Program Probes Causes, Aids for Arm Tremor


A device to help people with tremor of the arm feed themselves, write, and do other desk-top functions is one of several projects in a large program on tremor in the Department of Mechanical Engineering.

So far the device-called the CEDO, for controlled energy dissipating orthosis-"does seem to suppress tremor," said Allison S. Arnold, a graduate student who is one of the designers of the CEDO and ran clinical trials on it in January with six patients from the Burke Rehabilitation Center in White Plains, N.Y., and six able-bodied controls.

"In the most severe cases, we saw a reduction in tremor of 80 to 85 percent," Ms. Arnold said.

About one million people in the United States suffer from tremor of the arm associated with some head injuries and degenerative diseases like multiple sclerosis. Of those, a large proportion are disabled by "intention" tremor, or tremor that occurs when a person attempts to do a specific task (as opposed to "resting" tremor, seen with Parkinson's disease, where the limb shakes when not in use, or "postural" tremor, which occurs when a person can't hold his or her arm in a steady position).

The MIT program focuses on persons who suffer from intention tremor because "those are the people most disabled by tremor," Ms. Arnold explained.

Currently tremor is treated with drugs to control the unwanted movement, with mixed results. There are no mechanical devices on the market to reduce tremor enough to permit independence in everyday activities.

On a more basic level, doctors still need to know more about the physiological mechanisms that cause tremor. As a result, clinicians often have a hard time classifying people with tremor and prescribing drugs for them.

In the MIT program, led by Principal Research Scientist Michael J. Rosen, mechanical engineers are addressing these problems.

It all began in the mid 1970s when Dr. Rosen was a researcher at the Veterans Hospital in Miami. "I met a patient there with a head injury whose hand shook violently," he said, "so I suggested we try mounting a shock absorber across his wrist [to decrease the movement]-and it worked."

In 1975 Dr. Rosen brought his interest in pathological tremor to MIT and what is now the Eric P. and Evelyn E. Newman Laboratory for Biomechanics and Human Rehabilitation, where he and his students in mechanical engineering have been studying the disability ever since.

"It is a fascinating engineering problem in that, for one, whenever you see a system that oscillates-whether in a machine or a living organism-the analytical tools of engineering seem appropriate to use to figure out why that system oscillates," Dr. Rosen said. Or, put another way, "Here's something that shakes, it shouldn't, so what's going on?"

His group's other motivation comes from the conviction that in addition to using engineering to find out what causes tremor, they can use engineering "to do something about it."

As a result the tremor program covers three general areas: the development of devices like the CEDO to help people debilitated by tremor, the development of techniques to better diagnose and classify tremor, and basic research to understand the physical mechanisms that cause tremor.

Dr. Rosen notes that although he is the overall supervisor for the program, "students do virtually all the technical work and are major contributors to the creative effort." The whole Newman Lab, he said, is run that way. The lab is directed by Robert W. Mann, Whitaker Professor of Biomedical Engineering.

The CEDO, on which a US patent is pending, works by mechanically damping, or adding resistance, to the arm. The device is roughly analogous to the shock absorber on a car or the little cylinder that prevents a screen door from slamming.

Specifically, a user puts his or her forearm in a splint attached to a mechanism that allows movement sideways, forward, and backward, as well as up and down. The mechanism is mounted on the back of the wheelchair the user is sitting in and includes potentiometers to measure the position of the person's arm, a computer, an electronics box, and three magnetic particle brakes.

In general, then, the system works in the following way. The potentiometers send position signals to the electronics, which determine how fast the arm is moving. That information goes to the computer, which controls the brakes to produce the correct resistance to damp the excess motion.

When the CEDO is on, the user gets the overall feeling of "moving your arm through molasses," Ms. Arnold said.

Ms. Arnold has done a number of experiments to test the CEDO. For example, she explained, "we can adjust the damping to determine how much is necessary to reduce tremor without reducing intended movement."

Currently the researchers are planning a refined version of the CEDO, the CEDO-2, which would be attached to a desk top rather than a wheelchair. Dr. Rosen estimates that the CEDO-2 could be available commercially in three years for a cost of about $2-3,000 per unit.

Two other devices to help people with tremor have also been developed through the Newman Lab. Graduate student Jack Kotovsky is currently working on a device that suppresses tremor at the wrist joint. It is the tremor program's first wearable device, fitting under the user's sleeve.

The second device is a joystick for powered wheelchairs. Unlike conventional joysticks, however, this one uses damping to allow people with MS, for example, to control the movement of their hand and so control the movement of their wheelchair with greater accuracy.

The amount of damping is externally adjustable-joystick handles are interchangeable for different people depending on the characteristics of their grip. As an example, for people with no grip strength the joystick might be attached to the user's arm by means of a lightweight splint.

Dr. Rosen notes that MIT holds two patents on the joystick. One is for its use with a wheelchair, but the other is for use of an extended design with helicopters, rough-terrain vehicles, "or anything else where vibrations could make the arm of an able-bodied person slew around."

Another major part of the tremor program is the development of diagnostic techniques. Although clinicians know what kinds of diseases or injuries can lead to tremor, they don't know the specifics of what's going on in the nervous system and muscles to produce it. As a result, they "have a hard time classifying people into groups and prescribing drugs for them," Ms. Arnold said. Currently they "try one drug, and if that doesn't work, they try another."

In the diagnostic part of the program doctoral candidate Karen I. Palmer is developing a machine to measure tremor quantitatively. (This work, like that on the CEDO, expands on work by earlier graduate students.) Specifically, Ms. Palmer is recording tremor frequency and amplitude, or how fast and how large the movements are.

Most importantly, her system also monitors what happens to these variables when different loads are applied by the machine to the arm of a person with tremor. Theoretically, the results will reveal the physiological causes of the person's tremor.

Ultimately the researchers hope to use these measurements to "provide a road map from a particular type of tremor to selection of a particular drug, or to a decision that no drugs will work," Ms. Arnold said. For example, she explained, "if you have a group of people who react the same way to a particular load, and you know that one drug helps them, then if someone new comes in and responds the same way to the load you can better predict that [he or she] would react favorably to the same drug."

Underlying the entire program is basic research: what causes tremor? What are the physiological mechanisms? To that end Chen-An Chen is studying how tremors in different segments of the arm are related, and Jeffrey N. Snyder is developing a computer model of the anatomy of the human arm to understand what might go wrong to produce tremor. Both Mr. Chen and Mr. Snyder are graduate students.

The program has been funded by four organizations: the Burke Rehabilitation Center, the National Institute on Disability and Rehabilitation Research, the Department of Veterans Affairs, and the National Institutes of Health. Dr. Rosen also acknowledges support from MIT's Undergraduate Research Opportunities Program.

The funding from the Burke Rehabilitation Center grew from a special contact there: Mindy Lipson-Aisen, MD, who received the SB in mechanical engineering from MIT in 1976 and is currently Chief of the Spinal Cord Injury Service at Burke.

A version of this
article appeared in the
April 29, 1992

issue of MIT Tech Talk (Volume
36, Number
28).


Topics: Mechanical engineering

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