Experimental and modeling study of human tympanic membrane motion in the presence of middle ear liquid

Piezoelectric Multi-Channel Bilayer Transducer for Sensing and Filtering Ossicular Vibration

This paper presents an acoustic transducer for fully implantable cochlear implants (FICIs), which can be implanted on the hearing chain to detect and filter the ambient sound in eight frequency bands between 250 and 6000 Hz. The transducer dimensions are conventional surgery compatible. The structure is formed with 3  × 3 × 0.36 mm active space for each layer and 5.2 mg total active mass excluding packaging. Characterization of the transducer is carried on an artificial membrane whose vibration characteristic is similar to the umbo vibration. On the artificial membrane, piezoelectric transducer generates up to 320.3 mVpp under 100 dB sound pressure level (SPL) excitation and covers the audible acoustic frequency. The measured signal-to-noise-ratio (SNR) of the channels is up to 84.2 dB. Sound quality of the transducer for fully implantable cochlear implant application is graded with an objective qualification method (PESQ) for the first time in the literature to the best of the knowledge, and scored 3.42/4.5.

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.

Wavelength-specific optoacoustic-induced vibrations of the guinea pig tympanic membrane

SIGNIFICANCE

Optoacoustic-induced vibrations of the hearing organ can potentially be used for a hearing device. To increase the efficiency of such a hearing device, the conversion of the light energy into vibration energy within each type of irradiated tissue has to be optimized.

AIM

To analyze the wavelength-dependency of optoacoustic-induced vibrations within the tympanic membrane (TM), and to define the most efficient and best-suited optical stimulation parameters for a novel auditory prosthesis.

APPROACH

Single nanosecond laser pulses, continuously tunable in a range of visible to near-infrared, were used to excite the guinea pig TM. The induced vibrations of the hearing organ were recorded at the malleus using a laser Doppler vibrometer.

RESULTS

Our results indicate a strong wavelength-dependency of the vibration's amplitude correlating with the superposition of the absorption spectra of the different specific tissue components.

CONCLUSIONS

We investigated the spectrum of the vibrations of the hearing organ that were induced optoacoustically within a biological membrane embedded in air, in an animal model. First applications for these results can be envisioned for the optical stimulation of the peripheral hearing organ as well as for research purposes.

Dynamic Properties of Microresonators with the Bionic Structure of Tympanic Membrane

The structure of a microresonator will affect the vibration characteristics and the performance of the system. Inspired by the structural characteristics of the human tympanic membrane, this paper proposed a microresonator with the bionic structure of a tympanic membrane. The structure of a tympanic membrane was simplified to a regular shape with three structural parameters: diameter, height, and thickness. To imitate the tympanic membrane, the contour surface of the bionic structure was modeled based on the formula of transverse vibration mode of a circular thin plate. The geometric model of the bionic structure was established by using the three structural parameters and the contour surface equation. The dynamic properties of the bionic model were studied by the finite element method (FEM). We discuss the modal characteristics of the bionic structure and study the effect of structural parameters and scale on the dynamic properties. The advantages of the bionic structure were investigated by a comparison with circular plate microresonators. The results illustrate that the bionic structure can significantly improve the resonant frequency and have a much larger effective area of vibration displacement.

Analysis of the Human Middle Ear Dynamics Through Multibody Modeling

The dynamics of the human middle ear (ME) has been studied in the past using several computational and experimental approaches in order to observe the effect on hearing of different conditions, such as conductive disease, corrective surgery, or implantation of a middle ear prosthesis. Multibody (MB) models combine the analysis of flexible structures with rigid body dynamics, involving fewer degrees-of-freedom (DOF) than finite element (FE) models, but a more detailed description than traditional 1D lumped parameter (LP) models. This study describes the reduction of a reference FE model of the human middle ear to a MB model and compares the results obtained considering different levels of model simplification. All models are compared by means of the frequency response of the stapes velocity versus sound pressure at the tympanic membrane (TM), as well as the system natural frequencies and mode shapes. It can be seen that the flexibility of the ossicles has a limited impact on the system frequency response function (FRF) and modes, and the stiffness of the tendons and ligaments only plays a role when above certain levels. On the other hand, the restriction of the stapes footplate movement to a piston-like behavior can considerably affect the vibrational modes, while constraints to the incudomalleolar joint (IMJ) and incudostapedial joint (ISJ) can have a strong impact on the system FRF.

