The package is glued to the umbo so the accelerometer vibrates in response to eardrum vibrations. The moving mass generates an electrical signal that is amplified by the chip, which then connects to the conventional parts of a cochlear implant: a speech processor and stimulator wired to the electrodes in the cochlea.
"Everything is the same as a conventional cochlear implant, except we use an implantable microphone that uses the vibration of the bone," Young says.
To test the new microphone, the researchers used the temporal bones bones at the side of the skull and related ear canal, eardrum and hearing bones from four cadaver donors.
The researchers inserted tubing with a small loudspeaker into the ear canal and generated tones of various frequencies and loudness. As the sounds were picked up by the implanted microphone, the researchers used a laser device to measure the vibrations of the tiny ear bones. They found the umbo where the eardrum connects to the hammer or malleus produced the greatest sound vibration, particularly if the incus or anvil bone first was removed surgically.
The experiments showed that when the prototype microphone unit was attached to the umbo, it could pick up medium pitches at conversational volumes, but had trouble detecting quieter, low-frequency sounds. Young plans to improve the microphone to pick up quieter, deeper, very low pitches.
In the tests, the output of the microphone went to speakers; in a real person, it would send sound to the implanted speech processor. To demonstrate the microphone, Young also used it to record the start of Beethoven's Ninth Symphony while implanted in a cadaver ear. It is easily recognizable, even if somewhat fuzzy and muffled.
|Contact: Lee Siegel|
University of Utah