Lecture 6B - NMES Flashcards by r s

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)

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Describe electromotive force

The force created due to an imbalance in the number of electrons between two points

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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

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Describe current flow

The current will flow in the opposite direction –flowing from the positive ANODEto the negative CATHODE

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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

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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

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What is resistance?

Opposition to electron flow in a conducting material (to a DC current)

*A term used specifically for DC current

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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

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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

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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

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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

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What type of current does muscles respond better to?

Alternating current (AC)

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otophoresis done with a _____ style current

galvanic (Continuous DC)

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What does biphasic mean?

Biphasic means it goes into both the positive and negative realms

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Rectangular symmetrical biphasic pulsed current is good for which type of muscle group?

Larger

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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

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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