New tools for asthma control evaluation: expired nitric oxide (NO) and nasal NO.

Nitric oxide (NO) is present in the upper and lower human airways. Nasal and exhaled levels of NO can be determined by non-invasive techniques using chemiluminescence analysers. NO levels in the upper airways are 10–100-fold higher than in the lower airways. International recommendations for standardized measurement of nasal and exhaled NO have been published recently. Exhaled NO is increased in patients with untreated asthma, and this elevation reflects, at least partially, bronchial inflammation. Measurement of exhaled NO may be useful when the diagnosis is doubtfull and for differentiation from other causes of chronic cough. Nasal NO is usually also increased in asthma but this is related to the frequency of allergic rhinitis in asthmatic patients. However, in patients with nasal polyps and asthma, nasal NO is decreased in proportion to the extent of sinusoidal involvement. Levels of exhaled NO decrease rapidly in asthmatic patients treated with anti-inflammatory drugs. Further studies are needed to establish more precisely the place of exhaled NO measurement in monitoring the control of asthma, especially in comparison with other non-invasive markers of bronchial inflammation. [Copyright &y& Elsevier]