Functional electrical stimulation

Functional Electrical Stimulation - Schematic Representation: Illustration of motor neuron stimulation. (a) The cell nucleus is responsible for synthesizing input from dendrites and deciding whether or not to generate signals. Following a stroke or spinal cord injury, muscles are impaired because motor neurons no longer receive sufficient input from the central nervous system. (b) A functional electrical stimulation system injects electrical current into the cell. (c) The intact but dormant axon receives the stimulus and propagates an action potential to (d) the neuromuscular junction. (e) The corresponding muscle fibers contract and generate (f) muscle force. (g) A train of negative pulses is produced. (h) Depolarization occurs where negative current enters the axon at the “active” electrode indicated.

Functional Electrical Stimulation (FES) is a technique that uses low energy electrical pulses to artificially generate body movements in individuals who have been paralyzed due to injury to the central nervous system. More specifically, FES can be used to generate muscle contraction in otherwise paralyzed limbs to produce functions such as grasping, walking, bladder voiding and standing. This technology was originally used to develop neuroprostheses that were implemented to permanently substitute impaired functions in individuals with spinal cord injury (SCI), head injury, stroke and other neurological disorders. In other words, a consumer would use the device each time he/she wanted to generate a desired function.[1] FES is sometimes also referred to as Neuromuscular Electrical Stimulation (NMES).[2]

In recent years FES technology has been used to deliver therapies to retrain voluntary motor functions such as grasping, reaching and walking. In this embodiment, FES is used as a short-term therapy, the objective of which is restoration of voluntary function and not lifelong dependence on the FES device, hence the name Functional Electrical Stimulation Therapy or FES therapy or FET or FEST. In other words, the FEST is used as a short-term intervention to help the central nervous system of the consumer to re-learn how to execute impaired functions, instead of making the consumer dependent on neuroprostheses for the rest of her/his life.[3]

Principles

Neurons are electrically active cells.[4] In Neurons, information is coded and transmitted as a series of electrical impulses called action potentials, which represent a brief change in cell electric potential of approximately 80–90 mV. Nerve signals are frequency modulated; i.e. the number of action potentials that occur in a unit of time is proportional to the intensity of the transmitted signal. Typical action potential frequency is between 4 and 12 Hz. An electrical stimulation can artificially elicit this action potential by changing the electric potential across a nerve cell membrane (this also includes the nerve axon) by inducing electrical charge in the immediate vicinity of the outer membrane of the cell.[5]

FES devices take advantage of this property to electrically activate nerve cells, which then may go on to activate muscles or other nerves.[6] However, special care must be taken in designing safe FES devices, as passing electric current through tissue can lead to adverse effects such as decrease in excitability or cell death. This may be due to thermal damage, electroporation of the cell membrane, toxic products from electrochemical reactions at the electrode surface, or overexcitation of the targeted neutrons or muscles. Typically FES is concerned with stimulation of Neurons and nerves. In some applications, FES can be used to directly stimulate muscles, if their peripheral nerves have been severed or damaged (i.e., denervated muscles).[7] However, the majority of the FES systems used today stimulate the nerves or the points where the junction occurs between the nerve and the muscle. The stimulated nerve bundle includes motor nerves (efferent nerves—descending nerves from the central nervous system to muscles) and sensory nerves (afferent nerves—ascending nerves from sensory organs to the central nervous system).

The electrical charge can stimulate both motor and sensory nerves. In some applications, the nerves are stimulated to generate localized muscle activity, i.e., the stimulation is aimed at generating direct muscle contraction. In other applications, stimulation is used to activate simple or complex reflexes. In other words, the afferent nerves are stimulated to evoke a reflex, which is typically expressed as a coordinated contraction of one or more muscles in response to the sensory nerve stimulation.

