Functional electrical stimulation

Functional electrical stimulation (commonly abbreviated as FES) is a technique that uses electrical currents to activate nerves innervating extremities affected by paralysis resulting from spinal cord injury (SCI), head injury, stroke or other neurological disorders, restoring function in people with disabilities.

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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 people with paraplegia to stand, restore hand grasp function in people with quadriplegia, or restore bowel and bladder function.

Electrical stimulation for the purpose of helping persons with paralysis of the arms or legs mainly focuses on the neuromuscular transmission peripherally. E-stim can also be used for central nervous system stimulation to hasten awakening from coma or the vegetative state. There is a long history of neurosurgeons who have implanted electrodes into the brain and spinal cord, especially in Japan, for increasing cerebral blood flow and certain neurotransmitters in persons in long term coma states.

Beginning in 1991 in Greenville, North Carolina (East Carolina University) and shortly after that in Charlottesville,Virginia (University of Virginia), the right median nerve has been used as a portal to help awaken injured human brains. Trains of differentiated square electrical pulses at 40 Hz (a frequency for upregulation of the thalamus), 20 seconds on and 40 seconds off, have been applied to the palmar side of the right wrist for transdermal stimulation of the right median nerve at low amplitudes, enough to produce contraction of the thumb. Battery powered FDA approved electrical neuromuscular stimulators have been used in these research projects connected by wires to the pair of right wrist electrodes embedded in a custom made plastic orthosis to localize the stimulation target. The right median nerve was selected as the electrical portal as there is large cortical respresentation of that nerve in the dominant left cerebral hemipshere. By subcortical connections, the transmitted signals go to Broca's motor/speech planning area (whether the person is right or left handed, the majority are left hemisphere dominant). Awakening from deep coma from motor vehicle crashes with closed head injury in the Glasgow Coma Scale range of 4-6 can be expected to respond in half of the treated cases after two to four weeks of 8 hours/day electrical treatment,if started within one to two weeks of the severe brain trauma. The advantage of the shorter than expected period of unconsciousness is a quicker start into a neurorehabilitation program to encourage ambulation and talking.

Over the last decade, this RMNS project has spread from the USA East Coast to Central Japan, parts of Europe, and most recently in 2005 to Shanghai, China.

Beginning

FES is an important and complicated research subject in Biomedical Engineering.

References

• Crago P.E., Lan N., Veltink P.H., Abbas J.J., Kantor C.K. (1996) “New control strategies for neuroprosthetic systems”, J. Rehab. Res. Dev., Vol. 33, No. 2, 158-172.

• Crago P.E., Mortimer J.T., Peckham P.H. (Jun 1980) “Closed-loop control of force during electrical stimulation of muscle”, IEEE Transactions on Biomedical Engineering, Vol. 27, No. 6, 306-12

• Peckham P.H., Keith M.W. (1992) “Motor prostheses for restoration of upper extremity function” Ch 8 in Neural Prostheses. Replacing Motor Function After Disease or Disability. R.B. Stein, P.H. Peckham and D.B. Popovic Editors.

• Peckham P.H., Keith M.W., Freehafer A.A. (1988) “Restoration of functional control by electrical stimulation in the upper extremity of the quadriplegic patient,” J. Bone Joint Surgery, Vol. 70-A, 144-148

• Peckham P.H., Marsolais E.B., Mortimer J.T. (1980) “Restoration of key grip and release in the C6 tetraplegic patient through functional electrical stimulation”, J Hand Surg [Am].Vol. 5, No. 5, 462-9.

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Coma stimulation references:

Cooper E.B., Scherder E.J.A., Cooper J.B (2005) "Electrical treatment of reduced consciousness: experience with coma and Alzheimer's disease," Neuropsyh Rehab (UK).Vol. 15,389-405.

Cooper E.B,& Cooper J.B. (2003) "Electrical treatment of coma via the median nerve," Acta Neurochirurg Supp, Vol. 87, 7-10 .