Basics and Foundations of Electrotherapy PDF

Basics and Foundations of Electrotherapy Dr: Haitham M. Saleh Lecturer of physical therapy Basic sciences department  Students’ Learning Objectives  Recognize the structure of an atom.  Explain Polarity and Creation of Electric Force Fields.  understand measurements of elec...

Basics and Foundations of Electrotherapy Dr: Haitham M. Saleh Lecturer of physical therapy Basic sciences department  Students’ Learning Objectives  Recognize the structure of an atom.  Explain Polarity and Creation of Electric Force Fields.  understand measurements of electric current.  Determine Factors affecting current flow.  Differentiate between types of electric currents.  Mention classification of electrical current.  Mention the electrical current parameters.  Enumerate general contraindications to electrical stimulation.  PRINCIPLES OF ELECTRICITY  The structure of an atom  An atom is the smallest unit of ordinary matter that forms a chemical element.  Every atom is composed of a nucleus and one or more electrons bound to the nucleus.  The nucleus is made of one or more protons and a number of neutrons. The structure of an atom  More than 99.94% of an atom's mass is in the nucleus.  The protons have a positive electric charge, the electrons have a negative electric charge, and the neutrons have no electric charge.  If the number of protons and electrons are equal, then the atom is electrically neutral.  If an atom has more or fewer electrons than protons, then it has an overall negative or positive charge, respectively – such atoms are called ions.  The electrons of an atom are attracted to the protons in an atomic nucleus by the electromagnetic force.  The protons and neutrons in the nucleus are attracted to each other by the nuclear force.  The structure of an atom charge (Electromagnetic force& nuclear force)  Ionization  An atom or molecule that has gained or lost an electron is termed an ion, and the process by which an atom or molecule acquires a negative or positive charge is termed ionization.  Charge  Charge is the fundamental underlying property of electromagnetic force and serves as the mechanism by which living cells communicate with one another.  Measured in coulombs (C) or microcoulombs (C).  The concept of charge is specific to the net gain or loss of electrons.  Charge occurs when atoms of elements are acted upon by external physical forces such as friction, heat, and chemical or electrical sources.  Four fundamental properties of electrical charge explain how charge is used for therapeutic purposes:  1. There are two types of charge-positive and negative.  2. Like charges repel while opposites attract.  3. Charge is neither created nor destroyed.  4. Charge can be transferred from one object to another. Like charges are repelled away from each other. Opposite charges are attracted to move closer to each other. Polarity and Creation of Electric Force Fields  In a simple circuit, such as one created when electrodes are applied to a patient, one electrode is the positive pole and one is the negative pole.  The pole or electrode with net negativity is termed the cathode, and the pole or electrode with net positivity is the anode.  Voltage  The force of attraction or repulsion created by an electric field represents potential energy.  The greater the force, the greater the potential energy.  This force is termed voltage and represents the driving force that moves electrons.  The unit of electrical force is the volt (or millivolt).  A voltage force is best explained when considering the interaction of two magnets or two charged bodies as one approaches the other.  Voltage definition  Voltage may also be referred to as the electromotive force or electrical potential energy.  The term electromotive force refers to the property of the force inducing or causing movement and, in this case, movement of electrons.  In tissues, these charged particles are ions, such as sodium (Na+), potassium (K+), and chloride (Cl–).  This text focuses on the electrophysiological and therapeutic effects of electrical stimulation on the human body; thus the terms ions and electrons will be used in place of charged particles.  Current  The movement of ions or electrons in a conductor in response to a voltage force is termed current.  The flow of current is directly proportional to the magnitude of the driving force (i.e., the voltage).  Current is the quantity or amount of ions or electrons flowing at a given time.  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).  