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Biomedical subjects

M H Granat

Publications and source records attributed to M H Granat.

At least 19 recordsLinked to original sources
PubMed2000

The effects of knee and ankle flexion on ground clearance in paraplegic gait.

OBJECTIVE: To investigate the effects of knee flexion and ankle dorsiflexion on ground clearance during the swing phase of paraplegic gait.BACKGROUND. Limitations of currently available walking orthoses are high energy consumption and upper limb loading. Knee flexion in the swing phase has been suggested as a means of reducing these.METHODS. Kinematic data of paraplegic gait in two currently available orthoses were used to simulate the effects of knee flexion and ankle dorsiflexion on the swing foot ground clearance. This was used to validate a mathematical model of a simple ideal gait that was also developed.RESULTS. It was shown that the implementation of knee flexion alone leads to a loss or no change in ground clearance. Implementing knee flexion and ankle dorsiflexion can be used to increase ground clearance.CONCLUSION. Flexion at the knee and ankle during the swing phase can potentially be used to allow a reduction in compensatory mechanisms by easing swing foot ground clearance. RelevanceWalking orthoses are valuable in the clinical management of paraplegia, providing both physiological and psychological benefits. Functional improvements can only serve to encourage their greater usage.

Adult↗
PubMed2000

Therapeutic effects of functional electrical stimulation of the upper limb of eight children with cerebral palsy.

Functional electrical stimulation (FES) of the upper limb has been used for patients with a variety of neurological conditions, although few studies have been conducted on its use on the upper limb of children with cerebral palsy (CP). The aim of this study was to investigate the effect of cyclic FES on the wrist extensor muscles of a group of eight children (five boys, three girls) with hemiplegic CP (mean age 10 years). The study design involved a baseline (3 weeks), treatment (6 weeks), and follow-up (6 weeks). FES was applied for 30 minutes daily during the treatment period of the study. Improvements in hand function (p < or = 0.039) and active wrist extension (p = 0.031) were observed at the end of the treatment period. These improvements were largely maintained until the end of the follow-up period. No significant change was observed in the measurements of wrist extension moment during the treatment period (p = 0.274). Hand function in this group of children improved after they were exposed to FES of wrist extensor muscles. This suggests that FES could become a useful adjunct therapy to complement existing management strategies available for this patient population.

Cerebral Palsy↗
PubMed1999

Gait control system for functional electrical stimulation using neural networks.

In functional electrical stimulation (FES) systems for restoring walking in spinal cord injured (SCI) individuals, hand switches are the preferred method for controlling stimulation timing. Through practice the user becomes an 'expert' in determining when stimulation should be applied. Neural networks have been used to 'clone' this expertise but these applications have used small numbers of sensors, and their structure has used a binary output, giving rise to possible controller oscillations. It was proposed that a three-layer structure neural network with continuous function, using a larger number of sensors, including 'virtual' sensors, can be used to 'clone' this expertise to produce good controllers. Using a sensor set of ten force sensors and another of 13 'virtual' kinematic sensors, a good FES control system was constructed using a three-layer neural network with five hidden nodes. The sensor set comprising three sensors showed the best performance. The accuracy of the optimum three-sensor set for the force sensors and the virtual kinematic sensors was 90% and 93%, respectively, compared with 81% and 77% for a heel switch. With 32 synchronised sensors, binary neural networks and continuous neural networks were constructed and compared. The networks using continuous function had significantly fewer oscillations. Continuous neural networks offer the ability to generate good FES controllers.

Electric Stimulation↗
PubMed1999

Reliability of neural-network functional electrical stimulation gait-control system.

Functional electrical stimulation (FES) has been used for restoring walking in spinal-cord injured (SCI) persons. Using artificial intelligence (AI), FES controllers have been developed that allow the automatic phasing of stimulation, to replace the function of hand or heel switches. However, there has been no study to evaluate the reliability of these AI systems. Neural networks were used to construct FES controllers to control the timing of stimulation. Different numbers of sensors in the sensor set and different numbers of data points from each sensor were used. Two incomplete-SCI subjects were recruited, and each was tested on three separate occasions. The results show the neural-network controllers can maintain a high accuracy (around 90% for the two- and three-sensor groups and 80% for the one-sensor group) over a period of six months. Two or three sensors were sufficient to provide enough information to construct a reliable FES control system, and the number of data points did not have any effect on the reliability of the system.

Adult↗
PubMed1999

A practical gait analysis system using gyroscopes.

