Effects of ear-canal pressurization on middle-ear bone- and air-conduction responses

Performance of personalised prosthesis under static pressure: Numerical analysis and experimental validation

This study investigates the performance of personalised middle ear prostheses under static pressure through a combined approach of numerical analysis and experimental validation. The sound transmission performances of both normal and reconstructed middle ears undergo changes under high positive or negative pressure within the middle ear cavity. This pressure fluctuation has the potential to result in prosthesis displacement/extrusion in patients. To optimise the design of middle ear prostheses, it is crucial to consider various factors, including the condition of the middle ear cavity in which the prosthesis is placed. The integration of computational modelling techniques with non-invasive imaging modalities has demonstrated significant promise and distinct prospects in middle ear surgery. In this study, we assessed the efficacy of Finite Element (FE) analysis in modelling the responses of both normal and reconstructed middle ears to elevated static pressure within the ear canal. The FE model underwent validation using experimental data derived from human cadaveric temporal bones before progressing to subsequent investigations. Afterwards, we assessed stapes and umbo displacements in the reconstructed middle ear under static pressure, with either a columella-type prosthesis or a prosthetic incus, closely resembling a healthy incus. Results indicated the superior performance of the prosthetic incus in terms of both sound transmission to the inner ear and stress distribution patterns on the TM, potentially lowering the risk of prosthesis displacement/extrusion. This study underscores the potential of computational analysis in middle ear surgery, encompassing aspects such as prosthesis design, predicting outcomes in ossicular chain reconstruction (OCR), and mitigating experimental costs.

Relative importance and interactions of parameters of finite-element models of human middle ear

In the last decades, finite-element models of the middle ear have been widely used to predict the middle-ear vibration outputs. Even with the simplest linear assumption for material properties of the structures in the middle ear, these models need tens of parameters. Due to the complexities of measurements of material properties of these structures, accurate estimations of the values of most of these parameters are not possible. In this study, we benefited from the stochastic finite-element model of the middle ear we had developed in the past, to perform global sensitivity analysis. For this aim, we implemented Sobol' sensitivity analysis which ranks the importance of all uncertain parameters and interactions among them at different frequencies. To decrease the computational costs, we found Sobol' indices from surrogate models that we created using stochastic finite-element results and the polynomial chaos expansion method. Based on the results, the Young's modulus and thickness of the tympanic membrane, Young's modulus and damping of the stapedial annular ligaments, and the Young's modulus of ossicles are among the parameters with the greatest impacts on vibrations of the umbo and stapes footplate. Furthermore, the most significant interactions happen between the Young's modulus and thickness of the tympanic membrane.

Finite-Element Modelling Based on Optical Coherence Tomography and Corresponding X-ray MicroCT Data for Three Human Middle Ears

PURPOSE

Optical coherence tomography (OCT) is an emerging imaging modality which is non-invasive, can be employed in vivo, and can record both anatomy and vibrations. The purpose here is to explore the application of finite-element (FE) modelling to OCT data.

METHODS

We recorded vibrations for three human cadaver middle ears using OCT. We also have X-ray microCT images from the same ears. Three FE models were built based on geometries obtained from the microCT images. The material properties and boundary conditions of the models were obtained from previously reported studies.

RESULTS

Tympanic-membrane (TM) vibration patterns were computed for the three models and compared with the patterns measured using OCT. Frequency responses were also computed for all three models for several locations in the middle ear and compared with the OCT displacements and with the literature. The three models were compared with each other in terms of geometry and function. Parameter sensitivity analyses were done and the results were compared among the models and with the literature. The simulated TM displacement patterns are qualitatively similar to the OCT results. The simulated displacements are closer to the OCT results for 500 Hz and 1 kHz but the differences are greater at 2 kHz.

CONCLUSION

This study provides an initial look at the combined use of OCT measurements and FE modelling based on subject-specific anatomy. The geometries and parameters of the existing FE models could be modified for individual patients in the future to help identify abnormalities in the middle ear.

Inaccuracies of deterministic finite-element models of human middle ear revealed by stochastic modelling

For over 40 years, finite-element models of the mechanics of the middle ear have been mostly deterministic in nature. Deterministic models do not take into account the effects of inter-individual variabilities on middle-ear parameters. We present a stochastic finite-element model of the human middle ear that uses variability in the model parameters to investigate the uncertainty in the model outputs (umbo, stapes, and tympanic-membrane displacements). We demonstrate: (1) uncertainties in the model parameters can be magnified by more than three times in the umbo and stapes footplate responses at frequencies above 2 kHz; (2) middle-ear models are biased and they distort the output distributions; and (3) with increased frequency, the highly-uncertain regions spatially spread out on the tympanic membrane surface. Our results assert that we should be mindful when using deterministic finite-element middle-ear models for critical tasks such as novel device developments and diagnosis.

Effects of preloads on middle-ear transfer function and acoustic reflex in ossiculoplasty with PORP

INTRODUCTION

Surgical outcomes in ossiculoplasty with partial ossicular replacement prostheses (PORPs) are greatly influenced by the amount of preload imposed on the PORP. In this study, the attenuation of the middle-ear transfer function (METF) was experimentally investigated for prosthesis-related preloads in different directions, with and without concurrent application of stapedial muscle tension. Different PORP designs were assessed to determine functional benefits of specific design features under preload conditions.

