Penetration and spread of interferential current in cutaneous, subcutaneous and muscle tissues

Electric field envelope focality in superficial brain areas with linear alignment montage in temporal interference stimulation

Temporal interference stimulation (TIS) uses two pairs of conventional transcranial alternating current stimulation (tACS) electrodes, each with a different frequency, to generate a time-varying electric field (EF) envelope (EFE). The EFE focality in primary somatosensory and motor cortex areas of a standard human brain was computed using newly defined linear alignment montages. Sixty head volume conductor models constructed from magnetic resonance images were considered to evaluate interindividual variability. Six TIS and two tACS electrode montages were considered, including linear and rectangular alignments. EFEs were computed using the scalar-potential finite-difference method. The computed EFE was projected onto the standard brain space for each montage. Computational results showed that TIS and tACS generated different EFE and EF distributions in postcentral and precentral gyri regions. For TIS, the EFE amplitude in the target areas had lower variability than the EF strength of tACS. However, bipolar tACS montages showed higher focality in the superficial postcentral and precentral gyri regions than in TIS. TIS generated greater EFE penetration than bipolar tACS at depths <5-10 mm below the brain surface. From group-level analysis, tACS with a bipolar montage was preferred for targets <5-10 mm in depth (gyral crowns) and TIS for deeper targets. TIS with a linear alignment montage could be an effective method for deep structures and sulcal walls. These findings provide valuable insights into the choice of TIS and tACS for stimulating specific brain regions.

Transcranial temporal interference stimulation (tTIS) influences event-related alpha activity during mental rotation

Non-invasive brain stimulation techniques offer therapeutic potential for neurological and psychiatric disorders. However, current methods are often limited in their stimulation depth. The novel transcranial temporal interference stimulation (tTIS) aims to overcome this limitation by non-invasively targeting deeper brain regions. In this study, we aimed to evaluate the efficacy of tTIS in modulating alpha activity during a mental rotation task. The effects of tTIS were compared with transcranial alternating current stimulation (tACS) and a sham control. Participants were randomly assigned to a tTIS, tACS, or sham group. They performed alternating blocks of resting and mental rotation tasks before, during, and after stimulation. During the stimulation blocks, participants received 20 min of stimulation adjusted to their individual alpha frequency (IAF). We assessed shifts in resting state alpha power, event-related desynchronization (ERD) of alpha activity during mental rotation, as well as resulting improvements in behavioral performance. Our results indicate tTIS and tACS to be effective in modulating cortical alpha activity during mental rotation, leading to an increase in ERD from pre- to poststimulation as well as compared to sham stimulation. However, this increase in ERD was not correlated with enhanced mental rotation performance, and resting state alpha power remained unchanged. Our findings underscore the complex nature of tTIS and tACS efficacy, indicating that stimulation effects are more observable during active cognitive tasks, while their impacts are less pronounced on resting neuronal systems.

A comparison of interferential current efficacy in elderly intervertebral disc degeneration patients with or without sarcopenia: a retrospective study

BACKGROUND

Intervertebral disc degeneration and sarcopenia are both age-related diseases without effective treatments. Their comorbidities may worsen the prognosis, and further studies on interaction and therapy are needed. The purpose of the study was to investigate the prevalence of sarcopenia in intervertebral disc degeneration, and to compare the characteristics of intervertebral disc degeneration with and without sarcopenia and effects of interferential current.

METHODS

One hundred twenty disc degeneration patients were included from 2021 to 2022 in a single institute. Medical records, examination results and radiological reports were reviewed. Patients with sarcopenia were screened and grouped according to Asian Working Group for Sarcopenia 2019. VAS, ODI, SARC-F, SMI, gait speed (GS), grip strength, disc Pfirrmann grading, standard cross-sectional area (SCSA), degree of fatty infiltration (DFF), and nerve conduction velocity (NCV) were assessed before and after treatment.

RESULTS

The prevalence of sarcopenia in intervertebral disc degeneration was 28.3%. The difference of VAS, ODI, disc Pfirrmann grading, SCSA, DFF and NCV between two groups were significant before intervention (P < 0.05), SCSA and DFF were related to the degree of disc degeneration. The improvement of SMI, GS, grip strength, VAS, SARC-F and ODI in intervertebral disc degeneration with sarcopenia group was significant after intervention, as well as SMI, GS, grip strength, VAS and ODI in those without sarcopenia (P < 0.05). The improvement of grip strength, GS, ODI and SARC-F in intervertebral disc degeneration with sarcopenia group were greater than the one without sarcopenia (P < 0.05), whereas there was no significance in improvement degree of other indicators between the two groups (P > 0.05).

