Purpose
Both repetitive peripheral magnetic stimulation (rPMS) and transcutaneous electrical current stimulation (TES) could elicit the limb movements; it is still unclear how subjective sensation is changed according to the amount of limb movements. We investigated the pain and discomfort induced by newly developed rPMS and TES of peripheral nerves in the dorsal forearm.
Methods
The subjects were 12 healthy adults. The stimulus site was the right dorsal forearm; thus, when stimulated, wrist dorsiflexion was induced. The rPMS was delivered by the new stimulator, Pathleader at 10 stimulus intensity levels, and TES intensity was in 1-mA increments. The duration of each stimulation was 2 s. The analysis parameters were subjective pain and discomfort, measured by a numerical rating scale. The rating scale at corresponding levels of integrated range of movement (iROM) induced by rPMS or TES was compared. The subjective values were analyzed by two-way repeated measures ANOVA with the stimulus conditions (rPMS, TES) and the seven levels of iROM (20–140 ºs).
Results
In the rPMS experiments, stimuli were administered to all subjects at all stimulus intensities. In the TES experiments, none of the subjects dropped out between 1 and 16 mA, but there were dropouts at each of the intensities as follows: 1 subject at 17 mA, 20 mA, 22 mA, 23 mA, 27 mA, 29 mA and 2 subjects at 21 mA, 24 mA, 26 mA. The main effects of the stimulus conditions and iROM were significant for pain and discomfort. Post hoc analysis demonstrated that pain and discomfort in rPMS were significantly lower compared to TES when the iROM was above 60 ºs and 80 ºs, respectively.
Conclusion
New rPMS stimulator, Pathleader, caused less pain and discomfort than TES, but this was only evident when comparatively large joint movements occurred.
Many patients with cerebrovascular diseases and the elderly have difficulty ingesting foods because of dysphagia. We hypothesized that repetitive contraction of the suprahyoid muscles via peripheral nerve magnetic stimulation could lead to recovery of swallowing function. The magnetic stimulation coils currently on the market are problematic because not all tissues around the suprahyoid muscles should be affected during magnetic stimulation, such as the alveolar nerve. The problem is due to the wide area covered by magnetic stimulation. With this factor in mind, we designed and fabricated a coil optimized to provide only a narrow range of stimulation. By adopting use of a magnetic core, we ensured that the coil distributes only a local eddy current during stimulation. We confirmed that the magnetic stimulation using this prototype coil could cause large contractions of the suprahyoid muscles without stimulating the alveolar nerve.
Magnetic pules stimulation was carried out for the peripheral nerve of the forearm of five healthy adults by using the magnetic stimulation device. Dorsiflexion movement of the wrist was measured using a digital goniometer under the following stimulus conditions. Magnetic field strength : 3 stage. Stimulation frequency 10 Hz to 50 Hz. Stimulation time : 0.5 to 2 sec. According to the stimulation conditions, wide range in bending angle of the wrist over 100 degree was observed.
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