Nasal nitric oxide flux from the paranasal sinuses

Abstract

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.

FIGURE 1.

(a) Coronal slice from individual CT scan, showing nasal airway and nasal sinus outlines. CT scan slices were compiled to produce three-dimensional model (b, c).

FIGURE 2.

Sample NO tracing showing simulated results (under normal conditions, with NO diffusivity set to 0, and with ethmoid flux set to 0) compared with experimental results from source study [31,52^■]. NO, nitric oxide.