METHODS

The experiments were performed on fresh-frozen human cadaveric temporal bones. The effect of preloads along different directions were experimentally assessed by simulating anatomical variance and postoperative position changes in a controlled setup. The assessments were performed for three different PORP designs featuring either a fixed shaft or ball joint and a Bell-type or Clip-interface. Further, the combined effect of the preloads towards the medial direction with tensional forces of the stapedial muscle was assessed. The METF was obtained via laser-Doppler vibrometry for each measurement condition.

RESULTS

The preloads as well as the stapedial muscle tension primarily attenuated the METF between 0.5 and 4 kHz. The largest attenuations resulted from the preload towards the medial direction. The attenuation of the METF with stapedial muscle tension was reduced with concurrent PORP preloads. PORPs with a ball joint resulted in reduced attenuation only for preloads along the long axis of the stapes footplate. In contrast to the clip interface, the Bell-type interface was prone to lose coupling with the stapes head for preloads in the medial direction.

CONCLUSIONS

The experimental study of the preload effects indicates a direction-dependent attenuation of the METF, with the most pronounced effects resulting from preloads towards the medial direction. Based on the obtained results, the ball joint offers tolerance for angular positioning while the clip interface prevents PORP dislocations for preloads in lateral direction. At high preloads, the attenuation of the METF with stapedial muscle tension is reduced, which should be considered for the interpretation of postoperative acoustic reflex tests.

Characterization of middle ear soft tissue damping and its role in sound transmission

Damping plays an important role in the middle ear (ME) sound transmission system. However, how to mechanically characterize the damping of ME soft tissues and the role of damping in ME sound transmission have not yet reached a consensus. In this paper, a finite element (FE) model of the partial external and ME of the human ear, considering both Rayleigh damping and viscoelastic damping for different soft tissues, is developed to quantitatively investigate the damping in soft tissues effects on the wide-frequency response of the ME sound transmission system. The model-derived results can capture the high-frequency (above 2 kHz) fluctuations and obtain the 0.9 kHz resonant frequency (RF) of the stapes velocity transfer function (SVTF) response. The results show that the damping of pars tensa (PT), stapedial annular ligament (SAL) and incudostapedial joints (ISJ) can help smooth the broadband response of the umbo and stapes footplate (SFP). It is found that, between 1 and 8 kHz, the damping of the PT increases the magnitude and phase delay of the SVTF above 2 kHz while the damping of the ISJ can avoid excessive phase delay of the SVTF, which is important in maintaining the synchronization in high-frequency vibration but has not been revealed before. Below 1 kHz, the damping of the SAL plays a more important role, and it can decrease the magnitude but increases the phase delay of the SVTF. This study has implications for a better understanding of the mechanism of ME sound transmission.

Reference velocity of a human head in bone conduction hearing: Finite element study

A whole head or temporal bone has been used in experiments to understand the mechanism of bone conduction (BC) hearing. In these experiments, two assumptions are generally accepted: (1) a promontory can be a representative point to show the motion of a specimen in BC hearing, and (2) the promontory velocity is proportional to a cochlear response so that the higher the promontory velocity, the better the BC hearing. To confirm the two assumptions, we investigated the velocities of various points corresponding to different BC input types and directions in the head. In this investigation, we used the three-dimensional finite element model of a human head, including an auditory periphery. Results showed that a single promontory was insufficient to be a representative point to show the motion of a specimen because the specimen could have rotational motion at frequencies below 0.5 kHz and the localized deformation at frequencies above 3 kHz. The promontory velocity had the same pattern as the basilar membrane velocity at low and high frequencies. However, at mid-frequencies between 0.5 and 3 kHz, the promontory did not exhibit the same pattern of velocity as the basilar membrane. Therefore, one's BC hearing ability must be carefully determined on the basis of promontory velocity.

Effect of closing material on hearing rehabilitation in stapedectomy and stapedotomy: A finite element analysis

Stapedotomy or stapedectomy operations are often performed to treat otosclerosis. During the operation, the space created by bone removal is usually filled with a closing material such as fat or fascia. In this study, the effect of the Young's modulus of the closing material on the hearing level was investigated through the 3D finite element model of a human head including auditory periphery. The Young's moduli of the closing material used to implement stapedotomy and stapedectomy conditions in the model were varied from 1 kPa to 24 MPa. The results showed that the hearing level improved when the closing material was more compliant after stapedotomy. Therefore, when the stapedotomy was performed using fat whose Young's modulus is lowest among the potential closing materials, the hearing level recovered the best among all simulated cases. On the other hand, in stapedectomy, the Young's modulus did not have the linear relationship between the hearing level and the compliance of the closing material. Hence, the Young's modulus causing the best hearing rehabilitation in stapedectomy was found not at the end of the investigated range of Young's modulus but somewhere in the middle of the given range.

