Middle Ear Vibration Research Articles

Mechanical Effects of Medical Device Attachment to Human Tympanic Membrane.

Several treatment methods for hearing disorders rely on attaching medical devices to the tympanic membrane. This study aims to systematically analyze the effects of the material and geometrical properties and location of the medical devices attached to the tympanic membrane on middle-ear vibrations. A finite-element model of the human middle ear was employed to simulate the effects of attachment of medical devices. Various types of material and geometrical properties, locations, and modeling scenarios were investigated for the medical device. The attachment of the device magnifies the effects of anti-resonances of the middle ear. Additionally, the variations of the material properties of the device significantly alter the middle-ear resonance frequency while changes in the umbo and stapes footplate motions are negligible at frequencies above 5kHz. Furthermore, modeling the device as a point mass cannot accurately represent the implanted middle-ear behavior. The variations of the diameter and height of the medical device have negligible effects on the middle-ear vibrations at frequencies below 200Hz but can have considerable impacts at higher frequencies. The effects of changing the device height were negligible at frequencies above 2kHz. We also discuss the effects of medical device attachment on the vibration patterns of the tympanic membrane as well as the impacts of the variations of the location of the device on the stapes footplate responses. The findings of our study aid the development and optimization of new therapeutic devices, attached to the tympanic membrane, to have the least adverse effects on middle-ear vibrations.

Evaluation on the possibility of sound conduction independent of tympanic air cavity for severe tympanic adhesion patients by finite element analysis.

Background: For patients with severe tympanic adhesion, reconstructing the tympanic air cavity is often challenging, resulting in poor hearing reconstruction outcomes. Therefore, establishing a sound conduction pathway independent of the tympanic air cavity may be a viable method for reconstructing hearing in these patients. Purpose: The objective of this study was to evaluate the feasibility of sound conduction independent of the tympanic air cavity (i.e., replacing the original cavity with a tympanic vibrating material) using finite element analysis. Methods: We established a sound-structure coupling finite element model of the tympanum vibration conduction system, which included the tympanic membrane (TM), ossicular prosthesis, and tympanic vibrating material. This model was used to simulate middle ear vibrations under sound pressure, and we extracted the frequency response curve of the ossicular prosthesis' vibration displacement amplitude to evaluate the sound conduction effect of the middle ear. Next, we adjusted the structural and mechanical parameters of the tympanic vibrating material to analyze its impact on the sound conduction effect of the middle ear. Finally, we compared the frequency response curve of the stapes footplate in normal subjects to evaluate the feasibility of sound conduction independent of the tympanic air cavity. Results: The Shell tympanic vibrating material had a better vibration conduction effect compared to solid or porous tympanic vibrating material. The vibration amplitude decreases with the increasing elastic modulus of the tympanic vibrating material. Implantation of 40kPa-shell tympanic vibrating material had the lowest hearing loss less than 5dB, and the hearing loss with 1MPa-porous tympanic vibrating material was largest and less than 25dB. Conclusion: Our study suggests that replacing the tympanic air cavity with a tympanic vibrating material is feasible. The establishment of a sound conduction pathway independent of the tympanic air cavity could potentially provide a method for hearing reconstruction in patients with severe tympanic adhesion.

In Vivo Measurement of Ear Ossicle and Bony Wall Vibration by Sound Stimulation of Cartilage Conduction.

The cartilage-conduction pathway was recently proposed as a third auditory pathway; however, middle-ear vibrations have not yet been investigated in vivo. We aimed to measure the ossicles and bone vibration upon cartilage-conduction stimulation with a non-contact laser Doppler vibrometer. We recruited adult patients with normal ear structures who underwent cochlear implant surgery at our hospital between April 2020 and December 2022. For sound input, a cartilage-conduction transducer, custom-made by RION Corporation (Tokyo, Japan), was fixed to the surface of the tragus and connected to an audiometer to regulate the output. A posterior tympanotomy was performed and a laser beam was directed through the cavity to measure the vibration of the ossicles, cochlear promontory, and posterior wall of the external auditory canal. Five participants (three men, mean age: 56.4 years) were included. The mean hearing loss on the operative side was 96.3 dB HL in one patient, and that of the other patients was off-scale. The vibrations were measured at a sound input of 1 kHz and 60 dB. We observed vibrations of all three structures, demonstrating the existence of cartilage-conduction pathways in vivo. These results may help uncover the mechanisms of the cartilage-conduction pathway in the future.

