Electrical Agents Chapter 5

Direct Currents Characterized by a continuous flow of electrons in one direction Characterized by a continuous flow of electrons in one direction The basic pattern of DC flow is the square wave and is recognized by continuous current flow on only one side of the baseline The basic pattern of DC flow is the square wave and is recognized by continuous current flow on only one side of the baseline Despite fluctuations in voltage or amperage, the current flow remains in one direction and stays on one side of the baseline Despite fluctuations in voltage or amperage, the current flow remains in one direction and stays on one side of the baseline

The term galvanic is used to describe uninterrupted direct current The term galvanic is used to describe uninterrupted direct current Most common example of a DC current is a flashlight. Most common example of a DC current is a flashlight. –The battery possesses a positive flow, which lacks electrons, and a negative pole, which has excess electrons –Electrons leave the negative pole of the battery and flow through a wire to the bulb. –After leaving the bulb, the electrons return to the positive pole of the battery. –When the number of electrons at the negative pole equals the number at the positive pole, no further potential for current flow exsists –The battery is dead

Alternating Currents The direction and magnitude of the flow reverses with an AC, although the magnitude may not be equal in both directions The direction and magnitude of the flow reverses with an AC, although the magnitude may not be equal in both directions Unlike a DC, an AC circuit possesses no true positive or negative flow. Unlike a DC, an AC circuit possesses no true positive or negative flow. Electrons, rather than constantly moving in one direction, shuffle back and forth between the two electrodes as the electrodes take turns being the positive and negative poles Electrons, rather than constantly moving in one direction, shuffle back and forth between the two electrodes as the electrodes take turns being the positive and negative poles

Household electricity uses AC. Household electricity uses AC. Consider the flashlight example Consider the flashlight example If a battery were placed on a device that allowed it to rotate between the 2 wires, we could more or less duplicate an AC current. If a battery were placed on a device that allowed it to rotate between the 2 wires, we could more or less duplicate an AC current. Electrons would flow away from terminal A when the cathode is in line with it. Electrons would flow away from terminal A when the cathode is in line with it. When the anode aligns with terminal A electrons would flow towards it When the anode aligns with terminal A electrons would flow towards it The basic pattern of an AC is the sine wave The basic pattern of an AC is the sine wave

The amplitude, or “peak value,” of an AC wave is determined by measuring the maximal distance to which the wave rises above or below the baseline. The amplitude, or “peak value,” of an AC wave is determined by measuring the maximal distance to which the wave rises above or below the baseline. In the case of the pure sine wave, a peak value of 100V appears on one side of the baseline without regard to its duration In the case of the pure sine wave, a peak value of 100V appears on one side of the baseline without regard to its duration Peak-to-peak value is measured from the peak on the positive side of the baseline to the peak on the negative side Peak-to-peak value is measured from the peak on the positive side of the baseline to the peak on the negative side Peak-to-peak values are absolute. So if you have 100V on the positive side and -20V on the negative side it still equals 120V for the peak-to- peak value Peak-to-peak values are absolute. So if you have 100V on the positive side and -20V on the negative side it still equals 120V for the peak-to- peak value

The cycle duration of an AC is measured from the originating point on the baseline to its terminating point. The cycle duration of an AC is measured from the originating point on the baseline to its terminating point. It represents the amount of time required to complete one full cycle It represents the amount of time required to complete one full cycle The number of times that the current reverses direction in 1 second is the current’s number of cycles per second and is measured in hertz The number of times that the current reverses direction in 1 second is the current’s number of cycles per second and is measured in hertz An AC of 100Hz would change its direction of flow 100 times during 1 second An AC of 100Hz would change its direction of flow 100 times during 1 second One current of 1 MHz woud change its direction 1 million times a second One current of 1 MHz woud change its direction 1 million times a second

Because AC’s are measured in cycles per second, as the duration of the cycles increases, fewer cycles per second can occur Because AC’s are measured in cycles per second, as the duration of the cycles increases, fewer cycles per second can occur Although amplitude is often used to describe the magnitude of an electrical current, it does not take into account the actual amount of time that the current is flowing Although amplitude is often used to describe the magnitude of an electrical current, it does not take into account the actual amount of time that the current is flowing