Characterization of mechanical behaviour of healthy and injured human incus by eigenfrequency evaluation

The usage of finite element method techniques gives a possibility to replace time-consuming experiments or imitate physical process in the ear by numerical simulation. Especially, the research of spatial motion of ossicular chain in the middle ear is of high interest for the oto-surgeons and engineers. It is known that the most affected bone from the ossicular chain is the incus. After the cholesteatoma operation and tympanoplasty, the affected incus is removed or sacrificed; thus, the possibility of transducing noise lays on the stapes, new titanium or other material prosthesis. In this case, the affected incus was removed because of the cholesteatoma that was lying in front of it in the tympanic cavity. The removed incus with the affected long process passed micro-computed tomography. The computer-aided design systems allowed redesigning a 'healthy' incus with an intact long process. In this way, it was possible to evaluate the influence of damaged long process of incus in the vibrational analysis. This article analyses the problems of mechanical behaviour of injured and healthy human incus. The numerical simulation has demonstrated that the features of healthy incus and analysed injured incus do not differ significantly, especially at low (about 500 Hz) frequencies. It explains why there is no impact of cholesteatoma on hearing for a long time in the audiogram.

Surface Motion Changes of Tympanic Membrane Damaged by Blast Waves

Eardrum or tympanic membrane (TM) is a multilayer soft tissue membrane located at the end of the ear canal to receive sound pressure and transport the sound into the middle ear and cochlea. Recent studies reported that the TM microstructure and mechanical properties varied after the ear was exposed to blast overpressure. However, the impact of such biomechanical changes of the TM on its movement for sound transmission has not been investigated. This paper reports the full-field surface motion of the human TM using the scanning laser Doppler vibrometry in human temporal bones under normal and postblast conditions. An increase of the TM displacement after blast exposure was observed in the posterior region of the TM in four temporal bone samples at the frequencies between 3 and 4 kHz. A finite element model of human TM with multilayer microstructure and orthogonal fiber network was created to simulate the TM damaged by blast waves. The consistency between the experimental data and the model-derived TM surface motion suggests that the tissue injuries were resulted from a combination of mechanical property change and regional discontinuity of collagen fibers. This study provides the evidences of surface motion changes of the TM damaged by blast waves and possible fiber damage locations.

Influence of ossicular chain malformation on the performance of round-window stimulation: A finite element approach

As a novel application of implantable middle ear hearing device, round-window stimulation is widely used to treat hearing loss with middle ear disease, such as ossicular chain malformation. To evaluate the influence of ossicular chain malformations on the efficiency of the round-window stimulation, a human ear finite element model, which incorporates cochlear asymmetric structure, was constructed. Five groups of comparison with experimental data confirmed the model’s validity. Based on this model, we investigated the influence of three categories of ossicular chain malformations, that is, incudostapedial disconnection, incus and malleus fixation, and fixation of the stapes. These malformations’ effects were evaluated by comparing the equivalent sound pressures derived from the basilar membrane displacement. Results show that the studied ossicular chain malformations mainly affected the round-window simulation’s performance at low frequencies. In contrast to the fixation of the ossicles, which mainly deteriorates round-window simulation’s low-frequency performance, incudostapedial disconnection increases this performance, especially in the absence of incus process and stapes superstructure. Among the studied ossicular chain malformations, the stapes fixation has a much more severe impact on the round-window stimulation’s efficiency. Thus, the influence of the patients’ ossicular chain malformations should be considered in the design of the round-window stimulation’s actuator. The low-frequency output of the round-window simulation’s actuator should be enhanced, especially for treating the patients with stapes fixation.

