Exhaled nitric oxide: an emerging marker of inflammation in respiratory diseases

Fractional exhaled nitric oxide (FENO) is a recently introduced non invasive marker to measure inflammation and oxidative stress in the lung. The numerous roles of NO in respiratory pathophysiology have been extensively reviewed. There is contradictory evidence regarding the exact function of NO in lung diseases. In pathological states, the enzyme inducible NO synthase generates extraordinarily high concentrations of NO when the body faces an inflammatory response by attracting macrophages that generate NO and hence NO participate in host defense against specific organisms. Fractional exhaled nitric oxide measurements have been useful in asthma, chronic obstructive pulmonary disease, cystic fibrosis, and bronchiectasis. The technique used to measure FENO is well standardized, requires the same amount of time that spirometry takes, and is feasible to be performed in young children. Measuring FENO has added another dimension to the determination of adverse respiratory effects because it allows detection of inflammatory responses in the absence of functional impairments. This review provides an insight into measurement methods, physiological factors affecting FENO, interpretation of results and diseases related to changes in FENO levels. This will help physicians in diagnosing and monitoring their treatments for different respiratory diseases.