This study investigated the possibility of using uni-axial gyroscopes to develop a simple portable gait analysis system. Gyroscopes were attached on the skin surface of the shank and thigh segments and the angular velocity for each segment was recorded in each segment. Segment inclinations and knee angle were derived from segment angular velocities. The angular signals from a motion analysis system were used to evaluate the angular velocities and the derived signals from the gyroscopes. There was a good correlation between these signals. When performing a turn the signals of segment inclination and knee angle drifted. Two methods were used to solve this: automatically resetting the system to re-initialise the angle in each gait cycle, and high-pass filtering. They both successfully corrected this drift. A single gyroscope on the shank segment could provide information on segment inclination range, cadence, number of steps, and an estimation of stride length and walking speed.

Algorithms↗
PubMed1999

The application of air bag technology: an objective clinical measure of involuntary muscle spasm.

OBJECTIVES: To develop a technique which could objectively monitor and quantify spasms in spinal cord injured persons. METHODS: This technique used accelerometers to detect movements in the limb caused by spasms. Accelerometer signals from movements caused by spasms and a variety of movements caused by other subject activities (movement in a wheelchair, transfers etc) were recorded and linear discriminant analysis was used to distinguish between spasms and other activities. Individual spasms were quantified by their duration, magnitude and energy and were recorded over a 24-h period. RESULTS: Limb movements caused by spasms were shown to be well correlated with the EMG activity of the muscles causing the movement. Movements caused by spasms and movements caused by other subject activities could be reliably distinguished. Subjects showed a characteristic spasm pattern and it was possible to quantify the severity of the spasms and to determine precisely when they occurred. CONCLUSION: This technique for monitoring and quantifying spasms has the potential to be used as a clinical tool to aid in the evaluation and prescription of treatment.

Biomechanical Phenomena↗
PubMed1999

Demand for and use of functional electrical stimulation systems and conventional orthoses in the spinal lesioned community of the UK.

The use of and demand for functional electrical stimulation (FES) systems and conventional orthoses in the spinal cord lesioned population was assessed. The assessment was conducted by a postal survey of the members of the spinal injury associations in the U.K. Out of all the respondents, only 2% had used an FES system for walking. In comparison, 13% had used some kind of orthosis. Of the small numbers who had used an FES system for walking, more than half had no functional walking abilities. The majority of orthosis users had some independent walking ability. The demand for walking improvements was high among the respondents although this was not matched by the demand for improved orthotic solutions. In conclusion, it would appear that there is a need for simple FES systems offering walking improvement to the incomplete spinal cord lesioned (SCI) subject.

Age Factors↗
PubMed1999

Prevention of shoulder subluxation after stroke with electrical stimulation.

BACKGROUND AND PURPOSE: Subluxation is a significant problem in poststroke hemiplegia, resulting in pain and loss of function. Current treatments are not proved and not considered effective. It has been demonstrated that cyclical electrical stimulation of the shoulder muscles can reduce existing subluxation. The purpose of this study was to determine whether electrical stimulation could prevent subluxation in both the short and long terms. METHODS: A prospective, randomized controlled study was used to determine the efficacy of electrical stimulation in preventing shoulder subluxation in patients after cerebrovascular accidents. Forty patients were selected and randomly assigned to a control or treatment group. They had their first assessment within 48 hours of their stroke, and those in the treatment group were immediately put on a regimen of electrical stimulation for 4 weeks. All patients were assessed at 4 weeks after stroke and then again at 12 weeks after stroke. Assessments were made of shoulder subluxation, pain, and motor control. RESULTS: The treatment group had significantly less subluxation and pain after the treatment period, but at the end of the follow-up period there were no significant differences between the 2 groups. CONCLUSIONS: Electrical stimulation can prevent shoulder subluxation, but this effect was not maintained after the withdrawal of treatment.

Aged↗
PubMed1999

The functional use of the reciprocal hip mechanism during gait for paraplegic patients walking in the Louisiana State University reciprocating gait orthosis.

Reciprocally linked orthoses used for paraplegic walking have some form of linkage between the two hip joints. It has been assumed that flexion of the swinging leg is driven by extension of the stance leg. The aims of this study were to investigate the moments generated around the hip joint by the two cables in a Louisiana State University Reciprocating Gait Orthosis (LSU-RGO). Six (6) subjects were recruited from the Regional Spinal Injuries Centre at Southport, who were experienced RGO users. The cables were fitted with strain gauged transducers to measure cable tension. Foot switches were used to divide the gait into swing and stance phases. A minimum of 20 steps were analysed for each subject. Moments about the hip joint for each phase of gait were calculated. There were no moments generated by the front cable in 4 of the subjects. In only 2 subjects did the cable generate a moment that could assist hip flexion during the swing phase. These moments were very low and at best could only have made a small contribution to limb flexion. The back cable generated moments that clearly prevented bilateral flexion. It was concluded that the front cable, as used by these experienced RGO users, did not aid flexion of the swinging limb.

