August 1, 2007 — Otolaryngologists develop a new, implantable hearing aid. It works with a transmitter worn behind the ear that sends sound vibrations from her deaf side through the skull to her good ear. It's called the BAHA. The device is implanted in the skull through the scalp behind the ear and causes a vibration when sound enters the field which vibrates the entire skull.
Hearing with your bones? It may seem like the stuff of science fiction, but a new device is allowing some partially deaf patients to do just that.
A childhood case of chicken pox scarred Lara Lockwood's right eardrum, leaving her permanently deaf in that ear. Since traditional hearing aids don't work for patients with single sided deafness, Lara lived with her condition. "People always wondered like, 'Why is she turning her head? She's not looking at the movie, she's not looking at the speaker.' It's really that I was wanting to hear what the other person beside me was saying," Lockwood said. But now, Lara is "hearing" in both ears thanks to a new hearing aid implanted by her otolaryngologist. It works with a transmitter worn behind the ear that sends sound vibrations from her deaf side through the skull to her good ear. It's called the BAHA.
"The device is implanted in the skull through the scalp behind the ear and causes a vibration when sound enters the field which vibrates the entire skull," said John May, an otolaryngologist at Wake Forest University in Winston Salem, North Carolina.
Those vibrations travel to the cochlea in the healthy ear where they are perceived as sound. And because the BAHA doesn't go inside the ear, it is also a welcome alternative for patients who can't tolerate traditional hearing aids.
"This sort of bypasses the ear canal and ear drum to get sound directly to the cochlea," May explained. For Lara, the BAHA has brought back a sensation she's missed for more than thirty years.
"You know, you go through a field, you hear the grass and you can go with the wind blowing and you can hear the sound on your right side," said Lockwood.
Surgery is usually done in the doctor's office with a local anesthetic and takes about an hour. The BAHA costs about $12,000 to $15,000 and is sometimes covered by insurance.
The Acoustical Society of America contributed to the information contained in the TV portion of this report.
BACKGROUND: Researchers at Wake Forest Baptist Medical Center are developing a Bone-Anchored Hearing Aid (BAHA).
HOW IT WORKS: If you strike a tuning fork and hold the base of it against your teeth, you will be able to hear the tone just as clearly as you would were you holding it up next to your ear. This same principle is making it possible for patients with serious hearing problems in the outer and middle ear to hear perfectly through the cochlea in the inner ear. The BAHA is attached to a small post, which is surgically anchored to the skull behind the ear. The BAHA converts sound into vibrations that are transmitted to the skull, and thus, the cochlea, allowing the patient to hear. The BAHA works differently than cochlear implants, which simulate hearing by picking up sound through an external microphone located behind the ear and transmitting sound as electrical signals across the skin to an implanted receiver. A cochlear implant sends microcurrents directly into the auditory nerve, producing the sensation of hearing in the brain.
HEAR, HEAR: Our ears detect sound as vibrations in the air. Those sound waves cause the eardrum to vibrate, sending waves through a fluid inside the cochlea This in turn causes tiny hairs -- each tuned to the different pitches of the sound -- to vibrate as well, stimulating nerves which send electrical signals to the rain for processing. Having two ears makes it possible to determine from where a sound is coming. Time lag and differences in volume provide useful clues. For instance, sound coming from one direction will reach the ear furthest away about 1/500 second later than the closer ear, and the brain can detect this time lag. A difference in volume between the two ears depends on the frequency of the sounds. It is easier for us to tell the direction of high frequency sounds better than low frequency sounds, because the higher frequencies are more easily blocked by the hear, and therefore do not easily reach the far ear.
ABOUT HEARING LOSS: Loud sounds stress and potentially damage the delicate hair cells in the inner ear that convert mechanical vibrations (sound) into the electrical signals that the brain interprets as sound. Over time, the hair cells can become permanently damaged and no longer work, producing hearing loss. Noise-induced hearing loss can be caused by two types of noise: sudden busts, such as firearms or fireworks, or continuous exposure to loud noise, such as motorized recreational vehicles, loud sporting events, power tools, farming equipment, or amplified music. For the latter, it depends on the level and duration of the noise exposure. It takes repeated exposures over many years to cause a gradual onset of noise-induced hearing loss in both children and adults.
Note: This story and accompanying video were originally produced for the American Institute of Physics series Discoveries and Breakthroughs in Science by Ivanhoe Broadcast News and are protected by copyright law. All rights reserved.
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