Our center in Cleveland is focused on restoring function through the use of electrical stimulation, working to develop this technology that can improve the quality of life of individuals with disability, and to move that technology out into clinical deployment. While the Center has not focused on Multiple Sclerosis in its current research, the very action of preparing for this meeting has initiated the discussion.
We can, certainly, generate action potentials in peripheral nerve fibers. The question of interest is whether we can create action potential that will propagate either antidromically or orthdromically, as well as in both directions. The possibility of doing unidirectional propagation of action potentials provides an important tool, for example, in creating collision blocks with spastic abhorrent impulses that will collide with the unidirectionally generated action potential from the electrical stimulation. We can also selectively activate fibers of various sizes, and discriminate to some extent, for example, between the motor and sensory fibers.
We can also alter the metabolic and physiological properties of the muscles so that we can hypertrophy fibers. We can change contraction times. We can change the fatigability by the patterns of electrical excoriation that we induce. So we have electronic access to a nice plastic system that we can modify for both functional purposes. Finally, we can do this safely over long periods of time.
So we have some tools and much of our research has been focused on developing these tools. Those that have been coming into clinical utilization have been primarily oriented for people with spinal cord injury (SCI). Most have had complete injuries, although some work has been done with incomplete injuries. We have also had some success in activating lower limbs paralyzed as a result of stroke or head injury.
There has been some activity in applying FES techniques to assisting the MS population. Many appear to have been in the area of urological control which will be covered by Dr. Creasey's talk. There has been some work in the area of pain and spasticity management, some in movement restoration, and some in movement disorders. However, there does not appear to have been a concentrated effort for this population.
Some of the ways we might think about utilizing FES tools would include the following. For contracture, perhaps activating the antagonist muscles to mobilize joints in a more automated way might reduce the need for some of the therapeutic techniques presently employed. The focus on the urinary tract and bladder management has promise. Spasticity reduction would be a good target. One area of study would be the notion of collision blocking to annihilate impulses. Neutralizing naturally generated impulses by generating counter impulses artificially is, we think, a tool that has applicability, not only to MS, but to strokes and some of the upper-extremity problems. FES may also be useful in preventing skin breakdown.
In the area of fatigability, we might be able to hypertrophy some of the weak musculature and enhance the overall maximal voluntary capabilities, or modify the muscles to have a greater endurance. So that by using weight-supported walking and its analogues, we can perhaps change structure. Clearly, weight-supported walking is something that could be automated by FES, rather than having two therapists pulling on the legs. The techniques and the control provided in automated ways, through some of the tools currently existing in neuroprosthetic interventions, are relatively or directly translatable.
However, there are issues that we should not push under the carpet. One of them is pain, and there are some approaches to this that we have investigated. For example, with surface stimulation, there is a way of increasing what we call the dynamic range—the difference between the level of threshold activation for sensation and that where the patient reports pain. This technique is called the depolarizing pre-pulse. We have utilized indwelling electrodes extensively in developing neuroprosthetic techniques. We use them in therapeutic interventions as well and they may also be useful for blocking neuroactivity. There will be a lot of work on fundamental design and modeling of interfaces and exitation. Much work has already gone through animal trials and long-term activation, but some of the implanted pulse generators or stimulators need circuit revision. We need to look at ways of detecting these aberrant activities and directing responses to them.
Bladder management presents special problems of the reversibility and progression of the disease and the particular need to focus not only on activation, but also being able to deactivate the fibers. That is Graham Creasey's area and I will let him handle it.
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