Fractional exhaled nitric oxide for eosinophilic inflammation in stable COPD

Abstract

Introduction: Eosinophilic airway inflammation is now recognized as one of the important pathophysiology of chronic obstructive pulmonary disease (COPD). Objectives: To investigate the usability of fractional exhaled nitric oxide (FeNO) as a maker of eosinophilic inflammation compared with other biomarkers like blood eosinophil counts and serum IgE level in stable COPD patients. Patients and methods: A total of 146 stable COPD patients were enrolled from the outpatient clinic of respiratory medicine in our hospital from May 2011 to June 2016. The patients underwent spirometry and chest CT. FeNO was measured before spirometry. Peripheral blood eosinophil counts and serum IgE level were also measured. Using chest CT data, emphysematous lesions and the airway wall thickness were assessed by the percentage of low attenuation voxels (LAV%) and by the square root of airway wall area of the hypothetical airway with an internal perimeter of 10 mm (√Aaw at Pi10), respectively. Results: The participants were 10 females and 136 males with a mean age of 71.8 ± 7.3 (mean ± SD) years old. FEV1 %predicted was 68.5 ± 21.2% and FeNO was 29 ± 20 ppb. Laboratory findings showed that blood eosinophils were 237.0 ± 181.1/μL, and median serum IgE was 121.4 IU/ml (IQR, 27.9 - 439.3 IU/ml). FeNO was positively correlated with serum IgE (p=0.003), but not correlated with blood eosinophils (p=0.064). Serum IgE and blood eosinophils were positively correlated with each other (p=0.03). FeNO was not correlated with CT measured markers such as LAV% and √Aaw at Pi10. Conclusions: FeNO can be an easy, noninvasive and useful marker of eosinophilic airway inflammation in stable COPD patients.