Electrical Currents for Pain Control (week 5)

Gate Control Theory

Activation of nerves that carry vibration, stretching and mechanoreception inhibit the transmission of noxious (pain) signals from the spinal cord to the brain

Interferential ES

•Delivered through two sets of electrodes from separate channels that intersect

•Intersection of waves causes higher amplitude when the currents are in the same phase (working together) and lower amplitudes when they are in opposite phases (working against each other)

•The result of the interacting waves is pulses or beat.  Beat frequency is equal to 10 the difference between the frequencies of the original alternating current.    

•Ex: a 5000 Hs interfering with a 5100 Hz until result in 100 Hz wave

Interferential believed to be more comfortable because

a lower amplitude current is perceived at the skin while the higher amplitude waves are working at deeper tissues.

been found to be effective in decrease the pain associated with inflammation and ischemia

Transcutaneous electrical nerve stimulation (TENS)

•The use of transcutaneous electrical stimulation to modulate pain

•Variety of waveforms can be used (biphasic is most common)

4 main types of TENS

•Conventional TENS

•Low-rate/ acupuncture-like TENS

•Burst Mode Tens

•Electroacupuncture

Conventional TENS

•Shorter duration, higher frequency pulses

•Comfortable sensation without ms contractions

•Stimulates the A-beta nerves to inhibit transmission of pain signals

•Usually delivered with pulses of 50-80 microsecond pulse duration with 100-150 pulse per second frequency

•May interrupt the pain-spasm-pain cycle

Low-Rate/ Acupuncture-like TENS

•Motor nerves are stimulated to produce muscle contractions and/or brief stimulation of A-delta nerve fibers (quick pain stimuli)               

•Release of endogenous opioids

•Uses pulse frequency of 2-10 pps

•Wave length is usually around 200-300 microseconds

•controls pain for 4-5 hours after a 20-30 minute treatment because the half-life of endogenous opioids is usually 4.5 hours

Burst Mode TENS

•Burst mode is a current composed of a series of pulses delivered in in groups known as bursts.  The burst is generally delivered with a preset frequency and duration.

•Believed to work through the same mechanism as low-rate TENS

Electroacupuncture

•Can be performed with electrodes over acupuncture points or via acupuncture needles (very controversial!!)

•Thought to work via the release of endogenous opioids

Parameters of waveform

•Pulsed Biphasic

•Interferrential current

•Pulsed monophasic (premodulated)  - high voltage pulsed current

Parameters Electrode Placement

•On or around the area

•For interferential the channels must intersect!!

Parameters Pulse duration

•For biphasic: 50-80  microseconds to depolarize A-beta fibers only

•Low rate TENS: 200-300 microseconds to depolarize motor nerves and A-delta fibers

Parameters Frequency

•Conventional TENS: 100-150 pps

•Low rate TENS: 10 pps

•Burst: 10 burst per second with pulses at 100-150 pps

Parameters Applied continuously

•no on:off time

Parameters Current amplitude

Per patient tolerance. ”Gentle Sensation” for Conventional TENS and IFES

To small motor twitch or “sting” for low rate TENS

Parameters Treatment time

•Can be continuous for conventional TENS

•Low rate or burst mode TENS: up to 20-30 mins every 2 hours

•IFES – usually 20-30 mins.  Often combined with MHP or ice pack