Bronchial Responsiveness Is Related to Increased Exhaled NO (FENO) in Non-Smokers and Decreased FENO in Smokers

Rationale: Both atopy and smoking are known to be associated with increased bronchial responsiveness. Fraction of nitric (NO) in the exhaled air (FENO), a marker of airways inflammation, is decreased by smoking and increased by atopy. NO has also a physiological bronchodilating and bronchoprotective role. Objectives: To investigate how the relation between FENO and bronchial responsiveness is modulated by atopy and smoking habits. Methods: Exhaled NO measurements and methacholine challenge were performed in 468 subjects from the random sample of three European Community Respiratory Health Survey II centers: Turin (Italy), Gothenburg and Uppsala (both Sweden). Atopy status was defined by using specific IgE measurements while smoking status was questionnaire-assessed. Main Results: Increased bronchial responsiveness was associated with increased FENO levels in non-smokers (p = 0.02) and decreased FENO levels in current smokers (p = 0.03). The negative association between bronchial responsiveness and FENO was seen only in the group smoking less <10 cigarettes/day (p = 0.008). Increased bronchial responsiveness was associated with increased FENO in atopic subjects (p = 0.04) while no significant association was found in non-atopic participants. The reported interaction between FENO and smoking and atopy, respectively were maintained after adjusting for possible confounders (p-values<0.05). Conclusions: The present study highlights the interactions of the relationship between FENO and bronchial responsiveness with smoking and atopy, suggesting different mechanisms behind atopy- and smoking-related increases of bronchial responsiveness.