When a nerve is stimulated, i.e., when sufficient electrical charge is provided to a nerve cell, a localized depolarization of the cell wall occurs resulting in an action potential that propagates toward both ends of the axon. Typically, one “wave” of action potentials will propagate along the axon towards the muscle (orthodromic propagation) and concurrently, the other “wave” of action potentials will propagate towards the cell body in the central nervous system (antidromic propagation). While the direction of propagation in case of the antidromic stimulation and the sensory nerve stimulation is the same, i.e., towards the central nervous system, their end effects are very different. The antidromic stimulus has been considered an irrelevant side effect of FES. However, in recent years a hypothesis has been presented suggesting the potential role of the antidromic stimulation in neurorehabilitation.[8] Typically, FES is concerned with orthodromic stimulation and uses it to generate coordinated muscle contractions.

In the case where sensory nerves are stimulated, the reflex arcs are triggered by the stimulation on sensory nerve axons at specific peripheral sites. One example of such a reflex is the flexor withdrawal reflex. The flexor withdrawal reflex occurs naturally when a sudden, painful sensation is applied to the sole of the foot. It results in flexion of the hip, knee and ankle of the affected leg, and extension of the contralateral leg in order to get the foot away from the painful stimulus as quickly as possible. The sensory nerve stimulation can be used to generate desired motor tasks, such as evoking flexor withdrawal reflex to facilitate walking in individuals following stroke, or they can be used to alter reflexes or the function of the central nervous system. In the later case, the electrical stimulation is commonly described by the term neuromodulation.

Nerves can be stimulated using either surface (transcutaneous) or subcutaneous (percutaneous or implanted) electrodes. The surface electrodes are placed on the skin surface above the nerve or muscle that needs to be “activated”. They are noninvasive, easy to apply, and generally inexpensive. Until recently the common belief in the FES field has been that due to the electrode-skin contact impedance, skin and tissue impedance, and current dispersion during stimulation, much higher-intensity pulses are required to stimulate nerves using surface stimulation electrodes as compared to the subcutaneous electrodes. This statement is correct for all commercially available stimulators except MyndMove stimulator, which has implemented a new stimulation pulse that allows the stimulator to generate muscle contractions without causing discomfort during stimulation, which is a common problem with commercially available transcutaneous electrical stimulation systems.

A major limitation of the transcutaneous electrical stimulation is that some nerves, for example those innervating the hip flexors, are too profound to be stimulated using surface electrodes. This limitation can be partly addressed by using arrays of electrodes, which can use several electrical contacts to increase selectivity.[9][10][11]

Subcutaneous electrodes can be divided into percutaneous and implanted electrodes. The percutaneous electrodes consist of thin wires inserted through the skin and into muscular tissue close to the targeted nerve. These electrodes typically remain in place for a short period of time and are only considered for short-term FES interventions. However, it is worth mentioning that some groups, such as Cleveland FES Center, have been able to safely use percutaneous electrodes with individual patients for months and years at a time. One of the drawbacks of using the percutaneous electrodes is that they are prone to infection and special care has to be taken to prevent such events.

The other class of subcutaneous electrodes is implanted electrodes. These are permanently implanted in the consumer’s body and remain in the body for the remainder of the consumer’s life. Compared to surface stimulation electrodes, implanted and percutaneous electrodes potentially have higher stimulation selectivity, which is a desired characteristics of FES systems. To achieve higher selectivity while applying lower stimulation amplitudes, it is recommended that both cathode and anode are in the vicinity of the nerve that is stimulated. The drawbacks of the implanted electrodes are they require an invasive surgical procedure to install, and, as is the case with every surgical intervention, there exists a possibility of infection following implantation.

Typical stimulation protocols used in clinical FES involves trains of electric pulses. Biphasic, charged balanced pulses are employed as they improve the safety of electrical stimulation and minimize some of the adverse effects. Pulse duration, pulse amplitude and pulse frequency are the key parameters that are regulated by the FES devices. The FES devices can be current or voltage regulated. Current regulated FES systems always deliver the same charge to the tissue regardless of the skin/tissue resistance. Because of that, the current regulated FES systems do not require frequent adjustments of the stimulation intensity. The voltage regulated devices may require more frequent adjustments of the stimulation intensity as the charge that they deliver changes as the skin/tissue resistance changes. The properties of the stimulation pulse trains and how many channels are used during stimulation define how complex and sophisticated FES-induced function is. The system can be as simple such as FES systems for muscle strengthening or they can be complex such as FES systems used to deliver simultaneous reaching and grasping,[12] or bipedal locomotion.[13][14][15]

Note: This paragraph was developed in part using material from.[1] For more information on FES please consult that and other references provided in the paragraph.

