A Biomechanical Model For The Balance Mechanism Of Vestibular Semicircular Canals In The Inner Ear

The vestibular system in the inner ear plays a lead role in maintaining human balance function. However, the pathogenesis of common vestibular diseases has been fully unclear, the lateralization and localization diagnosis of lesion still lacks reliable clinical technology, and the treatment of vestibular disease is often based on the symptom. The reason is mainly due to the fact that the inner ear been deep buried in the temporal bone with fine complicated anatomy. It has been found that vestibular lesion and excessive environmental stimulation are the main factors leading to vestibular disorders with symptoms such as vertigo and dizziness, which seriously affect our daily life and cause aircraft accident. As we all know, biomechanics predominate in the process of maintaining equilibrium function of human vestibular system. It is reported that the ability of sensing angular movement for the vestibular semicircular canals mainly depends on the interaction between the endolymph flow and cupular deflection and mechano-electrical transduction processes. As a result, the basic theories and methods of mechanics have been developed to study the relativity between the anatomy of human inner ear vestibular system and its balance mechanism. In this study it will probe into the relationship between vestibular disorders and inner ear anatomy, promote lateralization and localization diagnoses of lesion, and provide quantitative basis for effective treatment of vestibular lesions. The main contents in this study are as follows:Firstly, we successfully obtained an effective method for reconstructing the three-dimensional geometry of guinea pig inner ear. Under this method, the inner ear geometry of a healthy human was reconstructed. The natural frequency and vibration mode for the endolymph-cupula system of this human inner ear was further obtained using finite element method. Based on our analysis, the first natural frequency is about13.46Hz, which is much higher than the maximum frequency of human daily activity and the examination frequency of clinical rotation test and caloric test.Secondly, we have numerically analyzed the balance mechanism of bilateral vestibular semicircular canals when a healthy human is subejected to postural changes. During head horizontal sinusoidal rotation or left-and-right rotation, the cupular vibration amplitude equals to each other between bilateral symmetrical semicircular canal with a phase difference of3.14rad, while both the cupular vibration amplitude and the phase are identical during head forth-and-back rotation. At the same time, corresponding afferent responses as well as the eye movement through vestibular ocular reflex will be induced. In this way, we are able to stabilize the visual image on the retina. Thirdly, in order to probe into the vibration characteristic of vestibular semicircular canals during head horizontal rotation, a frequency characteristic analysis for the right horizontal semicircular canal was made in the frequency range of human daily life. It was found that the vibration for the utricular side surface of the cupula is more sensitive to angular acceleration than head angular velocity, but that for the canal side surface is just opposite. Namely, the vibration of the canal side surface is more sensitive to angular velocity than angular acceleration. Furthermore, the difference of both vibration amplitude and phase across the two sides of the cupula will increase with the stimulus frequency. This phenomenon can be closely related to the localization diagnosis of horizontal semicircular canal lesion through clinical rotation test.Fourthly, the balance mechanism of bilateral vestibular semicircular canals was numerically analyzed when a healthy human is subejected to environmental temperature changes. Base on this analysis, anterior semicircular canal was found not considerably stimulated until20seconds after the horizontal semicircular canal did, while it was40seconds later when the posterior semicircular canal was considerably stimulated. It can be inferred that most clinical caloric tests, such as Hallpike test, were not suitable for effectively evaluating two vertical semicircular canals without enough irrigation, and it is applicable to any caloric test with different head position.Finally, a numerical model was developed in order to study the role of the utriculo-endolymphatic valve for the rotation-sensing capabilities of semicircular canals. Based on this model, we have found an unequal exchange of endolymph volume between the two parts of membranous labyrinth caused by head rotation. Both the bigger the stimulation and the larger the valve opening, the more endolymph volume would pass through. As a result, the larger effect would act on the cupular vibration as well as the balance mechanism. Naturally, the utriculo-endolymph valve plays an important role in modulating semicircular canals function. It will probably bring out Menier’s disease and benign paroxysmal positional vertigo with valve abnormality.