Electromagnetic implantable middle ear hearing device of the ossicular-stimulating type: principles, designs, and experiments

ACTIVE MIDDLE EAR VIBRANT SOUNDBRIDGE SOUND IMPLANT

The Vibrant Soundbridge represents a new approach to hearing improvement in the form of active implantable middle ear hearing device. Unlike conventional acoustic hearing aids, which increase the volume of sound that goes to the eardrum, the Vibrant Soundbridge bypasses the ear canal and eardrum by directly vibrating the small bones in the middle ear. Because of its design, no portion of the device is placed in the ear canal itself. The Vibrant Soundbridge has been approved by the FDA as a safe and effective treatment option for adults with moderate to severe sensorineural, conductive or mixed hearing losses who desire an alternative to the acoustic hearing aids, for better hearing. The paper presents a review of the active middle ear implant Vibrant Soundbridge, which has been also implanted at the Department of Otorhinolaryngology and Head and Neck Surgery, Sestre milosrdnice University Hospital Center, which is the Referral Center for Cochlear Implantation and Surgery of Hearing Impairment and Deafness of the Ministry of Health, Republic of Croatia.

The Vibrant Soundbridge® middle ear implant: A historical overview

OBJECTIVE

To present a historical overview of the Vibrant Soundbridge^® (VSB) middle ear implant (MEI), since its beginning in the 1990s to date and to describe its course and contemplate what it might become in the future.

HISTORY

MEIs started to take form in researchers' mind in the 1930s with the first experiment of Wilska. In the 1970s, several devices, such as the Goode and Perkins', the Maniglia's, or the Hough and Dormer's were created but remained prototypes. It is only in the 1990s the devices that emerged remained on the market. In 1994, Symphonix, Inc. was created and aimed to manufacture and commercialize its semi-implantable MEI, the VSB. The principle of the VSB lies on a direct drive of the sound to a vibratory structure of the middle ear through an electromagnetic transducer, the floating mass transducer (FMT). The particularity of the system VSB is the simplicity of the transducer which is made of both the magnet and the coil; thus, the FMT, fixed on a vibrating middle ear structure, mimics the natural movement of the ossicular chain by moving in the same direction. The goal of the VSB was to give an alternative to patients with mild-to-severe sensorineural hearing loss who could not wear hearing aids (HAs) or who were unsatisfied conventional HA users. Subsequent to Tjellström's experiment in 1997, implantations started to include etiologies such as otosclerosis, radical mastoidectomy, failed ossiculoplasty/tympanoplasty, and atresia. Nowadays, the VSB, with more than 20 years of experience, is the oldest and most used middle ear implant worldwide. It is well acknowledged that the straightforward design and reliability of the transducer have certainly contributed to the success of the device.

Adjustable intraocular lens power technology

We present an overview of the adjustable intraocular lens (IOL) technologies that are available or under development. This includes IOL technologies that can be adjusted using secondary surgical procedures, such as the multicomponent IOL, the mechanically adjustable IOL, and the repeatedly adjustable IOL; IOLs that can be adjusted noninvasively in the postoperative setting, such as the magnetically adjustable IOL, the liquid crystal IOLs with wireless control; and IOLs that can be adjusted using the femtosecond laser or 2-photon chemistry. Finally, we discuss the preclinical and clinical studies of the light-adjustable intraocular lens (LAL) that is available commercially in Europe and Mexico and in the final stages of clinical evaluation in the United States. The general principles of each technology, as well as their research status, are described.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

TORP vs round window implant for hearing restoration of patients with extensive ossicular chain defect

CONCLUSIONS

Round window implant (RWI) with a floating mass transducer (FMT) may be suggested as the first choice in hearing rehabilitation for patients with chronic otitis media (COM) and extensive destruction of the ossicular chain.

OBJECTIVE

To investigate the pros and cons of the total ossicular replacement prosthesis (TORP) vs the RWI in restoration of hearing in patients with COM.

PATIENTS AND METHODS

Thirty-eight patients with bilateral moderate to severe mixed or conductive hearing loss from COM without cholesteatoma and bilateral ossicular chain erosion (footplate residual) were alternately assigned to a titanium-TORP (T-TORP) and to RWI with the FMT of the Medel Vibrant Soundbridge (MVBS) located onto the RW niche. The therapeutic efficiency, preoperative vs postoperative air-conduction gain and speech recognition were investigated for the two groups and statistically analyzed at 36 months postoperatively. The following postoperative anatomic conditions were also evaluated for the two groups: 1) recurrence of infection, 2) retraction pocket, 3) extrusion rate, and 4) displacement of the prosthesis.

RESULTS

Good functional results and stability at 36 months were obtained with both procedures. The extrusion rates for T-TORP were low. So far no extrusion has been observed for RWI. Hearing results were statistically much better for RWI vs T-TORP for all investigated parameters.

Initial experiments to develop a MEMS transducer for a new implantable audioprosthesis to substitute the tympanic-ossicular system

CONCLUSION

We tested one prototype of a new audioprosthesis including the audioprocessor, the implemented algorithms and fitting platform in a small group of selected patients with mixed hypoacusis due to earlier bilateral radical mastoidectomy. It was effective to compensate the conductive and the neurosensory components of those patients. Results regarding the energy, frequency and other requirements of the output transduction make it possible to develop a suitable actuator with the available Micro-Electromechanic-Machine-System (MEMS) technology to substitute the conventional transducer of the prototype.

