Electrical Muscle Stimulation ESAT 3640 Therapeutic Modalities

Principles of Electricity

Electrical Modalities Electricity and water don’t mix. Right? Wrong! At least in the case of electricity as a stimulating current “To understand how current flow effects biological tissue, you must first be familiar with some of the principles that describe how electricity is produced and how it behaves in an electrical circuit”

Components of Electrical Current Ions Tend to move from an area of higher concentration to an area of lower concentration Electrical force creates electrical potentials The more ions present, the greater the potential (+) and (-) charged particles Contain electrical energy – have ability to move Electrical force is capable of propelling particles from higher to lower energy levels establishing electrical potentials Electrical potentials – difference between charged particles at a higher and lower potential

Components of Electrical Current continued Electrons Electrical current Flow of electrons is always from high potential to low potential Ampere Coulomb Coulombs Law (-) charged particles Net movement of electrons within a conducting medium 4. Rate of electrical current flow Indicates number of electrons in current 1 amp is movement of 1 coulomb (6.25 x 1018 electrons) per second Modalities are typically Milliamps = 1/1000 amp Microamps = 1/1,000,000 amp

Components of Electrical Current continued Electrons will not move unless an electrical potential difference in the concentration of these charged particles exists between 2 points Electromotive force (volt) Voltage 110 V or 220 V Must be applied to produce movement of electrons Difference in electron populations between points Ex. 1.5 volt Force resulting from an accumulation of electrons at one point in an electrical circuit. Usually corresponds to a deficit of electrons at another point in the circuit Suitable conductor between 2 points needed to create electron movement from high to low Battery example Modalities will modify voltage from volts to millivolts

Components of Electrical Current continued Path of least resistance Conductors Insulators Resistance Ohm’s law Permit free movement Metals – large number of free electrons that are given up asily Resists current flow Contain few free electrons = greater resistance to flow – wood, air, glass Impedance – opposition to electron flow in a conducting media (ohm) Increased resistance = decreased flow Current in electrical circuit is directly proportional to the voltage and inversely proportional to resistance Current flow = voltage/resistance

Electrotherapeutic Currents Direct (DC) Monophasic Alternating (AC) Biphasic Pulsed Polyphasic Unidirectional flow from (-) pole to (+) pole Change in direction requires off time Change in direction; change in polarity Grouped pulses interrupted for short period of time, repeated at regular intervals IFC, Russian

Direct Current

Alternating Current

Pulsed Current

Generators of Electrotherapeutic Currents Regardless of current type, all are transcutaneous electrical stimulators TENS Transcutaneous electrical nerve stimulator NMES (EMS) Neuromuscular electrical stimulator MENS Microcurrent electrical nerve stimulator Electrotherapeutic currents are all transcutaneous electrical stimulators (pads to skin) TENS Neuromuscular MENS

Generators of Electrotherapeutic Currents continued No relationship between the type of current being delivered by the generator and the type of current used as a power source for the generator

Components of Electrical Generator Transformer Rectifier Filter Regulator Amplifier Oscillator Reduces the amount of voltage from the power supply Converts AC current to pulsating DC current Changes pulsating DC to smooth DC Produces a specific controlled voltage output Used to magnify or increase the amplitude of the voltage output of the generator and control it at a specific level Used to produce and output a specific waveform, which may be different from that used to power or drive the stimulating unit

Waveforms Graphic representation of the shape, direction, amplitude, duration, and pulse frequency of the electrical current being produced by the electrotherapeutic device, as displayed by an oscilloscope

Sine Wave Rolling

Rectangular Wave Sharp rise, levels off, sharp decline Also referred to as square waves

Triangular Wave Fairly sharp rise; no leveling off, sharp decline Also called spiked

Pulse, Phase, Direction of Current Flow Pulse – Individual waveform Phase – portion of the pulse that rises above or below the baseline for some period of time Monophasic Biphasic Ployphasic One phase in each pulse 2 phases 3 or more grouped phases in 1 pulse IFC, Russian

Pulse Intervals Interpulse interval – Interruptions between individual pulses or groups of pulses Intrapulse interval – Period of time between individual pulses 2. Associated with polyphasic current

Pulse Amplitude Amplitude – Intensity of current flow as indicated by the height of the waveform from baseline Amplitude = Voltage = Current intensity Higher the amplitude; the greater the peak voltage or intensity Because of intervals, avg. current is low (interpulse period = 0) 2-100 milliamps Increase pulse duration or pulse frequency or combo of both

