What is Functional Electrical Stimulation?
Functional electrical stimulation (FES) can be applied to a wide variety of research and treatment approaches. Frequently asked questions about FES include: What is FES? How can FES help me? Will FES help me to walk again? FES is the most important application in the field of clinical treatment with currents or magnetism. This technique artificially generates neural activity in order to overcome lost functions of paralyzed, incontinent or sensory impaired persons. The term “functional electrical stimulation” can be used to describe a variety of therapeutic techniques and experimental treatment approaches. For example, scientists and physicians have developed a device called a cochlear implant for the ear that enables individuals with sensorineural deafness to hear certain kinds of sounds, and thus interpret the spoken word. Phrenic nerve stimulators are implanted devices that help people breathe without a respirator. Men with spinal cord injury who experience sexual dysfunction can, using a FES technique, induce ejaculation. Some researchers are using electrical stimulation to assist paralyzed individuals regain control of lost bladder function.
One important and promising area of FES research involves restoring function to a parson’s paralyzed arms and legs. First demonstrated as a possible treatment by Adrian Kantrowitz in 1960, it is currently being researched in depth by investigators throughout the world.
FES for Walking
Kantrowitz attached electrodes to the skin of a person with Paraplegia and applied electrical currents to stimulate the parson’s muscles. This technique enabled the person to walk several steps. Building upon Kantrowitz’s early work, other research groups began to develop systems designed to help people with paralysis walk again. Similar investigations are taking place in countries across the world. In the U.S., some of the sites researching FES include: Rancho Los Amigos Hospital in California, Case Western Reserve University in Ohio, Louisiana State University in Louisiana, The Miami Project in Florida, Pritzker Institute in Illinois, and the Shriners Hospital in Pennsylvania.
The task of attaching electrodes to the skin and obtaining movement from underlying muscles is not exceptionally difficult and has been achieved by all research groups investigating FES. The challenge lies in using FES to develop a practical, safe, and workable system for an individual’s daily use.
There are many facets to the problem. For example, it is not enough to just stimulate muscles to move; they must be stimulated at the correct time and in proper combination with other muscles in order to create the motions of actual Ambulation (walking). Although walking appears to be a simple process of placing one foot ahead of the other, it is actually a complex process involving many different muscles that must be precisely coordinated to allow someone to walk smoothly and correctly.
Researchers have addressed this problem by developing intricate computer programs that attached to the electrodes that stimulate the muscles. They have found that walking is a very individualized process requiring unique adjustments for every person.
Another challenge in terms of a practical application is the amount of energy required to ambulate with FES. To date, it still requires considerably more energy to walk using FES than to propel a wheelchair. Most individuals involved in FES ambulation research are highly motivated to walk again and are willing to use the extra energy required to participate in these important studies; however, FES-assisted walking will not be a practical alternative for individuals in the community until the amount of energy required to ambulate has been significantly reduced.
Motivation is required, but stamina is the key in FES ambulation
Ambulation on legs that are completely paralyzed or have severely reduced function and sensation is also complicated by the lack of sensory feedback that one usually gets when walking. In a research Environment such as a hospital corridor, the path is flat, clear and predictable. On a sidewalk, however, a small dent, a large pothole or an unseen pebble can wreak havoc on a computer program that does not recognize such obstacles.
Thus, a current area of research is focused on developing sensory feedback systems to alert the user of obstacles and to allow the computer program to compensate for them.
A truly workable FES system for everyday use must be relatively easy to use. Presently, participants in the ambulatory research projects use one of two types of systems. Some research groups use external electrodes that must be attached to the skin in the right places each and every time the system is used. There is a concern that this kind of system might be so inconvenient it would discourage long-term, daily use. The main advantage of this system is that it is “non-invasive” and therefore, does not require surgery in order to use it. Other investigators are exploring the use of implanted electrodes. The advantage of an implanted system is that the individual does not need to reattach the ambulation system every day. The wires, electrodes and other parts of the system are less inconvenient and also have less chance of being damaged.
Researchers have also developed hybrid FES systems. One such system combines electrical stimulation with the Reciprocating Gait Orthosis (RGO). An RGO is a full hi/knee/ankle/foot brace that uses locks and springs and forward momentum to produce reciprocal (one leg in front of the other) walking. When the RGO is combined with FES, the amount of energy required to walk is greatly reduced. This hybrid system also provides increased stability.
Developments such as those described here are promising. Nevertheless, it is important for individuals interested in using these devices for ambulation to remember that they are designed to enhance standing and exercise programs, not for general use in the community.
FES for Upper Extremity Function
People with a SCI at the Cervical level often have sharply reduced finger, hand, wrist, and/or arm function, depending upon the level and severity of their injuries. For someone with a C-5/6 injury, this reduced function can mean dependence upon others for many activities of daily living. Although FES cannot reverse the effects of a SCI, it has the potential to provide increased levels of function for people with Quadriplegia.
