Research Feature . . .
NEW MIDDLE-EAR HEARING DEVICE GIVES HOPE TO PEOPLE WITH MODERATE TO SEVERE HEARING LOSS
by Holly Wagner
COLUMBUS, Ohio - Until recently, a person somewhere between moderate hearing loss and total deafness had little choice but to use a conventional hearing aid.
"A hearing aid has its limits," he said. "Once those limits are reached, the patient's hearing is compromised."
Now, people with moderate hearing loss have another choice. About a year ago, two manufacturers earned FDA approval for a middle-ear hearing device, part of which is attached to a bone inside the middle ear.
Grant performed the first middle-ear surgery implant operation in Ohio last November.
"The middle-ear devices work well for patients who have reached the limits of what a conventional hearing aid can do," he said.
These people often perceive sound as muffled and have difficulty distinguishing voices when many people are talking. They typically have trouble hearing higher frequencies, such as birds singing and higher-pitched human voices. Turning up their hearing aid to compensate could generate annoying feedback.
"A moderately deaf person will get about an 85 percent improvement in hearing with a middle-ear device."
There are a number of hard-of-hearing patients who fall into this category - those who have hearing loss too severe for a conventional hearing aid, but not severe enough for a cochlear implant.
Cochlear implants are usually reserved for people with very severe to profound hearing loss. These devices are surgically placed in the cochlea, or inner ear. Cochlear implants rarely cure deafness, but they can help people discern sound and, to some extent, participate in spoken conversation.
Unlike traditional hearing aids, which convert sound to electricity, or cochlear implants, which use electricity to stimulate the auditory nerve, the middle-ear device operates on mechanical principles. It uses a tiny electromagnet to create a magnetic field within the middle ear. That magnetic field increases the vibrations of the three middle ear bones, or ossicles - the stapes, malleus and incus.
The electromagnet is surgically attached to the stirrup-shaped stapes, the smallest bone in the human body. The other part of the device, the external unit, resides either inside the pinna - or outer ear - or on the head just behind the ear. (The placement of the external unit depends on the design of the hearing device.)
When exposed to sound, this external unit generates an electromagnetic field which stimulates the magnet.
The ossicles transmit these vibrations to the cochlea, or inner ear. The cochlea turns sound waves into nerve impulses that are sent to the brain.
A hearing device based on mechanics rather than electricity produces a clearer, more natural sound by eliminating the feedback produced by conventional hearing aids.
"As a person's hearing worsens, they need to turn up their hearing aid" Grant said. "Turning it up too much causes some of the sound to re-enter the microphone, creating an annoying squeal that emanates from the hearing aid."
The FDA granted approval last year for two middle-ear implants: the Vibrant Soundbridge from Symphonix Devices, Inc. and the Direct System from Soundtec, Inc. The cost for an implant ranges from $6,000 to $14,000, depending in part on whether a patient undergoes local or general anesthesia.
Right now, each company offers a partially implantable middle-ear hearing device - fully implantable devices are under development. Although none are ready for FDA approval, early results with these devices have been quite encouraging, Grant said.
To date, Grant has placed the partially implantable middle-ear devices in six patients. So far, the preliminary results are promising, Grant said, as most patients are happy with the middle ear device.
To reach the middle ear, Grant creates a small opening on one side of the eardrum. Once inside the middle ear, he crimps the magnet to the stapes in a procedure that lasts about 45 minutes. Most of these surgeries are done on an outpatient basis.
It takes about two to three months for the magnet to completely adhere to the stapes. The patient can use his conventional hearing aid for most of the healing period. Once the ear heals, the patient receives the external unit from his doctor.
While the middle-ear device will help improve the hearing of a patient with moderate to severe hearing loss, Grant tells his patients to temper their expectations a bit.
"No device will give a person the hearing of a 20-year-old," Grant said. "But for patients reaching the limits of what a conventional hearing aid will do, a middle-ear implant is worth considering."