Electrotherapy

1
Electrotherapy

• Part I

2
Basic Principles of Electricity

• All matter has positive and negative charged ions
• Move from high to low concentrations
• Coulombs Law
• Opposites attract , likes repel

3
Basic Principles of Electricity

• Electrons
• Negative charged ions
• Flow always goes from higher to lower potential
• Negative pole cathode
• Positive pole anode
• How is an electrical force generated?
• imbalance

4
Basic Principle of Electricity

• Ampere
• Indicates rate at which electrical current or
  electrons flow
• 1 ampere 6.25 x 1018 electron per second
• Most modalities have current flow designated much
  lower
• Milliamperes or microamperes
• Coulomb
• Number of electrons passing by a point in one
  second
• 1 ampere is defined as the movement of 1 coulomb

5
Basic Principle of Electricity

• Voltage
• Electromotive force resulting from accumulation
  of electrons at one point in a circuit
• Measurement of the difference in electrons
  between two points in question
• Amount of work needed to move 1 Coulomb
• High volt vs low volt generators

6
Basic Principle of Electricity

• Electrons can only move in a current if there is
  an easy pathway to move along
• Conductors
• Insulators
• Number of amps flowing in a given conductor
  dependent on voltage and conductive
  characteristics
• Resistance to Electron Flow Ohms
• Ohms Law
• Current flow voltage/resistance
• Analogy

7
Electron Flow Analogy

• Volt
• Amperes
• Ohm (properties of conductor)

• Pump
• Gallons
• Resistance (length and distance of pipe)

Amount of energy produced by flowing water
gallons/unit of time and pressure created in pipe
Electrical energy produced is function of amperes
and voltage
8
Basic Principle of Electricity

• Impedance -- Form a resistance to AC Currents
• Measured in Ohms
• Inductance
• Capacitance
• Frequency dependent resistance
• Cell membranes act as these
• High vs low frequency capacitance

9
Basic Principle of Electricity

• Watts
• Watts Voltage x amperes
• Power of the electrical current
• The electrical power needed to produce current
  flow of 1 amp at a pressure of 1 volt
• Change in wattage reflects change in voltage and
  ampere

10
Basic Principles of Electricity Types of Current

• Direct Current (Galvanic Current)
• Continuous flow of electrons in one direction
• Negative to positive pole
• Polarity remains constant
• Square Wave

11
Basic Principles of Electricity

• Direct Current
• Alternating Current
• Flow changes direction
• Constantly changing polarity
• Negative to positive and then changing direction
  with polarity
• Closer Look at AC Current
• Peak value
• Peak-to-peak value
• Cycle duration
• frequency

12
Basic Principles of Electricity

• Pulsed Currents
• Unidirectional or bi-directional flow
• Usually 3 or more pulses grouped together
• Pulses are interrupted
• 3 Types of Waveforms
• Monophasic
• Biphasic
• Polyphasic (Russian Current)

13
A Closer Look at the Electrical Pulse

• Pulse Duration
• Distance wave covers on horizontal axis
• Length of time current is flowing in 1 cycle
• Phase Duration
• Important
• Monophasic Uninterupted
• Phase duration pulse duration
• Biphasic Uninterupted
• Pulse duration combined phase durations

14
A Closer Look at the Electrical Pulse

• Pulse Charge
• Measure of electrons delivered in pulse
• Phase Charge
• How do you know pulse charge is large enough to
  overcome capacitance of tissue?
• Pulsed Currents
• Interpulse interval
• Intrapulse Interval
• Pulse Period

15
A Closer Look at the Electrical Pulse

• Pulse Amplitude
• Reflects intensity of current
• Highest point in each phase
• Synonymous w/ voltage and current intensity

16
Strength-Duration Curve

• Nonlinear relationship between current duration
  and current intensity
• Shorter duration need higher intensities
• Nerve and muscle differ greatly in firing
  threshold

17
A Closer Look at the Electrical Pulse

• Adjusting Amplitude and Phase Duration to
  Increase Pulse Charge to Elicit Desired Response
• Rheobase
• Minimum amplitude needed to depolarize nerve
  fiber
• Chronaxie
• Minimum phase duration required to depolarize a
  nerve when peak amplitude is twice rheobase

18
A Closer Look at the Electrical Pulse

• Pulse Frequency
• Pulsed vs continuous AC current
• Units
• Each pulse represents a rise and fall in
  amplitude
• Inverse relationship between frequency and
  capacitive tissue resistance

19
A Closer Look at the Electrical Pulse

• Pulse Rise Time
• Pulse Decay Time
• Which waveforms may produce a rapid rise time?

20
Current Modulation

• Continuous
• Amplitude remains same
• Interrupted
• On- and off-time
• Monophasic and biphasic pulsed currents
• Burst
• Short duration on and offs repeated in a cycle
• Mon-, bi- and polyphasic waveforms
• Ramping
• Gradual rise or fall

21
Electric Circuit Types

• Closed vs Open Circuit
• Basic Components of Electrical Circuits
• Power Source
• Conducting Medium
• Group of Components driven by electron flow
• Series Circuit
• Parallel Circuit

22
Electrical Circuit Types

• Series Circuit
• Current can only flow along one path
• Components end to end
• Amperes same at any point
• Resistance Total R1 R2 R3
• Decrease in voltage at each component
• Vt VD1 VD2 VD3

23
Electrical Circuit Types

• Parallel Circuit
• Current can flow along 2 or more pathways
• Components side by side by connected end to end
• Each resistor receives same voltage
• Vt V1 V2 V3
• Current chooses path of least resistance

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Summary of Series and Parallel Circuits

• Series has higher resistance and lower current
  flow
• Parallel has lower resistance and higher current
  flow
• Why do we need to know?