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Breath nitric oxide concentrations

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Exhaled nitric oxide (eNO) concentrations are increased in both children and adults with asthma but whether eNO is a marker of airway inflammation or simply of atopy is debated. Two recent reports suggest the former.

In Belfast (

) 71 children (median age 9.4 years) were studied during admission for elective surgery. Twenty-nine had asthma, 15 were atopic but did not have asthma, and 27 had neither atopy nor asthma. Exhaled NO was measured using two techniques (tidal breathing and restricted breath) and nonbronchoscopic bronchoalveolar lavage fluid was obtained immediately after induction of anaesthesia. Concentrations of eNO were significantly raised in asthmatic children compared with both control groups combined (24.3 v 9.7 parts per billion). The atopic, nonasthmatic group had intermediate concentrations not significantly different from either the asthmatic or the nonasthmatic, nonatopic group. There were significant correlations between eNO concentration and both eosinophil percentage and eosinophilic cationic protein concentration in bronchoalveolar lavage fluid.

In rural new South Wales, Australia (JD Leuppi and colleagues. Ibid: 518–23) eNO and airway responsiveness to histamine were measured in winter and summer in 235 atopic children aged 8–14 years. Raised eNO concentrations were associated with sensitisation to perennial allergens such as house dust mite and Cladosporium but not to seasonal allergens such as grass pollen. They also correlated with airway hyperresponsiveness to histamine especially in children with current wheeze. Persistent dry cough was not associated with raised eNO.

Raised eNO concentrations are probably a marker of airway inflammation.