Functional Electrical Stimulation Parameters Research Articles

A review of functional electrical stimulation based on brain-computer interface

Individuals with motor dysfunction caused by damage to the central nervous system are unable to transmit voluntary movement commands to their muscles, resulting in a reduced ability to control their limbs. However, traditional rehabilitation methods have problems such as long treatment cycles and high labor costs. Functional electrical stimulation (FES) based on brain-computer interface (BCI) connects the patient's intentions with muscle contraction, and helps to promote the reconstruction of nerve function by recognizing nerve signals and stimulating the moving muscle group with electrical impulses to produce muscle convulsions or limb movements. It is an effective treatment for sequelae of neurological diseases such as stroke and spinal cord injury. This article reviewed the current research status of BCI-based FES from three aspects: BCI paradigms, FES parameters and rehabilitation efficacy, and looked forward to the future development trend of this technology, in order to improve the understanding of BCI-based FES.

Tremor Suppression Using Functional Electrical Stimulation.

Parkinson's disease (PD) and essential tremor are two major causes of pathological tremor among people over 60 years old. Due to the side effects and complications of traditional tremor management methods such as medication and deep brain surgery, non invasive tremor suppression methods have become more popular in recent years. Functional electrical stimulation (FES) is one of the methods used to reduce tremor in several studies. However, the effect of different FES parameters on tremor suppression and discomfort level, including amplitude, the number of pulses in each stimulation burst, frequency, and pulse width is yet to be studied for longer stimulation durations. Therefore, in this work, experiments were performed on 14 participants with PD to evaluate the effect of thirty seconds of out-of-phase electrical stimulation on wrist tremor at rest. Trials were conducted by varying the stimulation amplitude and the number of pulses while keeping the frequency and pulse width constant. Each test was repeated three times for each participant. The results showed an overall tremor suppression for 11 out of 14 participants and no average positive effects for three participants. It is concluded that despite the effectiveness of FES in tremor suppression, each set of FES parameters showed different suppression levels among participants due to the variability of tremor over time. Thus, for this method to be effective, an adaptive control system would be required to tune FES parameters in real time according to changes in tremor during extended stimulation periods.

Dynamics Combined With Hill Model for Functional Electrical Stimulation Ankle Angle Prediction.

Musculoskeletal models play an essential role in ankle rehabilitation research. The majority of the existing models have established the relationship between EMG and joint torque. However, EMG signal acquisition requires higher clinical conditions, such as sensitivity to external circumstances, motion artifacts and electrode position. To solve the nonlinear and time-varying nature of joint movement, a Functional Electrical Stimulation (FES) model was proposed in this study to simulate the whole process of ankle dorsiflexion. The model is combined with muscle contraction dynamics based on Hill model and ankle inverse dynamics to connect FES parameters, torques, and ankle angles. In addition, the extended Kalman filter (EKF) algorithm was applied to identify the unknown parameters of the model. Model validation experiment was performed by acquiring the actual data of healthy volunteers. Results showed that the root mean square error (RMSE) and normalized root mean square error (NRMSE) of this model were 11.93%±0.53% and 1.39°±0.26°, respectively, which means it can effectively predict the output variation of ankle joint angle while changing electrical stimulation parameters. Therefore, the proposed mode is essential for developing closed-loop feedback control of electrical stimulation and has the potential to help patients to conduct rehabilitation training.

A Co-driven Functional Electrical Stimulation Control Strategy by Dynamic Surface Electromyography and Joint Angle.

Functional electrical stimulation (FES) is widely used in neurorehabilitation to improve patients’ motion ability. It has been verified to promote neural remodeling and relearning, during which FES has to produce an accurate movement to obtain a good efficacy. Therefore, many studies have focused on the relationship between FES parameters and the generated movements. However, most of the relationships have been established in static contractions, which leads to an unsatisfactory result when applied to dynamic conditions. Therefore, this study proposed a FES control strategy based on the surface electromyography (sEMG) and kinematic information during dynamic contractions. The pulse width (PW) of FES was determined by a direct transfer function (DTF) with sEMG features and joint angles as the input. The DTF was established by combing the polynomial transfer functions of sEMG and joint torque and the polynomial transfer functions of joint torque and FES. Moreover, the PW of two FES channels was set based on the muscle synergy ratio obtained through sEMG. A total of six healthy right-handed subjects were recruited in this experiment to verify the validity of the strategy. The PW of FES applied to the left arm was evaluated based on the sEMG of the right extensor carpi radialis (ECR) and the right wrist angle. The coefficient of determination (R2) and the normalized root mean square error (NRMSE) of FES-included and voluntary wrist angles and torques were used to verify the performance of the strategy. The result showed that this study achieved a high accuracy (R2 = 0.965 and NRMSE = 0.047) of joint angle and a good accuracy (R2 = 0.701 and NRMSE = 0.241) of joint torque reproduction during dynamic movements. Moreover, the DTF in real-time FES system also had a nice performance of joint angle fitting (R2 = 0.940 and NRMSE = 0.071) and joint torque fitting (R2 = 0.607 and NRMSE = 0.303). It is concluded that the proposed strategy is able to generate proper FES parameters based on sEMG and kinematic information for dynamic movement reproduction and can be used in a real-time FES system combined with bilateral movements for better rehabilitation.