Three-dimensional quasi-static displacement of human middle-ear ossicles under static pressure loads: Measurement using a stereo camera system

The time delay and/or malfunctioning of the Eustachian tube may cause pressure differences across the tympanic membrane, resulting in quasi-static movements of the middle-ear ossicles. While quasi-static displacements of the human middle-ear ossicles have been measured one- or two-dimensionally in previous studies, this study presents an approach to trace three-dimensional movements of the human middle-ear ossicles under static pressure loads in the ear canal (EC). The three-dimensional quasi-static movements of the middle-ear ossicles were measured using a custom-made stereo camera system. Two cameras were assembled with a relative angle of 7° and then mounted onto a robot arm. Red fluorescent beads of a 106-125 µm diameter were placed on the middle-ear ossicles, and quasi-static position changes of the fluorescent beads under static pressure loads were traced by the stereo camera system. All the position changes of the ossicles were registered to the anatomical intrinsic frame based on the stapes footplate, which was obtained from µ-CT imaging. Under negative ear-canal pressures, a rotational movement around the anterior-posterior axis was dominant for the malleus-incus complex, with small relative movements between the two ossicles. The stapes showed translation toward the lateral direction and rotation around the long axis of the stapes footplate. Under positive EC pressures, relative motion between the malleus and the incus at the IMJ became larger, reducing movements of the incus and stapes considerably and thus performing a protection function for the inner-ear structures. Three-dimensional tracing of the middle-ear ossicular chain provides a better understanding of the protection function of the human middle ear under static pressured loads as immediate responses without time delay.

Three-dimensional wideband absorbance immittance findings in young adults with large vestibular aqueduct syndrome

Objective

To investigate the effect of large vestibular aqueduct syndrome (LVAS) on middle ear sound transmission using wideband absorbance immittance (WAI).

Methods

WAI results from young adult LVAS patients and normal adults were compared.

Results

Averaged energy absorbance (EA) at ambient and peak pressure in the LVAS group showed differences to the normal group. Under ambient pressure, the average EA of the LVAS group was significantly higher than the normal group at frequencies 472-866 Hz and 6169-8000 Hz (p < .05) and lower at frequencies 1122-2520 Hz (p < .05). Under peak pressure, absorbance was increased at frequencies 515-728, 841, and 6169-8000 Hz (p < .05) and decreased at 1122-1374 Hz and 1587-2448 Hz (p < .05). An investigation into the effect of external auditory canal pressure on EA across frequencies in the pressure-frequency domain, showed that EA differed significantly in the low-frequency region of 707and 1000 Hz from 0 to 200 daPa and 500 Hz at 50 daPa (p < .05). There was also a significant difference in EA between the two groups at 8000 Hz (p < .05) in the pressure range -200-300 daPa.

Conclusion

WAI is a valuable tool to measure the effect of LVAS on middle ear sound transmission. LVAS has a significant effect on EA at low and mid frequencies under ambient pressure, while the frequencies affected are mainly at low frequencies when positive pressure is presented.

Level of Evidence

Level 3a.

Vibration Measurements of the Gerbil Eardrum Under Quasi-static Pressure Sweeps

Tympanometry provides an objective measurement of the status of the middle ear. During tympanometry, the ear-canal pressure is varied, while the response of the ear to sound pressure is measured. The effects of the pressure on the mechanics of the middle ear are not well understood. This study is a continuation of our previous work in which the vibration response of the gerbil eardrum was measured in vivo under quasi-static pressure steps. In this study, we delivered a continuous pressure sweep to the middle ear and measured the vibration response at four locations for six gerbils. Vibrations were recorded using a single-point laser Doppler vibrometer and glass-coated reflective beads (diameter ~ 40 µm) at the umbo and on the mid-manubrium, posterior pars tensa and anterior pars tensa.The vibration magnitudes were similar to those in the previous step-wise pressurization experiments. Most gerbils showed repeatability within less than 10 dB for consecutive cycles. As described in the previous study, as the frequency was increased at ambient pressure, the vibration magnitude on the manubrium increased slightly to a broad peak (referred to as R1) and then decreased until a small peak appeared (referred to as R2), followed by multiple peaks and troughs as the magnitude decreased further. The low-frequency vibration magnitude (at 1 kHz) decreased monotonically as the pressure became more negative except for a dip (about 500 Pa wide) that occurred between - 700 and - 1800 Pa. The lowest overall magnitude was recorded in the dip at mid-manubrium. The vibration magnitudes also decreased as the middle-ear pressure was made more positive and were larger than those at negative pressures. R1 was only visible at negative and small positive middle-ear pressures, while R2 was visible for both positive and negative pressures. R2 split into multiple branches after the middle-ear pressure became slightly positive. No magnitude dip was visible for positive middle-ear pressures.The low-frequency vibration magnitudes at negative middle-ear pressures on the pars tensa were higher than those on the manubrium. R1 was not visible for large negative middle-ear pressures on the pars tensa. R2 appeared as a multi-peak feature on the pars tensa as well, and a higher-frequency branch on the posterior pars tensa appeared as a trough on the anterior pars tensa. The magnitude dip was not present on the pars tensa. The largest overall magnitude was recorded at the R2 peak on the posterior pars tensa.The results of this study expand on the findings of the step-wise pressurization experiments and provide further insight into the evolution of the vibration response of the eardrum under quasi-static pressures.

Transcutaneous Osseo-integrated Auditory Devices: Analysis of Two Different Implants in Adults With Different Audiological Inclusion Criteria

OBJECTIVE

To determine and compare audiological and speech/language discrimination results in patients with osteo-integrated auditory devices, by comparing two different systems including different audiological indications in adult population.

STUDY DESIGN

Descriptive and analytic, cross-sectional, cohort, and retrospective case review.

SETTING

Tertiary referral center.

