The envoy® totally implantable hearing system, st. Croix medical

A New Floating Piezoelectric Microphone for Fully Implantable Cochlear Implants in Middle Ear

OBJECTIVE

Our team designed a long-lasting, well-sealed microphone, which uses laser welding and vacuum packaging technology. This study examined the sensitivity and effectiveness of this new floating piezoelectric microphone (NFPM) designed for totally implantable cochlear implants (TICIs) in animal experiments and intraoperative testing.

METHODS

Different NFPM frequency responses from 0.25 to 10 kHz at 90 dB SPL were analyzed using in vivo testing of cats and human patients. The NFPM was tested in different positions that were clamped to the ossicular chains or placed in the tympanic cavity of cats and human patients. Two volunteers' long incus foot and four cats' malleus neck of the ossicular chain were clamped with the NSFM. The output electrical signals from different locations were recorded, analyzed, and compared. The NFPM was removed after the test without causing any damage to the middle-ear structure of the cats. Intraoperative tests of the NFPM were performed during the cochlear implant surgery and the cochlear implant surgery was completed after all tests.

RESULTS

Compared with the results in the tympanic cavity, the NFPM could detect the vibration from the ossicular chain more sensitively in cat experiments and intraoperative testing. We also found that the signal output level of the NFPM decreased as the acoustic stimulation strength decreased in the intraoperative testing.

CONCLUSION

The NFPM is effective in the intraoperative testing, making it feasible as an implantable middle-ear microphone for TICIs.

LEVEL OF EVIDENCE

4 Laryngoscope, 134:937-944, 2024.

Polyharmonic Vibrations of Human Middle Ear Implanted by Means of Nonlinear Coupler

This paper presents a possibility of quasi-periodic and chaotic vibrations in the human middle ear stimulated by an implant, which is fixed to the incus by means of a nonlinear coupler. The coupler represents a classical element made of titanium and shape memory alloy. A five-degrees-of-freedom model of lumped masses is used to represent the implanted middle ear for both normal and pathological ears. The model is engaged to numerically find the influence of the nonlinear coupler on stapes and implant dynamics. As a result, regions of parameters regarding the quasi-periodic, polyharmonic and irregular motion are identified as new contributions in ear bio-mechanics. The nonlinear coupler causes irregular motion, which is undesired for the middle ear. However, the use of the stiff coupler also ensures regular vibrations of the stapes for higher frequencies. As a consequence, the utility of the nonlinear coupler is proven.

The design of a lumped parameter model considering the stimulus path of round window

BACKGROUND:

Sound normally enters the ear canal, passes through the middle ear, and stimulates the cochlea through the oval window. Alternatively, the cochlea can be stimulated in a reverse manner, namely round window stimulation. The reverse stimulation is not well understood, partly because in classic lumped-parameter models the path of reverse drive during the round window stimulation is usually not considered.

OBJECTIVE:

The study goal is to gain a better understanding of the hearing mechanism during round window stimulation.

METHODS:

A piezo actuator was coupled to the oval and round window of the guinea pigs. The auditory brainstem response produced by the forward and reverse stimulation at four frequencies was recorded.

RESULTS:

The results show that the input voltage of the actuator required at the hearing threshold in the round window drive was higher than that in the oval window drive. In order to understand the data, we designed a lumped-parameter cochlear model that can simulate both forward and reverse drive. The model-predicted results were consistent with the experimental results.

CONCLUSIONS:

The response of the auditory system to stimulus of oval window and round window was quantified through animal experimentation, and guinea pigs were used as experimental animals. When the same stimulus was applied to the oval window and round window of the cochlea, the ABR signals were compared. A lumped parameter model was designed to incorporate the sound transmission paths in both oval and round window stimulation. The simulated results are consistent with those of animal experiments. This model will be useful in understanding the inner-ear response in round window.

