Total implantation of the active hearing implant TICA for middle ear disease: a temporal bone study.

A subpopulation of hearing-impaired patients has conductive hearing loss that cannot be improved by classic tympanoplasty. Other patients have a mixed hearing loss and cannot be helped by present forms of ear surgery or by hearing aids. Possible help for some patients may come from current implantable hearing devices if these are modified for the patient's specific anatomic situation. The TICA LZ 3001 is a hearing implant for total implantation used to treat moderate to severe sensorineural hearing loss. Most patients who use it have a normal ossicular chain that allows coupling of the implant to the incus. The present temporal bone study demonstrates that the TICA can also be used in patients with an interrupted ossicular chain. If the incus long process shows a defect, the TICA may be coupled to the incus body, and connection between the stapes and the long process of the incus can be achieved with a commercially available titanium-angle prosthesis or liquid ionomeric cement. In cases of an absent incus, the coupling axis of the transducer may be coupled to the stapes head via a modified coupling element. With an absent stapes, the coupling axis may be coupled directly to the perilymph by a coupling element similar to a gold stapes prosthesis.

Total implantation of the Implex TICA hearing amplifier implant for high frequency sensorineural hearing loss: the Tübingen University experience.

Hearing devices may be classified as sound-producing hearing aids, electrically stimulating devices, and vibratory hearing aids. Because patients may lose physiologic cochlear amplification, hearing devices for the treatment of sensorineural hearing loss are used as signal amplifiers. The totally implantable communication assistance (TICA) device is a European-approved totally implantable vibratory amplifier implant. It picks up the sound signal transcutaneously from the external auditory canal near the eardrum, amplifies the signal, and transduces the signal into microvibrations that are delivered to the ossicular chain.

In vivo experiments in the cat with an implantable piezoelectric hearing aid transducer.

We have recently developed an implantable piezoelectric hearing aid transducer that is suitable for implantation in patients with sensorineural hearing loss. The transducer does not transmit sound but conducts micromechanical vibrations to the cochlea. In ten cat ears we investigated the efficiency of the implantable transducer with respect to the direct transfer of vibrations within the audible frequency range via the ossicles to the cochlea or directly into the vestibule. The acoustically evoked brainstem potential (ABR) threshold was determined prior to implantation, and the middle ear was then opened and the piezoelectric transducer coupled to the ossicles or to the perilymph. Acoustically evoked brainstem potentials were recorded following stimulation at the umbo, long process of the incus, stapes head, stapes foot plate, and in the vestibulum. Comparisons of the acoustically and mechanically evoked thresholds revealed a good correlation of the two stimulation levels. An electrical transducer voltage of 1 V(RMS) produced equivalent sound pressure levels (SPL) of 100-128 dB at the tympanic membrane. To assess the hearing we compared stimulus-dependent latencies of the early potentials (peaks P1-P5) and thresholds. This evaluation was based on four ears with normal hearing in which the piezoelectric transducer was coupled to the long process of the incus. The mean values of the latencies and their scattering range correlated extremely well in the two stimulation modes. They were nearly identical when the equivalent SPL of 100 dB was assigned to the maximally applied electrical level of 0 dB. These in vitro and in vivo findings demonstrate that the characteristics of the transducer warrant its development further from the prototype stage to become a component of an implantable hearing device for patients with sensorineural hearing loss.

Human studies of a piezoelectric transducer and a microphone for a totally implantable electronic hearing device.