CONCLUSION

The prevalence of sarcopenia was high in intervertebral disc degeneration, and paravertebral muscles degeneration correlated with the degree of disc degeneration. Compared to those without sarcopenia, intervertebral disc degeneration patients with sarcopenia have more severe pain, poorer mobility and neurological function. Interferential current is effective in intervertebral disc degeneration patients and sarcopenia patients.

Comparing the effects of transcranial alternating current and temporal interference (tTIS) electric stimulation through whole-brain mapping of c-Fos immunoreactivity

The analysis of the topography of brain neuromodulation following transcranial alternating current (AC) stimulation is relevant for defining strategies directed to specific nuclei stimulation in patients. Among the different procedures of AC stimulation, temporal interference (tTIS) is a novel method for non-invasive neuromodulation of specific deep brain targets. However, little information is currently available about its tissue effects and its activation topography in in vivo animal models. After a single session (30 min, 0.12 mA) of transcranial alternate current (2,000 Hz; ES/AC group) or tTIS (2,000/2,010 Hz; Es/tTIS group) stimulation, rat brains were explored by whole-brain mapping analysis of c-Fos immunostained serial sections. For this analysis, we used two mapping methods, namely density-to-color processed channels (independent component analysis (ICA) and graphical representation (MATLAB) of morphometrical and densitometrical values obtained by density threshold segmentation. In addition, to assess tissue effects, alternate serial sections were stained for glial fibrillary acidic protein (GFAP), ionized calcium-binding adapter molecule 1 (Iba1), and Nissl. AC stimulation induced a mild superficial increase in c-Fos immunoreactivity. However, tTIS stimulation globally decreased the number of c-Fos-positive neurons and increased blood brain barrier cell immunoreactivity. tTIS also had a stronger effect around the electrode placement area and preserved neuronal activation better in restricted areas of the deep brain (directional stimulation). The enhanced activation of intramural blood vessels’ cells and perivascular astrocytes suggests that low-frequency interference (10 Hz) may also have a trophic effect.

Effect of premodulated interferential current versus diadynamic current on the management of lateral elbow tendinopathy

Study aim: To compare the effect of premodulated interferential current (PREMOD IFC) and diadynamic current (DD) with exercise training on the management of lateral elbow tendinopathy (LET).

Material and methods: One hundred and four patients with unilateral LET from both genders (55 females and 49 males) were randomly allocated into two groups. Group A received PREMOD IFC in addition to the exercises, and group B received DD with the same exercises. The outcomes were maximum grip strength assessed by the hand dynamometer, the pinch strength assessed by the pinch gauge dynamometer, and pain and functional disability of the forearm assessed by a patient-rated tennis elbow evaluation (PRTEE) questionnaire. All participants received electrical stimulation, consisting of three sessions per week for six weeks.

Results: The mean PRTEE score, and grip strength were significantly improved after six weeks in favour of group A, while there was no significant difference between the two groups in pinch strength. (p < 0.05).

Conclusion: The results revealed that the combination of PREMOD IFC with exercises could improve pain, functional disability, and grip strength compared to DD with exercises in LET patients without a significant difference between the two groups in pinch strength.

Review of Noninvasive or Minimally Invasive Deep Brain Stimulation

Brain stimulation is a critical technique in neuroscience research and clinical application. Traditional transcranial brain stimulation techniques, such as transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), and deep brain stimulation (DBS) have been widely investigated in neuroscience for decades. However, TMS and tDCS have poor spatial resolution and penetration depth, and DBS requires electrode implantation in deep brain structures. These disadvantages have limited the clinical applications of these techniques. Owing to developments in science and technology, substantial advances in noninvasive and precise deep stimulation have been achieved by neuromodulation studies. Second-generation brain stimulation techniques that mainly rely on acoustic, electronic, optical, and magnetic signals, such as focused ultrasound, temporal interference, near-infrared optogenetic, and nanomaterial-enabled magnetic stimulation, offer great prospects for neuromodulation. This review summarized the mechanisms, development, applications, and strengths of these techniques and the prospects and challenges in their development. We believe that these second-generation brain stimulation techniques pave the way for brain disorder therapy.

