Week 12: Intro to Electrical Currents & Ionto

Charge

Loss or gain of electrons of an atom measured in (coulombs)/microcoulombs.

Negative Charge

A net gain of negative electrons.

Positive Charge

A net loss of negative electrons.

Ionization

An atom or molecule that has gained or lost electrons is an ion, and the process of acquiring a charge is ionization.

Atoms are composed of

Positive protons and negative electrons

Charge occurs when atoms are acted on by

an external force like

Heat, pressure, friction, chemical or electrical source

4 principles of charge

1. Two types of charges positive and negative

2. Like charges repel while opposites attract

3. Charge is neither created nor destroyed

4. Charge can be transferred from one object to another

Polarity

The charge of an object which can be positive or negative.

Cathode

Negatively charged pole.

Anode

Positively charged pole.

Battery

One end has a concentration of electrons and the other a deficiency; positive end has less electrons so net charge is +, negative end has more electrons so net charge is -.

Cell membrane anode

side of cell membrane with + charge typically outside

cell membrane cathode

side of cell membrane with - charge

typically inside of the cell

Electric Field/Force

The force created by the separation of charge, which can be one of attraction (opposites) or repulsion (likes).

Like charges

repel

Unlike charges

attract each other

Attraction or repulsion of charges creates

an electrical field

Voltage

Force of attraction or repulsion created by an electrical field represented by potential energy; also called electromotive force or electrical potential.

Greater the force of voltage

the greater the potential energy

In the body, voltage forces are created by

uneven distribution of charged particle where regions are either more less positive or negative to an adjacent region

Positive ions in the body

Na+, K+;

negative ions in the body

Cl-

Cell membranes

Electrochemical gradient with potential energy

Greater concentrations of sodium (Na+) outside the cell

Greater concentrations of Cl-

Greater concentrations of Cl-

inside the cell

Greater concentrations of sodium (Na+)

outside the cell

If the charges are equal on each side of a cell membrane

, then the cells membrane is said to have no electrical potential or no voltage.

If instead there is a net positive charge on one side of the membrane,

that side has a positive voltage and the other side has a negative voltage

Conductors

Materials that permit the movement of ions, such as water/body fluids, nerve & muscle tissue & metal.

Insulators

Materials that slow the movement of ions, such as fat.

Myelin, which surrounds nerve axons, acts as an

insulator, allowing for rapid electrical signal transmission, if damage then transmission is diminished

Current (I)

Movement of ions/electrons in response to voltage force; current is the uninterrupted flow of ions.

Electrochemical gradient

A separation of force across the cell membrane that creates a voltage force allowing cells to depolarize and transmit signals by moving ions.

Current Measured in

ampere (amp or A)

Milliamperes (mA)

Thousandths of an ampere

Microcurrent

Less than 1mA

Ohm's law

Current = Voltage/Resistance, or I = V/R

Ohm

Standard unit of resistance

Capacitance

Current flowing in an insulated area with high resistance will slow and charge will start to store in that area

When current flow stops in an area with high capacitance

stored energy will flow back through the conductors

Electrical stimulation stopped abruptly may cause

a quick surge in energy and sensation of uncomfortable stinging/shock like sensation

Impedance

Resistance to the flow of alternating current

Gels and adhesive on electrodes

Decrease impedance and improve conductivity between the electrode and skin

Body tissues with higher resistance

Includes skin, hair, fascia, ligament, callus, fat, bone, tendon, and scar

Types of Current

Includes Direct current (DC), Alternating current (AC), and Pulsed current (PC)

Most common current in rehab

Pulsed

Waveform

A depiction of the characteristics that describe a current on a graph

X axis

time

Y axis

Amplitude or intensity of the current

Direct Current

Continuous unidirectional flow of electrons for at least 1 second

Types of Direct Current

Includes Interrupted, Reversed, and Interrupted/reversed

Interrupted direct current

Direction of flow ceases after 1 second, resumes in same direction

Flows in same direction but stops at specified intervals then restarts in same direction

Reversed direct current

Flows in a specific direction of polarity for >1 sec then reverses direction towards opposite polarity

interrupted reversed direct current

Direction of slow ceases after one second and resumes in the opposite direction

Clinical considerations of DC

One electrode positive (anode) and one electrode negative (cathode)

Uses of DC

Ionto and wound care

Iontophoresis

Drives medication through the skin to a specific problem area

Alternating Current

Uninterrupted bidirectional flow of electrons, must change direction at least once per second

Frequency

Rate AC current changes direction, measured in cycles per second = hertz (Hz)

Clinical Uses of AC

Includes pure sinusoidal AC current, Russian current, and interferential current

Russian Current

burst modulated alternating current

inferential current

Amplitude modulated AC current

Key Point of AC current

Must change direction at least one time per second

Pulsed Current

Unidirectional OR bidirectional flow of electrons that periodically ceases for a short time period, the interphase/interpulse interval, before the next event or pulse.

Burst

2 or more pulses separated from the next series of pulses separated by a time interval called the burst interval.

Burst frequency

Frequency bursts are generated.

Carrier frequency

Frequency of underlying waveform.

Waveform Shapes

Shapes of waveform can be Square, Rectangular, Triangular.

Shape of waveform affects how a

patient will tolerate E-stim and the effect of E-stim of skeletal muscle

Pulse-time

The current is on.

Phase

Flow of current in one direction for a short period of time.

Monophasic

Towards 1 polarity.

Biphasic

Alternates between + and - polarities before the interphase interval.

Interphase/pulse intervals

Time between the phases where the current is on.

Frequency (pps)

Cycles per second.

Time modulation (duty cycle)

On-time/total time (on time + off time) x 100%.

Duty Cycle

On-time/total time (on time + off time) x 100%.

Document off time in your note instead

duty cycle

Amplitude Modulation

Gradually/progressively increasing/decreasing current amplitude.

Purpose of amplitude modulation

Patient comfort

Achieve desired response with muscle stimulation

Ramp

Progressive increase (ramp up) or decrease (ramp down) in amplitude towards isoelectric line.

Ramp effect on total time

Current is being delivered during both ramp up and ramp down so part of on time

Long ramp up and down times greatly reduce

the overall current delivered

Ideally ramp time should be considered part of the

on time

ramp up time

the time it takes for the current amplitude to increase from zero, at the end of the off time, to its maximum amplitude during the on time.

Phase charge

Charge within one phase of a pulse.

Pulse charge

Charge within a total single pulse.

Monophasic waveforms

Pulse charge and phase charge are the same.

Biphasic waveforms

Can be symmetrical or asymmetrical.

Current with net positive or negative charge Results in

sustained cathode and anode and may cause adverse reactions if not used properly.

Commonly used currents that result in a net positive or negative charge

Direct current (DC), Monophasic pulsed current, Asymmetrical unbalanced biphasic current.

Monophasic pulsed current most commonly used in

wound care

Describing Pulsed Current

1. Waveform Type & Shape

2. Pulse Frequency

3. Pulse Duration

Pulse Duration

How long each pulse lasts

Parameters for Direct current

polarity, intensity

Intensity

The strength of the electrical current.

Symmetrical AC

Alternating current that has equal positive and negative phases.

Asymmetrical AC

Alternating current that does not have equal positive and negative phases.

Balanced Asymmetrical AC

Asymmetrical alternating current that maintains balance in its phases.

Unbalanced Asymmetrical AC

Asymmetrical alternating current that does not maintain balance in its phases.

parameters for symmetrical AC

Frequency

Intensity