B.J. Andrews

The role of functional electrical stimulation in the rehabilitation of patients with incomplete spinal cord injury -observed benefits during gait studies

The benefits of a functional electrical stimulation (FES) gait programme were assessed in a group of 6 incomplete spinal cord injured subjects. Measurements were made of quadriceps spasticity, lower limb muscle strength, postural stability in standing, spatial and temporal values of gait, physiological cost of gait and independence in activities of daily living. The subjects were assessed before commencement of the programme and after a period of gait training using FES. The benefits derived as a result of the FES gait programme included a reduction in quadriceps tone, an increase in voluntary muscle strength, a decrease in the physiological cost of gait and an increase in stride length.

Computer simulation of FES standing up in paraplegia: a self-adaptive fuzzy controller with reinforcement learning

Using computer simulation, the theoretical feasibility of functional electrical stimulation (FES) assisted standing up is demonstrated using a closed-loop self-adaptive fuzzy logic controller based on reinforcement machine learning (FLC-RL). The control goal was to minimize upper limb forces and the terminal velocity of the knee joint. The reinforcement learning (RL) technique was extended to multicontroller problems in continuous state and action spaces. The validated algorithms were used to synthesize FES controllers for the knee and hip joints in simulated paraplegic standing up. The FLC-RL controller was able to achieve the maneuver with only 22% of the upper limb force required to stand-up without FES and to simultaneously reduce the terminal velocity of the knee joint close to zero. The FLC-RL controller demonstrated, as expected, the closed loop fuzzy logic control and on-line self-adaptation capability of the RL was able to accommodate for simulated disturbances due to voluntary arm forces, FES induced muscle fatigue and anthropometric differences between individuals. A method of incorporating a priori heuristic rule based knowledge is described that could reduce the number of the learning trials required to establish a usable control strategy. We also discuss how such heuristics may also be incorporated into the initial FLC-RL controller to ensure safe operation from the onset.

Localized electrical nerve blocking

Localized electrical nerve blocking was investigated in computer simulation and in vivo trials for sinusoidal frequencies between 5 and 20 kHz. Computer simulations indicated that a localized transmission block of the axons could occur in each of the axon models. An approximation of nerve stimulation was derived from individual axon simulations conducted over axon diameters of 5-15 /spl mu/m and electrode to axon distances of 0.25 to 2.0 mm. Examination of the membrane voltage and ionic gate potentials indicated that the block could be attributed to an elevated membrane voltage. The elevated membrane voltage could prevent conduction of action potentials through the region of the sinusoidal currents. At lower amplitudes, the sinusoidal current could stimulate the axon and generate a continuous series of action potentials. In vivo trials demonstrated that the sinusoidal frequencies of greater than 10 kHz would cause a localized block in rats. Sinusoidal frequencies below 5 kHz would lead to a reduction in muscle force that appeared to be caused by depletion of transmitter at the neuromuscular junction. As indicated by the computer models of rat nerves, the endplate depletion block occurred at a lower frequency (below 5 kHz) than the block (above 10 kHz). A partial block of the axon was demonstrated, suggesting that sinusoidal currents could be used to provide selective stimulation if they are combined with distal electrical stimulation.

Reconstructing muscle activation during normal walking: a comparison of symbolic and connectionist machine learning techniques

One symbolic (rule-based inductive learning) and one connectionist (neural network) machine learning technique were used to reconstruct muscle activation patterns from kinematic data measured during normal human walking at several speeds. The activation patterns (or desired outputs) consisted of surface electromyographic (EMG) signals from the semitendinosus and vastus medialis muscles. The inputs consisted of flexion and extension angles measured at the hip and knee of the ipsilateral leg, their first and second derivatives, and bilateral foot contact information. The training set consisted of data from six trials, at two different speeds. The testing set consisted of data from two additional trials (one at each speed), which were not in the training set. It was possible to reconstruct the muscular activation at both speeds using both techniques. Timing of the reconstructed signals was accurate. The integrated value of the activation bursts was less accurate. The neural network gave a continuous output, whereas the rule-based inductive learning rule tree gave a quantised activation level. The advantage of rule-based inductive learning was that the rules used were both explicit and comprehensible, whilst the rules used by the neural network were implicit within its structure and not easily comprehended. The neural network was able to reconstruct the activation patterns of both muscles from one network, whereas two separate rule sets were needed for the rule-based technique. It is concluded that machine learning techniques, in comparison to explicit inverse muscular skeletal models, show good promise in modelling nearly cyclic movements such as locomotion at varying walking speeds. However, they do not provide insight into the biomechanics of the system, because they are not based on the biomechanical structure of the system.

Improving limb flexion in FES gait using the flexion withdrawal response for the spinal cord injured person

In the restoration of gait for paraplegics using functional electrical stimulation, the method most commonly used to produce hip flexion for the swing phase of gait has been the elicitation of the flexion withdrawal response. Several problems have been noted with the response: there is a decrease in the magnitude of the hip flexion to repeated stimuli (habituation); long latency; and inhibition of the response when stimulated bilaterally. These have been characterized and methods for overcoming the problems tested. Results show that increasing stimulation frequency reduces latency. Habituation can be reduced in some subjects by multiplexing two sites of stimulation. Habituation can further be reduced by applying single high-intensity pulses and this has been used in a one-step-ahead controller for regulating hip flexion angle. Inhibition due to bilateral stimulation had been significantly reduced by altering the timing of the stimulation to the two legs.

