The effect of nasal airway obstruction on the dispersion and deposition of inhaled volatile droplets in the human nasal cavity: A numerical study

Abstract

Nasal airway obstruction (NAO) is one of the main problems in the upper part of the human respiratory system. NAO may considerably affect the airflow and the behavior of droplets in the nasal cavity. In the present study, the effect of septal deviation as a special kind of NAO on the deposition and penetration of initially micron-sized inhaled droplets in the nasal cavities of two patients was numerically investigated. The geometries were constructed using CT scan images, and breathing zones were added to the models to make the inspiratory cycle more physically realistic. The motion of droplets was studied using the Lagrangian trajectory analysis approach, including the drag, Saffman's lift, and Brownian forces, as well as the evaporation process. The results showed that both unhealthy cases with obstruction had less heat transfer than the healthy nasal passage, which results in slower evaporation of droplets. On the other hand, due to the septal deviation, the deposition of droplets increased in the cases with nasal obstruction. Inertial impaction was the primary deposition mechanism, which was more critical than the diffusion in the region in which septal deviations diverted the airflow. The simulation results showed that due to less convoluted turbinate passages and smaller surface area to volume ratio (SAVR) of the nasal cavities with obstruction in comparison with a healthy nose, the size of droplets that escape from the human nasal cavity became smaller. As a result, for patients with septal deviations, small droplets could penetrate deep into the respiratory system and increase the risk of transmission of respiratory diseases.