Middle-ear disease is the most common cause of hearing loss. Otologic surgeons repair thousands of middle ears each year with mixed success, especially after severe middle-ear disease. Knowledge of structure-function relationships is crucial to improving reconstructive techniques. Attractive treatments for severe conductive hearing loss include direct mechanical stimulation of the cochlear windows and/or the application of bone-conduction hearing aids. In the past, we developed physiology-based models that relate structure and function in normal, pathological, and reconstructed ears. We focus now on four clinically-relevant structure-function issues using animal models: (1) We investigate the source and functional significance of observed delays in normal and modified middle-ear transmission in cat and chinchilla in the context of middle-ear impedance matching, the efficiency of sound transmission and the high-frequency response of the intact and pathologic middle ear. (2) We quantify the efficacy of direct round- and oval-window stimulation in a live animal model (chinchilla) and use these results to refine a model of cochlear function that accounts for the observed effectiveness of such stimulation in cases of round and oval-window fixation. (3) We build on our past research showing the significance of the inner-ear mechanism of bone conduction in chinchilla, and use this preparation to investigate (a) the mechanisms that contribute to the ear's response to bone conducted sound after ossicular pathology and (b) provide a fundamental test of the influence of cranial tissue vibrations on the ear's response to bone-conducted sound. (4) We use a newly developed bone-conduction-based method to quantify 'conductive'and 'sensorineural'hearing loss in mouse models of mixed hearing loss. Such a separation is critical in understanding the mechanisms of various genetic models of hearing loss.
Middle-ear disease is the most common form of hearing loss, and otologic surgeons routinely repair middle ears but with variable success. This proposal answers questions on the basic mechanisms of middle-ear sound transfer and how the inner ear is stimulated by ossicular prostheses. It also investigates the pathways for bone-conduction hearing and uses bone conduction to define measures that distinguish between middle-ear and inner-ear related hearing losses in animal models of human ear disease.
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