Week 14: E-stim for tissue healing

What are the three types of pain?

Acute Pain, Chronic Pain, Referred Pain

What characterizes acute pain?

Results from injury or disease, typically lasts less than 3 months.

What happens to acute pain after 3 months?

It becomes chronic pain.

Acute pain can be

superficial or deep

acute pain is biologically

meaningful

biologically meaningful

actual structural and physiological changes that explain the pain

Acute pain is associated with

measurable change

What is chronic pain?

Pain that begins as acute but becomes persistent, no longer serving as a protective mechanism.

Chronic pain is a

disease, no longer a symptom

Chronic pain is associated with

structural and functional changes in central nervous system (CNS)

What is central sensitization?

Amplification of neural signals in the CNS, often associated with psychosocial issues.

Approach for chronic pain

multi-modal

Biologically meaningful and chronic pain

not as much as acute

What is referred pain?

Pain felt at a site remote from the source due to convergence of nociceptors on the spinal nerve root

Peripheral sensitization

Activation threshold of nociceptors lowered by chemicals released as site of injury

What are A-delta fibers?

Small myelinated nociceptors that respond to mechanical and thermal stimuli, causing sharp pain.

What are C-fibers?

Small unmyelinated nociceptors that respond to a broad range of stimuli, causing dull, aching pain.

What is the main pathway for conscious pain perception?

The Spinothalamic Tract (STT).

type of second order neurons

High threshold and wide-dynamic

High threshold neurons

nociceptive-specific receiving input from peripheral nociceptors only

wide-dynamic neurons

receive input from nociceptive and non-nociceptive primary afferent fibers

As second order neurons become sensitized they result in

central sensitization

Central sensitization results in

↑ responsiveness to noxious and non-noxious stimuli,

↑ receptive field,

↓ activation thresholds

What is the role of the Periaqueductal Gray (PAG) in pain modulation?

It is an area in the midbrain that releases endogenous opioids to suppress pain signals.

Treating pain of unknown or unidentifiable origin is considered a

contraindication

Masking undiagnosed pain with TENS can

postpone proper treatment and lead to worsening of the underlying condition

common use of electrical stimulation (ES)

modulating Pain

Pros of TENS

Nonpharmacological

Non-invasive

Safe

Easy to use

Low cost

What is TENS?

Transcutaneous Electrical Nerve Stimulation, a method of using electrical currents to treat pain.

TENS works by using electrical currents to stimulate

ensory, motor other both nerves via electrodes on the pt's skin

Abbreviation TENS implies the use of ES to treat

Pain

TENS is inaccurately applied to imply use of

handheld stimulator for pain modulation

Most line powered clinical units can

set same stimulus parameters to effectively treat pain

What is the Gate Control Theory?

selective stimulation of large-diameter A-beta fibers blocks pain input from smaller unmyelinated nociceptive C fibers and small myelinated A-delta fibers

TENS mechanism of action

Activation of peripheral opioid receptors

Activation of central opioid receptors

What are the common waveforms used in TENS?

Biphasic symmetrical, hi-volt pulsed current, and burst modulating alternating current.

Pulse frequency

number of pulses per second Hz

pulse duration (pulse width)

Length of time one pulse lasts

Microseconds µ𝑠𝑒𝑐

amplitude

Magnitude of current or voltage (mA)

Modes of TENS

Conventional, acupuncture-like, burst mode, brief intense

Burst mode

Combination of conventional and acupuncture and works more like the low rate for treatment outcomes

Brief Intense TENS

high frequency, long pulse duration, and highest possible intensity

Intense TENS parameters

Highest tolerable intensity to noxious level short time (< 15 min)

Inherent discomfort, rarely used in clinic

brief intense Fx

100-150

brief intense pulse duration

long (150-200 usec)

Conventional/High Frequency TENS

AKA

Sensory or high-frequency/low intensity TENS

Conventional TENS preferentially activates

A beta afferent nerve fibers

Conventional TENS produces

sensation of comfortable paresthesia, sensory only, no motor response

Pain modulation of conventional TENS

primarily while the ES is on

waveform for conventional TENS

mono-phasic pulsed (hi-volt) or biphasic pulsed

What is the frequency range for Conventional/High Rate TENS?

80-110 Hz.

