Hyoid Bone Movement at Rest by Peripheral Magnetic Stimulation of Suprahyoid Muscles in Normal Individuals

Repetitive peripheral magnetic stimulation for preventing shoulder subluxation after stroke: a randomized controlled trial

BACKGROUND

Shoulder subluxation caused by paralysis after stroke is a serious issue affecting shoulder pain and functional prognosis. However, its preventive treatment has not been fully investigated.

AIM

To investigate the effects of repetitive peripheral magnetic stimulation (rPMS) on the prevention of shoulder subluxation.

DESIGN

A single-center, parallel-group, prospective randomized, open-blinded, end-point study.

SETTING

Convalescent rehabilitation ward.

POPULATION

We included 50 inpatients in the convalescent rehabilitation ward with post-stroke, having upper limb paralysis, and the acromio-humeral interval (AHI) was within 1/2 finger-breadth.

METHODS

A blinded computer-based allocation system was used to randomly assign patients into two groups: 1) conventional rehabilitation plus rPMS therapy (rPMS group, N=25); and 2) conventional rehabilitation alone (control group, N=25). Blinded assessors evaluated the patients before the intervention (T0), 6 weeks after (T1), and 12 weeks after (T2). The primary outcome was the change in AHIs from T0 to T1 between the groups. In contrast, the secondary outcomes were shoulder pain, spasticity, active range of motion, and Fugl-Meyer Assessment upper extremity (FMA-UE) score.

RESULTS

Twenty-two patients in the rPMS group and 24 in the control group completed T1, whereas 16 in the rPMS group and 11 in the control group completed T2. The change in AHI was significantly lower in the rPMS group than in the control group ([95% CI, -5.15 to -0.390], P=0.023). Within-group analysis showed that AHI in the rPMS group did not change significantly, whereas it increased in the control group (P=0.004). There were no significant differences between T1 and T2 within or between the groups. Moreover, AHI did not show differences in patients with severe impairment but decreased in the rPMS group in patients with mild impairment (P=0.001).

CONCLUSIONS

The rPMS may be a new modality for preventing shoulder subluxation. The association between motor impairment and the sustained effect needs to be further examined.

CLINICAL REHABILITATION IMPACT

Applying rPMS to the muscles of the paralyzed shoulder after a stroke may prevent shoulder subluxation.

A study of flex miniaturized coils for focal nerve magnetic stimulation

BACKGROUND

Peripheral magnetic stimulation (PMS) is emerging as a complement to standard electrical stimulation (ES) of the peripheral nervous system (PNS). PMS may stimulate sensory and motor nerve fibers without the discomfort associated with the ES used for standard nerve conduction studies. The PMS coils are the same ones used in transcranial magnetic stimulation (TMS) and lack focality and selectiveness in the stimulation.

PURPOSE

This study presents a novel coil for PMS, developed using Flexible technologies, and characterized by reduced dimensions for a precise and controlled targeting of peripheral nerves.

METHODS

We performed hybrid electromagnetic (EM) and electrophysiological simulations to study the EM exposure induced by a novel miniaturized coil (or mcoil) in and around the radial nerve of the neuro-functionalized virtual human body model Yoon-Sun, and to estimate the current threshold to induce magnetic stimulation (MS) of the radial nerve. Eleven healthy subjects were studied with the mcoil, which consisted of two 15 mm diameter coils in a figure-of-eight configuration, each with a hundred turns of a 25 μm copper-clad four-layer foil. Sensory nerve action potentials (SNAPs) were measured in each subject using two electrodes and compared with those obtained from standard ES. The SNAPs conduction velocities were estimated as a performance metric.

RESULTS

The induced electric field was estimated numerically to peak at a maximum intensity of 39 V/m underneath the mcoil fed by 70 A currents. In such conditions, the electrophysiological simulations suggested that the mcoil elicits SNAPs originating at 7 mm from the center of the mcoil. Furthermore, the numerically estimated latencies and waveforms agreed with those obtained during the PMS experiments on healthy subjects, confirming the ability of the mcoil to stimulate the radial nerve sensory fibers.

CONCLUSION

Hybrid EM-electrophysiological simulations assisted the development of a miniaturized coil with a small diameter and a high number of turns using flexible electronics. The numerical dosimetric analysis predicted the threshold current amplitudes required for a suprathreshold peripheral nerve sensory stimulation, which was experimentally confirmed. The developed and now validated computational pipeline will be used to improve the performances (e.g., focality and minimal currents) of new generations of mcoil designs.

