For Functional Electrical Stimulation Research Articles

Delphi consensus study and clinical practice guideline development for functional electrical stimulation to support upright mobility in people with an upper motor neuron lesion.

A Clinical Practice Guideline (CPG) is required to provide guidance on optimal service delivery for Functional Electrical Stimulation (FES) to support upright mobility in people living with mobility difficulties due to an upper motor neuron lesion, such as stroke or multiple sclerosis. A modified Delphi consensus study was used to provide expert consensus on best practice. A Steering Group supported the recruitment of an Expert Panel, which included a range of stakeholders who participated in up to three survey rounds. In each round, panelists were asked to rate their agreement with draft statements about best practice using a 6-point Likert scale and add free text to explain their answer. Statements that achieved over 75% agree/strongly agree on the Likert scale were included in the CPG. Those that did not were revised based on free text comments and proposed in the next survey round. The first round included 82 statements with seven substatements. Sixty-five people (84% response rate) completed survey round 1 leading to 62 statements and four substatements being accepted. Fifty-six people responded to survey round 2, and consensus was achieved for all remaining statements. The accepted statements are included within the CPG and provide recommendations about who can benefit from FES and how they can be optimally supported through FES service provision. As such the CPG will support advocacy for, and optimal design of, FES services.

繰り返し学習制御と機能的電気刺激によるペダリング運動

This paper deals with repetitive learning control for functional electrical stimulation (FES) pedaling exploiting pedal force direction with antagonistic biarticular muscles . FES pedaling motion with muscle contraction is expressed as an Euler Lagrange system. Asymptotic tracking for the closed-loop system by the proposed controller is analyzed through Lyapunov-based methods. Experiments were conducted in three healthy individuals to show the validity of the proposed method from a practical point of view.

Continuous Switching Control of an Input-Delayed Antagonistic Muscle Pair During Functional Electrical Stimulation

Existing controllers for functional electrical stimulation (FES) of upper limb muscles were initially designed to assist unilateral movements and may not be readily applicable to assist antagonistic muscle movements. Furthermore, it is yet unclear if electromechanical delays (EMDs) are present during the coactivation of muscles. In this article, a robust controller is designed to facilitate the FES of an antagonistic muscle pair during elbow flexion and extension. The controller uses a continuous switching law that maps a joint angle error to control the antagonistic muscle pair. Furthermore, the controller compensates for EMDs in the antagonistic muscle pair. A Lyapunov stability analysis yields uniformly ultimately bounded (UUB) tracking for the human limb joint. The experimental results on four participants without disabilities indicate that the controller is robust and effective in switching between antagonistic muscles. A separate set of experiments also showed that EMDs are indeed present in the coactivated muscle pair. The designed controller compensates for the EMDs and statistically improves root mean square error (RMSE) compared to a traditional linear controller with no EMD compensation. The proposed controller can be generalized to assist FES-elicited tasks that involve a weak antagonistic muscle pair.

Tracking Control for FES Alternate Knee Bending and Stretching Trike With Electric Motor Assistance

This paper deals with a new control method for functional electrical stimulation (FES) alternate knee bending and stretching trike with electric motor assistance. While FES-cycling is known as a beneficial exercise for people with movement disorders, a paraplegia patient could not pedal smoothly by applying the previous method. One of the possible reasons is that there is a dead point in the pedaling motion intrinsically. To overcome this drawback, we developed a trike system which can be moved by alternating knee bending and stretching of the left and right legs for paraplegia patients. Electric motor assistance plays an important role to recover deceleration of the trike when switching between flexion and extension. Stability of the developed control law is analyzed through Lyapunov-based methods.

Earable Ω (OMEGA): A Novel Clenching Interface Using Ear Canal Sensing for Human Metacarpophalangeal Joint Control by Functional Electrical Stimulation.

