Sponsor: Institute of Spinal Cord Injury, Iceland

1) Introduction

2) Respiration & Airway Clearance (Cough)

3) Gastric Clearance & Colon Transfer

4) Bladder Control

5) Deep Vein Thrombosis

Introduction: Because nerves are electromagnetically driven cells, it is not surprising that pulsed magnetic fields can initiate the neuronal propagation of signals to paralysis-affected muscles. Basically, this artificially initiated neural signal can stimulate muscle contractions if activated on a motor nerve.

The use of magnetic fields to promote functional or rehabilitative benefits is called functional magnetic stimulation (FMS). In individuals with SCI, FMS has been used to stimulate breathing, enhance digestion, control urination, speed bodily wastes through the colon, and enhance circulation. (Other electromagnetic SCI applications have been discussed previously).

Similar to functional electrical stimulation (FES) discussed elsewhere, FMS requires that target muscles or organs are innervated (peripheral nerves intact) to affect bodily functions and muscle contractions. Like FES, FMS is applied below the injury level to facilitate functions that have been lost or impaired.

FMS systems consist of three components: a high-current pulse generator, magnetic coil, and power source. FMS pulse generators discharge output currents of 5,000 amps or more with pulse durations usually close to 250 microseconds. This high electrical output requires a powerful energy source. Internal circuitry in the pulse generator includes a storage capacitor that charges up to several thousand volts, control circuitry, and a thyristor - a solid state device able to switch large amounts of electrical current in a few microseconds.

To induce signal propagation, FMS magnetic coils generate field strengths of two Tesla or more, a powerful electromagnetic force (comparable to magnetic resonance imaging, i.e. MRI). The magnetic coil (MC) typically consists of one or more well-insulated copper coils, temperature sensors, and safety switches - all housed in a molded plastic case. Either batteries or fixed electrical sources are used to generate FMS.

Unlike FES, which applies electrical current directly to the skin or nerves through external or implanted electrodes, FMS affects nerve cells through a pulsed magnetic field, which radiates from one or more magnetic coils placed outside the body over target nerves, or nerve roots. This difference between FMS and FES presents benefits and drawbacks.

Benefits include:

1. FMS penetrates tissues, including skin, fat, and bone, reaching peripheral nerves, the spinal cord, spinal nerve roots, the brain, and internal organs without surgery.
2. FMS induces an electric field under the area of application, providing a means for simultaneous stimulation of multiple nerves. [Note: If the functional stimulation of a muscle group is desired this property is beneficial, whereas it can be a drawback if the activation of a specific nerve or muscle is desired.]
3. FMS avoids risks associated with surgically implanted FES electrodes.
4. FMS can be applied over clothing; it does not require direct skin contact.

Drawbacks include:

1. FMS can activate inappropriate nerves that lie within its field, because FMS radiates a magnetic field rather than a focused electrical current.
2. Present FMS systems can be unwieldy.

According to Dr. Vernon Lin (USA), a leading pioneer in FMS for SCI applications, two technical factors have slowed FMS development for widespread home and clinical use – magnetic coil-field dispersion and battery size. However, changes in magnetic coil design are improving the ability to target specific nerves with FMS. Likewise, improvements in battery technology are making portable FMS a possibility for individual use. Although the small market represented by potential FMS users coupled with its present costs are slowing FMS commercial development, Lin believes that FMS will eventually serve multiple SCI applications.

FMS APPLICATIONS FOR SCI

Respiration & Airway Clearance (Cough): FMS breathing assistance may offer benefits superior to those presently gained through FES. Early on, it was shown that a magnetic coil placed over the cervical C7 vertebra stimulates diaphragm-controlling phrenic nerves without surgery. Compared to FES, FMS resulted in higher diaphragm pressures, which researchers believe resulted from the activation of not only the phrenic nerves but also nerves to upper chest-wall muscles.

Dr. Lin’s investigative team examined the effect of FMS in conditioning the muscles used for expiration (i.e. exhalation) in eight subjects with SCI. Of these subjects, seven had cervical injuries ranging between the C5 and C7 level, and one had a thoracic T5 injury. Subject age averaged 51 years, and the time lapsing since injury averaged 18 years. Each subject received a four-week conditioning program consisting of a 20-minute, twice-daily FMS session five times per week. The magnetic coil was placed at the T10-11 level while subjects were sitting in their wheelchairs. This placement stimulates the lower intercostal and abdominal muscles.

Pulmonary functional assessments were carried before, in the middle of, immediately after, and two weeks after the conditioning program. When compared to baseline functioning, FMS treatment resulted in considerable improvement in voluntary expiratory pressure (116%), volume (173%), and flow rate (123%). However, two weeks after conditioning terminated, these improvements receded to preconditioning levels, indicating that persistent stimulation would be required if the patients were to benefit over the long term.

Gastric Clearance & Colon Transfer: SCI can adversely affect the gastrointestinal tract, slowing the movement of solids though the stomach and colon. Signs of a neurogenic bowel include fecal impaction, constipation, abdominal distention, prolonged bowel care, and delayed colonic transit. It has been estimated that 41-86% of individuals with SCI have some of these problems, and 41% spend at least one hour daily on bowel care.

