Hearing and balance experts at Johns Hopkins report successful testing in animals of an electrical device that partly restores a damaged or impaired sense of balance.
Though human testing of the so-called multichannel vestibular prosthesis remains a few years away, the scientists say such a device, which is partially implanted in the inner ear, could aid the 30,000 Americans the experts estimate are coping with profound loss of inner ear balance. These people often suffer from unsteadiness, disequilibrium, or wobbly vision. Problems with vestibular sensation can be inherited at birth or result from use of antibiotics, chemotherapy drugs, Ménière’s disease, viral infection, stroke, or head trauma.
The Hopkins study, done in chinchillas because their inner ear function is well studied, "is proof of concept that we can restore three-dimensional sensation of head movement with a multichannel vestibular prosthesis," says Charles C. Della Santina, M.D., Ph.D., director of the Vestibular Neuroengineering Laboratory and an assistant professor of otolaryngology - head and neck surgery and biomedical engineering at The Johns Hopkins University School of Medicine.
"While everyone knows about the five senses of sight, smell, taste, touch and hearing, few people think about a possible sixth sense - the sensation of head orientation and movement - until the system fails," says Della Santina, who has been working on this prosthesis since 2002.
In their report in the June 2007 edition of the journal I.E.E.E. Transactions on Biomedical Engineering, the Hopkins team showed that a matchbox-size prototype device, weighing less than 3 ounces, effectively mimics the workings of the inner ear’s three semicircular canals by sensing head rotation and transmitting that information to the brain.
Della Santina says people disabled by loss of vestibular sensation often feel chronically off balance and lose the ability to keep the eyes steadily pointed at an object when they move their head, "seeing the world like the wobbly image on a shaky handheld video camera."
According to Della Santina, this is the first implantable device made with multiple sensors and channels of processing that can measure and encode head rotation in all directions.
Researchers say many hurdles remain before a human device will be available. Efforts are underway to reduce electrical interference to other nerve branches and to refine the timing patterns of electrical stimulation to make them more like normal. In addition, they plan to work on making the device smaller and hermetically sealed so that it can fit completely inside the head beneath the skin.
"People with profoundly impaired balance need better treatment options," says Della Santina. "Many cope through rehabilitation exercises or by restricting their activities, but the chronic disequilibrium and blurry vision can be disabling."
Illustration: Multichannel vestibular prosthesis. –Johns Hopkins University School of Medicine.
Johns Hopkins Medicine News Release (08/06/07)
Science Daily (08/08/07)
United Press International (08/08/07)
Medical News Today (08/09/07)
Biology News ( 08/09/07)