Abstract:
Otoacoustic emissions (OAEs) are believed to originate from outer hair cell movement and are considered to be transmitted to the external auditory meatus through the middle ear in a retrograde fashion. Therefore, the effect of the middle ear on OAEs seems to be large. However, few investigations of middle ear effects on OAEs have been published. In this study, first, applying the authors' own finite-element method (FEM) program, a three-dimensional FEM model of a human auditory periphery, which included the external auditory meatus, the tympanic membrane, ossicles, and middle ear cavities, was established. Then, the retrograde and anterograde transmission factors of the normal and pathologic middle ear were examined. The following conclusions can be drawn. (1) As expected, the value of the retrograde transmission factor is lower than that of the anterograde one. (2) This is mainly caused by the dynamic behavior of the tympanic membrane. (3) The levels of OAEs obtained from the patients such as atelectatic tympanic membrane, I--S joint separation, and otosclerosis are lower than the noise level of the OAE measurement system, because the value of the middle ear transmission factor of these patients is smaller than that of the normal subject.