Different Strokes


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Stroke is the third leading cause of death in the United States. It can happen to anyone, with little or no warning. There are drugs that can help minimize the loss of oxygen-starved brain cells, but there's nothing in the medicine cabinet yet that can fully repair stroke's biggest complication – impaired mobility. Fortunately, engineers are providing some welcome good news in stroke care: technology can train the brain to fix itself, without drugs.

A rehabilitation device developed by bioengineering start-up AMES Technology (Hillsboro, OR) recently won U.S. Food & Drug Administration approval and could be on the market within a year. The mechanism helps teach the brain and nervous system to relearn movements by manipulating how the patient's brain and muscles work together. The yet-to-be-named device promises a chance at renewed independence for many of the estimated 10 million Americans with limited movement due to stroke or spinal cord injuries.

Paul Cordo. Image: AMES Technology

Like a heart attack, an ischemic stroke occurs when a blocked blood vessel prevents blood from getting where it needs to be: the brain. Brain cells that rely on the blocked vasculature for oxygen and nutrients are damaged or completely destroyed. For clot-busting drugs like tPA to be effective, they must be administered as soon as possible after a stroke occurs. That isn't always an option for a disease that strikes with such stealth. According to AMES Chief Technology Officer Paul Cordo, Ph.D., about half of patients fortunate enough to survive a stroke will permanently lose mobility in one or more limbs. Even when physical rehabilitation restores some movement, patients tend to stop improving after the first few months.

"Clinicians have very few options for the most severely disabled people other than working around their disabilities," Cordo says. "How many other types of medical conditions can you think of where we give up on curing the worst affected 50 percent of the patient population?"

This new mechanical rehabilitation device could mean a new source of hope for stroke patients with mobility loss. Image: AMES Technology

Cordo, a biomedical engineer with a background in computational neuroscience, has long probed the controlled manipulation of muscles and surrounding nerves and tendons to trigger neurological responses. He co-founded AMES (for Advanced Mobility Engineering Systems) in 2004 to translate his research findings into a marketable product.

His device builds on a growing knowledge of brain-muscle communication pathways and the connections between muscle vibration and the brain's ability to recognize its role in controlling movement of those stricken muscles.

"Over the past 10 years we've been working to come up with [an] alternative that is effective with the severely disabled, or at least able to bring them to the point that other therapies will be effective," he says.

How It Works

The device is built around a motorized range-of-motion mechanism and one or more vibration units and can be configured as needed based upon the anatomic site to be treated. A standard approach is to position a patient's affected joint in the mechanism, sandwiched between a pair of reciprocating vibrators on the flexor and extensor sides of the target joint. As the apparatus guides the limb through a controlled range of motion, it causes passive stretching and shortening of the muscle. The vibrator attached to the flexor surface actuates during the extension of the joint, while the unit in contact with the extensor side kicks in during flexion. A computer display provides visual feedback to the patient to help discern motorized motion from any voluntary movements he or she might make.

By simultaneously vibrating muscle tissue and robotically exercising the limb, Cordo says he can produce an "exaggerated perception of movement" in the central nervous system. As the brain monitors the input from the nerves, it provides help to control the movements. The AMES device runs a series of computer-controlled therapeutic regimens based on findings from a multi-site clinical study documenting its effectiveness in improving movement and strength in the arms, hands or legs of a significant percentage of severely disabled patients.

In clinical trials in patients recovering from stroke and sports injuries, the therapy led to big improvements in mobility in many cases. For example, Cordo reported that a 72-year-old female stroke survivor experienced a 100% increase in strength and muscle mass in ankle flexors more than 11 years after her stroke. A 53-year-old male with severe paresis in his right leg and arm underwent therapy for 10 days, resulting in a 400% increase in strength of ankle dorsiflexion and a 100% increase in strength of ankle plantarflexion, with similar success for his effected elbow. Demonstrating the wider potential of the therapy beyond stroke care, a young baseball player with a shoulder injury made a faster return to the pitcher's mound after intensive work with the device.

Michael MacRae is an independent writer.

How many other types of medical conditions can you think of where we give up on curing the worst affected 50 percent of the patient population?

Paul Cordo, co-founder, AMES Technology

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August 2013

by Michael MacRae, ASME.org