(1) Background: A mouth-free interface is required for functional electrical stimulation (FES) in people with spinal cord injuries. We developed a novel system for clenching the human metacarpophalangeal (MP) joint using an earphone-type ear canal movement sensor. Experiments to control joint angle and joint stiffness were performed using the developed system. (2) Methods: The proposed FES used an equilibrium point control signal and stiffness control signal: electrical agonist–antagonist ratio and electrical agonist–antagonist sum. An angle sensor was used to acquire the joint angle, and system identification was utilized to measure joint stiffness using the external force of a robot arm. Each experiment included six and five subjects, respectively. (3) Results: While the joint angle could be controlled well by clenching with some hysteresis and delay in three subjects, it could not be controlled relatively well after hyperextension in the other subjects, which revealed a calibration problem and a change in the characteristics of the human MP joint caused by hyperextension. The joint stiffness increased with the clenching amplitude in five subjects. In addition, the results indicated that viscosity can be controlled. (4) Conclusions: The developed system can control joint angle and stiffness. In future research, we will develop a method to show that this system can control the equilibrium point and stiffness simultaneously.

CONTINUOUS ADAPTIVE CONTROL OF THE KNEE JOINT MOVEMENT

In this paper, we develop a control law for Functional Electrical Stimulation (FES) application fields. This work aims to command the knee joint movement of patients in the seated position suffering from neurological disorders that lead to a partial or total paralysis of the limb. For this purpose, we propose the synthesis of an adaptive continuous control that permits to the knee joint the tracking of a time-varying desired angle. The knee movement is represented by the dynamical model of the lower limb. The designed control ensures an asymptotic stability while considering constraints such as unknown model parameters, unknown perturbation effects and unknown spasticity and fatigue parameters. The applicability and the effectiveness of the designed control law are shown through the simulation results.

Evaluation of high-density, multi-contact nerve cuffs for activation of grasp muscles in monkeys

Objective. The objective of this work was to evaluate whether nerve cuffs can selectively activate hand muscles for functional electrical stimulation (FES). FES typically involves identifying and implanting electrodes in many individual muscles, but nerve cuffs only require implantation at a single site around the nerve. This method is surgically more attractive. Nerve cuffs may also more effectively stimulate intrinsic hand muscles, which are difficult to implant and stimulate without spillover to adjacent muscles. Approach. To evaluate its ability to selectively activate muscles, we implanted and tested the flat interface nerve electrode (FINE), which is designed to selectively stimulate peripheral nerves that innervate multiple muscles (Tyler and Durand 2002 IEEE Trans. Neural Syst. Rehabil. Eng. 10 294–303). We implanted FINEs on the nerves and bipolar intramuscular wires for recording compound muscle action potentials (CMAPs) from up to 20 muscles in each arm of six monkeys. We then collected recruitment curves while the animals were anesthetized. Main result. A single FINE implanted on an upper extremity nerve in the monkey can selectively activate muscles or small groups of muscles to produce multiple, independent hand functions. Significance. FINE cuffs can serve as a viable supplement to intramuscular electrodes in FES systems, where they can better activate intrinsic and extrinsic muscles with lower currents and less extensive surgery.

An Evaluation of the Effect of Stimulation Parameters and Electrode Type on Bicep Muscle Response for a Voltage-controlled Functional Electrical Stimulator

Millions of dollars worldwide are spent on electrodes for Functional Electrical Stimulation (FES) every year. With aging populations the increasing costs faced by healthcare providers are of significant concern. Conventional electrodes used for FES are of limited use and deteriorate with use. Washable E-textile electrodes have recently been used successfully for monitoring applications such as electromyography (EMG). E-textile electrodes could potentially reduce the costs faced by healthcare providers. However limited investigation has been conducted into the use of e-textile electrodes for actuation applications such as FES. This paper compares the effectiveness of e-textile electrodes with conventional hydrogel electrodes at a range of stimulation parameters. The electrodes performed similarly under variation of frequency (20-50 Hz) and ramp rate parameters (2-10 V/s). 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), however they must be wet to work which may be a barrier to their uptake.