[Coupling of active middle ear implants-biomechanical aspects]

Active middle ear implants or implantable hearing aids are used to treat sensorineural or combined hearing loss. Their coupling to the middle ear structures has a large impact on the success of rehabilitation. Practical issues such as the coupling site, influence of middle ear status, and forward and backward excitation of the inner ear are discussed in the context of biomechanics. For this purpose, experimental studies, model simulations, and current literature data are evaluated. The explanations are intended to contribute to a better understanding of certain procedures in hearing rehabilitation with active implants.

Implementation of a fully implantable middle-ear hearing device chip

BACKGROUND AND OBJECTIVE

Recently, with the increase in the population of hearing impaired people, various types of hearing aids have been rapidly developed. In particular, a fully implantable middle ear hearing device (F-IMEHD) is developed for people with sensorineural hearing loss. The F-IMEHD system comprises an implantable microphone, a transducer, and a signal processor. The signal processor should have a small size and consume less power for implantation in a human body.

METHODS

In this study, we designed and fabricated a signal-processing chip using the modified FFT algorithm. This algorithm was developed focusing on eliminating time delay and system complexity in the transform process. The designed signal-processing chip comprises a 4-channel WDRC, a fitting memory, a communication 1control part, and a pulse density modulator. Each channel is separated using a 64-point fast Fourier transform (FFT) method and the gain value is matched using the fitting table in the fitting memory.

RESULTS AND CONCLUSION

The chip was designed by Verilog-HDL and the designed HDL codes were verified by Modelsim-PE 10.3 (Mentor graphics, USA). The chip was fabricated using a 0.18 μm CMOS process (SMIC, China). Experiments were performed on a cadaver to verify the performance of the fabricated chip.

Effects of a particle placed on the ossicles for microphoneless cochlear implant design

In a typical cochlear implant design, the ambient sound is detected via a microphone and the transmission unit of the implant is placed at the back of the auricle. However, this design has several drawbacks. Firstly, the subject cannot bath or swim comfortably with the microphone unit on, and secondly having an external attached unit which may be visible is cosmetically disturbing. Herein, the idea is to explore obtaining the acoustic signals that would directly drive the cochlear nerves, without using a microphone, in which only the vibrations of the ossicles are employed. Thus, the natural filter caused by the anatomy of the ear may be maintained. The proposed method is to place or attach a micro-electro-mechanical-system (MEMS) type of tiny and lightweight accelerometer to sense or detect the vibrations of ossicles, namely malleus, incus and stapes. A quick analysis or first-thought revealed that physically longer extension of the incus is the most suitable and/or convenient place to attach such a sensor. The model adopted has been optimized to match the amplitude and phase response of the human ear from a system analysis point of view. Some simulation experiments had been done to study and understand the possible loading effects of placing a sensor on the incus. Purpose of the simulations is testing the feasibility before the very difficult surgical procedures. Preliminary results indicate that placing a sensor of weight up to 36 mg does not seriously affect the amplitude and the phase response of the ear. This study is yet another example of how simulations of physiological systems can be advantageous and facilitating in the design of biomedical systems.

Implantable microphones as an alternative to external microphones for cochlear implants

Totally implantable cochlear implants may be able to address many of the problems cochlear implant users have around cosmetic appearances, discomfort, and restriction of activities. The major technological challenges that need to be solved to develop a totally implantable device relate to implanted microphone performance. Previous attempts at implanting microphones for cochlear implants have not performed as well as conventional cochlear implant microphones, and in addition have struggled with extraneous body or surface contact noise. Microphones can be implanted under the skin or act as sensors in the middle ear; however, evidence from middle ear implants suggest body and contact noise can be overcome by converting ossicular chain movements into digital signals. This article reviews implantable microphone systems and discusses the technology behind them.

A new floating piezoelectric microphone for the implantable middle ear microphone in experimental studies

CONCLUSIONS

The new floating piezoelectric microphone is feasible for use as an implantable middle ear microphone in a totally implantable cochlear implant.

