Exhaled Nitric Oxide in COPD

Chronic obstructive pulmonary disease (COPD) is a common and progressive disorder which is characterised by pathological abnormalities driven by chronic airway inflammation. The assessment of airway inflammation in routine clinical practice in COPD is limited to surrogate blood markers. Fractional exhaled nitric oxide (FENO) is a marker of eosinophilic airway inflammation in asthma, and it can predict steroid responsiveness and help tailor corticosteroid treatment. The clinical value of FENO in COPD is less evident, but some studies suggest that it may be a marker of the eosinophilic endotype. More importantly, mathematical methods allow investigation of the alveolar/small airway production of NO which potentially better reflects inflammatory changes in anatomical sites, most affected by COPD. This review summarises the pathophysiological role of nitric oxide in COPD, explains the methodology of its measurement in exhaled air and discusses clinical findings of FENO in COPD.