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Electrical Agents


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  • 1. Electrical Agents Covering the principles of electricity for electrotherapy found in Chapter 9 of Knight & Draper’s Therapeutic Modalities: the Art and Science (2008) KIN 195
  • 2. A Common Language
    • To minimize confusion and increase transfer of knowledge, the APTA in 1990 published a common language for electrotherapy.
    • Mastering terminology improves electrotherapy education and facilitates discussions of electrical modalities with peers, sales reps, other health professionals, etc.
  • 3. The Basics of Electricity
    • Static & Current Electricity
      • Static electricity is frictional electricity; difficult to discharge other than all-or-nothing
      • Current electricity is a stream of electrons passed along a conductor. Current can be passed in a Direct Current (DC), unidirectional flow b/w anode & cathode of a battery. Current can also be passed as an Alternating Current (AC) that rhythmically flows b/w anode & cathode.
      • The most common form of electrotherapy is pulsed or interrupted AC.
  • 4. The Basics of Electricity, cont.
    • Brief Review of Chemistry & Physics
      • Know these terms: matter, element, atom, molecule, proton, neutron, electron, electrical charge, ion
      • electrolyte (substance w/ ions that is conductive)
      • Current Flow: flows from low concentration to high concentration (cathode to anode)
      • Conductors transports flow; insulators resists flow; semiconductors can transport with added heat/light/or voltage; partial conductors allow some flow of current under certain conditions
  • 5. The Basics of Electricity, cont.
    • A Review of Basic Chem & Physics, cont.
      • Quantifying Electricity
        • Coulomb: unit of charge
        • Voltage: force created by concentration gradient of electrons
        • Volt: unit of force that pushes current of 1 amp through a resistance of 1 ohm. Commercial voltage is 110 or 220V.
        • Ampere: unit of current flow equal to 1C/sec. Lights and motors use hundreds, e-stim use only mA
        • Ohm: unit of resistance equal to 1V/A.
        • Resistance or Impedance: electricity always flows in path of least resistance.
  • 6. The Basics of Electricity, cont.
    • Current Flow and Ohm’s Law
      • current= force/ resistance or
      • Amp (A) = volt (V)/ ohm ( Ω )
      • Example: with 6V and 6000 Ω , what is the A?
      • Answer: 0.001 A or 1mA.
      • Ex 2: with 100V applied to 20,000 Ω in a muscle, how much current would flow into the muscle?
      • Answer2: 5mA
      • What are the two ways of increasing current in a circuit?
  • 7. Electrical Equipment
    • The Generator: either a gas-type generator or a medical device that converts AC or DC into AC, DC, or pulsed
      • Recall that terminals must be paired (positive and negative) and closed to complete a circuit.
    • Medical Devices are divided into 2 classes
      • Neuromuscular electrical stimulators (NMES) cause muscle contraction
      • Transcutaneous electrical nerve stimulators (TENS) cause sensory nerve depolarization; some muscle contraction can occur
    • Safety Devices include circuit breakers and ground-fault interrupter (GFI); the GFI can trip at 5mA change in as little as 0.025 sec (electrocution can occur from 200mA thru the heart for 1-3 sec)
  • 8. The Generation of Electricity
    • Chemical Generation of electricity occurs in batteries by the migration of electrons through electrolyte medium from one terminal to another
    • Mechanical Power Generation : when electricity is passed through a wire, a magnetic field is created (electromagnetic induction). When insulated wire is moved relative to a magnet, electricity flows in wire. Electrical generators and electrical motors are conceptually based in E-M induction (how are they different?).
  • 9. Generation of Electricity, cont.
    • Alternating Current Terminology
      • Impulse: AC flow in a single direction
      • Cycle: 2 impulses
      • Frequency: rate measured in cycles/sec (cps) low freq is <1000cps and high freq is >10,000cps
  • 10. Output Current Characteristics
    • Current Modulation
      • Current can be in the form of DC, AC or pulsed. A pulse consists of phases (mono-,bi-,tri- or polyphasic).
      • Phase charge (measured in Coulombs) is the total charge in a single phase, the result of amplitude and duration.
