Life on Wheels (80 page)

Dr. Amy MacDermott of Columbia University is looking into the “selective excitotoxic death of GABAergic dorsal horn neurons.” Some people with SCIs become extremely sensitive to touch, which is often painful. Dr. MacDermott feels that there is a chemical process that overstimulates sensory nerves, and she hopes to develop a pharmaceutical treatment to minimize pain from this cause.

Dr. James Guest, when completing his doctoral dissertation at the Miami Project, demonstrated that human Schwann cells support regeneration and myelination in adult rat spinal cords.

Jian Zhou, PhD, of the University of Texas at Dallas addresses the “structural analysis of neurotrophin receptor signaling in neurons.” This work intends to better describe the process of how signals are delivered through nerves by neurotrophins, which also support the nourishment and growth of nerves.

Reading these newsletters can leave you wondering how all these detailed studies fit together. They don’t. There is intentional overlap, and various solutions are being explored for any given piece of the puzzle. One finding might shed light on another, or certain projects may suddenly add up to a solution that hadn’t been considered (just as the discovery of penicillin was an “accident”).

There seems to be more cause than ever to hope for some answers that will make a difference in the daily life of people with CNS disabilities. Hundreds of brilliant, highly educated, and highly trained people are working hard, and it is difficult to imagine that they won’t make a difference in our life on wheels.

There has been a great deal of emphasis on spinal cord research here, but SCI research will benefit people with other disabilities, such as spinal muscular atrophy, stroke, traumatic brain injury, multiple sclerosis, Guillan-Barré syndrome, myasthenia gravis, and Alzheimer’s and Parkinson’s diseases. Elderly people with severe osteoarthritis can suffer the degradation of the spinal column itself, which can ultimately impact the cord. There are dozens of vascular, neurodegenerative, and congenital diseases that impact the spinal cord. Spinal cord tumors can occur in cases of metastasized breast or prostate cancer. People affected by all these conditions can benefit from this research.

When combined, people with these conditions far outnumber those with traumatic SCI. But SCI happens more commonly to young people, whereas these other conditions often appear later in life. Older people with other conditions will become wheelchair users. But their survival is often short, for example, once a cancer has spread, whereas a young person with a spinal injury is likely to live a normal life span. That difference in longevity makes the longterm costs of SCI greater, cold as that might sound. The fact is that there are plenty of forms of human suffering, all with their advocates and scientists clamoring for money from the same corporate and government sources. The fact that young people are being injured with a lifetime ahead of them is part of what justifies the amount of work done on spinal cord research. Fortunately, many others will get the chance to benefit.

The first “cure” effort to get wide public exposure involved simulating walking by using electrical impulses to make muscles contract. In 1970, scientists at the Rancho Los Amigos Hospital near Los Angeles and another group in what was then Yugoslavia got a person with paraplegia standing up with this approach, known as functional neuromuscular stimulation

(FNS). In 1973, a test subject at the University of Virginia walked 40 feet, and a Vienna project got two people walking as far as 100 meters using crutches. In the United States, Dr. Jerold Petrofsky was a key player at Wright State University in Ohio and now leads the Petrofsky Institute, where FNS is featured.

FNS is a subset of FES, which is used in many other applications in which electrical impulse devices are used in places other than the muscles. A heart pacemaker is an example of FES, using electrical stimulation to balance the beating of the heart. FES is used for pain management and hearing enhancement and as an aid to male ejaculation, muscle strengthening, wound healing, and scoliosis correction. These uses are already accepted practice, and many other applications are either at the basic research level or as far advanced as clinical trials.

As with much “cure” research, FNS for standing and gait control has been overdramatized by the media. As a walking device, it is still at a very early stage, and its use is limited to a narrow population of qualified, potential users. Even with the increasingly small size of electrodes and the superfast processing speed of computer chips, walking with this technology is not at all like using healthy muscles. It is very exhausting, although participants in trials have shown improvements with hard work and regular therapy and practice.

Yet, researchers have accomplished a great deal, including subjects who have been able to walk up and down stairs using only the handrail. Some have gotten far enough to use it for brief walking tasks such as walking down the aisle at their own wedding. Several current projects are designed to achieve hands-free standing.

This is all meaningful progress, but FNS for walking still has a way to go before it is a valid alternative to wheeling. Researchers at the Ontario Neurotrauma Foundation are speculating that FES-assisted walking could have secondary health benefits. Their study, initiated in April 2005, is comparing the incidence of urinary tract infections, pressure sores, and spasticity in people doing walking compared with those doing aerobic exercise and resistance training. The study will be completed in April 2009.