OBJECTIVES

The objectives were: a) to evaluate the effectiveness of the whole fitting system, and b) to obtain information about the required energy to design the MEMS actuator.

MATERIALS AND METHODS

The experiments were conducted with the A prototype of the prosthesis equipped with an output transducer coupled to the oval window. Two algorithms and three cases were tested.

RESULTS

The audioprocessor with the implemented FIR filter-67 coefficients paradigm algorithms, and the fitting system were shown to be adequate for clinical use. Effectiveness parameters were: pure tone average gains 20-33.3 dB; gap closure 25.5-31.8 dB; speech reception thresholds improvement 15-20 dB. Required gain: 5-40 dB. Subjectively, patients considered the results very satisfactory.

Magnetically adjustable intraocular lens

PURPOSE

To provide a noninvasive, magnetic adjustment mechanism to the repeatedly and reversibly adjustable, variable-focus intraocular lens (IOL).

SETTING

University of Missouri-Rolla, Rolla, and Eggleston Adjustable Lens, St. Louis, Missouri, USA.

METHODS

Mechanically adjustable IOLs have been fabricated and tested. Samarium and cobalt rare-earth magnets have been incorporated into the poly(methyl methacrylate) (PMMA) optic of these adjustable lenses. The stability of samarium and cobalt in the PMMA matrix was examined with leaching studies. Operational force testing of the magnetic optics with emphasis on the rotational forces of adjustment was done.

RESULTS

Prototype optics incorporating rare-earth magnetic inserts were consistently produced. After 32 days in solution, samarium and cobalt concentration reached a maximum of 5 ppm. Operational force measurements indicate that successful adjustments of this lens can be made using external magnetic fields with rotational torques in excess of 0.6 ounce inch produced. Actual lenses were remotely adjusted using magnetic fields.

CONCLUSIONS

The magnetically adjustable version of this IOL is a viable and promising means of handling the common issues of postoperative refractive errors without the requirement of additional surgery. The repeatedly adjustable mechanism of this lens also holds promise for the developing eyes of pediatric patients and the changing needs of all patients.

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.

Semi-implantable electromagnetic middle ear hearing device for moderate to severe sensorineural hearing loss

Despite the many improvements in hearing aid technology, conventional hearing aids continue to have significant limitations, which has led to increased interest in implantable hearing devices. The SOUNDTEC Direct Drive Hearing System for moderate to moderately severe sensorineural hearing loss is one such device. In this article the authors present results on five individuals enrolled in a Food And Drug Administration Phase I feasibility study.

Semi-implantable Middle Ear Electromagnetic Hearing Device for Sensorineural Hearing Loss

A semi-implantable middle ear electromagnetic hearing device (SIMEHD) is proposed for limited clinical trial in adult patients to evaluate the implantable hearing device for moderate to severe sensorineural hearing loss. Food and Drug Administration (FDA) investigational device exemption (IDE) approval has been granted (May 1996) for clinical trials. The implant unit has been evaluated acutely and chronically in animals (cats) with excellent results. Five cats undergoing chronic implantation were allowed to survive an average of 9.6 months, showing that the SIMEHD is biocompatible, functional and without untoward complications. All implant units recovered from the cats were functional, except for wire breakage of the internal antenna. A new antenna was redesigned for human implantation.

The SIMEHD system consists of an external and internal unit. The external unit consists of a microphone, audio amplifier, modulator, radio frequency (RF) amplifier, antenna and battery. The internal unit is composed of a receiving antenna, hybrid electronic circuit, air core driving coil, and a target magnet cemented to the incus. All materials in contact with the body are biocompatible and expected to survive indefinitely. The implant unit is miniaturized and manufactured with existing fabrication technology by our industrial collaborator, Wilson Greatbatch, Ltd.

The specific aims and major tasks of the proposed research are: a) to evaluate reliability, safety and efficacy of the SIMEHD system in a selected group of patients diagnosed with sensorineural hearing loss, due mainly to presbycusis or aging of the inner ear; and b) to obtain objective and subjective evaluation of audiologic and psychoacoustic performance as compared to the acoustic hearing aid. This paper describes the design, illustrates the actual device (newest prototype) and details the technique for surgical implantation in the attic and mastoid antrum in humans.

Middle-ear transmission: acoustic versus ossicular coupling in cat and human

Otologic surgeons consider the action of sound pressure on the cochlear windows to be of major importance in certain cases of middle-ear pathology, yet previously published network models of mammalian middle ears do not include such a mechanism. A unified middle-ear model is developed in which it is assumed that the difference of acoustic pressures acting on the windows adds to the ossicular-chain pressure to produce cochlear input. From a network model of the cat middle-ear cavities we estimate the contributions of pressures on the cochlear windows for both normal and abnormal cat ears. For the human ear we use the model of Kringlebotn (1988) and measurements of Békésy (1947). We determine that the pressure difference across the cochlear windows is negligibly small in normal cat and human ears. Thus, it is a reasonable approximation to ignore this mechanism in normal ears. For ears with a drastically altered tympanic membrane and/or ossicular chain, acoustic coupling to the cochlear windows can--to a considerable extent--explain residual hearing in human. The model predicts hearing levels for type IV tympanoplastic reconstructions that agree with the best results obtained surgically.

Implantable hearing devices

The use of implantable hearing devices to help persons with hearing loss is still in its infancy. The advantages and disadvantages of various models of implantable hearing devices currently being developed are discussed, and their clinical use is described. Other hearing aid assistive devices are also discussed, particularly the electromagnetic implant hearing aid.