Highlights Computational fluid dynamics (CFD) Fluid-Structure Interaction (FSI) Discrete Phase Model (DPM) SARS-CoV-2 micro-droplet Human upper airway

Human pleural cavity pressure rises substantially because of Valsalva maneuver during sneezing. However, the deformations in the upper airway respiratory system significantly increase due to flow rate growth in sneezing, and laryngeal fracture can be mentioned as one of the symptoms of this severe deformation during the Valsalva maneuver. Therefore, the accurate study of the distribution of pressure and velocity, in this case, is very important. In the present study, using a real human upper airway model, the pressure and velocity of the air flow, generated in the tract during the sneezing, have been investigated. Moreover, using a spirometer device, the outlet flow rate from the mouth during the sneezing was obtained. The simulation results indicated that the inlet pressure to the tract, existing in the bronchus region, reached a maximum of 14 kPa. By having such pressure input, the highest deformation, created in the upper airway, was calculated using the fluid-structure interaction method and it has been confirmed that the majority of the deformation happened in the maxillary sinus as well as the thyroid cartilage.

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It is essential to study the viral droplet’s uptake in the human respiratory system to better control, prevent, and treat diseases. Micro-droplets can easily pass through ordinary respiratory masks. Therefore, the SARS-COV-2 transmit easily in conversation with a regular mask with 'silent spreaders' in the most physiological way of breathing through the nose, indoor and at rest condition. The results showed that the amount of deposited micro-droplets in the olfactory epithelium area is low. Also, due to receptors and long droplet residence time in this region, the possibility of absorption increases in the cribriform plate. This phenomenon eventually could lead to brain lesion damage and, in some cases, leads to stroke. In all inlet flow rates lower than 30 L/min inlet boundary conditions, the average percentage of viral contamination for upper respiratory tract is always less than 50% and more than 50% for the lungs. At 6L/min and 15L/min flow rates, the average percentage of lung contamination increases to more than 87%, which due to the presence of the Coronavirus receptor in the lungs, the involvement of the lungs increases significantly. This study's other achievements include the inverse relationship between droplets deposition efficiency in some parts of the upper airway, which have the most deformation in the tract. Also, the increased deformities per minute applied to the trachea and nasal cavity, which is 1.5 times more than usual, could lead to chest and head bothers.

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