Evaluation of Round Window Stimulation Performance in Otosclerosis Using Finite Element Modeling

A comprehensive finite-element human ear model to estimate noise-induced hearing loss associated with occupational noise exposure

BACKGROUND AND OBJECTIVE

Noise is a common occupational and environmental hazard; however, little is known about the use of computational tools to quantitively analyze data on basilar membrane (BM) damage in noise-induced hearing loss (NIHL). Here, we established a comprehensive three-dimensional finite-element human ear model to quantify the impact of noise exposure on BM and perilymph fluid.

METHODS

We used auditory risk units (ARUs) to evaluate the BM damage for subjects (3 men and 5 women; mean age, 32.75 ± 8.86 years; age range, 24-44 years). A 90-dB sound pressure level (SPL) was normally applied at the external auditory canal (EAC) entrance to simulate sound transmission from the EAC to the cochlea at frequencies of 0.2-10.0 kHz.

RESULTS

The pressure distribution of perilymph fluid is totally different on frequency responses under low and high sound-evoked (0.013-10.0 kHz). The highest ARUs were 18.479% at the distance of 1 mm from the base, and the second-highest to fourth-highest ARUs occurred at distances of 5-7 mm from the base, where their ARUs were 9.749%, 9.176%, and 11.231%. The total of the ARUs reached 81.956% at external frequencies' sounds of 3.2-5.0 kHz. Among these, the 3.8-kHz and 3.6-kHz frequencies yielded the highest and second-highest ARUs of 20.325% and 19.873%, respectively.

CONCLUSIONS

This study would inform our understanding of NIHL associated with occupational noise exposure. We present a FE modelling and describe how it might provide a unique way to unravel mechanisms that drive NIHL due to loud noises.

Effects of age-related tympanic-membrane material properties on sound transmission in the middle ear in a three-dimensional finite-element model

BACKGROUND AND OBJECTIVES

The Young's modulus of the tympanic membrane (TM) is an important modeling parameter in computer simulations of the sound transmission in the ear. Understanding the material mechanics of the TM is essential to improve the coupling between the tympanic membrane and the auditory ossicles. However, the impact of the age-related Young's modulus of the TM on sound transmission is not well known. The objective of this study was to use a comprehensive finite element (FE) model to assess the impact of Young's modulus on sound transmission from the ear canal to the stapes footplate over acoustic frequencies.

METHODS

The FE model of the ear canal, the middle ear, and the inner ear, was constructed. The model was constructed with identical geometries and boundary conditions, but with three different Young's moduli for the TMs. The auditory ossicles, suspensory ligaments and tendons, and manubrium were also modeled as isotropic elastic materials. Beside, we evaluated the age-related Young's moduli of the TMs on sound transmission with the FE element fluid-structural interaction (FSI) model under acoustic loading conditions.

RESULTS

The impact of the age-related Young's moduli on the sound pressure distributions in the ear canal was significant over two frequency ranges of 1.4-3.2 and 8.6-10 kHz. Meanwhile, the significant differences of the displacement of the stapes occurred at around 1.6 kHz, where the displacement of the stapes decreased from 0.352 nm to 0.287 nm.

CONCLUSIONS

The FSI model could demonstrate the influence of Young's modulus of the TM on the transfer of sound-induced vibrations form the ear canal to the stapes footplate. The FE model may provide appropriate information to the medical device development of artificial ossicles and hearing aids.

Finite element analysis of round-window stimulation of the cochlea in patients with stapedial otosclerosis

An active actuator coupled to the round window (RW) can transmit mechanical vibrations into the cochlea and has become a therapeutic option of hearing rehabilitation for patients with stapedial otosclerosis. A finite-element model of the human ear that includes sound transmission effects of the vestibular and cochlear aqueducts of the inner ear is adopted in this study for investigating the cochlear response to RW stimulation under stapes fixation. There are two effects due to otosclerosis of the stapes: the fixation of the stapedial annular ligament (SAL) and the increase of the stapes mass. The frequency responses of the middle ear and cochlea with normal and otosclerotic stapes are calculated under sound and RW stimulations. The results show that changes in the material property of the stapes have different effects on the cochlear responses under sound and RW stimulations. Because of the vestibuli aqueduct, the reduction in the low-frequency magnitude of the pressure difference across the cochlear partition due to SAL fixation is much smaller under RW stimulation than under sound stimulation. The results of this study help understand sound transmission during RW stimulation in patients with stapedial otosclerosis.

How Stapes Ankylosis and Fracture Affect Middle Ear Dynamics: A Numerical Study

Numerical models of the human middle ear have been developed throughout the last 30 years, for different purposes. While several types of pathologies have been studied, stapedial disorders were seldomly explored. This papers aims to clarify how stapes fracture and some forms of stapes ankylosis, such as stapedial tendon (ST) ossification, augmented pyramidal eminence (PE) and bony bar presence, affect the sound transmission through the middle ear. In addition, the stapes dynamics is also analyzed by means of total displacement and first principal strain. For the purpose of the study, first, a three-dimensional finite element model of the human middle ear is detailed and validated under normal (healthy) conditions. The model is then modified to represent the stapedial disorders of interest. A measure is established for evaluating how the disorders reduce sound transmission through the middle ear. Results of the reduction of sound transmission showed that the different forms of stapes ankylosis affect primarily low frequencies, while the stapes fracture mostly affects high frequency sound transmission. According to the results, an augmented PE does not restrict stapes movement unless followed by some ossification of the ST. In addition, the question whether the fracture is in the anterior or posterior crus and the distance of the fractured part from the stapes footplate have a relevant role in the reduction of the sound transmission. Finally, the analysis of total displacement and first principal strain of the stapes helped to highlight some differences among the stapedial disorders.