A patient-controlled functional electrical stimulation system for arm weight relief

A patient-driven control strategy for Functional Electrical Stimulation (FES), which amplifies volitionally-initiated shoulder abductions, is proposed to improve stroke patients’ rehabilitation. Based on the measured abduction angle, a FES-induced muscle recruitment is generated that yields a pre-specified percentage of this angle – yielding arm weight relief. To guarantee the correct recruitment also under fatigue and uncertain muscle activation we employ feedback control of the recruitment level determined by filtering the FES-evoked electromyogram. Filter parameters are user-optimized to obtain a linear relation between filter output and angle with a good signal-to-noise ratio. The auto-tuned recruitment controller (RC) was tested on five healthy subjects and compared to direct stimulation (DS) while muscle fatigue progressively occurred. Results showed a more linear relation between recruitment level and angle than between non-controlled stimulation intensity and angle (R2=0.93 vs. R2=0.79, angular range of 54°). After 6 min of stimulation, abduction decreased by 42% ± 14 for DS and by 0% ± 12 for RC, showing an effective compensation of fatigue. RC yielded significant smaller errors than DS in generating desired angles (0.23% ± 5.9 vs. 14.6% ± 9.7). When FES-induced arm weight support was provided, a mean reduction of the volitional effort (determined by Electromyography) of 78% was achieved compared to angular tracking without FES. First experiments with one acute stroke patient are also reported.

In Vitro Testing of an Implantable Wireless Telemetry System for Long-Term Electromyography Recordings in Large Animals.

Multichannel bio-signal recording in undisturbed in vivo conditions is a frequent demand in experimental work for development of methodology and associated equipment for functional electrical stimulation (FES) application, limb prosthesis, and diagnostic tools in contemporary rehabilitation efforts. Intramuscular electromyogram (EMG) recordings can provide comprehensive insight in complex interactions of agonistic and antagonistic muscles during movement tasks and in contrast act as reliable control signals for both neuroprosthesis and mechanical prosthesis. We fabricated a fully implantable device, which is capable of recording electromyography signals from inside a body and transmit these signals wirelessly to an external receiver. The developed analog front end uses only two electrodes per channel, provides a gain of 60 dB, and incorporates a band pass filter with lower cut-off frequency of 4 Hz and upper cut-off frequency of 480 Hz. The bidirectional wireless data link, which operates in the 2.4 GHz Industrial, Scientific and Medical band, is designed for transmission distances of 10 m using an application data rate of 1 kSps for each of the two channels. Performed in vitro tests with the devices coated in epoxy resin and inserted into a phantom with tissue-equivalent characteristics confirmed the functionality of our concept and the measurement results are consistent with those from preceding simulations.

Functional electrical stimulation for the upper limb in tetraplegic spinal cord injury: a systematic review

Technological advances have helped to improve functional ability in spinal cord injury survivors. The aim of this study is to systematically review the evidence for functional electrical stimulation (FES) on functional tasks involving the upper limb in people with spinal cord injuries. The authors systematically searched from September 2009 to September 2014 in relevant databases using a combination of keywords covering spinal cord injury and FES. Studies were selected using pre-determined criteria. The search yielded 144 studies. Only five studies met the inclusion criteria. All five reported improvements immediately and at follow-up in functional ability as a result of FES or FES combined with conventional therapy. There is some preliminary evidence that FES may reduce disability due to upper limb-related activity limitations in tetraplegic spinal cord injury. Further work needs to examine the role of FES in more detail and in combination with other treatments.

A muscle model for hybrid muscle activation

Abstract To develop model-based control strategies for Functional Electrical Stimulation (FES) in order to support weak voluntary muscle contractions, a hybrid model for describing joint motions induced by concurrent voluntary-and FES induced muscle activation is proposed. It is based on a Hammerstein model – as commonly used in feedback controlled FES – and exemplarily applied to describe the shoulder abduction joint angle. Main component of a Hammerstein muscle model is usually a static input nonlinearity depending on the stimulation intensity. To additionally incorporate voluntary contributions, we extended the static non-linearity by a second input describing the intensity of the voluntary contribution that is estimated by electromyography (EMG) measurements – even during active FES. An Artificial Neural Network (ANN) is used to describe the static input non-linearity. The output of the ANN drives a second-order linear dynamical system that describes the combined muscle activation and joint angle dynamics. The tunable parameters are adapted to the individual subject by a system identification approach using previously recorded I/O-data. The model has been validated in two healthy subjects yielding RMS values for the joint angle error of 3.56° and 3.44°, respectively.