On the influence of the middle ear on the sound pressure level generated in open and occluded earcanals under a bone-conducted stimulation

The occlusion effect is an acoustic discomfort commonly encountered by earplugs’ users, which corresponds to the increased auditory perception of the bone-conducted sound mainly at low frequencies. This perception is accompanied by the augmentation of the sound pressure level in the earcanal when occluded by the earplug compared to the open case. While the source of the SPL generated in the earcanal in both open and occluded cases is mainly attributed to the vibration of the earcanal wall, the sound radiation of the tympanic membrane that stems from the middle ear vibration is commonly considered as not significant. To investigate this phenomenon, a finite element model that incorporates the middle ear components into a realistic human outer ear is developed. First, the finite element model is evaluated by comparing the acoustic impedance computed at the eardrum surface to literature data obtained on human subjects. Second, the finite element model is used to quantify the contribution of the sound radiation that originates from the middle ear on the sound pressure level generated in both open and occluded earcanals under a bone-conducted stimulation.

How does prestrain in the tympanic membrane affect middle-ear function? A finite-element model study in rabbit

Experiments have shown that prestrain exists in the rabbit tympanic membrane (TM), also in the absence of external loads. To date, it is unclear how prestrain influences the vibration response of the middle ear (ME). In this study, a detailed 3D finite-element model of the rabbit ME was constructed based on experimentally validated material properties. The model incorporates different degrees of prestrain in the TM and simulates the ME vibration response to sound as a linear harmonic perturbation around the prestressed reference state. To account for finite deformations associated with large prestrains, a framework was developed that iteratively updates the initial unstrained geometry until the prestrained geometry is in agreement with the given reference geometry. After validating the model using quasi-static and acoustic measurement data, it was shown that small levels of prestrain already have a substantial impact on the normal umbo and footplate response due to a phenomenon known as prestress stiffening. Although the approach is not preferable, it was possible to replicate the effect of prestrain in the normal ME by appropriately scaling the elastic moduli and damping factors in the base model. To evaluate the effect of possible changes in TM prestrain when the normal state of the ear is altered due to pathological modifications in the ME structure, we created a model with a perforation in the TM. It was shown that the change in vibration response after perforation is affected at low frequencies by a release of TM prestrain. In future studies, it may be necessary to incorporate prestrain in ME models to better understand the function of the diseased or reconstructed ME, which may be relevant for the development of reconstructive tissue grafts in the middle ear.

Development and Characterization of a Biomimetic Totally Implantable Artificial Basilar Membrane System.

Cochlear implants (CIs) have become the standard treatment for severe-to-profound sensorineural hearing loss. Conventional CIs have some challenges, such as the use of extracorporeal devices, and high power consumption for frequency analysis. To overcome these, artificial basilar membranes (ABMs) made of piezoelectric materials have been studied. This study aimed to verify the conceptual idea of a totally implantable ABM system. A prototype of the totally implantable system composed of the ABM developed in previous research, an electronic module (EM) for the amplification of electrical output from the ABM, and electrode was developed. We investigated the feasibility of the ABM system and obtained meaningful auditory brainstem responses of deafened guinea pigs by implanting the electrode of the ABM system. Also, an optimal method of coupling the ABM system to the human ossicle for transducing sound waves into electrical signals using the middle ear vibration was studied and the electrical signal output according to the sound stimuli was measured successfully. Although the overall power output from the ABM system is still less than the conventional CIs and further improvements to the ABM system are needed, we found a possibility of the developed ABM system as a totally implantable CIs in the future.

Time-domain and frequency-domain effects of tensor tympani contraction on middle ear sound transmission in gerbil

The middle ear is a high-fidelity, broadband impedance transformer that transmits acoustic stimuli at the eardrum to the inner ear. It is home to the two smallest muscles in mammalian species, which modulate middle ear transmission. Of this pair, the function of the tensor tympani muscle (TTM) has remained obscure. We investigated the acoustic effects of this muscle in young adult gerbils. We measured changes in middle ear vibration produced by pulse-train-elicited TTM contraction – in the time-domain with a click stimulus and in the frequency-domain with multitone zwuis stimuli. In our click experiments, there was generally a small reduction in the primary peak of the response and a slight increase in the subsequent ringing, but there was essentially no change in the delay of the click response at the umbo (less than 1 µs change). In our multitone experiments, there were consistent patterns of attenuation and enhancement in the velocity responses at the umbo and ossicles. TTM contraction produced a narrow band of enhancement around 6 kHz (maximally ~5 dB) that can be modeled with an increased stiffness of an overdamped spring-mass resonance. At frequencies below 2 kHz and above 35 kHz, TTM contraction attenuated middle ear vibrations by as much as fivefold.

