The overall goal of this project is to understand the relationship between human middle ear morphemetry and the biomechanical processes that lead to physiological responses. The rational behind this study is that a lack of knowledge about the relationship between structures and middle ear sound transmission has resulted in unsatisfactory success of middle ear repairs and difficulties in interpreting otoacoustic emissions. Our approach is to deconstruct the middle ear into three sub systems that are each characterized through a combination of morphological and physiological measurements as well as three-dimensional mathematical analyses. The sub systems are: (1) the isolated tympanic membrane coupled to the ear canal, (2) the isolated malleus-incus complex, and (3) the isolated stapes footplate. For each sub system and for the intact middle ear, high-resolution microCT images will be used to image individual cadaveric ears. The microCT images are segmented and combined to obtain three-dimensional volume reconstructions of the ear canal, eardrum, ossicles, ligaments and tendons, which are further analyzed to obtain the desired morphemetry. Dynamic measurements are made in order to determine the biomechanical parameters of the morphologically based sub models. To characterize the eardrum sub system, the incus is removed, and the velocity from different sections, including anterior, inferior, and posterior sections will be measured. A mathematical model will be formulated, incorporating anatomical features of the eardrum, including its angular placement in the ear canal, conical shape and its highly organized circumferential and radial fiber layers. To characterize the malleus-incus complex, isolated by dissecting the eardrum and the stapes from the temporal bone, three-dimensional velocity at several points will be measured. An elastic model for the malleus-incus sub system will be developed that incorporates he incudo-malleolar joint slippage, ligaments and tendon attachments. To characterize the stapes sub model, reverse acoustic impedance measurements will be made. The outcome of our studies will result in an anatomically based mathematical analysis of the intact middle ear by combining each of the sub models. Measurements of forward and reverse acoustic measurements from the temporal bone ears, before deconstruction, will be used to test the validity of the analyses developed for cadaver ears. As in cadaver eardrums, the velocity from different sections of the eardrum of living subjects will be measured and similar analysis performed to derive its in-vivo biomechanical parameters. The studies will provide a solid foundation for the structural basis for middle ear sound transmission and will have applications in many areas of hearing health care.
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