Transcutaneous Electrical Nerve STimulation (TENS) (WEEK 9) Flashcards Preview

PTHER 555 - Therapeutic Modalities > Transcutaneous Electrical Nerve STimulation (TENS) (WEEK 9) > Flashcards

Flashcards in Transcutaneous Electrical Nerve STimulation (TENS) (WEEK 9) Deck (35):

What is TENS?

electrical stimulation: alternating electrical current is delivered to the surface of the skin through electrodes

Goal: stimulate nerve fibers (sensory, motor, and pain).


How does TENS work? (Flow of current)

- current flow between anode (+) and cathode (-) produces depolarization under the cathode and hyperpolarization under the anode


Physiological effect occurring

- At rest: nerve has resting potential of -40mV to -90mV (inside more negative than outside)

- Cathode: draws positively charged particles away from the nerves surface and the inside of nerve becomes relatively less negative until threshold potential is reached

- Action Potential: triggered anywhere along the nerve and will propagate down the nerve

- Motor nerve fires to muscle; sensory nerves fire to CNS


Pulse Duration - Current Strength curve

Left to right

- AB sensory
- Motor
- AD sharp pain
- C Dull pain
- denervated muscle


pulse duration: 40us
Amp little: 30mA

Fibers stimulated?

AB Sensory fibers


Pulse duration 200us
Amplitude 20mA

Fibers stimulated?

Sensory fibers


If sensory fibers are activated, and

1. we use a longer pulse duration, how do get the same response?

2. Keep pulse duration but increase amplitude

3. Further increase amplitude?

1. decrease/less amplitude

2. Stimulate sensory and motor nerves

3. Stimulate sensory, motor, and pain fibers


if you wanted to stimulate nociceptive fibers what pulse duration would allow you to do so at a lower amplitude (current strength)

> 300 usec


if you wanted to stimulate sensory fibers (a-beta) and no other fibers, what pulse duration would be the best option?

< 100usec


Parameters: Frequency

influence is not very clear

- High: paired with sensory stimulation - “close the gate”

- Low: paired with motor/pain stimulation - slow enough to get muscle contraction but not so high to fatigue the muscle too quickly


Therapeutic goal ofTENS (how does it work)?

1. Pain gate mechanism
2. Descending endogenous opioid system
3. Endogenous opioid release at thr level of SC


Body’s response to pain

- Brain does not passively receive nociceptive signals

-CNS receives signal, interprets, and responds

- block pain (pain gate)


Pain gate (Gate Control Theory) Mechanism.

Selectively stimulate A-B fibers to close the gate

- Nociceptive signals are transmitted to the dorsal horn of the spinal cord via A-D and C fiber’s (small diameter fibers)
- In the spinal cord, these peripheral receptors synapse with transmitter neurons and sends the pain signals to the brain
- Larger diameter A-B fibers (mechanoreceptos) also enter dorsal horn to synapse with transmitter neurons
- Large diameters overwhelm the smaller diameter and blocks pain signs from reaching the brain


Descending Endogenous Opiod System (DEOS): what is it?

Group of different opiod peptides and receptors that modulate pain


Descending Endogenous Opiod System (DEOS): mechanism

1. Pain triggers release of opioid peptides bind by interneurons in CNS

2. Peptides bind to receptors on pre-synaptic neurons = pre-synaptic inhibitions
- fewer NT released, nociceptive single becomes weaker

3. Peptides bind to post-synaptic neuron = post-synaptic inhibition
- hyperpolarize nerve, more NT needed to trigger an action potential


Nociceptive interpretation (pathway)

1. Nociceptive signal to the brain via 1st order afferent neutron to the dorsal horn of the spinal cord
2. 2nd order afferent neutrons takes the message to the brain via the spinothalamic tract


DEOS response

The brain stem responds

- pain results in stimulation of PAG matter
- PAG sends signal down to raphe nucleus
- raphe nucleus sends efferent signals down dorsolateral funiculus (tract) in the spinal cord
- efferent neurons release opioids into the synapse between the 1st and 2nd order afferent neurons
- opioids bind to the neurones and cause pre- and post-synaptic inhibition


Endogenous opined release: at the spinal cord

- pain triggers the release of endogenous opioid peptides by interneurons in the spinal cord
- results in further pre- and post-synaptic inhibition at the 1st and 2nd order afferent neurones


Pulse Duration:
- Conventional (High):

- Acupuncture (Low):

- Noxious (Brief):

- Conventional (High): 50-80us

- Acupuncture (Low): >150us

- Noxious (Brief): > 150us


Pulse rate:
- Conventional (High):

- Acupuncture (Low):

- Noxious (Brief):

- Conventional (High): 80-120Hz

- Acupuncture (Low): 10Hz

- Noxious (Brief): 120-200Hz


- Conventional (High):

- Acupuncture (Low):

- Noxious (Brief):

- Conventional (High): Sensory & Comfortable

- Acupuncture (Low): Sensory & Motor; generally less comfortable

- Noxious (Brief): sensory, motor, and pain; uncomfortable/pain


Pain mechanism:
- Conventional (High):

- Acupuncture (Low):

- Noxious (Brief):

- Conventional (High): Pain-gate

- Acupuncture (Low): DEOS & Opioid release at SC

- Noxious (Brief): DEOS & Opioid release at SC


Onset and Duration of pain relief:
- Conventional (High):

- Acupuncture (Low):

- Noxious (Brief):

- Conventional (High):
O: fast
D: short

- Acupuncture (Low):
O: slow
D: long

- Noxious (Brief):
O: fast
D: long


Conventional TENS: primary mechanism, what do you feel?

- pain gate: immediate pain relief but pain relief returns shortly after treatment ends

- intensity is set to produce sensory stimulation so that patient feels a tingle (fast enough to "close the gate")


Motor TENS: primary mechanism, what do you feel?

- release of endogenous opioids (Both spinal cord and DEOS) will not provide immediate pain relief but can get relief that continues for hours after treatment

- intensity: just at motor threshold - sensation of pinching


Noxious TENS: primary mechanism, what do you feel?

- release of endogenous opioids (Both spinal cord and DEOS) just enough to bring on pain

- intensity will provide pain relief that continues for hours


Clinical trials:
1. fMRI of High frequency TENS
2. Type of pain

1. decreased activity of brain areas linked to pain perception
2. Pressure pain, not experimental


Clinical trials: fMRI of Low frequency TENS

- decreased area of brain linked to pain perception


Clinical trials: fMRI of Noxious TENS

- effective for all types of experimental pain


Clinical trials: acute pain

- more effective than placebo

- intensity: strong, near noxious
- frequency 1-150Hz


Clinical trials: neuropathic pain (SCI and amputees)

SCI: low frequency tens more effective than placebo for SCI

Amputee: high frequency TENS x 60 minutes reduce pain intensity at rest and movement


Clinical trials: knee OA

inconclusive (Low quality studies)


Clinical trials: neck pain

inconsistent results, weak evidence TENS is better than placebo


Clinical trials: LBP

Poor evidence
- no difference with TENS and active treatment


Clinically meaningful change in pain

2 point change = clinically meaningful