April 03, 2008 –
Shkel’s vestibular prosthesis for restoring balance contains sensors and a circuit system.
“I’ve fallen and I can’t get up.” The oft-mimicked tagline to an old advertisement underlies a problem faced by many elderly and infirm: poor balance.
More than 90 million Americans older than age 16 have experienced dizziness or balance problems. Balance-related falls account for more than half of accidental deaths and 75 percent of emergency room visits in the elderly population.
UCI researchers are working to allay this dangerous condition on two fronts.
Implantable Prosthesis
One approach is to build a balance-replacement device known as a vestibular prosthesis. Using MEMS technology (micro-electro-mechanical systems), CALIT2 affiliate Andrei Shkel is constructing a tiny system-on-a-chip that will be implanted to replace a damaged balance system.
The 4×4-millimeter silicon chip contains sensors – gyroscopes for measuring rotation and accelerometers to detect motion – and a circuit system that translates this information into electrical pulses. The pulses activate implanted electrodes that stimulate the vestibular nerve to send the necessary information to the brain.
Shkel’s research group is building the sensors and electrodes; they are collaborating with School of Medicine faculty, who will determine the best surgical procedure for implanting the device.
Getting the device to market is still several years off. Shkel, associate professor of mechanical and aerospace engineering, hopes to have the complete system-on-a-chip prototype within three years, after which comes testing on animals and humans.
The MEMS device might also be used one day to enhance the balance system of pilots and elite athletes. “Our physiology is not designed to respond fast enough to certain motion changes. This chip could apply additional electric stimulation to the vestibular nerve, creating ‘super-humans,’” Shkel says.
Wearable and Functional
In addition to this implantable device, researchers are developing an external balance-augmentation tool that incorporates sensory stimulation and feedback to retrain the brain to provide balance.
Balance problems can be caused by inner ear organs or nerves in the legs that aren’t functioning properly. While stimulating the respective nerves is one approach, it requires invasive surgery and is not yet perfected.
Djalilian (left) brings his clinical expertise to research; Bachman calls himself “the gadget guy.”
Stimulating Substitute Nerves
Instead, sensory substitution – the theory that nerves can substitute for one another if they are stimulated properly – underlies a different approach. Bachman and Djalilian are using patients’ skin as a stand-in for the balance nerves.
If a person with normal balance is tilting too far to the right, explains Djalilian, the information about tilting to the right side is sent by the inner ear to the brain, which recognizes that and self-corrects. In a person with compromised balance, that information does not get to the brain, so “we have to give them that information using other stimuli such as vibration,” he says.
They are designing a sensor-and-electrode-loaded fabric that will stimulate nerves in the skin when a patient begins to fall.
As the person begins losing balance, accelerometers in the fabric sense that motion, relaying the information to a computer. The computer activates electrodes that stimulate specific nerves with heat or vibration. Those signals are processed and sent to the brain, which then alerts the patient that he is beginning to fall.
Currently, the sensors and stimulators are hooked up to a computer that processes the sensor information and sends a signal back to the stimulator. Eventually, both functions will be integrated onto chips, according to Bachman, and a prototype device could be ready for testing in the next couple of years.
Two iterations of the fabric are being tested. One is a patch worn on the patient’s thigh; the other is a lightweight vest worn next to the skin.
Researchers also are experimenting with pressure sensors, built into the soles of shoes, which operate on the same principle.
The challenge, of course, is that the information must be sent on its way instantly. “It has to be very real-time processing. If there is lag time, the patient will fall before the brain receives the message,” Djalilian says.
— Anna Lynn Spitzer
