Transcutaneous Electrical Nerve Stimulator

A Transcutaneous Electrical Nerve Stimulator, more commonly referred to as a TENS unit and pronounced /ˈtɛnz/ tens, is an electronic device that produces electrical signals used to stimulate nerves through unbroken skin. The name was coined by Dr. Charles Burton.^[1] The unit is usually connected to the skin using two or more electrodes. A typical battery-operated TENS unit consists of a pulse generator, small transformer, frequency and intensity controls, and a number of electrodes.

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Uses

TENS is considered a method of pain relief, and has a wide following for use in obstetric care, particularly labour. Nevertheless, there is little data on its actual efficacy, and some obstetricians maintain that it is ineffective.

In palliative care and pain medicine, TENS units are sometimes used in an attempt to alleviate neuropathic pain (pain due to nerve damage). Although results are modest, some patients benefit from this approach. However, a study published in the New England Journal of Medicine found that TENS therapy was no more effective against chronic lower back pain than a placebo^[2].

A suitable cream should be used to increase conductivity from the electrode to the skin. The position of the electrodes on the skin determine which nerve(s) is (are) stimulated.

TENS units are also used by the BDSM community for erotic play involving electrical stimulation. See also Erotic electrostimulation.

History

Electrical stimulation for pain control was used in ancient Greece, 63 A.D. It was reported by Scribonius Largus that pain was relieved by standing on an electrical fish at the seashore.^{[citation needed]} In the 16th through the 18th century various electrostatic devices were used for headache and other pains. Benjamin Franklin was a proponent of this method for pain relief. In the 1900's a device called the electreat, along with numerous other devices were used for pain control and other quack applications such as cancer cures. Only the electreat survived into the twentieth century, but was not portable, and had limited control of the stimulus.

The first modern, patient-wearable TENS was patented in the U.S.A. on June 18, 1974 (U.S. Patent 3,817,254 ). It was initially used for testing the tolerance of chronic pain patients to electrical stimulation before implantation of electrodes in the spinal cord dorsal column.^[3] The electrodes were attached to an implanted receiver, which received its power from an antenna worn on the surface of the skin. Although intended only for testing tolerance to electrical stimulation, many of the patients got so much relief from the TENS itself that they never returned for the implant.

A number of companies manufacturing TENS appeared after the commercial success of the Medtronic device became known. The neurological division of Medtronic, founded by Don Maurer, Ed Schuck and Dr. Charles Ray, developed a number of applications for implanted electrical stimulation devices for treatment of epilepsy, Parkinson's disease, and other disorders of the nervous system. Maurer founded Empi, Inc. in 1977, and in the late 1980's purchased the TENS product line from Medtronic.

Safety

TENS Electrodes should never be placed:

• On or near the eyes
• In the mouth
• Transcerebrally (on each temple)
• On the front of the neck (due to the risk of acute hypotension through a vasovagal reflex)
• On areas of numb skin/decreased sensation
• On broken skin areas or wounds
• On or near the trigeminal nerve if you have a history of herpes zoster induced trigeminal neuralgia (Postherpetic neuralgia)

Do not turn TENS up too high as this can cause over-stimulation which may make pain worse. There should be no muscle contraction.

TENS should also be used with caution in people with epilepsy or pregnant women (do not use over area of the uterus as the effects of electrical stimulation over the developing fetus are not known). TENS should not be used by people with an artificial cardiac pacemaker due to risk of interference and failure of their implanted device. Possible failure of these warnings can result in ventricular fibrillation.

In the situation where low frequency (or acupuncture-like) TENS is being used, it is necessary to increase the intensity of the stimulation to the point where a demonstrable muscle twitch is evident. This 2-6Hz (pulses per second) output increases the systemic release of endorphins which in turn cause pain relief.

See also

• Action Potential
• PTNS
• MENS
• SCENAR

References