Principles of Principles of Electrical StimulationElectrical Stimulation

Current TypesCurrent Types

Direct CurrentDirect Current Alternating CurrentAlternating Current Pulsed CurrentPulsed Current

Direct CurrentDirect Current

Description:Description: One-directional flow One-directional flow

of electronsof electrons Constant positive Constant positive

and negative polesand negative polesUse:Use: IontophoresisIontophoresis Low-voltage Low-voltage

stimulationstimulation

Alternating CurrentAlternating Current

Description:Description: Bidirectional flow of Bidirectional flow of

electronselectrons No true positive and No true positive and

negative polesnegative poles

Use:Use: Interferential stimulationInterferential stimulation Premodulated currentsPremodulated currents

Pulsed CurrentsPulsed Currents

MONOPHASIC CURRENTMONOPHASIC CURRENTDescription:Description: One-directional flow marked by periods of non-One-directional flow marked by periods of non-

current flowcurrent flow Electrons stay on one side of the baseline or the Electrons stay on one side of the baseline or the

otherotherUse:Use: High voltage pulsed stimulationHigh voltage pulsed stimulation

BIPHASIC CURRENTBIPHASIC CURRENTDescription:Description: Bidirectional flow of electrons marked by periods of Bidirectional flow of electrons marked by periods of

non-current flownon-current flow Electrons flow on both sides of the baseline Electrons flow on both sides of the baseline

(positive and negative)(positive and negative)Use:Use: Neuromuscular electrical stimulationNeuromuscular electrical stimulation Three types of biphasic currentsThree types of biphasic currents

Biphasic Current TypesBiphasic Current TypesSymmetricalSymmetrical

Mirror images on each side of the baselineMirror images on each side of the baseline No net positive or negative charges under the electrodes No net positive or negative charges under the electrodes

Balanced AsymmetricalBalanced Asymmetrical The shape of the pulse allows for anodal (positive) or The shape of the pulse allows for anodal (positive) or

cathodal (negative) effectscathodal (negative) effects No net positive or negative chargeNo net positive or negative charge

Unbalanced AsymmetricalUnbalanced Asymmetrical Positive or negative effects Positive or negative effects The imbalance in positive and negative charges results The imbalance in positive and negative charges results

in a net change over time. Can cause skin irritation if in a net change over time. Can cause skin irritation if used for long durationsused for long durations

Pulse AttributesPulse Attributes

Time-dependent AttributesTime-dependent Attributes

Pulse durationPulse duration Phase durationPhase duration Interpulse intervalInterpulse interval Intrapulse intervalIntrapulse interval Pulse periodPulse period Pulse frequencyPulse frequency Pulse trains (bursts)Pulse trains (bursts)Note: These attributes do not apply to direct and Note: These attributes do not apply to direct and

alternating currentsalternating currents

Pulse DurationPulse Duration

The time (horizontal distance) from when the pulse The time (horizontal distance) from when the pulse rises to the baseline to the point where it terminates on rises to the baseline to the point where it terminates on the baseline.the baseline.

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Monophasic Pulse Biphasic Pulse

Phase DurationPhase Duration

Phases are individual portions of the pulse that appear on one side Phases are individual portions of the pulse that appear on one side of the baselineof the baseline

For monophasic currents, pulse duration and phase duration are For monophasic currents, pulse duration and phase duration are synonymous (only 1 phase).synonymous (only 1 phase).

Biphasic pulses have two phase durationsBiphasic pulses have two phase durations The phase duration determines which nerve type is affected.The phase duration determines which nerve type is affected. [[instructor note: click to start animationinstructor note: click to start animation]]

1 1

Monophasic Pulse Biphasic Pulse

2

Interpulse IntervalInterpulse Interval

The time between the end of one pulse and the start of the next The time between the end of one pulse and the start of the next pulsepulse

Allows for mechanical changes in the tissues, such as when eliciting Allows for mechanical changes in the tissues, such as when eliciting muscle contractionsmuscle contractions

Increasing the pulse frequency decreases the interpulse interval and Increasing the pulse frequency decreases the interpulse interval and vice-versavice-versa

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Two Monophasic Pulses Two Biphasic Pulses