OBJECTIVES

A piezoelectric sensor that is driven by the acoustic vibration of the ossicles is one possible design for a microphone for a totally implantable cochlear implant. Such a new floating piezoelectric microphone has been manufactured in the lab. The purpose of this article was to study the frequency response of the new floating piezoelectric microphone in the intact ossicular chain and to identify whether it is usable and implantable.

METHODS

The frequency response of the new floating piezoelectric microphone was analyzed using in vitro testing of fresh cadaveric heads. The microphone, which was designed with an integrated unibody structure to ensure good biocompatibility and capsulation, was attached to the long process of the incus by a titanium clip, or placed in the tympanic cavity and stimulated with pure tones of different frequencies.

RESULTS

The new floating piezoelectric microphone can pick up the vibration of the long process of the incus and convert it into electrical signals sensitively and flatly.

A Fully-Implantable Cochlear Implant SoC with Piezoelectric Middle-Ear Sensor and Arbitrary Waveform Neural Stimulation

A system-on-chip for an invisible, fully-implantable cochlear implant is presented. Implantable acoustic sensing is achieved by interfacing the SoC to a piezoelectric sensor that detects the sound-induced motion of the middle ear. Measurements from human cadaveric ears demonstrate that the sensor can detect sounds between 40 and 90 dB SPL over the speech bandwidth. A highly-reconfigurable digital sound processor enables system power scalability by reconfiguring the number of channels, and provides programmable features to enable a patient-specific fit. A mixed-signal arbitrary waveform neural stimulator enables energy-optimal stimulation pulses to be delivered to the auditory nerve. The energy-optimal waveform is validated with in-vivo measurements from four human subjects which show a 15% to 35% energy saving over the conventional rectangular waveform. Prototyped in a 0.18 μm high-voltage CMOS technology, the SoC in 8-channel mode consumes 572 μW of power including stimulation. The SoC integrates implantable acoustic sensing, sound processing, and neural stimulation on one chip to minimize the implant size, and proof-of-concept is demonstrated with measurements from a human cadaver ear.

Sound transfer of active middle ear implants

Implantable hearing aids are gaining importance for the treatment of sensorineural hearing loss and also for mixed hearing loss. The various hearing aid systems, combined with different middle ear situations, give rise to a wide range of different reconstructions. This article attempts to summarize the current knowledge concerning the mechanical interaction between active middle ear implants (AMEIs) and the normal or reconstructed middle ear. Some basic characteristics of the different AMEIs are provided in conjunction with the middle ear mechanics. The interaction of AMEIs and middle ear and the influence of various boundary conditions are discussed in more detail.

Envoy Esteem Totally Implantable Hearing System: phase 2 trial, 1-year hearing results

OBJECTIVES

(1) To assess outcomes of the Envoy Esteem Totally Implantable Hearing System as measured by hearing results compared with preimplant baseline unaided (BLU) and best-fit aided conditions (BLA) and (2) to determine safety of the device.

STUDY DESIGN

Prospective, nonrandomized, multicenter, subject-as-own-control, US Food and Drug Administration (FDA) trial.

SETTING

Private practice and hospital-based.

SUBJECTS AND METHODS

Between January 2008 and August 2009, an FDA trial was performed at 3 sites. Fifty-seven subjects with bilateral, mild to severe sensorineural hearing loss, with discrimination greater than 40%, were implanted. Implanted components were (1) a sound processor and (2) 2 piezoelectric transducers (a sensor and a driver). A sound processor was implanted in the temporal bone. Transducers were coupled to the ossicles. Devices were activated 2 months postimplant. Hearing results were compared with ipsilateral BLU and BLA.

RESULTS

Speech reception thresholds (SRTs) improved from BLA of 41.2 dB to 29.4 dB with the Esteem (P ≤ .001). Word recognition score (WRS) at 50 dB hearing level (HL) improved from BLA of 46.3% to 68.9% with the Esteem. Pure tone averages improved by 27 ± 1 dB (confidence interval, 30-25). There were no changes in bone conduction. QuickSIN results showed no change. There were 6 serious adverse device effects: 2 wound infections (1 resolved medically, 1 required explantation), 1 delayed facial paralysis that resolved with medication, and 3 revisions due to limited benefit.