History

FES was initially referred to as Functional Electrotherapy by Liberson,[16] and it was not until 1967 that the term Functional Electrical Stimulation was coined by Moe and Post,[17] and used in a patent entitled, "Electrical stimulation of muscle deprived of nervous control with a view of providing muscular contraction and producing a functionally useful moment".[18] Offner's patent described a system used to treat foot drop.

The first commercially available FES devices treated foot drop by stimulating the peroneal nerve during gait. In this case, a switch, located in the heel end of a user's shoe, would activate a stimulator worn by the user.

Common applications

Spinal cord Injury

Injuries to the spinal cord interfere with electrical signals between the brain and the muscles, resulting in paralysis below the level of injury. Restoration of limb function as well as regulation of organ function are the main application of FES, although FES is also used for treatment of pain, pressure, sore prevention, etc.

Some examples of FES applications involve the use of Neuroprostheses that allow the people with paraplegia to walk, stand, restore hand grasp function in people with quadriplegia, or restore bowel and bladder function.[19]

High intensity FES of the quadriceps muscles allows patients with complete lower motor neuron lesion to increase their muscle mass, muscle fiber diameter, improve ultrastructural organization of contractile material, increase of force output during electrical stimulation and perform FES assisted stand-up exercises.[20]

Stroke

FES is commonly used in foot drop neuroprosthetic devices.

In the acute stage of stroke recovery, the use of cyclic electrical stimulation has been seen to increase the isometric strength of wrist extensors. In order to increase strength of wrist extensors, there must be a degree of motor function at the wrist spared following the stroke and have significant hemiplegia. Patients who will elicit benefits of cyclic electrical stimulation of the wrist extensors must be highly motivated to follow through with treatment, After 8 weeks of electrical stimulation, an increase in grip strength can be apparent. Many scales, which assess the level of disability of the upper extremities following a stroke, use grip strength as a common item. Therefore, increasing strength of wrist extensors will decrease the level of upper extremity disability.

Patients with hemiplegia following a stroke commonly experience shoulder pain and subluxation; both of which will interfere with the rehabilitation process. Functional electrical stimulation has been found to be effective for the management of pain and reduction of shoulder subluxation, as well as accelerating the degree and rate of motor recovery. Furthermore, the benefits of FES are maintained over time; research has demonstrated that the benefits are maintained for at least 24 months.[21].

Hemiparetic stroke patients, who are impacted by the denervation, muscular atrophy, and spasticity, typically experience an abnormal gait pattern due to muscular weakness and the incapacity to voluntary contract certain ankle and hip muscles at the appropriate walking phase [22]. Sabut et al. conducted an experiment on FES with conventional physical therapy, and it was concluded that there was a significant increase in walking speed at the end of the 12-week intervention.

FES for Drop Foot

The drop foot is a common symptom in hemiplegia, characterized by a lack of dorsiflexion during the swing phase of gait, resulting in short, shuffling strides. It has been shown that FES can be used to effectively compensate for the drop foot during the swing phase of the gait. At the moment just before the heel off phase of gait occurs, the stimulator delivers a stimulus to the common peroneal nerve, which results in contraction of the muscles responsible for dorsiflexion. There are currently a number of drop foot stimulators that use surface and implanted FES technologies.[23][24][25][26][27] Drop foot stimulators have been used successfully with various patient populations, such as stroke, spinal cord injury and multiple sclerosis.

FES for Walking

This image describes Functional Electrical Stimulation Therapy for walking. The therapy was used to help retrain incomplete spinal cord injured individuals to walk [30,31]. The therapy was delivered using two 4-channel Compex Motion stimulators [29].

