Electrical Stimulating Currents

1
Electrical Stimulating Currents

• Jennifer Doherty-Restrepo, MS, LAT, ATC
• FIU Entry-Level ATEP
• PET 4995 Therapeutic Modalities

2
Physiologic Response To Electrical Current

• 1 Creating muscle contraction through nerve or
  muscle stimulation
• 2 Stimulating sensory nerves to help in
  treating pain
• 3 Creating an electrical field in biologic
  tissues to stimulate or alter the healing process

3
Physiologic Response To Electrical Current

• 4 Creating an electrical field on the skin
  surface to drive ions beneficial to the healing
  process into or through the skin
• The type and extent of physiologic response
  dependent on
• Type of tissue stimulated
• Nature of the electrical current applied

4
Physiologic Response To Electrical Current

• As electricity moves through the body's
  conductive medium, changes in the physiologic
  functioning can occur at various levels
• Cellular
• Tissue
• Segmental
• Systematic

5
Effects at Cellular Level

• Excitation of nerve cells
• Changes in cell membrane permeability
• Protein synthesis
• Stimulation of fibroblasts and osteoblasts
• Modification of microcirculation

6
Effects at Tissue Level

• Skeletal muscle contraction
• Smooth muscle contraction
• Tissue regeneration

7
Effects at Segmental Level

• Modification of joint mobility
• Muscle pumping action to change circulation and
  lymphatic activity
• Alteration of the microvascular system not
  associated with muscle pumping
• Increased movement of charged proteins into the
  lymphatic channels
• Transcutaneous electrical stimulation cannot
  directly stimulate lymph smooth muscle or the
  autonomic nervous system without also stimulating
  a motor nerve

8
Systematic Effects

• Analgesic effects as endongenous pain suppressors
  are released and act at different levels to
  control pain
• Analgesic effects from the stimulation of certain
  neurotransmitters to control neural activity in
  the presence of pain stimuli

9
Physiologic Response To Electrical Current

• Effects may be direct or indirect
• Direct effects occur along lines of current flow
  and under electrodes
• Indirect effects occur remote to area of current
  flow and are usually the result of stimulating a
  natural physiologic event to occur

10
Muscle and Nerve Responses To Electrical Current

• Excitability dependent on cell membrane's voltage
  sensitive permeability
• Produces unequal distribution of charged ions on
  each side of the membrane
• Creates a potential difference between the
  interior and exterior of cell
• Potential difference is known as resting
  potential
• Cell tries to maintain electrochemical gradient
  as its normal homeostatic environment

11
Muscle and Nerve Responses To Electrical Current

• Active transport pumps cell continually moves
  Na from inside cell to outside and balances this
  positive charge movement by moving K to the
  inside
• Produces an electrical gradient with charges
  outside and - charges inside

12
Nerve Depolarization

• To create transmission of an impulse in a nerve,
  the resting membrane potential must be reduced
  below threshold level
• Changes in membrane permeability may then occur
  creating an action potential, which propagates
  impulse along nerve in both directions causing
  depolarization

13
Nerve Depolarization

• Stimulus must have adequate intensity and last
  long enough to equal, or exceed, membrane's basic
  threshold for excitation
• Stimulus must alter the membrane so that a number
  of ions are pushed across membrane exceeding
  ability of the active transport pumps to maintain
  the resting potential, thus forcing membrane to
  depolarize resulting in an action potential

14
Depolarization Propagation

• Difference in electrical potential between
  depolarized region and neighboring inactive
  regions causes the electrical current to flow
  from the depolarized region to the inactive
  region
• Forms a complete local circuit and makes the wave
  of depolarization self-propagating

15
Depolarization Effects

• As nerve impulse reaches effector organ or
  another nerve cell, impulse is transferred
  between the two at a motor end plate or a synapse

16
Depolarization Effects

• At the motor end plate, a neurotransmitter is
  released from nerve
• Neurotransmitter causes depolarization of the
  muscle cell, resulting in a twitch muscle
  contraction

Differs from voluntary muscle contraction only in
rate and synchrony of muscle fiber contractions!
17
Strength - Duration Curves

