An implantable device that reduces blood pressure by stimulating a nerve in the neck could someday be an alternative to drugs for controlling hypertension. The device is one of the latest efforts to use a nerve-stimulating implant to treat a medical condition.
Such implants might offer new hope to those with extreme hypertension. Up to 30 percent of people with high blood pressure cannot be fully treated with medication, and some patients taking the drugs suffer from side effects including fatigue and light-headedness.
“An implantable device would allow reducing the blood pressure in these patients, either alone or in combination with the already applied medication,” says Dennis Plachta, a microsystems engineer at the University of Freiburg in Germany. “It offers a second chance not available yet, and it can run in a tandem solution to a pharmaceutical treatment.”
Plachta and his team developed a micromachined cuff that wraps around the vagal nerve—a nerve found in the neck that exchanges critical physiological information between the brain and other major organs, including the heart. The 20-millimeter-long cuff positions a set of electrodes on a region of the nerve that the team determined would specifically stimulate the changes in blood pressure. The researchers tested their implant in five adult rats and found that a certain stimulation pattern could reduce the rodents’ blood pressure by 40 percent without any major side effects.
Plachta says the procedure for implanting the device in humans would be similar to one used in an existing technique that uses vagal-nerve stimulation to treat epilepsy. It would begin with a small incision on the left side of the neck, after which a surgeon would gently wrap the electrodes around the nerve. The device would then be connected to a capsule containing the pulse generator, which would be implanted under the chest muscle through an incision in the left armpit. The whole surgery should take an hour and a half or less, says Plachta.
Bisognano, a cardiologist who runs a resistant-hypertension clinic at the University of Rochester Medical Center in New York, knows well the need for more treatment options. He says all his patients are on several blood pressure medications, and some find that side effects make the drug regimens difficult to maintain. “The worst part is that the blood pressure is still high, which means they are at high risk for stroke, heart failure, and kidney failure,” he says.
Implanted electrical devices that control bodily functions have been used for many years. Pacemakers for heart patients are perhaps best known, but electrical devices are also used to control Parkinson’s disease and, experimentally, some psychiatric conditions (see “Brain Pacemakers” and “Brain Implants Can Rest Misfiring Circuits”). They may be helpful even for such unlikely conditions as bladder dysfunction and rheumatoid arthritis (see “Implanted Device Controls Rheumatoid Arthritis”).
Kristoffer Famm, vice president of bioelectronics research and development at GlaxoSmithKline, coauthored a paper last year on the emergence of the field that he and his academic colleagues call “electroceuticals.” The company has put forth $50 million to invest in companies developing such technologies.
Bisognano says that nerve stimulation is a logical mechanism for controlling blood pressure. It is well known that the nervous system can regulate the tension of the body’s arteries and control how vigorously and frequently the heart contracts, he says. But only with recent technological advances could that knowledge be used to develop device-based treatments. Bisognano has successfully reduced blood pressure with experimental implants that stimulate the carotid artery directly—an entirely different design from the implant developed by the German group.
With the new design, blood pressure in the rats dropped less than five seconds after the device stimulated the nerve. Plachta says he and his colleagues are also working on developing an “intelligent” version of the system that can detect blood pressure and respond to the body’s needs in real time. Whereas drugs cannot adapt to patient activities, an intelligent implant can, he says, which could offer a way to treat hypertension “on demand.”