Cochlear implants (CIs) are the most well-known of the implant technologies to improve hearing ability. Though we consider cochlear implant technology to be cutting-edge, its origins date back to the 1700s and Count Alessandro Volta of Como, Italy. A professor of physics at the Royal School in Como, Volta is credited with inventing the battery in 1800. His early experiments included placing electrodes that were connected to a battery into his ear canals. He discovered that sound could be perceived in this manner and he reported hearing a loud bang followed by a sound similar to boiling of thick soup. His early self-sacrificial experimentation led later researchers to investigate the use of electrical current to stimulate the auditory system in efforts to restore hearing. Today, electrical stimulation implants take a variety of forms – all far preferable to hotwiring yourself with a battery.
Cochlear implants and auditory brainstem implants (ABIs) are electronic devices surgically implanted to stimulate nerve endings in the inner ear (cochlea) or the brainstem in order to receive and process sound and speech. Cochlear implants were first approved by the United States Food and Drug Administration (FDA) in 1984 for use with individuals who have severe or profound sensori hearing loss due to congenital or acquired disorders affecting the cochlea. CIs are now approved for infants 12 months and older. The auditory brainstem implant received FDA approval in 2000 and is approved for persons 12 years and older. An auditory brainstem implant bypasses the cochlea and stimulates the cochlear nucleus in the brainstem and is designed for individuals with neural hearing loss due to tumors of the VIIIth nerve.
Although sensorineural hearing loss is typically presented as one category, when it comes to technology using electrical stimulation, treatment options will vary depending on the root cause of hearing loss – sensori or neural.
Cochlear Implants
Currently, there are three manufacturers of cochlear implant devices: Advanced Bionics Corporation, Cochlear Americas and MED-EL Corporation.
The HiResolution™ Bionic Ear System from Advanced Bionics Corporation features the HiRes™ 90K Implant with either the Auris™ behind-the-ear (BTE) processor or the Platinum Sound Processor (body style). One limiting factor of BTE processors has been the brief battery life; however, Bionic Ear has introduced the rechargeable Auris PowerCel Plus™ which provides a 17-hour average charge and the Auris PowerCel Slim™ which provides a nine-hour average charge. Auris accessories include monitoring headphones for parents and teachers to check the clarity of the processor’s microphone, cables that allow direct input from CD players, computers and TVs and a built-in t-coil. A lighted warning system alerts parents and teachers as to the function of the batteries as well as the processor itself.
Cochlear Americas products include the Freedom™ Contour Advance Electrode Implant with either the Nucleus® Freedom™ BTE processor or the Nucleus Freedom body-worn processor. Both processors feature SmartSound™ technology. SmartSound includes three technological advances: Beam™ for listening in crowded situations; ADRO™ for music and dynamic situations; and Whisper for soft and distant sounds. Freedom extras include: FM accessories for classroom or lecture applications; a personal cable for connection to an iPod® or Walkman®; a TV/stereo cable for connection to Xbox®, Sony Playstation® or computer; and audio listening earphones to allow parents or teachers to check the microphone for quality and loudness. A lighted warning system alerts the parent or teacher to possible complications of the device.
The PULSARCI100 by MED-EL has four electrode array options for different implanting needs. The standard electrode array has 12 electrode pairs for deep insertion stimulating a wide frequency range. A medium electrode array with 12 electrode pairs with medium spacing is recommended when insertion is limited due to anatomical considerations. A compressed electrode array is used when partial ossification of the cochlea has taken place or when malformation of the cochlea exists, and a split electrode array when severe ossification of the cochlea has occurred due to disease such as meningitis. The MED-EL TEMPO+ is designed with multiple wearing options including the BabyBTE™, the Angled Battery Pack, Children's Battery Pack, Straight Battery Pack and Remote Battery Pack.
Brainstem Implants
The Nucleus 24 Auditory Brainstem Implant System distributed by Cochlear Americas was developed by the House Ear Institute in Los Angeles and approved by the FDA in October 2000. The ABI system is used for individuals who have deafness due to acoustic neuromas or neurofibromatosis type 2 (NF-2) and are not cochlear implant candidates. The ABI bypasses the VIIIth nerve near the cochlea and stimulates neural fibers of the cochlear nucleus in the brainstem. Currently there are about a dozen ABI clinics scattered across the United States.
