Electrotherapy II Lecture Notes PDF

Electrotherapy II 1st lecture Introduction into electrical stimulation and electrical currents D r. A h m ed a b o u lfotouh  Objectives - Define electrical stimulation and electric current. - Differentiate between alternating, direct, and pu...

Electrotherapy II 1st lecture Introduction into electrical stimulation and electrical currents D r. A h m ed a b o u lfotouh  Objectives - Define electrical stimulation and electric current. - Differentiate between alternating, direct, and pulsed currents. - Categorize various waveforms and pulse characteristics. -Identify the different parameters of electrical stimulation.  Introduction Electrical stimulation is the application of stimulation by using electrical currents that have special characteristics to elicit or facilitate some desired therapeutic response. - The general 3 uses of electrical stimulation (ES) is : 1- Activate skeletal muscle for strengthening or improving volitional movement 2- Decreasing pain 3- Facilitating tissue healing all are based on the stimulation of tissues from applied electric currents.  Electrical stimulation , How? - Electrical stimulation can be applied to the body in a variety of ways. - The electricity may be delivered by a stimulator implanted in the body, as occurs with cardiac pacemakers and spinal cord stimulators, or an external stimulator can be used to deliver current to implanted or external, surface, transcutaneous electrodes. - In physical therapy clinical practice the electrical stimulation is conducted by using an external stimulator to deliver current through external, surface, transcutaneous electrodes.  Basics of electricity - To discuss clinical applications and use of electrotherapy without first addressing the fundamentals of electricity is like asking someone to play a game without telling them how. - A functional and useful understanding of electrotherapy must include and begin with the basics.  Electrical Current Electrical Current is the movement of ions or electrons in a conductor in response to a voltage force. - The flow of current is directly proportional to the magnitude of the driving force (i.e., the voltage). - The international unit for current is the ampere (amp or A), but most therapeutic applications of current use milliamperes (mA, or thousandths of an ampere) or microamperes (A or millionths of an ampere)  Types of currents and waveforms - There are two main types of electrical currents: direct current and alternating current. - Although these currents can be used for therapeutic purposes, the most common form of current used in electrotherapeutics is pulsed current, or pulsatile current. -In regard to applied science, pulsed current is the third major class of electrical current. So, - Electrical current waveforms can be considered to be of three types: direct current (DC), alternating current (AC), and pulsed current (PC).  The wave form - When you begin to use terms to explain the shape, magnitude, and duration of currents, you are describing the current waveform. - The waveform is simply a depiction or representation of the characteristics that represent a given current. - All currents have parameters in the vertical (y coordinate) and horizontal (x coordinate) directions. - Parameters in the horizontal axis are used to describe and quantify time or duration characteristics of current (in milli- or microseconds), whereas parameters in the vertical axis are used to describe or quantify magnitude or intensity (in milli- or microamps or milli- or microvolts). Waveforms  1- Direct Current (DC) - Direct current is the continuous unidirectional flow of ions or electrons for at least 1 second. - Here, the term direction implies flow from positive to negative or negative to positive. - By convention, deviation from the isoelectric baseline in the upward direction implies current flow in the positive direction; conversely, deviation in the downward direction implies flow in the negative direction. - The most common clinical uses of DC are for iontophoresis and wound care. - Direct current has traditionally been referred to as " galvanic" current.  Forms of DC - Variations of DC exist, but to accurately be called DC, they must remain unidirectional and uninterrupted for a period of time. Other forms of DC include: 1- Interrupted DC, where the direction of flow ceases after 1 second before resuming in the same direction for at least 1 second. 2- Reversed DC, where the flow ceases after 1 second before resuming in the opposite direction for at least 1 second. 3- Interrupted reversed DC, which is a combination of both.  2- Alternating Current (AC) - Alternating current (AC) is the uninterrupted bidirectional flow of ions or electrons and must change direction at least one time per second. - The rate at which AC switches direction is termed frequency and is described with the international unit hertz (Hz) or in the unit cycles per second. - The most common or familiar source of AC is the electricity coming from the wall outlets in our homes, supplying electricity to most appliances (e.g., your cell phone charger uses an AC source).. AC must change direction at least one time per second. If it does not, then what type of current would it be?  3- Pulsed Current (PC) Because the electrophysiological effects of DC or AC are not well suited for most electrotherapeutic applications, a third category of current has been designated: pulsed current (PC). - Pulsed current, sometimes termed pulsatile current, is the unidirectional- or bidirectional flow of ions or electrons that periodically ceases for a period of time before the next electrical event. - The definition of PC reflects flow of current that ceases before the next “event.” This event is a pulse Pulse is an isolated electrical event separated from the next by a period of time termed the interpulse interval. Shapes of pulse  Electrical current parameters - The characteristics of electrical currents can be described as parameters which include; - Waveform - Pulse and Phase - Pulse duration - Amplitude - Frequency  Wave forms There are variety of shapes for the waveform that represent the electric current as ; -Sine wave: It usually offers equal energy levels under positive and negative phases. -Rectangular (square) wave: This form of wave describes usually the direct current with a rapid instantaneous rise, prolonged duration and a sharp drop-off. -Spike wave: During such a waveform, the rise rate is rapid but not instantaneous, falling back rapidly to zero immediately after reaching the maximum. -Combined waves: It resembles a combination form of both rectangular (square) and spike waves. - Twin-spiked forms: With this waveform, more penetration is administered because of the extremely short- pulse width (microseconds), as in high-voltage galvanic stimulation Twin spike  Pulse and phase - In Pulsed current the current flows in a series of pulses separated by periods where no current flows. This event of current flow is a pulse while the period with no current flow is interpulse interval - Pulse is an isolated electrical event separated from the next by a period of time termed the interpulse interval. - The current may flow in only one direction during a pulse, which is known as a monophasic pulsed current, or it may flow back and forth during a pulse, which is known as a biphasic pulsed current. - Monophasic pulsed current is the delivery of repeated monophasic pulses separated from each other by an interpulse interval; - Biphasic pulsed current, therefore, is the delivery of repeated biphasic pulses separated from the next pulse by an interpulse interval.  