Biomechanical Phenomena↗
PubMed1998

Variability of the dishabituation of flexion reflexes for FES assisted gait in spinal injured man.

Flexion reflexes, elicited by surface stimulation, can be used to produce a simple form of stepping in spinal cord injured (SCI) humans. A drawback of this approach is a decreasing magnitude of flexion reflex to repeated presentations of the stimuli (habituation). Pilot data indicated that high intensity stimulation could produce dishabituation of the reflex. The aim of this study was to examine and quantify the inter- and intra-subject variability of the short and long term conditioning effect of high intensity stimulation on the magnitude of flexion reflexes in a larger number of SCI subjects. Dishabituation was observed in all subjects, however the amount of dishabituation observed was small and highly variable. However the use of high intensity conditioning stimulation may offer a means of coping with habituation in a small number of subjects.

Electric Stimulation Therapy↗
PubMed1998

Virtual artificial sensor technique for functional electrical stimulation.

In the control of Functional Electrical Stimulation (FES) gait systems artificial sensors are used to provide the controller with feedback information. The sensors used range in complexity from simple heel or hand switches to tri-axial accelerometers. There are three basic problems connected with the selection of sensors: the type(s) of sensor(s) to be used, the number of sensors required and the optimum location of the sensor set. In general the choice of the sensor sets has been based on the availability of actual sensors and the experts understanding of where these sensors should be located. Using motion analysis data it is possible to construct an almost unlimited number of virtual sensors on any location of the body surface. Our aim was to develop this technique for construction of virtual sensors and compare these virtual sensors with their physical counterparts. Virtual goniometers, inclinometers, accelerometers and foot switches were constructed and compared with their physical counterparts. In addition visualisation tools were developed to aid in the choice of sensor location. There was a very good correlation between all the virtual and physical sensors. This technique gives flexibility to place virtual sensors almost anywhere on the body surface and also allows the construction of novel sensors.

Acceleration↗
PubMed1998

Evaluation of patterned stimulation for use in surface functional electrical stimulation systems.

The rapid onset of muscle fatigue is one of the major limiting factors when using electrical stimulation to restore functional movement in individuals with a neurological deficit. It has been proposed that muscle efficiency can be improved by using variable frequency pulse trains (VFT), consisting of repeated doublets, rather than a constant frequency train (CFT) of stimulating impulses. The aim of this study was to test this hypothesis. Experiments were conducted on fifteen non-impaired and one spinal cord injured subjects. It was shown that a VFT delivering the same electrical energy with a CFT produces a relative increase in muscle output, attaining a maximum for VFTs composed of doublets with an inter-pulse interval of 5 ms. It was also shown that this effect is highly dependent on the experimental conditions and especially the intensity of applied stimulation and this effect diminishes at high intensity levels. We suggest that any improvement in muscle output observed when using a VFT can be attributed to changes in motor unit recruitment and is not an intrinsic property of the muscle. Our results show that there is practically no benefit in using VFTs for alleviating the problem of fatigue in functional electrical stimulation systems.

Adult↗
PubMed1998

Gait restoration in a spinal cord injured subject via neuromuscular electrical stimulation controlled by an artificial neural network.

Attempts to restore gait in spinal cord injured subjects have stumbled on control difficulties associated to the neuromuscular system's non-linearity and time-variance. Thus, a simple autoadaptive artificial neural network has been devised to control gait swing generation by means of neuromuscular electrical stimulation. Both theoretical and experimental approaches were taken. The computer-based system consisted of a three-layer artificial neural network that read angular data from the hip, knee and ankle joints. The output signal consisted of variations on the applied stimulation pulse width. Surface electrical stimulation was applied to the femoral and peroneal nerves of one leg. Neural network training included off-line supervised learning schemes. The system was tested on a male subject with an incomplete C6-level lesion. Several tests were run to determine whether the off-line trained neural network could correctly control the motion. The effect of on-line learning upon the control performance was also evaluated. The system was found to control the motion with success only at times. Control performance was found to improve in response to the application of on-line learning. Learning stability following on-line learning was found to be satisfactory. In a final test, the artificial neural system had appropriate responses to an initial perturbation, which suggests that further research in this area should be pursued.

