A More Sound Solution ( Hybrid Cochlear Implants)

[Guest guest]

The Los Angeles Times, December 11, 2006

http://www.latimes.com/features/health/la-he-lab11dec11,0,7368753.story

--------------------

A More Sound Solution

An experimental 'hybrid' device may give many with partial hearing loss the

extra boost they need. It's a new variation on the cochlear implant.

By Regina Nuzzo

Special to The Times

JEANNE YEOMAN had been dealing with her hearing loss for a couple of

decades, but listening still exhausted her. And technology wasn't really

helping her patience. She remembers driving down the road one day and coming

close to just hurling her hearing aids out the window.

" Hearing aids made everything louder, not clearer, " she says. " I didn't need

amplification. I needed clarification. "

Yeoman wasn't deaf. So she was surprised to learn she was an ideal candidate

for an experimental type of cochlear implant. Unlike hearing aids, cochlear

implants communicate directly with the brain by converting sounds into

electrical impulses and shooting them along the auditory nerve. Until now

these devices have been used only for profoundly deaf people. But this new

" hybrid " cochlear implant was designed specifically for partial hearing

loss — so that users could enjoy both their own natural hearing plus bionic

hearing for sounds where they need an extra boost.

Five years after surgery that implanted the device in her inner ear,

34-year-old Yeoman of Humboldt, Iowa, sometimes even forgets it's turned on.

" Everything sounds so crystal-clear, " she says.

Good solutions are scarce for many people with hearing loss, including

growing numbers of aging baby boomers. A large number of the 28 million

hard-of-hearing Americans have what is known as a " ski-slope " loss, in which

their ability to hear high-pitched sounds plummets dramatically. They can

hear sounds such as " aah " and " ooh " quite plainly, but not " ssss " or " shhh. "

Unfortunately, the latter types of sounds give speech the lion's share of

its legibility. Speech doesn't necessarily sound quiet; it sounds muddy.

Even at full blast, hearing aids often can't help enough, says Dr.

Battey, director of the National Institute on Deafness and Other

Communication Disorders at the National Institutes of Health. " This type of

hearing loss can become extremely socially isolating, " he says.

Traditional cochlear implants aren't a good answer. By bypassing damaged

inner ears to stimulate auditory nerve fibers directly, these devices can be

a boon for some deaf people. But the procedure — which involves threading a

tiny bundle of electronics into the inner ear through a hole in the skull —

aims to replace a patient's entire range of hearing. Any natural abilities

usually get wiped out by the surgery.

With the new hybrid implant, however, surgeons hope simply to supplement

natural hearing without destroying it, says Dr. Bruce Gantz, professor of

otolaryngology at the University of Iowa and developer of the device.

The secret lies in the inner ear's design. Normal hearing is sort of a Rube

Goldberg process. First, sound waves enter the ear as rhythmic pulses, which

set the eardrum vibrating in sync. This triggers quivering in three tiny

bones, with the last bone hammering against the entrance to the inner ear.

In response, fluid sloshes in rhythmic waves throughout the corridors of the

snail-shaped cochlea, which alerts sensory cells to electrically stimulate

auditory nerve fibers.

Strangely enough, the cochlea itself is laid out like a coiled piano

keyboard: Cells along the corridors are tuned to particular frequencies

entering the ear. In the case of a low-pitched sound, cells tucked away deep

inside the cochlea alert the auditory nerve; cells that respond to high

notes sit close to the cochlea's entrance. That's fortunate — because

cochlear regions where " ski-slope " patients need a boost are those most

accessible to surgeons.

Compared with traditional implants, hybrid systems use a thinner, shorter

bundle of electronics (10 millimeters in length compared with up to 28

millimeters for traditional implants). This short electrode is positioned

just at the opening end of the cochlea, stimulating the auditory nerve only

when high-frequency sound waves enter the ear. Since surgeons don't need to

probe as deeply into the delicate cochlea, tissue trauma is reduced.

Preserved natural hearing, amplified with a hearing aid if necessary, gives

patients an easier time in tough situations, such as crowded restaurants or

concert halls. The added high-frequency electronic hearing clears up muddy

speech.

Since 1999, about 80 patients have received the hybrid device, Gantz says,

and clinical trials are underway at 15 U.S. sites. Preliminary results,

released in November, reported that surgeons in the trial have been able to

retain hearing in about 96% of the patients. Before surgery, patients were

able to understand about one-third of words on standard hearing tests. After

one year or more with the implant, scores increased to an average of 75%.

Hybrid implant users also function better than traditional implant users in

noisy situations, says , audiology professor at the

University of Iowa and a study investigator. They are far more able to

follow and appreciate music.

Researchers expect to continue the trial through at least next year before

going to the Food and Drug Administration for approval, says

Parkinson, coordinator of clinical studies at Cochlear Corp. in Denver,

which manufactures the device. By some estimates, a successful hybrid device

could eventually reach a population up to twice the size of the current

implant market, he says. In the U.S. today, about 25,000 people use a

traditional cochlear implant.

Still, hybrid users need to devote time and energy to re-learning how to

hear, says Dawna Mills, an audiologist and clinical trials director at

L.A.'s House Clinic, which is participating in the study. At first, human

speech, full of new hisses and whistles, may not even be understandable. But

with time and months of training, the brain seems to adapt to its new world

of sound. " It's not normal hearing, " Mills says, " but it becomes normal for

them. "

Virginia Baker, 50, of Simi Valley says it did take effort to learn how to

hear again. (Her high-frequency hearing had been declining for unknown

reasons since age 19.) Still, that struggle was preferable to giving in to

the social isolation that she had seen envelope her deaf grandmother.

Before surgery, Baker had quit her job substitute teaching in elementary

schools because kids' squeaky voices started to fall outside her hearing

range. " I was almost afraid to go out, " she says. With a hybrid implant,

however, she felt secure enough in her new listening skills to get a

part-time job as an office manager and go back to college, where she is

earning As in her accounting courses. " The hybrid, " she says, " allows me to

go out there with the rest of the world and be a part of it. "