Cycling by means of functional electrical stimulation.

The goal of this paper was the development of an optimized stimulation pattern of leg muscles that would allow paraplegic subjects to perform the movement of pedaling and thereby to drive a tricycle by means of functional electrical stimulation (FES). To obtain maximum average power output with minimum muscle force, the start, duration and amplitude of the stimulation signal applied to the individual muscles had to be optimized depending on the pedaling frequency. For the basic theoretical investigations the rider-tricycle system was modeled as a rigid body system on which the muscle forces are applied as joint moments. The muscles gluteus maximus, rectus femoris, vastii, and hamstrings were stimulated and the passive forces of some other muscles were considered. The modeling and simulation approach was then used to produce maximum power pedaling and steady-state pedaling at 35 rpm. Hamstrings (41.9%) and vastii (35.8%) were the primary contributors to the optimization cost function of maximum power with minimum muscle loading. Based on these theoretical investigations an efficient stimulation pattern could be provided, taking into account the realistic possibilities of today's practical applications.     

The effect of joint angle on the timing of muscle contractions elicited by neuromuscular electrical stimulation

Neuromuscular electrical stimulation was used to evoke isometric knee extension contractions in seven individuals with spinal cord injury (SCI) and the time for knee extension torque to rise and fall was measured across a range of knee angles. The stimulated muscles took more than twice as long to develop 50% of maximum torque at an angle of 15 degrees, compared to an angle of 90 degrees. This time difference comprised both an increased delay before torque rose above resting levels (31 +/- 3 ms at 90 degrees, 67 +/- 24 ms at 15 degrees), and a prolonged duration over which torque was rising (72 +/- 14 ms at 90 degrees, 140 +/- 62 ms at 15 degrees). There was no change, however, in the time taken for torque to fall after cessation of stimulation at different knee angles (58 +/- 5-ms delay, 60 +/- 11-ms fall time). The difference in torque rise time with joint angle has implications for modeling functional activities that differ greatly in their joint angles. This study provides regression equations whereby activation times for the quadriceps muscles of individuals with SCI can be predicted for specific angles of knee flexion.     

A predictive fatigue model. I. Predicting the effect of stimulation frequency and pattern on fatigue

Previously we developed a mathematical force- and fatigue-model system that could predict fatigue produced by a wide range of frequencies and pulse patterns. However, the models tended to overestimate the forces produced by higher frequency trains. This paper presents modifications to our previously developed force- and fatigue-model system to improve the accuracy in predicting forces during repetitive activation of human skeletal muscle. By comparing the predictions produced by the modified force and fatigue models to those by our previous models, the modification appears to be successful. The current force- and fatigue-model system accounts for about 93% variance in experimental data produced by fatigue protocols consisting of trains with a wide range of frequencies and pulse patterns. In addition, the present models successfully predict the effect of stimulation frequency and pulse pattern on muscle fatigue. The success of our current force- and fatigue-model system suggests its potential use in helping to identify the optimal activation pattern to use during the clinical application of functional electrical stimulation.     

Development of a circuit for functional electrical stimulation

This paper examines the various design of a multiple-purpose portable functional electrical stimulator which is used in surface stimulation of paralyzed muscle of patients with stroke and results in limb activation. The functionality, circuit performance and reliability of the circuits will be examined. Analysis, design, and experimental results are presented.     

Optimal control of walking with functional electrical stimulation: a computer simulation study.