Algorithms↗
PubMed1997

Two artificial neural systems for generation of gait swing by means of neuromuscular electrical stimulation.

A three-layer artificial neural network was used for adaptive control of gait swing generated by neuromuscular electrical stimulation (NMES) in a spinal cord injured subject. Network inputs consisted of knee and ankle goniometer signals for System 1, and knee and hip angular data for System 2. Controller output was proportional to changes in applied NMES pulse width (PW). Stimulation was applied to the left femoral and common peroneal nerves. The neural networks were trained off-line and on-line. Network performance was assessed by applying a number of different stimulation PWs and later comparing the resulting motion to a sample good step observed during the same test session. On-line training consisted of negative and positive reinforcement applied at chosen times. Both on-line and off-line training algorithms consisted of an enhanced supervised backpropagation scheme. Performance evaluation results favour the use of System 1 over System 2. Also, a network trained off-line and later submitted to on-line punishment appears to be more reliable (in automatic mode) than the same network after it is submitted to on-line reward or to off-line training alone. Finally, the systems' immediate response to on-line learning was favourable in all cases. Based on the results, a version of System 1 was used to generate walking in the test subject. This test indicated that the system is promising.

Adult↗
PubMed1997

Further development of hybrid functional electrical stimulation orthoses.

In this study two aspects of hybrid functional electrical stimulation (FES) orthoses were investigated: joint motion constraints and FES control strategies. First, the effects of joint motion constraints on the gait of normal subjects were investigated using modern motion analysis systems, including electromyogram (EMG) and heart rate measurements. An orthosis was developed to impose joint motion constraints; the knee and ankle could be fixed or free, and the hip joint could rotate independently or coupled, according to a preset flexion-extension coupling ratio (FECR). Compared with a 1:1 hip FECR, a 2:1 hip FECR was associated with a reduced energy cost and increased speed and step length. The knee flexion during swing significantly reduced energy cost and increased walking speed. Ankle plantar flexion reduced the knee flexing moment during the early stance phase. Second, trials on 3 paraplegic subjects were conducted to implement some of these findings. It appeared that the 2:1 FECR encouraged hip flexion and made leg swing easier. A simple FES strategy increased walking speed and step length and reduced crutch force impulse using fixed orthotic joints.

Ankle↗
PubMed1997

Effects of electrical stimulation on flexion contractures in the hemiplegic wrist.

OBJECTIVE: To study the effects of electrical stimulation (ES) on flexion contractures in the hemiplegic wrist. DESIGN: The investigation was carried out following an OFF (two weeks with rehabilitation only)--ON (two weeks with ES treatment and rehabilitation)--OFF (two weeks rehabilitation only) fixed protocol. SETTING: A stroke ward and an outpatient stroke service. SUBJECTS: Eleven hemiplegic subjects with reduced range of extension and increased resistance to passive movement at the wrist. MAIN MEASURE: Quantitative measures of the hemiplegic posture at the wrist, passive range of extension and resistance to passive extension of the wrist. Measurements were taken at the start of the study and then at two-weekly intervals. Two extra measurements were taken at the end of the ON period. RESULTS: Following two weeks treatment with ES the posture of the wrist improved and the passive range of extension increased. However, there were no significant changes in the resistance to passive movement. These benefits appeared largely to be lost two weeks after ES was discontinued. CONCLUSIONS: Short-term ES gives temporary improvements in contractures at the wrist in poststroke hemiplegia.

Aged↗
PubMed1996

Effects of joint motion constraints on the gait of normal subjects and their implications on the further development of hybrid FES orthosis for paraplegic persons.

In this study the effects of angular motion constraints of the lower limbs on the gait of normal subjects were investigated. An assessment orthosis was developed with a new hip coupling mechanism which allows its ratio of reciprocal flexion to extension to be altered. The knee and ankle joints of the orthosis could also be set to be free or locked in specific directions of angular motion in the sagittal plane. A total of 12 different orthosis configurations was tested on three normal subjects. The kinematic, kinetic and electromyographic (EMG) data were collected using the VICON system, two Kistler forceplates, foot switches and an eight channel EMG system. The physiological cost index of walking was assessed by measuring the heart rate and walking speed. It was found that (1) a higher hip flexion-extension ratio was associated with lower energy cost and faster walking; (2) allowing the knee to flex significantly reduced the energy cost and increased the walking speed; (3) allowing the ankle to plantarflex during early stance phase reduced the knee flexing moment. The implications of these effects on the further development of hybrid functional electrical stimulation orthotic systems are discussed.

Adult↗