Phase Charge Total amount of electricity delivered during each pulse Monophasic always greater than zero Biphasic is = to the sum of the phase charges Symmetrical = zero Asymmetrical = net pulse charge is greater than zero Asymmetrical by definitions is DC current

Rise and Decay Times Rate of rise – How quickly a waveform reaches its maximum amplitude Decay time – Time required for a waveform to go from peak amplitude to zero volts Rate of rise and accommodation More rapid the rate of rise, the greater the currents ability to excite nervous tissue Constant level of stim = accomodation High peak intensity with short-phase duration produces comfortable type of current; effective stimulation of sensory, motor and pain fibers

Pulse Duration Duration of each pulse indicates the length of time current is flowing in one cycle Monophasic – phase duration = pulse duration Biphasic – pulse duration is determined by the combined phase durations Pulse period – Combined time of the pulse duration and the interpulse interval Pulse width

Pulse Frequency Indicates the number of pulses per second Increase in frequency, amplitude tends to increase and decrease more rapidly Muscular and nervous system responses depend on the length of time between pulses and on how the pulses or waveforms are modulated One to several hundred pulses per second Below 50 pulses/sec = twitch contractions At 50 pulses/sec or greater = tetanic contraction occurs

Stimulators Clinically speaking Low frequency generators Medium frequency generators High frequency generators In general, all stimulators are low-frequency generators Medium/High generators claim to have frequencies of 2500 to 10000 pulses per second Actually groups of pulses combined as bursts (combined set of three or more pulses; also referred to as packets or envelopes) that range in frequency from 1-200 pulses per second

Current Modulation Continuous – Amplitude of current remains same for several seconds or minutes Interrupted – on time, off time Burst – combined set of 3 or more pulses Ramped – current builds gradually to some maximum amplitude Iontophoresis works this way Muscle reeducation, strength training, increase ROM Muscle contraction

Series Circuit Circuit in which there is only one path for current to get from one terminal to another Components are placed end to end Resistance to flow is = to the resistance of all the components in the circuit added together RT = R1 + R2 +R3 Voltage decreased at each component VT = VD1+VD2+VD3 High resistance = low voltage Large voltage needed to drive current

Series Circuit

Parallel Circuit A circuit in which 2 or more routes exist for current to pass between the two terminals Component resistors are side by side, and the ends are connected Same voltage to each resistor Current flow depends on resistance at each component

Parallel Circuit Total voltage is exactly same as voltage at each component VT =V1=V2=V3 Adding alternative pathway improves ability of current to flow from one point to another Path of least resistance Resistance and Ohm’s law 1/RT = 1/R1+1/R2+1/R3 More pathways = decreased resistance Current flow = voltage/resistance

Parallel Circuit

Circuits Series have higher resistance and less current flow Parallel have lower resistance and higher current flow

Electrical Modalities Make use of combined series and parallel circuits Current through skin = series circuit Once through skin and fat, current comes into contact with many other tissues Parallel circuit

Body Circuit

Electric Stimulation Currents

Electrodes Electrode-skin interface Conducting mediums Electrode size Conversion of flow electrons to flow of ions Water, gels Size inversely affects density of current As size of electrode decreases, the current density increases

Electrode Placement Stimulation points Bipolar technique Motor Trigger Acupuncture Bipolar technique Monopolar technique Quadripolar Technique Bipolar tech. – current density is approx. = under each pad Monopolar tech. – 1 active, 1 dispersive, current density higher under one pad (usually active) Quadripolar – 4 pads, two channel

Current Flow Through Biologic Tissue Current flow through path of least resistance Tissue high in water content = high ion content = best conductor of electricity Skin is insulator The greater the impedance of the skin, the more voltage needed Blood is best conductor

Physiologic Responses to Electrical Currents Electricity will have an effect on each cell and tissue that is passes through Type and extent of response dependent on: 1) Type of tissue and its response characteristics 2) Nature of the current applied Skin impedance

Goals of Electric Stimulation Muscle contraction Pulse amplitude Pulse frequency Phase duration Pain control Control and reduction of edema Sensory-level stimulation Motor-level stimulation Decrease effect of atrophy, muscle reeducation, reduce edema, strength augmentation Increase amplitude = increase contraction Less than 50 p/s = twitch, 50 or greater = tetany Motor nerve – moderate phase duration Decrease pressure on nerve, decrease muscle spasm, eliminate mechanical and chemical mediators of pain Affect transmission of pain Control and reduction of edema Stop formation of edema by preventing fluids from escaping into surrounding tissue Sensory level is just that. Reduction in capillary pressure and capillary permeability ----- discourages plasma proteins from entering extracellular tissues Assist venous and lymphatic return Motor level = muscle pump

