Electrical AgentsElectrical Agents

Chapter 5Chapter 5

Direct CurrentsDirect Currents Characterized by a continuous flow of Characterized by a continuous flow of

electrons in one directionelectrons in one direction The basic pattern of DC flow is the The basic pattern of DC flow is the

square wave and is recognized by square wave and is recognized by continuous current flow on only one continuous current flow on only one side of the baselineside of the baseline

Despite fluctuations in voltage or Despite fluctuations in voltage or amperage, the current flow remains amperage, the current flow remains in one direction and stays on one in one direction and stays on one side of the baseline side of the baseline

The term galvanic is used to describe The term galvanic is used to describe uninterrupted direct currentuninterrupted direct current

Most common example of a DC current is a Most common example of a DC current is a flashlight.flashlight.– The battery possesses a positive flow, which lacks The battery possesses a positive flow, which lacks

electrons, and a negative pole, which has excess electrons, and a negative pole, which has excess electronselectrons

– Electrons leave the negative pole of the battery and Electrons leave the negative pole of the battery and flow through a wire to the bulb.flow through a wire to the bulb.

– After leaving the bulb, the electrons return to the After leaving the bulb, the electrons return to the positive pole of the battery.positive pole of the battery.

– When the number of electrons at the negative pole When the number of electrons at the negative pole equals the number at the positive pole, no further equals the number at the positive pole, no further potential for current flow exsistspotential for current flow exsists

– The battery is deadThe battery is dead

Alternating CurrentsAlternating Currents

The direction and magnitude of the The direction and magnitude of the flow reverses with an AC, although flow reverses with an AC, although the magnitude may not be equal in the magnitude may not be equal in both directionsboth directions

Unlike a DC, an AC circuit possesses Unlike a DC, an AC circuit possesses no true positive or negative flow.no true positive or negative flow.

Electrons, rather than constantly Electrons, rather than constantly moving in one direction, shuffle back moving in one direction, shuffle back and forth between the two electrodes and forth between the two electrodes as the electrodes take turns being as the electrodes take turns being the positive and negative polesthe positive and negative poles

Household electricity uses AC.Household electricity uses AC. Consider the flashlight exampleConsider the flashlight example If a battery were placed on a device If a battery were placed on a device

that allowed it to rotate between the that allowed it to rotate between the 2 wires, we could more or less 2 wires, we could more or less duplicate an AC current.duplicate an AC current.

Electrons would flow away from Electrons would flow away from terminal A when the cathode is in terminal A when the cathode is in line with it.line with it.

When the anode aligns with terminal When the anode aligns with terminal A electrons would flow towards itA electrons would flow towards it

The basic pattern of an AC is the sine The basic pattern of an AC is the sine wavewave

The amplitude, or “peak value,” of an AC The amplitude, or “peak value,” of an AC wave is determined by measuring the wave is determined by measuring the maximal distance to which the wave rises maximal distance to which the wave rises above or below the baseline.above or below the baseline.

In the case of the pure sine wave, a peak In the case of the pure sine wave, a peak value of 100V appears on one side of the value of 100V appears on one side of the baseline without regard to its durationbaseline without regard to its duration

Peak-to-peak value is measured from the Peak-to-peak value is measured from the peak on the positive side of the baseline to peak on the positive side of the baseline to the peak on the negative sidethe peak on the negative side

Peak-to-peak values are absolute. So if Peak-to-peak values are absolute. So if you have 100V on the positive side and -you have 100V on the positive side and -20V on the negative side it still equals 20V on the negative side it still equals 120V for the peak-to-peak value 120V for the peak-to-peak value

The cycle duration of an AC is measured The cycle duration of an AC is measured from the originating point on the baseline from the originating point on the baseline to its terminating point.to its terminating point.

It represents the amount of time required It represents the amount of time required to complete one full cycleto complete one full cycle

The number of times that the current The number of times that the current reverses direction in 1 second is the reverses direction in 1 second is the current’s number of cycles per second and current’s number of cycles per second and is measured in hertzis measured in hertz

An AC of 100Hz would change its direction An AC of 100Hz would change its direction of flow 100 times during 1 secondof flow 100 times during 1 second

One current of 1 MHz woud change its One current of 1 MHz woud change its direction 1 million times a seconddirection 1 million times a second

Because AC’s are measured in cycles Because AC’s are measured in cycles per second, as the duration of the per second, as the duration of the cycles increases, fewer cycles per cycles increases, fewer cycles per second can occur second can occur

Although amplitude is often used to Although amplitude is often used to describe the magnitude of an describe the magnitude of an electrical current, it does not take electrical current, it does not take into account the actual amount of into account the actual amount of time that the current is flowingtime that the current is flowing

Pulsed CurrentsPulsed Currents

Pulsed currents are the unidirectional Pulsed currents are the unidirectional (monophasic) or bidirectional (monophasic) or bidirectional (biphasic) flow of electrons that are (biphasic) flow of electrons that are interrupted by discrete periods of interrupted by discrete periods of noncurrent flow.noncurrent flow.

