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In order to investigate the tracheal pressures for different percentages of stenotic constriction, flow simulations are performed on a realistic geometry based on CT-scans of a patient for sedentary breathing (15 l/min) and normal breathing (30 l/min) conditions using a Reynolds Averaged Navier Stokes approach for unstructured hexahedral meshes. Tu...
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... features. The highly irregular and complex nature of the model makes the creation of structured grid tedious and work-intensive. For such complex geometries, unstructured meshes are more suited. Using Numeca's unstructured grid generator -Hexpress (2.2β), an all- hexahedral unstructured mesh was generated, containing approximately 750,000 cells. Fig. 3 shows the surface mesh and a zoom in the region of mouth-throat. Box-adaptation was used to locally refine the mesh near the tracheal ...
Citations
... Although previous studies have suggested that airflow during breathing is laminar, there is evidence that flow transition or turbulence could occur locally with partial airway obstruction [124,125]. Two most popular turbulence models used for airway flow simulations are the k-ɛ [126,127], and k-ω [40,128] models in which k represents turbulent kinetic energy, ɛ is the dissipation rate, and ω is the specific dissipation rate. However, previous work has shown that k-ω model is more appropriate to account for potential transitional and turbulent characteristics of the flow while satisfying acceptable accuracy in the laminar flow regime within the bulk of the upper airway [40]. ...
Obstructive sleep apnea (OSA) is a common respiratory disorder associated with the collapse of the upper airway during sleep. OSA may cause oxygen desaturation, arousals from sleep, and daytime sleepiness, in turn affecting quality of life. There is low success rate in existing OSA surgical treatments mainly due to heterogeneity of the OSA population and poor understanding of the mechanism of the upper airway collapse in each individual. However, advancements in computational simulation have led to some detailed structural modelling of the upper airway that may help to better understand its collapse mechanism in OSA. Alternative surgical treatment methods may be critically assessed with simulation prior to clinical adoption to provide personalized treatment insight for an OSA individual. This review summarizes the current literature related to the application of fluid structure interaction simulation for OSA analysis, with a focus on pharyngeal airway deformation mechanisms, airflow characteristics, and OSA surgical treatment efficacy; it also identifies the shortcomings of current models with suggestions for future studies. It is evident that the upper airway collapse mechanism, the anatomical factors affecting the location and timing of the collapse, and the association of the upper airway anatomical features with critical pressure (Pcrit) are still lacking. Moreover, numerical simulation has been shown to be a great tool in OSA surgical treatment efficacy. Future studies incorporating the practice of virtual surgery may further support clinical decision-making.
A two dimensional finite element model of upper airway respiratory function was developed emphasizing the effects of dilator muscular activation on the human retro-lingual airway. The model utilized an upright mid-sagittal computed tomography of the human head and neck to reconstruct relevant structures of the tongue, mandible, and the hyoid-related soft tissues, along with the retro-lingual airway. The reconstructed geometry was divided into fluid and solid domains and discretized into finite element (FE) meshes used for the computational model. Three cases were investigated: standing position; supine position; and supine position coupled with dilator muscle activation. Computations were performed for the inspiration stage of the breathing cycle, utilizing a fluid-structure interaction (FSI) method to couple structural deformation with airflow dynamics. The spatio-temporal deformation of the structures surrounding the airway wall were predicted to be in general agreement with known changes from upright to supine posture on luminal opening, as well as the distribution of airflow. The model effectively captured the effects of muscular stimulation on the upper airway anatomical changes, the flow characteristics relevant to airway reduction in the supine position and airway enlargement with muscle activation. The smallest airway opening in the retro-lingual section is predicted to occur at the epiglottic region in all the three cases considered, an unexpected vulnerable location of airway obstruction. The model also predicted that hyoid displacement would be associated with recovery from airway collapse. This information may be useful for building more complex models relevant to mechanisms and clinical interventions for obstructive sleep apnea.