Endoscopic optical coherence tomography with wide field-of-view for the morphological and functional assessment of the human tympanic membrane

An endoscopic optical coherence tomography (OCT) system with a wide field-of-view of 8 mm is presented, which combines the image capability of endoscopic imaging at the middle ear with the advantages of functional OCT imaging, allowing a morphological and functional assessment of the human tympanic membrane. The endoscopic tube has a diameter of 3.5 mm and contains gradient-index optics for simultaneous forward-viewing OCT and video endoscopy. The endoscope allows the three-dimensional visualization of nearly the entire tympanic membrane. In addition, the oscillation of the tympanic membrane is measured spatially resolved and in the frequency range between 500 Hz and 5 kHz with 125 Hz resolution, which is realized by phase-resolved Doppler OCT imaging during acoustical excitation with chirp signals. The applicability of the OCT system is demonstrated in vivo. Due to the fast image acquisition, structural and functional measurements are only slightly affected by motion artifacts.

Surface Motion of Tympanic Membrane in a Chinchilla Model of Acute Otitis Media

The conductive hearing loss caused by acute otitis media (AOM) is commonly related to a reduction of the tympanic membrane (TM) mobility in response to sound stimuli. However, spatial alterations of the TM surface motion associated with AOM have rarely been addressed. In this study, the TM surface motion was determined using scanning laser Doppler vibrometry (SLDV) in a chinchilla model of AOM. The AOM was established by transbullar injection of nontypeable Haemophilus influenzae. The TM surface vibration was measured in control (uninfected) animals and two AOM groups of animals: 4 days (4D) and 8 days (8D) post inoculation. To quantify the effect of middle ear pressure in those infected ears, the SLDV measurement was first conducted in unopened AOM ears and then in middle ear pressure released ears. Results showed that middle ear infection generally reduced the TM displacement across the entire surface, but the reduction in the umbo displacement over the time course, from 4 to 8 days post inoculation, was less than the reduction in the displacement at the center of each quadrant. The presence of middle ear fluid shifted the occurrence of traveling-wave-like motion on the TM surface to lower frequencies. The observation of the spatial variations of TM surface motion from this study will help refine our understanding of the middle ear sound transmission characteristics in relation to AOM.

In Vivo Vibration Measurement of Middle Ear Structure Using Doppler Optical Coherence Tomography: Preliminary Study

Objectives

Doppler optical coherence tomography (DOCT) is useful for both, the spatially resolved measurement of the tympanic membrane (TM) oscillation and high-resolution imaging. We demonstrated a new technique capable of providing real-time two-dimensional Doppler OCT image of rapidly oscillatory latex mini-drum and in vivo rat TM and ossicles.

Methods

Using DOCT system, the oscillation of sample was measured at frequency range of 1–4 kHz at an output of 15 W. After the sensitivity of the DOCT system was verified using a latex mini-drum consisting of a 100 μm-thick latex membrane, changes in displacement of the umbo and contacted area between TM and malleus in normal and pathologic conditions.

Results

The oscillation cycles of the mini-drum for stimulus frequencies were 1.006 kHz for 1 kHz, 2.012 kHz for 2kHz, and 3.912 kHz for 4 kHz, which means that the oscillation cycle of the mini-drum become short in proportional to the frequency of stimuli. The oscillation cycles of umbo area and the junction area in normal TM for frequencies of the stimuli showed similar integer ratio with the data of latex mini-drum for stimuli less than 4 kHz. In the case of middle ear effusion condition, the Doppler signal showed a tendency of attenuation in all frequencies, which was prominent at 1 kHz and 2 kHz.

Conclusion

The TM vibration under sound stimulation with frequencies from 1 kHz to 4 kHz in normal and pathologic conditions was demonstrated using signal demodulation method in in vivo condition. The OCT technology could be helpful for functional and structural assessment as an optional modality.

Transient response of the human ear to impulsive stimuli: A finite element analysis

Nowadays, the steady-state responses of human ear to pure tone stimuli have been widely studied. However, the temporal responses to transient stimuli have not been investigated systematically to date. In this study, a comprehensive finite element (FE) model of the human ear is used to investigate the transient characteristics of the human ear in response to impulsive stimuli. There are two types of idealized impulses applied in the FE analysis: the square wave impulse (a single positive pressure waveform) and the A-duration wave impulse (both of positive and negative pressure waveforms). The time-domain responses such as the displacements of the tympanic membrane (TM), the stapes footplate (SF), the basilar membrane (BM), the TM stress distribution, and the cochlea input pressure are derived. The results demonstrate that the TM motion has the characteristic of spatial differences, and the umbo displacement is smaller than other locations. The cochlea input pressure response is synchronized with the SF acceleration response while the SF displacement response appears with some time delay. The BM displacement envelope is relatively higher in the middle cochlea and every portion of BM vibrates at its best frequency approximately. The present results provide a good understanding of the transient response of the human ear.