OBJECTIVE: For the surgical treatment of patients with moderate and severe sensorineural hearing loss, the authors have developed a totally implantable hearing device, the totally integrated cochlea amplifier (TICA). To evaluate the effectiveness of transducer and microphone of this device, three separate human studies were conducted. STUDY DESIGN: The first study using transducer prototypes involved self experiments in investigators with normal hearing. The second study used the transducer prototypes in patients with hearing loss, and the third study involved the temporary implantation of the final transducer prototype and microphone in patients undergoing otologic surgery. PATIENTS: In routine middle ear surgery, transducer prototypes were coupled to the ossicular chain of 28 patients. In addition to the transducer, in 5 patients the microphone was placed beneath the skin of the auditory canal, allowing the skin to cover the microphone membrane completely. RESULTS: The piezoelectric transducer reached an equivalent sound pressure level of 145 dB SPL < or =10 kHz. The dynamics for music reached 32 dB, which was identical with the results of the preoperative investigations using high-fidelity headsets (33 dB). The low nonlinear distortions of <0.1% and the frequency range of 10 kHz are reflected in the positive evaluation of the sound quality by 84% of the patients involved. When phonetically balanced speech material and music were presented under free field conditions at a sound level of 65 dB SPL, understanding of the phonetically balanced speech material was 100%. Most patients judged the presentations of music as clear and undistorted with all broadband components. CONCLUSIONS: Data in humans on the performance of the two main components of the TICA implant, the transducer and the microphone, are reported.

[First implantation of a totally implantable electronic hearing aid in patients with inner ear hearing loss]. / Erste Implantationen eines vollständig implantierbaren elektronischen Hörsystems bei Patienten mit Innenohrschwerhörigkeit.

For the majority of patients with sensorineural hearing loss (SNHL) many available hearing aids often do not achieve satisfactory results. For these patients partially implantable hearing devices have been developed, allowing distortion-free hearing and speech intelligibility that may be superior to conventional hearing aids. The external parts of partial implants, however, may result in a patient's stigmatization. Furthermore, they do not use the acoustic properties of the external auditory canal. Recently, we published the successful development of the first totally implantable hearing device for the treatment of SNHL (HNO 46 [1998] 853-863). Here we report the first implantations of this unique, totally implantable electronic hearing system in patients with SNHL: Implex TICA LZ 3001. The implant microphone is implanted subcutaneously in the outer ear canal near the ear drum. The signal is processed by a digitally programmable multichannel audioprocessor located subcutaneously on the bony skull behind the ear. A piezoelectric transducer is coupled to the body of the incus and drives the ossicular chain by vibratory actions. Energy is provided by an implantable battery. Implanted patients describe hearing as being distortion-free and transparent. Speech intelligibility and the hearing of music are improved. Patients may achieve better speech discrimination, especially in the presence of background noise. The aid can be used during sports, including swimming. To our knowledge, this is the first report of the implantation of a totally implantable electronic hearing system in patients. These results encourage further implantations of the totally implantable hearing system in the course of an ongoing clinical study.

[A totally implantable hearing aid for inner ear deafness: TICA LZ 3001]. / Ein vollständig implantierbares Hörsystem für Innenohrschwerhörige: TICA LZ 3001.

Recently, Zenner et al. implanted the first totally implantable electronic hearing devices in patients with SNHL (HNO 46 [1998] 844-852). In the present report, technical and audiological features of the implant TICA are published. The development of the piezoelectric transducer and the microphone for implantation in the posterior wall of the auditory canal as components for the present fully implantable hearing system has already been described (HNO 45, 1997, 792-880). Here we report about our experience with the electronic main module that completes the TICA LZ 3001 system. This module is suited for implantation in the mastoid bone and contains the signal-processing electronics and an integrated battery that can be recharged transcutaneously with a portable charger. The recharging time is around 2 h for an implant operating time of 50 h. The microphone and transducer connectors allow for easy replacement of the main module when the battery lifetime is reached. This lifetime is around 3-5 years. A small wireless remote control allows volume adjustment, contains an on/off switch, and permits selection of four different individual hearing programs. The basic audiological features are provided by a flexible, digitally programmable 3-channel-AGC-system with a peak clipping function. The total bandwidth is around 10 kHz. To our knowledge this is the first fully implantable hearing system that has been in implanted in humans.

[A micromanipulator for intraoperative vibratory hearing assessment with an implantable hearing aid transducer]. / Ein Mikromanipulator für intraoperative vibratorische Hörprüfungen mit einem implantierbaren Hörgerätewandler.

