Sunday, July 1, 2001 - Page updated at 12:00 AM

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Region playing important role in research

Seattle Times medical reporter

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From highly sophisticated implants that can directly stimulate hearing nerves, to research into the genetic origins of hearing loss, local researchers are finding ways to help people who have hearing loss now and exploring new ways for the future. Here are some of the latest devices and findings.

Electronic hearing

A new generation of hearing aids and devices is creating a new world of sound for many.

"Patients who could not hear anything for years now call me on the phone," says Dr. Tom Rees, chief of audiology at UW-affiliated Harborview Medical Center.

Cochlear implants have steadily improved hearing for the most seriously impaired over the past 20 years. The devices use sound-activated electrodes threaded through the inner ear's impaired cochlear to directly stimulate hearing nerves.

Recently, researchers at Virginia Mason Medical Center began experimentally implanting the devices in both ears of some patients - providing better sound quality, filtering out background noise and enabling directional hearing. "I think we'll have excellent results with two implants," said Dr. Douglas Backous, director of Virginia Mason's Listen for Life Center.

For patients with middle-ear problems, Backous and others are testing two types of sophisticated hearing aids. One uses a tiny microphone and sound processor worn on the head that feeds a receiver and stimulator connected to the sound-sensitive bones of the middle ear. The other uses a microphone in the ear canal that feeds a similar system, directly stimulating one of the middle-ear bones.

UW researchers are testing a hearing aid that uses a magnetic coil to stimulate the middle-ear bones, eliminating feedback, or squeaking.

Genes affect hearing loss

Scientists estimate as many as 150 genes may be involved in hearing, but only about 20 have been identified. Finding mutations in enough genes or combinations of genes may lead to medications or other measures to help the hearing impaired.

UW geneticists study the genetics of hearing loss and balance, also centered in the ear, in two ways.

They look at gene-produced proteins common to mice and humans that, when absent, cause hearing or balance problems in mice.

UW researchers found that if they took away a specific gene in mice, the animals were deaf and waddled when they walked. Another gene deletion deafened the mice and caused them to quiver. The findings may offer clues to how hearing nerve cells function, says Dr. Bruce Tempel, a geneticist at the UW's Virginia Merrill Bloedel Hearing Research Center.

Researchers also are examining the DNA of five large families in the United States and Europe with abnormally high rates of hearing loss. By comparing the DNA of deaf family members with that of family members with full hearing, researchers may uncover clues to the genetic basis for hearing loss.

Aging arteries and hearing

Clogged arteries can cause hearing loss. Scientists have found that decreased blood flow in tiny arteries of the inner ear impairs the stria vascularis.

The stria, a sort of natural battery, contains a layer of cells that play a crucial role in helping hearing nerves function. When they don't get enough blood, the system breaks down, especially for low and midrange frequencies such as speech. The disorder is called strial presbycusis, from the Greek words "presby," for elder, and "akousis," for hearing.

"If you are in a family with this type of presbycusis, you may be able to change your lifestyle - things such as diet, exercise and smoking - to delay the onset of vascular (blood vessel) disease," says Dr. George Gates, director of the Bloedel Center, who soon will publish a new research report on presbycusis.


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