Panel 2: Anatomy (Eustachian Tube, Middle Ear, and Mastoid-Anatomy, Physiology, Pathophysiology, and Pathogenesis)

Objective In this report, we review the recent literature (ie, past 4 years) to identify advances in our understanding of the middle ear-mastoid-eustachian tube system. We use this review to determine whether the short-term goals elaborated in the last report were achieved, and we propose updated goals to guide future otitis media research. Data Sources PubMed, Web of Science, Medline. Review Methods The panel topic was subdivided, and each contributor performed a literature search within the given time frame. The keywords searched included middle ear, eustachian tube, and mastoid for their intersection with anatomy, physiology, pathophysiology, and pathology. Preliminary reports from each panel member were consolidated and discussed when the panel met on June 11, 2015. At that meeting, the progress was evaluated and new short-term goals proposed. Conclusions Progress was made on 13 of the 20 short-term goals proposed in 2011. Significant advances were made in the characterization of middle ear gas exchange pathways, modeling eustachian tube function, and preliminary testing of treatments for eustachian tube dysfunction. Implications for Practice In the future, imaging technologies should be developed to noninvasively assess middle ear/eustachian tube structure and physiology with respect to their role in otitis media pathogenesis. The new data derived from these structure/function experiments should be integrated into computational models that can then be used to develop specific hypotheses concerning otitis media pathogenesis and persistence. Finally, rigorous studies on medical or surgical treatments for eustachian tube dysfunction should be undertaken.

The effect of actuator and its coupling conditions on eardrum-stimulated middle ear implants: A numerical analysis

Consisting of the actuator and coupling layer, a finite element model of the human middle ear was used to analyze the effect of the actuator and its coupling conditions on the performance of the eardrum-stimulated middle ear implants. This model which was based on the right ear of a healthy adult was built via microcomputed tomography imaging and the technique of reverse engineering. Based on this finite element model, the linear viscoelasticity of the human middle ear soft tissues and three-layer structure of the eardrum pars tensa which was orthotropic were considered. The validity of the model was verified by comparing the model calculated results with experimental data. After that, the influence of the three main design parameters of the actuator and two aspects of the coupling layer were investigated by the finite element model. The results show that (1) the manubrium tip is the optimal position for the actuator to stimulate; (2) the increased cross-section of the actuator would worsen its hearing compensation performance, especially in the low frequencies; (3) both the patients’ residual hearing and the actuator’s hearing compensation performance at high frequencies will be deteriorated with the increase in the actuator’s mass; and (4) a coupling layer with a small Young’s modulus and an area approximating 80% of the eardrum would reduce the stress of the eardrum effectively.

Motion of tympanic membrane in guinea pig otitis media model measured by scanning laser Doppler vibrometry

Otitis media (OM) is an inflammatory or infectious disease of the middle ear. Acute otitis media (AOM) and otitis media with effusion (OME) are the two major types of OM. However, the tympanic membrane (TM) motion differences induced by AOM and OME have not been quantified in animal models in the literature. In this study, the guinea pig AOM and OME models were created by transbullar injection of Streptococcus pneumoniae type 3 and lipopolysaccharide, respectively. To explore the effects of OM on the entire TM vibration, the measurements of full-field TM motions were performed in the AOM, OME and untreated control ears by using scanning laser Doppler vibrometry (SLDV). The results showed that both AOM and OME generally reduced the displacement peak and produced the traveling-wave-like motions at relatively low frequencies. Compared with the normal ear, OME resulted in a significant change of the TM displacement mainly in the inferior portion of the TM, and AOM significantly affected the surface motion across four quadrants. The SLDV measurements provide more insight into sound-induced TM vibration in diseased ears.

