Principles of Electrotherapy Flashcards
What is NMES used for?
- muscle re-education
- pain modulation
- used in place of prosthetic device
- tactile stimulation
- strengthening
- ROM
- improved function
- contraction of denervated tissue
- wound healing
- edema control
What is charge measured in?
Coulombs (C) or micro coulombs
Net gain of electrons =
negative charge
Net loss of electrons =
postive charge
do like charges repel or attract?
repel
do opposite charges repel or attract?
attract
can charges be created or destroyed?
nope - neither
can charges be transferred from one object to another?
yep
anode =
net positive pole
attracts (-) ions
cathode =
net negative pole
attracts (+) ions
what is voltage?
- potential difference in distribution of ions
- also referred to as electromotive force
- a force that PUSHES charge
what is voltage measured as?
- volts or millivolts
What is current flow?
the flow of charged particles (ions or electrons)
what is current flow measured as?
- the number of electrons or ions that pass a certain point in a specified period of time
what is current flow measured in?
amperes or microamperes or as a rate (coulombs per second)
current flow moves from …
anode to cathode
current flow and electron flow are …
opposite
what is resistance/capacitance/impedance?
opposition to flow of charged particles
Formula for intensity
I = V/R
- which means that there is an inverse relationship between resistance and intensity
in an alternating current, what is the formula for intensity?
I = V/Z
- Z is the resistance stated above + any additional resistance found in the capacitance and inductance of an alternating current generator
what does resistance/ capacitance/ impedance depend on?
- nature of the material
- length of the pathway
- cross-sectional area of the pathway
what is skin impedance?
- a form of resistance
- resistance offered by the skin
- highly variable throughout the body
Skin impedance - Variables
- water content
- blood flow
- patient activity or position
- conducting medium
- hair
skin impedance - fixed factors
- distance between electrodes
- what is under the electrodes
Three types of currents
- Direct Current
- Alternating Current
- Pulsed Current
What is direct current?
- unidirectional current flow lasting for at least 1 second
- since current flow is only in one direction will lead to an accumulation of ions under the electrodes (OUCH!)
What is direct current used in?
- iontophoresis
- wound healing
- stimulation to denervated tissue
direct current - cathode
- depolarized membrane of excitable cells
- alkaline effect (hurts more)
- attracts hydrogen
- liquifies protein
- promotes fibroblastic migration (scarring)
direct current - anode
- hyper polarizes membrane of excitable cells
- acid effect
- attracts oxygen (bubbles)
- coagulates protein
- kills bacteria
What is alternating current
- continuous current flow alternating direction of at least once each second
- the number of electrons that pass in each direction is generally equal
what is alternating current used for?
- stimulation of nervous and muscular tissue
- may be used for denervated tissue (but nothing in US is strong enough)
how can alternating current be identified?
by waveform
what is pulsed current?
- unidirectional or bi-directional current flow with periodic interruptions
- current flow lasts for only a few milliseconds or less
what is the most common form of therapeutic e-stim used?
pulsed current
what isnt pulsed current used for?
iontophoresis
constant current
- current stays fixed even if resistance or impedance changes
- voltage varies
- how the generator is going to react to resistance
- typically dont want constant current in smaller area
Constant voltage
voltage will remain constant and current will change in proportion to resistance or impedance changes
Current parameters
- amplitude
- rise time and decay time
- pulse duration
- interphase and interpulse intervals
- total current and pulse charge
- frequency (rate)
What is amplitude?
- same as intensity
what is amplitude measured in?
Amperes
More often milliamperes
Sometimes expressed in voltage (# would be higher)
peak amplitude
highest intensity reached during one stimulus
rise time
elapsed time from onset of stimulus to peak amplitude of stimulus
decay time
elapsed time from peak amplitude to termination of stimulus
what is rise/decay time measured in?
- milliseconds or microseconds
- different from “ramp and fall” time which are modulations to an individual stimulus
Pulse duration
- length of time one pulse lasts
Phase duration
- in biphasic pulse
- length of time current flows in one phase of a pulse
interphase interval
- brief interruption between phases
interpulse interval
elapsed time between consecutive pushes in a pulsed current
what are interphase and interpulse intervals measured in?
microseconds
frequency (rate)
number of pulses or cycles per second
what is frequency measured as in pulsed current
pps
what is frequency measured as in alternating current?
Hz
low frequency
0-1,000 Hz
Medium frequency
1,000 - 10,000 Hz
High frequency
> 10,000 Hz
what does a change in frequency in alternating current lead to?
an automatic change in cycle duration
does a change in pulsed current frequency necessitate a change in pulse duration?
no
due to an interpulse interval
what decreases with decreasing pulse or cycle duration?