Factors affecting current flow through body tissues  1-Conduction characteristics of the material  The more electrons a material has, the less the resistance and the better current flow. Example: blood and nerves have more free electrons than skin or bone, so current prefers to travel along this path. 2- Cross sectional area of the path The greater cross sectional area of the path, the less resistance to current flow. Example: nerves having large diameter are depolarized before nerves having smaller diameters and have high velocity to nerve impulse. 3- Temperature  Increase temperature and increase random movement of free electrons thus, decreasing resistance to current flow Example: preheating the treatment area may increase the comfort of the treatment by decreasing the resistance and the need for higher output intensities TYPES OF ELECTRIC CURRENTS Direct Alternating Current Current Pulsed Current  Direct Currents  Direct currents are the uninterrupted, one-directional flow of electrons.  The basic pattern is recognized by continuous current flow on only one side of the baseline as the electrons travel from the cathode (negative pole) to the anode (positive pole).  Examples (galvanic & Iontophoresis).  The battery possesses a positive pole, which lacks electrons, and a negative pole that has an excess of electrons.  Electrons leave the negative pole of the battery and flow through a wire to the bulb.  When the number of electrons at the negative pole equals the number at the positive pole, no further potential for current flow exists. The battery is dead. Direct Current. Characterized by the constant flow of electrons in one direction, a direct current remains uninterrupted (does not return to the baseline) until the circuit is opened, thus stopping the flow of electrons. Example of a Direct Current. Electrons exit the battery through the cathode (negative pole), flow through the wire and bulb, and return to the anode (positive pole).  Variations of direct current  Variations of DC exist, but to accurately be called DC, they must remain unidirectional and uninterrupted for a period of time.  Interrupted DC, where the direction of flow ceases after 1 second before resuming in the same direction for at least 1 second.  Reversed DC, where the flow ceases after 1 second before resuming in the opposite direction for at least 1 second.  Interrupted reversed DC, which is a combination of both. Direct current (DC) comes in many forms, conventional DC (top) being the most commonly used.  Alternating Currents (AC)  In an AC, the direction of flow cyclically changes from positive to negative, although the magnitude of change may not be equal in both directions.  The cycle duration of an AC is measured from the originating point on the baseline to its terminating point and 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 (frequency) and is expressed in hertz (Hz).  Because ACs are measured in cycles per second, as the duration of the cycles increases, fewer cycles can occur per second.  Example: Interferential current (A) symmetrical and (B) asymmetrical pulses.  Pulsed Currents  Pulsed currents are the unidirectional (monophasic) or bidirectional (biphasic) flow of electrons for less than1 second that are interrupted by discrete periods of noncurrent flow.  Most commonly generated and clinically used current form.  The current is flowing for only microseconds (1/1,000,000 of a second, µsec) or milliseconds (1/1000 of a second, msec).  Monophasic pulses  Monophasic pulses have only one phase per pulse, and the current flows in only one direction. Examples of Monophasic Currents. Pulsatile current consists of discrete pulses. Like direct current, monophasic currents are characterized by the one-directional flow of electrons. (A) Three square waves. (B) Two twinpeaked monophasic. In a monophasic current pulses and phases are equivalent terms.  Monophasic currents have a known polarity under each electrode.  With this type of current one electrode is the cathode (negative electrode), and the opposite electrode is the anode (positive electrode).  High-voltage pulsed (H.V.P.C) stimulation uses a monophasic current.  Biphasic Currents  Biphasic currents consist of two phases, each on opposite sides of the baseline. Biphasic Pulse. An example of biphasic pulsed current commonly used with transcutaneous electrical nerve stimulation (TENS). In the above pulse the lead phase rises above the baseline; the terminating phase drops below the baseline.  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.  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 over time.  Unbalanced asymmetrical pulses may lead to residual physiological changes based on imbalances in charges..  Symmetrical biphasic waveforms tend to be the most comfortable because they deliver relatively lower charges per phase.  