Abstracts On Stroke and MS

Patients' Perceptions of the Odstock Dropped Foot Stimulator (ODFS)

Clinical Use of the Odstock Dropped Foot Stimulator. Its Effect on the Speed and Effort of Walking.

The effects of common peroneal stimulation on the effort and speed of walking. A randomised controlled trial with chronic hemiplegic patients

The effect of common peroneal nerve stimulation on quadriceps spasticity in hemiplegia

Correction of Bi-lateral Dropped Foot using the Odstock 2 Channel Stimulator (O2CHS)

The Relationship Between Abnormal Patterns Of Muscle Activation And Response To Common Peroneal Nerve Stimulation In Hemiplegia

Different Muscle Activation Patterns, Identified During Walking, In People With Spastic Dropped Foot

The Compustim 10B In Stroke: Control Algorithms And Patient Selection

Sensory Amplification By Cutaneous Electrical Stimulation For Retraining Proprioception

Electrical stimulation exercise to improve hand function and sensation following chronic stroke.

Pilot Trial To Determine Control Algorithms And Patient Selection Criteria For Two-Channel Stimulation Following Stroke

FES based training orthosis for hand function following stroke

The efficacy of Functional Electrical Stimulation in improving walking ability for people with Multiple Sclerosis

Using the Odstock Dropped Foot Stimulator: User and Partners Perspectives.

REPORT TO THE DEVELOPMENT & EVALUATION COMMITTEE: COMMON PERONEAL STIMULATION FOR THE CORRECTION OF DROP-FOOT


Patients' Perceptions of the Odstock Dropped Foot Stimulator (ODFS)

Paul N Taylor, Jane H Burridge, Anna L Dunkerley, Amanda Lamb, Duncan E Wood, Jonathan A Norton, Ian D Swain

Accepted for publication in the journal Clinical Rehabilitation to be published summer 1999 (Clinical Rehabilitation. 1999: 13: 333-340)

Objective: To determine the perceived benefit, pattern and problems of use of the Odstock Dropped Foot Stimulator (ODFS) and the users' opinion of the service provided.

Design: Questionnaire sent in a single mail shot to current and past users of the ODFS. Returns were sent anonymously.

Setting: Outpatient based clinical service. Subjects: 168 current and 123 past users with diagnoses of stroke (CVA), multiple sclerosis (MS), incomplete spinal cord injury (SCI), traumatic brain injury (TBI) & cerebral palsy (CP).

Intervention: Functional Electrical Stimulation (FES) to correct dropped foot in subjects with an upper motor neurone lesion, using the ODFS.

Main Outcome Measures: Purpose designed questionnaire.

Results:

· Return rate 64% current users (mean duration of use 19.5 months) and 43% past users (mean duration of use 10.7 months).

· Principal reason cited for using equipment was a reduction in the effort of walking.

· Principal reasons identified for discontinuing were an improvement in mobility, electrode positioning difficulties and deteriorating mobility.

· There were some problems with reliability of equipment.

· Level of service provided was thought to be good.

Conclusion: The ODFS was perceived by the users to be of considerable benefit. A comprehensive clinical follow up service is essential to achieve the maximum continuing benefit from FES based orthoses.


Clinical Use of the Odstock Dropped Foot Stimulator. Its Effect on the Speed and Effort of Walking.

Paul N Taylor, Jane H Burridge, Anna L Dunkerley, Duncan E Wood, Jonathan A Norton, Christine Singleton and Ian D Swain.

Accepted for publication, Achieves of Physical Medicine and Rehabilitation, 1999;80:1577-1583

Objective: To assess the clinical effectiveness of the Odstock Dropped Foot Stimulator by analysis of its effect on Physiological Cost Index (PCI) and speed of walking. This Functional Electrical Stimulation (FES) device stimulates the common peroneal nerve during the swing phase of gait.

Design: A retrospective study of patients who had used the device for four and a half months.

Subjects: 151 patients with a dropped foot resulting from an upper motor neurone lesion.

Setting: The Medical Physics and Biomedical Engineering Department of a District General Hospital specialising in the clinical application of FES and a Neurophysiotherapy Department in a separate hospital.

Main outcome measures: Changes in walking speed and effort of walking, as measured by PCI over a 10m course.

