Extended analysis of exhaled and nasal nitric oxide for the evaluation of chronic cough.

INTRODUCTION: Chronic cough is usually defined as a cough that lasts for eight weeks or longer. Its etiological diagnosis is not always straightforward, and the measurement of exhaled nitric oxide (FeNO) has been proposed in patients' evaluation. No studies have assessed the usefulness of extended exhaled NO measurement for the evaluation of chronic cough. Therefore, we aimed at evaluating the usefulness of an extended exhaled NO measurement and nasal NO for an initial evaluation of chronic cough.

METHODS: We studied 52 non-smoker patients with prolonged cough lasting more than eight weeks. Etiologies of cough were identified. Nasal NO and FeNO were assessed using multiple single-breath NO analysis at different constant expiratory flow-rates. From the fractional NO concentration measured at each flow-rate, the total NO flux between tissue and gas phase in the bronchial lumen (J'awNO), and the alveolar NO concentration (Cano) were extrapolated.

RESULTS: The patients were classified in four categories: cough variant asthma (CVA), nonasthmatic eosinophilic bronchitis (NAEB), upper airway cough syndrome (UACS) and gastro-esophageal reflux disease (GERD). Compared with UACS and GERD, both exhaled NO and J'awNO were higher in CVA and NAEB, and no differences were found in Cano and nasal NO level among the four groups.

CONCLUSIONS: Our study suggests a potentially useful role for FeNO measurement in the etiological diagnosis of chronic cough. We did not find any additive value of performing exhaled NO at multiple flow-rates and nasal NO measurements.