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AT 510 Physical Agents > Electrical Stimulation > Flashcards

Flashcards in Electrical Stimulation Deck (50)
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1

Direct Current

A continuous unidirectional flow of charged particles flowing for 1 second of longer.

Direct Currents can be completely described in terms of amplitude, direction and time.

2

Direct Currents are used for?

Iontophoresis
Wound Healing
Stimulating Denervated Muscle

3

Alternating Current

The uninterrupted flow of a bidirectional flow of charged particles.

4

Pulsatile Current

The unidirectional or bidirectional flow of current which ceases for a finite period of time.

Any pulsatile current could be used for TENS or NMES

5

Cathode

Away Road
Area of excess electrons
NEGATIVE pole
It is usually the active electrode and is BLACK

6

Anode

Toward Road
Area deficient in electrons
POSITIVE pole
It is usually the inactive dispersive pole and is usually RED or GREEN

7

Voltage or Electromotive Force

(EMF)
The "push" on electrons. Analogous tothe pressure in a hose.
Measured in volts.
1V=the EMF required to push 1 amp through 1 ohm of resistance.

8

Resistance

The resistance to electron flow. Analogous to the friction in a hose.
Resistance varies with properties such as length of conductor, cross sectional area, temperature and material.

9

Current

The number of electrons flowing past a point per unit of time.
Analogous to the volume of water flowing in a hose.
Measured in Amperes
1 AMP=6.24x10^18 electrons/sec=1 coulomb/sec

10

Impedance

The combinded effects of resistance and reactance (which consists of capacitive and inductive components) on current flow.
Impedance is measured in Ohms
Impedance = 1/(2piCF)

11

Single Pulse

An isolated electrical event separated by a finite time.

Phase: A part of a cycle.

12

Monophasic

A current flowing in only one direction during a pulse.

13

Biphasic

A current flowing in both directions during a cycle.

14

Polyphasic

A current changing direction more than twice during a cycle.

15

Symmetry

A comparison of the size and shape on both sides of the isoelectric line.

16

Symmetrical

A waveform which has the same size and shape on both sides of the isoelectric line.

17

Asymmetrical

A waveform which has a different size or shape on differing sides of the isoelectric line.

18

Balance of Phase Charge

A comparison of the amount of charge on each side of the isoelectric line. it is equal to the area under the curve.

If we don't have a balanced charge we could potentially burn the patient.

19

Balanced

The phase charge is equal in both directions (The area under the curve is the same on both sides of the isoelectric line.) The shapes do not need to be the same.

The importance of a balanced charge is that it does not lead to a buildup in charge which could lead to patient burns.

20

Unbalanced

The phase charge is unequal between sides of the isoelectric line.

21

Physiological Effects of Electricity

Affects motor, sensory, and autonomic nerve fibers.
Can also affect muscle fibers directly.
Electricity has an effect on all tissue -- all cells have membrane potentials and can be affected.
The action potential (AP) is produced by any adequate stimulus (Electrical, mechanical, thermal, chemical that reaches threshold).
There is an inverse relationship between fiber size and threshold. Therefore, large fibers are activated first.
Threshold for nerve is much less than that of muscle.

22

Resting Membrane Potential

RMP is -70mV -90mV

23

Sequence of Surface Stimulation

Sensory threshold
Motor threshold
Maximum motor contraction without pain
Pain threshold
Pain tolerance

24

Denervated muscle contaction

In denerveated muscle, the muscle fibers must be stimulated directly since the nerve is no longer functional.

Since the threshold is so high in muscle (-90 mV) high amounts of current are required to stimulate muscle. The treatment will be painful if sensation is intact. If sensation is not intact, there is the danger of burning the patient.

Denervated muscle requires a high amplitude, low frequency or DC to stimulate it.

25

Effects of Polartiy: Cathode (Negative Pole)

Under the negative pole, the interstiatial fluid will become less positive, thereby lowering the voltage difference across the cell membrane. When the difference is less than 55 mV, there will be an action potential.

The Cathode is therefore an active electrode for stimulating nerve.

26

Effects of Polarity: Anode (Positive Pole)

Under the positive pole, the interstitial fluid become more positive, thus increasing the voltage difference across the cell membraneand hyperpolarizing the membrane.

In the area of the anode, it therefore becomes more difficult to stimulate a nerve.

27

Anode Effects

Acidic
Hardens Tissue
Contracts Tissue
Decreases Hemorrhage
Decreases congestion sedative (elevates threshold)

28

Cathode Effects

Alkaline
Softens Tissue
Dilates Tissue
Increases Hemorrhage
Increases Congestion
Stimulating

29

Electrode Variables

The closer the electrodes, the more superficial the treatment.
The larger the electrode, the more superficial the treatment.
If electrodes are on opposite sides of the body part, the current flow will be deeper.
If electrodes are placed over a peripheral nerve, all muscles distal to and served by that nerve will be stimulated.
Stimulation of a motor point affects only that muscle.

30

Generator Variables

As amplitude increases, depth of penetration increases.
As rate increases, fatigue increases.
As pulse width (duration) increases, there is a greater depth of penetration (and more pain).
Duty cycle: best strengthening ratio is 1:3-5. Fatigue is best caused by continuous current.
Rate of Rise: A rapid rate of rise produces little accommodation. However, a slower rate of rise is more comfortable for the patient.