IFC and Tens Flashcards
General Overview of IFC and TENS
TENS and IFC use electric currents to stimulate peripheral nerves resulting in short-term pain relief (minutes to hours)
What is pain?
Unpleasant sensory and emotional experience associated with actual or potential tissue damage (acute-new to 3 months, persistent, chronic – synonymous with persistent)
Nociceptive input neither sufficient nor required
Ex: Nail in head vs paper cut
PERCEPTION
What is the biggest nerve type?
A Alpha Fibers
Ia afferent (Aa)
Myelinated: Yes
Conduction Velocity: 70-120 m/s
Specialized Ending: Muscle Spindle
Receptor Location: Skeletal Muscle
Sensory Function: Joint position/Movement
1b afferent (Aa)
Myelinated: Yes
Conduction Velocity: 70-120 m/s
Specialized Ending: GTO
Receptor Location: Musculotendinous junction
Sensory Function: Muscle Contraction Force
II afferent (AB)
Myelinated: Yes
Conduction Velocity: 25-70 m/s
Specialized Ending: Touch Receptors, Joint Receptors, Muscle Spindle Secondary
Receptor Location: Skin, Joint Capsule, Skeletal Muscle
Sensory Function: Touch/Pressure, Joint position/movement, Joint Position
What are the areas of the body process pain?
Dorsal Horn in Spine and Brain
- Each location can cause for the signal to turn up or turn down
- Brain is the only thing that can indicate pain.
Two mechanisms of pain inhibition we use clinically
Gate theory control (local spinal cord level)
Descending Pain Control (both supraspinal and spinal level – can be more systemic)
- Indigenous Opioids
- Internal NTs
Pain Gate Theory
Two sub-mechanisms:
- Basic mechanism: Highway analogy – explains temperature effects on pain perception: more temp sense = less “pain” sense
- Synaptic inhibition - explains effects of touch on pain (puscinian corpuscle, etc.)
Pain Gate Theory - Highway Analogy
- Temperature effects on pain perception: more temp sense = less “pain” sense
- Sensation and Nociception both carry Delta A and C (Travel into **spinal cord **at dorsal root ganglion at synapse)
Pain Gate Theory - Synaptic inhibition
- Stimulation of other receptors causes transmission on AB axons
- At spinal level, AB axons excite an interneuron which then inhibits the transmission of nociception in the spinothalamic tract (with the Delta A and C fibers)
- There are various types of inhibition and neurochemicals involved (pre- and post-synapse, GABA and Enkephalin, and probably others)
- Pain system is complex
Pain Gate Theory occurs….
locally at the levels of the spinal cord involved with peripheral stimuli
Descending Pain Control
(Endogenous Opiate System)
Two systems operate at supraspinal level to impact:
1. Involved spinal cord level through neural connections from the periaqueductal gray (PAG) and Raphe Nucleus
2. General Systemic Effects
Involved spinal cord level through neural connections from the periaqueductal gray (PAG) and Raphe Nucleus
(Both in midbrain and have direct connections in spinal cord; in the spinal cord where it ends releases release enkephalins, norepinephrine, serotonin – inhibition effects)
Ex: Stub toe, this system kicks in to dull pain. Kick in a minute or two after initial stub of toe.
General Systemic Effects - Descending Pain Control
Hypothalamus and Pituitary
1. Beta Endorphin and Dynorphin (Dumped in blood)
a. Widespread release through CNS and circulatory system – explains the classic exercise pain inhibition or “runner’s high”
b. One of the best ways to stimulate this is through exercise
Endogenous Opiate System
Works locally and systemically
These mechanisms work together and simultaneously, HOWEVER, it is convenient to conceptualize them as being recruited progressively as the pain experience intensifies or persists
Longer half life
Other mechanisms involved in pain modulation – Placebo Response
Symptom improvement based on expectation, a possibility with any intervention
For E-stim, reported as high as 30-40% of the response
Response can be blocked by Naloxone, and opiate anatagonist meaning placebo is a neurophysiologic response!