Researchers at Case Western Reserve University in Cleveland, Ohio have developed a stimulation program for the upper extremities that allows people with quadriplegia to regain enough hand and arm function to hold a sandwich and feed themselves. As a general rule, FES for upper extremities may provide the user with one additional Neurological Level of function. In other words, someone with an injury at the C-5/6 level may be able to function at a C-6/7 level with the use of FES.
Most people with SCI have reduced bladder control requiring the use of either an external or internal Catheter. Research is currently being done to develop a system using electrical stimulation to control urination or “voiding.”
A technique that has resulted in reliable, long-term restoration of bladder function involves implanting electrodes on the nerve roots that cause contraction of the bladder and bowel. One problem that exists with this type of implant stimulation is that it also causes the sphincter muscle to contract, thus restricting the expulsion of urine. Some researchers have solved this problem by cutting some of the nerves that supply the sphincter muscle. Other investigators are using electrical stimulation in short bursts to counteract this problem. At the end of each electrical burst, the sphincter muscle relaxes rapidly, while the bladder muscle relaxes slowly, creating sufficient pressure to expel urine. Repeating the bursts for about a minute effectively empties the bladder.
These procedures are being tested on people in the United States under an Investigational Device Exemption. It is hoped that the FDA may approve these devices and become commercially available in the US within this decade. Some commercial devices are currently available in
Another important application of FES is in the area of reproductive function. Because many men with SCI cannot get an erection and/or ejaculate, they have been unable to father children after their injuries. For these individuals, the use of electrical stimulation to induce ejaculation provides a very real and promising avenue.
Fertility clinics have reported limited success with electro-ejaculation. Some experts claim that a couple is just as likely to achieve the same results through sexual intercourse. Nevertheless, this is an area of research that appears to provide promise to many couples who would like to have children.
An important consideration in the use of FES for motor control is getting one’s muscles back in shape after months or years of non-use. Once a SCI has occurred, the muscles below the level of injury generally Atrophy and circulation becomes impaired due to inactivity. Many people also have problems with Osteoporosis, or brittle bones. Consequently, if one intends to use FES to stand or walk on paralyzed limbs, it is necessary to recondition the body and get it accustomed to the use of external stimulation.
One widely used exercise system is currently available commercially through Sinties Scientific in Tulsa, OK, which manufactures and sells a relatively inexpensive FES bicycle for home use. This device coordinates leg and arm movement to activate cycling. It is hoped that the use of an FES bicycle may reduce the number of medical complications resulting from immobilization and inactivity and lead to an improved and healthier lifestyle.
To address these areas, researchers at Wright State University in Dayton Ohio developed an exercise bicycle for use by SCI research subjects. With external electrodes attached to the appropriate muscles on their legs, these individuals “rode” the bicycle both to condition their bodies and to assist researchers in learning more about what kinds of stimulation were most effective in creating certain movements.
Therapeutic Alliances, Inc. produces and markets a FES cycling device for therapeutic use, the ERGYS, based on the Wright State University research. The product, described as a leg cycle ergometer, has been found effective for home and clinical use. The ERGYS employs computer controlled electrical impulses to the leg muscles thereby stimulating cycling movement. Therapeutic Alliances is located in Fairborn, OH.
Because of all the publicity that has surrounded the concept of functional electrical stimulation, it is important to realize a FES exercise program is a separate and distinct activity from FES for improved motor control or any other continuous application of electrical stimulation. Clinical studies have indicated that users of FES bicycles have been able to increase and maintain muscle mass, tone and cardiovascular fitness. The studies have also indicated that regular participation in a FES exercise program may improve immune functioning.
It is important to be aware that such machines are potentially dangerous if not used correctly. Additionally, not all people are appropriate candidates for a FES exercise program. Individuals interested in exercising with FES equipment should be evaluated by a physician specializing in SCI and should undergo an exercise program under the supervision of a clinician with expertise in the area of FES and paralysis.
Many clinical settings currently use FES exercise systems with what they consider to be positive results. Individuals interested in participating in such an exercise program may wish to contact the FES Information Center to obtain information about FES programs in their community.
FES clearly has many possible applications. When reading about FES or hearing about a program in which it is used, it is important to understand what kind of FES is being used and whether the program at the facility is a research project, a regular clinical offering, or a combination of both.
Factors to Consider
It must be recognized that all FES programs may not be appropriate for all people with SCI. Researchers and clinicians currently working on FES systems are attempting to develop criteria to determine for whom FES will be most successful. Some levels of injury, for example, are more adaptable to stimulation than others, and some personality types are more likely to have success with the system as well.