CONCLUSION

Phase 2 results at 12 months post implant demonstrated that (1) hearing results with the device are statistically superior to baseline best-fit hearing aids for SRT and WRS and (2) the device is safe.

Middle ear implantable hearing devices: an overview

Hearing loss affects approximately 30 million people in the United States. It has been estimated that only approximately 20% of people with hearing loss significant enough to warrant amplification actually seek assistance for amplification. A significant interest in middle ear implants has emerged over the years to facilitate patients who are noncompliant with conventional hearing aides, do not receive significant benefit from conventional aides, or are not candidates for cochlear implants. From the initial studies in the 1930s, the technology has greatly evolved over the years with a wide array of devices and mechanisms employed in the development of implantable middle ear hearing devices. Currently, these devices are generally available in two broad categories: partially or totally implantable using either piezoelectric or electromagnetic systems. The authors present an up-to-date overview of the major implantable middle ear devices. Although the current devices are largely in their infancy, indications for middle ear implants are ever evolving as promising studies show good results. The totally implantable devices provide the user freedom from the social and practical difficulties of using conventional amplification.

Implantable hearing aids

The aim of this article is to give readers a general overview of the concepts involved in the latest generation of implantable hearing aids. A section on ear biomechanics has also been included to familiarize readers with the basic concepts involved. These devices have been developed over the last 20 years, driven by problems with conventional hearing aids and by advances in the understanding of middle-ear mechanics. The use of technology borrowed from cochlear implants has enabled the first generation of fully implantable aids to be trialled. The author examines the theoretical advantages and disadvantages of implantable hearing aids over conventional aids and then reviews the technology and clinical results of a range of devices that have been trialled.

Initial Clinical Experience With a Totally Implantable Cochlear Implant Research Device

OBJECTIVE

To evaluate the effectiveness and issues associated with a research totally implantable cochlear implant (TIKI).

STUDY DESIGN

Limited patient trial.

SETTING

Tertiary referral center.

PATIENTS

Three adult human subjects with severe-to-profound sensorineural hearing loss.

INTERVENTIONS

Subjects were implanted with a research TIKI developed by Cochlear Limited and the Co-operative Research Centre for Cochlear Implant and Hearing Aid Innovation. The TIKI has a lithium ion rechargeable battery, a package-mounted internal microphone, and sound-processing electronics that enable the use of "invisible hearing" without the use of an external device. The TIKI also functions with an external ESPrit 3G sound processor as a conventional cochlear implant. The standard surgical technique was modified to accommodate the larger device package. Postoperatively, subjects used TIKI in both invisible hearing and the conventional ESPrit 3G modes.

MAIN OUTCOME MEASURES

Device use was recorded in both invisible hearing and ESPrit 3G listening modes. Performance of the internal battery and microphone was assessed over time. Psychophysical MAP data were collected, and speech perception was measured at 1, 3, 6, and 12 months postoperatively in both listening modes.

RESULTS

There were no surgical or postoperative complications. All subjects use both invisible hearing and conventional ESPrit 3G modes. Speech perception outcomes for all patients showed improvement from preoperative scores. As a consequence of the reduced sensitivity of the implanted microphone, speech perception results using the invisible hearing mode were significantly lower than the ESPrit 3G mode. Subjects reported some body noise interference that limited use of the invisible hearing mode; however, all continue to use the invisible hearing mode on a limited daily basis. The rechargeable battery functioned well, with a cycle time indicating the low-power implant design is effective and will deliver long battery life.

CONCLUSION

This study demonstrates that the challenges in developing a safe and effective TIKI can be overcome. Three subjects implanted with the research TIKI all reported benefit from routine use. For each subject, hearing outcomes using invisible hearing mode were not as good as when using the external ESPrit 3G sound processor in the conventional mode.

