Home' Technology Review : January February 2008 Contents REVIEWS
TECHNOLOGY REVIEW JANUARY/ FEBRUARY
Ahearing aid is a straightforward device.
Its microphone collects sound, its elec-
tronics amplify it, its tiny loudspeaker sends
the sound into a tube placed in the ear canal,
and the power comes from a disposable bat-
tery. There's just one problem: people hate
hearing aids. They get lost. They're hard
to wear while sleeping. They mustn't get
wet. They get chewed up by the dog. They're
awkward during sex.
I don't have a hearing aid. But I do have
a cochlear implant. Cochlear
implants are for people who
are so deaf that even the most
powerful hearing aids won't help.
A processor worn on my ear col-
lects sound and digitizes it, then
transmits it by radio to a receiver embedded
in my skull. The receiver sends pulses to elec-
trodes attached to my auditory nerves.
It should be called a cochlear semi-
implant, really, because half of it is on the
outside. It lets me hear, which is great, but it
has the same disadvantages as hearing aids.
For starters, I have to assemble myself in the
morning---literally. But more than that, my
cochlear implant feels like something decid-
edly attached to me. Naturally, I would love
to have a body that's whole and complete
in itself. A body that could plunge into the
water without sacrificing the ability to hear
friends' laughter when it emerged.
So far, no one's built a fully implantable
cochlear implant. But two fully implantable
hearing aids are now in clinical trials (that is
to say, they are considered investigational by
the U.S. Food and Drug Administration and
are not yet approved for commercial sale).
One, the Esteem, is built by Envoy Medical
of St. Paul, MN. The other, from Otologics
of Boulder, CO, is called the Carina. Hopes
are high that they will be the first successful
devices of their kind. Making such things
is a challenge. Where does the
microphone go? How is the
amplified sound sent into the
ear? What's the power source?
And how can it be kept in the
body without leaking?
I was curious to know whether the new
devices worked as well as conventional hear-
ing aids. I was even more curious to know
whether the technology could be applied
to cochlear implants. Otologics was game
to show me its work.
At Otologics, Brian Conn, the engineering
director, brought out a skull with the com-
pany's device bolted onto it. I realized after
a queasy moment that it was a real skull.
The device didn't look like a hearing aid.
There were four connected pieces designed
to be countersunk into the skull.
The first piece, the microphone, sat
behind the outer ear. The sensitivity of a
microphone drops by a factor of 10 when
it's buried under skin, so to compensate, the
microphone had a surface area 10 times as
big as a hearing aid's. It was about the size
of a fingernail. Its output went to the big-
gest component, the processing unit. Its
shell also contained a rechargeable lithium-
The battery was recharged, Conn told
me, by the third component: an inductive
coil. An inductive coil converts radio waves
into electricity. For an hour or two a day,
the user puts a small radio transmitter up
against the coil. Since both the coil and the
transmitter have magnets in them, they stick
together through the skin. The patient can
walk around wearing the charging unit until
the battery is full.
The fourth component was a vibrating
piston in the middle ear, secured by four
titanium bolts screwed to the skull. This
was what actually delivered the sound. The
middle ear consists of three tiny bones that
conduct vibrations from the eardrum to
the inner ear. The piston moved the bones
more forcefully than the eardrum would, so
it acted as an amplifier.
I peered at the skull, feeling like Hamlet
contemplating a high-tech Yorick. The
Carina was a strange-looking gadget. Big,
too: at about five inches long, it stretched
from behind the ear to just behind the
temple. The surgery would involve opening
a skin flap, drilling into the skull to counter-
sink the components, and then drilling into
the middle ear to install the piston. A lot of
hardware to get into place.
The Naked Ear
A FULLY IMPLANTABLE HEARING AID IS SHOWING PROMISE.
By MICHAEL CHOROST
$20,000 upon FDA
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