Fractional exhaled nitric oxide (FeNO) in chronic obstructive respiratory diseases is associated with the bronchodilator response

Background Among chronic obstructive respiratory diseases (CORDs), the fractional exhaled nitric oxide (FeNO) is a marker of eosinophilic airway inflammation. Few data on FeNO in CORD are available in Vietnam. In this study, we aimed to relate the FeNO with the clinical and functional characteristics of CORD in Vietnam. Methods A cross-sectional study was conducted in 235 patients with chronic respiratory symptoms and airways limitation. Clinical evaluation was obtained by questionnaire; pre- and post-bronchodilator (BD) spirometry, eosinophil counts, allergen skin tests and FeNO were measured. Patients were considered as chronic obstructive pulmonary disease (COPD), asthmatics or asthma COPD overlap (ACO) based on GINA/GOLD guidelines. The FeNO levels were related to clinical, spirometric and inflammatory parameters. Results They were 93 COPD, 93 ACO and 49 asthmatics. The concentration of FeNO was high (≥25 ppb) in 69.4% asthmatics, 55.9% of ACO and 34.4% COPD. A high FeNO was more frequent among women, younger, asthmatics, former- or non-smokers, low severity (fewer exacerbations and lower airways limitation), BD responsiveness and type 2 (T2) inflammation [history of allergy, elevated blood eosinophils count (BEC), positive skin tests]. A low FeNO was more frequent in patients with X-ray emphysema or history of tuberculosis. The FeNO level correlated positively with the blood eosinophils and the BD responsiveness in non-smokers but negatively with the basal level of airflow limitation. Conclusions In Vietnamese non-smokers with chronic obstructive respiratory disease, FeNO is a type 2 biomarker and a significant predictor of BD responsiveness. We hypothesized that this might predict the response to inhaled corticosteroids (ICS).