Foundations of Electrotherapy PDF

Foundations of Electrotherapy Foundations of Therapeutic Interventions  Introduction Electrotherapy, when used properly and appropriately, is a safe and effective form of therapy – Electrical stimulation is an adjunct to other therapeutic modalities...

Foundations of Electrotherapy Foundations of Therapeutic Interventions  Introduction Electrotherapy, when used properly and appropriately, is a safe and effective form of therapy – Electrical stimulation is an adjunct to other therapeutic modalities and rehabilitation exercises  Electrical Charges Charge: – Electrical potential of an atom or ion Measured in Coulombs (C) Electrical Potential: – Difference between charged particles at a higher and lower potential High Low Electrons: – Particles of matter possessing a negative charge and small mass Protons: – Particle of matter possessing a positive charge  Principles of Electrical Charges There are two types of charges – Positive – Negative Like charges repel, opposite charges attract – Coloumb’s Law Charge is neither created nor destroyed Charges can be transferred from one object to another  Conductors & Insulators Conductors: Materials that transmit or permits the passage of electrical current – Water, muscle Insulators: Materials the prevent or inhibit the passage of electrical current – Skin, adipose Conductance: Ease with which current flows along a conducting medium  Electricity Electrical current takes the path of least resistance – Cathode: Negative pole High electron concentration – Anode: Positive pole Low electron concentration This imbalance in electrical charge allows the free movement of electrons Isoelectrical Point: – Baseline at which the electrical potential between two poles are equal and no movement of electrons exist  Electricity Electricity flows along a complete pathway between two poles – Allows the free movement of electrons – From generating source to the pole(s) Closed Circuit: – Complete uninterrupted path between two poles Flipping a light switch Electrical stimulating currents in the body Open Circuit: – Incomplete or interrupted path between two poles  Electrical Current Electrical Current: – Net movement of electrons along a conducting medium Current flow is proportional to the magnitude of the force (Voltage) Current always moves from higher potential to lower potential Electrical current must have: – Source of electrons – Conductor – Driving force of electrons (Voltage) Current Flow (I)  Ampere Unit of measure that indicates the rate at which electrical current is flowing – Ampere (A) 1 Ampere = 1 coulomb passes a point in 1 second – 20 coulombs passing in 1 second = 20A  Voltage Electromotive force or potential difference between two poles – Measures the tendency for current flow to occur Electrons places within a field position themselves to move to opposite poles – Creating the potential for work – Work = Force x Distance Volt: – Force required to produce movement of electrons Measure of electrical power (V)  Ohms & Mhos Unit of measure that indicates resistance to current flow – 1 ohm = amount of resistance to develop 0.24 calories of heat when 1A of current is applied for 1 second Mhos – Reciprocal of Ohms – Conductance is a measure of the ease with which current flows Mathematical reciprocal of resistance  Ohm’s Law Ohm’s Law – I = V/R Current flow = I Voltage = V Resistance = R – Current flow is directly proportional to voltage and inversely proportional to resistance – 120V current, with 12 A What is the resistance of the current?  Electrical Power: Watt Watt – Measure of electrical power Electrical power needed to produce a current flow of 1A at a pressure of 1V – Watt = Volts x Amperes  Coulombs: Electrical Charge Electrical current results from the flow of electrons Measure in Coulombs (Q) – Large number of electrons described as a single unit Number of electrons – Charge produced by 6.28 x 1018 electrons or protons Coulomb’s Law: – Relationship between like and unlike charges Opposite charges attract Like charges repel  Resistance Opposition to the flow of electrons by the material through which current travels – Resistance (R) All materials present some degree of opposition to electrical flow – Skin is the primary biological resistor in electrical current flow Resistance is measured on Ohms  Factors Influencing Resistance Material of the Circuit – Conductors = less resistance Length of the Circuit – Shorter distance = less resistance Cross-Sectional Area of the Circuit – Greater cross-sectional area = less resistance Temperature of the Circuit – Higher temperature = Less resistance – Typically, more resistance in wires. Thought to be less in tissue. No evidence.  Factors Influencing Resistance How do these all relate clinically? How can we modify them and why would we want to modify them clinically? Material of the circuit – Think the human body Length of the circuit – Think pads Cross-Sectional area of the circuit – Think nerves Temperature of the circuit  Impedance Force that resists the flow of electrons – Related to resistance Sum of three components: – Resistance: Opposition to flow of electrical current – Inductance: Ability of a material to store electrical energy by means of a electromagnetic field – Created by changes in charged particles – Capacitance: Ability of a material to store energy by the system – Arises from storage of charge within the current  Circuit Types Series Circuit: – Circuit in which there is one path for the current to pass from one pole to another – Often used for sensory-level stimulation Pads close together Over site of pain or injury site Parallel Circuit: – Circuit in which two or more routes exist for current to pass between the two poles – Often used for motor-level stimulation Pads farther apart Over origin and insertion of muscle  Series Circuits Electrons in a series circuit have 1 pathway available for travel. – Connecting a wire between 2 poles The current remains the same in all components along the circuit – Resistance is equal to the sum of the individual resistors  Parallel Circuits Electrons are provided with alternate pathways to follow, often traveling the path of least resistance – Electrons can branch into other parallel or series circuits – Each path has its own A Electrical flow in each path is inversely proportional to the resistance – Amperage is varied, but voltage remains constant Circuit Type  Current Density Physiological effects of electrical stimulation related to the current density and the amount of current per unit area Current density inversely proportional to the size of electrode – Greater surface area = Less current density – Less surface area = Greater current density What does this mean for our patients?  