Dissociation between exhaled nitric oxide and hyperresponsiveness in children with mild intermittent asthma

Background-Bronchial hyperresponsiveness and airway inflammation are distin ctive features of asthma. Evaluation of nitric oxide (NO) levels in expired air have been proposed as a reliable method for assessing the airway infla mmatory events in asthmatic subjects. A study was undertaken to evaluate wh ether airway hyperresponsiveness is related to levels of exhaled NO. Methods-Thirty two steroid-naive atopic children with mild intermittent ast hma of mean (SD) age 11.8 (2.3) years and 28 age matched healthy controls w ere studied to investigate whether baseline lung function or airway hyperre sponsiveness is related to levels of exhaled NO. Airway responsiveness was assessed as the dose of methacholine causing a 20% decrease in forced expir atory volume in one second (FEV1) from control (PD20 methacholine) and exha led NO levels were measured by chemiluminescence analysis of exhaled air. Results-At baseline asthmatic children had significantly higher NO levels t han controls (mean difference 25.87 ppb (95% CI 18.91 to 32.83); p < 0.0001 ) but there were no significant differences in lung function parameters (fo rced vital capacity (FVC), FEV1 (% pred), and forced expiratory flows at 25 -75% of vital capacity (FEF25-75%)). In the asthmatic group exhaled NO leve ls were not significantly correlated with baseline lung function values or PD20 methacholine. Conclusions-These results suggest that levels of exhaled NO are not accurat e predictors of the degree of airway responsiveness to inhaled methacholine in children with mild intermittent asthma.