• Represents the threshold for depolarization of a
  nerve fiber
• Muscle and nerve respond in an all-or-none
  fashion and there is no gradation of response

18
Strength - Duration Curves

• Shape of the curve
• Relates intensity of electrical stimulus
  (strength) and length of time (duration)
  necessary to cause depolarization of muscle
  tissue

19
Strength - Duration Curves

• Rheobase
• Describes minimum current intensity necessary to
  cause tissue excitation when applied for a
  maximum duration

20
Strength - Duration Curves

• Chronaxie
• Describes length of time (duration) required for
  a current of twice the intensity of the rheobase
  current to produce tissue excitation

Manufacturers select preset pulse durations in
the area of chronaxie!
21
Strength - Duration Curves

• Aß sensory, motor, A? sensory, and C pain nerve
  fibers
• Durations of several electrical stimulators are
  indicated along the lower axis
• Corresponding intensities would be necessary to
  create a depolarizing stimulus for any of the
  nerve fibers

Microcurrent intensity is so low that nerve
fibers will not depolarize
22
Nonexcitable Tissue and Cells Response To
Electrical Current

• Cell function may speed up
• Cell movement may occur
• Stimulation of extra-cellular protein synthesis
• Increase release of cellular secretions

23
Nonexcitable Tissue and Cells Response To
Electrical Current

• Gap junctions unit neighboring cells
• Allow direct communication between adjacent cells
  (forms electrical circuit)
• Cells connected by gap junctions can act together
  when one cell receives an extracellular message
• The tissue can be coordinated in its response by
  the gap junctions internal message system

24
Nonexcitable Tissue and Cells Response To
Electrical Current

• All structures within the cell, membrane, and
  microtubes are dipoles
• Molecules whose ends carry opposite charge
• Therefore, all cell structures carry a permanent
  charge and are capable of
• Piezoelectric activity
• Electropiezo activity

25
Nonexcitable Tissue and Cells Response To
Electrical Current

• Piezoelectric activity
• Mechanical deformation of the structure causes a
  change in surface electrical charge
• Electropeizo activity
• Change in surface electrical charge causes the
  structure to change shape
• Important concepts regarding the effects
  electrical stimulation has on growth and healing

26
Nonexcitable Tissue and Cells Response To
Electrical Current

• As a structure changes shape, strain-related
  potentials (SRP) develop
• Results due to tension or distraction on the
  surface of the structure
• Compression negative SRPs
• Tension positive SRPs

27
Strain-Related Potentials (SRP)

• Bone (Wolffs Law)
• Stimulates osteoblast, osteocyte, and osteoclast
  activity to assist in bone growth and healing
• Skin Wounds
• Normal Biolelectric Field skin is negatively
  charged relative to dermis
• Current of Injury skin will change to positive
  charge producing a bioelectric current
• Stimulates growth and healing
• At the conclusion of the healing process, the
  Normal Bioelectric Field will be re-established

28
Nonexcitable Tissue and Cells Response To
Electrical Current

• Based on THEORY rather than well-proven,
  researched outcomes
• More research is needed on the effects of
  electrical current on nonexcitable tissue and
  cells

29
Effects of Changing Current Parameters

• Alternating versus Direct current
• Tissue impedance
• Current density
• Frequency of wave or pulse
• Intensity of wave or pulse
• Duration of wave or pulse
• Polarity of electrodes
• Electrode placement

30
Alternating vs. Direct Current

• Nerve doesnt know the difference between AC and
  DC
• With continuous DC, a muscle contraction occurs
  only when the current intensity reaches threshold
  for the motor unit

DC current influence on a motor unit
31
Alternating vs. Direct Current

• Once the membrane of the motor unit repolarizes,
  another change in the current intensity would be
  needed to force another depolarization to elicit
  a muscle contraction

DC current influence on a motor unit
32
Alternating vs. Direct Current

• Biggest difference between the effects of AC and
  DC is the ability of DC to cause chemical changes
• Chemical effects usually occur only when
  continuous DC is applied over a period of time