Intrapulse IntervalIntrapulse Interval

Intrapulse intervals are brief interruptions of current flow.Intrapulse intervals are brief interruptions of current flow. Are always shorter than the interpulse interval.Are always shorter than the interpulse interval. They allow for physiologic adaptations to the current and/or to They allow for physiologic adaptations to the current and/or to

decrease the total charge delivered by the pulse.decrease the total charge delivered by the pulse. Are normally not adjustable on the unit.Are normally not adjustable on the unit. Intrapulse intervals can also apply to monophasic currents.Intrapulse intervals can also apply to monophasic currents. [[instructor note: click to start animationinstructor note: click to start animation]]

Biphasic Pulse

Pulse PeriodPulse Period

The pulse period is the amount of time from the start of one pulse to The pulse period is the amount of time from the start of one pulse to the start of the next pulse.the start of the next pulse.

Includes the phase durations, intrapulse interval,and interpulse Includes the phase durations, intrapulse interval,and interpulse interval.interval.

Inversely proportional to pulse frequency. As the pulse frequency Inversely proportional to pulse frequency. As the pulse frequency increases, the pulse period decreases and vice-versa.increases, the pulse period decreases and vice-versa.

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Two Monophasic Pulses Two Biphasic Pulses

Pulse FrequencyPulse Frequency

The number of times a pulse occurs per The number of times a pulse occurs per secondsecond

With alternating currents this measure is With alternating currents this measure is described as cycles per seconddescribed as cycles per second

Pulse Trains (Bursts)Pulse Trains (Bursts)

Trains contain individual pulsesTrains contain individual pulses Pulses in the train still have time-dependent Pulses in the train still have time-dependent

characteristics: pulse duration, interpulse interval, etc.characteristics: pulse duration, interpulse interval, etc. Each train is separated by “off” times – the intertrain (or Each train is separated by “off” times – the intertrain (or

interburst) intervalinterburst) interval

Generator AttributesGenerator Attributes

Current DensityCurrent Density

The amount of current The amount of current per unit of areaper unit of area

The higher the current The higher the current density, the more density, the more intense the effectsintense the effects

10 in2

300 V30 V/in2

5 in2

300 V60 V/in2

Duty CycleDuty Cycle

The amount (percentage of time) that the The amount (percentage of time) that the current is flowing relative to the time it is not current is flowing relative to the time it is not flowingflowing Duty cycle = “ON”/(“ON + OFF”) * 100Duty cycle = “ON”/(“ON + OFF”) * 100

Example:Example: Current is on for 20 seconds and is off for 40 Current is on for 20 seconds and is off for 40

secondsseconds DC = 20/(20+40)*100DC = 20/(20+40)*100 DC = 20/60 * 100DC = 20/60 * 100 DC = 33.3% DC = 33.3%

Pulse RampPulse Ramp

Used with a duty cycleUsed with a duty cycle Gradually increases the currentGradually increases the current Produces a more natural contractionProduces a more natural contraction More comfortableMore comfortable

Electrical CurrentsElectrical Currents

Measures of Electrical Measures of Electrical CurrentCurrent

Charge: Charge: Microcoulomb, the charge delivered per pulseMicrocoulomb, the charge delivered per pulse

Voltage:Voltage: The potential for electrical flow to occur. The potential for electrical flow to occur. The difference in charges between the positive (anode) and negative The difference in charges between the positive (anode) and negative

(cathode) poles(cathode) poles Current:Current:

Amperage: The rate of electron flowAmperage: The rate of electron flow Wattage:Wattage:

Measure of the ability to perform workMeasure of the ability to perform work Calculated as W = Amperage * VoltageCalculated as W = Amperage * Voltage

Resistance:Resistance: Those structures (electrodes, wires, tissues) that do not transmit Those structures (electrodes, wires, tissues) that do not transmit

electrical energyelectrical energy

Average CurrentAverage Current

The amount of charge delivered by one-half of The amount of charge delivered by one-half of a pulse or a cyclea pulse or a cycle

Considers the amount of time required to Considers the amount of time required to deliver the chargedeliver the charge

Circuit TypesCircuit Types

Series CircuitSeries Circuit Electrons only have one path to flowElectrons only have one path to flow

Parallel CircuitParallel Circuit Electrons have multiple paths to travelElectrons have multiple paths to travel The less the resistance within the path, the more The less the resistance within the path, the more

flow that occursflow that occurs In the body, different tissues have different In the body, different tissues have different

resistancesresistances Nerves have relatively little resistanceNerves have relatively little resistance Bone has high resistanceBone has high resistance