Intensity for Conventional TENS?

highest to patient comfort without muscle contraction

Pulse duration of high frequency tens

Short (50 - 100 µsec)

Low Frequency/Acupuncture-like TENS

Low frequency/high intensity

Low Frequency/Acupuncture-like TENS activates

A beta sensory fibers & Alpha motor neurons leading to rhythmic muscle twitching

pain modulation for low frequency tens

may last several hours after completion of treatment

pt sensation for low frequency tens

sensation of prickling and stinging along with a visible motor response

waveform used in low frequencyTENS

mono-phasic pulsed (hi-volt) or biphasic pulsed

Frequency for low frequency TENS

below 10 Hz; 1-10Hz

Intensity of low frequency TENS

High - enough to provoke visible muscle contractions

What is the pulse duration for Low Rate TENS?

150-200 µsec.

What is the purpose of Burst Mode TENS?

To combine high-rate and low-rate stimulation for more comfortable muscle contractions.

Burst TENS pulses

High frequency trains of pulses (100Hz) delivered at low frequency (1-4Hz) and long pulse duration (150-200 µsec) at motor level

Conventional Tens frequency

100-150 pps

Conventional Tens pulse duration

≤100 usec

Conventional Tens amplitude

comfortable sensory level

Conventional Tens tx time

30 mins or less in clinic, 1 hr at a time at home with at least 30 min off prior to repeating

Low rate Tens frequency

<10 pps

Low rate Tens pulse duration

150-200 usec

Low rate Tens amplitude

motor level; visible contraction

Low rate Tens tx time

30 mins or less

Burst TENS frequency

Usually preset in unit, example 100 Hz delivered at 2Hz

Burst TENS pulse duration

150-200usec

Burst TENS amplitude

visible contraction

Burst TENS tx time

30 mins or less

High-rate TENS is recommended when

sensation, but not muscle contraction, will be tolerated such as after a recent injury when inflammation is present, or tissues may be damaged by contraction

Low-rate TENS is recommended when

longer duration of pain control is desired and muscle contraction is likely to be tolerated

What is analgesic tolerance?

A decrease in analgesic effectiveness from repeated use of TENS, or repeated stimulation of opioid receptors

What are the two main theories supporting TENS?

Gate control theory and central inhibition with release of endogenous opioids.

Gate control theory Primary theory for

High-rate TENS

Gate control theory

Activation of A-beta afferents to induce inhibitory circuits in dorsal horn to block A-delta and C-fiber input

Central inhibition and release of endogenous opioids Greater with

low-rate TENS

Selective activation of opioid receptors

Low TENS --> mew opioid receptors

High TENS --> Delta-Opioid Receptors

Low-frequency TENS: receptors

µ-opioid receptors

High-frequency TENS: receptors

δ-opioid receptor

Use of opioid medications can result in

analgesic tolerance due to cross-tolerance.

Most opioid medications activate

µ-opioid receptor, results in ↓ effectiveness from low-frequency TENS

Less analgesic cross-tolerance with

high frequency TENS

What is the treatment time for Conventional/High Rate TENS?

30 minutes or less in clinic, 1 hour at home with breaks.

What is the intensity level for Low-rate TENS?

High enough to provoke visible muscle contractions.

What is the primary mechanism of action for High-rate TENS?

Activation of A-beta afferents to block A-delta and C-fiber input.

What is the role of endogenous opioids in pain control?

They help suppress pain signals in the dorsal horn of the spinal cord.

What is the difference between A-beta and A-delta fibers?

A-beta fibers are larger and myelinated, causing sharp pain; A-delta fibers are smaller and myelinated, causing a prickling sensation.

What is the recommended intensity for TENS treatment?

Go to the strongest comfortable paresthesia.

How should electrode size be determined for TENS?

Electrode size should match the treatment area.

What is the common placement method for TENS electrodes?

Bracketing around or over the painful area.

Over the peripheral nerve that innervates painful area

Parallel to spine to stimulate nerve roots of spinal nerves innervating painful area

Over acupuncture points, motor points or trigger points

What is the significance of lead wire color in TENS setup?

Lead wire color is irrelevant; there is no net charge accumulation.

Electrodes may be positioned across the spine using one or two channels.

The goal in many cases is to cover as much of the painful area as possible

When attempting to stimulate unilateral nerve roots at multiple levels, the electrodes should be placed

parallel

First treatment time for TENS

30 min or less all applications