Bipedal locomotion was simulated to generate a pattern of activating muscles for walking using electrical stimulation in persons with spinal cord injury (SCI) or stroke. The simulation presented in this study starts from a model of the body determined with user-specific parameters, individualized with respect to the lengths, masses, inertia, muscle and joint properties. The trajectory used for simulation was recorded from an able-bodied subject while walking with ankle-foot orthoses. A discrete mathematical model and dynamic programming were used to determine the optimal control. A cost function was selected as the sum of the squares of the tracking errors from the desired trajectories, and the weighted sum of the squares of agonist and antagonist activations of the muscle groups acting around the hip and knee joints. The aim of the simulation was to study plausible trajectories keeping in mind the limitations imposed by the spinal cord injury or stroke (e.g., spasticity, decreased range of movements in some joints, limited strength of paralyzed, externally activated muscles). If the muscles were capable of generating the movements required and the trajectory was achieved, then the simulation provided two kinds of information: 1) timing of the onset and offset of muscle activations with respect to the various gait events and 2) patterns of activation with respect to the maximum activation. These results are important for synthesizing a rule-based controller.     

Prevention of muscle disuse atrophy by low-frequency electrical stimulation in rats

When muscles lose neural drive, they atrophy rapidly. Neuromuscular electrical stimulation (NMS) has been used in attempts to prevent or reverse the atrophy, but optimal stimulation programs and parameters are not well defined. In this study, we investigated the effects of four different stimulation patterns on disuse atrophy produced in the tibialis anterior, lateral gastrocnemius, and soleus muscles of rats paralyzed with tetrodotoxin for seven days. Stimulation paradigms differed from one another by their stimulation frequency (2 or 10 pulses/s) and by their stimulation period (2 or 10 h a day). Results showed that stimulation with 2 pulses/s, paradigms were more effective at preventing disuse muscle atrophy than higher-frequency stimulation. The most marked difference was in the slow soleus muscle, which had only 10% mean atrophy when stimulated at 2 pulses/s for 10 h, compared to 26% atrophy when stimulated at 10 pulses/s for either 2 or 10 h and 32% atrophy in unstimulated, paralyzed controls. The level of atrophic change was not correlated with the levels of serum creatine kinase, used as an index of muscle damage. Results suggest that remediation of disuse atrophy may be accomplished using unphysiologically low rates of motor-unit activation despite the relatively low force produced by such unfused contractions. This may have significant implications for the design of therapies for muscle paralysis consequent to upper-motoneuron lesions.     

Tremor suppression using functional electrical stimulation: a comparison between digital and analog controllers.

In this study, we compared digital and analog versions of a functional electrical stimulator designed to suppress tremor. The device was based on a closed-loop control system designed to attenuate movements in the tremor frequency range, without significantly affecting slower, voluntary movements. Testing of the digital filter was done on three patients with Parkinsonian tremor and the results compared to those of a functional electrical stimulation device based on an analog filter evaluated in a previous study. Additional testing of both the analog and digital filters was done on three subjects with no neurological impairment performing tremor-like movements and slow voluntary movements. We found that the digital controller provided a mean attenuation of 84%, compared to 65% for the analog controller.     

Implanted functional electrical stimulation system for mobility in paraplegia: a follow-up case report.

A 16-channel functional electrical stimulation (FES) system has been implanted in a person with T10 paraplegia for over a year. The system consists of two eight-channel radio frequency controlled receiver-stimulators delivering stimuli through a network of 14 epimysial and two intramuscular electrodes. Using this system and a walker for support, the subject was able to stand up for 8 min and walk regularly for 20 m. The standing duration was limited by arm fatigue since upper extremities supported an average of 25% of body weight. This was due to suboptimal hip extension and some undesired recruitment of rectus femoris and sartorius with stimulation of quadriceps electrodes. The left quadriceps exhibited rapid fatigue that limited walking distance and duration. The metabolic energy requirements were well within the aerobic limits of the sedentary paraplegic population. At one-year follow-up evaluation all electrodes are functional except one intramuscular electrode. The implant caused no adverse physiological effects and the individual reported health benefits such as increased energy and overall fitness as a result of the FES system use. With further improvements in muscle response through innovative surgical techniques, the 16-channel implanted FES system can be a viable addition to exercise and mobility function in persons with paraplegia.     