Implants with Osseointegrated Technology
An osseointegrated implant is a direct structural and functional connection between living bone and the surface of a load-carrying implant. This procedure, approved by the FDA in 1995 for persons ages five and older, can be used to sustain a bone conduction signal processor.
The Baha® system, by Cochlear Americas, is intended for individuals with conductive or mixed hearing loss who can still benefit from sound amplification. Candidates for the Baha system include those with medical conditions such as atresia of the ear canal or chronic middle ear problems. The Baha system is also used to treat those with single-sided deafness where only one cochlea functions normally. For children under five, the Baha® Softband is available.
The Baha system includes a small titanium implant and a detachable sound processor. The newest sound processor model, the Baha® Divino™, is the first Baha sound processor to feature digital signal processing. The system was initially FDA-cleared for use in 1996 and is currently being worn by more than 30,000 people worldwide.
Middle Ear Implantable Hearing Devices
Middle ear implantable hearing devices (MEIHD) are a new category of instruments that require a surgical procedure to implant a component in the middle ear. Current products in this category include the Soundbridge®, SoundTec® and Envoy®.
In 2000, the Vibrant® Soundbridge® manufactured by Vibrant-MED-EL, part of MED-EL (formerly Symphonix), was the first FDA-approved MEIHD intended to treat sensorineural hearing loss. The ideal candidate for the Vibrant Soundbridge is 18 years or older with moderate-to-severe sensorineural hearing loss with some hearing aid experience. The Soundbridge consists of three components: an external amplification system called the Audio Processor™, which has a microphone that picks up sound and transmits it across the skin; the Vibrating Ossicular Prosthesis™ implant; and the Floating Mass Transducer™, which is attached to the long process of the incus, one of the ossicles in the middle ear. Like other implants, the signal processor is digital and programmable.
The SOUNDTEC® Direct System by SOUNDTEC, Inc., received FDA approval in 2001. It was voluntarily withdrawn in 2004 when the company identified ways to improve it and the new version should be back on the market in 2007. This semi-implantable device converts sound energy to electromagnetic energy to directly stimulate the ossicles. A special surgically implanted magnet is attached to the ossicular chain. The electromagnetic coil assembly inserted deeply into the ear canal stimulates the magnet. The earmold is attached to a sound processor that is fit either in the canal or behind the ear, similar to a hearing aid. Approximately 600 SOUNDTEC devices have been implanted. The anticipated new magnet will have an additional point of fixation on the ossicular chain to further stabilize it and a redesigned sound processor with digital circuitry and design improvements to allow for tailoring of the coil length to the external auditory canal.
The Envoy Medical Corporation was founded in 1995 to design and develop implantable devices for sensory impairments. The Envoy® middle ear implant uses the eardrum to process incoming sound. The device, which uses technology similar to that of the pacemaker, is implanted under the skin behind the ear. Two leads extend into the middle ear from the device. When sound sets the eardrum in motion, the leads deliver the signal to the processor and a customized dose of energy to the cochlea, thereby transmitting signals to the brain. Envoy Medical is currently enrolling patients in an FDA-approved clinical trial to evaluate the use of its products for sensorineural hearing loss. Visit www.envoy-medical.com/clinical_sites.htm for more information on the clinical trial.
External Ear Semi-Implantable Hearing Devices
The RetroX® Hearing System received FDA approval in 2002 for Auric Hearing Systems, Inc., and for Gyrus ACMI, LLC, in 2004. The RetroX is a special type of hearing system designed to address moderate-to-severe sensorineural hearing loss limited to high frequencies in persons 18 years of age and older. This device consists of two components including a hearing aid and an implanted titanium tube. A canal is created to connect behind the ear and the ear canal – the titanium tube is mounted in this canal. The hearing aid sits behind the ear and connects to the titanium tube.
If you have severe or profound hearing loss and have never considered what implant technology can do for you, consulting a hearing health professional is the first step to determining if it is right for you. Many insurance companies assist in paying for implants even though they may not pay anything for an external hearing aid. With all of these technologies, once the device delivers sound to the brain, an intensive auditory training program is required to teach the brain how to make sound meaningful. Implant technology has had wide success and may be just what you need to restore your hearing.