Analgesic Effects of Interferential Current Therapy: A Narrative Review

Background and Objectives: Transcutaneous electrical stimulation of low- and medium-frequency currents is commonly used in pain management. Interferential current (IFC) therapy, a medium frequency alternating current therapy that reportedly reduces skin impedance, can reach deeper tissues. IFC therapy can provide several different treatment possibilities by adjusting its parameters (carrier frequency, amplitudemodulated frequency, sweep frequency, sweep mode or swing pattern, type of application (bipolar or quadripolar), time of application and intensity). The objective of this review article is to discuss the literature findings on the analgesic efficacy of IFC therapy. Conclusions: According to the literature, IFC therapy shows significant analgesic effects in patients with neck pain, low back pain, knee osteoarthritis and post-operative knee pain. Most of the IFC parameters seem not to influence its analgesic effects. We encourage further studies to investigate the mechanism of action of IFC therapy.

Multiscale Computational Model Reveals Nerve Response in a Mouse Model for Temporal Interference Brain Stimulation

There has been a growing interest in the non-invasive stimulation of specific brain tissues, while reducing unintended stimulation in surrounding regions, for the medical treatment of brain disorders. Traditional methods for non-invasive brain stimulation, such as transcranial direct current stimulation (tDCS) or transcranial magnetic stimulation (TMS), can stimulate brain regions, but they also simultaneously stimulate the brain and non-brain regions that lie between the target and the stimulation site of the source. Temporal interference (TI) stimulation has been suggested to selectively stimulate brain regions by superposing two alternating currents with slightly different frequencies injected through electrodes attached to the scalp. Previous studies have reported promising results for TI applied to the motor area in mice, but the mechanisms are yet to be clarified. As computational techniques can help reveal different aspects of TI, in this study, we computationally investigated TI stimulation using a multiscale model that computes the generated interference current pattern effects in a neural cortical model of a mouse head. The results indicated that the threshold increased with the carrier frequency and that the beat frequency did not influence the threshold. It was also found that the intensity ratio between the alternating currents changed the location of the responding nerve, which is in agreement with previous experiments. Moreover, particular characteristics of the envelope were investigated to predict the stimulation region intuitively. It was found that regions with high modulation depth (| maximum| − | minimum| values of the envelope) and low minimum envelope (near zero) corresponded with the activation region obtained via neural computation.

Analgesia for Sheep in Commercial Production: Where to Next?

Simple Summary

Increasing societal and customer pressure to provide animals with ‘a life worth living’ continues to apply pressure on industry to alleviate pain associated with husbandry practices, injury and illness. Although a number of analgesic solutions are now available for sheep, providing some amelioration of the acute pain responses, this review has highlighted a number of potential areas for further research.

Abstract

Increasing societal and customer pressure to provide animals with ‘a life worth living’ continues to apply pressure on livestock production industries to alleviate pain associated with husbandry practices, injury and illness. Over the past 15–20 years, there has been considerable research effort to understand and develop mitigation strategies for painful husbandry procedures in sheep, leading to the successful launch of analgesic approaches specific to sheep in a number of countries. However, even with multi-modal approaches to analgesia, using both local anaesthetic and non-steroidal anti-inflammatory drugs (NSAID), pain is not obliterated, and the challenge of pain mitigation and phasing out of painful husbandry practices remains. It is timely to review and reflect on progress to date in order to strategically focus on the most important challenges, and the avenues which offer the greatest potential to be incorporated into industry practice in a process of continuous improvement. A structured, systematic literature search was carried out, incorporating peer-reviewed scientific literature in the period 2000–2019. An enormous volume of research is underway, testament to the fact that we have not solved the pain and analgesia challenge for any species, including our own. This review has highlighted a number of potential areas for further research.

