Implantable Hearing Technology

The new frontier in hearing

Implantable Hearing Devices

Patients with moderate to severe sensorineural hearing loss may be good candidates for an implantable middle ear device. These devices simulate natural hearing with greater clarity than hearing aids, and have the added bonus of leaving the ear canal open. In addition, feedback and background noise are virtually eliminated. Dr. Shohet was the first Orange-County based surgeon to implant middle ear devices. In addition, Shohet Ear Associates is one of only eight sites worldwide and six in the United States engaged in clinical trials of a totally implantable hearing aid.

Several types of devices can be considered implantable hearing devices. These include cochlear implants, middle-ear implants, and bone-anchored hearing devices. More detail on each follow below.

• Cochlear Implants

  Patients with severe to profound hearing loss in both ears may benefit from a cochlear implant. This device allows patients to actually hear sound and improve their communication. A cochlear implant provides sound perception by means of an electrode surgically implanted into the cochlea. A sophisticated combination of a microphone, processor and transmitter is worn outside the ear. The device sends hearing sensations to the implant, which in turn transmits these signals to the auditory nerve of the brain. The signals are then interpreted as sound. Cochlear implants are usually performed on an outpatient basis. The implants are programmed in our office by a clinical audiologist.

• Bone-anchored hearing devices

  Bone-anchored hearing devices are used primarily for conductive hearing loss or single-sided deafness. They are popular for hearing rehabilitation in patients with congenital ear malformations or refractory chronic ear disease. A titanium fixture is implanted in the postauricular area. An external sound processor is attached to the abutment at will. A microphone in the processor, which vibrates the bone in the skull by means of the fixture, picks up sound. The sound is transmitted directly to the inner ear on the side with conductive hearing loss or better sensorineural hearing than the other.

• Implantable Middle-Ear Devices

  Implantable middle-ear hearing devices were developed to treat conductive and sensorineural hearing loss. These devices improved fidelity by directly stimulating the hearing bones, and they improve comfort by allowing the ear canal to remain open. In addition, most implantable middle-ear devices almost completely eliminate feedback, one of the most annoying adverse effects of conventional aids.

  Implantable middle-ear devices are generally available in 2 types: piezoelectric and electromagnetic. Piezoelectric devices operate by passing an electric current into a piezoceramic crystal, which changes its volume and thereby produce a vibratory signal.

  One promising piezoelectric device is the Envoy System—a totally implantable hearing aid. This device uses the eardrum as the microphone, taking advantage of the natural acoustics of the ear canal without obstruction, interference, or any external devices. The input signals are identical to those received by a person with normal hearing. This mechanical signal is detected from a piezoelectric transducer at the head of the sensor and converted to an electrical signal by using existing transducer technology. The electrical signal is amplified, filtered, and converted back to a vibratory signal. The vibratory signal is then delivered by means of a piezoelectric transducer to the inner ear.

  An audiologist programs the implant using a device called the commander. After the device is programmed, patients are given a personal programmer that allows them to turn the device on or off, to adjust the volume, and to remotely modify background noise filters. To learn more about the envoy, visit the Envoy Medical website.

  Shohet Ear Associates is one of only eight sites worldwide and six in the United States engaged in clinical trials of the Envoy System.

  Electromagnetic hearing devices function by passing an electric current into a coil, which creates a magnetic flux that drives an adjacent magnet. The small magnet is attached to one of the vibratory structures of the middle ear. So far, however, these devices are only partially implantable and still require an externally worn device to house the electric coil. The major disadvantage is that power is decreased by increased distance between the coil and the magnet—so they must be positioned closely. A slight shift of coil position in the external ear results in unpredictable or insufficient power output. In addition, the anatomy of the middle ear space restricts the size of the magnet or coil.

Click here for an article written by Dr. Shohet on implantable hearing devices. ( TOP )