Pulsed Currents Pulsed currents are the unidirectional (monophasic) or bidirectional (biphasic) flow of electrons that are interrupted by discrete periods of noncurrent flow. Pulsed currents are the unidirectional (monophasic) or bidirectional (biphasic) flow of electrons that are interrupted by discrete periods of noncurrent flow. Using the analogy from the DC flow, turning the switch no and off, causing the light to blink, is an example of a monophasic current. Using the analogy from the DC flow, turning the switch no and off, causing the light to blink, is an example of a monophasic current. However, the pulses occur at a much more rapid progression However, the pulses occur at a much more rapid progression

The building block of pulsed currents is the phase The building block of pulsed currents is the phase A phase is the individual section of a pulse that rises above or below the baseline for a measurable period of time A phase is the individual section of a pulse that rises above or below the baseline for a measurable period of time The number and type of phases than classify the type of pulse and, ultimately, the charge delivered by each phase is what affects the body’s tissue The number and type of phases than classify the type of pulse and, ultimately, the charge delivered by each phase is what affects the body’s tissue

Monophasic Currents Monophasic pulses have only one phase to a single pulse, and the current flow is unidirectional Monophasic pulses have only one phase to a single pulse, and the current flow is unidirectional Each pulse consists of only one component part, the phase. Each pulse consists of only one component part, the phase. Despite the different shapes involved, there is only one phase, and it remains on one side of the baseline Despite the different shapes involved, there is only one phase, and it remains on one side of the baseline

In this type of electrical current, amplitude is the maximal distance to which the wave rises above the baseline, and the duration is measured as the distance required to complete one full waveform In this type of electrical current, amplitude is the maximal distance to which the wave rises above the baseline, and the duration is measured as the distance required to complete one full waveform The horizontal baseline is labeled as “time,” so the distance a waveform travels represents the duration that the pulse is flowing The horizontal baseline is labeled as “time,” so the distance a waveform travels represents the duration that the pulse is flowing With monophasic currents, the terms “pulse,” “phase,” and “waveform,” are synonymous With monophasic currents, the terms “pulse,” “phase,” and “waveform,” are synonymous

Biphasic Currents Biphasic currents each occurring on opposite sides of the baseline Biphasic currents each occurring on opposite sides of the baseline The lead phase of the pulse is the first area rising above or below the baseline The lead phase of the pulse is the first area rising above or below the baseline Then the terminating phase occurs in the opposite direction Then the terminating phase occurs in the opposite direction The pulse represented in the figure is considered symmetrical because the 2 phases equal in their magnitude and duration The pulse represented in the figure is considered symmetrical because the 2 phases equal in their magnitude and duration

In this case, each phase has equal, but opposite, electrical balance In this case, each phase has equal, but opposite, electrical balance The next figures represent asymmetrical pulses because each phase in the pulse has a different shape The next figures represent asymmetrical pulses because each phase in the pulse has a different shape When asymmetrical pulses are used, the characteristics of each phase should be considered separately When asymmetrical pulses are used, the characteristics of each phase should be considered separately If the charges of both phases are equal, the pulse is balanced If the charges of both phases are equal, the pulse is balanced Otherwise it is unbalanced Otherwise it is unbalanced

Where as the phases in a symmetrical pulse or balanced asymmetrical pulse cause the physiological effects of positive and negative current flow to cancel each other out Where as the phases in a symmetrical pulse or balanced asymmetrical pulse cause the physiological effects of positive and negative current flow to cancel each other out Unbalanced asymmetrical pulses may lead to residual physiological changes based on the remaining net polarity Unbalanced asymmetrical pulses may lead to residual physiological changes based on the remaining net polarity Symmetrical biphasic waveforms tend to be the most comfortable because they deliver relatively lower charge per phase Symmetrical biphasic waveforms tend to be the most comfortable because they deliver relatively lower charge per phase

Next time Pulse attributes Pulse attributes Pulse and phase duration Pulse and phase duration Pulse interval Pulse interval Pulse period Pulse period Pulse charge Pulse charge Pulse frequency Pulse frequency Measures of electrical current flow Measures of electrical current flow

Pulse Attributes The charge produced by an electrical generator is dependent on the duration and amplitude of the pulse. The charge produced by an electrical generator is dependent on the duration and amplitude of the pulse. The relationship between intensity and duration of a single pulse determines the total charge delivered to the body The relationship between intensity and duration of a single pulse determines the total charge delivered to the body Increasing the amplitude and/or duration increases the total charge of the pulse. Increasing the amplitude and/or duration increases the total charge of the pulse.