First concepts of implantable hearing aids to be coupled to the ossicular chain are available for patients with combined or sensorineural hearing loss (SNHL). To ensure that hearing can be improved intraoperative coupling of a test transducer to the ossicular chain is mandatory for allowing surgical anatomy to be checked and vibratory hearing tests to be performed. To achieve this, the test transducer has to be held and positioned securely in situ for some minutes, avoiding risks for middle or inner ear structures. This is not possible using conventional surgical instruments. Thus, a micromanipulator to hold the test transducer during intraoperative hearing tests was developed. This surgical device allows the surgeon safe, risk-free, and controlled coupling of the test transducer to the ossicular chain with one axial and three rotational degrees of freedom. With the aid of a conventional ear retractor (2x2 prongs), the manipulator is fixed at the patient's ear. In conjunction with a piezoelectric test transducer, the manipulator was used in nine patients during local anesthesia. The test transducer is part of an electronic hearing implant (Tübingen implant) specifically designed for SNHL that may be coupled to a middle ear ossicle or the perilymph of the cochlea. The micromanipulator was easy to handle. It allowed accurate positioning of the test transducer in the ear and the desired coupling of the transducer's probe tip to the ossicular chain during auditory tests. According to the principles of integrated safety, the intraoperative risk of ossicular or inner ear injuries caused, for instance, by the patient's head movement is minimized. The design of the manipulator system is universal, also allowing its use for other electronic hearing implants or minimal invasive surgery after minor modifications.

[An osseointegrated micromanipulator as anchor for implantable hearing aid transducers. 1: Fitting to the surgical anatomy of the temporal bone and surgical technical properties]. / Ein osseointegrierter Mikromanipulator als Halterung für implantierbare Hörgerätewandler. Teil 1: Anpassung an die chirurgische Anatomie des Felsenbeins und operationstechnische Eigenschaften.

The first electronic implantable hearing aids for patients with hearing loss are coupled to the ossicular chain or perilymph during implantation and are now available. Our new Tübingen implant designed for sensorineural hearing loss (SNHL) is the combination of an implantable microphone and piezotransducer. To avoid hearing losses during implantation, the Tübingen piezotransducer will be (1) fixed to the mastoid cavity and (2) positioned to one of the ossicular target points. This can be done with a micromanipulator which will be implanted together with transducer and microphone in the mastoid cavity. The manipulator weights 0.7 g. With four degrees of freedom, it allows highly secure and safe positioning of the transducer's probe tip to the ossicular chain under close to stereotactic conditions. The main advantages of the present micromanipulator are (1) easy handling during surgery, (2) the transducer's precise positioning to the ossicular target point with sufficient degrees of freedom, and (3) the transducer's stable fixation in the mastoid cavity in the final position. Following integrated safety as the leading principle, ossicular or inner ear injuries caused, e.g., by the patient's head movement or unintentional manual contact by the surgeon, are minimized. The micromanipulator is, as it were, the surgeon's vibration-free "artificial hand". The manipulator's development and its optimization to the mastoid cavity by test implantation in 50 human temporal bones are shown in detail. While coupling the transducer to the body of the incus, transducer, microphone, and micromanipulator can be implanted into 76% of all mastoid cavities without protrusion. In the case of transducers coupling to the long process of the incus, the protrusion-free implantation rate of the above-mentioned three implant modules is 78%.

[Principles of energy sources of totally implantable hearing aids for inner ear hearing loss]. / Grundlagen der Energieversorgung vollständig implantierbarer Hörgeräte für Innenohrschwerhörige.

