In a famous commercial a few years ago, the world watched Christopher Reeve overcome his spinal-cord injury by standing up and walking across a room. The scene lead viewers to believe that with a little money and research, functional electrical stimulation (FES) would let paraplegics walk and give quadriplegics the use of their arms. But researchers have discovered this is easier said than done.

“We are seeing movement away from emphasis on spinal-cord injuries and toward development of some of the simpler applications that have clinical significance to a greater number of patients,” says Paul Meadows, president of the International Functional Electrical Stimulation Society (IFESS) and Senior Principal Engineer at Advanced Bionics Corporation. “If you ask anybody in a wheelchair what their biggest problem is, what they'd like to see addressed, it's not standing and walking. It's predominantly bowel and bladder control, and the treatment or prevention of pressure sores. We need to look at what's really important to these patients and provide something useful and broadly achievable, and not focus on what is depicted by Hollywood and which is not practical or obtainable in the near future,“ he adds.

One significant difficulty with spinal-cord injuries is that they're all different. “You may not even have access to the nerves needed to elicit muscle activity. Spinal-cord injuries not only damage the spinal cord but to a great extent to the peripheral nerves as well. When the peripheral nerves are lost it is orders of magnitude more difficult to achieve motor function,“ Meadows adds. “Added to this are connective tissue problems, bone integrity problems, and general health problems that make it difficult to find a one-size-fits-all solution.“

And not only are spinal cord injuries difficult to address, they also have one of the smallest patient populations. In the U.S. there are roughly 10,000 new spinal cord injuries each year. Compare that to 750,000 stroke patients every year. “A major distinction between the spinal-cord injury and stroke populations is that in stroke patients, lesions to the brain result in motor dysfunctions, but leave peripheral nerves intact. These patients are prime candidates for FES in that they retain a great deal of voluntary control and all of the peripheral nerves to the muscles are able to be used through electrical stimulation. Yet for the most part, the stroke patient population has been ignored for the last three decades in favor of the much smaller and more complicated spinal-cord injury population.”

Stimulating hand movement

A device that elicits hand and arm movement in stroke patients is the latest result of a long-term research study by the University of Southampton, England, and the Alfred Mann Foundation (AMF), (www.aemf.org), a non-profit medical research organization in Santa Clarita, Calif. The study explores the use of injectable microstimulators to improve motor recovery and re-learning of arm and hand function following strokes.

AMF's RF microstimulators are implanted into a patient's arm and act as “bionic neurons” mimicking messages from the brain to recreate useful function in paralyzed or weak arms. The cylindrical Bion microstimulators measure 1.7 cm long and 2.4 mm in diameter. Surgeons inject them into the body through small minimally invasive incisions, reducing the expense and risks of traditional complex surgical procedures. They are implanted next to a nerve or on a muscle at the motor point close to where it's attached to a nerve. Once implanted, the microstimulators receive power and stimulation commands over an RF coil (fitted to the arm) that is connected to a control unit. “The control unit generates signals and delivers them to the coil, and the coil delivers magnetic energy to the Bion,” says Jay Yonemoto, Applications Development Manager, Alfred Mann Foundation. “The coils power the Bion up and let us deliver commands. They control pulse width, amplitude, and rate. The control unit can have up to three different programs which let investigators program three different therapeutic routines such as strength training for different muscle groups.”

In a recent study, five Bion microstimulators were implanted close to the nerves supplying muscles in a female stroke patient's arm. A person who has suffered a stroke that causes hemiplegia, paralysis on one side of the body, often loses control of the extensor muscle group in that arm. The effect is the flexor muscles contract and the arm and hand curl up against the chest. Using the microstimulators, the patient should be able to extend her elbow and wrist and open her hand. By switching off the microstimulators controlling the muscle groups that open the hand, she should be able to use her own remaining control of finger and thumb to grasp objects, while stimulation to wrist extensors keeps the hand in position to grab something.

The goal of these therapeutic movements in the forearm and hand is to encourgage the brain to “re-wire” itself around the damage caused by the stroke. Eventually, the stimulation will be turned off and the patient will operate her arm independently with her newly “re-wired” brain.

The Southampton University project is led by Dr. Jane Burridge, senior lecturer in neurorehabilitation in the university's School of Health Professions & Rehabilitation Sciences. Burridge notes, “Following a stroke, between 30 and 66% of patients have problems regaining upper limb function. Many therapeutic approaches to recovery are available, although controversy exists about their effectiveness. However, until now electronic stimulation devices have not been well accepted, mainly because people have difficulty placing electrodes in the correct place on the skin to achieve useful movements, and implanted systems usually involve major surgery.”

“Because the system is implanted, electrodes do not need to be placed on the skin, and because individual muscles are activated, a more functional, natural movement is possible. The implantable microstimulator can remain implanted even if no longer needed. The system is designed to facilitate recovery by supporting voluntary movement rather than replacing it.”

