Ch. 9 Principles of Electrotherapy Flashcards
Define electricity and electric current:
Electricity : the flow of electrons
Electric Current : flow of electrons from negative to positive
Define coulomb:
Coulomb : the number of electrons
Define ampere:
Ampere : rate
To have current, what three things must be present?
To have a current, there must be:
1) A source of electrons
2) A conductor (material that allows passage of electrons)
3) Driving force of the electrons (voltage)
What is voltage?
Voltage (V) is the measure of electric potential deference
area of negative charge –> area of positive charge
What is resistance?
Resistance (R) is the opposition to the flow of electrons by material through which current travels
- Resistance is measured in Ohm’s
- Nerves take the past of least resistance
Define Ohm’s Law:
Ohm’s Law:
V = I * R
OR
I = V/R
Voltage = current X resistance
Define capacitance:
Capacitance (bucket) is the ability of a material to store an electrical charge
Define the types of electric currents:
Monophasic: uncommon, have uniquely positive and negative electrodes, do not cross midline
Biphasic: shift polarity continually and each electrode has identical effects, cross midline
Direct current is monophasic
Alternating current is biphasic
Pulsatile: temporary interruptions between each pulse, various shapes, phase durations, interpulse intervals, allows us to control frequency and phase duration
Define amplitude:
Amplitude: intensity or magnitude of the current
*Varies so highly that we do not even document this number
Define phase duration:
Phase duration: Time from when phase of current leaves the isoelectric (zero) line to when it returns
*Must be long enough to overcome capacitance of targeted nerve
How can we increase phase charge?
Increasing the phase duration or amplitude increases the phase charge
Define Rheobase:
Rheobase: smallest amplitude of current needed to cause tissue excitation when applied for a maximum duration (100-300usec)
Define Chronaxie:
Chronaxie: duration needed to excite the tissue when peak current is 2x the rheobase
Define frequency:
Frequency :
- Number of pulses generated per second (pps or Hz (hertz)
- Increasing the frequency causes the patient to feel a stronger sensation of stimulation because there are more waveforms within a given amount of time
- However, phase charge remains unaffected because frequency does NOT affect phase charge
Define rise time:
Rise time : time it takes to get from 0 to maximum amplitude within each pulse
Explain the Law of Dubois Reymond:
Law of Dubois Reymond:
1) Adequate intensity to reach threshold
2) Current onset fast enough to reduce accommodation
3) Phase duration long enough to exceed the capacitance of the tissue
Explain what ramping is?
- A ramp has a period of ‘ramp up’ , period of stand still called ‘plateau’, and a period of gradual release called ‘ramp down’
- A ramp is used for patient comfort only, has no other purpose
Explain how a duty cycle works?
A duty cycle is a pattern of on-off sequencing of electrical activity
- Used for muscle re-education, NOT pain control
ex: 10 sec on, 50 sec off
With extrinsic, you can set a duty-cycle
Choice of electrode is based on what two factors?
Choosing electrode size is based on:
1) area to be treated (size)
2) purpose of treatment (ex: trigger point = small electrode)
How can we minimize electrode resistance?
We can minimize electrode resistance by:
1) Use large electrodes
2) Even, firm contact with skin
3) Use clean electrodes and sponges
4) Keep the sponge interface well moistened
*Keep in mind that lotions and oils can interfere with stim
Define and explain current density:
Current density : concentration of current within the tissue, depends on two factors:
1) Size of the electrode
2) Distance between the electrodes
Explain current density in terms of electrode placement?
Electrodes close together : current concentrated in superficial tissues
Electrodes distant : potential to take deeper path through nerve and blood vessels which have less resistance
What is the difference between monopolar configuration and bipolar configuration?
Monopolar configuration :
-Two or more unequal-sized electrodes, placed at different locations
BENEFITS:
-Can be placed further apart for deeper penetration
-When a polarity effect is desired (wounds, iontophoresis)
-When point stimulation is needed
Bipolar configuration :
- Equal-sized electodes used, placed over treatment site
- Most common set-up for TENS