How a muscle is normally stimulated in the body is a very complex sequence of events. Muscle stimulation is not simply a matter of how much electricity to send to which part of a muscle. This is a very detailed matter of how the impulse intensity rises and drops and the maintenance of the impulse during a contraction.

The body, it turns out, does not simply send a continuous stream of electricity to the muscle but, rather, a stream of pulses. A continuous current quickly exhausts a muscle. Muscles also have different roles to play. Some are for posture, and some are for movement, each displaying very different electrical profiles. Matching the natural pattern of stimulation is one of the key challenges of FNS for walking, so that such a system can be used productively without overstimulation of the muscles. The system must mimic the body’s miraculous design, which makes the most efficient use of its muscles to minimize fatigue.

Walking involves thousands of simultaneous signals going back and forth between muscles and the brain, a tremendously intricate coordination of sensations and contractions. The most sophisticated systems presently use only 50 electrodes, though that number is sure to grow. At present, the only possible stimulus is to make the muscle contract—the users get no sensory feedback to know where their muscles are.

Electronics is one half of the system; the other half is bracing. In the past, some people were fitted with heavy leg braces, which only added to the weight that they had to balance, lift, and propel using crutches. This load made more work for the electronics, too, so part of the effort has been to develop lightweight bracing. The development of the reciprocating gait orthotic has been helpful thanks to its more lightweight design.

People who have been research subjects with early systems have been concerned with appearance. Most people don’t want to go out in public all wired up and braced in a way that attracts unwanted attention. Lightweight braces and small power and control devices that can be worn under the clothes are being developed to make FNS more practical and desirable.

There are several methods of stimulating the muscles. Some designs use tight-fitting, stretchable pants that contain the electrodes. This is the most discrete method, but placing electrodes on the surface of the skin is the least effective way of getting the signal to the muscle. The signal has to pass through layers of skin and fat. This approach has the disadvantage of stimulating muscles in groups, with much less individual control. There is also some risk of irritating or burning the skin with the stronger current it takes to reach through the skin to the muscles.

The alternative to electrodes on the skin is to implant electrodes directly into the body, so they can contract specific muscles. Electrodes are either sewn to the surface of the muscle or a cuff design is wrapped around the tissue. Another type is implanted deep into the muscle and can be inserted by a modified hypodermic needle without the use of a surgical incision. Implants bring with them the risk of infection and can break or slip out of position.

Implantable electrodes have become remarkably small, can operate without attachment of actual wires through the skin, and can even have their batteries recharged from the outside using a remote device. The BION® Microstimulator was developed at the Alfred E. Mann Foundation at the University of Southern California and was still in clinical trials as of 2008. As described by Jennifer French, a neurotechnology advocate—and user:

In 1997, the FDA approved the Parastep System, produced by Sigmedics of Northfield, Illinois (www.sigmedics.com) and originally developed at the

University of Illinois Medical School and the Michael Reese Hospital and Medical Center in Chicago. The user of Parastep operates controls on a walker, with buttons for sitting, standing, movement of the left and right legs, and intensity of the contractions. The Parastep System uses 12 externally applied electrodes. A small number of people are using the system with Lofstrand crutches—the type with the forearm loop. They use more of a swing-through gait, rather than the individual stepping that would be seen using a walker.

Parastep users like John Targowski, a student at the University of Michigan, report a variety of benefits. John values the increased muscle bulk from electrically stimulated contractions:

FES/FNS is sometimes promoted as a replacement for a wheelchair. It is a limited option, requires a lot of effort to use it, and still has a lot of development work left to increase its usefulness. It also should not be thought of just in terms of walking. Standing, in and of itself, is valuable for preventing bone loss and to promote circulation. For many people, it is a great psychological boost to be able to stand. Some systems are geared toward assisting in transfers from a bed, wheelchair, bath, commode, chair, or sofa. Others use FES for increasing muscle tone alone, which wards off atrophy. This can mean wearing shorts without self-consciousness in public or protection from pressure sores thanks to the cushioning value of muscle tissue. Again, just as with spinal cord regeneration research, you should not be excessively caught up in the image of walking again.

In 1997, NeuroControl Corporation gained FDA approval for its Freehand™ System, an implantable FNS device to provide a grasping and pinch grip for people with C5/C6 quadriplegia. Implantation of the device involved a surgical procedure, significant rehabilitation, and a 12-week period of increased impairment until the benefits were fully realized. Because of the limited size of the market for this device, and a degree of reluctance on the part of the surgeons to implant an electrical device, NeuroControl has taken itself out of the spinal cord market.