Study objectives: To assess whether the dual anatomic origin of exhaled nitric oxide (NO), namely alveolar and bronchial, could explain the link between exhaled NO and airway responsiveness, and could participate in the bronchodilatory effect of deep inspiration (DI) that may be evidenced during methacholine challenge.
Design and setting: Prospective study in a laboratory performing pulmonary function tests of an academic hospital.
Patients and interventions: Patients underwent multiple flow analysis of exhaled NO, allowing calculation of total maximum airway NO flux (J’awno) and NO concentration of expansible compartment (CAno), and received a cumulative methacholine dose of 2,000 μg. DI effect was assessed by continuous measurement of the resistance of respiratory system using the forced oscillation technique before and after DI.
Results: In a first phase involving 23 patients, a positive correlation between log values of J’awno and CAno was demonstrated with the degree of airway responsiveness (percentage of FEV1 decrease). In a second phase involving 38 patients, only log CAno was correlated with responsiveness, and no significant relationship was demonstrated between J’awno or CAno and the effect of DI. Patients with smaller airways and/or distal airflow limitation exhibited a constrictive response to DI.
Conclusion: Airway responsiveness is mainly associated with an increase in distal origin of NO output, and no relationship between exhaled NO and the effect of DI was evidenced.