Anatomical Vibrations That Implantable Microphones Must Overcome

HYPOTHESIS

The goal of this study was to measure the tissue vibration amplitude that would be associated with an implantable microphone.

BACKGROUND

Totally implantable hearing devices have been desired by the hard-of-hearing community for some time. However, an implanted microphone must pick up desired acoustic signals in the presence of undesired signals, including vibration. To design an effective microphone, the level of tissue vibrations originating from anatomical sources and the implanted transducer must be understood.

METHODS

Using a laser Doppler vibrometer and an accelerometer, tissue vibrations were measured under the following conditions: (1) Normal control subjects during vocalization (n=4); (2) Vocalization and biological sounds measured on cranium and in soft tissue on normal subjects (n=6); (3) Transducer vibration measured on Otologics semi-implantable hearing device wearer (n=1) and human cadavers (n=4 ears).

RESULTS

Anatomical noise vibrations are 20 to 25 dB greater in soft tissue for frequencies less than 1,000 Hz than on the cranium, whereas vibrations due to implanted transducers are 20 to 25 dB greater on the cranium than in soft tissue inferior to the mastoid. Chewing vibrations are 10 to 15 dB greater than vocalization on the mastoid. Mastoid vibration levels measured in patients are equivalent to those in cadavers. Vibration levels do not vary significantly with respect to location on the cranium next to the pinna.

CONCLUSION

The greatest anatomical vibrations that an implanted microphone must overcome are because of vocalization in the soft tissue inferior to the mastoid and chewing vibrations on the mastoid. A human cadaver is an appropriate model for transducer cranial vibration studies. If the implantable microphone is placed on the cranium near the pinna, it makes little difference with regard to actual location.

In vivo characterization of piezoelectric transducers for implantable hearing AIDS

BACKGROUND

Piezoelectric bimorph transducers may be used at the input stage of implantable hearing aids to convert ossicle vibrations into electrical waveforms, and at the output stage to convert electrical signals into mechanical motion that drives the ossicles. This study assessed transducer performance in anesthetized, acutely implanted cats using computer-averaged, laser-Doppler vibrometer measures and cochlear potentials.

METHODS

Measures of output linearity and distortion for a transducer placed on the umbo were obtained from averaged laser-Doppler vibrometer outputs. Frequency response and equivalent sound pressure level for transducers placed against the stapes were estimated by comparing compound action potentials and cochlear microphonics elicited preoperatively by acoustic signals with responses elicited postoperatively by signals presented through transducers.

RESULTS

The transducer placed on the umbo exhibited an effective bandwidth that exceeded 8 kHz, linear response behavior for driving voltages up to 2 Vrms, and harmonic distortion of -40 dB or better at all frequencies greater than 250 Hz. Except for a shorter latency, transducer-elicited cochlear potentials were indistinguishable from acoustically elicited responses. Frequency response varied widely across transducers, ranging from reasonably flat to possessing a bandpass characteristic with a peak at 2 to 4 kHz; 1-Vrms signals applied to transducers with various geometries yielded equivalent intensities of 62 to 108 dB sound pressure level at 4 kHz, 51 to 98 dB sound pressure level at 2 kHz, and 55 to 80 dB sound pressure level at 1 kHz. Differences in frequency response and equivalent sound pressure level stemmed from different resonance frequencies in transducers with dissimilar lengths and, more importantly, from variation in transducer-stapes contact force.

CONCLUSIONS

Appropriately designed piezoelectric transducers can provide the cochlea with high-fidelity, wide-bandwidth signals. However, using them in implantable hearing aids requires that geometry and contact force be optimized to reduce variability in output level. Recording cochlear potentials is a cost-effective means of assessing transducer performance intraoperatively, but care must be exercised to take into account any temporary, drill-induced sensitivity loss.