A fully implantable hearing aid consists of a sound receptor (microphone), an electronic amplifier including active audio-signal processing, an electromechanical transducer (actuator) for stimulating the ear by vibration, and an energy source. The energy source may be either a primary cell or a rechargeable (secondary) cell. As the energy requirements of an implantable hearing aid are dependent on the operating principle of the actuator, the operating principles of electromagnetic and piezoelectric transducers were examined with respect to their relative power consumption. The analysis showed that the energy requirements of an implantable hearing aid are significantly increased when an electromagnetic transducer is used. The power consumption of a piezoelectric transducer was found to be less than that of the electronic components alone. The energy needed to run a fully implantable hearing aid under these conditions would be 38 mWH per day. Primary cells cannot provide the energy needed for a minimum operation time of 5 years (70 WH), and therefore rechargeable cells must be used. A theoretical appraisal was carried out on nickel-cadmium, nickel-metal hydride, and lithium-ion cells to determine their suitability as well as to assess the risks associated with their use in an implant. Safety measures were drawn up from the results. Ni-MH cells were found to be the most suitable for use as an energy source for implantable hearing-aids because they are more robust than Li ion cells and their storage capacity is double that of Ni-Cd cells of similar size.

[Cold deformation elements for attaching an implantable hearing aid transducer to ear ossicles or perilymph]. / Kaltfliessende Elemente zur Ankopplung eines implantierbaren Hörgerätewandlers an Gehörknöchelchen oder Perilymphe.

Development and short-term implantation results of the Tübingen implantable hearing aid (TI = Tübingen implant) have been presented. The TI is designed for patients with sensorineural hearing loss due to a malfunction of the cochlear amplifier. This can be identified by the presence of positive recruitment and the absence of TEOAE (transitory evoked otoacoustic emissions). The Tübingen implant functions in two ways: it allows electronic amplification of the auditory signal and electromechanical signal transduction into a micromechanical vibratory stimulus. There are two paths by which vibratory stimulus reaches the cochlea: (1) directly through a perforation in the stapes foot plate into the perilymph or (2) via the ossicular chain. Made of pure titanium, the casing of the helium-tight welded transducer includes the piezoelectric actuator. An implantable manipulator device is designed for transducer positioning and anchoring in the mastoid cavity. Usually, the transducer probe tip is directly coupled to the body of the incus. This functions without a special coupling device by utilization of an Erbium-YAG laser. Special anatomical situations or the loss of incus and/or stapes suprastructure, however, requires coupling of the vibratory signal to other points of the ossicular chain or to the perilymph. A major problem, however, was an intraoperative, irreversible link between the titanium probe tip and coupling elements. To overcome this problem, the coupling elements were made of gold. A crimp technique was developed, allowing the surgeon to induce cold deformation of the gold. The cold deformation technique (crimp) results in an irreversible coupling between the titanium probe tip and the golden coupling element.

[Active electronic cochlear implants for middle and inner ear hearing loss--a new era in ear surgery. I: Basic principles and recommendations on nomenclature]. / Aktive elektronische Hörimplantate für Mittel- und Innenohrschwerhörige--eine neue Ara der Ohrchirurgie. Teil I: Grundprinzipien und Nomenklaturvorschlag.

Hearing aids have fundamental disadvantages: (1) stigmatization of the patient; (2) the sound is often found to be unsatisfactory due to the limited frequency range and undesired distortion; (3) in many patients, the ear canal fitting device generally necessary leads to an occlusion effect; (4) acoustic feedback when amplification is high. Conventional hearing aids transmit sound into the ear canal via a small microphone. Sound has the disadvantage of requiring high output sound pressure levels for its transmission. This along with the necessary miniaturization of the loudspeaker as well as the resonances and reflections in the closed ear canal contribute to the disadvantages mentioned. In contrast, implantable hearing aids do not make sound signals but micromechanical vibrations. An implantable hearing aid has an electromechanical transducer instead of the loudspeaker of a conventional hearing aid. The hearing signal does not leave the transducer as sound but as a mechanical vibration which is directly coupled to the auditory system bypassing the air. This implantable hearing aid is either coupled to the tympanic membrane, the ossicular chain, the perilymph of the inner ear, or the skull. An implantable hearing aid is expected to have: 1 Better sound fidelity than a hearing aid 2 No ear canal fitting device, free ear canal 3 No feedback 4 Invisibility Requirements on electronic hearing implants designed for patients with conductive hearing loss differ from those on implants for sensorineural hearing loss. Conductive hearing loss requires the implant to replace the impedance transformation, thus being an impedance transformation implant (ITI). In various respects, the demands on an ITI are lower than the demands on an electronic hearing aid for patients with sensorineural hearing loss. The latter are mostly patients with a failure of the cochlea amplifier (CA). A damage to the CA is clinically discernible by a positive recruitment and loss of otoacoustic emissions (OAE). Since these patients form the majority of cases with sensorineural hearing loss, an active hearing implant for such patients should partially replace the function of the CA. Therefore, the suggestion is to refer to a CAI (cochlea amplifier implant). The implant expressions ITI (for patients with conductive hearing loss) and CAI (for patients with sensorineural hearing loss) used in this context allow nomenclatural association with the CI (cochlear implant) for complete inner ear failure as well as with the BSI (brainstem implant) in the case of hearing nerve failure.

