The Dynamics Behavior Research Of Inner-Ear Structure Based On Analytical Method And Numerical Simulation

Human ear is a complex and delicate system,mainly including the external ear,middle ear and inner ear.As the very important part of the human ear,cochlea is more complicated than outer and inner ear,and made up by scala vestibule,scala media,and scala tympic.Cochlea also containing the delicate basilar membrance and Corti organ,they are all crucial to transduct sound signals.The sound pressure transmits from the external ear canal to inner ear,which applies an excitation in the perilymph through oval window.The pressure difference made in the perilymph causes the basilar membrane to vibrate vertically.Then those signals would cause a corresponding movement of the organ of Corti which resting on the basilar membrane.Finally hair cells and nerve fibers in the organ of Corti would transimit vibrations into nerve impulses and then the auditory center of the brain would receive those signals.Since the inner ear sense involves the fluid-structure interaction between cochlear lymph and the solid structure around of the sound I,sound mechanism is more complex and the sound mechanism of sensing is not fully understood,yet.And the experiments now,due to the structure of the inner ear is fine,are often destroyed,which increases the difficulty of the experiment.So it is an important and effective method to use the method of theoretical modeling and numerical simulation.In view of this,based on the variational principle,this paper establishes a mechanical model of part of the cochlear structure is established in this paper And the two finite element softwares,Patran/Nastran and Comsol,are used to establish the whole ear,cochlea,Organ of Corti and the inner stereocilia.The accuracy of the models is verified by the experimental data.By using the models,the mechanism of cochlear sensing is studied gradually.At the same time,the macro and micro mechanical behaviors of inner ear arestudied in two aspects: theory and numerical simulation.The main research contents of this paper are as follows:1 The CT images of the right ear from a healthy volunteer provided by Zhongsan Hospital attached to Fudan University in shanghai are digitalized and imported into PATRAN software to reconstruct an integrated 3D finite element model of the ear by a self-compiling program,which contains external ear that collects the sound,middle ear that transmits the sound and inner ear that senses the sound is established.Fluid-solid coupling analysis that is between the external air and the wall of the ear and between the lymph and the biological structures around it in the cochlea and frequency analysis is made for the whole ear model with Nastran and the displacements of tympanic membrane in the middle ear and basilar membrane that is the main supporting structure of inner ear cochlea are achieved.The results are in good agreement with experimental data,which confirms the validity of the finite element model.2 Based on the model,the input pressure value near oval window is achieved when excitation is applied on external auditory canal,which provides the basis for further research on mechanical behavior of the cochlea.A three dimensional spiral cochlear finite element model is established based on the experimental data of the actual right human ear.Based on the model,the effect of fluid viscosity to the cochlear impedance under external excitation in the passive cochlea and variation of the amplitude of the BM in a transverse direction under normal forward sound stimulation and reverse round window stimulation and the spiral structure have been discussed.3 According to the vibration characteristics of the round window,a mechanical model of round window membrane is established.The Euler equation of the round window and the complementary boundary conditions are derived by the variational principle.Combined with the Bessel function,the analytical solution of the round window displacement is obtained by using Mathematica.Combined with clinical characteristics of round window membrane lesion,the effect of sound transmission made by the thickening of round window membrane that caused by the otitis media,shrinkage of round window membrane area that caused by otosclerosis and hardening of round window membrane itself is analyzed.At the same time,the effect of different thickness and different elastic modulus of soft tissue on the total displacement of round window membrane and soft tissue is studied by analytical method.It provides theoretical basis for the reverse excitation of artific ial prosthesis.4 A two-dimensional model of the organ of Corti(OC)which includes basilar membrane(BM)?tectorial membrane(TM),inner and outer hair cells and reticular lamina(RL)is established by Comsol.Based on time-domain and frequency-domain analysis,the relative motion between stereocilia and tectorial membrane(TM)and reticular lamina(RL)is studied under sinusoidal excitation.After that,a three-dimensional model of the Organ of Corti(OC)is established.And the effect that made by the fluid which is in the Tunnel of Corti(ToC)on Organ of Corti(OC)is studied.5 According to the biomedical vibration characteristics of the organ of Corti(OC),by simplifing the structure of the model,a mechanical model of the organ of Corti is established.Using the variational princip le,the displacement analytical expression is solved.The effect that made by the hardening of the outer hair cells and outer stereocilia on Organ of Corti is studied.6 The cochlea is approximately modeled as a logarithmic spiral duct with active characteristic.Different cases for the velocity potential and pressure distribution pattern along the basilar membrane(BM)are obtained.Based on the active model,the parameters that influence the pressure distribution along the basilar membrane are analyzed under different cases.7 A three-dimensional miro-model of inner stereocilia is established.Based on finite element model,the effect that the movement of hair cells and fluid in the cochlear duct made on the x-displacement of stereocilia is studied.