Neuromuscular stimulation units often deliver asymmetrical biphasic current; transcutaneous electrical nerve stimulators use a balanced asymmetrical current Classification of electrical current according to their frequency. 1-Low Frequency Current 2-Medium Frequency 3-High frequency currents  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.  Examples of medium frequency currents are interefrential current (IF) and Russian current.  3-High frequency currents  Those current of 1,000,000 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).  Pulse and Phase Duration  The baseline (horizontal axis) represents time.  The distance that a pulse covers on the horizontal axis represents the pulse duration.  The duration of biphasic pulses is described by the time required for each phase to complete its shape: the phase duration.  In a monophasic current, “pulse duration” and “phase duration” are equivalent terms.  In biphasic currents, the pulse duration is the sum total of the two phase durations plus the intrapulse interval (if present). Pulse and Phase Durations for a Monophasic Current. Monophasic currents have phases and pulses of equal duration. (A) Square wave; (B) sawtooth wave; (C) twin- peaked wave. Pulse and Phase Durations for a Biphasic Current.  The phase duration, and its associated electrical power (charge), 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 capacitive resistance of the nerve membrane and no action potential will be elicited.  As the phase duration is increased, different tissues are depolarized by the electrical current.  Interpulse Interval, Intrapulse Interval, and Pulse Period  The interpulse interval is the time between the end of one pulse and the start of the next pulse. Two Monophasic Pulses Two biphasic Pulses  Intrapulse interval  A single pulse or phase may be interrupted by an intrapulse interval (also referred to as the “interphase interval”); the duration of the intrapulse interval cannot exceed the duration of the interpulse interval. Definition: Period of time within a discrete pulse that the current is not flowing. This is also known as electrical silence.  pulse period  The pulse duration and the interpulse interval and, if present, the intrapulse interval form the pulse period. ❑ Definition:  The elapsed time between the initiation of one pulse and the start of the subsequent pulse.  By definition, uninterrupted currents (alternating and direct currents) do not possess pulses.  Therefore, pulse duration and pulse periods do not exist for these types of currents.  pulse period Two Monophasic Pulses Two Biphasic Pulses  Pulse Charge  Definition:  The pulse charge is the number of electrons contained within a pulse and is expressed in coulombs.  The term pulse charge refers to the total amount of electricity being delivered to the patient during each pulse (measured in columbs or microcolumbs).  A coulomb is too large a unit to use when describing the charge produced by electrical stimulation units.  Most electrotherapeutic modalities produce charges measured in microcoulombs.  Increasing or decreasing the amplitude or duration alters the charge of the pulse accordingly.  The shape of the wave may also be altered to deliver more or less charge to the tissues per pulse.  With monophasic current, the phase charge and the pulse charge are the same and always greater than zero.  With biphasic current, the pulse charge is equal to the sum of the phase charges.  Pulse Frequency ❑Definitions:  Any waveform or pulse that repeats at regular intervals may be described in terms of its frequency or the number of events per second.  The frequency is measured by the number of pulses per second (pps).  The cycle frequency of an AC is measured by the number of cycles per second (cps) or Hertz (Hz).  Electrical stimulation units are grouped by their carrier frequency.  Low-frequency currents, less than 1000 cycles or pulses per second, are used for their biological effects.  Medium-frequency currents range from 1000 to 100,000 cps.  High-frequency currents, greater than 100,000 cps, are used for their heating effects, as seen with diathermy.  There is an inverse relationship between the frequency of an electrical current and the capacitive resistance offered by the tissues.  A current having 10 pps encounters more tissue resistance than a 1000 pps current and would require an increased intensity to overcome the resistance.  Pulse frequencies over 100 pps have little additive effect on nerve depolarization. Pulse Rise Time and Pulse Decay Time  Pulse rise is the amount of time needed for the pulse to reach its peak value and is usually measured in nanoseconds.  Rapidly rising pulses cause nerve depolarization.  If the rise is slow, the nerve accommodates to the stimulus and an action potential is not elicited.  