基于GA-SVR模型的肌力康复电刺激系统的设计研究

为了实现康复电刺激系统治疗参数的个性化定制及实时调整,提出了一种基于调制中频电刺激的下肢肌力康复闭环电刺激系统。设计低频调制中频刺激电路,基于遗传算法建立了电刺激参数与膝关节角度之间的支持向量机回归预测模型,并搭建基于模糊内模控制PID的闭环反馈系统,以达到更精确稳定的参数设置效果。通过膝关节运动实验表明,被试者在无痛感的前提下更接近预期的关节运动轨迹,30组膝关节运动角度与预期值最大均方根误差为10.21°,最小均方根误差为5.48°。相比传统低频电刺激,肌电平均振幅具有20μV以上提升。本文提出的电刺激系统参数可实现因人而异,且可根据闭环反馈结果进行实时调整,该系统能有效活化肌肉、提升肌力,在肌力康复步态训练中有较好的应用前景。     

A predictive fatigue model. II. Predicting the effect of resting times on fatigue

For pt. I see ibid., vol. 10, no. 1, p. 48-58 (2002). We have recently developed a force- and fatigue-model system that accurately predicted the effect of stimulation frequency on muscle fatigue (see pt. I). The data used to test the model were produced by stimulation trains with resting times of 500 ms. Because the resting times between stimulation trains affect muscle fatigue, this study tested the model's ability to predict the effect of resting times on fatigue. In addition, because this study included different subjects than those used to develop the model, the validity of the model could be tested. Data were collected from human quadriceps femoris muscles using fatigue protocols that included resting times of 500, 750, or 1000 ms. Our results showed that the model predicted fatigue as being a decreasing function of resting time, which was consistent with experimental data. Reliability tests between the experimental data and predictions showed interclass correlation coefficients of 0.97, 0.95, and 0.81 for the initial, final, and percentage decline in peak forces, respectively, suggesting strong agreement between the experimental data and the predictions by the model. The success of our current force- and fatigue-model system helps to validate the model and suggests its potential use in identifying the optimal activation pattern during clinical application of functional electrical stimulation.     

The optimal stimulation pattern for skeletal muscle is dependent on muscle length

Stimulation patterns can be optimized by maximizing the force-time integral (FTI) per stimulation pulse of the elicited muscle contraction. Such patterns, providing the desired force output with the minimum number of pulses, may reduce muscle fatigue, which has been shown to correlate to the number of pulses delivered. Applications of electrical stimulation to use muscle as a controllable biological actuator may, therefore, be improved. Although muscle operates over a range of lengths, optimized patterns have been determined only at optimal muscle length. In this study, the patterns with up to four pulses that produced the highest isometric FTI were determined at 10 muscle lengths for 11 rabbit tibialis anterior muscles. The interpulse intervals (IPIs) used ranged from 4 to 54 ms. At high muscle length, the optimal stimulation pattern consisted of an initial short IPI (doublet) followed by longer IPIs, in agreement with previous studies. However, at low length, the third pulse still elicited more than linear summation (triplet); furthermore, the relative enhancement of the FTI per pulse was considerably larger at low length than at high length, suggesting that optimal stimulation patterns are length dependent.     

Test bed with force-measuring crank for static and dynamicinvestigations on cycling by means of functional electrical stimulation

Cycling by means of functional electrical stimulation (FES) is an attractive training method for individuals with paraplegia. The physiological benefits of FES are combined with the psychological incentive of independent locomotion. In addition, cycling has the advantage in that the generated muscle forces are converted into drive power with relatively high efficiency compared to other means of locomotion, e.g., walking. For the design of an appropriate cycling device and the development of optimal stimulation patterns, it has to be investigated how the geometry for FES cycling, influenced by individual parameters of the FES-generated drive torques and the magnitude of variations among subjects with paraplegia, can be optimized. This study shows the design of a freely adjustable test bed with additional motor drive which allows static and dynamic measurements of force components and drive torque at the crank. Furthermore, the influence of geometry and various individual parameters on FES pedaling can be tested for each subject individually. A pedal path realized by a three-bar linkage that was optimized according to preliminary simulations further increases leg cycling efficiency. Safety precautions avoid injuries in case of excessive forces, e.g., spasms. Test results illustrate the application of the test bed and measurement routines. A test series with four paraplegic test persons showed that the presented static and dynamic measurement routines allow to provide optimal stimulation patterns for individual paraplegic subjects. While pedaling with these optimal stimulation patterns only negligible negative active drive torques, due to active muscle forces, were applied to the crank and sufficient drive power was generated to power a cycle independently     

