Physiology of Electrical Stimulation & ES Application for Pain Flashcards
artificial area of depolarization
an electrode placed in the periphery bypasses the CNS to stimulate muscle
orthodromic
traveling in the normal direction in a nerve fiber.
activate nerves and muscles
Antidromic
traveling in the opposite direction to that normal in a nerve fiber
pain relief
force generation via ES: volitional contraction
small diameter alpha motor neurons recruited first, then larger ones as more force is needed
rate coding
increase tension
-CNS increases firing rate of motor units contracting
Asynchronous
swapping motor units in & out to reduce fatigue
Natural recruitment order
slow twitch type 1
- -> fast twitch , fatigue resistant, type IIA
- -> fast twitch fatiqguable type II B
force generation via ES: Stimulated Contraction
larger diameter alpha motor neurons recruited first and then smaller ones last
which type of muscles are recruited first in stimulated contraction
fatigable
recruitment order for stimulated contraction
fast twitch, fatigable type IIB
–> fast twitch, fatigue resistance, type IIA
–> slow twitch type I
factors influencing muscle force production via ES
- frequency of activation
- amplitude of activation
- pulse duration
Frequency
increases firing rate, force, & increases fatigue
Twitch
initial pulse creates AP
Unfuse tetany
another pulse occurs before Ca+ reuptake occurs
oscillations (3-20 pps)
Fused Tetany
summative effect
greater than 20 pps
critical fusion frequency
can differ among muscles
amplitude
stimulated deeper and smaller fibers
increases force production
pulse duration
stimulate smaller fibers
increases force production
pain over 400 usec
clinical respones
sensory
motor
noxious
sensory
first response as stim is turned on “tingling”
motor
alpha motor neurons threshold is reached
-recruitment increases as stim increases
noxious
pain fibers are being stimulated
PD> 400 u sec activates all fibers
motor point
the point on skin which smallest amount of current activates the muscle
located near the point that peripheral nerve enters muscles
innervated muscle
muscle has intact peripheral nerve
denervated muscle
peripheral nerve is damaged
denervated & fibrotic
nerve is damaged plus muscle has undergone changes preventing contraction
anode (+) effects
- acid produces
- coagulates protein
- hardens tissue
- accelerates tissue growth
cathode (-) effects
- base produces
- liquifies protein
- softens tissue
- bacteriostatic effect (get rid of ecoli)
current density
size of the electrode influences the excitability of the tissue under it
(charge delivered over the area of the electrode)
ES for pain control relies upon two mechanism
Gate-theory (short lasting)
Central mechanisms (long lasting)
First order neurons
A-beta
A-delta
C afferents
A-betta (II)
joint, touch, muscle spindle receptors
A-delta (III)
free ending
fast pain
C afferents (IV)
free ending
slow pain
substantia gelatinosa
- act as a modulator
- when active, there is a decrease in sensory input to the 2nd order neuron
-A-beta first activate the 2nd order and then decrease through SG
Inhibitory interneuron
A-delta and C’s activate the 2nd order neurons
-also activate an inhibitory interneuron which inhibits the SG, causing increased activity
Pre-synpatic inhibition of 2nd order neuron
the SC acts pre-synaptically to alter the signal to the 2nd order neurons that affects the pain signals sent to higher centers for perception
WDR
central mechanism : 2nd order neurons to higher centers
1st path
axons 1 & V cross midline to ascend uninterrupted via the lateral spinothalamic tract which ascends on the contralateral side of the spinal cord
central mechanism : 2nd order neurons to higher centers
2nd path
spino-reticulo-thalamic tract requires multiple synapses as pain information ascends
medulla and pons are responsible for
autonomic responses to intense noxious stimuli
important in the affective components of pain
Thalamus
- recognition of location and type of pain occurs here
- initiating the behavioral reactions to pain
- sends projections to the cortex
endorphins
endogenous morphine
Endogenous Opioid System
Beta-endorphins are released by the pituitary and can have long lasting effect on pain (6-8 hours)
The medulla and pons role in Endogenous Opioid System
release neurotransmitters that are either inhibitory or excitatory on the SG
medulla
serotonin - inhibitory
pons
norepinephrine exciting
Counter Irritation Analgesia
idea that acute painful stimulus can alleviate ongoing pain
(acupunture )
works on endorphin system
Contraindications
Implanted Devices Carotid Sinus Damaged Skin Reproductive Organs Transcranial application Eyes Cancer Pregnancy Epilepsy Thrombosis Hemorrhage Radiated tissues Infection/Tuberculosis
Pre-Cautions
Undiagnosed pain Cancer Pregnancy Cognitive Impairment Cardiovascular disease Extreme edema Extreme adipose Adverse TENS experience Visual impairment Trans thoracic applications Impaired sensation/scar tissue