Structural stiffening in the human middle ear due to static pressure: Finite-element analysis of combined static and dynamic middle-ear behavior

The vibration response of the middle ear (ME) to sound changes when static pressure gradients are applied across the tympanic membrane (TM). To date, it has not been well understood which mechanisms lead to these changes in ME vibration response. In this study, a 3D finite-element model of the human ME was developed that simulates the sound-induced ME vibration response when positive and negative static pressures of up to 4 kPa are applied to the TM. Hyperelasticity of the soft-tissue components was considered to simulate large deformations under static pressure. Some ME components were treated as viscoelastic materials to capture the difference between their static and dynamic stiffness, which was needed to replicate both static and dynamic ME behavior. The change in dynamic stiffness with static preload was simulated by linearization of the hyperelastic constitutive model around the predeformed state. For the preloaded harmonic response, we found that the statically deformed ME geometry introduced asymmetry in the vibration loss between positive and negative pressure, which was due to the TM cone shape. As opposed to previous assumptions, the prestress in the ME due to static pressure had a substantial impact on the vibration response. We also found that material nonlinearity led to a higher stiffening at the umbo but a less pronounced stiffening at the footplate compared to the linear elastic condition. The results suggest that flexibility of the incudomalleolar joint (IMJ) enhances the decoupling of static umbo and footplate displacements, and that viscosity and viscoelasticity of the IMJ could play a role in the transfer of sound-induced vibrations from the umbo to the footplate. The components of the incudostapedial joint had minimal effect on ME mechanical behavior.

Middle ear vibration with stiff and flexible shape memory prosthesis

Herein, a two degree-of-freedom model of the reconstructed middle ear using shape memory prosthesis is investigated near the primary resonance for various prosthesis types. The polynomial model of shape memory alloy is used to characterise the properties of the prosthesis. To solve the differential equations of middle ear motion, the multiple time scales method is applied. The first- and second-order approximations of the primary resonance curves are compared with each other and verified through numerical simulations. The obtained analytical solutions studied for the stiff and flexible prosthesis reveal various accuracies depending on the prosthesis stiffness. The second-order approximation of the multiple scales method reveals unstable harmonic vibrations near the primary resonance zone, but are not found in the first-order approximation.

Average middle ear frequency response curves with preservation of curve morphology characteristics

For the validation of modelling results or the comparison of middle ear interventions, such as prostheses placement, average responses of middle ear vibrations are needed. One such response is the amplitude and phase of the vibration of the stapes footplate as a function of frequency. Average responses and their standard deviation are commonly obtained by calculating the mean of a number of measured responses at each frequency. A typical middle ear magnitude response curve shows a number of distinct peaks, and the location of these peaks varies between ears. By simply taking an average along the magnitude or phase response axis, the typical fine structure of the response curve is flattened out, delivering an average curve which no longer has the typical morphology of an individual response curve. This paper introduces methods to avoid this problem by first aligning the typical curve features along the frequency axis prior to calculating the average along the magnitude or phase axis, resulting in average magnitude and phase curves which maintain the typical morphology of the curve obtained for an individual ear. In the method, landmark points on the response magnitude curves are defined and the frequencies at which these points occur are averaged. Next, these average frequencies are used to align the landmark points between curves, prior to averaging values along the magnitude or phase axes. Methods for semi-automatic and manual assignment of landmark points and curve alignment are presented. After alignment, the correspondence between the original landmark frequencies and aligned frequencies is obtained together with the warping function which maps each original magnitude curve to its aligned version. The phase curves are aligned using the warping functions determined from the corresponding magnitude curves. Finally, a method is proposed to compare the data set of an individual measurement or model result to an aligned average curve in terms of magnitude and frequency by applying the alignment procedure to the individual curve.