The counterpart of pulse rise time is the pulse decay time, the amount of time required for the pulse to go from its peak back to zero. Pulse Rise and Decay Time for a Monophasic Current.  Pulse Trains (Bursts)  Pulse trains, or bursts, are currents that are regularly interrupted by periods of noncurrent flow.  These linked patterns repeat at regular intervals.  Bursts are regulated based on their duration and frequency, and the interburst interval, the length of time between bursts.  Each burst results in the nerve(s) depolarizing multiple times. An Example of a Pulse Train (Burst).  Amplitude ramp  The gradual increase in the amplitude of a pulse train is the amplitude ramp (ramp).  The ramp causes a gradual increase in the output intensity and the force of muscle contractions.  As the intensity of the ramp continues to increase, more and more motor units are recruited into the contraction as the amplitude increases.  The resulting contraction more closely resembles a voluntary muscle contraction than if no ramp were used.  The patient appreciates a slow rise time because the intensity is gradually increased, reducing the sensation of “shock.” Amplitude Ramp.  Wave forms  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. Wave forms.  The electrical current parameters  1- THE CURRENT AMPLITUDE:  The current amplitude is determined by measuring the maximal distance to which the wave rises above or below the baseline (beak amplitude).  The peak to peak amplitude: is the distance measured from the peak on the positive side to the peak on the negative side  2- PULSE CHARGE  The term pulse charge refers to the total amount of electricity being delivered to the patient during each pulse (measured in columbs or microcolumbs).  With monophasic current, the phase charge and the pulse charge are the same and always greater than zero.  With biphasic current, the pulse charge is equal to the sum of the phase charges.  If the pulse is symmetric, the net pulse charge is zero.  In asymmetric pulses the net pulse charge is greater than zero, which is a DC current by definition.  3- CURRENT DENSITY  Current density refers to the volume of current in the tissues.  If the electrodes are spaced closely together, the area of highest-current density is relatively superficial.  If the electrodes are spaced farther apart, the current density will be higher in the deeper tissues, including nerve and muscle.  Electrode size will also change current density.  As the size of one electrode relative to another is decreased, the current density beneath the smaller electrode is increased.  The larger the electrode, the larger the area over which the current is spread, decreasing the current density.  Using a large (dispersive) electrode remote from the treatment area while placing a smaller (active) electrode as close as possible to the nerve or muscle motor point will give the greatest effect at the small electrode.  The large electrode disperses the current over a large area; the small electrode concentrates the current in the area of the motor point.  4- PULSE FREQUENCY:  The number of electrical pulses that occur in a 1 second period.  It is expressed as pulse per second ( pps) or as pulse frequency in Hz.  An inverse relationship exists between the pulse frequency (pulse rate) and an electrical current and the resistance offered by the tissues.  A current with lower pulse frequency i.e. 10 pps would meet resistance than a current with pulse frequency 1000 pps and would require an increased intensity to overcome the resistance.  The frequency has an effect on.  Effects the type of muscle contraction.  Effects the mechanism of pain modulation. Frequency and its effects on muscle contraction  5- PULSE DURATION:  Sometimes referred to as pulse width.  It is the amount of time from the beginning of a phase to the end of the final phase (to the return to a zero).  The duration of a single pulse may be broken down into the time required for each component phase to complete its shape.  Phase duration:  the amount of time for a single phase to complete its rout.  Pulse duration and phase duration expressed in second (sec), millisecond (ms), or microsecond (μ sec).  The duration of time between the end of one pulse and the initiation of the following pulse is known as the interpulse interval.  A single pulse or phase may be interrupted by an intrapulse interval, however the duration of the intrapulse interval should not exceed the duration of the interpulse interval. Time and amplitude dependent parameters  6- PULSE RATE OF RISE AND DECAY TIMES:  The rate of rise in amplitude, or the rise time, refers to how quickly the pulse reaches its maximum amplitude in each phase.  