Kralj and his colleagues described a technique for paraplegic gait using surface stimulation, which remains the most popular method in use today.[28] Electrodes are placed over the quadriceps muscles and peroneal nerves bilaterally. The user controls the neuroprosthesis with two pushbuttons attached to the left and right handles of a walking frame, or on canes or crutches. When the neuroprosthesis is turned on, both quadriceps muscles are stimulated to provide a standing posture. The left button initiates swing phase in the left leg by briefly stopping stimulation of the left quadriceps and stimulating the peroneal nerve. This stimulation is applied suddenly, so as to trigger the flexor withdrawal reflex, resulting in simultaneous hip and knee flexion, as well as dorsiflexion. After a fixed period of time, peroneal nerve stimulation is stopped and quadriceps stimulation is initiated while the reflex is still active to complete the stride. Similarly, the right button initiates swing phase in the right leg. Many current FES systems for walking have employed this technique as the basic concept.[29] An alternative approach to Kralj techniques is the FES system for walking developed using the Compex Motion neuroprosthesis.[30][31] Compex Motion neuroprosthesis for walking is an eight to sixteen channel surface FES system used to restore voluntary walking in stroke and spinal cord injury individuals.[32] This system does not apply perineal nerve stimulation to enable locomotion. Instead, it activates all relevant lower limb muscles in a sequence similar to the one that brain uses to enable locomotion. The hybrid assistive systems (HAS) [33] and the RGO [34] walking neuroprostheses are devices that also apply active and passive braces, respectively. The braces were introduced to provide additional stability during standing and walking.

A major limitation of neuroprostheses for walking that are based on surface stimulation is that the hip flexors cannot be stimulated directly. Therefore, hip flexion during walking must come from voluntary effort, which is often absent in paraplegia, or from the flexor withdrawal reflex. Implanted systems have the advantage of being able to stimulate the hip flexors, and therefore, to provide better muscle selectivity and potentially better gait patterns.[35] Hybrid systems with exoskeleton have been also proposed to solve this problem.[36] These technologies have been found to be successful and promising, but at the present time these FES systems are mostly used for exercise purposes and seldom as an alternative to wheelchair mobility.

FES systems for walking have been used successfully in stroke and spinal cord injury patients.