33
Tissue Impedance

• Impedance resistance of tissue to the passage
  of electrical current.
• Bone and Fat high-impedance
• Nerve and Muscle low-impedance
• If a low-impedance tissue is located under a
  large amount of high-impedance tissue, the
  intensity of the electrical current will not be
  sufficient to cause depolarization

34
Current Density

• Current density refers to the volume of current
  in the tissues
• Current density is highest at the surface and
  diminishes in deeper tissue

35
Altering Current Density

• Change the spacing of electrodes
• Moving electrodes further apart increases current
  density in deeper tissues

36
Altering Current Density

• Changing the size of the electrode
• Active electrode is the smaller electrode
• Current density is greater
• Dispersive electrode is the larger electrode
• Current density is less

37
Frequency

• Effects the type of muscle contraction
• Effects the mechanism of pain modulation

38
Frequency

• Frequency of the electrical current impacts
• Amount of shortening in the muscle fiber
• Recovery time allowed the muscle fiber
• Summation shortening of myofilaments caused by
  increasing the frequency of membrane
  depolarization
• Tetanization individual muscle-twitch responses
  are no longer distinguishable, results in maximum
  shortening of the muscle fiber
• Dependent on frequency of electrical current, not
  intensity of the electrical current!

39
Frequency

• Voluntary muscle contraction elicits asynchronous
  firing of motor units
• Prolongs onset of fatigue due to recruitment of
  inactive motor units
• Electrically induced muscle contraction elicits
  synchronous firing of motor units
• Same motor unit is stimulated therefore, onset
  of fatigue is rapid

40
Intensity

• Increasing the intensity of the electrical
  stimulus causes the current to reach deeper into
  the tissue

41
Recruitment of Nerve Fibers

• An electrical stimulus pulse at a duration
  intensity just above threshold will excite the
  closest and largest fibers
• Each electrical pulse at the same intensity at
  the same location will cause the same fibers to
  fire

42
Recruitment of Nerve Fibers

• Increasing the intensity will excite smaller
  fibers and fibers farther away
• Increasing the duration will also excite smaller
  fibers and fibers farther away

43
Duration

• More nerve fibers will be stimulated at a given
  intensity by increasing the duration (length of
  time) that an adequate stimulus is available to
  depolarize the membranes
• Duration is typically adjustable on low-voltage
  stimulators

44
Polarity

• Anode
• Positive electrode
• Lowest concentration of electrons
• Cathode
• Negative electrode
• Greatest concentration of electrons
• AC electrodes change polarity with each current
  cycle
• DC polarity switch designates one electrode as
  positive and one as negative

45
Polarity

• With AC and Interrupted DC, polarity is not
  critical
• Negative polarity used for muscle contraction
• Facilitates membrane depolarization
• Usually considered more comfortable
• Negative electrode is usually positioned distally

46
Polarity With Continuous DC

• Important consideration when using
  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

47
Electrode Placement

• On or around the painful area
• Over specific dermatomes, myotomes, or
  sclerotomes that correspond to the painful area
• Close to spinal cord segment that innervates an
  area that is painful
• Over sites where peripheral nerves that innervate
  the painful area becomes superficial and can be
  easily stimulated

48
Electrode Placement

• Over superficial vascular structures
• Over trigger point locations
• Over acupuncture points
• In a criss-cross pattern surrounding the
  treatment area
• If treatment is not working, change electrode
  placement

49
Therapeutic Uses of Electrically Induced Muscle
Contraction

• Muscle re-education
• Muscle pump contractions
• Retardation of atrophy
• Muscle strengthening
• Increasing range of motion
• Reducing Edema

50
Therapeutic Uses of Electrically Induced Muscle
Contraction

• Muscle fatigue must be considered
• Variables that influence muscle fatigue
• Intensity
• Frequency
• On-time
• Off-time

51
Muscle Re-Education

• Primary indication muscular inhibition after
  surgery or injury
• A muscle contraction usually can be forced by
  electrically stimulating the muscle
• Patient feels the muscle contract, sees the
  muscle contract, and can attempt to duplicate the
  muscle contraction

