Principles of Electrical Stimulation

1
Principles of Electrical Stimulation
2
Current Types

• Direct Current
• Alternating Current
• Pulsed Current

3
Direct Current

• Description
• One-directional flow of electrons
• Constant positive and negative poles
• Use
• Iontophoresis
• Low-voltage stimulation

4
Alternating Current

• Description
• Bidirectional flow of electrons
• No true positive and negative poles
• Use
• Interferential stimulation
• Premodulated currents

5
Pulsed Currents

• BIPHASIC CURRENT
• Description
• Bidirectional flow of electrons marked by periods
  of non-current flow
• Electrons flow on both sides of the baseline
  (positive and negative)
• Use
• Neuromuscular electrical stimulation
• Three types of biphasic currents

• MONOPHASIC CURRENT
• Description
• One-directional flow marked by periods of
  non-current flow
• Electrons stay on one side of the baseline or the
  other
• Use
• High voltage pulsed stimulation

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Biphasic Current Types

• Symmetrical
• Mirror images on each side of the baseline
• No net positive or negative charges under the
  electrodes
• Balanced Asymmetrical
• The shape of the pulse allows for anodal
  (positive) or cathodal (negative) effects
• No net positive or negative charge
• Unbalanced Asymmetrical
• Positive or negative effects
• The imbalance in positive and negative charges
  results in a net change over time. Can cause skin
  irritation if used for long durations

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Pulse Attributes
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Time-dependent Attributes

• Pulse duration
• Phase duration
• Interpulse interval
• Intrapulse interval
• Pulse period
• Pulse frequency
• Pulse trains (bursts)
• Note These attributes do not apply to direct and
  alternating currents

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Pulse Duration
Monophasic Pulse
Biphasic Pulse

• The time (horizontal distance) from when the
  pulse rises to the baseline to the point where it
  terminates on the baseline.
• instructor note click to start animation

10
Phase Duration
1
1
2
Monophasic Pulse
Biphasic Pulse

• Phases are individual portions of the pulse that
  appear on one side of the baseline
• For monophasic currents, pulse duration and phase
  duration are synonymous (only 1 phase).
• Biphasic pulses have two phase durations
• The phase duration determines which nerve type is
  affected.
• instructor note click to start animation

11
Interpulse Interval
Two Monophasic Pulses
Two Biphasic Pulses

• The time between the end of one pulse and the
  start of the next pulse
• Allows for mechanical changes in the tissues,
  such as when eliciting muscle contractions
• Increasing the pulse frequency decreases the
  interpulse interval and vice-versa
• instructor note click to start animation

12
Intrapulse Interval
Biphasic Pulse

• Intrapulse intervals are brief interruptions of
  current flow.
• Are always shorter than the interpulse interval.
• They allow for physiologic adaptations to the
  current and/or to decrease the total charge
  delivered by the pulse.
• Are normally not adjustable on the unit.
• Intrapulse intervals can also apply to monophasic
  currents.
• instructor note click to start animation

13
Pulse Period
Two Monophasic Pulses
Two Biphasic Pulses

• The pulse period is the amount of time from the
  start of one pulse to the start of the next
  pulse.
• Includes the phase durations, intrapulse
  interval,and interpulse interval.
• Inversely proportional to pulse frequency. As the
  pulse frequency increases, the pulse period
  decreases and vice-versa.
• instructor note click to start animation

14
Pulse Frequency

• The number of times a pulse occurs per second
• With alternating currents this measure is
  described as cycles per second

15
Pulse Trains (Bursts)

• Trains contain individual pulses
• Pulses in the train still have time-dependent
  characteristics pulse duration, interpulse
  interval, etc.
• Each train is separated by off times the
  intertrain (or interburst) interval

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Generator Attributes
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Current Density
10 in2 300 V 30 V/in2

• The amount of current per unit of area
• The higher the current density, the more intense
  the effects

5 in2 300 V 60 V/in2
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Duty Cycle

• The amount (percentage of time) that the current
  is flowing relative to the time it is not flowing
• Duty cycle ON/(ON OFF) 100
• Example
• Current is on for 20 seconds and is off for 40
  seconds
• DC 20/(2040)100
• DC 20/60 100
• DC 33.3

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Pulse Ramp

• Used with a duty cycle
• Gradually increases the current
• Produces a more natural contraction
• More comfortable

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Electrical Currents
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Measures of Electrical Current

• Charge
• Microcoulomb, the charge delivered per pulse
• Voltage
• The potential for electrical flow to occur.
• The difference in charges between the positive
  (anode) and negative (cathode) poles
• Current
• Amperage The rate of electron flow
• Wattage
• Measure of the ability to perform work
• Calculated as W Amperage Voltage
• Resistance
• Those structures (electrodes, wires, tissues)
  that do not transmit electrical energy

22
Average Current

• The amount of charge delivered by one-half of a
  pulse or a cycle
• Considers the amount of time required to deliver
  the charge

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Circuit Types

• Series Circuit
• Electrons only have one path to flow
• Parallel Circuit
• Electrons have multiple paths to travel
• The less the resistance within the path, the more
  flow that occurs
• In the body, different tissues have different
  resistances
• Nerves have relatively little resistance
• Bone has high resistance