Foundations of Electrotherapy and Electrical Charges

Foundations of Electrotherapy

• Electrotherapy is a safe and effective form of therapy when used appropriately.
• It’s an adjunct to other therapeutic modalities.
• Electrical stimulation is used with rehabilitation exercises.

Electrical Charges

• Charge is the electrical potential of an atom or ion.
• It is measured in Coulombs (C).
• Electrical Potential is the difference between charged particles at a higher and lower potential.
• Electrons are particles possessing a negative charge and small mass.
• Protons are particles possessing a positive charge.

Principles of Electrical Charges

• Two types of charges exist: positive and negative.
• Like charges repel, opposite charges attract (Coulomb's Law).
• Charge is neither created nor destroyed.
• Charges can be transferred from one object to another.

Conductors & Insulators

• Conductors are materials that transmit or allow the passage of electrical current: water, muscle.
• Insulators are materials that prevent or inhibit the passage of electrical current: skin, adipose.
• Conductance is the ease with which current flows along a conducting medium.

Electricity

• Electrical current takes the path of least resistance.
• Cathode is the negative pole with a high electron concentration.
• Anode is the positive pole with a low electron concentration.
• The imbalance in electrical charge allows the free movement of electrons between poles.
• Isoelectrical point is the baseline where electrical potential between two poles is equal and no electron movement occurs.

Closed Circuit

• A closed circuit is a complete uninterrupted path between two poles.
• Examples include flipping a light switch or electrical stimulating currents in the body.

Open Circuit

• An open circuit is an incomplete or interrupted path between two poles.

Electrical Current

• Electrical current is the net movement of electrons along a conducting medium.
• It is proportional to the magnitude of the force (voltage).
• Current always moves from higher potential to lower potential.
• Electrical current requires: a source of electrons, a conductor, and a driving force of electrons (voltage).
• Current Flow (I).

Ampere

• Ampere (A) is the unit of measure that indicates the rate at which electrical current is flowing.
• 1 Ampere (A) = 1 coulomb passing a point in 1 second.
• 20 coulombs passing in 1 second equals 20A.

Voltage

• Voltage is the electromotive force or potential difference between two poles.
• It measures the tendency for current flow to occur.
• Electrons move from one pole to the opposite, creating a potential for work which is calculated by Force x Distance.
• Volt is a measure of electrical power (V).

Ohms & Mhos

• Ohm is the unit of measure that indicates resistance to current flow.
• 1 ohm is the amount of resistance needed to develop 0.24 calories of heat when 1A of current is applied for 1 second.
• Mhos is the reciprocal of Ohms.
• Conductance is the ease with which current flows and is the mathematical reciprocal of resistance.

Ohm's Law

• Ohm's Law states: I = V/R

  • Current flow = I
  • Voltage = V
  • Resistance = R

• Current flow is directly proportional to voltage and inversely proportional to resistance.

• Example: With a 120V current and a 12 A flow, the resistance is 10 ohms.

Electrical Power: Watt

• Watt is the measure of electrical power.
• It is the electrical power needed to produce a current flow of 1A at a pressure of 1V.
• Watt = Volts x Amperes.

Coulombs: Electrical Charge

• Electrical current results from the flow of electrons.
• Coulombs (Q) are a measure of the large number of electrons described as a single unit.
• They represent 6.28 x 10^18 electrons or protons.
• Coulomb's Law states the relationship between like and unlike charges: opposite charges attract and like charges repel.

Resistance

• Resistance (R) is the opposition to the flow of electrons by the material through which current travels.
• All materials have some degree of opposition to electrical flow.
• Skin is the primary biological resistor in electrical current flow.
• Resistance is measured in Ohms.

Factors Influencing Resistance

• Material of the Circuit: Conductors have less resistance.
• Length of the Circuit: Shorter distance equals less resistance.
• Cross-Sectional Area of the Circuit: Greater cross-sectional area equals less resistance.
• Temperature of the Circuit: Higher temperature equals less resistance (generally applies to wires, less evidence for tissue).