In popular culture

See also

References

  1. 1 2 M.R. Popovic, K. Masani and S. Micera, “Chapter 9 – Functional Electrical Stimulation Therapy: Recovery of function following spinal cord injury and stroke,” In press, Neurorehabilitation Technology – Second Edition, Z. Rymer, T. Nef and V. Dietz, Ed. Springer Science Publishers in November 2015.
  2. ↑ M. Claudia et al.,(2000), Artificial Grasping System for the Paralyzed Hand, International Society for Artificial Organs, Vol 24 No.3
  3. ↑ M.K. Nagai, C. Marquez-Chin, and M.R. Popovic, “Why is functional electrical stimulation therapy capable of restoring motor function following severe injury to the central nervous system?” Translational Neuroscience, Mark Tuszynski, Ed. Springer Science and Business Media LLC, pp: 479-498, 2016.
  4. ↑ Guyton and Hall Textbook of Medical Physiology, John Hall, 13th edition, Elsevier Health Sciences, May 31, 2015
  5. ↑ M.R. Popovic and T.A. Thrasher, “Neuroprostheses,” in Encyclopedia of Biomaterials and Biomedical Engineering, G.E. Wnek and G.L. Bowlin, Eds.: Marcel Dekker, Inc., vol. 2, pp. 1056-1065, 2004.
  6. ↑ Control of Movement for the Physically Disabled: Control for Rehabilitation Technology, Dejan Popovic and Thomas Sinkjaer, Springer Science & Business Media, December 6, 2012.
  7. ↑ Reichel M, Breyer T, Mayr W, and Rattay F. Simulation of the three-dimensional electrical field in the course of functional electrical stimulation. Artificial Organs 26: 252–255, 2002.
  8. ↑ Rushton D. Functional electrical stimulation and rehabilitation—an hypothesis. Med Eng Phys 25: 75–78, 2003.
  9. ↑ Kuhn A, Keller T, Micera S, and Morari M. Array electrode design for transcutaneous electrical stimulation: a simulation study. Medical engineering & physics 31: 945–951, 2009.
  10. ↑ Micera S, Keller T, Lawrence M, Morari M, and Popović DB. Wearable neural prostheses. Restoration of sensory-motor function by transcutaneous electrical stimulation. IEEE engineering in medicine and biology magazine : the quarterly magazine of the Engineering in Medicine & Biology Society 29: 64–69, 2010.
  11. ↑ Popović DB, and Popović MB. Automatic determination of the optimal shape of a surface electrode: selective stimulation. Journal of Neuroscience Methods 178: 174–181, 2009.
  12. ↑ Popovic MR, Thrasher TA, Zivanovic P, Takaki M, and Hajek P. Neuroprosthesis for Retraining Reaching and Grasping Functions in Severe Hemiplegic Patients. Neuromodulation 8: 58–72, 2005.
  13. ↑ Bajd T, Kralj A, Stefancic M, and Lavrac N. Use of functional electrical stimulation in the lower extremities of incomplete spinal cord injured patients. Artificial Organs 23: 403–409, 1999.
  14. ↑ Kapadia N, Masani K, Craven BC, Giangregorio LM, Hitzig SL, Richards K, and Popovic MR. A randomized trial of functional electrical stimulation for walking in incomplete spinal cord injury: Effects on walking competency. The Journal of Spinal Cord Medicine, 37(5): 511–524, 2014.
  15. ↑ Bailey SN, Hardin EC, Kobetic R, Boggs LM, Pinault G, and Triolo RJ. Neurotherapeutic and neuroprosthetic effects of implanted functional electrical stimulation for ambulation after incomplete spinal cord injury. Journal of rehabilitation research and development 47: 7–16, 2010.
  16. ↑ Liberson, W. T.; Holmquest, H. J.; Scot, D.; Dow, M. (1961). "Functional electrotherapy: Stimulation of the peroneal nerve synchronized with the swing phase of the gait of hemiplegic patients". Archives of physical medicine and rehabilitation 42: 101–105. PMID 13761879.
  17. ↑ J. H. Moe and H. W. Post, “Functional electrical stimulation for ambulation in hemiplegia,” The Lancet, vol. 82, pp. 285–288, July 1962.
  18. ↑ Offner et al. (1965), Patent 3,344,792
  19. ↑ Pow–ell, Joanna; David Pandyan; Malcolm Granat; Margart Cameron; David Stott (1999). "Electrical Stimulation of Wrist Extensors in Poststroke Hemiplegia". Stroke: Journal of the American Heart Association 30 (7): 1384–1389. Retrieved 11 May 2011.
  20. ↑ Kern H, Carraro U, Adami N, Biral D, Hofer C, Forstner C, Mödlin M, Vogelauer M, Pond A, Boncompagni S, Paolini C, Mayr W, Protasi F, Zampieri S (2010). "Home-based functional electrical stimulation rescues permanently denervated muscles in paraplegic patients with complete lower motor neuron lesion.". Neurorehabil Neural Repair 24 (8): 709–721. doi:10.1177/1545968310366129. PMID 20460493.
