Research

Electrical Stimulation: The Cure For Paralysis

Arya Reddy


Abstract

Functional Electrical Stimulation (FES) is an emerging technology that sends electrical impulses throughout the body or a specific part to stimulate muscle movement. This technology has improved in recent years, helping to reverse the effects of paralysis. The electronic micro-based processor is the primary component of FES in terms of determining when and how the stimulus is delivered. As of right now, FES is being used for the upper extremity, lower extremity, bowls, and it is even being applied to bikes to allow people to ride bikes. FES can also be used for the regeneration of bladder and respiratory functions and the prevention of pressure ulcers. This article discusses FES in the following aspects: its mechanism, applications, limitations, and scope in the future as a means of medical practice and prosthetics. 

 

Spinal Cord Injury (SCI)

A spinal cord injury occurs when the spinal cord or nerves situated at the end of the spinal canal are damaged. This causes loss of sensation and strength at the sites below the injury.  The severity of the injury is referred to as complete or incomplete based on whether there is a total loss of sensation and motor skills, or if there is still some sensation or functions.  Paralysis from a spinal cord injury is referred to as tetraplegia and paraplegia. Tetraplegia occurs when the arms, hands, trunk, legs, and pelvic organs are affected by the injury, whereas paraplegia only affects the trunk, legs, and pelvic organs. Some common causes of spinal cord injuries are motor vehicle accidents, alcohol use, acts of violence, falls, sports and recreation injuries, and other preexisting conditions {3}.

 

History of Functional Electrical Stimulation

Luigi Galvani was an Italian scientist born in 1737.  He obtained a degree from Bologna Medical School and made many contributions and achievements in the field, including his research on the genitourinary tract of birds and human anatomy. Galvani’s most notable discovery was discovering that a frog muscle could be made to contract by putting an iron wire on its muscle and a copper wire on its nerve. He created an instrument in which the nerve of the frog was attached to a single metal electrode, and a separate metal electrode was attached to the muscle of the frog and realized that when a voltage was applied to it, an animal body performed convulsive motions. This discovery led to the spark of functional electrical stimulation and many other discoveries such as bioelectricity {5}.

 

Functional Electrical Stimulation (FES)

Functional electrical stimulation (FES) is the practice of delivering a healthy amount of electrical current in a controlled fashion to activate weakened or impaired neuromuscular systems in an attempt to restore lost muscle control. Neuro-prosthesis is a technology that stimulates the nervous system through electrical stimulation. This initiates physiological-like activation of the preserved peripheral nerves, supplying neurologically disabled people with functional regeneration of separate body organs {2}.  FES succeeds when it applies electrical impulses to restore or improve the function of paralyzed muscles. The use of FES became more common after a college student who was paraplegic was able to stand up, and walked to get her diploma. Nan Davis performed this seemingly impossible feat in 1983 at Wright University. From this event, FES progressed and developed into the modern technology we know it as today {4}. 

 

Mechanism of FES

Electric current is the activating agent of both nerves and muscle fibers. However, FES is only used to specifically activate nerve fibers, as a much smaller level of current is needed to produce an action potential in a nerve than is required for muscle depolarization. The key component of the FES system is the electronic microprocessor-based stimulator that determines when and how the stimulus is delivered. It has channels linked to the neuromuscular system for the transmission of individual pulses through a series of electrodes. It contains programs such as sitting, standing, and walking and aims to produce a series of impulses for these programs that mimic the synaptic stimuli that would otherwise have passed through the spinal cord to the intended peripheral nerves below the spinal cord lesion. Thus, these stimuli induce action potentials in the peripheral nerves that cause muscle contractions in the corresponding muscle fibers. The FES system's feedback control can be either open-looped or closed-looped. For basic tasks such as muscle activation, open-looped control is used and involves a consistent electrical output from the stimulator. The conditions for electrical stimulation are changed in a closed-looped system by a computer using feedback information on muscle strength and joint posture, thereby stimulating multiple muscle groups at the same time, and leading to a mixture of muscle contractions required for a complex, sophisticated, and functional operation {2}. 