Results: There was a 92.7% compliance with treatment. Stroke patients showed a mean increase in walking speed of 27% (p<0.01) and reduction in PCI of 31% (p<0.01) with stimulation and changes of 14% (p<0.01) and 19% (p<0.01) respectively whilst not using the stimulator. Multiple sclerosis patients gained similar orthotic benefit but no "carry-over".

Conclusions: The measured differences in walking with and without stimulation were statistically significant in the stroke and multiple sclerosis groups. In this study use of the stimulator improved walking. Those with stroke demonstrated a short term "carry-over" effect.


The effects of common peroneal stimulation on the effort and speed of walking. A randomised controlled trial with chronic hemiplegic patients

Burridge, J.H., Taylor, P.N., Hagan, S.A., Wood, D.E., Swain, I.D

Clinical Rehabilitation 11: 201-210

Department of Medical Physics and Biomedical Engineering, Salisbury District Hospital

Abstract

Objective: The purpose of this study was to measure the effect of the Odstock Dropped Foot Stimulator (ODFS), a common peroneal stimulator, on the effort and speed of walking.

Design: A randomised controlled trial.

Subjects: Hemiplegic patients who had suffered a single stroke at least six months prior to the start of the trial whose walking was impaired by a drop-foot.

Interventions: The treatment, functional electrical stimulation (FES) group, used the stimulator and received a course of physiotherapy; the control group received physiotherapy alone.

Main outcome Measures: Changes in walking speed measured over 10 metres and the effort of walking measured by physiological cost index (PCI).

Results: 32 subjects completed the trial, 16 in the FES group and 16 in the control group. Mean increase in walking speed between the beginning and end of the trial was 20.5% in the FES group (when the stimulator was used,) and 5.2% in the control group. Improvement was also measured in PCI with a reduction of 32.6% in the FES group (when the stimulator was used) and 1% in the control group. No improvement in these parameters was measured in the FES group when the stimulator was not used.

Conclusion: Walking was statistically significantly improved when the ODFS was worn but no 'carry-over' was measured. Physiotherapy alone, in this group of subjects with established stroke, did not improve walking.


The effect of common peroneal nerve stimulation on quadriceps spasticity in hemiplegia

Burridge.J.H, Taylor.P.N, Hagan.S.A, Wood.D.E, Swain. I.D

Physiotherapy vol. 83, no 2, pp 82-89 1997

Department of Medical Physics and Biomedical Engineering, Salisbury District Hospital, Salisbury, Wiltshire. SP2 8BJ

Key words: Spasticity, Hemiplegia, Functional electrical stimulation (FES), Wartenburg Pendulum Test

Summary

Contemporary physiotherapy for the neurologically impaired patient puts emphasis on the management of spasticity. A randomised controlled trial of the Odstock Dropped Foot Stimulator (ODFS), a common peroneal stimulator used to correct drop-foot during walking, showed a reduction in spasticity of the quadriceps muscles in a sample of 32 chronic hemiplegic subjects. Both treatment (FES) and control groups received a course of 10 physiotherapy sessions during the first 4 weeks of the trial period. The treatment group used the stimulator as part of the physiotherapy sessions and independently each day as they found useful. Both groups received the same amount of therapy contact time. The treatment group continued to use the stimulator for the 12 week period. Assessments also included measurement of walking speed and effort of walking, gait analysis and mobility and quality of life questionnaires. Results of these tests are not presented in this paper but are referred to in relation to changes in spasticity. Spasticity of the quadriceps muscles was measured using the Wartenberg pendulum test. Results showed that during the first four week period both groups had a reduction in spasticity which was statistically significant in the control group; measured by both the Relaxation index (p=0.005) and the area beneath the curve (p=0.036) and in the FES group only as the area beneath the curve (p=0.028) At 12 weeks reduction in spasticity in the control group was no longer statistically significant in either of these parameters whereas in the treatment group reduction measured as area beneath the curve was statistically significant (p=0.001). There was no statistically significant difference between the two groups. These results are discussed in relation to the subject of measurement of spasticity, the effect of physiotherapy on spasticity and observations made on changes in speed and effort of walking.


Correction of Bi-lateral Dropped Foot using the Odstock 2 Channel Stimulator (O2CHS)

Taylor PN, Wright PA, Burridge JH, Mann GE, Swain ID

Abstract for IFESS 99 conference.