  21. ↑ Chantraine, Alex; Baribeault, Alain; Uebelhart, Daniel; Gremion, Gerald (1999). "Shoulder Pain and Dysfunction in Hemiplegia: Effects of Functional Electrical Stimulation". Archives of Physical Medicine and Rehabilitation 80: 328–331. doi:10.1016/s0003-9993(99)90146-6.
  22. ↑ Sabut, S. K., Sikdar, C., Mondal, R., Kumar, R., & Mahadevappa, M. (2010). Restoration of gait and motor recovery by functional electrical stimulation therapy in persons with stroke. Disability and Rehabiltation, 32(19), 1594-1603. Retrieved from http://web.b.ebscohost.com.mutex.gmu.edu/chc/pdf?sid=d6669a6b-e26a-4656-84eee3c01036ce12%40sessionmgr120&vid=1&hid=128
  23. ↑ Taylor PN, Burridge JH, Dunkerley AL, Wood DE, Norton JA, Singleton C, Swain ID (1999) Clinical use of the Odstock dropped foot stimulator: its effect on the speed and effort of walking. Archives of physical medicine and rehabilitation 80 (12):1577-1583
  24. ↑ Stein RB, Everaert DG, Thompson AK, Chong SL, Whittaker M, Robertson J, Kuether G (2010) Long-term therapeutic and orthotic effects of a foot drop stimulator on walking performance in progressive and nonprogressive neurological disorders. Neurorehabilitation and neural repair 24 (2):152-167.
  25. ↑ Hausdorff JM, Ring H (2008) Effects of a new radio frequency-controlled neuroprosthesis on gait symmetry and rhythmicity in patients with chronic hemiparesis. American journal of physical medicine & rehabilitation / Association of Academic Physiatrists 87 (1):4-13.
  26. ↑ Burridge JH, Haugland M, Larsen B, Svaneborg N, Iversen HK, Christensen PB, Pickering RM, Sinkjaer T (2008) Patients' perceptions of the benefits and problems of using the ActiGait implanted drop-foot stimulator. J Rehabil Med 40 (10):873-875.
  27. ↑ Kenney L, Bultstra G, Buschman R, Taylor P, Mann G, Hermens H, Holsheimer J, Nene A, Tenniglo M, van der Aa H, Hobby J (2002) An implantable two channel drop foot stimulator: initial clinical results. Artificial Organs 26 (3):267-270
  28. ↑ Kralj A, Bajd T, and Turk R. Enhancement of gait restoration in spinal injured patients by functional electrical stimulation. Clin Orthop Relat Res 34-43, 1988.
  29. ↑ Graupe D, Davis R, Kordylewski H, and Kohn K. Ambulation by traumatic T4-12 paraplegics using functional neuromuscular stimulation. Crit Rev Neurosurg 8: 221-231, 1998.
  30. ↑ Popovic MR, and Keller T. Modular transcutaneous functional electrical stimulation system. Medical engineering & physics 27: 81-92, 2005.
  31. ↑ Thrasher TA, Flett HM, and Popovic MR. Gait training regimen for incomplete spinal cord injury using functional electrical stimulation. Spinal Cord 44: 357-361, 2006.
  32. ↑ N. Kapadia, K. Masani, B.C. Craven, L.M. Giangregorio, S.L. Hitzig, K. Richards, and M.R. Popovic, “A randomized trial of functional electrical stimulation for walking in incomplete spinal cord injury: Effects on walking competency,” The Journal of Spinal Cord Medicine, vol. 37, no. 5, pp: 511–524, 2014.
  33. ↑ Popovic D, Tomović R, and Schwirtlich L. Hybrid assistive system--the motor neuroprosthesis. IEEE transactions on bio-medical engineering 36: 729-737, 1989.
  34. ↑ Solomonow M, Baratta R, Hirokawa S, Rightor N, Walker W, Beaudette P, Shoji H, and D'Ambrosia R. The RGO Generation II: muscle stimulation powered orthosis as a practical walking system for thoracic paraplegics. Orthopedics 12: 1309-1315, 1989.
  35. ↑ Triolo RJ, Bieri C, Uhlir J, Kobetic R, Scheiner A, and Marsolais EB. Implanted Functional Neuromuscular Stimulation systems for individuals with cervical spinal cord injuries: clinical case reports. Archives of physical medicine and rehabilitation 77: 1119-1128, 1996.
  36. ↑ Kobetic R, To CS, Schnellenberger JR, Audu ML, Bulea TC, Gaudio R, Pinault G, Tashman S, and Triolo RJ. Development of hybrid orthosis for standing, walking, and stair climbing after spinal cord injury. Journal of rehabilitation research and development 46: 447-462, 2009.
  37. ↑ "The Rap Sheet, "The Story Behind the Story: No Hard Feelings by Mark Coggins"". Retrieved February 10, 2016.

Further reading

External links

This article is issued from Wikipedia - version of the Wednesday, April 27, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.