Transcutaneous Electrical Nerve Stimulator
A Transcutaneous Electrical Nerve Stimulator, more commonly referred to as a TENS
unit and pronounced tens, is an electronic device that produces electrical signals used
to stimulate nerves through unbroken skin. 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.
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. 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.
Electrical stimulation for pain control was used in ancient Greece, 63 A.D. It was
reported by Scribonius Largus pain was relieved by standing on an electrical fish at
the seashore. 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 (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. 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 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 endorphines which in turn cause pain relief.