A single dropped foot can be successfully corrected using a single channel stimulator controlled by a foot switch. When an individual has bilateral dropped foot using two independent devices presents the difficulty that both channels can be active simultaneously, putting the user in an unstable situation. The O2CHS is a two channel device which can be controlled by one or two foot switches. It is intended for not only for bilateral common peroneal but for use in gait assistance, primarily augmenting common peroneal stimulation with calf, hamstrings, triceps, gluteus maximus or quadriceps. The sequence of stimulation can be selected using internal switches and trimmer controls. For Bilateral dropped foot a single heel switch is used, channel 1 is triggered by heel rise and ended by heel strike. Channel 2 is triggered by heel shrike and ended by heel rise. For all but the fastest walker it was found necessary to add a short delay between the channels, after heel strike.

Performance with the device was measured using walking speed and physiological cost index (PCI). Twenty subjects used the device (11 multiple sclerosis, 2 spinal cord injured, 1 stroke, 1 cerebral palsy and 5 with other spinal pathologies) of mean age 50.4 years. There was a mean increase in speed of 22.4% (p=0.022) and reduction in PCI of 12.2% (p=0.018) when the O2CHS was first used. For more able users, use of the device enables greater distances, reducing the risk of falling due to tripping. For the less able it enables mobility over short distances, delaying final dependence on the wheel chair.


The relationship between abnormal patterns of muscle activation and response

to common peroneal nerve stimulation in hemiplegia

JH Burridge1 and DL McLellan2

1 Department of Medical Physics and Biomedical Engineering, Salisbury District Hospital.

2 Southampton University Rehabilitation Research Unit

Objective

This study investigated the relationship between response to common peroneal nerve stimulation, timed to the swing phase of walking, and abnormal ankle movement and muscle activation patterns.

Method

Eighteen patients who took part had a drop-foot and had suffered a stroke at least six months prior to the study Twelve age-matched normals were also studied. Response to stimulation was measured by changes in the speed and effort of walking when the stimulator was used. Speed was measured over ten metres and effort by the Physiological Cost Index (PCI). Abnormal ankle movement and muscle activation were measured in a rig by: ability to follow a tracking signal moving sinusoidally at either 1 or 2Hz, resistance to passive movement and EMG activity during both passive and active movements. Indices were derived to define EMG response to passive stretch, co-activation and ability to activate muscles appropriately during active movement

Results

Different mechanisms underlying the drop-foot were observed. Results showed that patients who had poor control of ankle movement and spasticity, demonstrated by stretch reflex and co-activation, were more likely to respond well to stimulation. Those with mechanical resistance to passive movement and with normal muscle activation responded less well.

Conclusions

Results support the hypothesis that stimulation of the common peroneal nerve to elicit a contraction of the anterior tibial muscles also inhibits the antagonist calf muscles. The technique used may be useful for identifying patients suitable for botulinum toxin injections and may also be useful in directing physiotherapy.

Presented Society for Research in Rehabilitation Summer meeting 1999

 


Different muscle activation patterns, identified during walking, in people with spastic drop-foot

JH Burridge1 and DL McLellan2

1 Department of Medical Physics and Biomedical Engineering, Salisbury District Hospital.

2 Southampton University Rehabilitation Research Unit

Introduction

Upper Motor Neurone lesions result in a complex disorder of muscle activation including weakness and spasticity. Inability to effectively dorsiflex the ankle during the swing phase of walking is often a problem for people with spastic hemiplegia.

Subjects

Nine normal and fifteen hemiplegic subjects who had suffered a stroke at least six months prior to the study and had a drop-foot.

Method

Subjects were studied walking on a treadmill. EMG signals from the calf and anterior tibial muscles were recorded and force sensitive foot-switches enabled these to be related to phases of the gait cycle. Ankle movement was recorded using a Penny and Giles electrogoniometer. Normal activation periods for each muscle group were identified as percentiles of the gait cycle. Indices for muscle activation periods were then derived using ratios of integrated EMG during selected periods.

Results

Conclusion

The reasons for drop-foot are varied and complex. Indices defining different muscle activation patterns during walking may be useful for directing therapy such as botulinum toxin, muscle strengthening exercise or functional electrical stimulation.

