Intro to E-stim Flashcards
Columb’s Law
Forces exist between charges
Force depends on the size of the charges involved and the distance between them.
Distance has a huge impact on electrical forces
Forces can cause movement of ions
Electrical current (I)
Movement of electrons in Amperes (A) or Milliamps (mA)
Resistance
Opposition to electron flow, ohms
High Resistance = insulators (Fat, dry skin, poorly attached electrodes
Insulators create heat when current passes through
Conductance
Ease of currrent flowing in a medium, units are siemens
Neurons, Water, Muscle
Capacitance
Storage of charge
Works as an insulator, blocks direct current but allow alternating current to continue moving electrons (higher frequency = better flow)
DC = Iontophoresis
Impedance
High impedence = high resistance
Fat
Low impedance = low resistance
Regionally dependent and patient dependent
Ohm’s Law
Current Flow = Voltage/Resistance
Builds up heat and can cause burns
Resistance of tissues constantly flux
Most devices allow use to set current and keep it constant
BUT some don’t! Some keep Voltage constant so we must be aware because it could possibly cause burning if resistance drops
Anode
+, typically red
Cathode
-, typically black
What does a circuit contain?
Anode, cathode, conductor, restritors
To create physiologic effects we need…
A driving V (Battery or plug in)
A proper path for I to flow (Tissues, Nerves)
A way to overcome tissue impedance (Use pulsed or alternating current I)
Direct Current uses a
Battery
Alternating current uses a
plug in
DC
Continuous unidirectional flow of electrons; Doesn’t not flip between positive and negative
Microseconds (1 millionth of a second) or milliseconds (1 thousand of a second)
Doesn’t flow well through body tissues
May cause alkaline burn
**Used only for iontophoresis **
AC
Uninterrupted biphasic (positive to negative and back) flow of electrons
Pulsed Current
Unidirectional or bidirectional flow of electrons that periodically cease for a finite amount of time
+, -, + and -
A pulse is an isolated electrical event that repeats
If AC or Pulsed what type of waves can we get?
Sinusiodal (Hump), Spiked (Triangle), Square
If we have a pulsed current what is important about pulse duration?
Monophasic, biphasic and triphasic
If we have a pulsed current what is important about symmetry?
Symmetry from positive and negative side
If asymmetrical, is it balanced/unbalanced?
Balanced: Area below is the same as above
Unbalanced: Differing amounts of charge above and below baseline
Could irritate the skin
Will form acids and bases on skin
Monophasic can not be symmetrical nor balanced
Triphasic cannot be symmetrical BUT can be balanced **
Phase
Unidirectional flow of current
Phase duration is expressed in…
microseconds
Pulse
isolated event seperated by finite time from next event
Pulse duration
time from beginning to end of all phases within a single phase
Pulse Duration Influences neuronal excitation
Sensory nerve stimulation (20-60 usec)
Motor nerve stimulation (200-400 usec)
Nociceptor Stimulation (300-500 usec)
Pain is perceived
Nociceptor is a stimulus
Rise Time
Longer = More tolerable
Faster = Easier Nerve Stimulation
Decay Time (time going down)
Frequency
Number of pulses/time
PPS – Pulses per seconds
Sensory stimulation for Pain relief = 80-150 PPS
Muscle re-education or strengthening = 35-50 PPS
Amplitude
Magnitude of current (intensity)
Increased amplitude means increased charge
Modulation (Change)
Changing a feature of the waveform
Used in pain relief applications to prevent accommodation (desesitization) of nerve
Several types of modulation may change the total charge delivered to tissue
Whatever works for patient is best
Types of Modulation
- Amplitude (aka scan)
- Duration (change duration of pulse)
- Frequency (aka sweep)
- Strength-Duration (variable waveform changes)
Bursts
finite series of pulses
Function very similar to pulses
Beats
Another type of pulse, made out of AC
Beats and Bursts
Understand frequency, amplitude, phases, symmetry and balance
Same frequency guidelines as with pulses
Duty Cycle
For muscle strengthening use a duty cycle of 15% to 50%
For weak muscle: 5 sec on, 25 sec rest (5/30=17%)
Strong muscle: 10 s on, 10 sec off, (10/20 = 50%)
For muscle fatigue use a higher duty cycle
Electrodes
Skin Prep:
- Clean skin with a wet paper towel not EtOH (alcohol swipes) may break down the hydrogel of electrodes (Can use EtOH wipes for iontophoresis)
Clip hair (Do not shave)
- Hair is very sensitive to electricity when shaved
Prep products
- The more treatment someone requires consider using these
Monopolar
One big (dispersive) electrode and one small (active)
Active = Cathode (-)
Small concentrates it in one area
Bipolar
Two electrodes of equal size
Quadripolar
Four electrodes, two circuits or channels, use for large areas
Current Density (mA/cm^2)
With the same current, a larger electrode will have a smaller current density than a smaller electrode
Low current density is usually more comfortable but less specific
Smaller electrode can be more specific but has a higher current density
If an electrode peels off having less area of contact (very high current density), an electrical burn may occur
Distance between electrodes influences current density in tissues
- Closer together leads to less arching, more superficial tissues
- Farther apart, hits deeper tissue
