Computational fluid dynamics simulation of upper airway flow and soft tissue deformation in a mouth-breathing...

The primary objective of this study was to establish a three-dimensional fluid-structure interaction (FSI) model to compare the biomechanical effects of three distinct breathing modes-nasal (NA), oronasal (ONA), and oral (OA) ventilation-on upper airway dynamics in mouth-breathing patients. A key aim was to investigate a potential biomechanical link between mode-specific hydrodynamic forces and the soft tissue remodeling associated with adenoidal facies.

Mouth-breathing volunteer was selected, and cone-beam computed tomography (CBCT) and magnetic resonance imaging (MRI) images were collected. Subsequently,3D (Three-Dimensional) finite element models of the upper airway, oral airway, soft palate, and tongue body were reconstructed. Numerical simulations of the flow fields of the three different breathing modes, named nasal ventilation, oral nose ventilation, and oral ventilation, were performed using finite element analysis software.

The simulations revealed distinct, mode-specific biomechanical environments. Oral breathing (OA) generated significantly higher airflow velocity and stronger negative pressure in the palatopharyngeal and epiglottic regions compared to nasal and oronasal breathing. This led to pronounced posterior-inferior displacement of the tongue and increased deformation of the soft palate. In contrast, nasal breathing produced turbulence confined primarily to the nasal cavity. The model successfully captured the transition to turbulent flow in the pharynx during oral breathing.

This preliminary simulation suggests that, within the constraints of our model, oral breathing is associated with increased airflow velocity, higher negative pressure in the palatopharyngeal and epiglottic regions, and a greater posterior displacement of the tongue. These factors may collectively increase the susceptibility to pharyngeal airway collapse.