Ear implants for the deaf with no strings attached

[Guest guest]

Newscientist.com - April 4, 2011

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

Ear implants for the deaf with no strings attached

* By

<http://www.newscientist.com/search?rbauthors=Duncan+Graham-Rowe> Duncan

Graham-Rowe

COCHLEAR implants have helped thousands of deaf people around the world hear

for the first time. Now a tiny microphone implanted in a person's ear will

provide them with continuous hearing day and night.

Existing implants can't be worn all the time because only a small part of

the device is actually inside the cochlea. A fragile external unit

containing the power supply, processors and microphone has to be hooked onto

the ear and linked magnetically to the implant beneath the skin.

" Patients can't normally wear them in their sleep, in the shower, the rain

or when they swim, " says Herman , chair of otolaryngology

<http://www.ucdenver.edu/academics/colleges/medicalschool/departments/Otolar

yngology/faculty/Pages/jenkinsh.aspx> at the University of Colorado in

Aurora. " A fully implanted system would get rid of all that because you

could wear it round the clock, " says. But developing an internal

microphone for such a system is quite a challenge.

Four years ago Cochlear <http://www.cochlear.com/au> , a firm based in

Sydney, Australia, ran trials of a prototype implant in three patients, with

mixed results, says Jan Janssen, head of Cochlear's design and development.

" People clearly appreciated the ability to hear 24/7, " he says. But because

the microphone was actually inside the ear it would pick up not just

external sounds but also a wide range of bodily noises, including the sound

of eating, swallowing, the rustling of hair and the beating of the heart.

So Cochlear turned to Otologics <http://www.otologics.org/> , a company in

Boulder, Colorado, that was developing a fully implantable hearing aid with

a new microphone that incorporates two sensors.

One is designed to capture all sounds while the other is tuned to pick up

only internal noises. By comparing the two signals software can remove the

unwanted bodily noises, says Bedoya, the company's founder.

But it's not just a question of subtracting one set of sounds from the

other, he says. " The relationship is extremely sensitive and has to be

adjusted on a continuous basis, " Bedoya says, because the sound levels

constantly change. Another major difference is the size. The mic's diaphragm

is larger than normal, improving the quality of the external signal to stop

the sounds appearing muted.

So far four people have had the internal microphone implanted and hooked up

to their normal cochlear implant, with two more trials to follow later this

year, says , who has been assessing the devices. Cochlear is now

licensing Otologics's technology and hopes to have a complete system working

within five years.

will be presenting preliminary findings at the American

Otolaryngology Societ <http://www.ahns.info/meetings/index.php> y meeting in

Chicago later this month. The results look promising. In tests patients are

hearing about 80 per cent of what an external microphone would provide, he

says.

However, having a fully implantable hearing aid will increase the need for

surgery, says . The device's rechargeable batteries only have a

finite lifespan.

This means you would require a new implant at least every 10 years, instead

of having one device implanted for life, says Janssen. While surgery carries

a risk of infection and nerve damage to the cochlea, experience has shown

that these risks are very low, says Janssen. Ray Glover, of the National

Cochlear Implant User's Association in Amersham, UK, agrees and says

patients would rather have devices replaced more frequently if it means

access to more up-to-date technology. " My son has vvhad his implant for 17

years, " he says.

Bionic ear restores hearing

Perhaps the most successful bionic device ever, cochlear implants are

designed to restore hearing in chronically deaf people. They differ from

hearing aids in that they don't acoustically amplify sound. Instead, they

translate sound into electrical signals that are used to electrically

stimulate the cochlea - a spiral-shaped part of the inner ear attached to

the auditory nerve. Normally, cochlear implants receive their signal and

power through an induction loop linking the implant in the cochlea to an

external unit containing the microphone and battery. A fully implanted

device would still need an induction coil, but this would only be used for a

few hours every couple of days to top up the batteries.