Using the analogy from the DC flow, Using the analogy from the DC flow, turning the switch no and off, turning the switch no and off, causing the light to blink, is an causing the light to blink, is an example of a monophasic current.example of a monophasic current.

However, the pulses occur at a much However, the pulses occur at a much more rapid progressionmore rapid progression

The building block of pulsed currents The building block of pulsed currents is the phaseis the phase

A phase is the individual section of a A phase is the individual section of a pulse that rises above or below the pulse that rises above or below the baseline for a measurable period of baseline for a measurable period of timetime

The number and type of phases than The number and type of phases than classify the type of pulse and, classify the type of pulse and, ultimately, the charge delivered by ultimately, the charge delivered by each phase is what affects the body’s each phase is what affects the body’s tissuetissue

Monophasic CurrentsMonophasic Currents

Monophasic pulses have only one Monophasic pulses have only one phase to a single pulse, and the phase to a single pulse, and the current flow is unidirectionalcurrent flow is unidirectional

Each pulse consists of only one Each pulse consists of only one component part, the phase.component part, the phase.

Despite the different shapes involved, Despite the different shapes involved, there is only one phase, and it there is only one phase, and it remains on one side of the baselineremains on one side of the baseline

In this type of electrical current, amplitude In this type of electrical current, amplitude is the maximal distance to which the wave is the maximal distance to which the wave rises above the baseline, and the duration rises above the baseline, and the duration is measured as the distance required to is measured as the distance required to complete one full waveformcomplete one full waveform

The horizontal baseline is labeled as The horizontal baseline is labeled as “time,” so the distance a waveform travels “time,” so the distance a waveform travels represents the duration that the pulse is represents the duration that the pulse is flowingflowing

With monophasic currents, the terms With monophasic currents, the terms “pulse,” “phase,” and “waveform,” are “pulse,” “phase,” and “waveform,” are synonymoussynonymous

Biphasic CurrentsBiphasic Currents

Biphasic currents each occurring on Biphasic currents each occurring on opposite sides of the baselineopposite sides of the baseline

The lead phase of the pulse is the The lead phase of the pulse is the first area rising above or below the first area rising above or below the baselinebaseline

Then the terminating phase occurs in Then the terminating phase occurs in the opposite directionthe opposite direction

The pulse represented in the figure is The pulse represented in the figure is considered symmetrical because the considered symmetrical because the 2 phases equal in their magnitude 2 phases equal in their magnitude and durationand duration

In this case, each phase has equal, In this case, each phase has equal, but opposite, electrical balancebut opposite, electrical balance

The next figures represent The next figures represent asymmetrical pulses because each asymmetrical pulses because each phase in the pulse has a different phase in the pulse has a different shapeshape

When asymmetrical pulses are used, When asymmetrical pulses are used, the characteristics of each phase the characteristics of each phase should be considered separatelyshould be considered separately

If the charges of both phases are If the charges of both phases are equal, the pulse is balancedequal, the pulse is balanced

Otherwise it is unbalancedOtherwise it is unbalanced

Where as the phases in a symmetrical Where as the phases in a symmetrical pulse or balanced asymmetrical pulse pulse or balanced asymmetrical pulse cause the physiological effects of cause the physiological effects of positive and negative current flow to positive and negative current flow to cancel each other outcancel each other out

Unbalanced asymmetrical pulses may Unbalanced asymmetrical pulses may lead to residual physiological changes lead to residual physiological changes based on the remaining net polaritybased on the remaining net polarity

Symmetrical biphasic waveforms tend Symmetrical biphasic waveforms tend to be the most comfortable because to be the most comfortable because they deliver relatively lower charge per they deliver relatively lower charge per phasephase

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Pulse attributesPulse attributes Pulse and phase durationPulse and phase duration Pulse intervalPulse interval Pulse periodPulse period Pulse charge Pulse charge Pulse frequencyPulse frequency Measures of electrical current flowMeasures of electrical current flow

Pulse AttributesPulse Attributes

The charge produced by an electrical The charge produced by an electrical generator is dependent on the generator is dependent on the duration and amplitude of the pulse.duration and amplitude of the pulse.

The relationship between intensity and The relationship between intensity and duration of a single pulse determines duration of a single pulse determines the total charge delivered to the bodythe total charge delivered to the body

Increasing the amplitude and/or Increasing the amplitude and/or duration increases the total charge of duration increases the total charge of the pulse.the pulse.