Analytical and Experimental Investigation of Temporal Interference for Selective Neuromuscular Activation

This article presents an analytical method that offers both spectral and spatial information to predict local electric fields capable of driving neural activities for neuromuscular activation, and the findings of an experimental investigation on a common strategy utilizing multiple high-frequency (HF) electric fields to create an interference to recruit neural firing at depth. By introducing a cut-off frequency [Formula: see text] too high to recruit neural firing in a frequency-based field descriptor, the analytical method offers an effective means to position a focused temporal interference (TI) without mechanically moving the electrodes. The experiment, which was conducted on both forearms of five healthy volunteers, validates the feasibility of the method for selective neuromuscular stimulation, where three nerve/muscles that control human fingers were independently stimulated with two current channels. The numerical and experimental findings demonstrate that the frequency-based method overcomes several limitations associated with surface-based electrical stimulation.

Transcutaneous high-frequency alternating current for rapid reversible muscle force reduction below pain threshold

OBJECTIVE

The development of non-invasive, quickly reversible techniques for controlling undesired muscle force production (e.g. spasticity) could expand rehabilitation approaches in those with pathology by increasing the type and intensity of exercises that can be performed. High-frequency alternating current (HFAC) has been previously established as a viable method for blocking neural conduction in peripheral nerves. However, clinical application of HFAC for nerve conduction block is limited due to the invasiveness of surgical procedures and the painful onset response. This study aimed to examine the use of transcutaneous HFAC (tHFAC) at various stimulation frequencies to address these shortfalls.

APPROACH

Ten individuals participated in the study. Surface electrodes were utilized to apply tHFAC (0.5-12 kHz) to the median and ulnar nerves. Individual pain threshold was determined by gradual increase of stimulation amplitude. Subjects then performed a force-matching task by producing grip forces up to the maximal voluntary contraction level with and without application of tHFAC below the pain threshold.

MAIN RESULTS

Pain threshold current amplitude increased linearly with stimulation frequency. Statistical analysis showed that both stimulation frequency and charge injected per phase had significant effects (p   <  0.05) on grip force reduction. At the group level, application of tHFAC below pain threshold reduced grip force by a maximum of 40.7%  ±  8.1%. Baseline grip force trials interspersed between tHFAC trials showed consistent grip force, indicating that fatigue was not a factor in force reduction.

SIGNIFICANCE

Our results demonstrate the effectiveness of tHFAC at reducing muscle force when applied below the pain threshold, suggesting its potential clinical viability. Future studies are necessary to further elucidate the mechanism of force reduction before clinical application.

Effect of Tetrapolar Interferential Current on Primary Dysmenorrhea Associated with Low Back Pain: Randomized Clinical Trial

AbstractDysmenorrhea is described as pain or weight in the hypogastrium and can radiate to the lumbar region or to the thighs. The use of the vector interferential current (CIV) is based on two sinusoidal currents of medium frequency, modulated at low frequency, and can reach deep tissues in a pleasant way. Despite widespread use of this current under various conditions, there are few studies on its use in primary dysmenorrhea associated with low back pain. The aim of this study was to evaluate the analgesic effect of the Tetrapolar Interferential Current on primary dysmenorrhea associated with low back pain. The study consisted of 20 volunteers, divided into 2 groups: Placebo Group (GP) and Group Treatment (GT), with treatment for 3 days in two menstrual cycles. The variables analyzed were the McGill Pain Questionnaire at the beginning of the first intervention and on the last day after the procedure, and the Visual Analog Pain Scale, applied before and after each therapy. It was observed that for the McGill questionnaire there was reduction only for the treated group, for the Pain scale there were  differences again between groups and between evaluations, and the size of the effect showed favorable results in the treated group. The interferential current in the quadrilateral form was shown to be effective in reducing pain in young patients with primary dysmenorrhea.Keywords: Visual Analog Scale. Transcutaneous Electric Nerve Stimulation. Medição da Dor. Pain Measurement.ResumoA dismenorreia é descrita como dor ou peso no hipogástrio, podendo irradiar-se para a região lombar ou até as coxas. O uso da corrente interferencial vetorial (CIV) baseia-se em duas correntes sinusoidais de média frequência, moduladas em baixa frequência, podendo atingir tecidos profundos de forma agradável. Apesar de amplo uso desta corrente em várias condições, há poucos estudos sobre seu uso na dismenorreia primária associada à dor lombar. O objetivo do estudo foi avaliar o efeito analgésico da Corrente Interferencial tetrapolar na dismenorreia primária associada à dor lombar. Este estudo foi composto por 20 voluntárias, divididas em 2 grupos: Grupo Placebo (GP) e Grupo Tratamento (GT), com tratamento por 3 dias em dois ciclos menstruais. As variáveis analisadas foram o Questionário de Dor de McGill no início da primeira intervenção e no último dia após o procedimento, e a Escala Analógica Visual de Dor, aplicada antes e após cada terapia. Observou-se que para a o questionário de McGill houve reduç o apenas para o grupo tratado, para a escala de Dor houve diferenças novamente entre grupos e entre avaliações, sendo que o tamanho do efeito mostrou resultados favoráveis ao grupo tratado. A corrente interferencial na forma tetrapolar mostrou-se efetiva na redução do quadro de dor em jovens com dismenorreia primária.Palavras-chave: Escala Visual Analógica. Estimulação Elétrica Nervosa Transcutânea. Medição da Dor.