To be presented at IFESS99

 


The Compustim 10B in Stroke: Control Algorithms and Patient Selection Criteria

Wright PA1, Burridge JH1, Ewins DJ2, Mann GE1, McLellan DL3, Swain ID1, Taylor PN1 and Wood DE1

1 Department of Medical Physics and Biomedical Engineering, Salisbury District Hospital, Salisbury, Wiltshire SP2 8BJ, UK

2 Biomedical Engineering Group, Department of Mechanical Engineering, University of Surrey, Guildford, Surrey GU2 5XH, UK

3 Rehabilitation Research Unit, University of Southampton, Southampton General Hospital, Tremona Rd, Southampton, SO16 6YD, UK.

Aims of study:

· to identify patients most likely to benefit from two channel stimulation with the microcontroller based Compustim 10B

· to develop a database of control algorithms

Fourteen subjects (mean age 63.2±6.7 yrs, 9 Male 5 Female) were recruited who had been treated with a single channel common peroneal stimulator (ODFS) for a minimum of 6 months without any complications. These patients' walking performance, with and without stimulation, was regarded as stable over a 4 week measurement period prior to the study (paired t-tests of walking speed and Physiological Cost Index, p<0.05).

The study design for all subjects was CONTROL (12 weeks, single channel Compustim) _ TREATMENT (12 weeks, two channel Compustim) _ CONTROL (12 weeks, single channel Compustim). Walking speed and Physiological Cost Index were measured at approximately four-weekly intervals throughout the study. Gait analysis (comprising dynamic measurement of joint positions and velocities, force plate measurement of ground reaction forces, and EMG studies) was performed at weeks 0, 12, 24 and 36. This enabled investigation of both orthotic and possible re-education effects of using the second channel of stimulation

The second muscle group for stimulation was selected by clinical observation. Subjects observed to have poor 'push off' were selected for calf stimulation. Hamstrings stimulation was used to control knee hyperextension or improve flexion of the knee during swing phase.

A comparison of clinical observations and the preliminary results of gait analysis will be presented.

This work is funded by Action Research.

To be presented at IFESS99

 

 


Sensory Amplification By Cutaneous Electrical Stimulation For Retraining Proprioception

Paul Taylor, Jane Burridge

Department of Medical Physics and Biomedical Engineering, Salisbury, District Hospital, Salisbury, Wiltshire, SP2 8BJ.

5th IPBM Clinical FES Meeting, Salisbury, March 1997

Introduction

A patient (right side hemiplegic following CVA) presented at our clinic for electrical stimulation to improve his hand function. In fact his motor function was not greatly impaired, his main disability being in lack of proprioception. If a digit was touched while he was blind folded, he was unable to correctly identify the area that was touched although he was aware that he had been touched. Earlier work (1) had shown that electrical stimulation of the hand and wrist muscles could lead to an improvement in two point discrimination. By experimentation it was found that after repeated stimulation of the thumb and index finger pulps, the subject could better identify the areas when they were tested immediately after training. This paper describes the development of apparatus for the technique and initial results with one subject.

Materials and methods

The apparatus evolved through several stages. Initial experimentation was made using the University of Surrey Compustim 10B stimulator. Two FSRs (Force Sensitive Resistors) were placed either side of a block of high destiny foam, about 3cm thick.. Self adhesive active electrodes were placed on the pulp of the index finger and thumb. The stimulator was set up to give an output when a FSR was pressed. One channel stimulated at 10 Hz while the second stimulated at 40 Hz. The output level was set at comfortable level for the user giving sensation but no muscle contraction. With each FSR labelled as "finger or thumb" The subject was asked to repeatedly grasp and release the foam block. Initial results were encouraging but the system was limited by two factors. Firstly the equipment could only be used as training device and not for picking up other objects. Secondly it was hard to set the stimulator to respond to very small changes in the FSR, typical of light grip, without the FSRs drifting out of the range of operation.

The first problem could be solved by mounting the FSRs on the back of the electrodes. In order to keep the assembly as thin as possible electrodes were made from a flexible PCB. This also enabled both active and indifferent to be mounted on the pulp. Electrode gel was used as a conductive mediun. Tape was required to hold he electrode / sensor assembly in place. The second problem was solved by using a tracking comparitor input (2) for the FSR which avoided the problem of drift while enabling high sensitivity. This necessitated the construction of a second stimulator. These design modifications enabled orthotic use of the device for activities of daily living. However the use of wet conductive gel was not liked by the user as the electrodes tended to slip and was messy. This lead to a return to the use of self adhesive electrodes. Two Pals Plus 1 1/4 " electrodes were cut in half, close to the line of the central conductor. The two halves were then placed close together on the pulp to provide the active and indifferent. In order to maintain the separation later assemblies had a non conductive spacer between the electrodes. As the subject found it was necessary to wear gloves to protect the electrodes and sensors the FSR was mounted on the inside of a thin riding glove. However this was rejected by the user as it restricted him to clean activities. The FSRs were again mounted on the back of the electrodes leaving the user to chose his own gloves for activities such as gardening or washing up.