Pulse and phase durationPulse and phase duration

Time is represented on the horizontal axis (or Time is represented on the horizontal axis (or baseline)baseline)

The distance that a pulse covers on the The distance that a pulse covers on the horizontal axis represents the horizontal axis represents the pulse durationpulse duration

Pulse duration- Pulse duration- the time elapsed from the the time elapsed from the beginning of the phase to the conclusion of beginning of the phase to the conclusion of the final phase, including the pulse intervalthe final phase, including the pulse interval

Phase duration- Phase duration- the time required for each the time required for each component phase to complete its shapecomponent phase to complete its shape

In a monophasic current, the pulse In a monophasic current, the pulse duration and phase duration are duration and phase duration are equivalent terms.equivalent terms.

In biphasic currents, the pulse In biphasic currents, the pulse duration is the sum total of the two duration is the sum total of the two phase durations.phase durations.

Note that pulse durations cannot be Note that pulse durations cannot be measured for uninterrupted direct or measured for uninterrupted direct or alternating currents.alternating currents.

The phase duration is the most The phase duration is the most important factor in determining what important factor in determining what type of tissues will be stimulated.type of tissues will be stimulated.

If the phase duration is too short, the If the phase duration is too short, the current will not be able to overcome current will not be able to overcome the nerve membrane and no action the nerve membrane and no action potential will be elicitedpotential will be elicited

As the phase duration is increased, As the phase duration is increased, different tissues are depolarized by different tissues are depolarized by the electrical current the electrical current

Interpulse interval-Interpulse interval- the duration of the duration of time between the conclusion of one time between the conclusion of one pulse and the initiation of the next.pulse and the initiation of the next.

Intrapulse interval-Intrapulse interval- an interruption of an interruption of a single pulse or phase.a single pulse or phase.– The intrapulse interval allows time for The intrapulse interval allows time for

certain metabolic events, such as certain metabolic events, such as repolarization of cell membranesrepolarization of cell membranes

– An interpulse interval provides time for An interpulse interval provides time for mechanical and chemical recharging to mechanical and chemical recharging to occuroccur

The pulse period is the time elapsed The pulse period is the time elapsed between the initiation of one pulse between the initiation of one pulse and the start of the subsequent one.and the start of the subsequent one.– Basically the pulse duration and the Basically the pulse duration and the

pulse interval.pulse interval. Uninterrupted currents (alternating Uninterrupted currents (alternating

and direct currents) do not posses and direct currents) do not posses pulses.pulses.

Therefore, pulse duration and pulse Therefore, pulse duration and pulse periods do not exist for these types periods do not exist for these types of currentsof currents

Pulse ChargePulse Charge

Is a measurement of the number of Is a measurement of the number of electrons contained within a pulseelectrons contained within a pulse

A charge of a pulse is expressed in A charge of a pulse is expressed in microcoulombsmicrocoulombs

Most electrotherapeutic modalities Most electrotherapeutic modalities produce charges measured in produce charges measured in microcoulombs (10microcoulombs (10-6-6))

The pulse charge is a function of the The pulse charge is a function of the amount of area within the waveform amount of area within the waveform

Increasing or decreasing the Increasing or decreasing the amplitude alters the charge of pulse amplitude alters the charge of pulse accordingly accordingly

The shape of the waveform may also The shape of the waveform may also be altered to deliver more or less be altered to deliver more or less charge to the tissues per pulsecharge to the tissues per pulse

Pulse frequencyPulse frequency

Low <10pps= individual muscle Low <10pps= individual muscle contractions (twitch)contractions (twitch)

Moderate 10-50pps= summation of Moderate 10-50pps= summation of individual contractions resulting in individual contractions resulting in increased muscle toneincreased muscle tone

High >50 tonic contractionHigh >50 tonic contraction

Electrical stimulation goals and Electrical stimulation goals and techniquestechniques

Muscle contractionsMuscle contractions– Any type of electrotherapeutic modality Any type of electrotherapeutic modality

can elicit a contraction in normal, healthy can elicit a contraction in normal, healthy muscle, if applied at a sufficient intensity, muscle, if applied at a sufficient intensity, by causing a depolarization of the motor by causing a depolarization of the motor nerve’s membrane.nerve’s membrane.

Electrical stimulation has been Electrical stimulation has been demonstrated to be as effective as demonstrated to be as effective as voluntary muscle contraction in voluntary muscle contraction in strengthening the quads when used strengthening the quads when used during the first 4 weeks after ACL during the first 4 weeks after ACL surgery.surgery.

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Pulse amplitudePulse amplitude Pulse frequencyPulse frequency Phase durationPhase duration Strength augmentationStrength augmentation Pain controlPain control Wound healingWound healing Control and reduction of edemaControl and reduction of edema Fracture healing Fracture healing How and why to use the different How and why to use the different

modalitiesmodalities