Transcutaneous electrical nerve stimulation (acronym TENS) is the use of electric current produced by a device to stimulate the nerves for therapeutic purposes. TENS by definition covers the complete range of transcutaneously applied currents used for nerve excitation although the term is often used with a more restrictive intent, namely to describe the kind of pulses produced by portable stimulators used to treat pain.[1][page needed] The unit is usually connected to the skin using two or more electrodes. A typical battery-operated TENS unit is able to modulate pulse width, frequency and intensity. Generally TENS is applied at high frequency (>50 Hz) with an intensity below motor contraction (sensory intensity) or low frequency (<10 Hz) with an intensity that produces motor contraction
TENS is a non-invasive, safe nerve stimulation intended to reduce pain, both acute and chronic. While controversy exists as to its effectiveness in the treatment of chronic pain, a number of systematic reviews or meta-analyses have confirmed its effectiveness for postoperative pain, osteoarthritis, and chronic musculoskeletal pain.[6] Conversely, results from the Bone and Joint Decade 2000-2010 Task Force on Neck Pain, reported in early 2008, showed no clinically significant benefit to TENS for the treatment of neck pain when compared to placebo treatment.[7] A January 2010, systematic literature search published in the journal Neurology,[8] advised against recommending TENS for chronic low back pain since evidence is controversial for that type of pain. However, other reputable neurologists wrote in the same issue of the journal: “Absence of evidence is not evidence of absence,” and although the research on TENS may be thin, “there seems to be considerable empirical evidence that, at least in some patients, TENS is useful.”[9] Recent clinical studies and meta-analysis suggest that having an adequate intensity of stimulation is necessary to achieve pain relief with TENS.[10][11]
Scientific studies show that high and low frequency TENS produce their effects by activation of opioid receptors in the central nervous system[citation needed]. Specifically, high frequency TENS activates delta-opioid receptors both in the spinal cord and supraspinally (in the medulla) while low frequency TENS activates beta-opioid receptors both in the spinal cord and supraspinally[citation needed]. Further high frequency TENS reduces excitation of central neurons[citation needed] that transmit nociceptive information, reduces release of excitatory neurotransmitters (glutamate) and increases the release of inhibitory neurotransmitters (GABA) in the spinal cord, and activates muscarinic receptors centrally to produce analgesia (in effect, temporarily blocking the pain gate)[citation needed]. Low frequency TENS also releases serotonin and activates serotonin receptors in the spinal cord, releases GABA, and activates muscarinic receptors to reduce excitability of nociceptive neurons in the spinal cord[citation needed].
In palliative care and pain medicine, TENS units are used in an attempt to temporarily alleviate neuropathic pain [12] (pain due to nerve damage). Some patients benefit from this approach, while others do not, depending on individual differences, [13] and pain threshold. [14] Use of TENS causes cell death[citation needed] at the site of application and should not be used long term. The number of cells that die is insignificant and most patients heal without complaints. TENS is more effective at relieving chronic pain, whereas when used on new injuries it sometimes aggravates the pain. Further use is documented in the attached references: in obstetric care, particularly in labour; [15] knee pain;[16] [17] [18] lithotripsy or bladder-stone removal; [19] and limb pain. [20]
A significant number of TENS machine brands have been targeted for use for labour pain, although a 1997 report of a study done by the University of Oxford said that TENS “has been shown not to be effective in postoperative and labour pain
.