Electrotherapy PDF

Electrotherapy Physiological Background Overview of the Nervous System and Neuron Function Types of Neurons Sensory Neurons Motor Neurons Interneurons Neuron Structure Components: Dendrites, Axon, Myelin Sheath [Diagram of a Neuron] Resting Membrane Potential Resting Membrane Pot...

Electrotherapy Physiological Background Overview of the Nervous System and Neuron Function Types of Neurons Sensory Neurons Motor Neurons Interneurons Neuron Structure Components: Dendrites, Axon, Myelin Sheath [Diagram of a Neuron] Resting Membrane Potential Resting Membrane Potential The mechanisms responsible for the membrane having a net positive charge on its outer surface and a net negative charge on its inner surface are as follows: 1. Asodium-potassium pump actively transports sodium ions (Na+) to the outside and potassium ions (K+) to the inside, with three Na+ moved out for every two K+ moved in. 2. The cell membrane is more permeable to K+ than to Na+, so that the K+ , which is more concentrated inside the cell, diffuses outward faster than the Na+, which is more concentrated outside the cell, diffuses inward. Na+ and K+ move through the membrane using different channels. 3. The cell membrane is essentially impermeable to the large (negatively charged) anions that are present inside the neuron, therefore fewer negatively charged particles move out than positively charged particles. Action Potential  1. A stimulus from a sensory cell or another neuron causes the target cell to depolarize toward the threshold potential. 2. If the threshold of excitation is reached, all Na+ channels open and the membrane depolarizes. 3. At the peak action potential, K+ channels open and K+ begins to Action potential can be leave the cell. At the same time, divided into five steps, Na+ channels close. 4. The membrane becomes hyperpolarized as K+ ions continue to leave the cell. The hyperpolarized membrane is in a refractory period and cannot fire. 5. The K+ channels close and the Na+/K+ transporter restores the resting potential.  CURRENT FLOW An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor Electron Flow (shown in red) Between the generators and electrodes To and from the generator Ion Flow (shown in yellow) Occurs within the tissues + Negative ions flow towards the anode and + - away from the cathode - Positive ions flow towards the cathode and away from the anode How you should be thinking about electric circuits? Voltage: a force that pushes the current through the circuit (in this picture it would be equivalent to gravity)  N.B Many normal substances exist in the body as ions. Common examples include sodium, potassium, calcium, chloride, and bicarbonate. These substances are known as.electrolytes Which one is the active electrode ?  Electrical impedance Resistance: friction that impedes flow of current through the circuit (rocks in the river)  Excitable tissues and nonexcitable biological tissues possess an inherent resistance. The opposition to current flow the body is more accurately described by the term “impedance” rather than “resistance.” The body’s opposition essentially results from the combination of resistive and Electrical capacitive reactance properties of tissue. impedance Capacitance is the ability to store charge in an electric field and oppose change in current flow. Nerve and muscle membranes are examples of capacitors. Tissue resistive impedance varies throughout the body and conductivity depends on the water content of tissue. High water content decreases impedance and improves conductance. Electrical currents can be classified according to type Direct Current Description: One-directional flow of electrons Constant positive and negative poles Use: Iontophoresis Direct current (DC): Direct current is the continuous or uninterrupted unidirectional flow of ions or electrons for at least 1 second. Continuous direct current has traditionally been referred to as "galvanic" current. When using DC, one of the electrodes will be the anode (positive) and one will be the cathode (negative). This will remain so unless the direction of current reverses. The most common clinical uses of DC are for iontophoresis and wound care.  Alternating Current (AC): In contrast to DC, alternating current (AC) is the continuous 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 (cps). Alternating Current Description: bidirectional flow of electrons  Each of the previously mentioned forms of current may be Electrical administered in two major modes: - Continuous mode:. - Interrupted or pulsed mode: currents can also be classified according to the Modes: Electrical 1-Low Frequency Current Current in which the direction of electron flow changes currents can 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. also be 2-Medium Frequency Currents Current with frequency of 1 KHz. These currents can only classified stimulate sensory and motor nerves to after modulation as in interefrential current (IF) or interrupted as in Russian according to current. 