Effect of Peripheral Magnetic Stimulation for Dysphagia Rehabilitation: A Systematic Review

Recently, a therapeutic method to stimulate the suprahyoid muscle using peripheral magnetic stimulation for dysphagia rehabilitation has been reported. However, clinical evidence, application protocol, and intervention method remain unclear. Therefore, a systematic review of the published literature is needed. The objective of this study was to systematically review clinical studies of peripheral magnetic stimulation applied for rehabilitation of dysphagia. Issues to be considered in future studies are also suggested. This systematic review performed a literature search of four databases (Medline, Embase, CINAHL, and Web of Science) to identify relevant studies published on the application of repetitive peripheral magnetic stimulation (rPMS) for swallowing-related muscles between 2010 and 2022. Seven studies were reviewed. Randomized controlled trials and one-group pre-post, case study designs were included. In the included studies, rPMS was applied to strengthen the submental suprahyoid muscles. The intervention regime varied. The rPMS was applied at a frequency of 30 Hz for 2 s. Rest time ranged from 8 s to 27-28 s. The number of intervention sessions ranged from 2-3 to 30. The intensity ranged from pain-inducing minimum intensity (90% of maximum stimulus output) to non-painful intensity (70-80% of maximum intensity). The rPMS on the suprahyoid muscles had positive effects on physiological changes in the swallowing function, such as displacement of the hyoid bone, muscle strength (cervical flexor, jaw-opening force), swallowing safety, swallowing performance, and swallowing-related quality of life. Participants also reported little pain and adverse reactions during rPMS. Although rPMS is a therapeutic option that can help improve the swallowing function as a non-invasive stimulation method in the rehabilitation of dysphagia, clinical evidence is needed for the development of clear stimulation protocols and guidelines.

Effects of Peripheral Electromagnetic Fields on Spasticity: A Systematic Review

Electromagnetic fields are emerging as a therapeutic option for patients with spasticity. They have been applied at brain or peripheral level. The effects of electromagnetic fields applied to the brain have been extensively studied for years in spasticity, but not so at the peripheral level. Therefore, the purpose of our work is to analyze the effects of electromagnetic fields, applied peripherally to spasticity. A systematic review was conducted resulting in 10 clinical trials. The frequency ranged from 1 Hz to 150 Hz, with 25 Hz being the most commonly used and the intensity it was gradually increased but there was low homogeneity in how it was increased. Positive results on spasticity were found in 80% of the studies: improvements in stretch reflex threshold, self questionnaire about difficulties related to spasticity, clinical spasticity score, performance scale, Ashworth scale, spastic tone, Hmax/Mmax Ratio and active and passive dorsal flexion. However, results must be taken with caution due to the large heterogeneity and the small number of articles. In future studies, it would be interesting to agree on the parameters to be used, as well as the way of assessing spasticity, to be more objective in the study of their effectiveness.

Possible Rehabilitation Procedures to Treat Sarcopenic Dysphagia

Sarcopenic dysphagia requires the presence of both dysphagia and generalized sarcopenia. The causes of dysphagia, except for sarcopenia, are excluded. The treatment for sarcopenic dysphagia includes resistance training along with nutritional support; however, whether rehabilitation procedures are useful remains unclear. In this narrative review, we present possible rehabilitation procedures as a resistance training for managing sarcopenic dysphagia, including Shaker exercise, Mendelsohn maneuver, tongue-hold swallow exercise, jaw-opening exercise, swallow resistance exercise, lingual exercise, expiratory muscle strength training, neuromuscular electrical stimulation, and repetitive peripheral magnetic stimulation. We hope that some procedures mentioned in this article or new methods will be effective to treat sarcopenic dysphagia.

Effect of electromyography-triggered peripheral magnetic stimulation on voluntary swallow in healthy humans

BACKGROUND

Electrical stimulation therapy is effective for patients with dysphagia. However, because of the pain, strong stimulation cannot be applied. Although magnetic stimulation induces less pain, there are no reports on magnetic stimulation being synchronised with a swallowing reflex.

OBJECTIVE

This study aimed to determine whether it is possible to induce magnetic stimulation during a voluntary swallowing using electromyography (EMG)-triggered peripheral magnetic stimulation and to evaluate its effect on healthy individuals.

METHODS

A total of 20 healthy adults in seated position were instructed to swallow saliva and 10 ml of barium under videofluoroscopy. For concomitant use of magnetic stimulation, a magnetic stimulus for suprahyoid muscles at 30 Hz frequency was applied for 2 s when the EMG level in the sternohyoid muscle exceeded the threshold. During the voluntary swallowing, the movement of the hyoid bone and opening width of the upper oesophageal sphincter (UES) were measured. Furthermore, pressure topography was evaluated in 6 subjects using high-resolution manometry.

RESULTS

The magnetic stimulation significantly extended the movement time of the hyoid bone (p < 0.001). During liquid deglutition, significant increases were observed in the anterior maximum movement distance of the hyoid bone (p < 0.05), opening width of the UES (p < 0.001) and anterior movement distance of the hyoid bone at the maximum UES opening (p < 0.01). In the pressure topography, the maximum pressure immediately after UES closure significantly decreased with magnetic stimulation (p < 0.05).

