Introduction Both exhaled nitric oxide (FeNO), a non-invasive marker of eosinophilic airway inflammation, and lung clearance index (LCI), an effort independent assessment of distal airway function, are increased in pre-school children with multiple trigger wheezing (Sonnappa JACI 2010;126:519–26). However, whether there is any relationship between the two measures is unknown. We hypothesised that FeNO and LCI are positively related in pre-school children with a range of respiratory symptoms and this relationship would be strongest in pre-school wheeze.

Methods Patients aged between 2 and 6 years were recruited from the paediatric respiratory department at our tertiary centre. FeNO was measured using the offline technique (Niox Mino, Aerocrine AB, Sweden) and LCI was measured using the multiple breath washout technique (Sulphur hexafluoride tracer gas, photoacoustic gas analyser (Innocor, Innovision, Denmark)).

Results 19 children (median age 4.2, range 2.7–5.8 years) had assessments of both FeNO and LCI on the same day. Respiratory diagnoses were: multiple trigger wheeze (MTW) n=10, episodic viral wheeze (EVW) n=5, cough n=1, recurrent infections n=1, obliterative bronchiolitis (OB) n=1, sleep disordered breathing n=1. A significant correlation was found between FeNO and LCI, in pre-school children with respiratory symptoms (Spearman correlation coefficient r=0.5, p=0.02) (figure 1). When the MTW and EVW groups were compared, there was no correlation between FeNO and LCI in EVW, but there was a significant relationship in MTW (r=0.6, p=0.05).

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Abstract P88 Figure 1

Relationship between offline exhaled nitric oxide (FeNO) and lung clearance index (LCI). MTW: multiple trigger wheeze.

Conclusions There was a positive relationship between FeNO and LCI in pre-school children with a range of respiratory symptoms. The relationship was strongest in those with recurrent multiple trigger wheeze. These data provide further evidence for different pathophysiologies in MTW and EVW, implying the need for different treatment approaches.