LAUSR

Purpose of review Upper airway nitric oxide (NO) is physiologically important in airway regulation and defense, and can be modulated by various airway inflammatory conditions, including allergic rhinitis and chronic rhinosinusitis – with and without polyposis. Paranasal sinuses serve as a NO ‘reservoir’, with concentrations typically exceeding those measured in lower airway (fractional exhaled NO or FeNO) by a few orders of magnitude. However, the dynamics of NO flux between the paranasal sinuses and main nasal airway, which are critical to respiratory NO emission, are poorly understood. Recent findings Historically, NO emissions were thought to be contributed mostly by the maxillary sinuses (the largest sinuses) and active air movement (convection). However, recent anatomically-accurate computational modeling studies based on patients’ CT scans showed that the ethmoid sinuses and diffusive transport dominate the process. Summary These new findings may have a substantial impact on our view of nasal NO emission mechanisms and sinus physiopathology in general.