3-High frequency currents their frequency Those current of 1000,000 (106) 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). CURRENT CHARACTERISTICS Current Amplitude Current Amplitude: is determined by measuring the maximal distance to which the wave rises above or below the baseline (peak amplitude). The peak to peak amplitude: is the distance measured from the peak on the positive side to the peak on the negative side. N.B.: For monophasic waves, there is no peak-to-peak value. The amplitude of each pulse reflects the intensity of the current, the maximum amplitude being the tip or highest point of each phase. Amplitude is measured in amperes, microamps, or milliamps (mA)..  total amount of electricity being delivered to the patient during each pulse (measured in columbs or microcolumbs). PULSE CHARGE Amperes indicate the rate of electron flow, whereas coulombs indicate the number of electrons. 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  the amount of current per unit area volume of current in the tissues. CURRENT It depends on two factors; distance between DENSITY the electrodes (electrodes placement) and the size of the electrode. 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. As the current density increases, the perception of the stimulus increases.  Sometimes referred to as pulse width. PULSE It is the amount of time from the DURATION: 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: the phase duration.  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 (interphase interval), Pulse Attributes F A B D C B A = Amplitude E = Intrapulse Interval F B = Phase Duration F = Pulse Period E C = Pulse Duration D = Interpulse Interval Interpulse Interval Two Monophasic Pulses Two Biphasic Pulses The time between the end of one pulse and the start of the next pulse Allows for mechanical changes in the tissues, such as when eliciting muscle contractions Increasing the pulse frequency decreases the interpulse interval and vice- versa Intrapulse Interval Biphasic Pulse Intrapulse intervals are brief interruptions of current flow. Are always shorter than the interpulse interval. They allow to decrease the total charge delivered by the pulse. Are normally not adjustable on the unit. Intrapulse intervals can also apply to monophasic currents. 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: Its effects the type of muscle contraction. Its effects the mechanism of pain modulation. Effect of Pulse Frequency on Muscle Contractions 1 pulse per second 20 pulses per second 40 pulses per second Twitch Contraction Summation Tonic Contraction The amount of time The amount of time The current is flowing so between pulses – the between pulses allows rapidly that there is not interpulse interval – is some elongation of the sufficient time to allow the long enough to allow the fibers, but not to their fibers to elongate muscle fibers to return to starting point. their original position  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 level. 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. Rate of rise and decay times are generally short, ranging from nanoseconds (billionths of a second) to milliseconds (thousandths of a second).  By observing the different waveforms, it is apparent that the sine wave has a gradual increase and decrease in amplitude for alternating, direct, and pulsatile currents. The rectangular wave has an almost instantaneous increase in amplitude, which plateaus for a period of time and then abruptly falls off. The spiked wave has a rapid increase in amplitude. The shape of these waveforms as they reach their maximum amplitude or intensity is directly related to the excitability of nervous tissue. The more rapid the increase in amplitude or the rate of rise, the greater the current's ability to excite nervous tissue.  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(on time) by the total cycle time(on time +off time)multiply one hundred. Duty Cycle The amount (percentage of time) that the current is flowing relative to the time it is not flowing Duty cycle = “ON”/(“ON + OFF”) * 100 Example: Current is on for 20 seconds and is off for 40 seconds DC = 20/(20+40)*100 DC = 20/60 * 100 DC = 33.3%  Duty 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. 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.  POLARITY 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. With AC waves, these electrodes change polarity with each current cycle. With a direct current generator, the therapist can designate one electrode as the negative and one as the positive, and for the duration of the treatment the electrodes will provide that polar effect.  Current 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: when pulsed current flows for a short duration and then is turned off for a short duration Physiological Effects of Electrical Currents Thermal, Chemical, and Physiological Effects Direct vs. Indirect Effects Excitatory Responses Nerve Responses to Electrical Stimulation Depolarization and Action Potentials Non-Excitatory Effects Overview of Non-Excitatory Effects Electrotaxis and Cellular Modulation