Interferential electrical stimulation for improved bladder management following spinal cord injury

Patients with spinal cord injury (SCI) with neurogenic bladder (NB) represent a major medical problem, which initiated the search for a non-invasive and effective treatment that is easy to apply and without side effects. A study was performed using interferential medium frequency current electrical stimulation (IMFC ES) on 332 patients shortly after SCI diagnosed with NB dysfunction. All subjects received standard care and patients of the experimental group additionally received IMFC ES. Urinary management results included volitional control of voiding, intermittent catheterization, post-voidance residuum (PVR) quantity and quantity of urine lost (LOSS). Results were assessed based on the American spinal cord injury association impairment scale (AIS). The IMFC ES included two channels of medium frequency stimulation that were marginally different. Within the body, a low frequency field was generated through the interaction of the medium frequencies, which stimulated the urinary structures. In the IMFC ES group, interference stimulation was applied for 10 min with frequencies cycling from 0-100 Hz and back in 10 sec intervals. The strength of the low frequency stimulation, achieved by the interference of the two medium-frequency fields, was adjusted to the patients' vibration sensation. The intensities triggering vibration sensation were between 20-80 mA for patients with AIS levels B, C and D. For patients with AIS level A intensities <20 mA were used for therapeutic effects without causing skin injuries. Safety of IMFC ES was based on occurrence of adverse events of which none were recorded in the experimental group. IMFC ES was effective in patients with AIS levels B and C, significantly decreasing PVR and LOSS compared with patients receiving standard care No significant improvements in urinary management were observed following IMFC ES treatment of patients with AIS level A. Patients with SCI and NB classed as AIS levels B and C that exhibit preserved sensitivity were the best beneficiaries of IMFC ES therapy.

Efficiency of Tissue Penetration by Currents Induced by 3 Electrotherapeutic Techniques: A Comparative Study Using a Novel Deep-Tissue Measuring Technique

BACKGROUND

Electrotherapy provides a wide range of treatment alternatives for musculoskeletal pathologies. However, for the electrical stimulation to exert a significant therapeutic effect, the induced current must often penetrate deep inside the target tissue.

OBJECTIVE

The objective was to systematically compare the penetration efficiency of 3 electrotherapeutic stimulation modalities: transcutaneous electrical nerve stimulation (TENS), interferential (IF) stimulation, and combined therapy with pulsed ultrasound and IF current (CTPI).

DESIGN

This was a comparative, experimental laboratory study.

METHODS

The penetration efficiency was evaluated as a voltage difference between 2 of an 8-contact spinal cord stimulation array. Each of 20 participants with a preimplanted spinal cord stimulation array was stimulated with TENS (3 different electrode configurations), IF current (3 configurations), and CTPI (1 configuration).

RESULTS

Significant differences in penetration efficiency were found between the various stimulation conditions and electrode configurations. CTPI showed the highest penetration efficiency, followed by IF, and finally TENS. Penetration efficiency was inversely and significantly correlated with skinfold thickness in all conditions, but this correlation was lowest for the CTPI stimulation.

LIMITATIONS

Our study design did not include a condition of combined therapy with pulsed ultrasound and TENS, and it did not directly control for current or voltage density under the stimulating electrodes. In addition, further research is required to determine whether a higher stimulation intensity of the target tissue is advantageous clinically.

CONCLUSIONS

Pending further testing, CTPI stimulation could prove more effective than IF and TENS in reaching deeper tissues, especially considering the variability in adipose tissue thickness in the population, for example, in cases of patients with obesity.