52
Muscle Re-Education Protocol

• Intensity must be adequate for muscle
  contraction
• Patient comfort must be considered
• Pulse Duration must be set as close as possible
  to chronaxie for motor neurons
• 300 µsec - 600 µsec
• Frequency should be high enough to give a
  tetanic contraction
• 35 to 55 pps
• Muscle fatigue must be considered

53
Muscle Re-Education Protocol

• On/Off Cycles dependent on patient
• On-time should be 1 - 2 seconds
• Off-time may be 11, 14, or 15 contraction to
  recovery ratio
• Current interrupted or surged current
• Treatment Time should be about 15 minutes
• May be repeated several times daily

54
Muscle Re-Education Protocol

• Instruct patient to allow the electricity to make
  the muscle contract, feeling and seeing the
  response desired
• Next, patient should alternate voluntary muscle
  contractions with electrically induced
  contractions

55
Muscle Pump Contractions

• Used to duplicate voluntary muscle contractions
  that help stimulate circulation
• Pump fluid and blood through venous and lymphatic
  channels back to the heart
• Helps re-establish proper circulatory pattern
  while protecting the injured area

56
Muscle Pump Contractions Protocol

• Intensity must be high enough to provide a
  strong, comfortable muscle contraction
• Pulse Duration must be set as close as possible
  to chronaxie for motor neurons
• 300 µsec - 600 µsec
• Frequency should be at beginning of tetany range
  
• 35 to 50 pps

57
Muscle Pump Contractions Protocol

• Current interrupted or surged current
• On/Off Cycles
• On-time should be 5 to 10 seconds
• Off-time should be 5 to 10 seconds
• Patient Position part to be treated should be
  elevated
• Treatment Time should be 20 to 30 minutes
• May be repeated 2-5 times daily

58
Muscle Pump Contractions Protocol

• Instruct patient to allow electrically induced
  muscle contractions
• AROM may be encouraged at the same time if it is
  not contraindicated
• Use this protocol in addition to R.I.C.E. for
  best results

59
Retardation of Atrophy

• Electrically induced muscle contractions
  stimulate the physical and chemical events
  associated with normal voluntary muscle
  contractions
• Used to.
• Maintain normal muscle function
• Prevent or reduce atrophy

60
Retardation of Atrophy Protocol

• Intensity should be as high as can be tolerated
  by the patient
• Should be capable of moving the limb through the
  antigravity range
• Should achieve 25 or more of the normal maximum
  voluntary isometric contraction (MVIC) torque for
  the muscle
• May be increased during the treatment as sensory
  accommodation occurs

61
Retardation of Atrophy Protocol

• Pulse Duration must be set as close as possible
  to chronaxie for motor neurons
• 300 µsec - 600 µsec
• Frequency should be in the tetany range
• 50 to 85 pps
• Current interrupted or surged current
• Medium-frequency AC stimulator is the machine of
  choice

62
Retardation of Atrophy Protocol

• On/Off Cycles
• On-time should be between 6 -15 seconds
• Off-time should be at least 1 minute
• Treatment Time should be 15 to 20 minutes or
  enough time to allow a minimum of 10 contractions
• May be repeated 2 times daily

63
Retardation of Atrophy Protocol

• Should provide resistance
• May be provided by gravity, weights, or fixing
  the joint so that the contraction becomes
  isometric
• Instruct the patient to work with the
  electrically induced contraction
• But, voluntary muscle contractions is not
  necessary

64
Muscle Strengthening

• Electrically induced muscle contractions may be
  helpful in treating athletes with muscle weakness
  or denervation of a muscle group
• More research is needed

65
Muscle Strengthening Protocol

• Intensity should be enough to make muscle
  develop 60 of torque developed in a maximum
  voluntary isometric contraction (MVIC)
• Pulse Duration must be set as close as possible
  to chronaxie for motor neurons
• 300 µsec - 600 µsec

66
Muscle Strengthening Protocol

• Frequency should be in the tetany range
• 70 to 85 pps
• Current interrupted or surged current with a
  gradual ramp to peak intensity
• Medium-frequency AC stimulator is machine of
  choice