      • Amplitude (intensity, output) is measured by voltage delivered to electrodes or current through the circuit (including the patient)
      • Wave form can be many shapes, but most commonly DC is rectangular & AC is sinusoidal
  • 11. Commonly Used Wave Forms (Knight & Draper, p. 142)
    • Direct wave form: DC, rectangular (ionto)
    • Interrupted DC: rectangular (monophasic)
    • Sinusoidal: pure AC (biphasic, IF, Russian)
    • Faradic wave: asymmetrical AC w/ spike
    • Rectangular: interrupted DC, modulated AC
    • Biphasic: symmetrical, balanced, rectangular, pulsed
    • Twin pulse wave form: monophasic, pulsed, twin spiked (high volt muscle stim)
    • Interferential (IF): symmetrical, sinusoidal, hi freq 2000-5000 Hz AC, using two channels simultaneously
    • Russian: 2500Hz AC, polyphasic, symmetrical, sinusoidal, burst modulated every 10msec (50x/min)
  • 12. Tissue Responses to E- Stim
    • Chemical Effects
      • Drives ions of medication into the body; anions to cathodes and cations to anodes
      • Iontophoresis uses mild uninterrupted DC to drive medication through skin into tissues
    • Magnetic Effects
      • Electrical current flows in a conductor, causing a magnetic field to form. Responses of tissues to magnetic fields are poorly understood
  • 13. Tissue Responses to E- Stim, cont.
    • Kinetic Effects (include sensation & muscle contraction)
      • Electricity can help depolarize cells, causing action potentials (obey all-or-nothing law)
      • Real nerves are mixes of A- ά , β , γ , δ (motor & sensory), B (autonomic motor), and C (sensory) fibers; larger nerves conduct faster, more responsive, have lower thresholds, shorter durations of response, & shorter refractory periods
      • The more Superficial or larger the nerve, the more excitable. (A sensory > motor, & motor nerves > C sensory/pain fibers)
      • Frequency of steady stimulation can increase to tetany
      • Motor points are the locations where current elicit the greatest muscle contraction, found through trial and error (unique to each patient)
  • 14. Tissue Responses to E- Stim, cont.
    • Electrodes (3 most common)
      • Metal-sponge electrodes, held in place with straps; require sponge to be wet to conduct current
      • carbon or silicon rubber electrodes, held in place with straps; require conductive gel
      • Adhesive carbon or silicon rubber electrodes, quicker, easier, less durable, more expensive
      • Some companies are making a true single use electrode…
    • Functions
      • Active electrodes are smaller than dispersive electrodes
      • Electrode placement technique includes bipolar (bipasic), unipolar (active/ dispersive)—polarity dependent (each pt. is unique), quadpolar (IF)
      • Current travels 4x better along muscle fiber than perpendicular to it.
  • 15. Therapeutic Uses of E- Stim
    • Five types of tissue responses to electricity; four can be therapeutically useful
      • Ion migration, where ions move through tissue in response to continuous DC current (iontophoresis)
      • Fused response, moderate-amplitude, high frequency pulsed or AC stimulation that facilitates wound healing (twin pulse), edema reduction (twin pulse), and pain reduction (interferential)
  • 16. Therapeutic Uses of E- Stim, cont.
    • Five types of tissue responses to electricity; four can be therapeutically useful
      • Twitch contraction, followed by relaxation from low freq, moderate amp AC facilitates muscle re-education (biphasic, Russian) and tendinitis treatments (twin pulse, biphasic, & Russian)
      • Tetanic contraction from high amp, high freq AC (>20-30pps) helps strength development (biphasic, Russian) and spasm reduction (biphasic, Russian)
  • 17. Phases of the Inflammatory Process
    • Phase I: Acute Phase ( 2 subphases)
      • Early (Acute): inflammatory response lasts 2-4 days (includes vasodilation)
      • Late (Sub-Acute): continue inflammatory phase which is usually complete in 2 weeks (includes phagocytosis, margination)
      • This does not include chronic inflammation
    • Phase 2: Tissue Formation (Proliferation)
      • Tissue rebuilding approximately 2-3 weeks (includes regeneration and collagen synthesis)
    • Phase 3: Remodeling Phase
      • Adapt to original tissue
      • Continues for up to 1 year post injury
  • 18. Inflammatory phases