Subject

Male, aged 64 years, 3 years post CVA, right side hemiplegic

Assessments

Three assessments were made.

The Jebson test: A standardised hand function test consisting of 6 tasks (card turning, picking up small objects, simulated feeding, stacking draught pieces, picking up empty tins, picking up 500gm full tins). The time to complete each task is recorded.

Rolyon nine hole peg test: Nine pegs are picked up from a dish and inserted into holes in the Rolyon board. The times to insert all nine pegs and then place them back in the dish are recorded.

Sensation discrimination: Discrimination was tested by moving a single blunt metal pin across the pulp of either the 1st finger or the thumb. With the subject blindfolded, they were asked to identify whether it was the thumb or finger that was touched. If the subject did not respond a score of 0 was recorded. For the correct answer 1 was scored while the wrong answer scored -1. The test was repeated ten times and the scores added for a total score, the maximum score being 10, the minimum score -10.

The subject used the device daily at home, Assessments were made prior to treatment and at 1, 4 and 6 weeks. Sensation tests were performed with and without stimulation

Results

Jebson test

week

card turning

small objects

simulated feed

stacking dr’ts

empty tins

full tins

-10

11.2s

36.6s

21.8s

18.0s

14.3s

9.5s

6

9.9s

29.3s

20.1s

60s

19.5s

10.3s

Rolyon nine hole peg test

 

hemi hand

hemi hand

non-hemi hand

week

time in (s)

total time (s)

total time (s)

-1

372

399

24

0

280

371

25

1

410

429

25

4

223

237

26

6

217

235

25

Sensation discrimination

 

hemi

 

 

 

 

 

non-

hemi

 

pre stm

 

with stm

 

post stm

 

no stm

 

week

thumb

index

thumb

index

thumb

index

thumb

index

-10

1

0

 

 

 

 

10

10

-1

1

-1

 

 

 

 

10

10

0

-2

1

6

3

2

0

10

10

1

4

3

7

7

-1

4

10

10

4

6

4

5

6

8

7

10

10

6

0

8

10

10

6

6

10

10

It was noted after about 1 month of use of the device that the user required a significant reduction in stimulation amplitude from about 60 mA to 15 mA. The lower current amplitude is typical of that found comfortable by individuals with unimpaired sensation. The subject reported that he was much more aware of his hand. He was able to carry a bag and believed his balance to be improved. For example, he was now able to carry a bucket while walking over his rockery with less fear of falling. He felt that use of the system gave him improved awareness for several hours after use.

The results suggest that there was a training effect due to the electrical stimulation both in sensory and motor function. The Jebson test may not be representative as the subject’s tone was raised due to his anxiousness to perform well on the test.

References

1. Taylor PN, Burridge JH, Hagan SA, Swain IDS. Electrical stimulation exercises to improve hand function and sensation following chronic stroke. Pro. 5th Vienna International Workshop on Functional Electrostimulation 1995 ISBN 3-900928-03-7 pp359-3

2. Taylor PN, Burridge JH. Multipurpose Two Channel Stimulator For Gait Correction Proceedings of the IPEMB FES Meeting, Salisbury March 1997

 


 

Electrical stimulation exercise to improve hand function and sensation following chronic stroke.