Conversely, decay time refers to the time in which a pulse goes from peak amplitude to 0 V. The rate of rise is important physiologically because of the accommodation phenomenon, in which a fiber that has been subjected to a constant level of depolarization will become unexcitable at that same intensity or amplitude. Ramp up and Ramp down  7- POLARITY  During the use of any stimulator, an electrode that has a greater level of electrons is called the negative electrode or the cathode.  The other electrode in this system has a lower level of electrons and is called the positive electrode or the anode.  The negative electrode attracts positive ions and the positive electrode attracts negative ions and electrons.  8- DUTY CYCLE:  The duty cycle is the ratio of the amount of time the current is flowing (ON) to the amount of time without current (OFF) and expressed as a percentage or ratio.  Duty cycle is calculated by dividing the time the current is flowing by the total cycle time.  Duly cycles play a role in neuromuscular stimulation by preventing muscle fatigue.  Muscular stimulation is started with a 25% duty cycle and is progressively increased as the condition improves. DUTY CYCLE  For example, if the on time equals 10 seconds and the off time equals 30 seconds, the duty cycle such a pattern of stimulation would be 25%.  A very different pattern of stimulation with an on time of 5 seconds and an off time of 15 seconds yields the same 25% duty cycle.  Current Modulation  Modulation is alteration in the current parameters in order to reduce or minimize accommodation.  Amplitude modulations;Variations in the peak amplitude of a series of pulses.  Pulse or phase duration modulations: Regular changes in the time over which each pulse in a series acts.  Frequency modulations: consist of cyclic variations in the number of pulses applied per unit time.  Surged (ramped) modulations: are characterized by an increase(ramp up) or decrease (ramp down) of pulse amplitude, pulse duration, or both, over time.  Burst modulation  a series of groups of pulses or groups of alternating current cycles delivered at a specified frequency over a specified time interval followed by a brief time interval without charged particle movement  Burst duration: The time interval over which the finite series of pulses or AC cycles is delivered.  Interburst interval: The time period between bursts.  Burst frequency: The number of bursts delivered per unit of time.  Beat Modulation  A beat modulation will be produced when two interfering alternating current waveforms with differing frequencies are delivered to two separate pairs of electrodes through separate channels within the same generator.  The two pairs of electrodes are set up in a crisscrossed or cloverleaf-like pattern so that the circuits interfere with one another.  This interference pattern produces a beat frequency equal to the difference in frequency between the two alternataing current frequencies.  As an example, one circuit may have a fixed frequency of 4000 Hz, while the other is set at a frequency of 4100 Hz, thus creating a beat frequency of 100 beats per second.  This type of beat-modulated alternating current is referred to as interferential current and will be discussed further in. Beat modulation  General Contraindications to Electrical stimulation  Unreliable patient which not understand the command.  Stimulation of the abdominal and pelvic region during pregnancy and menstruation.  Stimulation of the thorax or neck may result in disruption of normal respiration or cardiac function.  Exposed metal implants.  Areas of the carotid sinus, esophagus, larynx, or pharynx may affect respiration.  Patient with pacemaker, as it may interfere with its function.  A- Based on the study of these figures choose the most appropriate answer 1- Each phase in the pulse has a different shape but the charges (area) under the curve in both negative and positive direction (both phases) are equal. a) Fig A b) Fig B c) Fig C d) Fig D 2. Charges (area) under the curve in both negative and positive direction (both phases of biphasic pulses) are unequal. a) Fig A b) Fig B c) Fig C d) Fig D  The imbalance in positive and negative charges results in a net change over time.  Fig A  Fig B  Fig C  Fig D  4- Two phases are equal in their magnitude, duration and shape.  Fig A  Fig B  Fig C  Fig D  5- Symmetrical biphasic current, Mirror images on each side of the baseline.  a) Fig A  b) Fig B  c) Fig C  d) Fig D   6- The constant flow of electrons in one direction.  a) Fig A  b) Fig B  c) Fig C  d) Fig D  7- Tend to be the most comfortable because they deliver relatively lower charges per phase.  a) Fig A  b) Fig B  c) Fig C  d) Fig D