The Numerical Simulation Study Of Middle Ear Ventilation

ObjectiveThe purpose of this study was to establish a three-dimensional model of the middle ear of normal adults in China,and to complete the following researches through computer numerical simulation.?To simulate the process of middle ear ventilation after the Eustachian tube is opened under normal conditions and draw the pressure distribution cloud map during middle ear ventilation in order to study the variation of pressure.?To simulate the pressure changes in the external auditory canal and the middle ear cleft during middle ear ventilation when the tympanic isthmus is blocked by space occupying lesion.Compare the difference of middle ear ventilation with and without the occupation in tympanic isthmus and explore the influence of tympanic isthmus blockage on middle ear ventilation.MethodHigh resolution CT scan of temporal bone was performed on a healthy adult cadaver head specimen from the ENT department of Peking Union Medical College Hospital.The imaging data obtained were based on DICOM data standard.Mimics 20.0 software was used for multi-layer medical image segmentation and three-dimensional reconstruction.The major reconstruction sites include the portion of the Eustachian tube adjacent to the tympanum,tympanum,the whole ossicular chain,tympanic membrane,mastoid process and external auditory canal.After the smooth processing of the 3D model,finite element meshing(FEM)was performed.Then,a fluid mechanics calculation software called"Xflow" was used for numerical simulation of ventilation process,and a nonlinear finite element calculation software called"ABAQUS" was used for structural mechanical calculation of tympanic membrane.Fluid-solid interaction(FSI)algorithm was used to calculate pressure changes in the middle ear and external auditory canal during middle ear ventilation.After that,establish 3 tympanic isthmus occupied models of different lesion sizes by artificial modification to the model.Use the identical calculation process in the normal model to simulate the pressure distribution changes of external auditory canal and middle ear under the pathological condition.Four sensors were set up respectively in the external auditory canal,tympanic cavity,tympanic cavity-mastoid process connecting area and mastoid process to compare the pressure variation rules of these 4 parts in the middle ear ventilation process.ResultAccording to the numerical simulation of middle ear ventilation in this research,we can obtain the following results:?After the Eustachian tube is opened once,the overall pressure changes in the middle ear could be divided into four stages:the pressure ascending stage,the pressure maintenance stage,the pressure descending stage and the zero-pressure maintenance stage.?The result of numerical simulation indicates that during the middle ear ventilation process,the mastoid process does act as a buffer against pressure changes.?The stenosis of tympanic isthmus caused by space occupying lesions will lead to more drastic changes of pressure in the middle ear and affect the stability of middle ear ventilation.This instability can be reflected in the reduced pressure peak in the external auditory canal caused by the movement of tympanic membrane.The larger the tympanic isthmus occupied lesion is,the lower the pressure peak will be in the external auditory canal(assumed that there is no other force causing the vibration of tympanic membrane).ConclusionTo a certain extent,the numerical simulation model in this research simulates the process of middle ear ventilation under normal circumstance and when the tympanic isthmus is occupied.It reflects the changes of middle ear and external auditory canal in terms of pressure and shape.The numerical simulation could help to solve the problem that the experiments related to middle ear ventilation are usually difficult to implement and meanwhile it also assists otolaryngologists to have better understanding of the physical changes during middle ear ventilation.