67
Muscle Strengthening Protocol

• On/Off Cycles
• On-time should be 10 - 15 seconds
• Off-time should be 50 seconds to 2 minutes
• Treatment Time should include a minimum of 10
  contractions
• Mimic normal active resistive training protocols
  of 3 sets of 10 contractions
• May be repeated at least 3 times weekly
• Muscle fatigue must be considered

68
Muscle Strengthening Protocol

• Should provide resistance
• Immobilize limb to produce isometric contraction
  torque equal to or greater than 25 of the MVIC
  torque
• Instruct the patient to work with the
  electrically induced contraction
• But, voluntary muscle contractions is not
  necessary

69
Increasing Range of Motion

• Electrically induced muscle contractions pull
  joint through limited range
• Continued contraction of muscle group over
  extended time results in joint and muscle tissue
  modification and lengthening
• May reduce muscle contractures

70
Increasing Range of Motion Protocol

• Intensity should be strong enough to move the
  limb through the antigravity range
• Pulse Duration must be set as close as possible
  to chronaxie for motor neurons
• 300 µsec - 600 µsec

71
Increasing Range of Motion Protocol

• Frequency should be at the beginning of the
  tetany range
• 40 to 60 pps
• Current interrupted or surged current
• On/Off Cycles
• On-time should be between 15 - 20 seconds
• Off-time should be equal to, or greater than,
  on-time
• Fatigue must be considered

72
Increasing Range of Motion Protocol

• Treatment Time should be 90 minutes
• Three 30-minute treatments daily
• Patient Position stimulated muscle group should
  be antagonistic to joint contracture
• Patient should be positioned so joint will be
  moved to the limits of available range
• Patient is passive in treatment and does not work
  with electrically induced contraction

73
Reducing Edema

• Theory 1 sensory level DC stimulation may be
  used to move interstitial plasma protein ions in
  the direction of oppositely charged electrode
• Theory 2 microamp stimulation may cause
  vasoconstriction and reduce permeability of the
  capillary wall
• Limits migration of plasma proteins into the
  interstitial spaces
• More research is needed

74
Reducing Edema Protocol

• Intensity should be 30V - 50V
• 10 less than intensity needed to produce a
  visible muscle contraction
• Frequency 120pps
• Sensory level stimulation
• Current short duration interrupted DC currents
• High-voltage pulsed generators are effective

75
Reducing Edema Protocol

• Electrode Placement distal electrode should be
  negative
• Treatment Time should be approximately 30
  minutes
• Should begin immediately, within 24 hours, after
  injury

76
Stimulation of Denervated Muscle

• Denervated muscle has lost its peripheral nerve
  supply
• Results in a decrease in size, diameter, and
  weight of muscle fibers
• Decrease in amount of tension which can be
  generated
• Increase the time required for contraction
• Electrical currents may be used to produce a
  muscle contraction in denervated muscle to
  minimize atrophy

77
Stimulation of Denervated Muscle

• Degenerative changes progress until muscle is
  re-innervated by axons extending across site of
  nerve lesion
• If re-innervation does not occur within 2 years,
  fibrous connective tissue replaces contractile
  elements
• Recovery of muscle function is not possible

78
Denervated Muscle Protocol

• Intensity should be enough to produce moderately
  strong contraction
• Pulse Duration must be equal to or greater than
  chronaxie of denervated muscle
• Current asymmetric, biphasic (faradic) waveform
• After 2 weeks, other waveforms may be used
• Interrupted DC square, Progressive DC
  exponential, or Sine AC

79
Denervated Muscle Protocol

• Frequency as low as possible but enough to
  produce a muscle contraction
• On/Off Cycles
• On-time should be 1 - 2 seconds
• Off-time may be 14 or 15 contraction to
  recovery ratio
• Fatigue must be considered

80
Denervated Muscle Protocol

• Electrode Placement either a monopolar or
  bipolar electrode setup can be used
• Small diameter active electrode placed over most
  electrically active point on muscle
• Treatment Time should begin immediately after
  injury or surgery
• 3 sets of 5 -20 repetitions 3 x per day