Postural control during turn on the light task assisted by functional electrical stimulation in post stroke subjects

Postural control mechanisms have a determinant role in reaching tasks and are typically impaired in post-stroke patients. Functional electrical stimulation (FES) has been demonstrated to be a promising therapy for improving upper limb (UL) function. However, according to our knowledge, no study has evaluated FES influence on postural control. This study aims to evaluate the influence of FES UL assistance, during turning on the light task, in the related postural control mechanisms. An observational study involving ten post-stroke subjects with UL dysfunction was performed. Early and anticipatory postural adjustments (EPAs and APAs, respectively), the weight shift, the center of pressure and the center of mass (CoM) displacement were analyzed during the turning on the light task with and without the FES assistance. FES parameters were adjusted to improve UL function according to a consensus between physiotherapists’ and patients’ perspectives. The ANOVA repeated measures, Paired sample t and McNemar tests were used to compare postural control between the assisted and non-assisted conditions. When the task was assisted by FES, the number of participants that presented APAs increased (p = 0.031). UL FES assistance during turning on the light task can improve postural control in neurological patients with UL impairments.

Optimal multi-field functional electrical stimulation parameters for the “drinking task - reaching phase” and related upper limb kinematics repeatability in post stroke subjects

BackgroundNo specific guidelines for the management of functional electrical stimulation (FES) parameters in post stroke patients have been defined yet, despite its frequent use. The purpose of this study is to characterize the optimal FES parameters that assist the reaching phase of drinking task (“drinking task - reaching phase”) on post stroke subjects and to analyze the related upper limb (UL) movement quality indicators repeatability. MethodsAn observational study with a test and re-test design involving ten post stroke subjects with UL dysfunction was performed. End-point and joint kinematics of contralesional UL were assessed during the “drinking task - reaching phase” with FES through a test and retest design. FES parameters were adjusted to improve UL function according to a consensus between physiotherapists and patients’ perspective. FindingsIt was possible to establish reliable FES parameters that assisted the “drinking task - reaching phase”. All FES parameters presented high to very high repeatability and led to moderate to very high repeatability in almost UL movement quality indicators during the “drinking task - reaching phase”. InterpretationThese findings show that the main characteristics of FES parameters that improves patient perception of change are quite stable, which facilitate its implementation in clinical practice by allowing consistence between intervention sessions.

On the way home: a BCI-FES hand therapy self-managed by sub-acute SCI participants and their caregivers: a usability study

BackgroundRegaining hand function is the top priority for people with tetraplegia, however access to specialised therapy outwith clinics is limited. Here we present a system for hand therapy based on brain-computer interface (BCI) which uses a consumer grade electroencephalography (EEG) device combined with functional electrical stimulation (FES), and evaluate its usability among occupational therapists (OTs) and people with spinal cord injury (SCI) and their family members.MethodsUsers: Eight people with sub-acute SCI (6 M, 2F, age 55.4 ± 15.6) and their caregivers (3 M, 5F, age 45.3 ± 14.3); four OTs (4F, age 42.3 ± 9.8). User Activity: Researchers trained OTs; OTs subsequently taught caregivers to set up the system for the people with SCI to perform hand therapy. Hand therapy consisted of attempted movement (AM) of one hand to lower the power of EEG sensory-motor rhythm in the 8-12 Hz band and thereby activate FES which induced wrist flexion and extension. Technology: Consumer grade wearable EEG, multichannel FES, custom made BCI application. Location: Research space within hospital. Evaluation: donning times, BCI accuracy, BCI and FES parameter repeatability, questionnaires, focus groups and interviews.ResultsEffectiveness: The BCI accuracy was 70–90%. Efficiency: Median donning times decreased from 40.5 min for initial session to 27 min during last training session (N = 7), dropping to 14 min on the last self-managed session (N = 3). BCI and FES parameters were stable from session to session. Satisfaction: Mean satisfaction with the system among SCI users and caregivers was 3.68 ± 0.81 (max 5) as measured by QUEST questionnaire. Main facilitators for implementing BCI-FES technology were “seeing hand moving”, “doing something useful for the loved ones”, good level of computer literacy (people with SCI and caregivers), “active engagement in therapy” (OT), while main barriers were technical complexity of setup (all groups) and “lack of clinical evidence” (OT).ConclusionBCI-FES has potential to be used as at home hand therapy by people with SCI or stroke, provided it is easy to use and support is provided. Transfer of knowledge of operating BCI is possible from researchers to therapists to users and caregivers.Trial registration Registered with NHS GG&C on December 6th 2017; clinicaltrials.gov reference number NCT03257982, url: https://clinicaltrials.gov/ct2/show/NCT03257982.