Impedance

• Impedance is the force that resists the flow of electrons and is related to resistance.
• It comprises three components:
  • Resistance: Opposition to the flow of electrical current.
  • Inductance: Ability of a material to store electrical energy by means of an electromagnetic field. It results from changes in charged particles.
  • Capacitance: Ability of a material to store energy through the system. It arises from the storage of charge within the current.

Circuit Types

• Series Circuit:

  • One path for current to flow from one pole to another.
  • Often used for sensory-level stimulation.
  • Electrode placement is close together, such as over a pain site or injury site.

• Parallel Circuit:

  • Two or more routes for current to flow between poles.
  • Often used for motor-level stimulation.
  • Electrode placement is farther apart, such as over the origin and insertion of a muscle.

Series Circuits

• Electrons have one pathway to travel in a series circuit.
• Current remains the same in all components along the circuit.
• Resistance is equal to the sum of the individual resistors.

Parallel Circuits

• Electrons have alternate pathways to follow in a parallel circuit, choosing the path of least resistance.
• Electrons can branch into other parallel or series circuits.
• Each path has its own Amperage (A).
• Electrical flow in each path is inversely proportional to the resistance.
• Amperage varies but voltage remains constant.

Current Density

• Current density is the physiological effect of electrical stimulation related to the amount of current per unit area.
• Current density is inversely proportional to the size of the electrode.
  • Greater surface area equals less current density.
  • Less surface area equals greater current density.

Types of Electrical Currents

• Direct Current (DC):

  • Galvanic flow of ions that flows in the same direction.
  • Positive and negative.

• Alternating Current (AC):

  • Current flow that periodically changes its polarity and direction of flow.

• Pulsed Current:

  • Unidirectional or bidirectional flow of ions that ceases for a period of time before the next flow.
  • Interpulse Interval: Period of time between pulses of ion movement.

Modality Generators

• Shapes Current Waveform: Creates the waveform, whether AC or DC.
• Creates Carrier Frequency: Determines the frequency of the electrical wave, as determined by the electrical modality machine.

Carrier Frequency

• Low: 0.1 - 1000 Hz

  • Most electrical muscle stimulation.

• Medium: 1001 - 10,000 Hz

  • Russian stimulation.

• High: 10,000 - ↑ Hz

  • Diathermy.

Transformers

• Transformers change voltage in alternating current (AC).

• Step-up transformer: Allows an electrical device to operate from a lower voltage source.

  • Hand-held modality units.

• Step-down transformer: Allows a device to operate from a higher voltage source.

  • Wall modality units.

Waveform Terminology

• Amplitude: Intensity of the current. Height of the wave from the baseline. Measured in each individual waveform.
• Frequency: Number of cycles per second.

Phase & Pulse

• Phase: Portion of the wave that rises above or below the baseline.
• Pulse: Finite period of charged particle movement, separated from other pulses with periods of no current flow.
  • Pulses can consist of one or more phases.

Alternating Current Impulses

• Biphasic Current:

  • Bidirectional flow of ions.
  • Includes a negative phase and a positive phase.
  • Electrons move from negative to positive pole, reversing direction with polarity reversal.
  • Cycle equals AC phase.

• Monophasic Current:

  • Also known as Galvanic current.
  • Uninterrupted unidirectional flow of ions toward a pole.
  • Positive or negative.

Phase & Pulse Characteristics

• Phase Shape: Shape of the output current (Rectangular, Triangular, Spike).
• Phase Charge: Total electrical charge of a single phase (measured in coulombs).
• Pulse Charge: Amount of electrical charge of a single pulse (sum of the phase charges).
• Burst: Finite series of pulses flowing for a limited time, followed by no current flow.

Pulse Rate (Frequency)

• Waveform repeated at regular intervals.

• Number of events per second.

• For Direct Current: Frequency = Pulses per Second (pps).

• For Alternating Current: Frequency = Cycles per Second (cps) or Hertz (Hz).

Common Rates in Electrical Modalities