Principles of Electrical Currents

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Principles of Electrical Currents

• HuP 272

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Electricity is an element of PT modalities most
frightening and least understood.

• Understanding the basis principles will later aid
  you in establishing treatment protocols.

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General Therapeutic Uses of Electricity

• Controlling acute and chronic pain
• Edema reduction
• Muscle spasm reduction
• Reducing joint contractures
• Minimizing disuse/ atrophy
• Facilitating tissue healing
• Strengthening muscle
• Facilitating fracture healing

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Contraindications of Electrotherapy

• Cardiac disability
• Pacemakers
• Pregnancy
• Menstruation (over abdomen, lumbar or pelvic
  region)
• Cancerous lesions
• Site of infection
• Exposed metal implants
• Nerve Sensitivity

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Terms of electricity

• Electrical current the flow of energy between
  two points
• Needs
• A driving force (voltage)
• some material which will conduct the electricity
• Amper unit of measurement, the amount of current
  (amp)
• Conductors Materials and tissues which allow
  free flow of energy

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Fundamentals of Electricity

• Electricity is the force created by an imbalance
  in the number of electrons at two points
• Negative pole an area of high electron
  concentration (Cathode)
• Positive pole and area of low electron
  concentration (Anode)

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Charge

• An imbalance in energy. The charge of a solution
  has significance when attempting to drive
  medicinal drugs topically via inotophoresis and
  in attempting to artificially fires a denervated
  muscle

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Charge Factors to understand

• Coulombs Law Like charges repel, unlike charges
  attract
• Like charges repel
• allow the drug to be driven
• Reduce edema/blood

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Charge Factors

• Membranes rest at a resting potential which is
  an electrical balance of charges. This balance
  must be disrupted to achieve muscle firing
• Muscle depolarization is difficult to achieve
  with physical therapy modalities
• Nerve depolarization occurs very easily with PT
  modalities

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Terms of electricity

• Insulators materials and tissues which deter the
  passage of energy
• Semiconductors both insulators and conductors.
  These materials will conduct better in one
  direction than the other
• Rate How fast the energy travels. This depends
  on two factors the voltage (the driving force)
  and the resistance.

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Terms of electricity

• Voltage electromotive force or potential
  difference between the two poles
• Voltage an electromotive force, a driving force.
  Two modality classification are
• Hi Volt greater than 100-150 V
• Lo Volt less than 100-150 V

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Terms of electricity

• Resistance the opposition to flow of current.
  Factors affecting resistance
• Material composition
• Length (greater length yields greater resistance)
• Temperature (increased temperature, increase
  resistance)

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Clinical application of Electricity minimizing
the resistance

• Reduce the skin-electrode resistance
• Minimize air-electrode interface
• Keep electrode clean of oils, etc.
• Clean the skill on oils, etc.
• Use the shortest pathway for energy flow
• Use the largest electrode that will selectively
  stimulate the target tissues
• If resistance increases, more voltage will be
  needed to get the same current flow

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Clinical application of Electricity Temperature

• Relationship
• An increase in temperature increases resistance
  to current flow
• Applicability
• Preheating the tx area may increase the comfort
  of the tx but also increases resistance and need
  for higher output intensities

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Clinical Application of Electricity Length of
Circuit

• Relationship
• Greater the cross-sectional area of a path the
  less resistance to current flow
• Application
• Nerves having a larger diameter are depolarized
  before nerves having smaller diameters

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Clinical Application of Electricity Material of
Circuit

• Not all of the bodys tissues conduct electrical
  current the same
• Excitable Tissues
• Nerves
• Muscle fibers
• blood cells
• cell membranes

• Non-excitable tissues
• Bone
• Cartilage
• Tendons
• Ligaments
• Current prefers to travel along excitable tissues

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Laws and Principles of Electricity

• Ohms Law V-IR (V is voltage, a measure of the
  driving force which is equal to the IxR where
  I is the Ampere (the amount of current flow) and
  R is the resistance. Or, expressed differently
  The Ampere is equal to the Voltage divided by the
  resistance.
• If you know the inter-relationship you can
  understand if one increased what happens to the
  other
• Watt electrical powervolt x amps- ohms

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Stimulation Parameter

• Amplitude the intensity of the current, the
  magnitude of the charge. The amplitude is
  associated with the depth of penetration.
• The deeper the penetration the more muscle fiber
  recruitment possible
• remember the all or none response and the
  Arndt-Schultz Principle

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Simulation Parameter

• Pulse duration the length of time the electrical
  flow is on also known as the pulse width. It
  is the time of 1 cycle to take place (will be
  both phases in a biphasic current)
• phase duration important factor in determining
  which tissue stimulated if too short there will
  be no action potential

