Transcript Principles of Electrical Stimulation

Principles of
Electrical Stimulation
Current Types
 Direct Current
 Alternating Current
 Pulsed Current
Direct Current
Description:
 One-directional flow
of electrons
 Constant positive
and negative poles
Use:
 Iontophoresis
 Low-voltage
stimulation
Alternating Current
Description:
 Bidirectional flow of
electrons
 No true positive and
negative poles
Use:
 Interferential stimulation
 Premodulated currents
Pulsed Currents
MONOPHASIC CURRENT
Description:
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One-directional flow marked by periods of noncurrent flow
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Electrons stay on one side of the baseline or the
other
Use:
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High voltage pulsed stimulation
BIPHASIC CURRENT
Description:

Bidirectional flow of electrons marked by periods of
non-current flow
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Electrons flow on both sides of the baseline
(positive and negative)
Use:

Neuromuscular electrical stimulation

Three types of biphasic currents
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
Pulse Attributes
Time-dependent Attributes
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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
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.
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[instructor note: click to start animation]
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.
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[instructor note: click to start animation]
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]
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]
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]
Pulse Frequency
 The number of times a pulse occurs per
second
 With alternating currents this measure is
described as cycles per second
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
Generator
Attributes
Current Density
 The amount of current
per unit of area
 The higher the current
density, the more
intense the effects
10 in2
300 V
30 V/in2
5 in2
300 V
60 V/in2
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/(20+40)*100
 DC = 20/60 * 100
 DC = 33.3%
Pulse Ramp
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Used with a duty cycle
Gradually increases the current
Produces a more natural contraction
More comfortable
Electrical Currents
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
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
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