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.
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.
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.
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