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Stimulation Parameter

• Pulse rise time the time to peak intensity of
  the pulse (ramp)
• rapid rising pulses cause nerve depolarization
• Slow rise the nerve accommodates to stimulus and
  a action potential is not elicited
• Good for muscle re-education with assisted
  contraction - ramping (shock of current is
  reduced)

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Stimulation Parameters

• Pulse Frequency (PPSHertz) How many pulses
  occur in a unit of time
• Do not assume the lower the frequency the longer
  the pulse duration
• Low Frequency 1K Hz and below (MENS .1-1K Hz),
  muscle stim units)
• Medium frequency 1K to 100K Hz (Interferential,
  Russian stim LVGS)
• High Frequency above 100K Hz (TENS, HVGS,
  diathermies)

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Stimulation Parameter

• Current types alternating or Direct Current (AC
  or DC)
• AC indicates that the energy travels in a
  positive and negative direction. The wave form
  which occurs will be replicated on both sides of
  the isoelectric line
• DC indicated that the energy travels only in the
  positive or on in the negative direction

DC
AC
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Stimulation Parameter

• Waveforms the path of the energy. May be smooth
  (sine) spiked, square,, continuous etc.
• Method to direct current
• Peaked - sharper
• Sign - smoother

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Stimulation Parameter

• Duty cycles on-off time. May also be called
  inter-pulse interval which is the time between
  pulses. The more rest of off time, the less
  muscle fatigue will occur
• 11 Raito fatigues muscle rapidly
• 15 ratio less fatigue
• 17 no fatigue (passive muscle exercise)

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Stimulation Parameter

• Average current (also called Root Mean Square)
• the average intensity
• Factors effective the average current
• pulse amplitude
• pulse duration
• waveform (DC has more net charge over time thus
  causing a thermal effect. AC has a zero net
  charge (ZNC). The DC may have long term adverse
  physiological effects)

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Stimulation Parameter

• Current Density
• The amount of charge per unit area. This is
  usually relative to the size of the electrode.
  Density will be greater with a small electrode,
  but also the small electrode offers more
  resistance.

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Capacitance

• The ability of tissue (or other material) to
  store electricity. For a given current intensity
  and pulse duration
• The higher the capacitance the longer before a
  response. Body tissues have different
  capacitance. From least to most
• Nerve (will fire first, if healthy)
• Muscle fiber
• Muscle tissue

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Capacitance

• Increase intensity (with decrease pulse duration)
  is needed to stimulate tissues with a higher
  capacitance.
• Muscle membrane has 10x the capacitance of nerve

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Factors effecting the clinical application of
electricity

• Factors effecting the clinical application of
  electricity Rise Time the time to peak intensity
• The onset of stimulation must be rapid enough
  that tissue accommodation is prevented
• The lower the capacitance the less the charge can
  be stored
• If a stimulus is applied too slowly, it is
  dispersed

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Factors effecting the clinical application of
electricity

• An increase in the diameter of a nerve decreased
  its capacitance and it will respond more
  quickly. Thus, large nerves will respond more
  quickly than small nerves.
• Denervated muscles will require a long rise time
  to allow accommodation of sensory nerves. Best
  source for denervated muscle stimulation is
  continuous current DC

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Factors effecting the clinical application of
electricity

• Ramp A group of waveforms may be ramped (surge
  function) which is an increase of intensity over
  time.
• The rise time is of the specific waveform and is
  intrinsic to the machine.

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Law of DuBois Reymond

• The amplitude of the individual stimulus must be
  high enough so that depolarization of the
  membrane will occur.
• The rate of change of voltage must be
  sufficiently rapid so that accommodation does not
  occur
• The duration of the individual stimulus must be
  long enough so that the time course of the latent
  period (capacitance), action potential, and
  recovery can take place

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Muscle Contractions

• Are described according to the pulse width
• 1 pps twitch
• 10 pps summation
• 25-30 pps tetanus (most fibers will reach
  tetany by 50 pps)

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Frequency selection

• 100Hz - pain relief
• 50-60 Hz muscle contraction
• 1-50 Hz increased circulation
• The higher the frequency (Hz) the more quickly
  the muscle will fatigue

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Electrodes used in clinical application of
current

• Electrodes used in clinical application of
  current At least two electrodes are required to
  complete the circuit
• The body becomes the conductor
• Monophasic application requires one negative
  electrode and one positive electrode
• The strongest stimulation is where the current
  exists the body
• Electrodes placed close together will give a
  superficial stimulation and be of high density

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Electrodes used in clinical application of
current

• Electrodes spaced far apart will penetrate more
  deeply with less current density
• Generally the larger the electrode the less
  density. If a large dispersive pad is creating
  muscle contractions there may be areas of high
  current concentration and other areas relatively
  inactive, thus functionally reducing the total
  size of the electrode
• A multitude of placement techniques may be used
  to create the clinical and physiological effects
  you desire

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General E-Stim Parameters
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E-Stim for Pain Control typical Settings