Functional Electrical Stimulation. With your hosts: Robin Engel and Agnes Leitner

Transcription

1 Functional Electrical Stimulation With your hosts: Robin Engel and Agnes Leitner

2 What is Functional Electrical Stimulation? Functional electrical stimulation (FES) is the application of electrical current to excitable tissue to supplement or replace function that is lost in neurologically impaired individuals. It is a developing field that addresses both motor and sensory problems including MS, Cerebral Palsy, Orthopaedic Healing, Muscle Atrophy, Treatment of Chronic Pain, Spinal Cord or Peripheral Nerve injury, hearing and vision loss etc. FES systems used to substitute lost neurological function are often referred to as neuroprostheses. 2

3 FES Regarding Neuromuscular Activation Often the goal is to restore voluntary control over a muscle or group of muscles by electrically stimulating in tact lower motor neurons. As a result of this approach FES can only be used when lower motor neurons are excitable and neuromuscular junctions are in tact. There are many problems associated with FES including timing and sites of stimulation to cause a complex movement like walking, voltage, frequency, and current used to generate impulse, biocompatability (immune response, tissue damage), portability, power, and aesthetics. 3

4 Let s s Talk Nerves Two segments of the nervous system: -The Central Nervous System -The Peripheral Nervous System Two Major Cell Types: -Neurons signalling -Glial Support 4

5 Central Nervous System The CNS consists of the brain and the spinal cord and is the starting point for all motor impulses and ideally the endpoint for all sensory impulses. The CNS is made up of both grey matter and white matter. White matter is made up of two cell type: Astrocytes, and Neurons. Grey matter is made up of two cell types: Oligodendrocytes, Microglia. 5

6 Peripheral Nervous System The peripheral nerves branch off the spinal cord and are responsible for the innervations throughout the body. Cranial Nerves that connect the spinal cord to the rest of the body include C1-C8, C8, T1- T12, L1-L5, L5, S1-S5. S5. 6

7 PNS Continued Cells that make up the PNS are Neurons and Schwann Cells. Immune defence for the PNS is provided by the immune cells found in the blood, including T-cells T and Macrophages. Two types of neurons that exist in both the CNS and PNS are sensory and motor. In the PNS the sensory neurons are referred to as afferents, and the motor neuron are referred to as efferents. 7

8 Key Differences Between CNS and PNS Neurons in the CNS are post-mitotic and the glia inhibit axon growth and regeneration. Neurons in the PNS, however, can regenerate. Glia produce growth factors and macrophages remove debris. Axons can grow up to 1mm/day. 8

9 Nerve Conduction An action potential is initiated by a stimulus that depolarizes the local membrane of a neuron, allowing Na+ to enter the cell. The inside of the cell membrane becomes briefly positive which causes depolarization at the next node of Ranvier propagating the signal along the nerve. 9

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11 Contraction occurs when the myosin heads attach and walk along the thin filaments. As a result the thin filaments slide inward and meet at the centre of the sarcomere. Muscle Contraction 11

12 Innervation of a Muscle Fibre 12

13 Summation of Stimulation 13

14 History of electrical Stimulation 46 A.D.: Scribonius Largus (Roman physician) recommends treating pain (headache and gout) by using electrical discharge of the torpedo fish Application of torpedo fish until 17 th century also for treating migraine, melancholy and epilepsy 14

15 History of electrical Stimulation 1672: Otto von Guericke constructs first electrostatic generator 1791: Galvani produces muscle contraction in frog legs 15

16 History of ES 1855: G. B.Duchenne established electrotherapy as a separate discipline. By 1900: plenty of machines had been invented: Pain treatment (rheumatism, fractures,...) Treatment of Cardiocirculatory problems Treatment of diseases Devices for the cure of weak, nervous and debilitated conditions of the generative organs Exorcism 16

17 First serious efforts in ES 1931: success in resuscitating animals and humans after cardiac arrest 1952: first cardiac pacemaker was implanted 1961: first FES application for treatment of footdrop Until today: many different applications of ES Restoring sensory function Restoring motor function Therapeutic electrical stimulation 17

18 FES to the neuromuscular system Electrical pulses applied to nerve elicit action potential Potential propagates away from the site of stimulation (in both directions) AP that propagate distally are transmitted across the neuromuscular junction Muscle fibres contract 18

19 Activation of nerve easier than activation of muscle directly Threshold charge for producing activation is in neurons lower than in muscle 19

20 Neuroprosthetic Systems Surface systems (transcutaneous( transcutaneous) Percutaneous systems Implanted systems S = stimulator, A = anode (reference electrode), C = cathode (active electrode), ECU = external control unit 20

