0.040 ). LCI was raised in 1/7 mild-moderate and 13/21 severeasthmatics. S cond was raised in 2/7 mild-moderate and 11/21 severeasthmatics. S acin was raised in 1/7 mild-moderate and 4/21 severeasthmatics. 18/28 asthmatics had uncontrolled symptoms as assessed by the C-ACT/ACT. Of these, 14 had abnormal LCI but only 4 had abnormal FEV 1 . 8/28 asthmatics had raised LCI despite normal FEV 1 . Conclusions LCI, a measure of ventilation heterogeneity, is raised in a high proportion of children with severeasthma. Most children with raised LCI had normal spirometry. This suggests that LCI is more sensitive to detect lung function deficits in asthma compared to spirometry. LCI also correlates well with symptom control. MBNW and LCI may be useful in the monitoring of children with severeasthma.