MATERIALS AND METHODS

Fifty patients >14 years old, with conductive, mixed, or unilateral sensorineural hearing loss were compared. The variables studied were the following: pure tone audiometry results, air-bone gap, and the percentage of speech/language discrimination using Disyllabic Word Test. The patients were tested preoperative and 12 months after surgical procedure. Subsequently, a comparative analysis of the both systems was carried out.

RESULTS

With both implants, pure tone audiometry results and the difference in auditory thresholds and between the air-bone gap improved significantly. Speech discrimination increased significantly after implantation too. A significant difference was observed after implantation of both devices. Patients implanted with one of the implants showed better audiological results, but no significant differences were found with the other device. So, it was shown that the type of device and the type of hearing loss have no influence on the audiological results or complications.

CONCLUSION

Both implants represent a good choice for audiological rehabilitation in patients with transmissive hearing loss, mixed hearing loss, or unilateral sensorineural hearing loss with a high success and low complication rates.

Development of a finite element model of a human head including auditory periphery for understanding of bone-conducted hearing

A three-dimensional finite-element (FE) model of a human head including the auditory periphery was developed to obtain a better understanding of bone-conducted (BC) hearing. The model was validated by comparison of cochlear and head responses in both air-conducted (AC) and BC hearing with experimental data. Specifically, the FE model provided the cochlear responses such as basilar membrane velocity and intracochlear pressure corresponding to BC stimulations applied to the mastoid or the conventional bone-anchored-hearing-aid (BAHA) positions. This is a strength of the model because it is difficult to obtain the cochlear responses from experiments corresponding to the BC stimulation applied at a specific position on the head surface. In addition, there have been few studies based on an FE model that can calculate the head and cochlear responses simultaneously from a BC stimulation. Moreover, in this study, the intracochlear sound pressure at multi-positions along the BM length was calculated and used to clarify the effect of stimulating force direction on the cochlear and promontory velocities in BC hearing. Also, the relationship between BC and AC stimulation and the basilar membrane velocity in the FE model was used to calculate the stimulation level at hearing thresholds which has been investigated only by psychoacoustical methods.

Conductive hearing loss in large vestibular aqueduct syndrome -clinical observations and proof-of-concept predictive modeling by a biomechanical approach

OBJECTIVE

The purpose of this study was to investigate the effect of a dilated vestibular aqueduct on conductive hearing loss (CHL). A biomechanical method was proposed for modeling the patterns of CHL in patients with large vestibular aqueduct syndrome (LVAS).

STUDY DESIGN

High resolution computed tomography (CT) scans and pure tone audiometry (PTA) were retrospectively collected from 16 patients who were diagnosed with LVAS. Seventeen ears with measurable air-bone gaps (ABGs) on PTA were applied for model development. The sizes of midpoint, operculum and distal segment were measured from CT to calculate the biomechanical parameters of each vestibular aqueduct. The mechanical effect of the dilated vestibular aqueduct on sound conduction was simulated using a lumped-parameter model. The CHL levels predicted by the model were compared with the observed ABGs at 250, 500 and 1000 Hz respectively.

RESULTS

The model was able to predict the trend that greater ABGs occurred at lower frequencies, which were consistent with clinical observations. However, deviations between the predicted and the observed ABGs became larger as the frequency increased. None of the correlation coefficients between the radiologic measures and the observed ABG levels were significant.

CONCLUSION

These findings lend support to the feasibility of this approach in modeling CHL in LVAS. The presence of a dilated vestibular aqueduct leads to altered impedance and sound pressure, suggesting the impact of a pathological third window. High individual variability of the observed ABGs implies additional factors may also be involved, especially at 500 Hz and 1000 Hz.

Contribution of the flexible incudo-malleal joint to middle-ear sound transmission under static pressure loads

The incudo-malleal joint (IMJ) in the human middle ear is a true diarthrodial joint and it has been known that the flexibility of this joint does not contribute to better middle-ear sound transmission. Previous studies have proposed that a gliding motion between the malleus and the incus at this joint prevents the transmission of large displacements of the malleus to the incus and stapes and thus contributes to the protection of the inner ear as an immediate response against large static pressure changes. However, dynamic behavior of this joint under static pressure changes has not been fully revealed. In this study, effects of the flexibility of the IMJ on middle-ear sound transmission under static pressure difference between the middle-ear cavity and the environment were investigated. Experiments were performed in human cadaveric temporal bones with static pressures in the range of +/- 2 kPa being applied to the ear canal (relative to middle-ear cavity). Vibrational motions of the umbo and the stapes footplate center in response to acoustic stimulation (0.2-8 kHz) were measured using a 3D-Laser Doppler vibrometer for (1) the natural IMJ and (2) the IMJ with experimentally-reduced flexibility. With the natural condition of the IMJ, vibrations of the umbo and the stapes footplate center under static pressure loads were attenuated at low frequencies below the middle-ear resonance frequency as observed in previous studies. After the flexibility of the IMJ was reduced, additional attenuations of vibrational motion were observed for the umbo under positive static pressures in the ear canal (EC) and the stapes footplate center under both positive and negative static EC pressures. The additional attenuation of vibration reached 4~7 dB for the umbo under positive static EC pressures and the stapes footplate center under negative EC pressures, and 7~11 dB for the stapes footplate center under positive EC pressures. The results of this study indicate an adaptive mechanism of the flexible IMJ in the human middle ear to changes of static EC pressure by reducing the attenuation of the middle-ear sound transmission. Such results are expected to be used for diagnosis of the IMJ stiffening and to be applied to design of middle-ear prostheses.