21 Surface Systems Pros Non-invasive Relatively technologically simple Easily reversible Relatively inexpensive Cons Repeated placement of the electrodes needs skill and is time-consuming Difficult to achieve isolated contraction or activate deep muscles 21

22 Percutaneous systems Intramuscular electrodes, implanted into the muscle, pass through the skin Pros Activation of deep muscles possible Isolated muscle contractions Less likely to cause pain (less effect on sensory afferents in the skin) Minimal invasive Cons Minimal invasive Care of skin at electrode site to reduce risk of complication 22

23 Implanted systems Stimulator is implanted (chest, abdomen) Electrodes are connected to stimulator by leads under skin Pros: Leads can be larger and more durable do not have to pass through skin Cons: Surgery 23

24 Implanted systems High power demands no implanted batteries Stimulator receives power and command instructions through a radio-frequency (RF) link to an external control unit (ECU) 12 channel implanted upper extremity neuroprosthesis with myoelectric control capability 24

25 Electrodes At least two electrodes 1 active electrode 1 reference electrode Multichannel systems Stimulation of more than one muscle Different motion patterns Smith et al Mulcahey et al. 25

26 Electrical Stimulation Electrical current pulses Characterized by Pulse frequency Amplitude Duration These parameters control strength of muscle contraction 26

27 Pulse frequency Low frequency leads to a series of twitches Above fusion frequency smooth contraction Higher frequencies produce stronger contraction Increased rate of muscle fatigue at high frequencies Typically, the frequency is set constant and as low as possible 27

28 Control of strength of contraction Activation of more motor units higher strength of muscle contraction (spatial summation) Increase pulse amplitude Increase pulse duration Increased electric charge injected leads to Larger electric field, which leads to a Broader region of activation 28

29 Restoration of Upper Extremity Function Primarily for individuals with spinal cord injury (SCI) But also for individuals with stroke and traumatic brain injury 29

30 The hand The wide number of possible motions that the hand can make 30

31 Hand muscles and motion Large muscles in forearm generate most of the power of the hand, force is transmitted by the tendons to the fingers Fine movements are controlled by small muscles in the hand 31

32 The hand Individual finger movements require selective activation of particular sets of muscles Long et al.,

33 Hand muscles and motion Most important Hand motions: Lateral or key-pinch grasp (handling small objects, spoon, pen) Palmar grasp (holding glass, book) 33

34 Stimulated muscles extensor pollicis longus (EPL) flexor pollicis longus (FPL) adductor pollicis (ADP) abductor pollicis brevis (AbPB) extensor digitorum (EDC) flexor digitorum superficialis (FDS) flexor digitorum profundus (FDP) 34

35 Physical requirements for FES in the hand Hand and forearm muscles must be sufficiently innervated Upper arm muscle (bicep), shoulder muscles (deltoid, rotator cuff) must have enough strength to control hand placement Patient must be able to see well enough (hand lacks sensation) 35

36 Command sources Pushing a button Measuring wrist movements Voice Shoulder motion EMG Brain-Computer Computer-Interface (BCI) detection of specific EEG-patterns 36

37 Freehand Implanted system, developed at Case Western Reserve University (CWRU) 37

38 Mulcahey et al

39 FES controlled by BCI Pfurtscheller et al

40 Gait Analysis Gait is the manner of walking, stepping or running. The main goal of walking is to move oneself forward and the most efficient way to do so is alternates ones body weight from one foot to the other while propelling oneself forward and limiting unnecessary body movements. Able bodied individuals produce a cyclic and symmetric gait pattern. 40

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42 Cerebral Palsy CP patients have difficulty with gait as a result of spasticity or abnormal muscle tone, and gait problems will persist if not treated. Currently it is the trend for CP patients to undergo a thorough evaluation including a complete patient history, a comprehensive physical exam, consultation with other specialists, and a gait analysis. Instrumented Gait Analysis (IGA) has the capability helping to identify gait abnormalities. By putting together information about the 3D position of the pelvis, hip, femur, knee, tibia, ankle and foot at any point in the gait cycle with dynamic electromyography (D-EMG), more is understood about that individuals gait cycle allowing treatment options to emerge. 42

43 Stiff Knee Gait in CP Patients Stiff knee gait is one of the most common patterns found in CP patients, seen in 80% of cases in a 2005 study. The reduction of swing and phase in knee flexion makes foot clearance and the task of advance difficult. It can result in tripping and use of another less efficient motion to compensate. Notice the lack of left knee flexion in CP patient 43

