Lecture 6B - NMES Flashcards
Describe electrical current
Flow of electrons through a conducting medium when a difference of potential in the pathway exists (Hartley, 2007)
Gives rise to electromotive force
Charged particles that can move and a driving force to move them
In biological tissue: electrolytes (a substance that contains ions) form the charged particles and the driving force is established by applying a voltage (an electromotive force)
Describe electromotive force
The force created due to an imbalance in the number of electrons between two points
Describe electron flow
flow of electrically charged particles (electrons) from one point to another.
Electrons move from the negative electrode (CATHODE) to the positive electrode (ANODE) through the conducting material
Describe current flow
The current will flow in the opposite direction –flowing from the positive ANODEto the negative CATHODE
Describe units of flow
Amperes: passage of 1 C per second
Note: several hundred amperes needed for lights
For biological applications, much less is needed and flow is reported in miliamperes(mA) in therapeutic applications
What does rate of current flow depend on?
DEPENDS ON:
1.Electromotive force driving the electrodes
•Likened to a pump creating the water movement through a pipe
2.Amount of resistance of the conductor
•Length, diameter and smoothness of the pipe
What is resistance?
Opposition to electron flow in a conducting material (to a DC current)
*A term used specifically for DC current
What does resistance depend on?
Depends on: The conductor material The length of the pathway The cross-sectional area of the conductor The temperature of the conductor
*The larger the pads are the more effective they are and the less resistance they come up against
What is impedance ?
Impedance: Opposition to alternating current (AC)
Also describes the ability to store an electric charge as well as the resistive oppositions to the movement of charged particles
*Term used with regard to alternating currents - which is what we use in the clinic
Is biological tissue a resistor or capacitor of electrical current?
Biological tissue can be either a resistor or a capacitor of electrical current
**The higher the
current frequency of stimulation the lower the tissues impedance*
Capaciters can make it easier for a current to travel or resist it
What are the factors effecting rate ?
1.Conductor material
•Higher water content (water / blood) *will help facilitate the travel of current
•Fat, skin and bone are poor conductors *Gel, gel like pads and mositened skin with water will help us get by the skin being a poor barrier
2.Length of pathway
•Longer pathway encounters more impedance
3.Cross-sectional area of the conductor
•Bigger is better –greater area more electrons
4.Temperature of the conductor
•Increase in temperature will impede the current
What type of current does muscles respond better to?
Alternating current (AC)
otophoresis done with a _____ style current
galvanic (Continuous DC)
What does biphasic mean?
Biphasic means it goes into both the positive and negative realms
Rectangular symmetrical biphasic pulsed current is good for which type of muscle group?
Larger
Unbalanced asymmetrical biphasic pulsed current is better for which type of tissue ?
Certain tissues respond better to this type of wave, typically nerve tissue and sometimes smaller muscle
Describe direct current
galvanism or constant current
unidirectional flow of electrons through a conductor (mA)
Build up of positive ions under the negative cathode
Build up of negative ions under positive anode
There will be depolarizationunder the cathodeand hyper polarization under the anode
Describe cathode (Negative)
- Tendency to depolarize nerve fibresandproduce stimulation
- producesa softening of tissue
- a hyperemic reaction
- production of alkalinesubstances
Describe anode (positive)
- Tendency to hyperpolarize nerve fibresand prevent stimulation
- produces a hardening of tissue
- a hyperemic reaction
- production of acidsubstances
______ current has the current go on and off at regular intervals
Sudden rise and fall of the intensity with very _____ duration
Ie. Twin Peak Galvanic
No ____ build up
Interrupted
Short
chemical
Which type of monophasic (Modified DC interrupted) wave is preferred for nerve tissue?
A sudden rise in the intensity is generally perferred for nerve tissue. Saw-tooth, twin peak are examples
Do you get chemical build up with AC (Alternating current)? Do the negative and positive pads matter?
