Pain Modulation with Electrotherapy

Question 1

Gate Control Theory

Answer 1

Uses a-Betas to block C fibers
- C and A-delta inhibit/block inhibitory interneurons
- a-Beta fibers activate inhibitory interneurons
- Theory is that e stim activates inhibitory interneurons to block fibers from going to the brain

Question 2

What is Stimulation Produced Analgesia

Answer 2

• Stimulation of the Periaqueductal gray region produces profound, selective analgesia
• Not associated with general inhibition of afferent input
• Can still respond to touch, pressure and temperature

Question 3

How does stimulation produced analgesia work?

Answer 3

• Descending projections block the output of neurons from laminae I and V via direct and indirect inhibitory actions.
• They also interact with endogenous opioid containing circuits in the brain

Question 4

Endogenous Opioids

Answer 4

• Manufactured by the brain
• Bind to opioid receptors distributed widely in the CNS, but are particularly concentrated in areas that process nocicepetive information (PAG, raphe nuclei and dorsal horn)
• we are trying to get opioids to bind to receptor sites to decrease sensation of pain

Question 5

Which is the better pain control theory for chronic pain?

Answer 5

Stimulation Produced Analgesia

Question 6

What nerve fibers are recruited with high frequency TENS

Answer 6

large diameter, superficial cutaneous nerve fibers
(sensory-level TENS)

Question 7

High frequency TENS parameters

Answer 7

• Frequency: 50-100 + pps
• Amplitude: Perceptible “tingling”
• Phase duration: low (<150 microsec)
• Treatment time: 30 mins
• Analgesia time:: minimal residual effect

Question 8

Low Frequency TENS

Answer 8

• Produces a visible muscle contraction
• A.k.a. low rate TENS and motor TENS
• Some “acupuncture-like TENS” is based on the same principle
• Supported by endogenous opiate mode of pain modulation

Question 9

Low frequency TENS parameters

Answer 9

• Frequency: 2-4 pps
• Amplitude: Strong visible contraction
• Phase duration: > 150 microsec (200-300)
• Treatment time: 30-45 min
• Analgesia time: hours
• passive treatment

Question 10

Noxious level stimulation

Answer 10

• A.k.a. hyperstimulation
• Can be performed in a remote site
• Endorphin mediated mechanism
• May get motor nerve stimulation, but often
  applied to area with minimal motor nerve
  fibers
• Point stimulation (right over area that hurts)

Question 11

Noxious level stimulation parameters

Answer 11

• similar to motor level stimulation except:
• phase duration is long ( up to 1 msec)
• treatment time is seconds to minutes

Question 12

Comparison - Conventional

Answer 12

• higher frequency
• low intensity
• short phase duration
• moderate treatment time
• minimal carry over

Question 13

Comparison - Motor/Noxious level

Answer 13

• lower frequency
• High intensity
• Long phase duration
• Long/short treatment time
• long carry over

Question 14

Frequency

Answer 14

• Abeta few synapses, myelinated –> moves fast –> high frequency
• SPA or opioid modulation need time to build up chemicals –> no need for high frequency; also, higher frequency –> stronger motor contraction (not desirable)

Question 15

Phase duration

Answer 15

Need longer phase duration to recruit motor nerves and very long PD to stimulate areas related to noxious nociceptors such as C-fibers

Question 16

Multiple methods of electrode placement

Answer 16

– At site of pain
– Follow nerve path
– Dermatonal
– Acupuncture points
– Crossing (ICF)

Question 17

What is Interferential Current

Answer 17

• uses “medium frequency” (>1000 Hz); most often 2500 Hz or 4000 Hz
• Need two circuits of slightly different frequency
• Current #1: 4000 Hz
• Current #2: 4100 Hz
• Interference Frequency = 100 Hz

Question 18

How is IFC modulating pain?

Answer 18

• Carrier frequency is 4000Hz (4000 cycles
  per second) –> 1/4000 =250sec –> ½ for
  phase (1/2 cycle) duration = 125 microsec

Question 19

What kind of nerve fiber can we recruit at 125 microseconds?

Answer 19

A beta sensory fibers

Question 20

What do the crossing circuits of IFC do

Answer 20

• “clover leaf” distribution of stimulation
• More 3-D effect
• Theory that higher frequency –> less skin impedance –> more penetration

Question 21

How is IFC different from TENS?

Answer 21

• Scan feature gives even larger coverage area
• Many modulations
  – Scan for amplitude ?
  – Always use “sweep” which is a frequency modulation
• Electrodes must be crossed to get all effects

Question 22

What does scan allow?

Answer 22

• allows amplitude to go down then come back up and repeat
• Dr Conroy is ok with 20% scan

Question 23

What is sweep

Answer 23

a frequency modulation that is predetermined
- helps prevent accommodation
- 80-150 is pretty common

Question 24

Comparison - TENS

Answer 24

• relatively low frequency (2-100 pps)
• uses gate control theory or opiate theory
• multiple electrode configurations