Matthias Bornitz

Acoustic Properties of Different Cartilage Reconstruction Techniques of the Tympanic Membrane

Objectives/Hypothesis The use of cartilage in reconstruction of the tympanic membrane has been established especially in cases such as tubal dysfunction and adhesive processes. Cartilage offers the advantage of higher mechanical stability compared with membranous transplants but may alter the acoustic transfer characteristics of the graft. Apart from material properties, it can be assumed that, also, the microsurgical reconstruction technique might influence the sound transmission properties of the reconstructed tympanic membrane. The purpose of the study was to investigate the acoustic transfer characteristics of different cartilage transplants being typically used in different reconstruction techniques of the tympanic membrane.

Experimental investigations of the use of cartilage in tympanic membrane reconstruction

BACKGROUND Temporalis fascia, perichondrium, and cartilage are commonly used for reconstruction of the tympanic membrane in middle ear surgery. Cartilage grafts offer the advantage of higher mechanical stability, particularly in cases of chronic tubal dysfunction, adhesive processes, or total defects of the tympanic membrane, in contrast to fascia and perichondrium, which presumably offer better acoustic quality. HYPOTHESIS The purpose of this study was to determine the acoustic transfer characteristics of cartilage of varying thickness and its mechanical deformation when exposed to fluctuations in atmospheric pressure. METHOD Ten pairs of cartilage specimens from the cavum conchae and the tragus were obtained from fresh human cadavers. Youngs modulus was determined by mechanical tension tests and statistically evaluated using the t test. The acoustic transfer characteristics of an additional 10 specimens were measured by a laser Doppler Interferometer after stimulation with white noise in an external auditory canal--tympanic membrane model. Mechanical stability was determined by measuring displacement of the cartilage using static pressure loads of < or = 4 kPa. RESULTS Youngs modulus determinations for conchal and tragal cartilage were 3.4 N/mm2 and 2.8 N/mm2, respectively, but the difference was not significant. Acoustic testing showed a 5-dB higher vibration amplitude in the midfrequency range for conchal compared with tragal cartilage, but the difference was not significant. Reducing cartilage thickness led to an improvement of its acoustic transfer qualities, with a thickness < or = 500 microm resulting in an acceptable acoustic transfer loss compared with the tympanic membrane. CONCLUSION Both conchal and tragal cartilage are useful for reconstruction of the tympanic membrane from the perspective of their acoustic properties. The acoustic transfer loss of cartilage can be reduced by decreasing its thickness. A thickness of 500 microm is regarded as a good compromise between sufficient mechanical stability and low acoustic transfer loss.

Noise Exposure of the Inner Ear During Drilling a Cochleostomy for Cochlear Implantation

Objectives: Inserting an electrode array into the cochlea may cause inner ear trauma, which has to be minimized, particularly in cochlear implant patients with substantial residual hearing. Another potential inner ear trauma has, to a large extent, been neglected so far: the acoustic trauma that can occur during cochleostomy using different techniques. In this study, the noise exposure of the inner ear during the drilling procedure was re‐evaluated. In experiments on temporal bones, quantitative measurements of sound pressure level (SPL) were carried out while a cochleostomy for cochlear implantation was drilled.

Modelling of Components of the Human Middle Ear and Simulation of Their Dynamic Behaviour

In order to get a better insight into the function of the human middle ear it is necessary to simulate its dynamic behaviour by means of the finite-element method. Three-dimensional measurements of the surfaces of the tympanic membrane and of the auditory ossicles malleus, incus and stapes are carried out and geometrical models are created. On the basis of these data, finite-element models are constructed and the dynamic behaviour of the combinations tympanic membrane with malleus in its elastic suspensions and stapes with annular ligament is simulated. Natural frequencies and mode shapes are computed by modal analysis. These investigations showed that the ossicles can be treated as rigid bodies only in a restricted frequency range from 0 to 3.5 kHz.

TORP-vibroplasty: a new alternative for the chronically disabled middle ear.

Objective: Surgery can often eradicate chronic middle ear disease in patients with recurrent cholesteatoma, tubal dysfunction, and others; however, in many cases, social hearing cannot be restored even after multiple revision tympanoplasties. A hearing aid is then recommended. Placement of an implantable hearing aid with its advantage of an unoccluded ear canal, irrespective of middle ear function, seems to be a promising alternative. Study Design: After establishing the biomechanics of the ear in our temporal bone laboratory, various locations and attachments of a Vibrant transducer were investigated. These experiments resulted in the development of a new titanium clip holder for a Vibrant integrated total ossicular replacement prosthesis assembly with placement on the footplate. Four patients with permanent severe combined hearing loss were implanted with this device after multiple revision tympanoplasties. The first case is described in detail. Results: Placing a transducer directly on the footplate via a rod transmission gave a better gain for the high frequencies than in the round window location. The acoustic results of the patients showed an improved gain in speech understanding, unobtainable by a conventional hearing aid. Conclusion: The concept of a total ossicular replacement prosthesis-vibroplasty establishes a straightforward procedure in the tympanic cavity similar to a normal tympanoplasty. The open ear canal and its superior acoustic performance offer a promising perspective for revision operations in cases of incurable middle ear dysfunction.

