History
For several thousand
years, people have recognized that electrical stimulation can have an impact on
pain. Hippocrates, the father of medicine, is said to have used electric fish
to cause numbness, and a report of gout being “cured” by accidental contact
with a fish called an electric ray dates back to the first century. Later
reports also described pain resolution that occurred when similar types of
“electric” fish were placed on afflicted body parts.
It was not until
the 18th century when a more formal device to deliver electricity to decrease
pain was created. Although initially developed in Europe, Benjamin Franklin is
credited with reforming the original electric condenser, which was used to
shock patients in an effort to treat various ailments.
What is TENS?
Transcutaneous
electrical nerve stimulation (TENS) is the application of an electrical current
through electrodes attached to the skin. Many different electrical current
waveforms with different characteristics can be used for this application but a
biphasic pulsed waveform with alternating positive and negative polarity is
most commonly used. By carefully adjusting the intensity and duration of the
pulses, a comfortable tingling sensation without pain or muscle contraction, or
a tingling with a muscle contraction, can be produced. This is possible because
nerves that control muscle contractions and the nerves that transmit pain
information to the brain are not as responsive to electrical stimulation as the
nerves that transmit other sensory information. Thus, if a low intensity and
short pulse is used only the sensory nerves and not the motor or pain
transmitting nerves will respond. If a slightly higher in- tensity, or longer
pulse duration, is used, both the sensory and the motor nerves, but not the
pain transmitting nerves, will respond. The electrodes used most commonly at
this time for the applica tion of
TENS are made of fabric or thin plastic and are coated on one side with a
self-adhesive conductive gel. A pair of these electrodes, connected by wires to
an electrical stimulator, is adhered to the patient’s skin in the area where
the stimulation is desired. Usually the electrodes are approximately 2 - 5 cm
by 2 - 5 cm and are placed about 5 to 20 cm apart. The electrical stimulator is
generally battery driven and approximately the size of a pager/beeper.
Types of TENS
Are there different
types of TENS?
Electrical stimulation
can be used in the following ways:
* Conventional TENS
— This is the most typical type of treatment. It uses a high stimulation
frequency, but the intensity of the electrical stimulus is low. Patients
usually leave the electrodes on for long periods of time, turning them on and
off at intervals. A typical treatment might last 30 minutes, but the length can
vary depending on patient needs. Pain often is relieved only while the
treatment is under way, but the relief may last longer.
* Acupuncturelike
TENS — In this case, the stimulation frequency is low, but the electrical
impulse is quite intense. Some patients find this more effective or longer
lasting than conventional TENS. Other patients find acupuncture like TENS too
uncomfortable.
* Percutaneous electrical
nerve stimulation — PENS, as it is known, is a combination of acupuncture and
electrical stimulation. Instead of electrodes, PENS uses needles to penetrate
the skin and deliver the electrical stimulation.
Common Applications
The most common
clinical application of TENS is for pain management. The treatment can produce
a prickling sensation but is not painful. Transcutaneous electrical nerve
stimulation is considered highly effective in controlling pain. It can reduce
the feelings of pain and prevent them from coming back in the future. It is
very popular for labor pains.
It is thought that
electrical stimulation of nerves via the skin may cause chemical changes in the
brain.
A number of studies
have suggested that the use of TENS machines may produce short-lived
improvement in some of the cognitive aspects of dementia as well.
Side Effects of TENS
Transcutaneous
electrical nerve stimulation therapy is considered mostly safe. On rare
occasions, an electrical current will be too intense for a patient, causing
burning or irritation on the skin.
The effect of TENS
on fetuses is unknown at this time, so pregnant women should not use electrical
stimulation for pain relief. Heart patients should use caution as well.
Some patients with
skin allergies may react to the electrode pads used with the units. People with
pacemakers, infusion pumps, defibrillators, and similar devices should not be
exposed to the electrical currents produced by a TENS unit.
Theory
Electricity has
been used medicinally for thousands of years. Stone carvings from ancient Egypt
depict electric fish being used to treat pain. In ancient Greece, electrogenic
torpedo fish were used to treat arthritis and headache.
There are several
proposed explanations for how TENS may work:
* It may affect the
nerves that perceive pain or light touch.
* It may interfere
with nerve pathways.
* It may alter the
natural chemicals (such as encephalins, endorphins, opioids or substance P)
that affect the way pain is perceived and transmitted.
None of these
mechanisms has been clearly demonstrated in scientific research, and the basis
of potential activity of TENS is controversial.
Theories
traditionally used to explain acupuncture, such as effects on flow of vital
energy, have also been offered to explain TENS. It is sometimes suggested that
TENS may affect the cardiovascular system, increasing heart rate and reducing
blood pressure.
TENS and Alzheimer’s
Several studies
report that TENS may improve some symptoms of Alzheimer's disease, such as
mood, memory and cycles of daily rest and activity.
Preliminary
evidence reports improvements in mood and mild cognitive impairment in elderly
patients who do not suffer from Alzheimer's disease or early dementia. However,
this early research does not provide enough high-quality scientific evidence to
draw a firm conclusion about effectiveness.
In several studies,
transcutaneous electrical nerve stimulation (TENS) was found to improve various
aspects of explicit memory and affective behavior in patients in a relatively
early stage of Alzheimer’s disease (AD). This effect is probably mediated by
activation of the septo-hippocampal region and the hypothalamus, which play an
essential role in memory processes and affective behavior and are affected in Alzheimer’s
patients. The hypothesis of hypothalamic activation was recently further
supported by the finding that TENS also improved circadian rhythm disturbances,
i.e. nightly restlessness, in patients in an early stage of AD, since these
disturbances most likely result from degeneration of the hypothalamic
suprachiasmatic nucleus (SCN).
So, the peripheral
nerve stimulation may efficiently activate brain areas involved in memory
(hippocampus) and affective regulation (hypothalamus), providing a novel
nonpharmacologic pathway for "exercising" brain pathways that are
dysfunctional in Alzheimer's disease.
The later studies,
produce very encouraging results, showing that TENS could also improve
disturbances in the rest–activity rhythm of more severely demented (midstage)
AD patients.
Sources and Additional Information:
