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.
The Soundbridge is the first U.S. Food and Drug Administration
(FDA) approved implantable middle ear hearing device to treat
sensorineural hearing loss. People who participated in the
Soundbridge clinical trial reported improved sound clarity,
better fit and comfort, increased gain (loudness of sound),
and fewer maintenance issues than they experienced with hearing
aids. Soundbridge is a proven, safe and effective treatment
that leaves the ear canal completely open.
Candidates for Soundbridge include adults who have moderate-to-severe
sensorineural hearing loss and desire an alternative to a
traditional hearing aid. It uses technology that directly
drives the ossicular chain (middle ear bones), bypassing the
ear canal and tympanic membrane (eardrum). It consists of
two major components: 1) the implanted component, and 2) the
externally-worn receiver, which is approximately the size
of a quarter. Unlike a hearing aid, which simply amplifies
sound, the Soundbridge consists of a prosthetic driver which
mechanically vibrates the bones in the middle ear without
surgically altering the structures of the middle ear. For
more information, log on to http://www.vibrant-medel.com/Lang/eng/Function/index.asp?m=2&u=1.
Study participants reported statistically significant improvement
in their ability to hear and communicate while using the
Soundbridge in a variety of difficult listening situations,
such as: improved ability to hear familiar talkers, increased
ease of communication, better performance in environments
with high levels of reverberation or background noise, less
distortion of sound, better performance when other listening
cues were reduced, and fewer uncomfortable or unpleasant
sounds.
In 2000, Dr. Shohet was the first surgeon to implant the
Soundbridge in Orange County (then called the Symphonix Soundbridge).
Since then, he has implanted many patients with significant
success including one patient who is now wearing one in both
ears.