Taylor PN, Burridge JH, Hagan SA, Swain ID

Pro. 5th Vienna International Workshop on Functional Electrostimulation 1995 ISBN 3-900928-03-7 pp359-362

Twenty chronic Stroke subjects received electrical stimulation exercises of the hand and wrist muscles. Wrist and finger extensors were stimulated reciprocally with lumbricals, finger flexors or triceps. Subjects exercised twice a day for two periods of up to one hour for a period of three months. Three assessments were made, the Jebson-Taylor hand function test, static two point discrimination and palmer, pinch and key grip strength measurements. Results. 15 subjects improved their jebson test score while 3 reduced their score and 2 were unchanged. The 16 subjects who were unable to complete the full test at the start of the trial, were able to complete an average of an additional 3.4 tests, an increase of 24.7% (p<0.001) There was a significant increase in key grip of 38 % (p < 0.01). The mean two point discrimination score increased from 1.80 to 2.44 (p<0.02). There was a significant difference between groups at the start of the trial but no statistical difference at the second static two point discrimination score. While statistically significant differences were found in function, sensation and grip strength, it is not clear if these benefits were carried over into activities of daily living. Some subjects however reported improved function in activities such as fastening trouser buttons using both hands, and writing. Further investigation now required to verify these results.


Human Motor Performance: the interaction between science and therapy

Submitted abstract to the scientific meeting (21st - 23rd July 1998)

University of East London

Pilot trial to determine control algorithms and patient selection criteria for two-channel stimulation following stroke

Wood DE1, Burridge JH1, Taylor PN1 and Ewins DJ2

1 Department of Medical Physics and Biomedical Engineering, Salisbury District Hospital, Salisbury, Wiltshire SP2 8BJ

2 Biomedical Engineering Group, Department of Mechanical Engineering, University of Surrey, Guildford, Surrey GU2 5XH

The correction of dropped foot following stroke may be achieved by stimulating the common peroneal nerve during the swing through of the hemiplegic leg. A randomised controlled trial of a single channel stimulator developed at Salisbury, showed significant improvements in walking speed of 18% and reduction in the effort in walking of 46%. This device has now been used by over 400 patients, but many still have problems with control of the hip, knee and ankle. These may be addressed by stimulating a second muscle group.

Funded by Action Research, a programmable, two-channel stimulator (Compustim-10B) has been developed to improve walking in these more complex cases. Using pressure sensors under the heel and first metatarsal head, the stimulator can identify specific periods of the gait cycle and control the two channels accordingly. Control is prescribed by internal algorithms set up for a given patient, which define parameters such as timing and initiation and termination conditions. Currently the algorithms are designed by experimentation, observation and using data from published EMG studies. A feasibility study identified gastrocnemius, for improved push-off prior to limb advancement, and hamstrings, for knee flexion during the swing phase, as perhaps the two most useful muscle groups for further study. Initial results showed that the addition of a second channel further improved walking speed and effort in walking. There was also a measured carry-over effect in gait re-education for these two muscle groups, of 56% in speed for both and 18% and 51% in effort respectively.

A pilot study has been constructed to examine the effect of two channel stimulation with these two muscle groups. Its aims will be to investigate whether there is any conflict between simple clinical assessment and full gait analysis data; in selecting appropriate patients, the second muscle group and in algorithm design.


FES based training orthosis for hand function following stroke

Paul Taylor, Paul Chappell*.

Department of Medical Physics and Biomedical Engineering, Salisbury District Hospital, Salisbury, Wiltshire, SP2, 8BJ, Tel. 01722 429040 E-mail p.taylor@mpbe-sdh.demon.co.uk Web page www.mpbe-sdh.demon.co.uk * Department of Electrical Engineering, University of Southampton, Highfields Southampton, Hampshire, S17 1BJ E-mail phc1@soton.ac.uk

6th IPEM Clinical FES Conference 12th 13th April 2000 University of Surrey

Introduction

In Britain each year there are approximately 100,000 people who suffer their first ever stroke of which approximately two thirds will survive.1 Of all acute stroke patients starting rehabilitation, about half will have a marked impairment of function of one arm and only about 14 % of these will regain useful function.2 A significant problem is spasticity, typically causing over-activity in the flexor muscle groups in the upper limb. While often some ability to make a voluntary grip remains, the ability to selectively activate extensor muscles to enable release of a grasp is frequently lost.

Electrical stimulation exercises have been demonstrated to be beneficial in re-educating the ability to open the hand3, 4 . However it has been suggested that if a functional aspect can be added to these exercises, the retraining effect could be improved5. This paper describes a FES device designed to stimulate the radial nerve, producing a general extension pattern of the fingers, thumb and wrist, controlled by the weak EMG signal detected from the same wrist extensors. In this way, residual activity can be boosted, enabling the flexor spasticity to be overcome.