44 More On IGA IGA is a tool that had been used in a clinical setting for more than 40 years and assists in finding the best possible solution to improve the gait of an individual. Big thing to watch out for when interpreting information obtained from IGA is the difference between the primary gait abnormalities and the compensatory deformities. 44

45 Transcutaneous Electrical Nerve Stimulation on Children with CP Case Study This case study was specifically done to explore the possibility of using TENS to reduce spasticity in hip adductors which has been reported to improve gait. Surgical and medical managements are currently the most common intervention to reduce hip adductor spasticity. TENS has been used to reduce spasticity in various distal muscles but not proximal muscles. Two TENS management programs were used the one-time trial program and the one-week trial program. The one time trail program involved the application of conventional mode TENS to the bilateral hip abductors during passive hip abduction and walking 300cm of the total length of the balance master platform. The one-week trail program involved the ongoing application of TENS to the bilateral hip adductors while walking for 15 minutes 3 times a day for a week. 45

46 Case Study Continued The TENS were used with a pulse duration of 0.25ms at a frequency of 100Hz and an intensity to cause just a tingling sensation. Four standard adhesive electrodes were used to transmit TENS. 46

47 Balance Master Platform 47

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49 Results of Study The study results showed that the TENS programs significantly improved the step length and speed, but not the step width of the experimental group. Hip adductor spasticity was significantly reduced in both the one-time and one-week trial. Results show that TENS can be used to reduce spasticity in more proximal muscles and improve gait. 49

50 Conclusion Neuroprostheses have already provided hundreds of individuals the capability to move and regain essential functions lost after their paralysis FES-based devices have proven safe and effective Users continue to use them on a nearly daily basis Control must be made more natural to the user 50

51 References Bruce Wainman.. (2009). Neurotransmission. Unpublished manuscript. Dr. Vickie Galea.. (2009). Muscle physiology. Unpublished manuscript. Frank M Chang, Jason T Rhodes, Katherine M Flynn, & James J Carollo. (2010). The role of gait analysis in treating gait abnormalities in cerebral palsy. Organization of the muscular system. (2009). Unpublished manuscript. P Hunter Peckham,, & Jayme S Knutson. (2005). Functional electrical stimulation for neuromuscular applications. Principles of anatomy and physiology(2009). (12th ed.). United States of America: John Wiley & Sons. Sami S AlAbdulwahab,, & Maha Al-Gabbani Gabbani.. (2010). Transcutaneous electrical nerve stimulation of hip adductors improves gait parameters ofchildren with spastic diplegic cerebral palsy 51

52 References Functional electrical stimulation : applications in neural prostheses / edited by F. Terry Hambrecht, James B. Reswick.. New York : M. Dekker, c1977 Peckham PH, Knutson JS. Functional electrical stimulation for neuromuscular ular applications. Annu.. Rev. Biomed. Eng. 2005;vol. 7: Smith B, Peckham PH, Keith MW, Roscoe DD. An externally powered, multichannel, implantable i stimulator for versatile control of paralyzed muscle. IEEE Trans. Biomed. Eng. 34, (1987) Mulcahey MJ, Betz R, Smith B, Weiss AA, Davis SE. Implanted functional electrical e stimulation hand system in adolescents with spinal injuries: an evaluation. Arch Phys Med Rehabil ;78: Long C2, Conrad PW, Hall EA, Furler SL. Intrinsic-extrinsic muscle control of the hand in power grip and precision handling. An electromyographic study. Journal of Bone & Joint Surgery - American. 1970;Volume 52: Morita I, Keith MW, KannoT.. Reconstruction of upper limb motor function using functional electrical e stimulation (FES). Acta Neurochir Suppl. 2007;97(Pt 1):403-7 G. Pfurtscheller, G. R. Müller, M J. Pfurtscheller, H. J. Gerner, Rüdiger R Rupp. 'Thought'-control of functional electrical stimulation to restore hand grasp in a patient with tetraplegia.. Neuroscience Letters 351, 33-36, 36, G. R. MüllerM ller-putz, R. Scherer, G. Pfurtscheller, R. Rupp. EEG-based neuroprosthesis control: a step towards clinical practice. Neuroscience Letters 382, , 174, Pancrazio,, Joseph J, and P Hunter Peckham.. "Neuroprosthetic" devices: how far are we from recovering movement in paralyzed patients?" p Expert Review of Neurotherapeutics 9.4 (2009): Academic OneFile.. Web. 6 Oct therapies.info/fes.htm 52