Pulse and phase duration Time is represented on the horizontal axis (or baseline) Time is represented on the horizontal axis (or baseline) The distance that a pulse covers on the horizontal axis represents the pulse duration The distance that a pulse covers on the horizontal axis represents the pulse duration Pulse duration- the time elapsed from the beginning of the phase to the conclusion of the final phase, including the pulse interval Pulse duration- the time elapsed from the beginning of the phase to the conclusion of the final phase, including the pulse interval Phase duration- the time required for each component phase to complete its shape Phase duration- the time required for each component phase to complete its shape

In a monophasic current, the pulse duration and phase duration are equivalent terms. In a monophasic current, the pulse duration and phase duration are equivalent terms. In biphasic currents, the pulse duration is the sum total of the two phase durations. In biphasic currents, the pulse duration is the sum total of the two phase durations. Note that pulse durations cannot be measured for uninterrupted direct or alternating currents. Note that pulse durations cannot be measured for uninterrupted direct or alternating currents.

The phase duration is the most important factor in determining what type of tissues will be stimulated. The phase duration is the most important factor in determining what type of tissues will be stimulated. If the phase duration is too short, the current will not be able to overcome the nerve membrane and no action potential will be elicited If the phase duration is too short, the current will not be able to overcome the nerve membrane and no action potential will be elicited As the phase duration is increased, different tissues are depolarized by the electrical current As the phase duration is increased, different tissues are depolarized by the electrical current

Interpulse interval- the duration of time between the conclusion of one pulse and the initiation of the next. Interpulse interval- the duration of time between the conclusion of one pulse and the initiation of the next. Intrapulse interval- an interruption of a single pulse or phase. Intrapulse interval- an interruption of a single pulse or phase. –The intrapulse interval allows time for certain metabolic events, such as repolarization of cell membranes –An interpulse interval provides time for mechanical and chemical recharging to occur

The pulse period is the time elapsed between the initiation of one pulse and the start of the subsequent one. The pulse period is the time elapsed between the initiation of one pulse and the start of the subsequent one. –Basically the pulse duration and the pulse interval. Uninterrupted currents (alternating and direct currents) do not posses pulses. Uninterrupted currents (alternating and direct currents) do not posses pulses. Therefore, pulse duration and pulse periods do not exist for these types of currents Therefore, pulse duration and pulse periods do not exist for these types of currents

Pulse Charge Is a measurement of the number of electrons contained within a pulse Is a measurement of the number of electrons contained within a pulse A charge of a pulse is expressed in microcoulombs A charge of a pulse is expressed in microcoulombs Most electrotherapeutic modalities produce charges measured in microcoulombs (10 -6 ) Most electrotherapeutic modalities produce charges measured in microcoulombs (10 -6 ) The pulse charge is a function of the amount of area within the waveform The pulse charge is a function of the amount of area within the waveform

Increasing or decreasing the amplitude alters the charge of pulse accordingly Increasing or decreasing the amplitude alters the charge of pulse accordingly The shape of the waveform may also be altered to deliver more or less charge to the tissues per pulse The shape of the waveform may also be altered to deliver more or less charge to the tissues per pulse

Pulse frequency Low <10pps= individual muscle contractions (twitch) Low <10pps= individual muscle contractions (twitch) Moderate 10-50pps= summation of individual contractions resulting in increased muscle tone Moderate 10-50pps= summation of individual contractions resulting in increased muscle tone High >50 tonic contraction High >50 tonic contraction

Electrical stimulation goals and techniques Muscle contractions Muscle contractions –Any type of electrotherapeutic modality can elicit a contraction in normal, healthy muscle, if applied at a sufficient intensity, by causing a depolarization of the motor nerve’s membrane. Electrical stimulation has been demonstrated to be as effective as voluntary muscle contraction in strengthening the quads when used during the first 4 weeks after ACL surgery. Electrical stimulation has been demonstrated to be as effective as voluntary muscle contraction in strengthening the quads when used during the first 4 weeks after ACL surgery.

Next time Pulse amplitude Pulse amplitude Pulse frequency Pulse frequency Phase duration Phase duration Strength augmentation Strength augmentation Pain control Pain control Wound healing Wound healing Control and reduction of edema Control and reduction of edema Fracture healing Fracture healing How and why to use the different modalities How and why to use the different modalities