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 walk, 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 representation of that nerve in the dominant left cerebral hemisphere. 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.
Functional electrical stimulation (FES) of paraplegics allows paraplegics with complete paralysis due to spinal cord injury at the thoracic level of their spinal cord to walk distances that average 450 meters per walk under some training procedures and 110 meters per walk when undergoing less demanding training, when using the noninvasive Parastep FES system that received the USA FDA approval in 1994. Certain such patients can walk one mile using that same system. FES for ambulation also shows improvements in blood flow to lower extremities and in other medical and psychological parameters including bone density.
FES is an important and complicated research subject in Biomedical Engineering.
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 . ___________________________
Paraplegia stimulation for walking - references:
Klose K.J., Jacobs P.L., Broton J.G., Guest J.G., Needham-Shropshire B.M., Lewohl N., Nash M.S., Green B.A (1997) "Evaluation of a training program for persons with SCI paraplegia using the Parastep-I ambulation system, Part 1: Ambulation performance and anthropometric measures", Arch. Phys. Med. Rehab., Vol. 78, 789-793.
Nash M.S., Jacobs P.L., Montalvo P.M., Klose K.J., Guest, R.S., Needham-Shrpshire B.B., Green B.A. (1997) "Evaluation of a training program for persons with SCI paraplegia using the Parastep-I ambulation system, Part 5: Lower extremity blood flow and hypermic responses to occlusion are augmented by ambulation training", Arch. Phys. Med. Rehab., Vol. 78, 808-814.
Graupe D. (2002) "An overview of the state of the art of noninvasive FES for independent ambulation by thoracic level paraplegics" Neurological Research, Vol. 24, 431-442.
Graupe D. Cerrel-Bazo H. (2007) "Performance and patient training in walking with FES by toracic level paraplegics", Basic and Appl. Myology, Vol 17, 129-132.
Lichy A., Libin A., Ljunberg I., Groach L., (2007) " Preserving bone health after acute spinal cord injury: Differential responses to a neuromuscular electrical stimulation intervention", Proc. 12th Annual Conf. of the International FES Soc., Philadelphia, PA, Session 2, Paper 205.