Exhaled nitric oxide and exercise-induced bronchoconstriction in young male conscripts: association only in atopics

This study was conducted to evaluate how bronchial responsiveness to direct and indirect stimuli relate to nitric oxide producing airway inflammation, and whether the relationship differs between atopic and nonatopic patients with various degrees of bronchial hyperresponsiveness and airway inflammation in a group of otherwise homogenous young men. We studied 181 consecutive non-smoking steroid-naive young male conscripts referred to military hospital because of respiratory symptoms suggesting asthma. Skin prick tests, spirometry, measurement of exhaled nitric oxide (FENO), and standardized airway challenges with histamine and exercise were performed. 128 patients were atopic. FENO was significantly higher in the atopic group, median 21.2 ppb, compared to 10.2 ppb in the nonatopic group. Still, 36% of all nonatopic patients had elevated FENO. Bronchial responsiveness to histamine (HIB) was similar in the two groups, but exercise-induced bronchoconstriction (EIB) was stronger in atopics (P < 0.01). FENO associated significantly with atopy (P < 0.001), severity of EIB (P < 0.001) and HIB (P = 0.006) in multiple linear regression model. In separate regression models for atopic and nonatopic patients FENO associated with severity of EIB and HIB in atopic patients only. The results were similar when patients with confirmed diagnosis of asthma were analyzed separately. Our results indicate that FENO significantly associates with EIB and HIB in atopic, but not in nonatopic steroid-naïve patients with asthmatic symptoms. The finding suggests that in such atopic patients degree of airway hyperresponsiveness may reflect severity of airway inflammation. However, in nonatopic patients with similar symptoms other mechanisms of airway hyperresponsiveness may be more important.