Lecture 1: Basic Principles of Electricity and Electrical Stimulation (PDF)

Introduction Basics of Electricity-Electrical safety Electrotherapy is the use of electrical energy in the treatment of impairments of health and conditions of abnormal functioning. It is composed of the use of electric currents for therapeutic p...

Introduction Basics of Electricity-Electrical safety Electrotherapy is the use of electrical energy in the treatment of impairments of health and conditions of abnormal functioning. It is composed of the use of electric currents for therapeutic purposes.  Electricity: Itis a form of energy that can be converted to light, heat, sound & motion. Electrical Engineer’s Definition of electricity: It is the flow of electrons from one atom to another.  This flow of electrons is controlled in an electric circuit.  The amount of energy produced depends on the number of electrons in motion. Electricity in the body  Muscles control all the body movements  Including those that keep us alive - Breathing and Heart  The brain controls voluntary muscles using current pulses along nerves External current through the body causes  Loss of muscle control  Spasms & Involuntary movement  Inability to let go  Burns - external & internal CAUSES OF ELECTRICAL ACCIDENTS Accidents and injuries with electricity are caused by one or a combination of the following: 1  - Unsafe equipment and/or installation. - Unsafe workplaces caused by environmental factors. - Unsafe work practices. Safety guiding principles Protection from electrical hazards is one way to prevent accidents. Use low & safe voltages Select equipment appropriate for environment & use Use equipment as per manufacturer’s instruction & design Ensure adequate maintenance Insulation: Insulators are elements that do not readily allow electrical current to flow through them. Placed on electrical conductors to protect from hazards. Examples: rubber or plastic.  An electric cable is one example of how conductors and insulators are used. Electrons flow along a copper or aluminum conductor to provide energy to the electric device.  An insulator around the outside of the copper is provided to keep electrons in the conductor. Grounding Grounding is an important safety feature. Most electrical power systems are grounded to protect against electrical shock, fire and damage to electrical equipment. 2   Electrical cables & plugs  Brown Live - power  Blue Neutral  Green/yellow Earth Personal protective Equipment ( PPE ) - Electrical protective equipment that is appropriate for body parts for protection include: * Gloves * Insulated boots or shoes Basic principles of Electricity and Electrical StimulationCurrent Electrical stimulation current Application of therapeutic electrical current devices to stimulate excitable tissues, with the aim of producing physiological reaction for therapeutic benefits. Waveforms related parameters Waveform is a graphic representation of “shape, direction, amplitude, duration and frequency” of the electrical current 3 1-Waveform Shape: There are different shapes of electrical current each has different physiological effect and the body react to it differently. It includes sine, rectangular, square, triangular, and spike waveform. Square waveform 2. Current Direction Alternating current (AC): Itis an electric current in which the flow of electric charge periodically reverses direction. Itis consisting of positive and negative phases. AC can be used for pain relief as well as for neuromuscular stimulation. 4  Direct current (DC) :  Itis unidirectional flow of electrical charge that does not change direction with a duration of at least 1 second.  There is a build-up of charge since it is moving in one direction causing a strong chemical reaction on the tissue under the electrode, so there is an increased risk of chemical skin burns with DC.  Most commonly used for wound care, with iontophoresis and to stimulate denervated muscle. 5 So, the biggest difference between direct current and alternating current is the ability of direct current to produce chemical reaction. Phases of electrical current (Monophasic, biphasic, polyphasic) Monophasic: One phase. Current flows in one direction only. Biphasic: Two phases. Current flows in both directions. 6  Polyphasic : Many phase Balanced vs unbalanced currents Biphasic currents consist of two phases, each occurring on opposite side of the baseline. Balanced currents:  Balanced currents have balanced amount of energy throughout the current.  If the two phases are equal in their shape; it is considered as symmetrical biphasic pulses. 7  If the charges (area or total current) under the curve in both negative and positive direction (both phases) are equal in asymmetrical biphasic pulses, is termed asymmetrical balanced biphasic pulses. Unbalanced current:  Unbalanced currents have unbalanced distribution of energy throughout the current. When each phase in the pulse has a different shape it is considered as asymmetrical biphasic pulses. If the charges (area or total current) under the curve in both negative and positive direction (both phases of biphasic pulses) are unequal in asymmetrical biphasic pulses, is termed unbalanced asymmetrical biphasic pulses. In asymmetrical biphasic pulses, there is the mild accumulation of ions polarity beneath the electrodes. This causes discomfort with the 8  asymmetric waveform due to the accumulation of ions under the electrodes. Symmetrical biphasic waveforms are the most comfortable because they deliver relatively lower charges per phase. 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 or the time it takes for a signal to complete an on-and- off cycle. 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. On time Duty Cycle = ______________________________ X 100% (On time + Off time) 9   For example, if the on time equals 10 seconds and the off time equals 30 seconds, the duty cycle for 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. Duty cycle may be expressed as the time the signal is active, from total period of the signal. Thus, a 60% duty cycle means the signal is on 60% of the time but off 40% of the time 10 3. Frequency Frequency is defined as a number of cycles or oscillations per unit time, unit of frequency is the hertz (Hz), cycles per second 11 4. Wavelength It is the distance between identical points in the adjacent cycles of a waveform signal propagated in space or along a wire, as shown in the illustration, this length is usually specified in meters, centimeters, or millimeters. 12 Frequency vs. wave length Wave length and frequency are inversely proportional. The higher the frequency the shorter the wavelength. V =λ f where, λ =Wavelength of the wave, f = frequency of the wave, V= velocity or speed of the wave. 5. Pulse Period Pulse Period =pulse duration (PD) + the inter-pulse interval (IPI). 1- Pulse duration (PD) = pulse width: It is the time from the beginning of first phase to the end of the final phase of a pulse (to the return to a zero). 2- Interpulse interval (IPI); is the time where electrical flow is “off 3- Phase duration: is a duration of one phase of pulse. 4- Pulse duration and phase duration expressed in second (sec), millisecond (ms), or microsecond (µ sec) Burst: A series of pulses flowing for a limited time, followed by no current flow. 13 Burst period = burst interval (BI) + inter-burst interval (IBI). 1-Burst interval (BI): is the length of the time during which burst occurs. 2-Interburst interval (IBI): is length of the time between two successive bursts, and current flow is “off”. 6. Current Amplitude Current amplitude (also called magnitude or intensity) is defined as amount of charge which passes in a conductor per unit of time. Peak current amplitude: is the maximum (highest) amplitude from zero value of the phase. 14  The peak to peak amplitude: is the distance measured from the peak on the positive side to the peak on the negative side only for biphasic current. Current Amplitude or intensity is expressed in milliampere (mA), microampere (µ A) or voltage (V). With increasing the current intensity, the subject experience different level of sensations start with no sensation and end with maximum tolerance of the current. Tissue impedance Impedance is the resistance of the tissue to the passage of electrical current. High – impedance tissue: skin, bone & fat Low – impedance tissue: Nerve & muscle. How to overcome resistance to passage of current? 1.Decrease distance between electrodes 2.Increase the size of electrodes 3.Minimize air-electrode interface 4.Use electrodes jelly or moisten the electrodes 5. Pre-warming the skin by moisten heat modalities (e.g. hot packs) 15  General Therapeutic Uses of Electrotherapy: 1. Relaxation of muscle spasms 2. Prevention and minimizing of disuse atrophy 3. Increase of local blood circulation 4. Muscle rehabilitation, and reeducation by electrical muscle stimulation 5. Maintaining and increasing range of motion of joint 6. Management of acute and chronic pain 7. Edema reduction 8. Facilitating tissue healing 16