THE EFFECT OF IMPLANTABLE TRANSDUCERS ON MIDDLE EAR TRANSFER FUNCTION — A COMPARATIVE NUMERICAL ANALYSIS

Several types of middle ear implants (MEIs) have been invented as an alternative to conventional hearing aids for the rehabilitation of sensorineural hearing loss. Temporal bone and clinical studies have shown that the implantation of MEIs’ transducers influences middle ear transfer function. But there is little comparative data available about these influences. We conducted comparative studies on the influences of three principal types of MEI transducers in respect to their attachment points on the ossicular chain. To aid the investigation, a human middle ear finite element model was constructed. The model was built based on a complete set of micro-computerized tomography section images of a human ear by reverse engineering technology. The validity of the developed model was verified by comparing the motions obtained by this model with published experimental measurements on human temporal bones. The results show that the eardrum driving transducer (EDT) and the floating mass transducer (FMT) decrease stapes displacement prominently at high frequencies. The greater these transducers’ mass, the smaller is the displacement of the stapes footplate. In contrast, the incus body driving transducer (IBDT) decreases stapes displacement severely at low frequencies, and its adverse effect on residual hearing increases with increasing stiffness of the IBDT’s driving rod.

Morphological changes in the tympanic membrane associated with Haemophilus influenzae-induced acute otitis media in the chinchilla

OBJECTIVE

The tympanic membrane (TM) couples sound waves entering the outer ear canal to mechanical vibrations of the ossicular chain in the middle ear. During acute otitis media (AOM), dynamic structural changes in the TM can occur, which potentially affect sound transmission. It has remained unclear whether TM changes contribute significantly to the conductive hearing loss associated with human AOM. Studies that systematically and quantitatively assess the impact of morphological and mechanical characteristics of the TM on hearing in animal models of AOM have been few in number and lack detail. Our current study focused on the identification of quantitative morphological changes in the TM of the adult chinchilla.

METHOD

AOM was produced by transbullar injection of the nontypeable (acapsular) Haemophilus influenzae strain 86-028NP into two treatment groups of chinchillas: one 4 days (4D) post bacterial challenge, and a second treatment group after 8 days (8D) post challenge. Structure and thickness were examined histologically at nine locations over the TM in untreated controls and in animals from both AOM treatment groups.

RESULTS

TM thickness was found to have increased significantly (110-150%) at all measured locations of H. influenzae-infected ears when compared with uninfected (normal) TMs at 4D post bacterial challenge. Cellular proliferation and infiltration in the outer epithelial layer were primary contributors to this thickening. In ears infected for 8D, the TM was substantially thicker, a 200-300% increase from uninfected control values, due to edema and cell proliferation in both the outer and inner epithelial layers. In both 4D and 8D ears, thickening of the TM was more prominent in the superior-anterior quadrant.

CONCLUSION

This study provides unequivocal structural evidence that significant TM thickness increases are associated with AOM induced by a well characterized H. influenzae human clinical isolate of low passage number. These and additional thickness data from early and later stages in middle ear infection will be used to derive the mechanical properties of the TM in a future study from our laboratory.

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.

Three-dimensional vibrometry of the human eardrum with stroboscopic lensless digital holography

The eardrum or tympanic membrane (TM) transforms acoustic energy at the ear canal into mechanical motions of the ossicles. The acousto-mechanical transformer behavior of the TM is determined by its shape, three-dimensional (3-D) motion, and mechanical properties. We have developed an optoelectronic holographic system to measure the shape and 3-D sound-induced displacements of the TM. The shape of the TM is measured with dual-wavelength holographic contouring using a tunable near IR laser source with a central wavelength of 780 nm. 3-D components of sound-induced displacements of the TM are measured with the method of multiple sensitivity vectors using stroboscopic holographic interferometry. To accurately obtain sensitivity vectors, a new technique is developed and used in which the sensitivity vectors are obtained from the images of a specular sphere that is being illuminated from different directions. Shape and 3-D acoustically induced displacement components of cadaveric human TMs at several excitation frequencies are measured at more than one million points on its surface. A numerical rotation matrix is used to rotate the original Euclidean coordinate of the measuring system in order to obtain in-plane and out-of-plane motion components. Results show that in-plane components of motion are much smaller (<20%) than the out-of-plane motions’ components.