TRANSCUTANEOUS ELECTRICAL STIMULATION

TRANSCUTANEOUS ELECTRICAL STIMULATION

Transcutaneous electrical stimulation (TENS) Transcutaneous electrical stimulation ; An electronic device that produces electrical signals used to stimulate nerve through unbroken skin A form of electrical stimulation with surface electrodes to modulate pain perception

Why TENS? Non-invasive and Readily applicable method - few side effects - no drug interaction - no potential toxicity - less costly compared with drug treatment

Common medical conditions Analgesic effects of TENS Relief of acute pain Postoperative pain Labor pain Dysmenorrhoea Musculoskelectal pain Bone fracture Relief of chronic pain Low back Arthritis Stump and phantom Postherpetic neuralgia Trigeminal neuralgia Causalgia Peripheral injury Facial pain Metastatic bone pain Non-analgesic effects of TENS Improving blood flow Reduction in ischemia due to reconstrutive sugery Reduction of symptoms associated with diabetic neuropathy Improved healing of wounds and ulcers

Theories about the physiological effects of TENS Gate control theory (Melzack et al., 1965) Opiate-mediated control theory (Köke et al., 2004) Local vasodilation of blood vessel (Leandri et al., 1986)

Thalamus and Reticular Formation Dorsal Column Nuclei RVM (5- HT) Aβ + + 5- HT3 Endo/G ABA A δ/c - Glu + + Spinal neuron

Mechanisms of action Activation of mu- or delta- opioid, serotonin and cholinergic receptors in spinal cord and mu- or delta- opioid receptors supraspinally (Kalra et al., 2001; Sluka et al., 2003) increases of GABA release in spinal cord (kawamata et al., 2002)

Physical principles

Physical principles Sensory TENS (high-rate TENS) Used mostly in acute phase of pain or postoperatively Pain reduction due to spinal gate mechanism Depolarization results in a tingling sensation Motor TENS (low-rate TENS) To treat subacute pain or trigger points Targets the motor pain modulation theory Pain relief may be delayed in comparison to that with sensory TENS Pain relief lasts longer than with sensory TENS Noxious TENS Pain relief through central biasing mechanism Commonly used with point stimulators

The characteristics of different type of TENS Aim of currents Main fiber type responsible for effects Desired outcome patient experience Optimal electrical characteristics Electrode position Analgesic profile Duration of treatment Conventional TENS Activate large diameter nonnoxious cutaneous afferents A-beta Mechanoreceptors Strong comfortable electrical paraesthesia with minimal muscle activity High frequency/ low intensity Amplitude=low Duration=100-200us Frequency=10-200pps Pattern=continuous Over site of pain Dermatomal Rapid onset<30 min after switch-on Rapid offset,30 min after switch-off Continuously when in pain Acupuncturelike TENS Active motor efferents to produce phasic muscle twitch leading to activation of small diameter non-noxious muscle afferents A-delta Strong comfortable phasic muscle contraction Low frequency/high intensity Amplitude=high Duration=100-200us Frequency=~100pps with burst Pattern=burst Over motor point/muscle at site of pain Myotomal Delayed onset.30 min after switch-on Delayed offset>1h after switch off ~30 min/ session Intense TENS Activate small diameter pinprick cutaneous afferents A-delta nociceptor Highest intensity tolerable with minimal muscle contraction High frequency/high intensity Amplitude=highest tolerable Duration.1000us Frequency=~200pps Pattern=continuous Over site of pain or proximal over main nerve bundle Rapid onset<30 min after switch-on Delayed offset>1h after switch off ~15 min/ session

Conventional TENS Acupuncture-like TENS Intense TENS

Electrode placement : In order to get the maximal benefit from the modality, target the stimulus at the appropriate spinal cord level (appropriate to the pain). Placing the electrodes either side of the lesion or pain areas, is the most common mechanism employed to achieve this. There are many alternatives that have been researched and found to be effective most of which are based on the appropriate nerve root level : Stimulation of appropriate nerve root(s) Stimulate the peripheral nerve Stimulate motor point Stimulate trigger point(s) or acupuncture point(s) Stimulate the appropriate dermatome, myotome or sclerotome If the pain source is vague, diffuse or particularly extensive, one can employ both channels simultaneously. A 2 channel application can also be effective for the management of a local + a referred pain combination one channel used for each component.

Contraindications TENS should also be used with caution in people with 1. Epilepsy 2. Pregnant women (do not use over area of the uterus as the effects of electrical stimulation over the developing fetus are not known) 3. 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. TENS Electrodes should never be placed: 1. On or near the eyes 2. In the mouth 3. On the front of the neck (due to the risk of acute hypotension through a vasovagal reflex) 4. On areas of numb skin/decreased sensation 5. On broken skin areas or wounds 6. 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.

Recent Papers concerning Electrical stimulation and pain management

randall selitto plethysmometer

DAMGO ([D-Ala 2, N-MePhe 4, Gly-ol]-enkephalin) is a synthetic opioid peptide with high μ-opioid receptor specificity. Deltorphin is one of the highest affinity and most selective naturally occurring opioid peptides known, acting as a very potent and highly specific agonist of the δ-opioid receptor.

μ-opioid receptor δ-opioid receptor

Withdrawal thresholds from animals that received (A) no TENS (B) low frequency (C) high frequency TENS for the time before (circles) after (triangles) application of TENS. *, Significantly different from before induction of inflammation (base), 1, significantly different from before TENS on the same day.

Withdrawal thresholds from animals treated with either low or high frequency TENS on day 6 only. Animals received anesthesia for 20 min on days 1 5 and the received one treatment of TENS on day 6. Notice an increase in withdrawal threshold after treatment with TENS on day 6.

Withdrawal thresholds from animals on day 6 that intrathecally injected with cumulative doses of either (A) the d-opioid receptor agonist, SNC-80 (B) the m-opioid receptor agonist, morphine, in groups that received no TENS (circles), low frequency TENS (triangles) or high frequency TENS (squares) for 6 days. *, Significantly different from the no TENS group

Arch Phys Med Rehabil Vol 89, April 2008

Effects of TENS with high frequency on spasticity after SCI 14 12 10 Control (N=10) * * Treated (N=10) * 4 3 Control (N=10) Treated (N=10) BBB Score 8 6 4 2 MAS Score 2 1 + * * 0 90 Pre 1D 3D 5D 7D 9D Time course 1 Control (N=10) Treated (N=10) 60 0 Pre 1D 3D 5D 7D 9D Time course CBS Score 30 * * * * 0 Pre 1D 3D 5D 7D 9D Time course Kim et al., unpublished (2006)