IOWA CITY, Iowa -- How much hearing an individual has before receiving a cochlear implant may partially predict how beneficial the device will be, according to University of Iowa Health Care research findings.
"The more hearing you have before your implant, the better you do," explained Jay Rubinstein, M.D., Ph.D., UI assistant professor of otolaryngology, and physiology and biophysics.
A cochlear implant is an electronic device that doctors surgically place in the cochlea of the ear to restore hearing in individuals with profound hearing loss or deafness. The device, which receives signals from a processor worn outside the body, acts as the ear's hair cells, which have become damaged or are missing and result in the hearing problems. The cochlear implant converts acoustic information into electrical signals that can be transmitted to the brain and perceived as sound.
Rubinstein decided to investigate the factors affecting the success of cochlear implants after noticing that patients whom he treated at the Iowa City Veterans Affairs Medical Center (VAMC) showed marked improvements in average word perception after implantation as compared to patients treated with the same device at the UI Hospitals and Clinics (UIHC) five years earlier.
The VAMC patients' average word perception scores were 40 percent -- nearly identical to those of the UIHC patients who by then were using a technologically upgraded model. Five years earlier, the UIHC patients' average word perception scores had been about 30 percent.
"It didn't seem like the device was responsible for the improvement," Rubinstein said. "It seemed like there was something different about the patients."
In fact, something had changed in terms of the patients. During the five-year period, the Food and Drug Administration (FDA) had modified the eligibility criteria for receiving cochlear implants. When cochlear implants first came on the market, the FDA allowed their use only for patients who were completely deaf. The federal agency then revised the eligibility criteria to include individuals who had a speech reception limited to less than 40 percent words in sentences in the "best-aided condition."
"This residual hearing is partially responsible for the better performance," Rubinstein said.
When someone receives a cochlear implant, what, if any, hearing a person still has is destroyed. Therefore, finding that all-important cost-benefit equilibrium point is important, Rubinstein said.
"You have to be careful because the more hearing they have, the more they have to lose," he said. "At some point, there is going to be a cutoff in the benefit realized. Where that cutoff is, we currently don't know. So, we are going to start testing those waters now."
Researchers at the UI Cochlear Implant Clinical Research Center will begin that testing process armed with data from their analysis of VAMC and UIHC patients.
"We don't know exactly where the cutoff is, but we can predict, based on our current experience, how people with more hearing will do," he said.
The UI investigators have developed a predictive index. The researchers, knowing the duration of individuals' hearing loss and their level of residual hearing, can plot this data and determine how effective cochlear implantation will be. For example, if a patient has been deaf for 15 years and has 10 percent residual hearing before surgery, there is 95 percent certainty that the person will have an after-surgery word perception score greater than 25 percent.
The index is based on patient information from the UIHC and VAMC. "If the predictive index holds out to be true in a bigger population, it is going to be an incredibly valuable tool," Rubinstein said.
Portions of Rubinstein's research appear in recent issues of the American Journal of Otology and Current Opinion in Neurobiology. Rubinstein's collaborators include Mary Lowder, an audiologist in the UI Department of Otolaryngology; Richard S. Tyler, Ph.D., UI professor of otolaryngology, and speech pathology and audiology; and Bruce J. Gantz, M.D., UI professor and head of otolaryngology.