Sites of neuronal excitation by epiretinal electrical stimulation.

Action potentials arising from retinal ganglion cells ultimately create visual percepts. In persons blind from retinitis pigmentosa and age-related macular degeneration, viable retinal ganglion cells remain, and the retina can be stimulated electrically to restore partial sight. However, it is unclear what neuronal elements in the retina are activated by epiretinal electrical stimulation. This study investigated the effects of cellular geometry, electrode to neuron distance, stimulus duration, and stimulus polarity on excitation of a retinal ganglion cell with an epiretinal electrode. Computer-based compartmental models representing simplified retinal ganglion cell morphology provided evidence that the threshold for excitation was lower when an electrode was located in proximity to the characteristic 90 degrees bend in the axon of the retinal ganglion cell than when it was located over a passing axon of the nerve fiber layer. This electrode-position-dependent difference in threshold occurred with both cathodic and anodic monophasic stimuli, with point source and disk electrodes, at multiple electrode-to-neuron distances, and was robust to changes in the electrical properties of the model. This finding reveals that the physical geometry of the retinal ganglion cells produces stimulation thresholds that depend strongly on electrode position. The low excitation thresholds near the bend in the axon will result in activation of cells local to the electrode at lower currents than required to excite passing axons. This pattern of activation provides a potential explanation of how epiretinal electrical stimulation results in the production of punctuate, rather than diffuse or streaky phosphenes.     

The function of the finger intrinsic muscles in response to electrical stimulation.

The actions of the dorsal interosseous, volar interosseous, and lumbrical muscles were investigated using applied electrical stimulation and recording the moments that were generated across the metacarpophalangeal joint in flexion/extension and abduction/adduction, the proximal interphalangeal joint in flexion/extension, and the distal interphalangeal joint in flexion/extension. These measurements were made isometrically at various joint angles and levels of stimulation with both able bodied subjects and persons who had sustained tetraplegia. It was determined that the dorsal interossei, including the first, were strong abductors of the fingers and generated a significant moment in metacarpophalangeal (MP) joint flexion and interphalangeal (IP) joint extension. The volar interossei were the primary adductors of the fingers, as well as providing a significant moment in MP joint flexion and IP joint extension. The lumbrical muscles were found to be MP joint flexors and IP joint extensors, although the moments that were generated were on average 70% lower than the interossei. The role of the lumbricals as finger abductors or adductors could not be determined from the data. This information on the actions and moment generating capabilities of the intrinsic muscles led to the incorporation of the interossei into electrically induced hand grasp provided by an implanted neuroprosthesis. The evaluation of the intrinsic muscles in the neuroprosthesis was accomplished by recording the moment generating capabilities of these muscles across each of the joints of the finger. These muscles were capable of generating moments that were 80-90% of the average attained by the able bodied subjects, and have provided a substantial improvement to the electrically induced hand grasp.     