81
Therapeutic Uses of Electrical Stimulation of
Sensory Nerves

• Gate Control Theory
• Descending Pain Control
• Central Biasing
• Opiate Pain Control Theory
• Refer to Chapter 3 to review pain control theories

82
Gate Control Protocol

• Intensity adjusted to tolerance
• Should not cause muscular contraction
• Pulse Duration 75 - 150 µsec
• Or maximum possible on the e-stim unit
• Current transcutaneous electrical stimulator
  waveform
• Frequency 80 - 125 pps
• Or as high as possible on the e-stim unit

83
Gate Control Protocol

• On/Off Cycles continuous on time
• Electrode Placement surround painful area
• Treatment Time unit should be left on until pain
  is no longer perceived, turned off, then
  restarted when pain begins again
• Should have positive result in 30 minutes, if
  not, reposition electrodes

84
Central Biasing Protocol

• Intensity should be very high
• Approaching noxious level
• Pulse Duration should be 10 msec.
• Current low-frequency,high-intensity generator
  is stimulator of choice
• Frequency 80 pps

85
Central Biasing Protocol

• On/Off Cycles
• On-time should be 30 seconds to 1 minute
• Electrode Placement should be over trigger or
  acupuncture points
• Selection and number of points used varies
  according to the part treated
• Treatment Time should have positive result
  shortly after treatment begins
• If not, reposition electrodes

86
Opiate Pain Control Protocol

• Intensity should be high, at a noxious level
• Muscular contraction is acceptable
• Pulse Duration 200 µsec to 10 msec
• Frequency 1 5 pps
• Current high-voltage pulsed current or
  low-frequency, high-intensity current

87
Opiate Pain Control Protocol

• On/Off Cycles
• On-time should be 30 to 45 seconds
• Electrode Placement should be over trigger or
  acupuncture points
• Selection and number of points used varies
  according to part and condition being treated
• Treatment Time analgesic effect should last for
  several (6-7) hours
• If not successful, expand the number of
  stimulation sites

88
Specialized Currents

• Low-Voltage Continuous DC
• Medical Galvanism
• Iontophoresis
• Low-Intensity Stimulators (LIS)
• Analgesic Effects
• Promotion of healing
• Russian Currents (Medium-Frequency)
• Interferential Currents

89
Low-Voltage Continuous DC

• Physiologic Changes
• Polar effects
• Acid reaction around the positive pole
• Alkaline reaction around the negative pole
• Vasomotor Changes
• Blood flow increases between electrodes

90
Low-Voltage Continuous DC Medical Galvanism

• Intensity should be to tolerance
• Intensity in the milliamp range
• Current low-voltage, continuous DC
• Frequency 0 pps
• Electrode Placement equal-sized electrodes are
  used over saline-soaked gauze
• Skin should be unbroken
• Precaution skin burns
• Treatment Time should be 15 - 50 min

91
Low-Voltage Continuous DCIontophoresis

• Discussed in detail in Chapter 9

92
Low-Intensity Stimulators

• LIS is a sub-sensory current
• Intensity of LIS is limited to lt1000 microamps (1
  milliamp)
• Exact mechanism of action has not yet been
  established
• More research is needed

93
Low-Intensity StimulatorsAnalgesic Effects

• LIS is sub-sensory, therefore it does not fit
  existing theories of pain modulation
• May create or change current flow of the neural
  tissues
• May have some way of biasing transmission of
  painful stimulus
• May make nerve cell membrane more receptive to
  neurotransmitters
• May block transmission

94
Low-Intensity StimulatorsWound Healing

• Intensity
• 200 - 400 µamp for normal skin
• 400 - 800 µamp for denervated skin
• Pulse Duration long, continuous, uninterrupted
• Current monophasic DC is best
• May use biphasic DC
• Frequency maximum

95
Low-Intensity StimulatorsWound Healing

• Treatment Time 2 hours
• Followed by a 4 hour rest time
• May administer 2 - 3 treatment per day
• Electrode Placement
• First 3 days
• Negative electrode positioned in the wound area
• Positive electrode positioned 25 cm proximal

