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Basic Principle of Electrotherapy

Basic Principle of Electrotherapy

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Basic Principle of Electrotherapy

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  1. Basic Principle of Electrotherapy Mobile:0966542115404 Office number: 2074 Building: 24 Mohammed Taher Ahmed Ph.D. PT Associate Professor Rehabilitation Science CAMS-KSU

  2. Objectives Define electricity, potential difference, ampere, &watt, resistance Interpret Ohm’s law and its mathematical expression. Categorize different waveforms & pulse characteristics. Discriminate between series and parallel circuit. Establish the various treatment parameters that must be considered with electrical stimulation Describe the differences between alternating direct and pulsatile currents Describe the differences between alternating direct and pulsatile currents Explain the association between current density & electrodes size. Explain the effects of frequency of muscle contraction. Determine the reaction associated with different polarity. Categorize the types of electrodes and their configurations used with electrical stimulation application.

  3. Electrical Current is a flow of electron (e-) from higher to lower concentration. Basic Terminology Electrotherapyis the application of electrical energy modalities for therapeutic purposes Electrical Stimulation (ES) is the application of therapeutic electrical current to stimulate excitable tissues, with the aim of producing physiological reaction for therapeutic benefits.

  4. Basic Terminology • Cathode (-): • The electrode connected to the negative terminal of battery • Point of high e-concentration • Color code is black. Anode (+): • The electrode connected to the positive terminal of battery • Point of low e-concentration • Color code is red

  5. Basic Terminology • Intensity (Magnitude) of Current • It is the rate of an (e-)flow through a conductor from cathode (-) to anode (+), per second. • Usually measured in Ampere or (mA= 1/1,000 ampere) or (μA; 1/1,000,000 ampere) 1 amp = 6.25 x 1018 e- / sec Electrical Power: • It is the rate of work that produces in unit of time. • The unit to measure the power is watt. • Watt = Volts x Amperes (VI) • 1 Watt = 1 amp of current flowing with a force of 1 V

  6. Basic Terminology • Voltage (electrical potential difference ): • A difference of potential exists between similar bodies charged with different quantities of electricity. The force that produces this motion is called EMF. The force resulting from an accumulation of e- at one point in an electrical circuit. • Higher voltages result in deeper penetration • High Volt: ≥150 V • Low Volt: ≤150 V • Volt: Potential difference necessary to move 1 A of current in 1 sec against a resistance of 1 Ω

  7. Basic Terminology Resistance:is a quantitative degree of opposition to the flow of electron. • It depends on; • Type of the material • Length • Cross-sectional area • Temperature • Resistance is directly proportional to lengthand inversely proportional to cross section area of a conductor.

  8. Ohm's lawcurrent is directly proportion to voltage & inversely proportional to resistance” I = V/R Where: I=current flow, V=Potential differences, R=Resistance • Ohm: (Ω) unit to measure resistance to current flow; • 1 ohm = the amount of resistance needed to develop 0.24 calories of heat when 1 A of current is applied for 1 second

  9. Self test: • What is the current flow in a 40-V circuit possessing 10 ohms of resistance? • I = V/R • I = 40 V/10 Ω • I = 4 A • What is the resistance found in a 40-V circuit possessing a current flow of 10A? • I = V/R • 10 A = 40 V/R • R = 4 Ω • What is the voltage of a circuit providing 4 ohms of resistance when 10 A are flowing? • I = V/R • 10 A = V/4 Ω • V = 40 V

  10. Clinical Application to Overcome skin Resistance • Decrease distance between electrodes (length) • Increase the size of electrodes (cross section area) • Minimize air-electrode interface • Use electrodes jelly or moisten the electrodes • Pre-warming the skin by moisten heat (i.e. hot packs) • N.B. Preheating the treatment area may increase the comfort of the patient but also increases resistance and need for higher output intensities

  11. Basic Terminology Conductor is the elements whose atoms have few {e- } in their outer orbit, and facilitate passage of an electrical current. Higherconductance materials: free flow of e-s • Silver, Copper, • Electrolyte solutions • Blood cell: highest ionic & H20 • Inner layer of the skin • Nerves • Muscle fibers • Cell membranes Low conductance materials: few free e-s • Air, Wood, Glass, Rubber • Bone • Cartilage • Tendons • Ligaments • Outer layer of Skin has keratinized epithelium (little H20) acts as insulator In human body: The greater is the percentage of H2O in the tissues, the better is the conductance of electricity.