数字调制参数校准仿真研究

表征信号调制质量的数字调制参数是数字通信系统的主要技术指标,数字调制参数校准可以保证通信设备的质量。为给通信装备数字调制参数校准工作提供技术支持,本文总结研究了数字调制参数校准的基本方法,在建立数字调制参数校准仿真通用模块的基础上,进行了QPSK与FSK数字调制参数校准方法研究,并通过仿真及试验证实了两种方法的有效性。通过校准仿真,大大减少了校准方法研究过程中的硬件损耗、降低了研究成本。     

The effect of corrosion myths on national electrical standards

It is argued that stainless steel does corrode and should not be listed as an acceptable, perhaps preferred, material for ground rods. A review of corrosion basics and a detailed account of how stainless steel does corrode are provided. Examples of other misconceptions on the part of electrical engineers, as well as corrosion engineers, are also discussed. This discussion underlines the need for a strong liaison between the IEEE and the National Association of Corrosion Engineers (NACE)     

Cycling induced by electrical stimulation improves muscle activation and symmetry during pedaling in hemiparetic patients

A randomized controlled trial, involving 35 post-acute hemiparetic patients, demonstrated that a four-week treatment of cycling induced by functional electrical stimulation (FES-cycling) promotes motor recovery. Analyzing additional data acquired during that study, the present work investigated whether these improvements were associated to changes in muscle strength and motor coordination. Participants were randomized to receive FES-cycling or placebo FES-cycling. Clinical outcome measures were: the Motricity Index (MI), the gait speed, the electromyography activation of the rectus femoris and biceps femoris, and the mechanical work produced by each leg during voluntary pedaling. To provide a comparison with normal values, healthy adults also carried out the pedaling test. Patients were evaluated before, after training, and at follow-up visits. A significant treatment effect in favor of FES-treated patients was found in terms of MI scores and unbalance in mechanical works, while differences in gait speed were not significant (ANCOVA). Significant improvements in the activation of the paretic muscles were highlighted in the FES group, while no significant change was found in the placebo group (Friedman test). Our findings suggested that improvements in motor functions induced by FES-cycling training were associated with a more symmetrical involvement of the two legs and an improved motor coordination.     

Excitability of chronic hemiparetic muscles: determination of chronaxie values and strength-duration curves and its implication in functional electrical stimulation.

Central nervous system disorders affect the anatomy and physiology of the lower motoneuron. This fact has an impact on the stimulation parameters, especially on the duration of the stimulating impulses, for functional electrical stimulation in chronic hemiparetic patients. The aim of this study was thus to test the excitability and to determine chronaxie values and strength-duration curves of weak wrist and finger extensor muscles and spastic finger and wrist flexor muscles in the hemiparetic arm. Twelve patients with chronic hemiplegia (>6 months after the onset of the cerebral lesion) participated in the study. A constant current stimulator was used. As to chronaxie values no significant differences were found between the extensor muscles (mean+/-SD: 0.44+/-0.16 ms) and flexor muscles (mean+/-SD: 0.36+/-0.22 ms). A moderate variability was seen for both extensor muscles (0.2-0.8 ms) and flexor muscles (0.1-0.9 ms). These values are well within the normal range determined for innervated muscles. All strength-duration curves were completely normal for each muscle. We conclude that in chronic hemiparetic muscles, impulses of the same duration can be used as in muscles of healthy subjects.     

Colon emptying induced by sequential electrical stimulation in rats.

Electrical stimulation could be used to induce colon emptying. The present experiments were performed to establish a stimulation pattern to optimize the stimulation parameters and to test neural involvement in propulsion induced by electrical stimulation. Colon segments were sequentially stimulated using rectangular pulses. The resulting propulsive activity displaced intraluminal content in consecutive propulsion steps. The propulsion steps differed in displacement latency, distance, and velocity along the stimulated colon. Increasing the pulse duration or amplitude resulted in a decrease of the latency. Increasing the stimulation amplitude doubled the displacement distance. The frequencies tested in the present study did not affect propulsion. Inhibition of cholinergic and nitrergic pathways inhibited propulsion. Electrical stimulation can induce colonic propulsion. Motor differences are present along the descending colon. The most suitable combination of pulse parameters regarding colon stimulation is 0.3 ms, 5 mA, 10 Hz. Neural circuits are involved in propulsion when using these values.