Monophasic or Biphasic - Pulsed current may be monophasic or biphasic, with a phase being the flow of current in one direction for a short period of time. - A monophasic pulse deviates from the isoelectric line in only one direction. - It is produced by intermittently interrupting a DC current source. Some sources commonly use the term pulsed DC. - A biphasic pulse is one that deviates from the isoelectric line first in one direction, then in the other direction. - By definition, with monophasic pulsed current, a pulse and a phase are synonymous.  Difference between Monophasic and Biphasic -The biggest difference in the effects of biphasic and monophasic currents is the ability of monophasic current to cause polarity effect and chemical changes. - Chemical effects from using monophasic current usually occur only when the stimulus is continuous and applied over a period of time. Think about it: What is the longest duration a pulse can have and still be termed a pulse?  Pulse duration & Phase duration Pulse duration is the total time elapsed from the beginning to the end of a single pulse, including the interphase (intrapulse) interval. - Phase duration is the time from the beginning of one phase to its end. - Pulse duration is the time from the beginning to the end of all phases + the interphase interval within one pulse. - The interphase interval (or intrapulse interval) is the time between phases of a single pulse, whereas the interpulse interval is the time between successive pulses. - Phase and pulse duration are most commonly reported in milliseconds (msec) or microseconds (sec).  Phase and Pulse Charge This represents the total charge delivered in each phase or pulse. Phase charge is the charge within one phase of a pulse, and pulse charge is the cumulative charge of all phases within a single pulse. - For monophasic pulses, phase charge and pulse charge are synonymous. - The magnitude of the electrophysiological response is largely influenced by the total amount of current delivered to the patient—that is, the phase or pulse charge.  Symmetrical & asymmetrical waveforms - For biphasic waveforms, if the sum of current amplitude and duration of the first phase (i.e., phase charge) are identical to the second, the phases are termed symmetrical. On a current- time plot, the phases will look identical in shape. - If the amplitude and duration characteristics between the two phases of the biphasic waveform differ in any manner, the phases are termed asymmetrical and the graphical depiction on a current-time plot will not be identical—that is, the phases will not be the same shape.  Balanced & unbalanced - If the phases of a biphasic waveform are not symmetrical, then it is necessary to determine if the integrated sums of the phases are equal (i.e., have equal phase charges). - Despite not being symmetrical in shape, the area under the curve (the phase charges) can be equal or unequal. - If the area under the curve of the first phase is equal to that of the second phase, the phases are termed balanced. In this case, the average charge is zero because equal amounts of current flow in both directions of the biphasic wave. - If the phases are not of equal area, they are termed unbalanced. In this case, the average charge is not zero and the total pulse charge will have the polarity of the phase with greater charge.  Red & black electrode and polarity In symmetrical biphasic or asymmetrical balanced waveforms there is no need to determine the lead wires with a black and red or white lead to indicate a cathode and anode because neither of these waveforms result in a net charge or polarity, so the designation of a cathode and anode is incorrect in theses waveforms.  Amplitude - Amplitude, often referred to as intensity, is the magnitude of current or voltage with respect to the isoelectric or baseline on the x-y current-time plot. - Amplitude is reported in units of current (amps, milliamps, or microamps) or voltage (volts, millivolts, or microvolts) and can be described in terms of a single phase or both phases. - Most uses of ES use milliampere amplitude. - The highest current or voltage reached in a phase of a monophasic pulse or in any one phase of a biphasic waveform is termed the peak amplitude.  Frequency - Frequency is the term used to describe the number of pulses occurring in 1 second and is reported as pulses per second. - Earlier it was stated that frequency, in hertz (Hz), is used to describe the number of times AC switches direction in 1 second. - However, hertz and pulses per second are both used to describe the frequency of pulsed current. - There is inverse relation between frequency and pulse duration.  Frequency Electrical currents can also be classified according to their frequency, the current frequency is very important factor to be considered as it determines which tissues to be stimulated: 1-Low Frequency Current Current in which the direction of electron flow changes periodically with a frequency of 1- 1000 Hz. Low frequency currents can stimulate both sensory and motor nerves, with the best effect form 1-100 Hz. Examples of low frequency currents are faradic current (FC), diadynamic current (DD), High voltage galvanic (HVG) current. 2-Medium Frequency Currents Current with frequency of 1 KHz. These currents can only stimulate sensory and motor nerves to after modulation as in interefrential current (IF) or interrupted as in Russian current. 3-High frequency currents Those current of 1000,000 Hz or more. At this frequency the current has no effect on sensory and motor nerve. Example of high frequency currents are short wave (SW) and microwave (MW).  Burst The generation of two or more consecutive pulses separated from the next series of consecutive pulses is termed a burst, and the time between bursts is the interburst interval. - The frequency at which bursts are generated is the burst frequency, while the frequency of the underlying waveform in the burst is termed the carrier frequency. - In some cases, the uninterrupted generation of pulses at a fixed frequency is used. This is termed a train of pulses and is different from bursts in that there is no interruption of the pulses at a set frequency