96
Low-Intensity StimulatorsWound Healing

• Electrode Placement continued
• After 3 days
• Polarity reversed and positive electrode is
  positioned in the wound area
• In the case of infection
• Negative electrode should be left in wound area
  until signs of infection disappear for at least 3
  days
• Continue with negative electrode for 3 more days
  after infection clears

97
Low-Intensity StimulatorsFracture Healing

• Intensity just perceptible to patient
• Pulse Duration should be the longest duration
  allowed on unit
• 100 to 200 msec
• Current monophasic or biphasic current
• TENS units
• Frequency should be set at lowest frequency
  allowed on unit
• 5 to 10 pps

98
Low-Intensity StimulatorsFracture Healing

• Treatment Time 30 minutes to 1 hour
• May repeat 3 - 4 times per day
• Electrode Placement
• Negative electrode placed close to, but distal to
  fracture site
• Positive electrode placed proximal to
  immobilizing device

99
Russian Currents

• Medium-frequency polyphasic AC
• 2,000 -10,000 Hz
• Two basic waveforms (fixed intrapulse interval)
• Sine wave
• Square wave
• Pulse duration varies from 50 - 250 µsec
• Phase duration is half of the pulse duration
• 25 - 125 µsec

100
Russian Currents

• Current produced in burst mode with 50 duty
  cycle
• To make intensity tolerable, it is generated in
  50-burst-per-second envelopes with an interburst
  interval of 10 msec
• Increasing the bursts-per-second causes more
  shortening in the muscle to take place

101
Russian Currents

• Dark shaded area represents total current
• Light shaded area indicates total current minus
  the interburst interval
• With burst mode, total current is decreased thus
  allowing for tolerance of greater current
  intensity

102
Russian Currents

• As intensity increases, more motor nerves are
  stimulated
• This increases the magnitude of contraction
• Russian current is a fast oscillating AC current,
  therefore, as soon as the nerve re-polarizes it
  is stimulated again
• This maximizes the summation of muscle
  contraction

103
Interferential Currents

• 2 separate generators (channels) are used
• Sine waves are produced at different frequencies
  and may interfere with each other resulting in
• Constructive interference
• Destructive interference

104
Interferential Currents

• If the 2 sine waves are produced simultaneously,
  interference can be summative
• Amplitudes of the current are combined and
  increase
• Referred to as constructive interference

105
Interferential Currents

• If the 2 sine waves are produced out of sync, the
  waves cancel each other out
• Referred to as destructive interference

106
Interferential Currents

• If the 2 sine waves are produced at different
  frequencies, they create a beat pattern
• Blending of waves caused by constructive and
  destructive interference
• Called heterodyne effect

107
Interferential Currents

• Intensity set according to sensations created
• Frequency set to create a beat frequency
  corresponding to treatment goals
• 20 to 50 pps for muscle contraction
• 50 to 120 pps for pain management

108
Interferential Currents

• Electrode Placement arranged in a square
  surrounding the treatment area
• When an interferential current is passed through
  a homogeneous medium, a predictable pattern of
  interference will occur

109
Interferential Currents

• When two currents cross, an electric field is
  created between the lines of current flow
• Electrical field is strongest near the center
• The strength of the electrical field gradually
  decreases as it moves away from center

110
Interferential Currents

• Scanning moves electrical field around while the
  treatment is taking place
• Allows for larger treatment area
• Adding another set of electrodes will create a
  three-dimensional flower effect called a
  stereodynamic effect
• Allows for larger treatment area

111
Interferential Currents

• Human body is NOT homogeneous therefore, unable
  to predict exact location of interferential
  current
• Must rely on patient perception
• Electrode placement is trial-and-error to
  maximize treatment effect

112
Summary

• Electrical therapy is dynamic
• Advances in research
• Engineering
• Technology
• ATs must have strong foundational knowledge in
  electrical therapy
• Educated choices in purchasing
• Able to manipulate treatment parameters to
  optimize physiologic effects