Numerical study on nitric oxide transport in human nasal airways

Any slight clinical problem in the nasal system may result in inconveniences in our daily lives, being related with respiratory ventilation and nitric oxide (NO) concentration in the respiratory air. It is known that NO is produced and absorbed by the mucosal layer, especially in the nasal system and its concentration is upregulated or downregulated along with nasal inconveniences or nasal deformities. This study numerically investigates the air flows and the transport of gaseous NO in the human nasal system comprising nasal cavity and paranasal sinuses in order to understand the relations among nasal air flow rates, NO concentrations, and nasal structures. Using commercial mesh generation and fluid dynamics simulation codes, we predicted flow fields in the nasal system according to respiration volumes flowing through nasal cavity and entrance diameters of maxillary sinus. Three dimensional simulations with sinusoidal respiratory flow rates show that NO concentrations in frontal sinus are greater than 10000 ppb that are considerably higher than those in other systems, since the former has only one ostium of small diameter while other systems have two gateways of nasal air flowing in and out. Therefore, major mechanism for NO transportation in the former is diffusion, while those in the latter are both convection and diffusion. Concentrations of NO exhaled from nasal cavity are less than 100 ppb and those in maxillary sinus are greater than 2000 ppb, which agree well with experimental observations available in literature.