 

Applications of FES

FES can have many applications to benefit humans, but FES is mainly used to restore function in the upper and lower extremities. When FES is used with neuroprosthesis, it can often lead to function in the hand being restored. Similarly, when FES is used with the lower extremity,  it can often lead to function in the legs. FES can also be used to improve trunk and posture control. After an SCI injury, a damaged posture might be hard to fix, but with FES technology this issue could be resolved. Pressure ulcers are also sometimes caused by an SCI.  A pressure ulcer could be classified as a deep tissue injury (DTI). Early use of FES can prevent pressure ulcers {1}.  Some other examples include FES bikes, bladder or bowel FES, upper extremity FES, walking with FES, and cyberkinetics. FES bikes make a stationary leg-cycle called an ergometer to pedal individuals with little to no leg movement. FES can also stimulate bladder or bowel function in paralyzed patients, and these implants have proven to improve control of these organs in the majority of patients. FES has also been applied to the upper extremities to improve function in the hands and arms, with devices such as Parastep having been shown to improve the function of leg muscles {4}. 

 

Limitations of FES

There are two FES device implementations that are scientifically designed to support SCI patients according to their needs. Cardiovascular conditioning and the treatment of muscular atrophy by exercise have clinical applications, while essential body functions missing due to SCI are supported by practical applications. Examples include ambulation and locomotive aid in cases of paraplegia, respiratory assistance or hand grip in cases of quadriplegia, and electro-ejaculation, which is the automatic voiding of the intestines or bladder. Many commercial as well as research-based FES instruments have been produced in various centers around the world for other therapeutic and practical uses {2}.

 

Future Scope of FES

While recent advancements and improvements in the development of the FES system have paved the way for SCI patients to be provided with some functionality and functions, FES itself still has many inherent drawbacks at present, and further analysis is needed to restore the missing function safely, fully, and effectively. There are various problems that need to be solved before the SCI population can use them on a daily basis. As a product of CNS dysfunction, FES promises a new age of recovery and provides tremendous optimism for patients who are in a wheelchair or suffering from ambulatory difficulties. In the near future, however,  total motion and function are not expected to be seen. Experimental versions are under production for FES systems with implantable electrical stimulators and compact microprocessors.  Intraspinal microstimulation (ISMS) is a development paradigm in which the spinal-cord-locomotor-circuits named Central Pattern Generators (CPG) are specifically tapped for stimulation and regeneration of limb movements. Future experiments on these neural surgical devices will concentrate on interpreting the cerebral motor cortex's expected motion trajectories, as well as the use of this signal to regulate the FES devices. Hybrid neural-prosthetics are being studied and can contribute to the development of a neurological attachment to these neural prosthetic devices from the cerebral motor cortex. In other words, FES is constantly improving and having ground-breaking discoveries {2}.

 

Conclusion

SCI can cause paralyzation, which is the loss of sensation and strength at the sites below the injury. In an effort to regain lost power, functional electrical stimulation (FES) is the process of administering a healthy amount of electrical current doses in a controlled manner to stimulate the compromised or damaged neuromuscular system. FES is a technology that could revolutionize the way we view paralysis. It can lead to advanced prosthetics that can revert function back to the muscles and many more impeccable applications. As of now, this technology has developed into  FES bikes, bladder or bowel FES, upper extremity FES, walking with FES, and cyberkinetics. The triggering agent in both nerves and muscle fibers is the electric current. FES, however, is used only to stimulate nerve fibers directly, since a much lower level of current is needed to create an action potential in a nerve than is required for muscle depolarization.


References


  1. Ho, Chester et al. (01/05/2014). Functional Electrical Stimulation and Spinal Cord Injury. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4519233/. Retrieved: 10/22/2020.

  2. Hamid, Samar & Hayek, Ray. (17/09/2008). Role of electrical stimulation for rehabilitation and regeneration after spinal cord injury: an overview.  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2527422/ Retrieved: 10/22/2020.

  3. (17/09/2019). Spinal Cord Injury. https://www.mayoclinic.org/diseases-conditions/spinal-cord-injury/symptoms-causes/syc-20377890. Retrieved: 10/23/2020.

  4. Functional Electrical Stimulation. https://www.christopherreeve.org/living-with-paralysis/rehabilitation/functional-electrical-stimulation. Retrieved: 11/06/2020.

  5. Luigi Galvani. https://www.famousscientists.org/luigi-galvani/. Retrieved: 11/06/2020.

  6. Controlled Functional Electrical Stimulation for Rehabilitation Purposes. https://www.mpi-magdeburg.mpg.de/1377984/Controlled-Functional-Electric-Stimulation-for-Rehabilitation-Purposes. Retrieved: 12/10/2020.

Arya Reddy

Arya Reddy


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