Transcript Principles of Electrical Stimulation

Principles of Electrical
Stimulation
© FA Davis, 2005
Current Types
• Direct Current
• Alternating Current
• Pulsed Current
© FA Davis, 2005
Direct Current
Description:
• One-directional flow
of electrons
• Constant positive and
negative poles
Use:
• Iontophoresis
• Low-voltage
stimulation
© FA Davis, 2005
Alternating Current
Description:
• bidirectional flow of
electrons
• No true positive and
negative poles
Use:
• Interferential
stimulation
• Premodulated
currents
© FA Davis, 2005
Pulsed Currents
MONOPHASIC
Description:
•
One-directional flow marked by periods of noncurrent flow
•
Electrons stay on one side of the baseline or the
other
Use:
•
High voltage pulsed stimulation
© FA Davis, 2005
BIPHASIC
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
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
© FA Davis, 2005
Pulse Attributes
© FA Davis, 2005
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
© FA Davis, 2005
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]
© FA Davis, 2005
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]
© FA Davis, 2005
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]
© FA Davis, 2005
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]
© FA Davis, 2005
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]
© FA Davis, 2005
Pulse Frequency
• The number of times a pulse occurs per second
• With alternating currents this measure is
described as cycles per second
© FA Davis, 2005
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
© FA Davis, 2005
Generator Attributes
© FA Davis, 2005
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
© FA Davis, 2005
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%
© FA Davis, 2005
Pulse Ramp
•
•
•
•
Used with a duty cycle
Gradually increases the current
Produces a more natural contraction
More comfortable
© FA Davis, 2005
Electrical Currents
© FA Davis, 2005
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
© FA Davis, 2005
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
© FA Davis, 2005
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
© FA Davis, 2005