New clinical applications for laser Doppler vibrometry in otology

An instrument to measure vibration in the middle ear needs to be sensitive enough to detect displacement on ananometer scale, yet not affect the vibration itself. Numerous techniques have been described in the literature, but laser Doppler vibrometry (LDV) has nowadays become established as the standard method in hearing research. This article aims to present possible clinical applications of an LDV system in otology. Acommercially available single-point vibrometer was used. Measurements were carried out both with the sensor head mounted on an operating microscope and as ahandheld device with the sensor head manually inserted in the ear canal. For the latter, acustom-made unit containing an electrically tunable lens was attached to the sensor head. Middle ear vibrations were measured in atemporal bone model as well as in patients during and after implantation of aVibrant Soundbridge (VSB; MED-EL Corp., Durham/NC, USA). Different types of middle ear pathologies can be distinguished by the frequency response of the umbo. The LDV technique can be used for intraoperative quantification of the coupling quality of the VSB's Floating Mass Transducer (FMT; MED-EL) to the ossicle chain during VSB implantation. Postoperatively, the method serves as afollow-up testing tool if adeterioration in aided hearing threshold occurs. The measurement can reveal changes in the umbo transfer function, e. g., due to middle ear scarring or dislocation of the FMT. Many clinical questions in otology can be addressed by LDV. However, due to the high acquisition costs of an LDV system, the relatively large instrumental setup, and the large inter-ear variability of middle-ear function, the technique has not (yet) become established in clinical routine.

Middle ear vibrations with SMA prosthesis. Experimental research

The paper focuses on experimental research of a middle ear prosthesis made of shape memory alloy. The prosthesis provides better adjustment to individual patient than classical prosthesis. The shape memory prosthesis is implemented to a fresh temporal bone and vibrations of the round window are recorded by means of the Laser Doppler Vibrometer. Finally, the results are presented in the form of transfer function and compared to the intact and damaged middle ear.

New Imaging Modalities in Otology.

Despite steady improvements in cross-sectional imaging of the ear, current technologies still have limitations in terms of resolution, diagnosis, functional assessment and safety. In this chapter, state-of-the-art imaging techniques in current clinical practice are presented including cone-beam computerized tomography, non-echo planar imaging magnetic resonance imaging, imaging for labyrinthine hydrops and imaging of the central auditory pathways. Potential future imaging modalities are also presented, including optical coherence tomography (OCT) and high-frequency ultrasound (HFUS) of the ear. These experimental modalities offer new opportunities for the assessment of ear structure and function. For example, middle ear structures can be visualized through the tympanic membrane, basilar membrane vibrations can be assessed through the round window and the passage of cochlear implants can be assessed in decalcified cochlear. Functional assessment of the middle ear using Doppler techniques are also discussed, including measurement of tympanic membrane and middle ear vibration amplitudes, visualization of dynamic changes, such as tensor tympani movements and movement of the tympanic membrane with breathing. These new modalities currently have limitations that preclude mainstream clinical use. For example, OCT is limited by the optical scattering of the thickened tympanic membrane and HFUS needs a coupling medium such as gel or fluid from the transducer to the imaged structure although it can visualize through thicker tissues. Nevertheless, further development of these novel techniques may provide an enhanced ability to assess the ear in conjunction with current technologies.

The Impact of a Cochlear Implant Electrode Array on the Middle Ear Transfer Function.

As a treatment for partial deafness with residual hearing in the lower frequency range, the combined acoustic and electric stimulation of the cochlea has become widespread. Acoustic stimulation is provided by a hearing aid's airborne sound and the electric stimulation by a cochlear implant electrode array, which may be inserted through the round window or a cochleostomy. To take advantage of that concept, it is essential to preserve residual hearing after surgery. Therefore, the intracochlear electrode array should not compromise the middle ear vibration transmission. This study investigates the influence of different electrode types and insertion paths on the middle ear transfer function and the inner ear fluid dynamics. Sound-induced oval and round window net volume velocities were calculated from vibration measurements with laser vibrometers on six nonfixated human temporal bones. After baseline measurements in the "natural" condition, a cochleostomy was drilled and closed with connective tissue. Then, four different electrode arrays were inserted through the cochleostomy. Afterwards, they were inserted through the round window while the cochleostomy was patched again with connective tissue. After having drilled a cochleostomy and electrode insertion, no systematic trends in the changes of oval and round window volume velocities were observed. Nearly all changes of middle ear transfer functions, as well as oval and round window volume velocity ratios, were statistically insignificant. Intracochlear electrode arrays do not significantly increase cochlear input impedance immediately after insertion. Any changes that may occur seem to be independent of electrode array type and insertion path.

