Turbulent Flow Pattern in Upper Airway with Obstructed Sleep Apnea

Computational fluid dynamics (CFD) techniques were used to model the turbulent flow in upper airway model of two subjects with obstructive sleep apnea (OSA). The upper airway models were reconstructed by Mimics software based on computerized tomography (CT) scanned images obtained during quiet tidal breathing. The Large Eddy Simulation (LES), a more accurate approach in unsteady flow, was selected to solve the unsteady flow. Only the inspiratory process was conducted with six periods (about 15second) and the mesh with the unstructured grid were generated from nostrils to trachea for both preand post-surgery models. From the numerical visualization, it can be seen that the pressure and shear stress drop rapidly from the choanae to the collapse region caused by area restriction, especially in the overlap region there exists a large negative pressure that induced the collapsing for OSA subjects before treatment. After surgical treatment, the distribution of airflow in the upper airway is more uniform. The results suggest the CFD techniques can show the turbulent flow pattern clearly and may help to evaluate the effect of the surgery.