Optimal Multifield Functional Electrical Stimulation Parameters for the “Turn on the Light” Task and Related Upper Limb Kinematics Repeatability in Poststroke Subjects

ObjectiveTo characterize the optimal functional electrical stimulation (FES) parameters that assist the turn on the light task (TOTL) on poststroke participants and to analyze the related upper limb (UL) kinematics repeatability. DesignCross-sectional study. SettingHuman movement research center. ParticipantsPoststroke individuals (N=11) with history of a single unilateral stroke that resulted in a motor control dysfunction of the contralesional UL. InterventionsFES based on surface multifield technology applied to the contralesional wrist and finger extensors during the TOTL. Main Outcome MeasuresFES outcome metrics (virtual electrodes, stimulation duration, intensity) and kinematic metrics (end-point kinematics [absolute and relative duration, mean and peak velocities, relative instant of peak velocity, index of curvature, number of movement units] and joint kinematics [shoulder, elbow, wrist end position and range of movement]). Outcome measures were assessed 2 times with a 72-hour maximum time interval. ConclusionIt was possible to establish reliable FES parameters that assisted the TOTL on poststroke participants. These stimulation parameters led to high to very high repeatability in terms of UL kinematics for most of the cases.

SEMG-Driven Functional Electrical Stimulation Tuning via Muscle Force

Accurate force control plays a crucial role but still faces many challenges in functional electrical stimulation (FES) based neuroprosthesis applications. This study proposes an surface electromyography (sEMG) driven solution for FES sequential parameter estimation including its amplitude and pulsewidth (PW). The algorithm forms the mapping relationship from voluntary sEMG to the two FES parameters via the correlated muscle forces as an intermediate variable. Six able-bodied subjects are recruited to optimize and validate the proposed method based on the triangular and random grip force. The estimated amplitude and PW are evaluated respectively by stimulating the ipsilateral and contralateral muscle of the sEMG recording points. The accuracy of muscle force reconstruction achieve by the method are investigated by comparing the FES-induced grip force and the originally recorded voluntary grip force (VGF), in terms of the correlation index ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$R$</tex-math></inline-formula> ). The experimental results reveals excellent performance of the method on inducing functional muscle contraction closely matched the VGF ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$R&gt;0.9$</tex-math></inline-formula> ), regardless of the estimated amplitudes or PW. Furthermore, the performance differences between the estimated PW and amplitude are not significant ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$p&gt;0.05$</tex-math></inline-formula> ). These results not only demonstrate the feasibility of the proposed proportional FES control method, but also confirms its practical potential for muscle force control and strengthening in neuroprosthesis applications.

An investigation into the effect of electrode type and stimulation parameters on FES-induced dynamic movement in the presence of muscle fatigue for a voltage-controlled stimulator

Functional Electrical Stimulation (FES) is very useful in Stroke Rehabilitation for rebuilding muscle strength, both in a clinical setting and for home-based rehabilitation, however it is limited in its usage due to the resulting FES-induced muscle fatigue, as well as a large variation in muscle response. This paper compares the effectiveness of e-textile electrodes with conventional hydrogel electrodes at a range of stimulation parameters. The e-textiles produced a stronger response at a lower voltage than the hydrogels (3–4 V difference for a stimulation intensity voltage range of 8–22 V) and offer more consistency across different FES sessions. A simple model was then developed which relates the variation of the stimulation parameters (voltage, pulse-width, and frequency) to a change in angle for the elbow joint (Bicep muscle) using the e-textile electrodes. Step responses for various combinations of FES parameters were measured for 8 different healthy subjects for a total of fifty 10 min long tests. Overall the model produced good predictions of the arm response and it was found that the model was more accurate and consistent for combinational parameter steps than for individual parameter steps. The R2 value for the measured step change compared with the predicted step change for FES-induced contractions for all step types and subjects combined was 0.76 for one of the methods using the model

Strategies for Rapid Muscle Fatigue Reduction during FES Exercise in Individuals with Spinal Cord Injury: A Systematic Review.