Development of an indoor rowing machine with manual FES controller for total body exercise in paraplegia

Concept 2 indoor rowing machine (Concept 2 Inc., USA) was modified for functional electrical stimulation (FES) rowing exercise in paraplegia. A new seating system provides trunk stability and constrains the leg motion to the sagittal plane. A 4-channel electrical stimulator activates the quadriceps and hamstrings in Drive and Recovery phases of the rowing cycle, respectively. Two force-sensing resistors (FSR) on the handle measure the thumb press as the command signal to the electrical stimulator. Optical encoders measure the positions of the seat and handle during rowing. To synchronize the voluntarily controlled upper body movement with the FES controlled leg movement, a novel manual control system was developed. It uses the voluntary thumb presses to control the timing of the stimulation to the paralyzed leg muscles. The manual control system was intuitive and easy to learn and resulted in well-coordinated rowing. Evaluation of the modified rower by paraplegic volunteers showed that it is effective, safe, and affordable exercise alternative for paraplegics.

Fuzzy logic control of FES rowing exercise in paraplegia

An indoor personal rowing machine (Concept 2 Inc., Morrisville, VT) has been modified for functional electrical stimulation assisted rowing exercise in paraplegia. To successfully perform the rowing maneuver, the voluntarily controlled upper body movements must be coordinated with the movements of the electrically stimulated paralyzed legs. To achieve such coordination, an automatic controller was developed that employs two levels of hierarchy. A high level finite state controller identifies the state or phase of the rowing motion and activates a low-level state-dedicated fuzzy logic controller (FLC) to deliver the electrical stimulation to the paralyzed leg muscles. A pilot study with participation of two paraplegic volunteers showed that FLC spent less muscle energy, and produced smoother rowing maneuvers than the existing On-Off constant-level stimulation controller.

The use of functional electrical stimulation to assist gait in patients with incomplete spinal cord injury

The use of FES (functional electrical stimulation) for gait reproduction in six patients with spinal cord injury is described. Following a detailed neuromuscular assessment the patients commenced a muscle conditioning programme using electrical stimulation applied via surface electrodes. Once patients were strong enough to stand, gait synthesis was initiated in the laboratory utilizing a programmable electrical stimulator. When a satisfactory gait pattern had been achieved, patients used their portable stimulator at home. All six patients became able to stand and walk using the FES system and completed the home phase of the programme. Three patients continue to use the system at home for exercise and walking; the other patients have discontinued using the system, preferring a wheelchair or their original orthoses. We conclude that FES-assisted walking is feasible in patients with incomplete spinal cord injury, even with severe motor loss. Further advances in technology are needed for the system to become applicable to a larger number of patients.

Reduction of muscle fatigue in man by cyclical stimulation

In order to develop a control system for electrical stimulation of paralysed muscle and improve muscle resistance to fatigue, it is useful to investigate the possibilities of simulating the control systems of the normal body. One way is the periodic shifting of stimulation from one muscle to another. This technique is called sequential stimulation and allows sufficient rest time for each muscle to reduce fatigue and consequently prolong muscle strength. It can also be seen to improve the muscle recovery time. In the following study, the muscles rectus femoris, vastus lateralis and vastus medialis were used to keep the knee locked and extended during stimulation. Several experiments were carried out using a three-channel computer controlled stimulator. The results for three-phase sequential stimulation (33% duty cycle per muscle) were most effective and significantly improved the muscle fatigue characteristics.

Cardiorespiratory responses during arm ergometry, functional electrical stimulation cycling, and two hybrid exercise conditions in spinal cord injured

Purpose. The purpose of this study was to compare peak functional aerobic power (VO2 peak) across four different types of exercise: arm crank ergometry (ACE), functional electrical stimulation (FES) cycling, and two hybrid exercise conditions: FES cycling combined with ACE and FES rowing using a newly developed rowing device (ROWSTIM). Methods. Five participants (C7 – T12), four male paraplegics with neurologically complete spinal cord injury (SCI), and one male with neurologically incomplete SCI, underwent a progressive maximal peak oxygen exercise test to ascertain peak physical work capacity during arm cranking, FES cycling, FES cycling combined with arm cranking and FES rowing. Results. Metabolic variables were significantly lower for FES cycling versus ACE, FES cycling combined with ACE and FES rowing measures (P < 0.05). However there were no significant differences between ACE, FES cycling combined with ACE and FES rowing. Conclusions. Preliminary results suggest that the ROWSTIM is as effective an exercise device or training tool for persons with SCI as ACE or combined FES-cycling and ACE, and more effective than FES-cycling. A larger sample size and further technological developments of the ROWSTIM are needed to demonstrate the efficacy of rowing over other hybrid exercise modalities and ACE.