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2013-02-16 02:23:20

electrophys final review
Show Answers:

  1. Uses of estim?
    • acute and chronic pain
    • edema
    • muscle spasm
    • joint contractures
    • decrease atrophy
    • tissue healing
    • strengthening
    • fracture healing
  2. contraindications?
    • cardiac issues
    • pacemakers
    • pregnancy
    • menstruation
    • cancerous lesions
    • infection
    • exposed metal implants
    • nerve sensitivity
  3. what is current?
    directed flow of charge from one place to another
  4. What is the driving force of electrons?
    electromotor force
  5. how many electrons per second is one ampere?
    6.25c10^18 electrons/sec
  6. What is voltage?
    a measure of the electromotive force. it is the magnitude of the difference between the + and - pole
  7. electrons only flow between two points if theres what?
    a difference between the two points
  8. what is voltage measured in?
  9. what is resistance?
    the ability of a material to resist the flow of electrons measured in ohms
  10. what is the formula for resistance?**
    Ohms law:

    Resistance = Voltage/Current
  11. Three factors that affect resistance?
    • material composition
    • length (greater = greater resistance)
    • temperature (greater = greater resistance)
  12. How can skin-electrode resistance be reduced?
    • minimize air-electrode interface
    • keep electrode and skin clean of oils
  13. how can resistance be reduced?
    • use the largest electrode that will selectively stimulate the target tissues
    • reduce the skin-electrode resistance
  14. in what way does increased resistance affect the patient?
    if there is increased resistance the voltage has to be increased in order for the patient to feel it. This is not comfortable for the patient.
  15. relationship between length and resistance?
    • the greater the cross-sectional area of a path the less resistance to current flow. 
    • ex: nerves having a larger diameter are depolarized before nerves having smaller diameters.
  16. 4 excitable tissues?
    • nerves
    • muscle fibers
    • blood cells
    • cell membranes
  17. What is direct current?
    constant flow of electrons for a period of 1 second without interruption. the polarity remains constant.
  18. How can direct current be modulated?
    • by interrupting the current flow after 1 second
    • reversing polarity
    • changing the amplitude
  19. uses of direct current?
    • ionto
    • low-voltage stimulation
  20. What is alternating current?
    polarity that is continually changing from + to - with a change in current flow
  21. What is alternating current measured in**?
    • Hertz or cycles per second (frequency)
    • this is the rate at which AV switches direction
  22. In what form is AC used?
    in a modulated form as burst or time modulated
  23. What is pulsatile current?
    The non-continuous flow of DC or AC
  24. What is a pulse?
    a discrete electrical event separated from other pulses by a period of time in which no activity exists (interpulse interval)
  25. Monophasic?
    • one phase for each pulse, + or -
    • produces a polarity effect since current flows through the tissue in one polarity for a given period of time
  26. biphasic?
    • Two phases, one + and one -
    • can be symmetric or asymmetric
    • can be balanced or unbalanced
  27. When is a monophasic pulse current produced?
    when a DC source is interrupted
  28. When is a biphasic pulse current produced?
    when an AC current source is interrupted
  29. define a burst.
    The generation of two or more continuous pulses separated from the next series of pulses
  30. What happens during a monophasic current?
    Electrons stay on one side of the baseline or the other
  31. What are monophasic currents used for?
    high voltage pulsed stimulation
  32. What happens during a biphasic current?
    Electrons flow on both sides of the baseline (+ and -)
  33. What are biphasic currents used for?
    neuromuscular electrical stimulation
  34. Three types of biphasic current types?
    • Symmetrical
    • Balanced asymmetrical
    • unbalanced asymmetrical
  35. Problem with unbalanced asymmetrical biphasic current?
    the imbalance in + and - charges results in a net change over time and can cause skin irritation if used for long durations.
  36. 5 types of wave forms?
    • Sinusodal
    • square
    • spiked
    • triangular
    • sawtooth
  37. What electrodes are required to administer electrical current to the body?
    at least two electrodes of opposing charges
  38. Describe the anode and cathode of DC.
    one remains the cathode (+) and the other is the anode (-)
  39. Describe the anode and cathode of AC.
    The cathode and anode are constantly changing
  40. Describe the differences between small and large electrodes.
    Small electrodes are used for small areas of the body or small muscles that require low levels of stimulation. Large electrodes are used for the opposite.
  41. When should an electrode be changed?
    • If feeling "zaps"/sharp stinging pain
    • if notice a decrease in stimulus
  42. What is current density?**
    Tge amount of charge per unity area, measured in mA/cm^2
  43. What is current density influenced by?
    • electrode size (inversely)
    • electrode placement
  44. How is current density affected by electrode size?
    • When using electrodes of the same size the current density under each electrode is the same.
    • when using different sizes, current is concentrated under the smaller electrode
  45. How is current density affected by electrode placement?
    • The closer the electrodes are the denser the current is in the superficial tissues
    • the farther apart the electrodes are the denser the current is in the deeper tissues (more parallel paths formed)
  46. What is the monopolar electrode placement technique?
    Active electrode is placed over the targeted area while a second dispersive electrode is placed away from the targeted area (active electrode smaller than dispersive)
  47. When is the monopolar electrode placement technique used?
    • wounds
    • ionto
    • edema
  48. What is the bipolar electrode placement technique?
    Two active electrodes that are typically equal in size are placed over the targeted area
  49. When is the bipolar electrode placement technique used?
    • muscle weakness
    • neuromuscular facilitation
    • spasms
    • ROM
  50. What is parameter effectiveness dependent on?
    • Amplitude (adequate intensity)
    • rise time
    • phase duration
  51. What is capacitance?
    The ability of tissue to store electricity. The higher the capacitance the longer before a response.
  52. list body tissues from least to most capacitance.
    Least: nerve --> muscle fiber --> muscle tissue