Goals Continued Wound healing Strength augmentation Fracture healing Increased hydration, increased # of growth factor receptors, increased rate of collagen formation, stimulates growth of fibroblasts and granulation tissues, reduces # of mast cells present Russian wave Body does not recognize difference from one healing current and one introduced from outside

TENS Transcutaneous Electrical Nerve Stimulation Process of altering the perception of pain through the use of an electrical current Gate theory Endogenous opiate Setup dependent

TENS Pain reduction is primarily through modulation of the nervous system May activate the preganglionic and postganglionic neurons, causing mild vasoconstriction Caffeine warning Caffeine warning 200 mg (2-3 cups) decreases effectiveness Competes with adenosine for receptor sites Adenosine – primary mediator of TENS induced pain reduction Caffeine binds to site --- adenosine can’t --- decreases effectiveness of TENS

TENS Only alters perception of pain Little effect on the underlying pathology Use with other therapies that attempt to treat source of pain Manual exercise

High Frequency TENS Sensory level High pulse frequency 60 – 100 pps Short pulse duration Less than 100  sec Activates gate pain modulation at spinal cord level Stimulation of large diameter sensory nerve fibers  = micro Works on gate control mechanisms

High Frequency TENS Accomodation is concern with long term use Current modulation can diminish accomodation Burst & frequency modulation

High Frequency TENS Effective for: Pain associated with musculoskeletal disorders Post operative pain Inflammatory condition Myofascial pain Myofascial pain = musculoskeletal pain Trigger points Fibromyalgia = chronic inflammation of muscle or connective tissues

Low Frequency TENS Motor level Low pulse frequency Long pulse duration 2 – 4 pps Long pulse duration 150 – 250  sec 45 minute treatment time Beta endorphin release

Low Frequency TENS Activates small diameter nociceptors and motor fibers Release of -endorphin Results in narcotic like pain reduction Stimulates pituitary gland Release of chemicals that trigger production of pain reducing -endorphin Narcotic like pain reduction --- enkephalin release Pituitary gland??? Most likely hypothalamus --- blood brain barrier issue

Low Frequency TENS Actual relief may take some time following treatment Lasts longer than high ƒ TENS Uses: Chronic pain Pain due to damage to deep tissues Myofascial pain Pain caused by muscle spasm

Brief – Intense TENS Noxious level, motor level High pulse frequency Greater than 100 pps Long pulse duration 300 – 1000  sec Treatments lasting a few seconds to a few minutes

Brief – Intense TENS Pain relief through activating mechanisms in the brain stem Dampen or amplify pain impulses Feedback loop High level of analgesia Effects tend to be transitory Recommended for pre-exercise Endogenous opiate central biasing theory

IFC Interferential current 2 ACs on 2 channels 1 channel produces constant high frequency sine wave 4000 – 5000 Hz Other channel produces a sine wave of variable frequency X pattern Premodualtion – 2 pad setup; interference current generated in machine

IFC Two independent channels combine to form an interference wave Frequency of 1 – 100 Hz Constructive interference 2 waves in perfect phase collide and form one single larger wave Destructive interference 2 waves perfectly out of phase, cancel each other out, producing no wave

IFC IFC combines constructive and destructive interference patterns to form a continuous interference pattern Occurs when 2 circuits have slightly different frequency (+ 1 Hz) Resultant waveform drifts between constructive and destructive interference patterns

IFC Rate of change is known as beat pattern Difference in frequency between the 2 circuits Beat produced elicits responses similar to TENS, but is capable of delivering a greater total current to the tissues (70 –100 mA) Beat pattern = difference between the 2 circuits

IFC Low skin resistance Inside tissues, interference between 2 waves reduces the frequency to a level that has biological effects on tissue Low skin resistance – inverse relationship to frequency 4000 Hz = 40 Ohms

IFC and Pain Control High beat frequency Sensory level stimulation 100 Hz Sensory level stimulation Gate theory Low beat frequency 2 – 10 Hz Motor level stimulation Opiate release

IFC and Neuromuscular Stimulation Medium beat frequency 15 Hz Muscle pump Increased venous and lymphatic return Edema reduction

IFC and Time Modulated AC AKA Russian wave Theory – 2500 Hz carrier sine wave, burst modulation Dr. Yakov Kots 30 – 40% increase in strength compared to isometric training alone Increased muscular endurance Changes in velocity of contraction These results have never been replicated in USA Isokinetic principles related to velocity change Rocky III or IV??