[Numerical study on the effect of middle ear malformations on energy absorbance]

In order to study the effect of middle ear malformations on energy absorbance, we constructed a mechanical model that can simulate the energy absorbance of the human ear based on our previous human ear finite element model. The validation of this model was confirmed by two sets of experimental data. Based on this model, three common types of middle ear malformations, i. e. incudostapedial joint defect, incus fixation and malleus fixation, and stapes fixation, were simulated by changing the structure and material properties of the corresponding tissue. Then, the effect of these three common types of middle ear malformations on energy absorbance was investigated by comparing the corresponding energy absorbance. The results showed that the incudostapedial joint defect significantly increased the energy absorbance near 1 000 Hz. The incus fixation and malleus fixation dramatically reduced the energy absorbance in the low frequency, which made the energy absorbance less than 10% at frequencies lower than 1 000 Hz. At the same time, the peak of energy absorbance shifted to the higher frequency. These two kinds of middle ear malformations had obvious characteristics in the wideband acoustic immittance test. In contrast, the stapes fixation only reduced the energy absorbance in the low frequency and increased energy absorbance in the middle frequency slightly, which had no obvious characteristic in the wideband acoustic immittance test. These results provide a theoretical reference for the wideband acoustic immittance diagnosis of middle ear malformations in clinic.

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.

Mechanical Effects of Cochlear Implants on Residual Hearing Loss: A Finite Element Analysis

The effects of cochlear implants on residual hearing loss is investigated through a finite element model of human auditory periphery consisting of the cochlea and middle ear. The simulation results show that a round window stiffness is the dominant factor in residual hearing loss. The increased round window stiffness to five times caused over 4 dB residual hearing loss at low frequencies below 500 Hz. Without considering round window ossification, inserting a cochlear implant can show at most 4 dB difference of residual hearing loss in magnitude from the no-implant case although the cochlear implant's geometry and position has been varied. If the stiffness of the round window is the same, the simulation results suggest to use a thin-straight-cochlear implant inserted into the lateral side in order to preserve residual hearing at frequencies below 700 Hz. In addition, when the distance between the basilar membrane and a cochlear implant is closer, the residual hearing loss becomes severe at high frequencies above 1 kHz. The results would be helpful for choice of a cochlear implant depending on a patient's condition.

Dependence of skull surface wave propagation on stimulation sites and direction under bone conduction

In order to better understand bone conduction sound propagation across the skull, three-dimensional (3D) wave propagation on the skull surface was studied, along with its dependence on stimulation direction and location of a bone conduction hearing aid (BCHA) actuator. Experiments were conducted on five Thiel embalmed whole head cadaver specimens. Stimulation, in the 0.1-10 kHz range, was sequentially applied at the forehead and mastoid via electromagnetic actuators from commercial BCHAs, supported by a 5-N steel band. The head response was quantified by sequentially measuring the 3D motion of ∼200 points (∼15-20 mm pitch) across the ipsilateral, top, and contralateral skull surface via a 3D laser Doppler vibrometer (LDV) system, guided by a robotic positioner. Low-frequency stimulation (<1 kHz) resulted in a spatially complex rigid-body-like motion of the skull that depended on both the stimulation condition and head support. The predominant motion direction was only 5-10 dB higher than other components below 1 kHz, with no predominance at higher frequencies. Sound propagation direction across the parietal plates did not coincide with stimulation location, potentially due to the head base and forehead remaining rigid-like at higher frequencies and acting as a large source for the deformation patterns across the parietal sections.

Vibroplasty combined with tympanic membrane reconstruction in middle ear ventilation disorders

Although the Vibrant Soundbridge is one of the most frequently used active middle ear implants, data regarding how middle ear ventilation disorders may affect the transmission behavior of its floating mass transducer are still insufficient. Studies involving coupling the floating mass transducer to the stapes head are particularly lacking. This temporal bone study evaluated the influence of simulated middle ear ventilation disorders on the middle ear transfer function in the reconstructed middle ear. The middle ear transfer function was measured using Laser Doppler Vibrometry after vibroplasty onto the stapes head, with or without tympanic membrane reconstruction. Middle ear ventilation disorders were simulated through changes in static pressure via the external ear channel with a maximum pressure of +3 kPa. Slice thickness of tympanic membrane reconstruction material was measured using micro-CT. When the reconstructed ossicular chain and the reconstructed tympanic membrane were mechanically excited by the floating mass transducer under conditions of ambient static pressure, the transmission behavior was found to be independent of the type of tissue used. Increase in static pressure up to +3 kPa caused maximum low frequency transmission loss of 15 dB when elastic grafts were used and 5 dB when stiff tissue was inserted. At high frequencies, measured loss of up to 5 dB was relatively independent of the tissue stiffness. Increase in static pressure led to displacement of the tissues towards the vestibulum and caused stiffening, especially of the annular ligament. Stiffening-induced transmission losses were mainly found at low frequencies and could not be compensated by the floating mass transducer in this range. Above 1300 Hz, the continuous force spectrum of the actuator sufficiently protected against loss of amplitude. To minimize postoperative transmission loss due to persisting ventilation disorders, choosing a very stiff tympanic membrane reconstruction material seems to be appropriate.

