Physiologic Effects of Electrical Stimulation
- Decrease Pain: gate-control theory / endorphin release
- Decrease Muscle Spasm
- Reduce Edema
- Simulate exercise by muscle contraction: increase muscle fiber recruitment and retard atrophy
- Stimulate Healing
Capacitance
ability of a material to store a charge
Ohm’s Law
V (volts)
I (current)
R (resistance)
V= I * R R= V/I I= V/R
Types of Currents
Monophasic or Biphasic
Monophasic Current
- Current flow in 1 direction
- Unique positive and negative electrodes
- direct current (DC)
- aka: Galvanic
Biphasic Current
- Alternating Current (AC)
- Flow of electrons changes direction regularly (changes polarity)
- Wave form: symmetrical (same shape in both phases) / asymmetrical (different positive and negative)
- Net charge: balance - equal electrical charge in both phases / unbalanced - unequal charge
- Shape: sinusoidal, square, rectangular, triangular
Phase Duration
- Time it takes current to leave the isoelectric line to when it returns to this line
- Tissues respond to phase duration not pulse duration
- Must be long enough to overcome capacitance and cause an action potential - large diameter nerves have low capacitance and reach threshold quickly
Amplitude
- Intensity or Magnitude of the current
- Peak Current - maximum amplitude of the current regardless of duration
- Must be high enough to reach threshold of muscle or nerve - beta is close to skin and has lower threshold so will be stimulated first, give sensory response before motor
- High peak current is associated with greater depth of penetration
Average Current
- Amount of current supplied over a period of time
- Takes into consideration peak amplitude and the phase duration
- Higher average current needed for some physiologic responses
- Too high average current can cause tissue damage
- Depending on wave form, can have high peak but low average current
Root Mean Square (RMS)
- Measure of the effective current contained in the waveform
- Complex calculation
- Similar to average but more accurate
- Preferred over average
Strength Duration Curve
- Describes the relationship between amplitude (strength) of the electrical current and the duration (phase duration)
- If charge is sufficient to overcome the capacitance of a nerve fiber it will depolarize
- If charge does not exceed the capacitance then no depolarization will take place
- Likewise if the amplitude is too low no depolarization will occur no matter how long the duration
- Short duration requires a higher amplitude for the nerve response
- Longer duration allows a lower intensity for the same nerve response
Strength Duration Curves
Ab - tingle
Aa - muscle contraction
Ag - pain
C - a lot of pain
Rheobase
- Minimum amplitude needed to depolarize a nerve fiber when phase duration is infinite
- If peak amplitude fails to exceed rehabs the nerve will not depolarize regardless of phase duration
- Rheobase will never cause depolarization
Chronaxie
- The time (or phase duration) required to depolarize a nerve fiber when the peak current is twice rheobase
- When amplitude is twice rehabs and the phase duration is slightly greater than chronaxie the result will be greatest comfort for the patient
Frequency
- Number of pulses or cycles generated per seconds (pos or Hz)
- Affects the number of action potentials elicited during the stimulation
- Higher frequency leads to summation (motor neuron: tetany)
- The absolute refractory period is the rate-limiting factor of the number of impulses that can be generated by a nerve
Summation
- Single Twitch: contraction and then relaxation
- Summation: force from two twitches, no relaxation after first twitch
- unfused tetanus
- fused tetanus
Wedenski’s Inhibition
- Stimulation at high frequency near refractory period of the sensory nerve causes inhibition
- > 1000 Hz sensory nerves
- Action Potential Failure
- Results in anesthesia between the electrodes
Temporal Summation
35-50 pps / tetanic contraction
Low Frequency Generators
up to 1,000 Hz contraction (rehab muscle) Produce action potential 1-10 Hz or 60-100 Hz are common treatment frequencies TYPES: EMS (electrical muscle stim) HV (low frequency) / best contract LVG (low volt galvanized - drug pusher) Sine Faradic (RD) (used with people who are paralyzed) Interference (IF and RS) / best contract TENS (milliamps) / help with pain
Medium Frequency Generators
1,000 - 100,000 Hz
Russian Stim: 2,500 Hz
IF: 4,000 - 5,000 Hz
Intrinsic duty cycle of 10ms on and 10ms off creates a burst frequency of 50 Hz
It gets in with Medium Frequency but treats with Low Frequency (one side 4,200 and the other side 4,300 - the difference is 100 so it gets in with the high number and treats with the difference (100).
High Frequency Generators
Greater than 100,00 Hz
used for chronic issues
Used for thermal (heat) purposes
Diathermy uses high frequency and creates minimal sensory effects
SUPERFICIAL HEAT:
IR (infrared) - mc
UV (skin and bones)
DEEP HEAT: (diathermy)
MWD (micro wave diathermy)
SWD (short wave diathermy)
US (1 MHz - 3 MHz) (continuous has heat / pulsed US removes heat and you can use for acute) / 1 MHz goes deep and 3MHz is superficial - opposite of normal electricity - increase electricity you increase the depth - opposite with US - increase electricity decrease depth / reverse piezoelectric effect
Electrodes are attached to the current generator by wires called?
leads
There must be how many leads to complete a circuit?
