Flashcards in Electrical Stimulation Deck (50)
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.
Direct Currents are used for?
Stimulating Denervated Muscle
The uninterrupted flow of a bidirectional flow of charged particles.
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
Area of excess electrons
It is usually the active electrode and is BLACK
Area deficient in electrons
It is usually the inactive dispersive pole and is usually RED or GREEN
Voltage or Electromotive Force
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.
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.
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
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)
An isolated electrical event separated by a finite time.
Phase: A part of a cycle.
A current flowing in only one direction during a pulse.
A current flowing in both directions during a cycle.
A current changing direction more than twice during a cycle.
A comparison of the size and shape on both sides of the isoelectric line.
A waveform which has the same size and shape on both sides of the isoelectric line.
A waveform which has a different size or shape on differing sides of the isoelectric line.
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.
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.
The phase charge is unequal between sides of the isoelectric line.
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.
Resting Membrane Potential
RMP is -70mV -90mV
Sequence of Surface Stimulation
Maximum motor contraction without pain
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.
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.
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.
Decreases congestion sedative (elevates threshold)
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.