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Easier Said Than Done: Using Implants to Electrically Stimulate Paralyzed Vocal Cords

A mechanical engineer hopes to restore function to stroke-paralyzed vocal cords, although stimulating the correct nerves could be challenging--and risky
speech,surgery



COURTESY OF AXION BIOSYSTEMS

Vocal cord paralysis can strike as a result of a stroke, disease or trauma to the head or neck, thereby making breathing, swallowing and speaking difficult. Depending on the severity of the paralysis—it can affect either one or both of the elastic bands of muscle tissue that give us our voices—treatment can involve speech therapy, surface electrical stimulation or even surgery. Now a team of researchers is pursuing a way of alleviating such paralysis through a hybrid approach that involves placing electrodes just under the skin, where they can stimulate very specific nerves and potentially restore movement to a damaged vocal cord.

Vocal cords create one's voice only when closed: air from the lungs passes between them and causes them to vibrate. When a person is not speaking the vocal cords remain apart so the trachea (air passage to the lungs) is open for breathing. A paralyzed vocal cord, however, never closes, which not only makes speech difficult but also exposes the trachea and lungs to food and liquid. Damage to both vocal cords is less common but causes breathing problems because they block air passage to the trachea.

Focusing specifically on stroke victims with one paralyzed vocal cord, Alexander Leonessa, an assistant professor of mechanical engineering at Virginia Polytechnic Institute and State University in Blacksburg, is working with other researchers to develop an electrode-studded pad that could be affixed to the side of the throat (think: Velcro) and use electrical signals to activate the nerves that govern vocal cord movement. Leonessa says he is working with Atlanta's Axion BioSystems to develop just such a pad, which will have 32 pins that would be pushed just under the skin. Each of the pins could be stimulated individually, depending on where the nerves are located, and the pad itself would be connected via a wire to a small electrical device that clips to a belt.

The researchers face several challenges if they are to successfully build such a device. For one, the vocal cords are located in a very delicate area of the neck layered with muscles and nerves that control the head and neck—in particular breathing and swallowing, Leonessa acknowledges. Finding and stimulating the right nerves for the paralyzed vocal cord would not be easy.

Others question whether stimulating damaged nerves would have any effect. Most cases with vocal-fold paralysis affecting the voice or speech result from injury to the nerve endings near the larynx, so even stimulating the nerve trunk would not produce the desired effect, because the signal cannot reach the muscle, says Christy Ludlow, a professor of communication sciences and disorders and director of James Madison University's Laboratory on Neural Bases of Communication and Swallowing in Harrisonburg, Va.

Ludlow is also skeptical of Leonessa's approach because stroke victims are more likely to develop voice or speech problems due to lesions in the brain's speech centers, rather than vocal cord paralysis. In short, the development of a minimally invasive technique for stimulating the recurrent laryngeal nerve from the skin surface is both "innovative and exciting," but still a long shot, she says.

Long shot or not, Leonessa recently won a $480,000 National Science Foundation Faculty Early Career Development (CAREER) award to further develop his research. "The NSF does fund high-risk projects because when these projects do succeed they have a big impact," he says.

Over the next five years, he and his team will work with doctors at the Center for Voice and Swallowing Disorders, part of Wake Forest University Baptist Medical Center in North Carolina. There, patients with paralyzed vocal folds will undergo electrical stimulation tests to see if small shocks can reinvigorate their ability to talk through forced contraction.

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