[Active electronic hearing implants for middle and inner ear hearing loss--a new era in ear surgery. II: Current state of developments]. / Aktive elektronische Hörimplantate für Mittel- und Innenohrschwerhörige--eine neue Ara der Ohrchirurgie. Teil II: Genenwärtiger Entwicklungsstand.

Active hearing implants have been developed to varying degrees for conductive hearing loss as well as for sensorineural hearing loss. Implants for conductive hearing loss match impedance transformation by the middle ear. They will be referred to as ITI (impedance transformation implants). Three partial ITIs have been developed for routine clinical use: the Swedish transcutaneous BAHA, the American subcutaneous AUDIANT, and the Japanese P-MEI. Of greater importance with respect to the number of patients are electronic implants for sensorineural hearing loss. These implants are designed to replace parts of the function of the cochlea amplifier (CA). Therefore, in this study, they will be called CAI (cochlea amplifier implant). The CAI consist of four parts: (1) transducer, (2) microphone, (3) control unit, and (4) battery. A CAI for routine clinical use does not yet exist. Two transducer principles have thus far been developed for use in CAIs: the electromagnetic (EM) and the piezoelectric (PE) principle. Most of the transducers that have been described are EM transducers. The American Maniglia implant and the American floating mass transducer have been tested in humans. Both belong to the category of high energy consuming (HEC) implants with a limited frequency range that does not contain the whole speech spectrum. This is in contrast to the Canadian electromagnetic Fredrickson-HEC implant which is capable of transmitting broad band signals of up to 10 kHz. All ot he HEC-EM transducers lack an implantable microphone and an implantable battery. The German CAI, one of the piezoelectrical implants, was recently implanted acutely in humans. It consists of a piezoelectrical, ossicle coupled, low energy consuming (LEC) transducer, as well as an implantable microphone. It allows a broadband signal of up to 10 kHz, yet at a considerably lower level of energy.

[Active electronic hearing implants for middle and inner ear hearing loss--a new era in ear surgery. III: prospects for inner ear hearing loss]. / Aktive elektronische Hörimplantate für Mittel- und Innenohrschwerhörige--eine neue Ara der Ohrchirurgie. Teil III: Perspektiven für Innenohrschwerhörige.

The perspectives for active hearing implants lie in the treatment of patients with sensorineural hearing loss (SNHL). The majority of patients with SNHL suffer from a cochlea amplifier (CA) failure which is discernible by a positive recruitment and loss of otoacoustic emissions (OAE). Therefore, the electronic implant is expected to partially replace functions of the CA. Thus, the implant is thought to function as a CAI (cochlea amplifier implant). An approved implant for routine use is not yet available. Clinical studies have thus far only used the high energy consuming (HEC), narrow-band, electromagnetic floating-mass transducer, as well as the Maniglia-HEC implant. The high energie consuming, yet broadband Canadian Fredrickson implant is soon to be used in humans. Of the piezoelectrical implants, a German CAI (Tübingen implant) at present consisting of a piezoelectrical transducer and a microphone has thus far been acutely implanted in first patient. It is a low energy consuming (LEC), broad-band implantable system for patients with sensorineural hearing loss. Routine surgical treatment of patients with sensorineural hearing loss with a CAI will only be achieved if complete implants (with transducer, microphones, batteries, and control unit) are made available. They combine distinct acoustic superiority with invisibility (end of stigmatization), an open ear canal, and hopefully, the end of feedback whistling. Among the implants mentioned, the German CAI is the only LEC implant. Its energy requirements are so low that with today's technologie implantable batteries (e.g., in pacemakers), the additional implantation of an energy carrier seems feasible. Since the implantable microphone is already available in the German system, the only essential part missing for a totally implantable CAI is the implantable control unit.

