BIOMED 10/17a Stim II Flashcards
define alternating current
- uninterrupted and bidirectional flow of charged particles
descriptive characteristics of AC
- biphasic
- symmetrical
- balanced
- varied shapes: sine wave, rectangular, triangular
- zero net current flow
what is pulsed current?
- interrupted (Break) bidirectional flow of charged particles
- flow ceases for a finite period
descriptive characteristics of pulsed current?
- mono or biphasic
- symmetrical or asymmetrical
- balanced or unbalanced
- various shapes (waveforms)
Burst modulation
russian current
- AC current with a break
- both ac and biphasic pulsatile (electrons move in one direction and then the other)
what are different pulse characteristics?
- wave form
- pulse/phase duration
- current amplitude
- pulse/phase charge
- frequency
- frequency modulation
- carrier frequency modulation
what are different kinds of wave forms?
- mono/biphasic
- symmetrical/asymmetrical
- balanced/unbalanced
- shape
what are the most common types of e stim wave forms?
- symmetrical
2. balanced
what is phase duration?
time elapsed from beginning to end of one phase (crosses 0) (microseconds)
what is pulse duration?
whole pulse duration, time elapsed from beginning to end of all phases,
- how long the wave comes on for
- should have the ability to change
what is current amplitude?
the peak amplitude
what is pulse charge in terms of duration and amplitude?
Q = Pulse Duration x Pulse Amplitude
what is pulse charge vs phase charge?
area under curve for current on y and microseconds on x
- phase = half
- pulse = whole thing
what does pulse duration have a direct impact on?
direct impact on the voltage that is created through the phase/charge
modifying what parameters makes them more excitable?
- duration
2. intensity
when you have a longer pulse _____, you need less ______ to stimulate the nerve
duration, intensity
what is the pulse frequency?
the IPI (interpulse interval) is time between successive pulses can be for monophasic or biphasic pulses frequency = 1/period
units: 1/second or hertz
what triggers a tetanic contraction?
greater than 50 pulses per second
what is a tetanic contraction?
isometric/continuous contraction
is period is 1 millisecond, what is the frequency?
frequency = 1/0.001s = 1,000 Hertz
if pulse duration is 8msec and IPI is 2msec, what is frequency?
T = pulse duration + IPI Frequency = 1/T
T = 0.008 s + 0.002s = 0.01
F = 1/0.01 = 100
what is frequency modulation?
requires a lot of pulses with a high frequency to generate tetany
-AC current with a break, how fast you put the bursts together is the frequency modulation
what is carrier frequency?
- used only for burst modulated AC currents
- interferential waveforms
ion response around the nerve membrane/characteristics of a pulse that are most important for nerve recruitment?
- AC and DC current affect the polarity of the membrane
- Capacitance is the ability for systems to store charge
- neuron activation
- membrane time constant
how do AC and DC charge affect the polarity of the nervous tissue?
positive paticles go to negative electrode and can cause depolarization of the membrane if the charge is sufficient
how does the capacitance impact the ion response around nerve membrane
- property of a system of conductors and insulators that allows them to store charge
- very similar to the cell membrane in the sense that it acts like a resistor and a capacitor to block easy movement of charged particles
how does estim trigger neuron activation
local current produced increased Na conductance which depolarizes the membrane and further depolarizes.
- when Na influx is greater than potassium efflux, threshold is reached
- *** if amplitude and duration aren’t enough, then the AP won’t be generated
what is the membrane time constant?
tau = resistance x capacitance = slope of time vs voltage
- determines how easily a nerve is excited
- since size impacts resistance, the smaller the diameter the higher the time constant and the harder it will be to stimulate
do all nerves have the same time constant?
NO!
different nerves have different time constants
-the bigger the nerve, the less resistance, so the more easily it will be stimulated
-the smaller the nerve, the more resistance, so the harder it will be to stimulate it
different nerve fiber activations
- Largest diameter lowest internal resistance are the most easily excitable
- Requires shorter pulse durations to get stimulated
- Requires less intensity to get stimulated - Denervated muscles - SCI or cut peripheral nerve, you’re really trying to stimulate the muscle membrane rather than the nerve
- That individual will require longer duration and larger intensity of the charge - Aα—muscle spindle primary afferent; GTO (golgi tendon) afferent; skeletal muscle efferent
- Aβ—touch pressure receptor afferent; muscle spindle secondary afferent
- Aδ—mechanical and thermal afferents
- C—mechanical and thermal afferents
why does one feel sensory tingling when stim is started?
- This is because there are sensory receptors closer to the surface even though they are smaller
- You have to jack up the stim even more to get motor contractions
- Unfortunately, you start to get the pain receptors as well as you jack it up which may yield to a dosing problem
what are key device characteristics that should be known for your stim faciltation?
- Allow control on:off times
- Allow control of pulse frequency (2-150pps)
- Allow control of pulse duration (50 - at least 400microseconds)
- Has adequate power (up to 100mA through 100 ohm resistor)
What are possible mechanisms for stim to reduce edema?
- Reduction in microvasculature permeability
- Motor-level contractions -> improve venous and lymphatic drainage (stimulate contractions that moves fluid)
- Pain reduction -> improve/increase limb use that will accelerate venous and lymphatic drainage and return to function (secondary effect on swelling because you get patient moving and more active by reducing their pain)
results for animal model using stim for edema reduction on hamsters
used High Voltage pulsed current (HVPC) in hamsters
- Monophasic
- Work on reducing microvasculature of permeability
- Different types of anodal and cathodal current were successful in halting edema in the hamster cheek pouch
results for animal model using stim for edema reduction on different kinds of rats
HVPC (High Voltage Pulsed Current) was used
□ Looked at swelling in hind limb □ 3 different strains of rats □ In 2 of the 3 there was evidence that high volt pulse current retarded swelling/edema
what were the findings in the systematic review about using stim for edema reduction in humans
-
All over the place, after acute ankle sprain there isn’t positive evidence on reducing swelling
what were the findings in the systematic review about using stim for pain reduction in humans
small study, but found that there was a moderate effect
what were the findings in the systematic review about using stim for function improvement in humans
2 studies, 4 different kinds of settings, all crossing 0 and stim was not really effective