Numerical Study and Optimization of a Novel Piezoelectric Transducer for a Round-Window Stimulating Type Middle-Ear Implant

Round window (RW) stimulation is a new application of middle ear implants for treating hearing loss, especially for those with middle ear disease. However, most reports on it are based on the use of the floating mass transducer (FMT), which was not originally designed for round window stimulation. The mismatch of the FMT's diameter and the round window membrane's diameter and the uncontrollable preload of the transducer, leads to a high variability in its clinical outcomes. Accordingly, a new piezoelectric transducer for the round-window-stimulating-type middle ear implant is proposed in this paper. The transducer consists of a piezoelectric stack, a flextensional amplifier, a coupling rod, a salver, a plate, a titanium housing and a supporting spring. Based on a constructed coupling finite element model of the human ear and the transducer, the influences of the transducer design parameters on its performance were analyzed. The optimal structure of the supporting spring, which determines the transducer's resonance frequency, was ascertained. The results demonstrate that our designed transducer generates better output than the FMT, especially at low frequency. Besides this, the power consumption of the transducer was significantly decreased compared with a recently reported RW-stimulating piezoelectric transducer.

Intracochlear Sound Pressure Measurements in Normal Human Temporal Bones During Bone Conduction Stimulation

Bone conduction (BC) is heavily relied upon in the diagnosis and treatment of hearing loss, but is poorly understood. For example, the relative importance and frequency dependence of various identified BC sound transmission mechanisms that contribute to activate the cochlear partition remain unknown. Recently, we have developed techniques in fresh human cadaveric specimens to directly measure scalae pressures with micro-fiberoptic sensors, enabling us to monitor the input pressure drive across the cochlear partition that triggers the cochlear traveling wave during air conduction (AC) and round-window stimulation. However, BC stimulation poses challenges that can result in inaccurate intracochlear pressure measurements. Therefore, we have developed a new technique described here that allows for precise measurements during BC. Using this new technique, we found that BC stimulation resulted in pressure in scala vestibuli that was significantly higher in magnitude than in scala tympani for most frequencies, such that the differential pressure across the partition-the input pressure drive-was similar to scala vestibuli pressure. BC (stimulated by a Bone Anchored Hearing Aid [Baha]) showed that the mechanisms of sound transmission in BC differ from AC, and also showed the limitations of the Baha bandwidth. Certain kinematic measurements were generally proportional to the cochlear pressure input drive: for AC, velocity of the stapes, and for BC, low-frequency acceleration and high-frequency velocity of the cochlear promontory. Therefore, our data show that to estimate cochlear input drive in normal ears during AC, stapes velocity is a good measure. During BC, cochlear input drive can be estimated for low frequencies by promontory acceleration (though variable across ears), and for high frequencies by promontory velocity.

A model and experimental approach to the middle ear transfer function related to hearing in the humpback whale (Megaptera novaeangliae)

At present, there are no direct measures of hearing for any baleen whale (Mysticeti). The most viable alternative to in vivo approaches to simulate the audiogram is through modeling outer, middle, and inner ear functions based on the anatomy and material properties of each component. This paper describes a finite element model of the middle ear for the humpback whale (Megaptera novaeangliae) to calculate the middle ear transfer function (METF) to determine acoustic energy transmission to the cochlea. The model was developed based on high resolution computed tomography imaging and direct anatomical measurements of the middle ear components for this mysticete species. Mechanical properties for the middle ear tissues were determined from experimental measurements and published values. The METF for the humpback whale predicted a better frequency range between approximately 15 Hz and 3 kHz or between 200 Hz and 9 kHz based on two potential stimulation locations. Experimental measures of the ossicular chain, tympanic membrane, and tympanic bone velocities showed frequency response characteristics consistent with the model. The predicted best sensitivity hearing ranges match well with known vocalizations of this species.

Analytical and numerical modeling of the hearing system: Advances towards the assessment of hearing damage

Hearing is an extremely complex phenomenon, involving a large number of interrelated variables that are difficult to measure in vivo. In order to investigate such process under simplified and well-controlled conditions, models of sound transmission have been developed through many decades of research. The value of modeling the hearing system is not only to explain the normal function of the hearing system and account for experimental and clinical observations, but to simulate a variety of pathological conditions that lead to hearing damage and hearing loss, as well as for development of auditory implants, effective ear protections and auditory hazard countermeasures. In this paper, we provide a review of the strategies used to model the auditory function of the external, middle, inner ear, and the micromechanics of the organ of Corti, along with some of the key results obtained from such modeling efforts. Recent analytical and numerical approaches have incorporated the nonlinear behavior of some parameters and structures into their models. Few models of the integrated hearing system exist; in particular, we describe the evolution of the Auditory Hazard Assessment Algorithm for Human (AHAAH) model, used for prediction of hearing damage due to high intensity sound pressure. Unlike the AHAAH model, 3D finite element models of the entire hearing system are not able yet to predict auditory risk and threshold shifts. It is expected that both AHAAH and FE models will evolve towards a more accurate assessment of threshold shifts and hearing loss under a variety of stimuli conditions and pathologies.

