a measure of the electromotive force. it is the magnitude of the difference between the + and - pole
electrons only flow between two points if theres what?
a difference between the two points
what is voltage measured in?
what is resistance?
the ability of a material to resist the flow of electrons measured in ohms
what is the formula for resistance?**
Resistance = Voltage/Current
Three factors that affect resistance?
length (greater = greater resistance)
temperature (greater = greater resistance)
How can skin-electrode resistance be reduced?
minimize air-electrode interface
keep electrode and skin clean of oils
how can resistance be reduced?
use the largest electrode that will selectively stimulate the target tissues
reduce the skin-electrode resistance
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.
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.
4 excitable tissues?
What is direct current?
constant flow of electrons for a period of 1 second without interruption. the polarity remains constant.
How can direct current be modulated?
by interrupting the current flow after 1 second
changing the amplitude
uses of direct current?
What is alternating current?
polarity that is continually changing from + to - with a change in current flow
What is alternating current measured in**?
Hertz or cycles per second (frequency)
this is the rate at which AV switches direction
In what form is AC used?
in a modulated form as burst or time modulated
What is pulsatile current?
The non-continuous flow of DC or AC
What is a pulse?
a discrete electrical event separated from other pulses by a period of time in which no activity exists (interpulse interval)
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
Two phases, one + and one -
can be symmetric or asymmetric
can be balanced or unbalanced
When is a monophasic pulse current produced?
when a DC source is interrupted
When is a biphasic pulse current produced?
when an AC current source is interrupted
define a burst.
The generation of two or more continuous pulses separated from the next series of pulses
What happens during a monophasic current?
Electrons stay on one side of the baseline or the other
What are monophasic currents used for?
high voltage pulsed stimulation
What happens during a biphasic current?
Electrons flow on both sides of the baseline (+ and -)
What are biphasic currents used for?
neuromuscular electrical stimulation
Three types of biphasic current types?
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.
5 types of wave forms?
What electrodes are required to administer electrical current to the body?
at least two electrodes of opposing charges
Describe the anode and cathode of DC.
one remains the cathode (+) and the other is the anode (-)
Describe the anode and cathode of AC.
The cathode and anode are constantly changing
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.
When should an electrode be changed?
If feeling "zaps"/sharp stinging pain
if notice a decrease in stimulus
What is current density?**
Tge amount of charge per unity area, measured in mA/cm^2
What is current density influenced by?
electrode size (inversely)
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
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)
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)
When is the monopolar electrode placement technique used?
What is the bipolar electrode placement technique?
Two active electrodes that are typically equal in size are placed over the targeted area
When is the bipolar electrode placement technique used?
What is parameter effectiveness dependent on?
Amplitude (adequate intensity)
What is capacitance?
The ability of tissue to store electricity. The higher the capacitance the longer before a response.
list body tissues from least to most capacitance.
Least: nerve --> muscle fiber --> muscle tissue
therefore nerve is most excitable (less time before a response)
Order of nerve depolarization?
What is the average amplitude?
Average amount of current supplied over a period of time
What is the peak amp?
max point from zero where the pulse is maintained. the higher the amplitude the greater the peak amplitude
What is rise time?
The time it takes for current to move from zero to the peak intensity within each phase
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)
What is decay time?
time it takes for current to move from peak intensity (amp) to zero
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.
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.
What type of phase duration depolarizes sensory nerves?
What type of phase duration depolarizes motor nerves?
What type of phase duration depolarizes pain nerves?
What type of phase duration depolarizes muscle fiber?
What is PULSE duration?
Time it takes for two phases of a pulse with biphasic current. measured in microseconds.
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
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
What does the interpulse interval allow for?
Allows for mechanical changes in the tissues, such as when eliciting muscle contractions.
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.
What is the pulse period inversely proportional to?
What is pulse frequency ("rate")?
The number of pulses delivered through each channel per second.
PPS or Hertz
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
What does pulse frequency determine?
The time for mechanical adaptation. Lower pps allows more time (longer interpulse intervals)
Pulse frequency to elicit summation?
the amount of time between pulses allows some elongation of the fibers, but not to their starting point
Pulse frequency to elicit tetanus?
The current is flowing so rapidly that there is not sufficient time to allow the fibers to elongate
Pulse frequency to elicit twitch?
the interpulse interval is long enough to allow the muscle fibers to return to their original position
What frequency is used for pain relief?
What frequency is used for muscle contraction?
What frequency is used for increased circulation?
Pulse frequency's effect on fatigue?
The higher the frequency the more quickly the muscle will fatigue
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
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.
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
What is duty cycle?
the percentage of time that the current is flowing relative to the time it is not flowing
duty cycle equation?
On / (On + off time) x 100
Gradually increases the current he decreases the current.
Produces a more natural and comfortable contraction
used with on/off time
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
3 methods of TENS?
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.
Uses of TENS?
acute or chronic pain
post-traumatic acute pain
Conventional TENS affects what?
Sensory level - activates spinal gate
output must be modulated to reduce accommodation.
Low Frequency TENS affects what?
Causes the release of B-endorphins from pituitary. binds to the A-beta and C fiber receptor sites and blocks the transmission of pain
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)
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.
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
What is IFC?
Two alternating currents form a single interference current. Pre-modulated output is based on a single alternating current.
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.
Acute and chronic pain (most frequently used for motor-level pain control)
muscle contractions (neuromuscular re-education and edema reduction)
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
What is the polarity of acetic acid?
What is the polarity of lidocaine and epinephrine?
What is the polarity of Dexamethasone?
How often should you check underneath the electrodes to check for skin sensitivity?
Every 5 minutes for a 20 minutes treatment
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
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)
Effects of High volt pulsed stimulation?
edema control and reduction
wound healing (DC more effective)
High volt pulsed stimulation electrode placement?
for acute pain: + electrode over painful site
for chronic pain: - electrode over painful site
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