Commenced in January 2007
Frequency: Monthly
Edition: International
Paper Count: 72582
Extended High Frequency Impact of Age-Related Tympanic-Membrane Material Properties on Sound Transmission in the Human Ear: Based on a Finite Element Model

Authors: Tzu-Ching Shih, You-Cheng Yu, Tang-Chuan Wang

Abstract:

The aim of this study is to use the finite element ear model to investigate the sound transmission from the outer to the inner ear, to evaluate the impact of age-related tympanic-membrane material properties, and to simulate the influence of the cochlear lymph fluid flow on auditory nerves when considering the acoustic source excitation of the extended high frequency. The range of extended high frequency was from 8 to 20 kHz. Meanwhile, the comprehensive finite element ear model was created from high-resolution computer tomographic images and the excitation of sound pressure level at 90 dB in simulation. Furthermore, the auditory ossicles, suspensory ligaments and tendons, and manubrium in the finite element model were also considered as isotropic elastic material materials. Numerical results showed that the maximum displacements of the tympanic membrane and the stapes for children, young adults, and old adult groups were 1.01x10⁻⁵, 9.92x10⁻⁶, 1.02x10⁻⁵ mm at the frequencies of 3.6, 1.4, and 1.2 kHz, respectively. Meanwhile, the displacements of the children, young adults, and old adult groups were 4.18x10⁻⁷, 4.08x10⁻⁵, and 3.38x10⁻⁵ for the routine pure tone audiometry in which the upper limit frequency is around 8 kHz. For the extended high frequencies (i.e., frequency > 8 kHz), the significant displacements of the children, young adult, and old adult groups occurred at 11.5 kHz, and their corresponding displacements were 2.59x10⁻⁶, 2.47x10⁻⁶, and 2.21x10⁻⁶ mm, respectively, in which these values were the maximum in the extended high-frequency range (i.e., 8 kHz < frequency < 20 kHz). Moreover, for the routine pure tone audiometry test (i.e., frequency < 8 kHz), the maximum displacement of the stapes for children, young adult, and old adult groups were 4.63x10⁻⁶, 4.43x10⁻⁶, and 4.32x10⁻⁶ mm, respectively. In contrast, for the extended high frequency, the maximum displacements of the stapes also occurred at 11.5 kHz, where the maximum displacements of the stapes for children, young adults, and old adults were 3.1x10⁻⁷, 2.96x10⁻⁷, and 2.62x10⁻⁷ mm, respectively. Besides, the displacements of the tympanic membrane and the stapes for children, young adults, and old adults at 20 kHz were 8.87x10⁻⁸, 8.08x10⁻⁸, 6.59x10⁻⁸ mm, and 5.26x10⁻⁹, 4.81x10⁻⁹, 3.85x10⁻⁹ mm, respectively. By comparing the children and young adult groups, the impact of the age-related Young’s moduli on the displacement of the tympanic membrane and the stapes was significant over five frequencies of 19 kHz, 20 kHz, 17 kHz, 2.6 kHz, and 18 kHz. Meanwhile, the significant differences of the displacement of the stapes occurred at around frequencies of 2.6 kHz, 18 kHz, 19 kHz, 0.4 kHz, and 20 kHz. It is obvious that the extended high frequency may affect the sound transmission in the ear. The extended high-frequency audiometry is more sensitive to the effects of tympanic-membrane aging. The comprehensive finite element ear model may provide insight into appropriate information for early diagnosis of hearing loss with the extended high-frequency audiometry.

Keywords: extended high frequency, finite element method, tympanic-membrane material properties, sound transmission

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