    therefore nerve is most excitable (less time before a response)
  53. Order of nerve depolarization?
    • Sensory nerves
    • motor nerver
    • pain nerves
    • muscle fiber
  54. What is the average amplitude?
    Average amount of current supplied over a period of time
  55. What is the peak amp?
    max point from zero where the pulse is maintained. the higher the amplitude the greater the peak amplitude
  56. What is rise time?
    The time it takes for current to move from zero to the peak intensity within each phase
  57. When are fast rise times required?
    • With low capacitance tissues such as large motor nerves
    • (sinusoidal wave = gradual rise time, square wave = instantaneous increase in amplitude)
  58. What is decay time?
    time it takes for current to move from peak intensity (amp) to zero
  59. What is PHASE duration?
    The amount of time it takes for one phase or pulse. Begins when the current departs from the zero line and ends when it returns.
  60. Why is phase duration important when causing an AP?
    the length of the phase duration must be sufficient to exceed the capacitance of the targeted nerve in order to cause an AP. If the phase isn't sufficient, a higher intensity will be required to stimulate the tissue.
  61. What type of phase duration depolarizes sensory nerves?
  62. What type of phase duration depolarizes motor nerves?
  63. What type of phase duration depolarizes pain nerves?
  64. What type of phase duration depolarizes muscle fiber?
  65. What is PULSE duration?
    Time it takes for two phases of a pulse with biphasic current. measured in microseconds.
  66. When are the pulse and phase duration the same? different?
    • in a monophasic pulse
    • different in biphasic because there are two phase durations for each pulse
  67. What is the interpulse interval?
    The time between the end of one pulse and the start of the next pulse. increasing the pulse frequency decreases the interpulse interval and vice-versa
  68. What does the interpulse interval allow for?
    Allows for mechanical changes in the tissues, such as when eliciting muscle contractions.
  69. What is the pulse period?
    The amount of time from the start of one pulse to the start of the next. Includes the phase durations and inter pulse interval.
  70. What is the pulse period inversely proportional to?
    Pulse frequency
  71. What is pulse frequency ("rate")?
    • The number of pulses delivered through each channel per second. 
    • PPS or Hertz
  72. What does pulse frequency affect?
    The number of APs elicited during stimulation. Same number of fibers are recruited, but the higher frequency causes them to fire at a more rapid rate
  73. What does pulse frequency determine?
    The time for mechanical adaptation. Lower pps allows more time (longer interpulse intervals)
  74. Pulse frequency to elicit summation?
    • 10-35 pps
    • the amount of time between pulses allows some elongation of the fibers, but not to their starting point
  75. Pulse frequency to elicit tetanus?
    • 35-50 pps
    • The current is flowing so rapidly that there is not sufficient time to allow the fibers to elongate
  76. Pulse frequency to elicit twitch?
    • 1-10 pps
    • the interpulse interval is long enough to allow the muscle fibers to return to their original position
  77. What frequency is used for pain relief?
  78. What frequency is used for muscle contraction?
    50-60 Hz
  79. What frequency is used for increased circulation?
    1-50 Hz
  80. Pulse frequency's effect on fatigue?
    The higher the frequency the more quickly the muscle will fatigue
  81. What is a burst?
    • Contains individual pulses, these pulses still have time-dependent characteristics (ex: pulse duration, interpulse interval, etc.)
    • each burst is separated by "off" times - the interburst interval
  82. What is on-off time?
    The ratio of the time muscle is being stimulated to the time the simulation is off. Allows muscle to recover etween repetitions.
  83. 1:1 duty cycle ratio vs 1:5 duty cycle ratio?
    1:1 has a decline in force and muscle pH compared to a 1:5
  84. What is duty cycle?
    the percentage of time that the current is flowing relative to the time it is not flowing 
  85. duty cycle equation?
    On / (On + off time) x 100
  86. RAMP time?
    • Gradually increases the current he decreases the current. 
    • Produces a more natural and comfortable contraction
    • used with on/off time
  87. Primary use of tens?
    To control pain through gate control theory and opiate pain relief through stimulation of naloxone (antagonist to endogenous opiates)