Pelvic floor electrical stimulation and muscles training: a combined rehabilitative approach for management of non-neuropathic urinary incontinence in children

PURPOSE

To assess the efficacy of combined transcutaneous interferential (IF) electrical stimulation and pelvic floor muscle training through biofeedback on non-neuropathic urinary incontinence in children.

METHODS

This prospective study comprised of 46 anatomically and neurologically normal children (9 boys, 37 girls; mean age of 8.4 ± 2.2 years old) with non-neuropathic urinary incontinence. All children were evaluated by kidney and bladder ultrasounds, uroflowmetry with electromyography (EMG), a complete voiding diary and a dysfunctional voiding scoring questionnaire at the baseline. Children were randomly allocated into two treatment groups including group A (n = 23) who underwent biofeedback therapy in addition to IF electrical stimulation and group B (n = 23) who received only biofeedback therapy. Re-evaluation was performed 6 months and one year after completion of the treatment sessions.

RESULTS

Improvement of non-neuropathic urinary incontinence was significantly higher in group A in comparison to group B at two follow ups (P < 0.05). Daytime incontinence was improved in 19/23(82%) and 13/23(56.5%) of children in groups A and B respectively after the treatment (P < 0.01). There was no significant difference in uroflowmetry measures between two groups after the treatment.

CONCLUSIONS

Combination of biofeedback therapy and transcutaneous IF electrical stimulation is a potential effective modality in treating non-neuropathic urinary incontinence in children.

LEVEL OF EVIDENCE

Type of study: Treatment study. Level I: Randomized controlled trials with adequate statistical power to detect differences (narrow confidence intervals) and follow up >80%.

Effect of high-frequency alternating current transcutaneous stimulation over muscle strength: a controlled pilot study

Background

High-frequency alternating currents of greater than 1 kHz applied on peripheral nerves has been used in animal studies to produce a motor nerve block. It has been evidenced that frequencies higher than 5 kHz are necessary to produce a complete peripheral nerve block in primates, whose nerve thickness is more similar to humans. The aim of the study was to determine the effect on muscle strength after the application of a high-frequency stimulation at 5 and 10 kHz compared to sham stimulation in healthy volunteers.

Findings

Transcutaneous stimulation at 5 kHz, 10 kHz and sham stimulation were applied to eleven healthy volunteers over the ulnar and median nerves for 20 min. Maximal handgrip strength was measured before, during, immediately after the intervention, and 10 min after the end of intervention. The 10 kHz stimulation showed a lower handgrip strength during the intervention (28.1 N, SEM 3.9) when compared to 5 kHz (31.1 N, SEM 3.6; p < 0.001) and to sham stimulation (33.7 N, SEM 3.9; p < 0.001). Furthermore, only stimulation at 10 kHz decreased handgrip strength when compared to baseline.

Conclusions

These findings suggest high-frequency stimulation has an inhibitory effect over muscle strength. Future studies are required in patients that are characterized by motor hyperactive such as spasticity or tremors.

Clinical trial registration

NCT, NCT03169049. Registered on 30 May 2017

Technical development of transcutaneous electrical nerve inhibition using medium-frequency alternating current

Background

Innovative technical approaches to controlling undesired sensory and motor activity, such as hyperalgesia or spasticity, may contribute to rehabilitation techniques for improving neural plasticity in patients with neurologic disorders. To date, transcutaneous electrical stimulation has used low frequency pulsed currents for sensory inhibition and muscle activation. Yet, few studies have attempted to achieve motor nerve inhibition using transcutaneous electrical stimulation. This study aimed to develop a technique for transcutaneous electrical nerve inhibition (TENI) using medium-frequency alternating current (MFAC) to suppress both sensory and motor nerve activity in humans.

Methods

Surface electrodes were affixed to the skin of eight young adults to stimulate the median nerve. Stimulation intensity was increased up to 50% and 100% of the pain threshold. To identify changes in sensory perception by transcutaneous MFAC (tMFAC) stimulation, we examined tactile and pressure pain thresholds in the index and middle fingers before and after stimulation at 10 kHz. To demonstrate the effect of tMFAC stimulation on motor inhibition, stimulation was applied while participants produced flexion forces with the index and middle fingers at target forces (50% and 90% of MVC, maximum voluntary contraction).