Other mechanisms of pain modulation with E-stim Vasodilation
Areas of myofascial pain (trigger points) may be ischemic, contributing to pain experience
Electrical stimulation induces local vasodilation in patients with myofascial symptoms
Vasodilation may reduce ischemic pain
Indications for TENS (sensory component)
Treating pain syndromes
- Acute
- Chronic
- Post-Op
- Neurological (Ex: Shingles)
- Phantom
Before/during painful treatments
- Stretching
- Debridement
Indications – Populations with Evidence of TENS efficacy
LBP
Neck pain
Myofascial pain
RA
OA
Dysmenorrhea
Labor/post labor
Post op pain: abdominal, thoracic, shoulder
Painful shoulder post CVA (stoke)
Peripheral neuropathy
Trigeminal neuralgia
Headache (migraine and other)
Post amputation and phantom limb
Acute pos-traumatic
And others…
Precautions for TENS
Cardiac pacemaker
- Recommend ECG monitoring for 1st treatment
Implantable Cardioverter defibrillator
- Need to inactive during sessions
- ECG monitoring
Allergic skin reactions under electrode
Low cognitive function
Monitor Caffeine intake (3 cups/day or 200 mg/day; Can reduce effect)
Abnormal skin sensation
While driving
Keep out of reach of children
Be aware of medication usage (Ex: Opiods)
Neural Depolarization
When considering activation of neural tissue with current, you must consider
- Relative size and myelination of neurons
– Larger are easier to stimulate
- Anatomical depth of tissue relative to depth of penetration of current
–Closer to the surface are easier to stimulate
Typical Equipment - TENS/IFC
Intensity/Amplitude
Pulse rate/Frequency
Pulse duration
Common Wave characteristics:
- Biphasic with a negative spike component
- Monophasic with a positive rectangular component only (Charge imbalance, may get skin irritation)
Some modulation (change) option
Typical Tens Devices
Battery Operated
Common ranges on parameters:
Pulse duration range
20-200 usec
Pulse rate (frequency) range
1-150 pps
Amplitude (intensity) for each channel range
1-80 mA
TENS - Modes
3 types of application
Conventional-common
Low rate – not common
Noxious – rare at best
Conventional or High Rate TENS
Short duration pulses of 20 to 80 microsec and with a current amplitude that causes strong but tolerable sensation
- AB fibers are larger and myelinated. This mode is selected for these
- **Trying to create a strong but tolerable tingly sensation **
Pulse frequencies of 80 to 150 pps are recommended.
Modulation selection based on what is available or patient preference
Conventional TENS - Big Picture
Create a strong tingling sensation that reduced the perception of pain while the stimulus is present, primarily through spinal cord pain modulation (pain gate theory)
Low Rate TENS
Create “pain” by stimulating delta A and C fibers to produce inhibitory effects with endogenous opiates
Generally less than 10 pps
Higher amplitude
Longer pulse duration (200-600usec)
Associated uncomfortable muscle contractions
- Twitch
Treatment Duration 20-40 min
Low Rate TENS - Adv and Dis
Indicated for Chronic Pain Syndromes
Advantages
- Improved post treatment reduction of pain
- Low accommodation
Disadvantages
- Motor response – uncomfortable
- Not for acute conditions
- Less effective in patients on opiods
Half Life of endogenous opiates is 4-5 hours
Stimulation time limited due to potential muscle soreness
Onset of analgesia is generally delayed 20-30 minutes
Get a longer lasting effect from a shorter treatment – can get pain relief that doesn’t require constant use of the device
Noxious level or brief intense TENS
Works in the same way Low Rate TENS but seems to be effective at eliciting endorphin release
May have longer lasting effects (6+ hours)
1-5 pps, longer pulse duration up to 1000 usec
30-45 seconds on, 2-3x per point
IFC
- Interferential current is an alternative to TENS
- Same basic concepts as TENS
- Different wave characteristics
IFC Stimulation
- Interferential current is the waveform produced by the interference of two sinusoidal alternating currents of slightly different frequencies
- These are delivered through two different sets of electrodes via separate channels.
- Electrodes are positioned so that the currents intersect.
- When the two currents intersect they interfere.
- This produces a higher amplitude if they are in the same phase and lower amplitude if they are in opposite phases
IFC and Beats
- When there is a difference in the two frequencies this produces an “envelope” of pulses referred to as beats.
- Beat frequency is equal to the difference in frequencies of the two currents.
- In this example the difference is 5100-5000=100 Hz therefore the beat frequency will be 100 Hz.
- Carrier frequency by definition is the lower of the two frequencies, in this case 5000 Hz.
IFC
Carrier frequency usually 1000 to 10,000 Hz
This overcomes skin impedance better due to high frequency
More adverse reactions have been reported
Treatment Parameters for IFC
Based on the beat frequency (same range for TENS)
Spinal cord level pain inhibition (80-150 bps)
Endogenous opiate mechanisms (1-10 bps)
TENS vs IFC: Which to choose?
Availability
Body area location (TENS can function with a single channel)
Tissue depth (IFC might stimulate deeper)
Patient preference
TENS/IFC Skin Prep
Skin Prep Wipes for long term
Electrode Placement
No consistent evidence for preferred sites:
- Place it near the pain site
- Along nerve path
- At the contralateral, homologous site
–Phantom limb pain
- Closer the electrode are the more superficial and concentrated to stimulus
– Should not be closer than 1 cm to each other
Home Programs - Patient Education
Battery Changing
Reviewing hardware
Skin care
Removing electrode – peel skin away not electrode
Where/when to use/not use device
Prescribed schedule
- Conventional (during)
- Low rate (before)
- Pain dependent
- Time dependent
– Used for prescribed duration regardless of symptoms combined with activity
Home Program Essentials
Verbal and written instructions
Supervised clinical trial
Home program of sufficient duration/intensity
Appropriate outcome measure (pain function, medication usage, others)
Follow up appt
Increasing likelihood of success
Emphasize FUNCTION as the overall outcome, amongst many other complex outcomes beyond pain