  12. Types of Electric Circuits Parallel Circuit • More than one pathway for flow of electrons • 1/R total = 1/R1+1/R2 +1/R3 • Voltage will not decrease at each resistance component • Lower resistance and higher current flow Series Circuit • Only one pathway for current flow • R total = R1 + R2 + R3 • Voltage will decrease at each resistance component • Higher resistance and lower current flow

  13. Electrical Circuits in the Human Body Current enters the body through a SERIES circuit (skin &fat). Once the current enters the tissues, it takes many different PARALLEL paths

  14. Waveforms Waveform is a graphic representation of shape, direction, amplitude, duration and frequency of the electrical current. 1-Waveforms Shape: • Sine wave • Rectangular wave • Square wave • Triangular wave • Saw tooth wave • Trapezoid wave All types of current may take on any of the waveform

  15. . Symmetrical waveforms Each phase Equal in amplitude, Equal in shape & size Net charge is zero Waveforms Asymmetrical waveforms : Each phase Not equal in amplitude, Not equal in shape &size Net charge > than zero.

  16. Parameters of electrical Current Parameters • Types of currents: Alternating vs. direct current • Frequency • Intensity of current • Pulse attributes • Tissue impedance • Current density • Electrodes considerations 8-A-Polarity8-B-Types and size8-C-placement8-D-Configurations8-F-Orintation

  17. 1-Alternating vs. Direct Current

  18. 1-Alternating vs. Direct Current Nerve doesn’t know the difference between AC and DC The biggest difference between direct and alternatingcurrent is the ability of direct current to produce chemical reaction. This reaction usually occurs with continuousunidirectional, long pulse duration current. • In low voltage direct current (LVDC) the chemical reaction may occurs. • In high voltage pulsed direct current (HVPC), the chemical reaction may not created due to short pulse duration. • In alternating current, the chemical reaction my not occur due to reversed polarity

  19. 2-Frequency (CPS, PPS, Hz) Frequency of stimulus is a number of pulse generated in seconds (Hz, PPs, CPs)

  20. 2-Frequency (CPS, PPS, Hz) Amount of muscle muscles tension (contraction) and amount of recovery is function of frequency • Effects the mechanism of pain modulation • Spinal pain modulation > 80Hz • Supraspinal pain modulation <20Hz • Effects the type of muscle contraction • Twitch response < 20 Hz • Individual twitches become less distinguishable =20-35 Hz • Tetanic muscles contraction >50 Hz

  21. 3-Intensity=Amplitude Peak current Amplitudeisthe maximum tip of highest point of each phase from baseline. Peak to peak amplitude: is the maximum tip of highest point of in one phase to highest point in the next phase

  22. 3-Intensity=Amplitude • Intensity should be high enough to exceed the threshold of nerve and muscles • Increase intensity will increase • Strength of stimulus sensory and motor (e.g. contraction). • Depth of penetration of current to deeper tissue (nerve & muscles) • Number of motor unit recruited A stimulus pulse at a duration-intensity just above threshold will excite the closest and largest fibers Increasing the intensity will excite smaller fibers and fibers farther away.

  23. 4-Pulse Attributes • Pulse: • An individual waveform is referred to as a pulse and may contain (one , two or more phases). It measured in microseconds or milliseconds • Pulse Period isthe combined time of the pulse duration (PD) and the inter-pulse interval (IPI). • 1-Pulse interval (PD)=pulse width:is the length of time electrical flow is “on” • 2-Interpulse interval (IPI) ;is the length of time electrical flow is “off” • In monophasic current (pulse duration = phase duration). • In biphasic current (pulse duration is combination of phase durations) • Phase:Phase is a part of pulse. • Phase duration is length of time current flow in one direction before turning to isoelectrical line • In monophasic current (pulse = phase) . • In biphasic (alternating) current (pulse= two separate phases) • In polyphasic current (pulse= polyphasic)

  24. 4-Pulse Attributes Burst duration is the combined time of the burst duration (BD) and the inter-burst interval (IBI). 1-Burst is series of pulses flowing for a definite time period followed by no current flow. 1-Burst interval (BI)is the length of the time during which burst occurs.2-Interburst interval (IBI)is length of the time between bursts, and current flow is “off”

