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School of Medicine
HeadWay - Blazing a New Pathway to Hearing
HeadWay Fall 2010
Blazing a New Pathway to Hearing
Date: November 30, 2010
C. Matthew Stewart says that bone-anchored hearing aids, which conduct sound through the skull, can help a variety of patients in which traditional hearing aids have failed.
Traditional hearing aids have been a godsend for many people with hearing loss, transforming how they experience the world of sound. But what if a traditional hearing aid isn’t the best fit, or isn’t even possible for a patient to use? According to otologist C. Matthew Stewart, the answer may lie in bone-anchored hearing aids.
These unique devices have been Stewart’s longstanding focus ever since he arrived at The Johns Hopkins Hospital for his residency in 2003. He recently brought his expertise to Johns Hopkins Bayview Medical Center, where he not only provides the usual range of otology services, such as surgically managing intracranial tumors that affect hearing or treating cholesteatoma and chronic ear disease, but also evaluation and surgical placement of these osteointegrated hearing aids.
Some of the patients who come to Stewart for these devices have conductive hearing loss, with conditions including arthritis that have affected the stapes or birth defects that leave them without ears or ear canals. Others have mixed hearing loss involving deficits in both conduction and nerve function. A third category of potential users has single-sided deafness, hearing loss that leaves them profoundly unable to experience sound from one side of their body.
The osteointegrated hearing devices take advantage of sound’s ability to travel through the skull, explains Stewart. A surgically implanted titanium post holds a sound processor that sends signals through the skull to the inner ear, enabling hearing.
While it’s clear that these devices work for the thousands of users who now wear them, what isn’t apparent is why they work so well, Stewart notes. Experimental evidence suggests that people with a bone-anchored hearing device can hear better when sound goes through the bone even if they have nerve hearing loss. Additionally, people with one-sided deafness who wear these devices are often able to locate the source of sounds better than auditory physiology research predicts. “It’s a complete mystery to us why and how these devices deliver sounds so clearly to listeners,” Stewart says.
To better understand these devices, which could lead to better osteointegrated hearing aids and optimize methods for patient rehabilitation in the future, Stewart is collaborating with Brad May and his colleagues at May’s world-class Neural Encoding Lab facilities at Johns Hopkins to investigate what elements of speech allow osteointegrated hearing aid wearers to distinguish sounds from background noise or pull out one speaker’s voice from a multitude.
In these studies, volunteers who wear bone-anchored hearing aids and people with normal hearing sit in a sound booth and listen to recorded voices that guide the listener through tasks. The voices vary in pitch, tone, volume and direction, which give Stewart’s team some clues about which of these elements holds the highest importance for helping hearing aid users understand speech.
This combined research and care approach, says Stewart, will provide bone-anchored hearing aid patients the best options for treatment now and in the future: “We’re not just an implant institute.”
To refer a patient, call 410-955-3492.