Axial distribution of nitric oxide airway production in asthma patients

In healthy subjects, axial distribution of nitric oxide (NO) airway production is likely heterogeneous: notably a distal peak of production in terminal bronchioles and a quasi-nil NO production in the most of the conducting airways. In asthma, few information exists about the contributions of the proximal and distal airways to NO overproduction. In 18 asthma patients, sites of constriction after methacholine and adenosine 5′-monophosphate (AMP) challenges were assessed by ventilation distribution tests with He and SF6. The resulting decreases in fractional exhaled NO (FENO) were measured. Changes in He and SF6 slopes indicated a pre-acinar bronchoconstriction due to AMP and a more proximal action for methacholine. FENO decreased by 38.7% and 20.2% (p < 0.001) after AMP and methacholine challenges, respectively. Significant FENO decreases after AMP and methacholine implies substantial pre-acinar but also, contrary to healthy subjects, more proximal airway production. In conclusion, nitric oxide overproduction in asthma patients appears to involve the most part of the conducting airways.

► Challenges-induced exhaled NO decreases reflect production in the involved areas.
► Distal and proximal sites are both involved in NO overproduction in asthma.
► In asthma patients, NO overproduction involves the most part of the airways.