Vibroplasty for mixed and conductive hearing loss.

Objective To summarize new application methods of an active middle ear implant (Vibrant Soundbridge) in patients with conductive or mixed hearing loss. Data Sources Publications listed in the Medline/PubMed database. Study Selection All publications published in English language; search term Vibrant Soundbridge AND floating mass transducer in all fields. Data Extraction Structured analysis of all publications. Data Synthesis Extraction of significant findings and conclusions and audiometric data. Conclusion Modern application methods of an active middle ear implant (VSB) open new therapeutic options for patients with various outer and middle ear diseases resulting in conductive or mixed hearing loss. Titanium couplers can help to couple the active middle ear implant in a standardized way to remnants of the ossicular chain or to the round window. Thus, the active middle ear implant has been established as an alternative treatment option for patients with mixed and conductive hearing. However, the heterogeneity of the studies published so far complicates the analysis of the audiometric results, and thus, the functional hearing gain after VSB implantation varies a lot.

Evaluation of implantable actuators by means of a middle ear simulation model.

The extension of indication of implantable hearing aids to cases of conductive hearing loss pushed the development of these devices. There is now a great variety of devices available with different actuator concepts and different attachment points to the middle ear or inner ear fluid. But there is little comparative data available about the devices to provide an insight into advantages and disadvantages of different types of actuators and attachment points at the ossicular chain. This paper investigates two principle (idealized) types of actuators in respect of attachments points at the ossicular chain and direction of excitation. Other parts of implantable hearing aids like microphone, amplifier and signal processing electronics were not incorporated into this study. Investigations were performed by means of a mathematical simulation model of the middle ear (finite element model). Actuator performance and theoretical gain were calculated by harmonic analysis in the frequency range of 100-6000 Hz and were compared for the different situations. The stapes head proofed to be an ideal attachment point for actuators of both types as this position is very insensitive to changes in the direction of excitation. The implantable actuators showed higher ratio of equivalent sound pressure to radiated sound pressure compared to an open hearing aid transducer and should therefore allow for more functional gain.

Identification of Parameters for the Middle Ear Model

This paper presents a method of parameter identification for a finite-element model of the human middle ear. The parameter values are estimated using a characterization of the difference in natural frequencies and mode shapes of the tympanic membrane between the model and the specimens. Experimental results were obtained from temporal bone specimens under sound excitation (300–3,000 Hz). The first 3 modes of the tympanic membrane could be observed with a laser scanning vibrometer and were used to estimate the stiffness parameters for the orthotropic finite-element model of the eardrum. A further point of discussion is the parameter sensitivity and its implication for the identification process.

Experimental Investigation of Rotational Tomography in Reconstructed Middle Ears with Clinical Implications

A large air-bone-gap after ossiculoplasty may be due to a malpositioned or displaced prosthesis. Rotational tomography (RT) has the potential to provide high-resolution images of implants without artifacts and with less radiation dosage than CT scan. Twenty-seven temporal bone specimens underwent measurements of middle ear transfer function using Laser-Doppler-Vibrometry (LDV) before and after placement of ossicular replacement prostheses (PORPs, TORPs) made of titanium. RT was performed on all specimens. RT allowed 3-dimensional viewing of the temporal bone, accurate localization of implants within the reconstructed middle ear and determination of angles between the inserted prostheses and the tympanic membrane (TM) and/or the malleus handle (MH). Presence or absence of contact between the implant and the TM, malleus or stapes could be clearly visualized. Displaced prostheses were readily identified. The functional LDV-measurements for TORPs showed a trend favoring coupling to the malleus handle, while for PORPs, coupling to the TM was favored. For PORPs, sound transmission was worse with increasing angles between the PORP and stapes superstructure (p<0.05). Following our experimental results RT is an innovative, relevant and useful imaging technique to obtain immediate postoperative feedback after ossicular reconstruction and to precisely determine the position of middle ear implants.

Investigation of the human tympanic membrane oscillation ex vivo by Doppler optical coherence tomography.

Investigations of the tympanic membrane (TM) can have an important impact on understanding the sound conduction in the ear and can therefore support the diagnosis and treatment of diseases in the middle ear. High-speed Doppler optical coherence tomography (OCT) has the potential to describe the oscillatory behaviour of the TM surface in a phase-sensitive manner and additionally allows acquiring a three-dimensional image of the underlying structure. With repeated sound stimuli from 0.4 kHz to 6.4 kHz, the whole TM can be set in vibration and the spatially resolved frequency response functions (FRFs) of the tympanic membrane can be recorded. Typical points, such as the umbo or the manubrium of malleus, can be studied separately as well as the TM surface with all stationary and wave-like vibrations. Thus, the OCT methodology can be a promising technique to distinguish between normal and pathological TMs and support the differentiation between ossicular and membrane diseases.