Long-range, wide-field swept-source optical coherence tomography with GPU accelerated digital lock-in Doppler vibrography for real-time, in vivo middle ear diagnostics.

We present the design, implementation and validation of a swept-source optical coherence tomography (OCT) system for real-time imaging of the human middle ear in live patients. Our system consists of a highly phase-stable Vernier-tuned distributed Bragg-reflector laser along with a real-time processing engine implemented on a graphics processing unit. We use the system to demonstrate, for the first time in live subjects, real-time Doppler measurements of middle ear vibration in response to sound, video rate 2D B-mode imaging of the middle ear and 3D volumetric B-mode imaging. All measurements were performed non-invasively through the intact tympanic membrane demonstrating that the technology is readily translatable to the clinic.

Simulations and Measurements of Human Middle Ear Vibrations Using Multi-Body Systems and Laser-Doppler Vibrometry with the Floating Mass Transducer.

The transfer characteristic of the human middle ear with an applied middle ear implant (floating mass transducer) is examined computationally with a Multi-body System approach and compared with experimental results. For this purpose, the geometry of the middle ear was reconstructed from μ-computer tomography slice data and prepared for a Multi-body System simulation. The transfer function of the floating mass transducer, which is the ratio of the input voltage and the generated force, is derived based on a physical context. The numerical results obtained with the Multi-body System approach are compared with experimental results by Laser Doppler measurements of the stapes footplate velocities of five different specimens. Although slightly differing anatomical structures were used for the calculation and the measurement, a high correspondence with respect to the course of stapes footplate displacement along the frequency was found. Notably, a notch at frequencies just below 1 kHz occurred. Additionally, phase courses of stapes footplate displacements were determined computationally if possible and compared with experimental results. The examinations were undertaken to quantify stapes footplate displacements in the clinical practice of middle ear implants and, also, to develop fitting strategies on a physical basis for hearing impaired patients aided with middle ear implants.

Middle ear vibration sensor using multiple transducers

A hearing assistance system includes multiple middle ear transducers for sensing vibrations of an ossicle or other auditory element. The hearing assistance system is configured to accommodate an unknown or variable direction of the vibration. Two transducers are arranged to transduce nonidentical directional components of the vibration into electrical signals which are then combined. The combined electrical signal is approximately independent of the direction of the vibration, or has improved frequency response, or has an amplitude that is approximately independent of the direction of the vibration. The combined electrical signal may result from a square root of sum-of-squares, sum of individually filtered signals, differentiation, or other techniques. The hearing assistance system analogously accommodates three dimensional variability of the direction of vibration using three middle ear transducers.

F-0803 耳小骨靭帯硬化耳の振動特性 : 有限要素法による解析(S43-1 生体現象に対する計算力学的アプローチ)(S43 生体力学シミュレーション)

The middle ear plays an important role in auditory mechanics, transmitting sound signals efficiently from the ear canal to the cochlea. If ligaments, which support ossicles, become fixed, conductive hearing loss occurs. A diagnosis of these fixations of the ligaments is difficult. Especially, as the anterior malleal ligament (AML) is a tiny ligament, its fixation is often overlooked. In this study, the effect of the AML fixation on the middle-ear vibration was analyzed by using a finite-element model of the middle ear and by measuring vibrations of temporal bones with a laser Doppler interferometer. Then, based on our findings, a diagnostic method for detecting the AML fixation was suggested.

Measurement of Dynamic Frequency Characteristics of Guinea Pig Middle Ear by a Laser Doppler Velocimeter.

The objective of the present study is to clarify the dynamic behavior of the middle ear by measuring the middle ear vibration directly. The velocity amplitudes of the tympanic membrane and ossicles of guinea pigs are measured before and after the manipulation of the cochlea and bulla using a laser Doppler velocimeter coupled to a compound microscope. The frequency characteristics of the middle ear vibration after the manipulation are different from those before it. These differences are explained by considering mass and damping components of the cochlear impedance and mass and stiffness components of the bulla's impedance.

Middle Ear Vibration and Sound Pressure Measurements in the Isolated Cochlea Preparation

A wide variety of auditory functions and responses are measured in terms of the sound pressure at some reference location in the ear canal. Another common measure that has been used to specify the mechanical input to the ear is the vibration of the malleus at the umbo