Method

The main problem in recording voluntary EMG from a stimulated is the stimulation artefact, which is of the order of 10,000 the level of the desired signal. This artefact will saturate any standard EMG amplifier. Secondly, following the stimulation pulse is the compound action potential or M wave due to the synchronous firing of motor units which is an order of magnitude greater than the voluntary EMG. Difficult problems are often best ignored, so in this case the artefact and M wave can be prevented from entering the system by disconnecting the front end amplifier for 15 - 20 ms following the stimulation pulse. In this period a sample and hold circuit is used to maintain the level of the signal to minimise variation due to the DC off set of the system. However, the instantaneous level of the signal from the front end amplifier is not the same at the end of the blanking period as at the beginning resulting in a step response followed by a decay curve due to the RC time constant of the sample and hold. This new artefact can again be removed by a second stage of blanking following the band pass and rectifier stages of the circuit. However, to effectively reduce the time period of the artefact the lower end of the pass band has the relatively high frequency of 200Hz. This leaves sufficient signal to produce an EMG envelope, which is used to control a modified Odstock Dropped Foot Stimulator. The stimulator's output can be either driven directly by the envelope producing an output proportional to the EMG envelope or used to trigger a fixed amplitude output for a fixed or adaptive (started and stopped by EMG) time.

The circuit is realised in surface mount technology as a head amplifier (70mm x 35mm) with electrodes attached directly to the under side of the board.

Results

The system has been tried by three individuals who have had a stroke. It was found possible to detect EMG in the wrist extensors of all three subjects. However the effort of producing wrist extension had the effect of increasing the spastic tone in the flexor muscles of the hand, sometimes resulting in clawing of the fingers when the extensors were stimulated. This effect was greatest when proportional control was used, as it required the greatest effort by the user. All three subjects were able to use the system to open their hand to acquire objects such as a door handle or large objects such as food cans. Two of the three subjects used the device daily at home. Both reported that their hand felt more relaxed and that they felt more aware of their affected arm than before. However, no significant changes in hand function were recorded using the Jebsen Test.

There was some evidence that users of the EMG systems could learn to relax their muscles after some practice suggesting that using the device may help train self control of spasticity. Additionally, stretch reflexes induced in flexor muscles, being velocity dependent, could be reduced by using a slow rise in the stimulation amplitude to the extensor muscle. This was difficult to achieve using proportional control and slows down the response of the system.

It was also observed that the stimulation it's self had an inhibiting effect on the voluntary EMG in normal subjects, effectively reducing the gain of the system as the contraction strength rose. This may be due to unloading of the Golgi tendon organs or shortening of the muscle spindles leading to an inhibition or reduction of drive to the a motor neurone. This affect has not yet been observed in stroke subjects but if present, it is not known what the implication of this effect would be for the re-education of movement.

Conclusion

This study has demonstrated that it is possible to control hand opening by EMG from the same muscles that are stimulated. However, the rise in spasticity that this some times caused may be detrimental, reinforcing undesired patterns of movement. Further work is required to better understand the neurological effects of this technique.

References

1. Bamford J, Sandercock P, Dennis M, Burn J, Warlow C. A prospective study of acute cerbrovascular disease in the community. The Oxford Community Stroke Project 1981-86. Incidence, case fatality rates and overall outcome at one year of cerebral infarction, primary intracerabral and subarachnoid haemorrhage. J. Neurol Neurosurg Psychiatry 1990 53:16-22

2. Wade DT, Langton-Hawer R, Wood VA, Skilbeck CE and Ismail HM. The hemiplegic arm after stroke: measurement and recovery. J Neurol Neurosurg Psychiatry 1983; 46: 521-524

3. Baker LL, Yeh C, Wilson D, Waters RL. Electrical stimulation of wrist and fingers for hemiplegic patients. Physical Therapy 1979; 59 (12): 1495 - 1499.

4. Taylor PN, Burridge JH, Hagan SA, Swain IDS. Electrical stimulation exercises to improve hand function and sensation following chronic stroke. Pro. 5th Vienna International Workshop on Functional Electrostimulation 1995 ISBN 3-900928-03-7 pp359-362

5. Kraft GH, Fitts SS and Hammond, MC. Techniques to improve function of the arm and hand in chronic hemiplegia. Arch. Phys. Med. Rehabil. 1992; 73: 220-227. This work was funded by the Wessex Rehabilitation Association.


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