Finite element modelling of sound transmission from outer to inner ear

The ear is one of the most complex organs in the human body. Sound is a sequence of pressure waves, which propagates through a compressible media such as air. The pinna concentrates the sound waves into the external auditory meatus. In this canal, the sound is conducted to the tympanic membrane. The tympanic membrane transforms the pressure variations into mechanical displacements, which are then transmitted to the ossicles. The vibration of the stapes footplate creates pressure waves in the fluid inside the cochlea; these pressure waves stimulate the hair cells, generating electrical signals which are sent to the brain through the cochlear nerve, where they are decoded. In this work, a three-dimensional finite element model of the human ear is developed. The model incorporates the tympanic membrane, ossicular bones, part of temporal bone (external auditory meatus and tympanic cavity), middle ear ligaments and tendons, cochlear fluid, skin, ear cartilage, jaw and the air in external auditory meatus and tympanic cavity. Using the finite element method, the magnitude and the phase angle of the umbo and stapes footplate displacement are calculated. Two slightly different models are used: one model takes into consideration the presence of air in the external auditory meatus while the other does not. The middle ear sound transfer function is determined for a stimulus of 60 dB SPL, applied to the outer surface of the air in the external auditory meatus. The obtained results are compared with previously published data in the literature. This study highlights the importance of external auditory meatus in the sound transmission. The pressure gain is calculated for the external auditory meatus.

The importance of the hook region of the cochlea for bone-conduction hearing

For the most part, the coiled shape of the cochlea has been shown to have only minor importance for air-conducted hearing. It is hypothesized, however, that this coiled shape may play a more significant role for the bone-conducted (BC) route of hearing, through inertial forces exerted by the middle ear and cochlear fluid, and that this can be tested by comparing the results of applying BC stimuli in a variety of different directions. A three-dimensional finite element model of a human middle ear coupled to the inner ear was formulated. BC excitations were simulated by applying rigid-body vibrations normal to the surface of the basilar membrane (BM) at 0.8 (d(1)), 5.8 (d(2)), 15.6 (d(3)), and 33.1 (d(4)) mm from the base of the cochlea, such that relative motions of the fluid within the cochlea produced excitations of the BM. The vibrational direction normal to the BM surface at the base of the cochlea (d(1)) produced the highest BM velocity response across all tested frequencies-higher than an excitation direction normal to the BM surface at the nonbasal locations (d(2)-d(4)), even when the stimulus frequency matched the best frequency for each location. The basal part of the human cochlea features a well-developed hook region, colocated with the cochlear vestibule, that features the largest difference in fluid volume between the scala vestibuli (SV) and scala tympani (ST) found in the cochlea. The proximity of the hook region to the oval and round windows, combined with it having the biggest fluid-volume difference between the SV and ST, is thought to result in a maximization of the pressure difference between the SV and ST for BC stimuli normal to the BM in this region, and consequently a maximization of the resulting BM velocity.

Effect of modeling parameters on the frequency response of the middle ear by means of finite element analysis

A 3D finite element model of the human middle ear was developed for the investigation of the modeling parameters' effect on the frequency response. In this study, we incorporated realistic reconstructed geometries from microCT imaging data. The geometric representation of the stapedial annular ligament provided additional damping and the Rayleigh parameter β was adjusted to lower values in comparison to previous computational studies. The maximum displacement of the stapes footplate, equal to 0.168 μm, was observed at a frequency of 1050 Hz. The computational results were validated with experimental measurements. Good agreement is observed between our results and the experimental data and other finite element studies.

Restoration of middle-ear input in fluid-filled middle ears by controlled introduction of air or a novel air-filled implant

The effect of small amounts of air on sound-induced umbo velocity in an otherwise saline-filled middle ear (ME) was investigated to examine the efficacy of a novel balloon-like air-filled ME implant suitable for patients with chronically non-aerated MEs. In this study, air bubbles or air-filled implants were introduced into saline-filled human cadaveric MEs. Umbo velocity, a convenient measure of ME response, served as an indicator of hearing sensitivity. Filling the ME with saline reduced umbo velocity by 25-30 dB at low frequencies and more at high frequencies, consistent with earlier work (Ravicz et al., Hear. Res. 195: 103-130 (2004)). Small amounts of air (∼30 μl) in the otherwise saline-filled ME increased umbo velocity substantially, to levels only 10-15 dB lower than in the dry ME, in a frequency- and location-dependent manner: air in contact with the tympanic membrane (TM) increased umbo velocity at all frequencies, while air located away from the TM increased umbo velocity only below about 500 Hz. The air-filled implant also affected umbo velocity in a manner similar to an air bubble of equivalent compliance. Inserting additional implants into the ME had the same effect as increasing air volume. These results suggest these middle-ear implants would significantly reduce conductive hearing loss in patients with chronically fluid-filled MEs.

An incus-body driving type piezoelectric middle ear implant design and evaluation in 3D computational model and temporal bone

A new incus-body driving type transducer relying on piezoelectric stack, with broad frequency bandwidth, is proposed for use in a middle ear implant. To aid the design process of this transducer, a coupling biomechanical model of the human middle ear and the piezoelectric transducer was established by reverse engineering technology. The validity of this model was confirmed by comparing model predicted motions with experimental measurements. Based on this verified biomechanical model, the main parameters of the transducer were determined. And its power consumption was calculated. Finally, to verify the capability of the designed piezoelectric transducer, a human temporal bone experimental platform was built. And the dynamic characteristics and the stimulated performance of the piezoelectric transducer were tested. The result showed that stapes displacement stimulated by the transducer excitation at 10.5 V RMS was equivalent to that from acoustic stimulation at 100 dB SPL, which is an adequate stimulation to the ossicular chain. The corresponding power consumption is 0.31 mW per volt of excitation at 1 kHz, which is low enough for the transducer to be used in a middle ear implant. Besides, this transducer demonstrates high performance at high frequencies.