    may produce muscle contractions
  88. 3 methods of TENS?
    • High TENS
    • Low TENS
    • Brief-intense TENS
  89. What is adjustable on TENS units?
    phase durations, they specifically target sensory, motor, and pain fibers. it is matched with pulse frequency to produce specific effects.
  90. Uses of TENS?
    • acute or chronic pain
    • post-surgical pain
    • post-traumatic acute pain
  91. Conventional TENS affects what?
    • Sensory level - activates spinal gate
    • output must be modulated to reduce accommodation.
  92. Low Frequency TENS affects what?
    • Motor-level output
    • Causes the release of B-endorphins from pituitary. binds to the A-beta and C fiber receptor sites and blocks the transmission of pain
  93. Brief-intense TENS affects what?
    • Noxious-level output (very short treatment duration)
    • Creates a negative feedback loop in the CNS. "short circuits" the pain carrying loop.
    • Opiates inhibit the release of substance P (blocks or reduces pain transmission)
  94. What is modulated tens?
    • Implies that the specific waveform parameters (pulse duration and frequency) are periodically altered or modulated by the device.
    • lessens the chance of the patient accommodating to the electrical stimulus.
  95. Precautions for TENS?
    • Do not use in the presence of unknown pain or pain of central origin
    • Can cause electrode burns, skin irritation
    • motor-level use can cause muscle spasm or muscle soreness
  96. What is IFC?
    Two alternating currents form a single interference current. Pre-modulated output is based on a single alternating current.
  97. Theory behind IFC?
    High-frequency waves easily overcome skin resistance. The two waves are slightly out of frequency. They cancel each other out and produce a frequency of 1 to 299 Hz in the tissues. Results in a comfortable stimulation capable of depolarizing sensory and motor nerves.
  98. IFC uses?
    • Acute and chronic pain (most frequently used for motor-level pain control)
    • Muscle spasm
    • muscle contractions (neuromuscular re-education and edema reduction)
  99. IFC precautions?
    • Don not use in the presence of unknown pain or pain of central origin
    • can cause electrode burns, skin irritation
    • motor-level use can cause muscle spasm or muscle soreness
  100. What is the polarity of acetic acid?
  101. What is the polarity of lidocaine and epinephrine?
  102. What is the polarity of Dexamethasone?
  103. How often should you check underneath the electrodes to check for skin sensitivity?
    Every 5 minutes for a 20 minutes treatment
  104. High volt pulsed stimulation theory**?
    • Short-duration, high amplitude pulses can produce comfortable moderate contractions. Short phases duration targets sensory nerves and motor nerves.
    • **Wave for is modified to decrease total current to improve comfort - low average current
  105. Uses of High volt pulsed stimulation?
    • Reeducation of peripheral nerves
    • delay denervation and disuse atrophy by stimulating muscle contractions
    • reduction of post-traumatic edema
    • increase in local blood circulation
    • restoring range of motion (reduction of muscle spasm, inhibition of spasticity, reeducation of partially denervated muscle, facilitation of voluntary motor function)
  106. Effects of High volt pulsed stimulation?
    • neuromuscular stimulation
    • pain control
    • edema control and reduction
    • blood flow
    • wound healing (DC more effective)
  107. High volt pulsed stimulation electrode placement?
    • for acute pain: + electrode over painful site
    • for chronic pain: - electrode over painful site
  108. High volt pulsed stimulation precautions?
    • Motor-level stimualtion can cause unwanted tension on the muscle fibers, the tendons, or the bony insertion
    • muscle fatigue can occur if the duty cycle is too high
    • intense or prolonged stimulation may result in muscle spasm and/or muscle soreness.
    • improper use can cause electrode burns or irritation