MARCH 30, 2006


Hybrid cochlear implant works
wonders in elderly

Experimental device ups treble but keeps bass,
preserving residual hearing

Dr Bruce Gantz's Iowa/Nucleus Hybrid Cochlear Implant

Treating severe hearing loss has always forced doctors to make tough decisions. Cochlear implants have long been used as a last resort when hearing aids no longer cut it. Trouble is they tend to accentuate high pitch sounds and destroy any residual low frequency hearing. Ten years ago Dr Bruce Gantz, who heads the otolaryngology department at the University of Iowa, decided the status quo just wasn't good enough for his patients and set out to come up with an alternative.

The result, his experimental hybrid cochlear implant, melds bionic technology with traditional hearing aids. But the key to his device is that it's far less invasive than traditional cochlear implants and appears to preserve low frequency hearing. "I started with the concept of trying to stimulate only the areas of the inner ear that seem to be major sources of hearing loss — the high frequency areas. This fits most people who have hearing loss due to aging, genetic causes or noise exposure," he explains. The 2000Hz and higher region is where consonants are interpreted. "When you start losing significant hearing, speech becomes muddled because you don't understand all the consonants that are there," he says.

So far, 65 patients have been fitted with Dr Gantz's hybrid cochlear device. And trials are going well. "We've been able to save most of the low frequency hearing in all those patients," he said. "People who have an average of 25% word understanding with hearing aids are up to over 70% word understanding with the hearing aid plus the implant."

Though originally only used in very extreme cases, more recently cochlear implants have seen their indication expand to folks with a modicum of hearing left. This didn't sit too well with Dr Gantz. "There's a potential downside of putting a traditional cochlear implant in a patient who has some residual hearing because you'll most likely destroy it."

Dr Gantz figured that smaller is better. "We used a small electrode — only 0.2mm by 0.4mm — whereas standard electrodes are about 1.2mm in diameter," he explains. When you start advancing a traditional electrode into the cochlea, which is coiled like a snail, it tends to ride against the outer wall, pushing the device up towards the hair cells — acoustic sensors that convert vibration into an electrical signal in the inner ear. So by placing larger electrodes in the cochlea there's a good chance you'll end up damaging the inner ear. "Our thought was to try and limit the amount of damage to only that area in the inner ear where high frequency is," says Dr Gantz.

The Iowa/Nucleus Hybrid Cochlear Implant System — as it's officially called — won't be widely available for a while yet. "We're probably going to go to the FDA mid-year or so and let them evaluate our results," says Dr Gantz. "Even then it will only be able to be fitted by very specialized ear doctors because there's still a risk to the inner ear and it will require some training," he adds.

If they do come on the market, what kind of patients would be right for the hybrid device? "It'd be people who have a lot of trouble understanding, who aren't able to use hearing aids very well to improve their word understanding, and people with trouble hearing in noise," says Dr Gantz.

And the device holds promise for music-lovers too. "We're doing a lot of testing involving music," says Dr Gantz. "Melody recognition in subjects with the device is almost on par with those with normal hearing because those low frequencies are preserved, so it's a very important step. Most patients with [traditional] cochlear implants don't do very well with music," he adds.



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