Review Define these terms: – Charge – Coloumb’s Law – Conductor/Insulator/Conductance – Cathode/Anode – Draw an open/closed circuit and a Series/Parallel Circuit – Current Flow/Voltage – Ohms Law – Watt – Factors Influencing Resistance – Current Density  Current Density Lab Part 1 Attach the adhesive electrode to your forearm Lay the second electrode (carbon electrode) on the table with the active side up Place the palm of your hand firmly on the second electrode Set the machine – Frequency – 2 pps – Phase Duration – 100 µsec Increase the output intensity until you feel moderate current Slide your hand from the carbon electrode until only the tip of your index finger is in contact with the electrode. Note how the current sensation changed at the forearm and at the finger. Part 2 Use carbon flex (non-adhesive) electrodes for this activity. You will also need an elastic band/wrap to hold the electrodes, and a moistened paper towel for both electrodes. Secure one electrode on the forearm – use a moist paper towel. Lay (do not secure it) the second electrode on the forearm (do not use a moist paper towel with this electrode). Increase intensity until you feel a muscle contraction. Note the current intensity and strength of contraction. Now, firmly attach the second electrode to the forearm with an elastic band/wrap (do not use a moist paper towel with this electrode). Increase intensity until you feel a muscle contraction. Note the current intensity and strength of contraction. Place a moistened paper towel on the forearm and then firmly attach the second electrode to the forearm with an elastic wrap – on top of the moistened paper towel. Increase intensity until you feel a muscle contraction. Note the current intensity and strength of contraction.  Thinking Questions Part 1 – How did the current sensation change at the forearm and at the finger? Why? Part 2 – How did the current intensity and strength of contraction change in Part 2 with the different electrode configurations? Why is it important to firmly attach electrodes? Why is it important to use a moistened paper towel? As you are increasing the current intensity during an ES treatment with a monopolar electrode configuration, the person describes feeling the current primarily at the dispersive electrode. Identify at least three steps you could take to have stimulation perceived under the active electrode only. Types of Electrical Currents & Waveforms  Types of Electrical Currents Direct Current (DC) – Galvanic flow of ions that always flows in the same direction Positive Negative Alternating Current (AC) – Current flow that periodically changes its polarity and direction of flow Pulsed Current – Unidirectional or bidirectional flow of ions that ceases for a small period of time before the next flow of ions Interpulse Interval: Period of time in between pulses of ion movement  Modality Generators Shapes current wave form – Creates the waveform – AC or DC Creates carrier frequency – The frequency of the electrical wave – Determined by the electrical modality machine  Carrier Frequency Low = 0.1 - 1000 Hz – Most electrical muscle stimulation used Medium = 1001 - 10,000 Hz – Russian stimulation High = 10,000 - ↑ Hz – Diathermy  Transformers Device changes voltage in alternating current (AC) Step-up transformer Allows an electrical device that requires a high voltage power supply to operate from a lower voltage source – Hand-held modality units Step-down transformer Allows a device that requires a low voltage power supply to operate from a higher voltage – Wall modality units  Waveform Terminology Amplitude – Intensity of the current – Height of the wave from the baseline – Amplitude occurs in each individual waveform Frequency – Number of cycles per second  Phase & Pulse Phase – Portion of the wave that rises above or below the baseline Pulse – Finite period of charged particle movement, separated from other pulses with periods of time of no current flow Pules consist of 1 or more phases  Alternating Current Impulses Biphasic Current – Bidirectional flow of ions Negative Phase Positive Phase – Electrons always move from negative to positive pole, reversing direction when polarity is reversed Cycle = AC phase Monophasic Current – Also known as Galvanic current – Uninterrupted unidirectional flow of ions toward a pole Positive or Negative  Phase & Pulse Characteristics Phase Shape – Shape of the output current Rectangular, Triangular, Spike Phase Charge – Total electrical charge of a single phase Measured in coulombs Pulse Charge – Amount of electrical charge of a single pulse Sum of the phase charges Burst – Finite series of pulses flowing for a limited time, followed by no current flow  Pulse Rate (Frequency) Wave form repeated at regular intervals – Number of events per second Direct current – Frequency = Pulses per Second (pps) Alternating current – Frequency = Cycles per second (cps) or – Measured in Hertz (Hz)  Common Rates in Electrical Modalities ------------------------------------------------------------------------------ Descriptor PPS Neuromuscular Effects ------------------------------------------------------------------------------ Low Motor