The Mechanism Of Bone Conduction Hearing In Congenital Aural Atresia Basing On The Clinical Data Analysis As Well As Animal And Temporal Bone Model Experiments

Congenital malformation of external and middle ear is one of the common defects in Otology Clinic, with the incidence of1/8,000～10,000. The typical presentations are combining with microtia, atresia and malformation of the middle ear, and the patients show conductive hearing loss. Previous studies mostly focus on the patients’conductive hearing loss. Few of them mentioned the patients’bone conduction hearing loss, which is not very true for that kind of situation. That’s because those patients normally do not have sound radiation from the ear canal, or innertiation of the ossicle chain, which are the two most important factors in the bone conduction hearing. Therefore, we want to discuss the effect of the two factors on those patients’bone conduction hearing by using analysis the clinical hearing data, simulated animal experiment, and Laser Doppler Vibrometer (LDV) measurement on the temporal bone.The first part of the study focus on the analysis of the clinical hearing data. In this part, we collect15patients with unilateral microtia, and find that all of them showing typical conductive hearing loss with air-conductive hearing threshold of65.41±11.91dB HL, and air-bone gap of43.16±8.43dB HL. In addition, we also find that there are33.3%of them presenting the typical Carhart Notch, which is defined as a depression of bone conduction thresholds at2kHz, initially reported by Carhart in1950.In the second part, we want to explore the effect of the aforementioned two factors on the bone conduction hearing through the animal model. Firstly, we investigate both the normal air-and bone-conductive hearing from the analysis of12cats’ABR. Then, we try to simulate the four different situations:1) immobilization of the ossicular chain,2) blockage of the ear canal,3) immobilization of the ossicular chain+blockage of the ear canal, and4) control, by surgeries. And we find that all the surgical methods are successful. Lastly, we choose another12cats and divide them into four groups with3in each of them for simulating the four different situations. By comparing the pre-and post-surgical bone-conductive hearing, we find that the immobilization of the ossicular chain plays an important part in bone conduction hearing, especially for the high frequencies.In the third section, we want to simulate the four different situations by using temporal bone and then try to explore the aforementioned two factors’affection on bone conduction hearing by using LDV measurement. Firstly, we simulate the temporal bone model surgically and prove its’feasibility. Secondly, we explore whether Bone Anchored Hearing Aid (BAHA) can be used in this kind of research, and end up with failure due to the output of the device. Based on previous researches, we change to shaker, and define the protocol of using shaker in this research. Finally, we simulate the four different situations on temporal bone and find that ossicular chain inertial can influence the bone conduction hearing from the frequency of0.25to5kHz, especially around the frequency of1.5kHz, which is the resonance frequency of osscilar chain.In a word, in this study, we find that there are some bone conduction hearing loss of the patients with malformation of external and middle ear, which is due to the disappear of ossicular chain’s inertial. In addition, in our animal experiment, we find that the influence to bone conduction hearing will increase with the frequency becoming higher, and in the temporal bone study, we find that the bone conduction hearing will be affected from the frequency of0.25to5kHz, especially around the frequency of1.5kHz, which is the resonance frequency of osscular chain.