October 29, 1999
UW to begin clinical trials of an implantable hearing aid system
A new implantable hearing aid system will undergo clinical trials at the University of Washington’s Virginia Merrill Bloedel Hearing Research Center, one of five sites selected to study its effectiveness. The Food and Drug Administration has authorized implantation of the device on an experimental basis in a total of 100 patients, including 20 at the UW.
Dr. George A. Gates, director of the center and UW professor of otolaryngology-head and neck surgery, says that the new system has a number of benefits over older hearing-aid technology: superior sound quality, no squeals and no occlusion (plugging of the ear canal). He notes that five people who received the implant in a preliminary study report improved hearing and better quality of sound. Gates will head the study at the UW, with audiologists Dr. Sharon Kujawa and Dr. Tom Rees.
“Standard hearing aids move the middle ear by sound pressure and require a tight-fitting and often uncomfortable ear mold to occlude or close off the ear canal,” said Gates. “If the ear mold is loose, it results in the familiar and annoying squeal of the hearing aid. The new system utilizes an electromagnetic coil in the ear canal. The coil acts on a tiny magnet surgically implanted on the stapes bone, which causes movement in the middle ear. There is no squeal or occlusion effect.”
Any adult with hearing loss in both inner ears, who has worn hearing aids for at least six months and who is not happy with the aids, may be eligible for the study. The surgery to implant the magnet on the stapes is done on the worse ear under local anesthesia on an outpatient basis, and takes less than an hour. After healing, the long ear mold that accommodates the electromagnetic coil is fitted. The participant uses only the experimental device for the next eight weeks. After repeat testing, participants may resume wearing an aid in the better ear. The surgery and other study costs are free to participants.
The new system, the Direct Drive Hearing System (DDHS), was developed by SoundTec, Inc., of Oklahoma City. For information, contact study coordinator Wayne Blinne at (206) 616-2840 or wblinne@u.washington.edu, or visit the study’s website at http://depts.washington.edu/hearing/Implantable.html.
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BACKGROUND ON HEARING LOSS AND HEARING AIDS
Hearing loss is the most common chronic disability and the number-one contributor to quality-of-life problems in older adults. Nearly 30 million people in the U.S. have enough loss of hearing to have a communication problem.
Hearing aids are basically amplifiers: they make sounds louder. As hearing worsens, the amplifier must be turned up. The tiny loudspeaker has to move the eardrum with increasing air pressure as hearing decreases. An air leak around the ear mold can cause the hearing aid to squeal. To prevent squealing, the ear mold must fit tightly, often causing discomfort and pressure. The user must choose between better hearing and discomfort on one hand, and greater comfort but worse hearing on the other.
The new device undergoing clinical trials at the UW uses a tiny magnet surgically implanted on the third bone of the middle ear, the stapes. The electromagnetic coil is housed in a long, soft, custom-made ear mold, which does not cause the wearer discomfort. The coil receives current from an external amplifier, a standard multi-channel compression aid worn behind the ear. (An digital aid worn in the ear canal will become available.)
The output of the amplifier causes the electromagnetic coil to radiate energy through the ear drum to the magnet on the stapes. As the magnet moves back and forth in the electromagnetic field, the stapes and the inner ear fluids vibrate in unison. As the fluid moves, the microscopic hair cells of the inner ear are stimulated to vibrate. These stimulate the nerve, resulting in superior hearing.