Flexible multi-channel microelectrode with fluidic paths for intramuscular stimulation and recording

Biomedical microelectrodes play a significant role in motor paralysis recovery caused by spinal cord injury (SCI). As most researchers focused on implantable microelectrodes with multiple functions for neural studies and application, we developed flexible intramuscular microelectrodes integrated wire electrodes for functional electrical stimulation (FES) and electromyogram (EMG) recording with micro tube channels for fluidic drug delivery. The electrodes were electrochemically deposited with conducting polymer (PEDOT/pTS) coating to improve the electrode performance including electrochemical impedance and charge storage capacity (CSC). Moreover, the excellent mechanical and electrochemical stability of PEDOT/pTS coated electrodes was verified by withstanding ultrasonic bath and experiencing repeated cyclic voltammetry (CV) scan. Furthermore, the fluidic property of the micro channels of electrodes was investigated to be suitable for intramuscular drug delivery. In addition, electrophysiological experiments in vivo comprising FES and EMG recording were performed to evaluate the practical application of flexible intramuscular microelectrodes. As a consequence, the developed multi-functional intramuscular microelectrodes are suitable for intramuscular implantation and electrophysiological application, and open a new gate for future researchers on intramuscular motor prostheses for paralysis recovery.

Control system for neuro-prostheses integrating induced and volitional effort

To increase the rehabilitation outcomes of stroke patients with weak residual muscle activity, a novel control strategy for Functional Electrical Stimulation (FES) was designed and tested during a tracking task. The system includes an electromyography (EMG)-based feedback controller and a trial-to-trial adaptation of the FES support. The first modulates the stimulation intensity to achieve a desired amount of FES-evoked muscle activity corresponding to a desired FES-induced angular support trajectory. The second iteratively updates this trajectory in order to minimize the error between the target displayed to the patient and the measured angle trajectory. This support adaptation only takes place in case the subject actively contributes to the movement. If the estimated volitional effort is too low, FES support is quickly withdrawn to remind the subject to actively contribute to the tracking task. The EMG signal of the stimulated muscle is used to estimate both the FES-induced and the volitional muscle activity. The feasibility of the proposed control scheme was experimentally investigated in one healthy subject by stimulating the medial deltoid muscle to support shoulder abduction. First, the controller was tested simulating different volitional contributions of a potential patient. The control system adjusted the amount of FES-support as expected. Then, the compensation of muscle fatigue by the feedback controller was demonstrated by repeatedly applying the same desired FES-induced angular trajectories, while the subject was asked to be relaxed. As a result, the control system was able to provide the desired support for about 7 minutes until the stimulation intensity saturated.

LEARNING TO CONTROL THE THREE-LINK MUSCULOSKELETAL ARM USING ACTOR–CRITIC REINFORCEMENT LEARNING ALGORITHM DURING REACHING MOVEMENT

Learning to control the planar three-link musculoskeletal arm by using an Actor–Critic learning algorithm during reaching movements to stationary target is presented. The arm model used in this study includes three skeletal links (hand, forearm and upper arm), three joints (wrist, elbow and shoulder without redundancy) and six nonlinear monoarticular muscles with redundancy which are modeled based on Hill model. The learning system is composed of Actor and Critic parts. For each part, a single layer neural network is used. This learning system applies six activation commands to six muscles at each instant of time. It also uses a reinforcement (reward) feedback for learning process and controlling the arm movement direction. The results showed that with a learning rate α = 0.9 and after 20 episodes, Mean square error (MSE), average reward and average time of reaching the target are gradually converged to the values: 0.0056, 0.02262 and 187 s, respectively. After the 20th episode, the learning will be completed. The research suggests a new direction for designation of learning-based controllers for functional electrical stimulation (FES) applications and for arm movement of autonomous robots.

A fully implanted intramuscular bipolar myoelectric signal recording electrode.

The objective of this study is to develop a fully implanted, intramuscular, bipolar, myoelectric signal (IM-MES) recording electrode for functional electrical stimulation (FES), prosthetic myoelectric control, and other permanently implantable systems. An existing fully implanted intramuscular stimulating electrode was modified at each end to allow bipolar recording. The design change also required a modification of the implantation method. Mechanical and in vivo testing was performed on the novel components of the electrode. The first clinical application also is described. The electrode design modifications did not create any areas of excess mechanical strain on the wires at the distal end where the leads were wound into electrode surfaces. In vivo testing showed that the IM-MES electrode recorded myoelectric signals that were equivalent to an existing epimysial MES electrode. The modified implantation method was simple to implement. The IM-MES electrode was used in an upper extremity FES system in an individual with a spinal cord injury and provided signals that were suitable for a command signal. A fully implanted, bipolar intramuscular recording electrode (IM-MES) was developed. Implantation of the IM-MES is straightforward, and almost any muscle can be targeted. Testing has been performed to demonstrate the suitability of the IM-MES electrode for clinical use. Initial clinical applications were successful.

