The human body is a biological mechanism, impressive and complex, the various components of which work harmoniously to maintain homeostasis and interact with the external environment.
The vestibular organ is located in the inner ear and receives information about head movements, such as the orientation of the gravity vector relative to the tilt of the head, linear and rotational accelerations of the head, and sends it to the brain. After that, the brain processes this information to maintain balance by regulating skeletal muscle. In addition, it controls the eyes to compensate for head movements, which allows you to drive or read while walking. In simple words, it provides “feeling” and control over the body. The vestibular apparatus of a person has 3 main functions:
• maintaining balance;
• maintaining a sense of orientation in space;
• image stabilization on the retina to maintain visual acuity during head movement.
Various disorders of the vestibular organ disrupt the daily functioning of a person. Unfortunately, in our time there is no effective medication for vestibular disfunction. However, the vestibular implant was designed to replace lost vestibular functions.
The main tasks are:
1. The study of the anatomy and physiology of the inner ear.
2. The study of the physical (electrical) mechanisms of the vestibular organ.
3. The study of modern methods for obtaining three-dimensional images of biological objects with high resolution.
4. Obtaining a high-resolution image of the inner ear of a guinea pig and rat.
5. Construction of a 3D-geometric model of the inner ear of a guinea pig and rat based on image segmentation.
6. Constructing a model of electrical conductivity using software for modeling by the finite element method (FEM) or by the equivalent circuit.
7. Performing simulation and comparing the results with the experiment.
The goal of this study is to obtain a model of the electrical conductivity of the inner structure of the inner ear based on methods for obtaining high-resolution images.
The images of the inner ears of laboratory animals were obtained using the micro CT- tomography. 3D-models of the inner ears were constructed. Geometrical parameters of the labyrinths of laboratory animals were measured. Three different models of electrical conductivity of inner ear were proposed: 3D-Finite Element Model and two equivalent circuits. Models were evaluated using experimental data on the electrical impedances in human inner ear in vitro.
It has been shown that the electrode-electrolyte interface plays an important role in propagation of the electrical current through biological object by introducing the reactive component to the impedance. Therefore, it is necessary to take into account the effect of the electric double layer. Since equivalent circuit shows good results both in saline and in human samples.
All presented equivalent models showed good accordance with the experimental data. But the model including both electrode-electrolyte domain (Randles) and tissues of the inner ear may be overloaded with the parameter. It is suggested in the future to perform the sensitivity analysis to identify the most important parts in the model.
Finite element model describes the propagation of electrical current in the human inner ear well, but it is necessary to select the parameters of the permittivity and conductivity of the double electric layer to obtain better results. In the future, it is also necessary to conduct the sensitivity analysis to geometric parameters, including the distance between measurements, the size of the electrodes and the inner ear. On top of that the model can be extended in terms of more precise geometry. The accuracy of the model can also be improved by introducing the effect of ionic polarization in the EDL, described by Cole-Cole equation. It can improve the frequency dependence of the EDL.
All objectives are completed:
1. The 3D-model of the inner ear was constructed;
2. The electrical conductivity model was developed in COMSOL Multiphysics and Matlab;
3. Simulation of electric currents in the vestibular system were performed;
4. Experimental validation of the model has shown good results.