[Principle requirements for an electromechanical transducer for implantable hearing aids in inner ear hearing loss. I: Technical and audiologic aspects]. / Prinzipielle Anforderungen an einen elektromechanischen Wandler für implantierbare Hörgeräte bei Innenohrschwerhörigkeit. Teil I: Technische und audiologische Aspekte.

In order to overcome the disadvantages of hearing aids, a significant amount of research aimed at replacing them by implanted ossicular-coupled electronic hearing devices is being carried out. The technical and audiological demands on the electromechanical transducer of an implantable hearing aid for moderate to severe sensorineural hearing losses include high transmission quality of the equivalent sound-pressure level without significant linear or nonlinear distortion, and an energy balance suitable for implantation. Fundamental specifications for a transducer are a high spectral bandwidth of up to 10 kHz, an elongation amplitude of at least 100 nm within this range, a small ripple of the elongation frequence response of around +/- 3 dB, a total harmonic distortion (THD) of less than 0.5%, and a maximum electric power consumption of 0.1 mW. The demands on construction, such as hermetic sealing, biocompatibility, and biostability, are also discussed in detail. It appears that optimum transducer design is essentially a compromise between the physical requirements which are in part conflicting regardless of the transducer principle employed.

[An implantable piezoelectric hearing aid transducer for inner ear hearing loss. I: Development of a prototype]. / Ein implantierbarer piezoelektrischer Hörgerätewandler für Innenohrschwerhörige. Teil I: Entwicklung eines Prototypen.

Implantable hearing aids can form the basis of new surgical techniques for dealing with hearing problems originating in the inner ear, provided they are fully implantable. Accordingly, a comprehensive, interdisciplinary, combined project was initiated at the ENT clinic of the University of Tübingen which was to conclude with operations to improve hearing via fully implantable hearing aids. A novel electromechanical transducer for implantable hearing aids based on the piezoelectric principle is described. Unlike the piezoelectric transducers reported so far, this transducer does not rely on the bimorphic principle but on a circle-shaped, heteromorphic combination system consisting of a piezoceramic disc and metal membrane. The transducer can be hermetically sealed and is designed for implantation into the mastoid. Transfer of mechanical oscillations to an ossicle in the middle ear is effected by a directly fixed coupling rod or via suitable coupling elements. The transducer is highly tuned with a resonance frequency at the upper end of the spectral transfer range (greater than 10 kHz). Below this resonance and down to low frequencies, the frequency response of elongation is smooth with amplitudes of around 20 nm. At low and middle frequencies of up to 1 kHz, these vibration amplitudes correspond to sound-pressure levels of around 90 dB SPL. At higher frequencies of up to 10 kHz, the output level increases to about 130 dB SPL. Nonlinear distortions are also very small at the highest levels (less than 0.1%) throughout the whole transfer range. Electric power consumption at maximum levels is in the range of a few microwatts and is therefore significantly lower than that of electromagnetic systems. Particularly, this makes it possible to use the transducer in fully implantable hearing aids for rehabilitation of sensorineural hearing loss.

[An implantable piezoelectric hearing aid transducer for inner ear deafness. II: Clinical implant]. / Ein implantierbarer piezoelektrischer Hörgerätewandler für Innenohrschwerhörige. Teil II: Klinisches Implantat.