The negative and positive pads do not matter because they change polarity throughout the treatment - this is specific to alternating current (AC)
Because of this you won’t get any chemical buildup even if the duration is prolonged
Describe alternating current (AC)
An alternating current causes a continual
change in polarity so that one electrode is positive, the other negative then they reverse.
The current alternates at a fixed frequency or can be pulsed.
What is the preferred wave for large muscle groups with biphasic (AC) and why?
Sym Sine
You will see it used with russian stim specifically
preferred wave of large muscle groups because it is the most comfortable
Asym rectangular is generally a ___ wave
TENS
Asym spike is generally a ___ wave
TENS
What are the depolarization criteria?
1.The current rise quicker for nerves slower for muscles 2.Stimulus has adequate intensity ~30mA *The dial that the patient or therapist turns up - typically 30mA is the minimum (adequate intensity) but in some cases patients dont have the tolerance for this intensity and if you dont get this intensity you dont get the depolarization and thus dont get the desired effect 3.Stimulus has long enough duration ~micro/millisecond *If not a strong depolarization you wont get the effect your looking for
EXAM Q: Describe the strength duration curve
A graph relating the intensity of an electrical stimulation to the length of time it must flow to be effective
*in order for muscle tissue to depoliraed there must be enough stimulus introudcued and for a long enough period of time for depolirazation to occur.
Define rheobase
Rheobase:minimum strength of an electrical stimulus of indefinite duration that is able to cause excitation of tissue
define chronaxie
Chronaxie:the shortest durationof an effective electrical stimulus having a strength equal to twice the minimum strength required for excitation.
What are the steps to determine if the flow of current will be effective?
Step 1. Find the rheobase
*Rheobase is minumum amount of current needed
Step 2. Multiply it by 2
Step 3. Calculate the Chronaxie
What are the parameters for NMES?
1.Pulse rate 35 -50 pps 2.Pulse duration 250 microsec *250 microsec is what it takes for chronaxie to occur in motor nerve fibres 3.Amplitude or Intensity ~30mA *Minimum 30mA for it to be effective Determined by the patient *NEVER ADJUST INTENSITY BY THE NUMBERS, ITS ALL BASED ON PATIENT FEEDBACK **** THIS IS KEY FOR PRACTICAL
What are factors affecting depolarization?
1.Tissue impedance Dependent on water content of tissue Muscle conducts better in a longitudinal direction 2.Size of electrode pads Smaller = greater current density generally the cathode (active pad) over the motor point 3.Pad placement 4.Electrode coupling 5.Parameters of the electrical current
What are go to areas to find superficial nerves?
Fossa’s
Describe the pulse rate
Pulses per unit time pps, cps, bps, Hz tetany from 15 -50 pps(average 30 –35) ideal pulse rate = when the muscle just reaches tetany because it can be stimulated longer without fatigue
Describe russian stimulation - Kots
Frequency -2500, modulated at 50 cps 50 bursts per second with 50 pulses per burst 200 -300 μsec duration 10 sec on, 50 off intensity -maximum tolerated ramp 4 -5 sec 10 maximum contractions
Describe Pulse Duration
Length of time the current is flowing –higher for muscle tissue than for neural tissue The longer the duration the more uncomfortable it is for the patient For….. 1.Nerve stimulation 100 -300 μsec 2.Innervated muscle 300 μsec 3.Denervatedmuscle 10 millisecond
Describe treatment parameters for NMES
1.Treatment time 10 -30min 2.Ramp time before and after contraction (2 –5 sec) 3.On -Off time (sec) simulate activity less time on in the upper quadrant 10-30, 10-10, 10-50
Describe the mono polar technique
Asymmetrical current
larger pad on nerve root (anode +)
smaller pad on motor point (cathode -)
The monopolarapplication is superior for muscle stimulation in a normal innervated muscle
best anode placement is on the nerve or nerve root supplying the muscle
Describe the bipolar technique
Two electrodes of equal size
One electrode on the muscle near its insertion and one electrode on the muscle near the origin
The bipolar application is superior for denervated muscles or small muscles
for specific muscles that are served by one nerve
