Transcutaneous Electrical Nerve Stimulation (TENS) is a method of electrical stimulation that aims to provide pain relief by exciting sensory nerves and stimulating the pain gate mechanism and/or opioid system. TENS works through several mechanisms including activation of pain-gating mechanisms in the spinal cord and stimulation of the descending pain suppression system and endogenous opioid release. Different TENS waveforms, frequencies, pulse widths and intensities can be used depending on the type of pain and desired effects. Common types of TENS include conventional high frequency TENS and acupuncture-like low frequency TENS. Care must be taken with electrode placement and TENS is generally contraindicated for those with pacemakers or heart conditions.

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TENS

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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.

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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

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Primary afferent fibres
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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
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DRG: Dorsal Root Ganglion,
PAG: Periaqueductal Grey Matter

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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

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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

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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.

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

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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
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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

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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

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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

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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

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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.

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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.

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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.

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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.

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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.

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Electrode Placement

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Electrode Placement

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

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Electrode Placement

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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

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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.

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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.

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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.

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

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