She adds, “it is also less invasive than previous generations of neural implants and because the electrodes are so small they can be implanted into many different muscles, providing the potential to create the fine, graded movement essential for hand and arm function.”

Stimulating pain relief

Another FES system is Precision Spinal Cord Stimulation from Advanced Bionics, a subsidiary of Boston Scientific Corp., (advancedbionics.com), Valencia, Calif. Its implanted and rechargeable stimulator delivers signals to the dorsal columns of spines to mask the perception of pain signals that move along the spinal nerve pathways. Spinal-cord stimulation helps patients with chronic pain in the limbs, trunk, and back who have not gotten pain relief from physical therapy or medications.

The stimulator is about 2 inches long and less than 0.5-in thick. Leads are placed next to the nerves targeted for stimulation. “The Precision system is a parallel, 16-channel constant-current system, so every single contact is controlled by its own current source,” says Paul Meadows, senior principal engineer at Advanced Bionics. “Two percutaneous leads support up to eight contacts, which can be active at the same time,” he adds. Patients control the signal intensity and location with a remote control, programmed by health care professionals.

The future is here

FES systems are being developed to treat a myriad of disabilities. Cyberonics Inc., Houston, (www.cyberonics.com) recently earned FDA approval to treat depression with Vagus Nerve Stimulation Therapy. VNS therapy is delivered from a small pacemaker-like generator implanted in the chest. It sends preprogrammed, intermittent, mild electrical pulses through the vagus nerve in the neck to the brain. The system is the first FDA-approved implantable device-based treatment for depression and the first treatment developed, studied, approved, and labeled specifically for patients with treatment-resistant depression.

Another technology with future potential is the implantable Responsive Neurostimulator (RNS) from NeuroPace Inc., Mountain View, Calif., (neuropace.com). It is supposed to suppress seizures in patients with drug refractory epilepsy. The RNS is implanted under the scalp and connected to one or two wires placed in the brain. RNS constantly monitors the brain's electrical activity over these wires, looking for the onset of seizure activity. If RNS detects activity, it delivers mild electrical stimulation through the wires. The goal is to stop seizure activity before the patient experiences clinical symptoms.

The NeuroBionix division of Quebec City-based Victhom Human Bionics Inc., (victhom.com) is testing a device that treats urinary problems. The implant is in clinical trials and the company hopes to prove the implantable device is an answer to long-term bladder voiding, as well as rehabilitation and stabilization of the bladder. It is designed for individuals with spinal cord injury.

There is also a push for visual prosthesis. Second Sight Medical Products Inc, Sylmar, Calif., (www.2-sight.com) is developing an implantable device that acquires power and data from external hardware and electrically stimulates the retina through an array of electrodes. Simple arrays, used in short-term experiments, have generated vision in patients with retinitis pigmentosa. Further, research conducted by Second Sight shows that more advanced array designs are possible, and these arrays should significantly improve the quality of the images seen by patients.

FES 101

Functional electrical stimulation (FES) applies low-level electrical currents to the body to restore or improve function. A heart pacemaker is one example. Other applications are found in patients who've suffered strokes, spinal-cord injuries, head injuries, or have cerebral palsy or multiple sclerosis.

There are generally three components that make up an FES system: electrodes, stimulator, and sensors. Electrodes are applied to the skin or implanted in the body. Skin surface electrodes are made of a flexible material that conducts electricity to the skin and tissues beneath it. They are widely used in rehabilitating injuries. But surface electrodes only stimulate groups of muscles, not individual ones.

Implanted electrodes selectively stimulate particular muscles. They may be fine wire coils inserted in muscles (intramuscular electrodes), flat metal foils placed against the spinal cord or muscle surfaces (epimysial electrodes), or soft cuffs of rubber and metal foil surrounding nerves (nerve electrodes).

Insulated wires or leads connect electrodes to stimulators. The stimulator sends electrical signals through the leads to the electrodes where the electrical charge is delivered to the nerve, muscle, or other tissue. Most stimulators are external units and can be as small as a calculator or as large as a computer workstation. Usually, stimulators have computer controllers built in. They can have several stimulation channels, each sending pulses to one or more electrodes.

More advanced systems have implanted electrodes and also may have implanted stimulators. Implanted electrodes and their leads can be completely inside the body or the leads may pass through the skin (percutaneous leads) and connect to an external stimulator. The surgery for implanting an FES stimulator is similar to that used in implanting a heart pacemaker. The electrodes are connected to the stimulator inside the body. The stimulator has a built-in radio receiver that receives command signals from an external control unit.

For more FES information

There is a wealth of information available for patients and others interested in FES. Here are a few places to start a search:

The FES Center at Case Western Reserve University: fescenter.case.edu

International Functional Electrical Stimulation Society: ifess.org

International Neuromodulation Society: www.neuromodulation.com

The Alfred E. Mann Institute at the University of Southern California: ami.usc.edu

National Clinical FES Center (UK) www.salisburyfes.com