In recent 10 years there has been an explosion of interest in the analysis of breath constituents as a way of monitoring airway inflammation in lung diseases. Monitoring of inflammation may assist in differential diagnosis of lung diseases, assessment of their severity and response to appropriate treatment. Among these novel non-invasive methods, exhaled nitric oxide has been the most extensively studied. Its measurement has recently been standardized, and there are now commercially available nitric oxide analyzers. Concentration of exhaled nitric oxide is markedly elevated in asthma, and its elevation is positively related to the degree of eosinophilic airway inflammation, airway hyperresponsiveness and symptoms. Furthermore, evidence suggests that exhaled nitric oxide-driven asthma treatment provides more precise asthma control compared to conventional treatment protocols. With regard to other lung diseases, in chronic obstructive pulmonary disease exhaled nitric oxide may be useful in predicting steroid responsiveness, while in lung transplant recipients its measurement could contribute to the detection of asymptomatic infections and rejection process.
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