- skin impedance
- increasing frequency may increase current penetration
what is perceived as being more comfortable and why?
- higher frequency
- because skin impedance is reduced in AC current
When is more fatigue seen over time?
- with higher frequency
- varying the rate may reduce this fatigue
relationship between frequency and recruitment of fiber type
Type I: 10-20 Hz
Type II: 30-60 Hz
What is a modulation?
- any parameter that is altered or varied during a series of pulses or cycles
- usually seen in amplitude, frequency, phase duration, or waveform
Burst Modes
- multiple pulses or groups of cycles carried out in bursts
- modulation in AC
Carrier Frequency
- number of cycles/second before burst modulation in AC current
Burst Frequency
Burst occurring to deliver the carrier frequency
resting membrane potential
resting electrical potential difference across a membrane of nerve or muscle cells caused by the difference in distribution of charged particles on either side of the membrane
Where is there more Na? Where is there more K?
- There is more Na+ on the outside
- There is more K+ on the inside of the cell
Resting membrane potential
-70 mV
Action potential
an electrical event that occurs when the cell is excited by a stimulus adequate to cause a decrease in the electrical potential across the membrane
local excitatory response
allows cell membrane to increase its permeability to Na+
depolarization
- reduction in negative charge caused by Na+ entering the cell
what occurs when threshold is reached?
a rapid reversal of electrical potential (action potential)
what does the resting membrane potential change from during the action potential?
it changes from -70 mV to +30 mV
What causes the membrane to become hyper polarized?
As the permeability to Na+ begins to shut down, the slower movement of K+ is just reaching its equilibrium
Absolute refractory period
- depolarization phase
- another AP cannot occur under any circumstance
relative refractory period
during hyper polarization another AP could occur if a stimulus of a much greater magnitude occurs
voluntary contraction
small, slow deeper units are recruited first in all or non fashion
electrically stimulated contraction
larger, faster motor units fire first
what is the biggest factor of motor unit recruitment?
- electrode placement
- the closer the motor unit is to the electrode, the faster it will be recruited
cell type recruitment
sensory n > motor n > deep pain n > muscle fibers
What do you need in order to get a response?
- adequate total current
- either have to increase amplitude or pulse duration to get the desired response
- all or nothing
what does a strength duration curve show?
the relationship between the amplitude and pulse duration to produce a threshold stimulus for different nerve types and skeletal muscle
Rheobase
minimal amplitude needed to create an action potential given an infinite pulse duration
Chronaxie
Minimal pulse duration that will cause an action potential at two times rheobase
Contraindications
- Severe cardiac condition; use of demand type pacemaker
- active bleeding or risk of hemorrhage
- active osteomyelitis
- pregnancy (over lumbar region and uterus)
- carotid bodies/ anterior neck
- phrenic nerve, eyes, gonads
- when active motion is contraindicated
Precautions
- sensory loss
- Areas of scarring
- Thick adipose tissue
- Severe edema
- Over malignancy/neoplasm
- Open wounds
- Severe depression
- Disoriented patients
- Superficial metal
Verbal preparation
explain what, why, how it will feel, the patients responsibility, encourage open conversation
should you demonstrate e stimulation
yep
positioning
thing about patient comfort, goals for use, good visibility for patient and you
skin impedance
clean with alcohol, abrade, hydrate, heat, dont shave
canvas conductive medium
clean with water, cover with gauze, make conductive with water
carbon/silicon rubber
use of conductive gel or sponges, clean electrodes by washing
carbon/silicon self-adhesive
disposable, requires slight film of water to make tacky
probe
cover with gauze, soak button, check that switch is in good working order
size of electrode
- make as large as target area but not larger
- large electrodes decrease skin impedance
- can cut some electrodes to shape and size desired
location of electrodes
- have current run longitudinally
- not too close together
- not too far apart
- try to use motor points
- be sure adhesion is firm to keep in place, but does not construct if motion is desired
- use straps, body weight, tape, sand bags to help keep in place
Unipolar or Monopolar
- One electrode is considered active based on its function or differences in size
- use over motor point
- delivery of medication
- one small active electrode and one large dispersive electrode so current density is greater under the active one
what are unipolar/monopolar leads used for?
- usually for isolating single or small muscle groups whether innervated or denervated and for training functionally after transplant or repair
Bipolar
- both electrodes are of equal size with equal current density under both
- place one over the motor point and one distally over the nerve
what are bipolar leads used for?
primarily to stimulate larger muscles and muscle groups for functional activities
quadripolar
- specific to iaterfererntial stimulation
- circuits are crossed