Dr. Lin and associates demonstrated that FMS increases rectal pressures and shortens colon-transfer time in individuals with SCI. This study was divided in two protocols, the first designed to assess FMS’ impact on rectal pressure and the second, FMS’ effect on colonic transit times. In the first protocol, after carrying out preliminary, procedure-establishing experiments in several able-bodied men, the investigators studied nine men with both complete and incomplete injuries, ranging from the C3 cervical to lumbar L1 level.  The MC was placed over the lower abdomen, which tenses abdominal musculature, and then the lumbosacral region, which stimulates colon- and rectum-controlling sacral nerves. With the abdominal stimulation rectal pressure increased 42% and with lumbosacral stimulation, 80%.   

In protocol 2, the colonic transit times were assessed in four individuals with SCI before and after a five-week magnetic-stimulation period. Basically, with these studies, subjects consumed with breakfast on the first three days 20 radiopaque markers (i.e., shows up with x-ray), which are then followed as they transit through the GI system. The five-week FMS program consisted of twice daily 20-minute sessions that increased in intensity over time. After the five-week treatment period, colonic transit time decreased on average from 105 to 89 hours.

In a study published the following year (2002), Lin and colleagues evaluated gastric emptying with and without FMS in five able-bodied men and four subjects with SCI (three men and 1 women). After fasting overnight for 12 hours, all subjects were fed a breakfast that included fried eggs with a radioactive tracer. Subjects laid down face up with a radioactivity detector positioned over the abdomen and the magnetic coil placed underneath at the T9-vertebral level. Thirty minutes of on-off magnetic stimulation was administered. Although FMS enhanced gastric emptying in all subjects, it especially accelerated the process in individuals with SCI. Specifically, in able-bodied subjects, FMS shortened gastric emptying by 8%; in contrast, in individuals with SCI, FMS shortened emptying by 33%. In one subject with SCI, gastric emptying was 38 minutes faster with FMS.   

In a more recent study with more subjects, Dr. Po-Yi Tsai et al (Taiwan) further documented the benefits of FMS to enhance bowel function after SCI. This study recruited 22 patients (19 men; 3 women) averaging 47-years old and who had sustained their injuries on average 39 months earlier. The subjects were divided into subgroups, consisting of those with lower-level and higher-level injuries. This distinction was important because higher and lower level injuries affect bowel-function physiology differently. As such, due to the nerves that are stimulated by FMS, treatment efficacy could conceivably vary considerably.

All subjects underwent a three-week FMS program consisting of twice daily 20-minute sessions. The magnetic coil was placed at the T9 vertebral level for the first 10 minutes and then at the L3 level for 10 minutes. Bowel function was measured before and after the program by 1) assessing colonic transit time through following the progression of ingested radiopaque markers, 2) a questionnaire ascertaining the patients’ impressions of bowel function and health, and 3) telephone follow-up interviews every other week for three months.

After the FMS program, the average colonic transit time decreased from 63 to 50 hours. Improvements in colonic transit were noted in both the higher-injury and lower-injury groups. The before-and-after questionnaire also documented bowel-function improvement. For example, improvements were noted in frequency of laxative use, unsuccessful evacuation attempts, feeling of incomplete defecation, difficulty with evacuation, and time taken.

Bladder Control: Dr. Vernon Lin’s investigative team showed that magnetic stimulation of the sacral nerves could trigger urination in 17 of 22 subjects with SCI. The study found that individuals with reflex or spastic bladders (spontaneously empty as a reflex when filled) responded well to using FMS for bladder control. Reflex bladders most often occur in individuals with higher spinal cord lesions. FMS wasn’t as effective for individuals whose bladders did not empty of their own accord (flaccid bladders). 

Deep Vein Thrombosis: With deep vein thrombosis (DVT), a blood clot forms in a deep vein of the leg, pelvis or occasionally the arm. This clot potentially can dislodge and travel to the lungs, where it can create a life-threatening pulmonary embolism. Overall, the reported incidence of DVT in SCI ranges from 47 to 72%. In the acute phase of injury, the incidence is 13.6%, with risk dropping about 20 days after the injury. DVT is more common in patients with paraplegia and in those with complete injuries.

Dr. Vernon Lin, Dr. Ian Hsiao and colleagues evaluated the effect of stimulating leg muscles with FMS on the break down of the blood-clotting protein fibrin (i.e., a process called fibronolysis). In the clotting process, fibrin molecules combine to form long strands that enmesh platelets, gradually forming a mass that hardens into a clot. Specifically, the researchers analyzed fibronolysis before and after 60 minutes of FMS-induced leg contractions in 22 patients with SCI. The idea behind the research is that promoting fibrin breakdown should lessen DVT risk. The investigators concluded from the results that FMS produces “a sustained enhancement of systemic fibronolysis that may prove useful in DVT” prevention.