Exhaled nitric oxide in the assessment of asthma

Asthma is now defined as a TH2-mediated inflammatory disease involving both large and small airways. However, assessment of airways inflammation is limited by techniques that are time consuming and possibly distressing to the patient. Exhaled nitric oxide, an easily and rapidly obtained noninvasive study, is a potential surrogate for measuring airways inflammation, but its clinical utility remains to be determined. This review examines the role of exhaled nitric oxide in assessing and directing therapy of asthmatic airways inflammation.

It is well established that exhaled nitric oxide is increased in patients with untreated asthma and decreases with corticosteroid treatment. Exhaled nitric oxide also generally correlates with eosinophilic inflammation in asthmatic patients. Recent studies show that this correlation is especially pronounced in atopic subjects with asthma when compared with nonatopic subgroups. Recent studies also show that exhaled nitric oxide may be useful in identifying subclinical inflammation, assessing the antiinflammatory effects of asthma medications other than inhaled or oral corticosteroids, and heralding an asthma exacerbation. A number of new studies assert the utility of exhaled nitric oxide as a diagnostic tool for asthma.

Exhaled nitric oxide may be a useful parameter for monitoring asthmatic inflammation, adjusting therapy, and diagnosing asthma, although prospective longitudinal trials investigating the correlation between exhaled nitric oxide and clinical outcomes are necessary to determine its utility.