BackgroundRapid muscle fatigue during functional electrical stimulation (FES)-evoked muscle contractions in individuals with spinal cord injury (SCI) is a significant limitation to attaining health benefits of FES-exercise. Delaying the onset of muscle fatigue is often cited as an important goal linked to FES clinical efficacy. Although the basic concept of fatigue-resistance has a long history, recent advances in biomedical engineering, physiotherapy and clinical exercise science have achieved improved clinical benefits, especially for reducing muscle fatigue during FES-exercise. This review evaluated the methodological quality of strategies underlying muscle fatigue-resistance that have been used to optimize FES therapeutic approaches. The review also sought to synthesize the effectiveness of these strategies for persons with SCI in order to establish their functional impacts and clinical relevance.MethodsPublished scientific literature pertaining to the reduction of FES-induced muscle fatigue was identified through searches of the following databases: Science Direct, Medline, IEEE Xplore, SpringerLink, PubMed and Nature, from the earliest returned record until June 2015. Titles and abstracts were screened to obtain 35 studies that met the inclusion criteria for this systematic review.ResultsFollowing the evaluation of methodological quality (mean (SD), 50 (6) %) of the reviewed studies using the Downs and Black scale, the largest treatment effects reported to reduce muscle fatigue mainly investigated isometric contractions of limited functional and clinical relevance (n = 28). Some investigations (n = 13) lacked randomisation, while others were characterised by small sample sizes with low statistical power. Nevertheless, the clinical significance of emerging trends to improve fatigue-resistance during FES included (i) optimizing electrode positioning, (ii) fine-tuning of stimulation patterns and other FES parameters, (iii) adjustments to the mode and frequency of exercise training, and (iv) biofeedback-assisted FES-exercise to promote selective recruitment of fatigue-resistant motor units.ConclusionAlthough the need for further in-depth clinical trials (especially RCTs) was clearly warranted to establish external validity of outcomes, current evidence was sufficient to support the validity of certain techniques for rapid fatigue-reduction in order to promote FES therapy as an integral part of SCI rehabilitation. It is anticipated that this information will be valuable to clinicians and other allied health professionals administering FES as a treatment option in rehabilitation and aid the development of effective rehabilitation interventions.

Implantable neurotechnologies: electrical stimulation and applications.

Neural stimulation using injected electrical charge is widely used both in functional therapies and as an experimental tool for neuroscience applications. Electrical pulses can induce excitation of targeted neural pathways that aid in the treatment of neural disorders or dysfunction of the central and peripheral nervous system. In this review, we summarize the recent trends in the field of electrical stimulation for therapeutic interventions of nervous system disorders, such as for the restoration of brain, eye, ear, spinal cord, nerve and muscle function. Neural prosthetic applications are discussed, and functional electrical stimulation parameters for treating such disorders are reviewed. Important considerations for implantable packaging and enhancing device reliability are also discussed. Neural stimulators are expected to play a profound role in implantable neural devices that treat disorders and help restore functions in injured or disabled nervous system.

Analysis of functional electrical stimulation parameters by muscular contraction time and knee joint angular variation

In the present study, five FES profiles were compared in order to find the best combination of activeperiod and burst frequency that might artificially sustain muscle contraction for the longest time with the lowest knee joint variation. Spinal cord injured volunteers (N=10) participated in this study. The frequency of each FES profile was 1 kHz with variable pulse active period (100 μs or 200 μs) and pulse inactive period (900 μs or 800 μs). The setup burst frequencies had either 50 Hz (3 ms active time and 17 ms rest time) or 70 Hz (3 ms active time and 11 ms rest time). The best results were obtained to FES profiles P2 (burst frequency of 70 Hz and pulse active period of 100 μs), P3 (burst frequency of 50 Hz and pulse active period of 200 μs) and P4 (burst frequency of 70 Hz and pulse active period of 200 μs). In order to maintain the SCIV’s knee angle with minimal variation, the best results occurred with the application of P2, P3 and P4 FES profiles.

