Ch. 9 Principles of Electrotherapy

Question 1

Define electricity and electric current:

Answer 1

Electricity : the flow of electrons

Electric Current : flow of electrons from negative to positive

Question 2

Define coulomb:

Answer 2

Coulomb : the number of electrons

Question 3

Define ampere:

Answer 3

Ampere : rate

Question 4

To have current, what three things must be present?

Answer 4

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)

Question 5

What is voltage?

Answer 5

Voltage (V) is the measure of electric potential deference

area of negative charge –> area of positive charge

Question 6

What is resistance?

Answer 6

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

Question 7

Define Ohm’s Law:

Answer 7

Ohm’s Law:

V = I * R
OR
I = V/R

Voltage = current X resistance

Question 8

Define capacitance:

Answer 8

Capacitance (bucket) is the ability of a material to store an electrical charge

Question 9

Define the types of electric currents:

Answer 9

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

Question 10

Define amplitude:

Answer 10

Amplitude: intensity or magnitude of the current

*Varies so highly that we do not even document this number

Question 11

Define phase duration:

Answer 11

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

Question 12

How can we increase phase charge?

Answer 12

Increasing the phase duration or amplitude increases the phase charge

Question 13

Define Rheobase:

Answer 13

Rheobase: smallest amplitude of current needed to cause tissue excitation when applied for a maximum duration (100-300usec)

Question 14

Define Chronaxie:

Answer 14

Chronaxie: duration needed to excite the tissue when peak current is 2x the rheobase

Question 15

Define frequency:

Answer 15

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

Question 16

Define rise time:

Answer 16

Rise time : time it takes to get from 0 to maximum amplitude within each pulse

Question 17

Explain the Law of Dubois Reymond:

Answer 17

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

Question 18

Explain what ramping is?

Answer 18

• 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

Question 19

Explain how a duty cycle works?

Answer 19

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

Question 20

Choice of electrode is based on what two factors?

Answer 20

Choosing electrode size is based on:

1) area to be treated (size)
2) purpose of treatment (ex: trigger point = small electrode)

Question 21

How can we minimize electrode resistance?

Answer 21

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

Question 22

Define and explain current density:

Answer 22

Current density : concentration of current within the tissue, depends on two factors:

1) Size of the electrode
2) Distance between the electrodes

Question 23

Explain current density in terms of electrode placement?

Answer 23

Electrodes close together : current concentrated in superficial tissues

Electrodes distant : potential to take deeper path through nerve and blood vessels which have less resistance

Question 24

What is the difference between monopolar configuration and bipolar configuration?

Answer 24

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