  25. 4-Pulse Attributes Shorter phase durations require greater intensity (amplitude) to evoke an action potential. Longer phase durations require less intensity (amplitude) to evoke an action potential. Muscle contraction: Optimum duration – 300-500μsec Stimulation of denervated muscle: Optimum duration > 1msec

  26. 4-Pulse Attributes Pulse Train: individual patterns of waveforms, durations &/or frequencies that are linked together (repeat @ regular intervals) Amplitude Ramp: gradual rise &/or fall in amplitude of a pulse train (causes a gradual  in the force of m. contractions by progressive recruitment of motor units) • Ramp up • Time during which the intensity increases • Plateau • Time during which pulses remain at maximum preset intensity • Ramp down • Time during which the intensity decreases

  27. Self Questions: Pulse Attributes F • A = Amplitude • B = Phase Duration • C = Pulse Duration • D= Inter-pulse Interval • F=Pulse period A B D C B

  28. 5-Tissue impedance Impedance is the resistance of the tissue to the passage of electrical current. Z=1/2πFC • High – impedance tissue skin, bone & fat • Low – impedance tissue Nerve & muscle. • Dray skin resistance (100.000-600,000Ω) • Moist skin resistance (1000-20,000 Ω) How to overcome resistance to passage of current? • Decrease distance between electrodes • Increase the size of electrodes • Minimize air-electrode interface • Use electrodes jelly or moisten the electrodes • Pre-warming the skin by moisten heat modalities (e.g. hot packs)

  29. 6-Current Density (CD) Current Density (CD) is theamount of current flow per cubic volume in the tissue. CD is highest where electrodes touch skin and decreased as the electricity penetrates the deeper tissues. Increases CD increase perception of stimulus If there is a large fat layer between electrodes and nerve, a high current density dose not depolarize the nerve.

  30. Altering Current Density: Spacing of Electrode A A placed closely electrodes produces highCD in superficial tissues. A spaced apart electrodes produces highCD in the deeper tissue (nerve& muscle). B A B

  31. Altering Current Density : Electrodes size Current density is inversely proportional to electrode size • Large electrode (dispersive electrode) remote from the treatment area, ) CD is lesse • Small electrode (active electrode) closed relatively to treatment area (nerve and muscle) CD is greater

  32. 7-Electrodes Consideration: PolarityTypes and sizeplacementConfigurationsOrintation

  33. 8-A Polarity • Anode Positive Electrode With Lowest Concentration of Electrons • Cathode • Negative Electrode With Greatest Concentration of Electrons • With AC Current and Interrupted DC Current Polarity Is Not Critical • Select Negative Polarity For Muscle Contraction • Facilitates Membrane Depolarization • Usually Considered More Comfortable • Negative Electrode Is Usually Positioned Distally

  34. 8-A-Polarity • Important Consideration When Using (DC) Iontophoresis • Positive Pole • Attracts - Ions • Acidic Reaction • Hardening of Tissues • Decreased Nerve irritability • Negative Pole • Attracts + Ions • Alkaline Reaction • Softening of Tissues • Increased Nerve Irritability

  35. 8-BTypes and size I-Size (same size, unequal size) II-Types (carbon rubber, metal, self adhesive electrode)

  36. 8-C-Electrodes placement : Locations • II-Locations • On and /or around the painful area. • Over specific dermatome corresponding to the painful area. • Over specific myotomes corresponding to the painful area . • Spinal cord segment. • Course of peripheral nerve. • Motor point. • Over trigger point. • Acupuncture point.

  37. 8-D-Electrodes Configuration Monopolar, • Active electrode (s) [smaller] is stimulating electrode and placed on the target muscle, greatest current density – treatment effect. • Dispersive electrode [larger] –required to complete the circuit, low current density – little or no sensation is felt from this electrode

  38. 8-D-Electrodes Configuration Bipolar Configuration • Bipolar: two electrodes are placed on the target muscle, close to the origin and insertion. • Electrodes are of equal (or near equal) size. • Current density will be equal under each electrode

  39. 8-D-Electrodes Configuration Quadripolar Configuration • Quadripolar: four electrodes are placed on the target tissue Interferential.

  40. 8-F-Electrodes Orientation Muscle fibers are 4 times more conductive when the current flows with the direction of the fibers than when it flows across them