Scientists developing fully internal cochlear implants

From New Scientist:

Cochlear implants (pictured) 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 Jenkins, chair of otolaryngology 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," Jenkins says. But developing an internal microphone for such a system is quite a challenge.

Four years ago Cochlear, 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, 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 Jose 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 Jenkins, who has been assessing the devices. Cochlear is now licensing Otologics's technology and hopes to have a complete system working within five years.

Jenkins will be presenting preliminary findings at the American Otolaryngology Society 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 Jenkins. 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 had his implant for 17 years," he says.