CONCLUSION

EMG-triggered peripheral magnetic stimulation made it possible to apply magnetic stimulation during a voluntary swallowing.

Difference in Pain and Discomfort of Comparable Wrist Movements Induced by Magnetic or Electrical Stimulation for Peripheral Nerves in the Dorsal Forearm

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.

Numerical Analysis of Eddy Current Distribution in Submental Region Induced by Magnetic Stimulation for Treating Dysphagia

Induced contraction of the suprahyoid muscles via magnetic stimulation is considered to be effective for the rehabilitation of dysphagia. In our previous study, a magnetic stimulation coil with a U-shaped core for stimulating the suprahyoid muscles was developed based on the results of numerical analysis using a simplified human head model. It was confirmed that magnetic stimulation by the coil causes large contraction of the muscles. However, the human head has a complex structure that includes bone structures through which current cannot easily pass. To accurately predict the current density distribution induced by magnetic stimulation, a model that accurately describes the human head is required for numerical analysis. Therefore, in this study, numerical analysis using the finite element method with a human head model that includes the bone structure obtained from computed tomography scans was performed. The results for the model with bone structure show that the coil with a U-shaped core can stimulate the motor points of the suprahyoid muscles in the middle of the submental region. When compared with the current density observed in a model without the bone structure, that in the model with the bone structure was reduced by 29% at a point 20 mm below the mandibular surface. It is thus necessary to perform a numerical analysis using a model with the bone structure to obtain accurate analysis results.

Effects of Repetitive Peripheral Magnetic Stimulation on Shoulder Subluxations Caused by Stroke: A Preliminary Study

OBJECTIVES

Shoulder subluxation is a common problem after stroke. It causes shoulder pain that affects activities of daily living. This study aimed to investigate the effect of repetitive peripheral magnetic stimulation on shoulder subluxation after stroke.

METHODS

We enrolled 12 consecutive patients who, as a result of stroke, suffered shoulder subluxations, measuring at half of a fingerbreadth or more. All subjects underwent conventional rehabilitation, as well as repetitive peripheral magnetic stimulation of their supraspinatus, posterior deltoid, and infraspinatus muscles. We assessed the following parameters: shoulder subluxation, evaluated as the acromio-humeral interval using measurements taken from X-rays; shoulder pain, evaluated using the Numerical Rating Scale; the active range of motion of shoulder abduction; and the motor impairment of the upper extremities, evaluated using the upper extremity of the Fugl-Meyer Assessment scale.

RESULTS

The acromio-humeral interval before treatment was 22.8 ± 5.7 mm (mean ± SD). It significantly decreased to 19.6 ± 7.0 mm (p = 0.004) after treatment. Shoulder pain (p = 0.039), active range of motion of shoulder abduction (p = 0.016), and total (p = 0.005), subscale A (p = 0.005), and subscale C (p = 0.008) Fugl-Meyer Assessment scores also improved significantly after treatment.

CONCLUSIONS

Repetitive peripheral magnetic stimulation effectively reduced shoulder subluxations and shoulder pain caused by stroke and improved voluntary upper-limb movements in stroke patients.

Repetitive Peripheral Magnetic Stimulation for Strengthening of the Suprahyoid Muscles: A Randomized Controlled Trial

OBJECTIVE

Head lift exercise is a widely known form of training in the rehabilitation of patients with dysphagia. This study aimed to compare muscular strength reinforcement training of the suprahyoid muscles using repetitive peripheral magnetic stimulation (rPMS) with head lift exercises in a randomized controlled trial.

MATERIALS AND METHODS

Twenty-four healthy adults were randomly assigned to either the magnetic stimulation group (M group) or the head lift exercise group (H group). Both groups underwent training five days a week for two weeks. The primary outcome was the cervical flexor strength, and secondary outcomes were jaw-opening force, tongue pressure, muscle fatigue of the hyoid and laryngeal muscles, displacement of the hyoid bone and opening width of the upper esophageal sphincter (UES) while swallowing 10 mL of liquid, training performance rate, and pain.

RESULTS

No dropouts were reported during the two-week intervention period. Cervical flexor strength significantly increased solely in the M group. Tongue pressure significantly improved in both groups. There were no significant differences in the jaw-opening force, median frequency rate of the anterior belly of the digastric muscle, sternohyoid muscle, sternocleidomastoid muscle, anterior and superior hyoid bone displacement, and UES opening width in both groups.

CONCLUSIONS

Two-week rPMS of the suprahyoid muscles increased the strength of these muscles compared with the head lift exercise during the same period.