Transcutaneous Electrical Nerve Stimulation (TENS) SRS

Transcutaneous Electrical Nerve Stimulation (TENS) in Physiotherapy

1. Sreeraj S R TENS

2. Definition Transcutaneous Electrical Nerve Stimulation (TENS) is a method of electrical stimulation which primarily aims to provide a degree of pain relief (symptomatic) by specifically exciting sensory nerves and thereby stimulating either the pain gate mechanism and/or the opioid system.

3. Mechanism of Action Possible Pain-Relieving Mechanisms; Activation of ‘pain-gating’ mechanisms. Stimulation of the descending pain suppression system and endogenous opiate mechanisms. The Central Biasing Theory Removal of the substances which stimulate pain nerve endings from within the damaged area

4. Primary afferent fibres 4/4/2020

5. Ascending Pain Pathway The spinothalamic tract: transmits signals that are important for pain localisation. The spinoreticular tract: This pathway is involved in the emotional aspects of pain. The major role of these fibers is thought to be general arousal rather than sensory discrimination per se 4/4/2020 DRG: Dorsal Root Ganglion, PAG: Periaqueductal Grey Matter

6. Inhibition of pain transmission Gate control theory of pain The gate control theory of pain was proposed by Melzack and Wall in 1965 It describe a process of inhibitory pain modulation at the spinal cord level. By activating Aβ fibres with tactile, inhibitory inter neurones in the dorsal horn are activated leading to inhibition of pain signals

7. Inhibition of pain transmission Descending inhibition The Periaqueductal Grey (PAG) in the midbrain and the Rostral Ventromedial Medulla (RVM) are involved. These centres contain high concentrations of opioid receptors and endogenous opioids. Descending pathways project to the dorsal horn and inhibit pain transmission. These pathways are monoaminergic, which modulate the serotonin, dopamine, norepinephrine, and/or histamine neurotransmitter systems in the brain. 4/4/2020

8. Opiate-mediated control Endogenous opioids Endorphins Dynorphins Enkephalins Neurophysiology background: The brain can secrete its own analgesic substance such as endorphins to modulate pain. Endorphins are neuropeptides that act on the CNS and peripheral nervous system to reduce pain. They have the similar pharmacological effect as morphine.

9. Parameters used for TENS Waveforms Frequency or Rate Pulse width or Duration Amplitude or Intensity

10. Wave forms Square / rectangular Instantaneous rise Less skin irritating as approaches sine wave form For nerve damage associated with pain pathology For hypersensitive and chronic pain patients Delayed, long-lasting analgesia Triangular / spike Rapidly rising, but not instantaneous More skin irritating therefore requires frequent movement of electrodes or shorter treatment times to avoid skin irritation For acute pain or resistant tissue Immediate, short lasting pain relief 4/4/2020

11. Frequency or Rate High Frequency (80-120): Large myelinated fibers respond effective > 100Hz Immediate relief of pain Acute pain Low Frequency (1-20): Small unmyelinated fibers respond effectively at <100Hz Increase endorphin production, thus analgesia following stimulation Chronic pain

12. Pulse width or Duration Pulse width Indications 50μs Large myelinated fibers (sensory touch) 100 - 150μs Normal neuromuscular system 200 μs Small myelinated fibers 200 – 300 μs Patients with neurological damage

13. Amplitude or Intensity TENS units intensity ranges form 1 mA to 100 mA TENS is only effective when the patient actually feels the stimulus Patients need to increase the intensity when the body accommodates to the stimulus (when they don’t feel the stimulation anymore) Dying batteries can cause fading intensities

14. Types of TENS Conventional TENS or High Frequency TENS Acupuncture-like TENS (AL-TENS) or Low Frequency TENS Brief TENS or Intense TENS Burst TENS Modulated TENS or Modified TENS

15. Conventional or High TENS Frequency – 50 Hz to 100 Hz Pulse Width – 20 μs to 60 μs Intensity – (0 mA to 30 mA). The intensity until a prickling or tingling sensation is felt. Principle –Presynaptic inhibition by pain gate mechanism by stimulating Aα and Aβ fibres. Duration – 30 to 60 minutes once or twice daily .

16. Acupuncture or Low TENS Frequency – 1 Hz to 4 Hz Pulse Width – 150 μs to 250 μs Intensity – 30 mA to 60 mA. applied to acupuncture points or motor points of muscle in the segmentally related myotome. Principle –This stimulates the high threshold Aδ and C fibres, which lead to release of endogenous opioids and provides further sensory input from muscle spindle afferents (chemical theory). Duration – 20 to 30 minutes once a day .

17. Burst TENS Burst TENS is a series of pulses (i.e. a train), repeated 1-5 times a second, commonly twice. Each train or burst consists of a number of individual pulses at the usual conventional TENS frequencies of 50 Hz to 100 Hz but at higher intensity.  It combines both the conventional and acupuncture-like TENS and therefore provides pain relief by both routes. 

18. Brief or Intense TENS Frequency – More than 100 Hz Pulse Width – 150 μs to 250 μs Intensity – Highest level tolerated by the patient. Principle –Activity in cutaneous Aδ afferents induced by intense TENS produce peripheral blockade of nociceptive afferent activity (Central biasing mechanism). Duration – 30 to 60 minutes once or twice daily .

19. Modulated or Modified TENS In modulated TENS the pulse length, frequency, and amplitudes can be constantly and automatically varied. This cyclical variation is believed to prevent adaptation of the nerves to the current (no accommodation) is particularly appropriate as a variant of conventional TENS used over long periods.

20. Electrode Placement

21. Electrode Placement

22. The position of electrodes and electrical characteristics of TENS when used to manage labour pain Electrode Placement

23. 4/4/2020 Electrode Placement

24. Contraindication Someone with a pacemaker Someone with undiagnosed pain. Someone with a heart condition On head or neck of someone with epilepsy Someone with venous or arterial thrombosis or thrombophlebitis Someone with indwelling phrenic nerve or urinary bladder stimulators Near operating diathermy device

25. Contraindication Around the head On the eyes Over mucosal surfaces Using electrodes on infected skin Electrodes across the chest of a patient with cardiac disease Electrodes should not be placed near carotid artery in the anterolateral region of the neck. There is a potential risk that stimulation at this site might cause heart block by exciting the vagus nerve.

26. Precautions Areas of skin irritation, damage or lesions Areas with impaired sensation Over abdominal, lumbosacral or pelvic regions during pregnancy other than for labor/delivery Tissues vulnerable to hemorrhage or hematoma Athletes should not be permitted to participate in sports while under the influence of TENS analgesia Extreme caution is needed with patients taking narcotic medication or who are known to have hyposensitive areas.

27. Precautions Incompetent patients may not be able to manage the device and it must be kept out of reach of children. For patients with diagnosed malignancies that have been diagnosed as terminal, TENS can be used for pain control with informed consent of the patient. Otherwise, TENS should not be used when malignancies are present.

28. References Tim Watson. http://www.electrotherapy.org/modality/transcutaneous-electrical-nerve-stimulation-tens http://www.answers.com/topic/pain-1 http://www.david.curtis.care4free.net/painrev.htm Transcutaneous Electrical Nerve Stimulation. McGill Lecture Notes – January 22nd, 2002 Mark Johnson. Transcutaneous electrical nerve stimulation (TENS). P 259-286 Foster A, Palastanga N. Clayton’s electrotherapy,9 th edition, AITBS Publishers, pp 100- 106 Singh Jagmohan. Textbook of Electrotherapy, 2 edition, 2012;pp 129 – 133

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