2
Leads can be split or
bifurcated
leads usually are wired into pairs that plug into a
single channel
Unequal size electrodes will
concentrate the current in the smaller electrode and it will give the perception of increased intensity
When sizes vary greatly one may not be able to perceive current under the larger electrode. This becomes the
dispersal electrode
If pads are placed close together the current is most concentrated in
superficial tissues
When pads are far apart the current has the potential to take a
deeper path through the nerve and blood vessels that have less resistance
When you use one big pad and one small pad
the focus/feeling will be on the small pad
the big pad is used for dispersement
Monopolar Electrode Configuration
- Two or more unequal sized electrodes are used
- Can be used with either biphasic (AC) or monophonic (DC) currents
- One is the active and one is the dispersive electrode
- Active at the target site and dispersive away from target site
- 3 reasons for this placement: (1) leads placed far apart - deeper penetration (2) greater comfort (3) to create an electrical field with specific polarity
Bipolar Electrode Configuration
- Can be used with either monophonic (DC) or biphasic (AC) currents
- Two equal sized electrodes are placed over the treatment site
- Most common for TENS
Quadripolar Configuration
- Often used with IF
- Two separate medium frequency currents are used with electrodes placed as cross currents
- Current is interfered with in the center of the two currents
- Can change this location of interference where ou feel the beat frequency
CURRENT: AC or DC
AC =
Biphasic (no polarity)
CURRENT: AC or DC
DC =
Monophasic (polarity)
AC Current types
Sine
Faradic
Interferential
DC Current types
Galvanic
High Volt
Sine
AC - biphasic - no polarity
symmetrical / best contractor / no charge left in patient
Faradic
AC - biphasic - no polarity
asymmetrical / sporadic
Interferential
AC - biphasic - no polarity
two sine waves
Galvanic
DC - monophasic - polarity
make and break
High Volt
DC - monophasic - polarity
Twin Pulsed Peak
Electrothermal
Heat
micro-vibration, electrically leads to heat
Joule’s Law
Electrochemical
Iono and Opiods
Iontophoresis is DC current
Opiod frequency 1-10 (endorphins), 70-120 (enkephalins)
Electrophysical
Kinetic
ions push other molecules around shifting Na+/K+ pump resulting in contraction
Increase frequency = ______ penetration
deeper penetration
Medium frequency = _______ skin impedance
decreased
best to use a bigger electrode and increased voltage
Motor Point or Muscle Belly
isolates the muscle ( 1 pad)
Either side of the Muscle Belly
if the muscle is especially weak (2 pads)
Pad Rule
1 mA per square inch of pad size (3” square pad = 9mA)
Monopolar
large area or trigger / acupuncture point
Dispersal aka Indifferent - large pad (ground)
Active Pad or Pads - small pad
Bipolar
small muscle group
Dispersal and Active Pads are the equal size
Quadripolar
Crisscross Pattern
mA problem
If the dispersal pad is too small or active sites are too large ( too many) = tingle
EMS: Continuous
Use: Pain
Duty Cycle: None
EMS: Surge
Use: Exercise / Rehab
Duty Cycle: 1:3
EMS: Pulsed / Tetanizing
Use: Fatigue / Spasm
Duty Cycle: 1:1
EMS: Reciprocating
Use: contract agonist, then antagonist
Duty Cycle: none
EMS: Modulation
Use: Avoids accommodation
Duty Cycle: none
EMS: Burst / TENS
Use: Packages of stimulation
Duty Cycle: none
Low Frequency: Pain
1-20 endorphins
70-150 enkephalin
Low Frequency: Edema
3-5
Low Frequency: Exercise
15-25
Low Frequency: Fatigue
50
Electricity: Increase mA (amps) =
Increased Muscle Contraction
Electro-induction
charges lie up = electrical lines of force
one object produces electromagnetic property in another
Coulomb
charge
Waveform
pulse width
interpulse width
frequency
Amplitude
magnitude depth
Current (AMP)
electricity that flows
number of electrons
Transformer
increase or decrease volts
Capacitance (OHM)
stores up energy
Resistance
property of substance to oppose current
measured in OHMs
decreased resistance = increased conduction
(shorter path, lower temp, increased diameter)
EMF (electromagnetic force)
measured in Volts (force behind electrons)
difference between force in two objects (whether connected or not)
greater the charge = increase EMF
greater the distance = decrease EMF
Impedance
slow it down (dampen)
increased by oily skin
Strength Duration Curve
Chronaxie = the time necessary for contraction when the rehabs is doubled
Rheobase (threshold) = the minimum volts necessary to excite a nerve
Reaction of Degeneration (RD Factor)
Innervated muscle responds different than denervated muscle
Galvanic & Faradic current are compared to determine extent of damage and prognosis
EMG (electromyography)
used to test muscle best
NCV (nerve conduction velocity)
used to test nerve best
Arndt-Schultz Principle
energy of modality has to be absorbed by body to stimulate physiological response
Law of Grotthus-Draper
inverse relationship between penetration and absorption of energy (US)