Results

tMFAC stimulation intensity significantly increased tactile and pressure pain thresholds, indicating decreased sensory perception. During the force production task, tMFAC stimulation with the maximum intensity immediately reduced finger forces by ~ 40%. Finger forces recovered immediately after stimulation cessation. The effect on motor inhibition was greater with the higher target force (90% MVC) than with the lower target (50% MVC). Also, higher tMFAC stimulation intensity provided a greater inhibition effect on both sensory and motor nerve activity.

Conclusion

We found that tMFAC stimulation immediately inhibits sensory and motor activity. This pre-clinical study demonstrates a novel technique for TENI using MFAC stimulation and showed that it can effectively inhibit both sensory perception and motor activity. The proposed technique can be combined with existing rehabilitation devices (e.g., a robotic exoskeleton) to inhibit undesired sensorimotor activities and to accelerate recovery after neurologic injury.

Transcutaneous electrical stimulation on the anterior neck region: The impact of pulse duration and frequency on maximum amplitude tolerance and perceived discomfort

Maximum amplitude tolerance (MAT) has been known as a primary factor determining the depth of electrical current penetration. However, the effect of varying transcutaneous electrical stimulation (TES) parameters on MAT and discomfort level is poorly understood. Furthermore, limited information exists regarding the biopsychological factors that may impact MAT and discomfort. The primary aims of this study were to compare the effects TES protocol with varying levels of pulse duration (300 μs vs 700 μs) and frequency (30 Hz vs 80 Hz) on the MAT and discomfort in healthy older adults. The exploratory aim of this study was to examine relationships between submental adipose tissue thickness, pain sensitivity and gender with MAT and discomfort. Twenty-four healthy older adults participated in this study. Transcutaneous electrical stimulation was delivered to the submental region. Maximum amplitude tolerance and discomfort were measured for each condition. Furthermore, submental adipose tissue thickness and pain sensitivity were measured for each subject. Maximum amplitude tolerance was significantly increased for the TES protocols with short-pulse duration [F (3, 69) = 38.695, P < .0001]. Discomfort was similar across different TES protocols. Submental adipose tissue thickness (r = .30, P < .003) and pain sensitivity (r = -.43, P < .0001) were related to MAT. Pain sensitivity rating was also related to discomfort (r = .45, P < .0001). In conclusion, using TES protocols with short-pulse duration may increase the MAT. Higher amplitude stimulation may increase the impact on deep swallowing muscles. In addition, submental adipose tissue thickness and pain sensitivity are potential biopsychological factors that may affect MAT and discomfort.

Neuromodulation via Interferential Electrical Stimulation as a Novel Therapy in Gastrointestinal Motility Disorders

The concept of therapeutic percutaneous neuromodulation has, until recently, been limited by the ability to penetrate deeply enough to stimulate internal organs. By utilizing 2 medium frequency, slightly out of phase electrical currents passing diagonally through the abdomen, a third, low frequency current is created at the point of bisection. This interferential current appears to stimulate nerve fibers in the target organs and may have a therapeutic action. The aim of the study is to review the use of transcutaneous interferential electrical stimulation with a focus on its application in gastroenterology, particularly in motility disorders. Studies involving use of interferential current therapy were searched from Medline, PubMed, and Scopus databases, and articles pertaining to history, its application and all those treating abdominal and gastrointestinal disorders were retrieved. Seventeen studies were identified, 13 involved children only. Eleven of these were randomised controlled trials (3 in adults). Four trials were from the one center, where each paper reported on different outcomes such as soiling, defecation frequency, quality of life, and colon transit studies from the one pool of children. All studies found statistically significant improvement in symptom reduction. However, weaknesses in study design were apparent in some. In particular, finding an adequate placebo to interferential current therapy has been difficult. Interferential current therapy shows potential as a novel, non-pharmacological and economical means of treating gastrointestinal dysfunction such as constipation. More studies are needed particularly in the adult population. However, the design of a suitable placebo is challenging.

Nerve excitation using an amplitude-modulated signal with kilohertz-frequency carrier and non-zero offset

BACKGROUND

Incorporating kilohertz-frequency signals in transcutaneous electrical stimulation has been proposed as a means to overcome the impedance of the skin, thereby reaching deeper nerves. In particular, a transdermal amplitude modulated signal (TAMS), composed of a 210 kHz non-zero offset carrier modulated by rectangular pulses, was introduced recently for the treatment of overactive bladder. However, the contribution of the components of TAMS to nerve fiber activation has not been quantified.