A miniature, hermetically sealed implant was development and manufactured in several clinical and technical iteration steps based on the prototype of an implantable piezo-electric hearing-aid transducer described in Part 1 of the work presented here. The transducer is made of pure titanium (medical grade 2, ASTM F67) and designed to be implanted into the mastoid cavity. Transfer of mechanical oscillations to an ossicle in the middle ear is effected by a fixed directly coupling rod of pure titanium or via suitable coupling elements. The transducer is highly tuned with a resonance frequency in the range of 7-10 kHz, depending on the dynamic mass load. Below this resonance and down to low frequencies, the frequency response of elongation is smooth with a very small ripple of less than +/- 1 dB. Unlike the prototype, an increase in vibration amplitude of around 10 dB was achieved for a comparable power consumption. Vibration amplitude at low and middle frequencies is about 60 nm with a transducer voltage of 1 V, corresponding to an equivalent sound-pressure level of around 100 dB SPL at up to 1 kHz. At higher frequencies of up to 10 kHz, the output level increases to beyond 130 dB SPL. Nonlinear distortions at maximum volume (1 V) are extremely small (THD < 0.1%) throughout the whole transfer range. Due to an extremely short attack time (50 microseconds) and short release time (approximately 2 ms), the dynamic properties of the transducer allow good transmission of audio signals with fast changes in the time domain, i.e., plosives in speech signals. Electric power consumption at full volume and broadband signals is in the region of 1 microW. Unlike electromagnetic transducers described in the literature, the low power consumption of this piezoelectric transducer allows the realization of fully implantable hearing aids for rehabilitation of moderate to severe sensorineural hearing loss.

[An implantable microphone for electronic hearing aids]. / Ein implantierbares Mikrofon für elektronische Hörimplantate.

Fully implantable hearing aids and cochlea implants of the future require an implantable microphone. A hermetically sealed implantable microphone based on the idea of a microphone implanted in the posterior wall of the auditory canal, as suggested by Ohno et al. in 1988, is presented. Through consistent technological and clinical design optimization, it was possible to achieve a membrane diameter of only 4.5 mm (as opposed to 8 mm in the Japanese system) and a significant volume reduction of nearly 50%. The microphone weights only 0.4 g. In spite of this miniaturization, the performance characteristics of the microphone equal those of the Japanese model or are superior. The sound-pressure transfer function shows a very small ripple and the bandwidth amounts to approximately 10 kHz. Because of its high tuning and high no-load resonance frequency, the microphone is mostly insensitive to post-operational changes to the loading mass on the microphone membrane initiated by the covering skin of the auditory canal. The sound-pressure transfer factor at 1000 Hz is approximately 1.5 mV/Pa. Using different manufacturing technologies, this value can be increased in the range of 6-8 dB with a corresponding reduction in bandwidth. Due to the small mass, the microphone is highly insensitive to environmental mechanical disturbances. The module is made of pure titanium and is hermetically sealed according to Mil-Std 883 D. Full metal encapsulation and additional internal electronic components protect the microphone well against environmental electromagnetic influences (EMC).

[In vivo studies of a piezoelectric implantable hearing aid transducer in the cat]. / In-vivo-Untersuchungen eines piezoelektrischen implantierbaren Hörgerätewandlers an der Katze.

Recently, we presented an implantable piezoelectrical hearing aid transducer. Its characteristics make it suitable for implantation in patients with sensorineural hearing loss. The transducer transmits micromechanical vibrations instead of sound into the hearing organ. Efficiency of the transducer implant was investigated in ten cat ears. After determining preoperative (acoustical) BERA threshold, the middle ear was opened and the piezoelectrical transducer coupled to various ossicles or the perilymph. BERA responses were recorded following stimulation of umbo, long incus process, stapes head, stapes foot plate, and vestibulum. By comparing the acoustical and mechanical threshold, a correlation was found between the stimulus level of acoustical and mechanical stimulation. An electrical transducer voltage of 1 Vrms was equivalent to sound-pressure levels between 100 and 128 dB SPL at the tympanic membrane. To judge hearing impression, stimulus-dependent latencies of the early acoustically and mechanically evoked potentials (waves P1 to P5) and their thresholds were analyzed. After coupling the piezoelectrical transducer to the long incus process, latencies corresponded well to stimulation. They were almost completely similar when the equivalent sound-pressure level of 100 dB SPL was achieved by the transducer voltage level.