Dynamic Optimization of FES and Orthosis-Based Walking Using Simple Models

Computation of an analytical control solution for functional electrical stimulation (FES) and orthosis-based walking is a daunting task due to the inherent nonlinear structure of the human muscle and walking dynamics. Furthermore, since muscle fatigue and available muscle force are major limiting issues, we explored the domains of numerical optimal control methods to address these issues. We first focused on the development of simple models to represent walking movement. These models account for walking produced via a limited number of activated muscles using FES along with a novel orthosis, and an assistive device such as a walker. Using dynamic optimization, the lower limb joint angle trajectories and control inputs were computed by minimizing the cost function comprising muscle stimulation variables and forces required to push a walker. Computer simulations for optimizations were performed across a range of step lengths to find the optimal step length (minimum cost per distance). Then, the optimal steady-state initial angular velocity (for optimal step length) was computed from a range of angular velocities of the lower-limb segments. We found considerable differences between able-bodied walking trajectories and the optimal walking trajectories for FES and orthosis-based walking. Based on this computer simulation study, we recommend that instead of arbitrary selection of stimulation profiles or gait parameters, dynamic optimization can be utilized to compute gait parameters such as step length, steady state velocity, and joint angle trajectories in future clinical implementation of FES and orthosis-based walking.

Hierarchical beamformer and cross-talk reduction in electroneurography

Electroneurography (ENG) is a method of recording neural activity within nerves. Using nerve electrodes with multiple contacts the activation patterns of individual neuronal fascicles can be estimated by measuring the surface voltages induced by the intraneural activity. The information about neuronal activation can be used for functional electric stimulation (FES) of patients suffering from spinal chord injury, or to control a robotic prosthetic limb of an amputee. However, the ENG signal estimation is a severely ill-posed inverse problem due to uncertainties in the model, low resolution due to limitations of the data, geometric constraints and the difficulty in separating the signal from biological and exogenous noise. In this paper, a reduced computational model for the forward problem is proposed, and the ENG problem is addressed by using beamformer techniques. Furthermore, we show that using a hierarchical statistical model, it is possible to develop an adaptive beamformer algorithm that estimates directly the source variances rather than the voltage source itself. The advantage of this new algorithm, e.g., over a traditional adaptive beamformer algorithm, is that it allows a very stable noise reduction by averaging over a time window. In addition, a new projection technique for separating sources and reducing cross-talk between different fascicle signals is proposed. The algorithms are tested on a computer model of realistic nerve geometry and time series signals.

Development of a low-cost non-invasive neurostimulator for applications in post stroke hemiplegics

A noninvasive low-cost, programmable single channel stimulator with generating various patterns of waveforms for Functional Electrical Stimulation (FES) applications has been developed. The prototype is small, battery-operated, and flexible for various clinical applications in home and in clinics. A microcontroller is heart of the stimulator used for generating rectangular waveforms and natural pattern of Tibialis Anterior (TA) muscle waveform and controls the pulse rate and frequency. This FES system is used for rehabilitation of persons who suffered a central nervous system lesion and lost voluntary control over muscles necessary for standing, walking, hand-grasp etc., and to regain lost functions.

J1602-1-1 指・手首運動筋のFES運動点探索装置の開発([J1602-1]機械の知能化と脳工学応用)

There are motor point maps as index of stimulation points to move each muscle for functional electrical stimulation (FES). However we'll usually have to search detailed motor points by trial and error when arranging electrodes since individual differences are large. In this research, we developed a system aids searching motor points of fingers and wrist muscles. It contains 12 × 10 electrodes which cover a forearm and sensors which catch movement of each finger and wrist. It chooses a pair of electrodes in order and stimulates a subject. When the response was measured, it records the response movement and the position of electrode pair. As a result, we obtained the generated motor point map.