The effects of air pressure on spontaneous otoacoustic emissions of lizards

Small changes of air pressure outside the eardrum of five lizard species led to changes in frequency, level, and peak width of spontaneous otoacoustic emissions (SOAE). In contrast to humans, these changes generally occurred at very small pressures (<20 mbar). As in humans, SOAE amplitudes were generally reduced. Changes of SOAE frequency were both positive and negative, while in humans, they are mostly positive. In addition, in lizards, these effects often showed obvious hysteresis and non-repeatability. The correlation between peak width and height was negative in two species (comparable to humans) and positive in one species. In two other species, no correlation was found. Consequently, a simple oscillator model that explained the negative correlation in humans could not be generally applied to lizards. This presumably reflects the fact that in lizards, the spontaneous otoacoustic emission of sound from the ear consists of a combination of stable oscillations (as in humans), unstable narrow-band oscillations, and broad-band emissions, evident as "plateaus" in emission spectra.

Békésy's contributions to our present understanding of sound conduction to the inner ear

In our daily lives we hear airborne sounds that travel primarily through the external and middle ear to the cochlear sensory epithelium. We also hear sounds that travel to the cochlea via a second sound-conduction route, bone conduction. This second pathway is excited by vibrations of the head and body that result from substrate vibrations, direct application of vibrational stimuli to the head or body, or vibrations induced by airborne sound. The sensation of bone-conducted sound is affected by the presence of the external and middle ear, but is not completely dependent upon their function. Measurements of the differential sensitivity of patients to airborne sound and direct vibration of the head are part of the routine battery of clinical tests used to separate conductive and sensorineural hearing losses. Georg von Békésy designed a careful set of experiments and pioneered many measurement techniques on human cadaver temporal bones, in physical models, and in human subjects to elucidate the basic mechanisms of air- and bone-conducted sound. Looking back one marvels at the sheer number of experiments he performed on sound conduction, mostly by himself without the aid of students or research associates. Békésy's work had a profound impact on the field of middle-ear mechanics and bone conduction fifty years ago when he received his Nobel Prize. Today many of Békésy's ideas continue to be investigated and extended, some have been supported by new evidence, some have been refuted, while others remain to be tested.

The effect of static ear canal pressure on human spontaneous otoacoustic emissions: spectral width as a measure of the intra-cochlear oscillation amplitude

Spontaneous otoacoustic emissions can be detected as peaks in the Fourier spectrum of a microphone signal recorded from the ear canal. The height, center frequency, and spectral width of SOAE peaks changed when a static pressure was applied to the ear canal. Most commonly, with either increasing or decreasing static pressure, the frequency increased, the amplitude decreased, and the width increased. These changes are believed to result from changes in the middle ear properties. Specifically, reduced middle ear transmission is assumed to attenuate the amplitude of emissions. We reconsidered this explanation by investigating the relation between peak height and width. We showed that the spectral width of SOAE peaks is approximately proportional to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ 1/\sqrt {{{\hbox{peak}}\;{\hbox{height}}}} $$\end{document}. This is consistent with a (Rayleigh) oscillator model in which broadening of the SOAE peak is caused by broadband intra-cochlear noise, which is assumed to be independent of static ear canal pressure. The relation between emission peak height and width implicates that the intra-cochlear oscillation amplitude attentuates relative to the intra-cochlear noise level when a static ear canal pressure is applied. Apparently, ear canal static pressure directly affects the active mechanics in the inner ear.

Inertial bone conduction: symmetric and anti-symmetric components

Of the two pathways through which we hear, air conduction (AC) and bone conduction (BC), the fundamental mechanisms of the BC pathway remain poorly understood, despite their clinical significance. A finite element model of a human middle ear and cochlea was developed to gain insight into the mechanisms of BC hearing. The characteristics of various cochlear response quantities, including the basilar membrane (BM) vibration, oval-window (OW) and round-window (RW) volume velocities, and cochlear fluid pressures were examined for BC as well as AC excitations. These responses were tuned and validated against available experimental data from the literature. BC excitations were simulated in the form of rigid body vibrations of the surrounding bony structures in the x, y, and z orthogonal directions. The results show that the BM vibration characteristics are essentially invariant regardless of whether the excitation is via BC, independent of excitation direction, or via AC. This at first appeared surprising because the cochlear fluid pressures differ considerably depending on the excitation mode. Analysis reveals that the BM vibration responds only to the lower-magnitude anti-symmetric slow-wave cochlear fluid pressure component and not to the symmetric fast-wave pressure component, which dominates the magnitude of the total pressure field. This anti-symmetric fluid pressure is produced by the anti-symmetric component of the window volume velocities. As a result, the BM is effectively driven by the anti-symmetric component of the OW and RW volume velocities, irrespective of the type of excitation. Middle ear modifications that alter the anti-symmetric component of the OW and RW volume velocities corroborate this assertion. The current results provide further clarification of the mechanisms underlying Békésy's "paradoxical motion" concept.