Exhaled nitric oxide in persistent rhinitis with or without lower airway involvement: a review of the literature.

The link between upper and lower respiratory airways has been investigated in the past decade leading to the concept of united airways disease. This hypothesis was suggested by several epidemiological observations, which had shown the high prevalence of rhinitis and sinusitis in patients with asthma, and indirectly, by observing the effects of drugs used for rhinitis on asthma symptoms. A broad spectrum of airway involvement severity can be associated with rhinitis or rhinosinusitis: from a subclinical/asymptomatic inflammatory involvement with an increase in eosinophils in induced sputum cell count, to asthma-like symptoms without functional features of asthma with or without extrathoracic airway hyperresponsiveness, to respiratory symptoms with clinical and functional criteria of asthma. The aim of this paper is to review the literature about the role of breath analysis in the relationship between nose and lung, focusing on exhaled nitric oxide (FE(NO)) measurement, a non-invasive marker of inflammation, in rhinitis and in chronic rhinosinusitis in patients complaining or not of asthma symptoms.