The place of expired nitric oxide measurements in asthma

INTRODUCTION: The production of nitric oxide (NO) can be assessed by measuring the fraction of NO during a prolonged expiration (FENO) or by estimating other parameters of NO exchange including the alveolar NO concentration (CalvNO). STATE OF THE ART: Changes in the production of NO are seen in association with clinical events (allergen exposure, minor symptoms, acute crises, changes of treatment) and functional (bronchial hyper-reactivity) or pathological (eosinophilia, remodeling markers) features characterising asthmatic phenotypes. PERSPECTIVE: Measurement of NO is a non-invasive tool for the evaluation of atopy, particularly in the course of allergic asthma. The interpretation of a single measurement is limited by the variability of the values associated with a stable state in the allergic population: the use in practice (risk of exacerbation, follow up, adjustment of steroid treatment) depends on analysis of sequential variations in FENO. Calculation of CalvNO may provide information about small airway inflammation and assist the optimal control of the disease. CONCLUSION: Ambulatory measurement of expired NO and the estimation of parameters describing NO exchange, independently of expiratory flow, could become the key evaluations in the monitoring of allergic asthma.