Background: Airway inflammation is a key component in the pathophysiology of asthma. However, neither its role in the clinical features of asthma nor the factors affecting the degree of inflammation have been fully defined.

Methods: We determined the fractional exhaled nitric oxide concentration (FENO) using a portable device (NIOX-MINO, Aerocrine, Solna, Sweden) in a consecutive sample of 149 asthmatic children aged 6 to 14 years. In order to establish an association with FENO, we analyzed symptoms, spirometric parameters before and after a bronchodilator test, and the impact of asthma on quality of life during the previous 4 weeks. We also investigated how clinical variables that regulate inflammation affected FENO.

Results: In patients not treated with inhaled corticosteroids (ICs), FENO was higher when specific symptoms (wheeze and cough) had been present during the previous 4 weeks; however, we were unable to establish a relationship with symptom frequency, bronchodilator use, asthma crises, hospital admissions, limitation of daily activities, or spirometry results. In patients treated with ICs, FENO was not related to the clinical expression of asthma, except for a reduced ratio of forced expiratory volume in 1 second to forced vital capacity, both before and after bronchodilation. The main determinant of FENO level in untreated patients was sensitization to house dust mite. In patients treated
with ICs, FENO was only associated with adherence to therapy.

Conclusion: Airway inflammation, as determined by FENO, is only weakly associated with the clinical expression of asthma and spirometry results. Adherence to treatment is the main determinant of the degree of inflammation in patients taking ICs.

Key words: Asthma. Nitric oxide. Inflammation. Spirometry. Cross-sectional studies. Signs and symptoms, respiratory. Child. Adolescent.