High Voltage Pulsed Stimulation Monophasic current Twin-peaked waveform or Train of 2 single pulses phase duration of 5 to 260 sec Average current does not exceed 1.5 mA Pulse charge less than 4 microcoulombs Voltage > 150 V needed to stimulate motor and sensory nerves Electrode placement in general terms Monopolar: focus of treatment is over a wide area Sensory level pain control Edema reduction Point stimulation

Uses Muscle reeducation Nerve stimulation Edema reduction Pain control

Muscle Reeducation Intensity Strong, comfortable contraction Pulse Frequency Low (<15 pps) individual contraction Moderate (35 – 50 pps) tonic contraction Polarity + or – Electrode placement Bipolar: proximal & distal to muscle Monopolar: motor point Most useful purpose Re-teach muscle to contract

Pain Control: Gate Theory Intensity Sensory level Pulse frequency 60 – 100 pps Phase duration < 100sec Mode Continuous Electrode placement Directly over painful site (+) Polarity for acute pain Repels acid reaction (-) Polarity for chronic pain Vasodilation properties

Pain Control: Opiate Release Mechanism Intensity Motor level Pulse Rate 2 – 4 pps Phase duration 150 – 250 sec Mode Continuous Electrode Placement Over painful site, trigger point, acupuncture point, or distal to the spinal nerve root

Pain Control: Brief-Intense Protocol Intensity Noxious Pulse rate > 120 pps Phase duration 300 – 1000 sec Mode Probe (15-60 s at each site) Probe placement Gridding technique

Edema Control: Sensory Level Intensity Sensory level Pulse duration Max duration allowed Pulse frequency 120 pps Polarity – electrode over injured tissue Mode Continuous Electrode placement Immersion, grouped Treatment duration 4 – 30 min treatments, 60 min rest Low pps does not affect edema 1 treatment a day will not reduce edema Pain relief – long term Start within 6 hours to increase effectiveness of treatments

Edema Control: Motor Level Intensity Strong, comfortable contraction Pulse frequency Low Polarity + or – Mode Alternating Electrode placement Bipolar: ends of muscle Monopolar: course of venous return system Milking Elevate limb

MENS Microcurrent Electrical Nerve Stimulation Subsensory level 1/1000 amperage of TENS Pulse duration 2500 x TENS Does not excite peripheral nerves DC, AC, or pulsed Use is not substantiated in professional literature Anecdotal and sport personnel testimonials

MENS Does it work? Theory: Currents below 500 A increase the level of ATP Increased ATP production encourages amino acid transport and increased protein synthesis Tissue trauma affects electrical potential of injured cells Creates greater resistance to flow

MENS Theory continued Body’s bioelectric current follow path of least resistance Not through injured tissue MENS introduces current flow through injured site increasing ATP production Studies have shown that subthreshold electrical stimulation has a effect on cell membrane properties, neurological responses and ionic responses Used implanted electrodes Skin resistance? DC would seem to benefit more, but does not overcome skin resistance at low amperage AC pulsed is used Therefore, providing metabolic energy for healing

Neuromuscular Electrical Stimulation Muscle reeducation Spasticity reduction Atrophy delay Strengthening Recruitment order reversed Isometric Stimulates (recruits) type II motor fibers 1st, produces much stronger contraction Large amp, long pulse duration Stronger stimulation than other forms of electrical stim

NMES Peak amperage To tolerance Pulse duration 50 – 300 sec Pulse frequency 1 – 200 pps Pulse charge < 10 mQ

Iontophoresis Introduction of medication ions into skin using low-voltage, high amperage DC 0 – 5 mA Skin impedance 500 ohms – 100 kohms Primary path of current/medication flow is through hair follicles and skin pores

Iontophoresis Applied current must be sufficient to overcome skin resistance Once medication is in tissue, it spreads via passive diffusion Electric current no longer plays role Medication tends to remain highly concentrated within tissues directly below introduction site Rate of diffusion is low

Iontophoresis Electrode setup is monopolar Electrode with medication is active electrode Biophysical effect obtained is dependent on the medication used Typical use is to decrease inflammation Dexamethasone Dosage delivery based on relationship between amperage of current and treatment duration Current amperage (milliamps) x treatment time = mA/min 5mA x 10 in = 50mA/min

Iontophoresis Warning Burns or severe skin irritation may result due to application of DC Related to hydrogen and hydroxide ions generated by current