METHODS

We conducted in vivo experiments and applied direct stimulation to the sciatic nerve of cats and rats. We measured electromyogram and compound action potential activity evoked by pulses, TAMS and modified versions of TAMS in which we varied the size of the carrier.

RESULTS

Nerve fiber activation using TAMS showed no difference with respect to activation with conventional pulse for carrier frequencies of 20 kHz and higher, regardless the relative amplitude of the carrier. For frequencies lower than 20 kHz, the offset needed to generate half of the maximal evoked response decreased significantly with respect to the pulse. Results of simulations in a computational model of nerve fiber stimulation using the same stimulation waveforms closely matched our experimental measurements.

CONCLUSION

Taken together, these results suggest that a TAMS with carrier frequencies >20 kHz does not offer any advantage over conventional pulses, even with larger amplitudes of the carrier, and this has implications for design of waveforms for efficient and effective transcutaneous stimulation.

Transcutaneous interferential electrical stimulation for the management of non-neuropathic underactive bladder in children: a randomised clinical trial

OBJECTIVES

To assess the efficacy of transcutaneous interferential electrical stimulation (IFES) and urotherapy in the management of non-neuropathic underactive bladder (UAB) in children with voiding dysfunction.

PATIENTS AND METHODS

In all, 36 children with UAB without neuropathic disease [15 boys, 21 girls; mean (sd) age 8.9 (2.6) years] were enrolled and then randomly allocated to two equal treatment groups comprising IFES and control groups. The control group underwent only standard urotherapy comprising diet, hydration, scheduled voiding, toilet training, and pelvic floor and abdominal muscles relaxation. Children in the IFES group likewise underwent standard urotherapy and also received IFES. Children in both groups underwent a 15-session treatment programme twice a week. A complete voiding and bowel habit diary was completed by parents before, after treatment, and 1 year later. Bladder ultrasound and uroflowmetry/electromyography were performed before, at the end of treatment course, and at the 1-year follow-up.

RESULTS

The mean (sd) number of voiding episodes before treatment was 2.6 (1) and 2.7 (0.76) times/day in the IFES and control groups, respectively, which significantly increased after IFES therapy in IFES group, compared with only standard urotherapy in the control group [6.3 (1.4) vs 4.7 (1.3) times/day, P < 0.002). The mean (sd) bladder capacity before treatment was 424 (123) and 463 (121) mL in the control and IFES groups, respectively, which decreased significantly at 1 year after treatment in the IFES group compared with the controls, at 227 (86) vs 344 (127) mL (P < 0.01). Maximum urine flow increased and voiding time decreased significantly in the IFES group compared with controls at the end of treatment sessions and 1 year later (P < 0.05). All the children had abnormal flow curves at the beginning of the study. The flow curve became normal in 14/18 (77%) of the children in the IFES group and six of 18 (33%) in the control group by the end of follow-up (P < 0.007). At the end of the treatment course, night-time wetting was improved in all children who had this symptom before the treatment in the IFES group (P < 0.01).

CONCLUSION

Combining IFES and urotherapy is a safe and effective therapy in the management of children with UAB.

A computational study to evaluate the activation pattern of nerve fibers in response to interferential currents stimulation

Interferential current (IFC) is one of the most popular electrical currents used in electrotherapy. However, there have been limited studies investigating how this stimulation affects the nerve fibers. The aim of this computational study was to evaluate the temporal and spatial patterns of fiber activation in IFC therapy for different modulation and carrier frequencies. The interferential currents were applied by two pairs of point electrodes perpendicular to each other in an infinite homogeneous medium, and a model of myelinated nerve fibers was implemented in NEURON to study the neural response. The activation thresholds for different positions of the fiber and the resultant firing patterns were evaluated. The results suggest that the fibers may fire continuously or in bursts, with frequencies equal or higher than the modulation frequency, or may be blocked, based on their position relative to the electrodes, the modulation frequency and the stimulus strength. The results confirm traditional belief about the role of the modulation frequency in firing frequency of nerve fibers and describe a possible mechanism for less sensation of pain, due to blockage of the fibers by the high-frequency nature of the interferential currents.