People who have suffered paralyzing injuries sometimes can regain limited control of their muscles, thanks to electrical stimulation techniques now under development, but pulse patterns should be varied to help patients stay strong longer, University of Delaware researchers report in the new Journal of Neurophysiology.
This finding, described in the journal's April 1998 issue, may suggest a better way to stimulate the muscles of people with paralysis, says Stuart A. Binder-Macleod, associate chairperson of UD's Department of Physical Therapy, a top 10 national program, according to U.S. News & World Report.
"Patients can move their muscles much more forcefully for a longer period of time if their muscles are stimulated at varying rather than regular intervals," Binder-Macleod says. "This study is the first to show the effectiveness of a variable pulse pattern, and it's very exciting."
For people like "Superman" actor Christopher Reeve, who in 1995 broke several upper cervical vertebrae in a Virginia steeplechase accident, the prognosis traditionally has been poor, Binder-Macleod notes. Unfortunately, he says, such devastating accidents are not uncommon. Binder-Macleod and his UD colleagues say they hope that such tragedies someday can be reversed--at least in part--through artificial stimulation of skeletal muscles.
But first, he says, researchers must find a way to maintain the strength of artificially stimulated muscles, which tend to become progressively fatigued in response to small electrical shocks.
Mimicking the central nervous system
"When a person's central nervous system 'turns on' a muscle, it uses an irregular pattern of pulses during activation," says Binder-Macleod, whose research team included doctoral student Samuel C.K. Lee and undergraduates April D. Fritz and Lorin J. Kucharski. "A similarly varied pulse pattern may prove useful in clinical applications of electrical stimulation to a wide range of patients."
To test the effectiveness of different pulse patterns, the UD researchers asked volunteers to sit in a chair-like device called a dynamometer, which measures muscle force. Volunteers were then instructed to "straighten out their knees as hard as they could," using the quadriceps femoris muscles on the front of their thighs, Binder-Macleod says. After the volunteers relaxed, their muscles were artificially stimulated to respond with about 20 percent of the force they were able to exert naturally.
"We used a range of frequencies, going from 8 pulses per second to 100 pulses per second, and we used variable frequency 'trains,' or sets of pulses, with some closer together than others," Binder-Macleod explains. "Then we looked at the force produced in response to these different pulse patterns." The most effective pulse pattern was a variable frequency train, which allowed the volunteers to move their muscles 25 percent to 35 percent more forcefully, compared to more traditional, consistent stimulation.
Doctors and physical therapists use electrical-stimulation techniques to treat patients with various disabilities. The pacemaker, for example, is a now-common strategy for correcting an irregular heartbeat. In addition, Binder-Macleod says, "physical therapists use electrical stimulation to improve the performance of muscles in people with central-nervous-system problems--such as a foot that drags following a stroke. You can put on an ankle brace, or you can stimulate the foot so that it lifts up when the patient walks." Pulse patterns typically range from 20 to 40 pulses per second.
Unfortunately, he adds, muscles "get tired more easily when you activate them artificially." And, researchers still are "a very long way from getting someone with severe paralysis to stand up and walk again," Binder-Macleod emphasizes. Stimulating many large muscle groups to move together smoothly is a highly complex problem, he notes. But, the new UD study shows promise for providing patients with a greater degree of control, he says. Binder-Macleod's research is supported by a five-year, $500,000 grant from the National Institutes of Health.
With six faculty members, the graduate UD physical therapy program currently serves 80 students pursuing master's degrees and eight doctoral candidates. Doctoral students are part of the Interdisciplinary Biomechanics and Movements Sciences graduate program, a collaborative effort involving many UD departments and the Applied Science and Engineering Laboratory, a cooperative effort of the University and the Alfred I. Du Pont Children's Hospital. March 31, 1998
Materials provided by University Of Delaware. Note: Content may be edited for style and length.
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