Functional Electrical Stimulation in Spinal Cord Injury: From Theory to Practice

This article outlines steps to practical application of functional electrical stimulation (FES) within activity-based restorative therapy (ABRT). Drawing from current evidence, specific applications of FES intended to help restore function lost to spinal cord injury and associated neurologic disease are discussed. The medical and therapeutic indications, precautions, and contraindications are reviewed to help participants with appropriate patient selection, treatment planning, and assessment. Also included are the physiological implications of FES and alterable parameters, including dosing and timing, for a desired response. Finally, approaches to improve cortical representation and motor learning and to transition emerging movement into functional tasks are reviewed.

The Effects of K(+) Channel Blockade on Eccentric and Isotonic Twitch and Fatiguing Contractions in situ.

K+ channel blockers like 3,4-diaminopyridine (DAP) can double isometric muscle force. Functional movements require more complex concentric and eccentric contractions, however the effects of K+ channel blockade on these types of contractions in situ are unknown. Extensor digitorum longus (EDL) muscles were stimulated in situ with and without DAP in anesthetized rats and fatigability was addressed using a series of either concentric or eccentric contractions. During isotonic protocols (5–100% load), DAP significantly shifted shortening- and maximum shortening velocity-load curves upward and to the right and increased power and work. Maximum shortening, maximum shortening velocity, and power doubled while work increased by ∼250% during isotonic contraction at 50% load. During isotonic fatigue, DAP significantly augmented maximum shortening, work, shortening velocity, and power. During constant velocity eccentric protocols (2–12 mm/s), DAP increased muscle force during eccentric contractions at 6, 8, 10, and 12 mm/s. During eccentric contraction at a constant velocity of 6 mm/s while varying the stimulation frequency, DAP significantly increased muscle force during 20, 40, and 70 Hz. The effects of DAP on muscle contractile performance during eccentric fatigue varied with level of fatigue. DAP-induced contractile increases during isotonic contractions were similar to those produced during previously studied isometric contractions, while the DAP effect during eccentric contractions was more modest. These findings are especially important in attempting to optimize functional electrical stimulation parameters for spinal cord injury patients while also preventing rapid fatigue of those muscles.

Predicting the voluntary arm forces in FES-assisted standing up using neural networks.

For individuals with paraplegia, standing up requires activation of paralyzed leg muscles by an artificial functional electrical stimulation (FES) controller and voluntary control of arm forces by the individual. Any knowledge of such voluntary control, particularly its prediction, could be used to design more effective FES controllers. Therefore, artificial neural network models were developed to predict voluntary arm forces from measured angular positions of the ankle, knee, and hip joints during FES-assisted standing up in paraplegia. The training data were collected from eight paraplegic subjects in repeated standing-up trials, and divided into two categories for training and validation. The predictions of the models closely followed both the training and validation data, showing good accuracy and generalization. The comparison of the models showed that, although there are striking similarities among the voluntary controls adopted by different subjects, each subject develops his/her own 'personal strategy' to control the arm forces, which is consistent from trial to trial. The level of consistency was dependent on the experience in using FES, injury level, body weight, and other subject-specific parameters.

Selection of patients with urinary incontinence for application of functional electrical stimulation.

Contradictory data from the literature along with our own experience using functional electrical stimulation (FES) have facilitated the determination of objective criteria for the application of FES in correcting urinary incontinence. Simultaneous urodynamic, neurophysiological, and radiological examinations employed during our studies enabled us to determine changes in these parameters due to FEX. Among a large number of patients with urinary incontinence (for example: paraplegics, patients with spina bifida, stress incontinence following prostate operations, or resistant enuresis) we have determined that FES is appropriate if applied to properly selected patients. FES is indicated on the basis of the following criteria: the degree of morphological lesion of the urinary tract, the peripheral denervation of the muscles of the pelvic floor, the condition of the spinal center for miction, and, above all the quality of response to FES. FES not only activates the closing muscles of the bladder, but also inhibits the reflex contractions of the detrusor. Here, it should be noted that FES is indicated for cases of reflex incontinence. During FES of the pelvic floor muscles intravesical pressure normally diminishes and the reflex contractions of the detrusor subside. Sometimes, however, the reflex of miction occurs. In such a case, two reflex mechanisms are engaged. Their equilibrium, i.e. controlled miction, can be achieved with an afferent in flow which inhibits the reflex of miction. The use of FES for the correction of urinary incontinence can be a very good method if the FES parameters are individually chosen and patients properly selected.