1. Principles of Electrical Currents
HuP 272

2. Electricity is an element of PT modalities most frightening and least understood.
Understanding the basis principles will later aid you in establishing treatment protocols.

3. General Therapeutic Uses of Electricity
Controlling acute and chronic pain
Edema reduction
Muscle spasm reduction
Reducing joint contractures
Minimizing disuse/ atrophy
Facilitating tissue healing
Strengthening muscle
Facilitating fracture healing

4. Contraindications of Electrotherapy
Cardiac disability
Pacemakers
Pregnancy
Menstruation (over abdomen, lumbar or pelvic region)
Cancerous lesions
Site of infection
Exposed metal implants
Nerve Sensitivity

5. Terms of electricity
Electrical current: the flow of energy between two points
Needs
A driving force (voltage)
some material which will conduct the electricity
Amper: unit of measurement, the amount of current (amp)
Conductors: Materials and tissues which allow free flow of energy

6. Fundamentals of Electricity
Electricity is the force created by an imbalance in the number of electrons at two points
Negative pole an area of high electron concentration (Cathode)
Positive pole and area of low electron concentration (Anode)

7. Charge
An imbalance in energy. The charge of a solution has significance when attempting to “drive” medicinal drugs topically via inotophoresis and in attempting to artificially fires a denervated muscle

8. Charge: Factors to understand
Coulomb’s Law: Like charges repel, unlike charges attract
Like charges repel
allow the drug to be “driven”
Reduce edema/blood

9. Charge: Factors
Membranes rest at a “resting potential” which is an electrical balance of charges. This balance must be disrupted to achieve muscle firing
Muscle depolarization is difficult to achieve with physical therapy modalities
Nerve depolarization occurs very easily with PT modalities

10. Terms of electricity
Insulators: materials and tissues which deter the passage of energy
Semiconductors: both insulators and conductors. These materials will conduct better in one direction than the other
Rate: How fast the energy travels. This depends on two factors: the voltage (the driving force) and the resistance.

11. Terms of electricity
Voltage: electromotive force or potential difference between the two poles
Voltage: an electromotive force, a driving force. Two modality classification are:
Hi Volt: greater than V
Lo Volt: less than V

12. Terms of electricity
Resistance: the opposition to flow of current. Factors affecting resistance:
Material composition
Length (greater length yields greater resistance)
Temperature (increased temperature, increase resistance)

13. Clinical application of Electricity: minimizing the resistance
Reduce the skin-electrode resistance
Minimize air-electrode interface
Keep electrode clean of oils, etc.
Clean the skill on oils, etc.
Use the shortest pathway for energy flow
Use the largest electrode that will selectively stimulate the target tissues
If resistance increases, more voltage will be needed to get the same current flow

14. Clinical application of Electricity: Temperature
Relationship
An increase in temperature increases resistance to current flow
Applicability
Preheating the tx area may increase the comfort of the tx but also increases resistance and need for higher output intensities

15. Clinical Application of Electricity: Length of Circuit
Relationship:
Greater the cross-sectional area of a path the less resistance to current flow
Application:
Nerves having a larger diameter are depolarized before nerves having smaller diameters

16. Clinical Application of Electricity: Material of Circuit
Not all of the body’s tissues conduct electrical current the same
Excitable Tissues
Nerves
Muscle fibers
blood cells
cell membranes
Non-excitable tissues
Bone
Cartilage
Tendons
Ligaments
Current prefers to travel along excitable tissues

17. Laws and Principles of Electricity
Ohm’s Law: V-IR (V is voltage, a measure of the driving force which is equal to the IxR where I is the Ampere (the amount of current flow) and R is the resistance. Or, expressed differently: The Ampere is equal to the Voltage divided by the resistance.
If you know the inter-relationship you can understand if one increased what happens to the other
Watt= electrical power=volt x amps- ohms

18. Stimulation Parameter:
Amplitude: the intensity of the current, the magnitude of the charge. The amplitude is associated with the depth of penetration.
The deeper the penetration the more muscle fiber recruitment possible
remember the all or none response and the Arndt-Schultz Principle

19. Simulation Parameter
Pulse duration: the length of time the electrical flow is “on” also known as the pulse width. It is the time of 1 cycle to take place (will be both phases in a biphasic current)
phase duration important factor in determining which tissue stimulated: if too short there will be no action potential

20. Stimulation Parameter:
Pulse rise time: the time to peak intensity of the pulse (ramp)
rapid rising pulses cause nerve depolarization
Slow rise: the nerve accommodates to stimulus and a action potential is not elicited
Good for muscle re-education with assisted contraction - ramping (shock of current is reduced)

21. Stimulation Parameters
Pulse Frequency: (PPS=Hertz) How many pulses occur in a unit of time
Do not assume the lower the frequency the longer the pulse duration
Low Frequency: 1K Hz and below (MENS .1-1K Hz), muscle stim units)
Medium frequency: 1K to 100K Hz (Interferential, Russian stim LVGS)
High Frequency: above 100K Hz (TENS, HVGS, diathermies)

22. Stimulation Parameter:
Current types: alternating or Direct Current (AC or DC)
AC indicates that the energy travels in a positive and negative direction. The wave form which occurs will be replicated on both sides of the isoelectric line
DC indicated that the energy travels only in the positive or on in the negative direction DC AC

23. Stimulation Parameter:
Waveforms; the path of the energy. May be smooth (sine) spiked, square,, continuous etc.
Method to direct current
Peaked - sharper
Sign - smoother

24. Stimulation Parameter:
Duty cycles: on-off time. May also be called inter-pulse interval which is the time between pulses. The more rest of “off” time, the less muscle fatigue will occur
1:1 Raito fatigues muscle rapidly
1:5 ratio less fatigue
1:7 no fatigue (passive muscle exercise)

25. Stimulation Parameter:
Average current (also called Root Mean Square)
the “average” intensity
Factors effective the average current:
pulse amplitude
pulse duration
waveform (DC has more net charge over time thus causing a thermal effect. AC has a zero net charge (ZNC). The DC may have long term adverse physiological effects)

26. Stimulation Parameter:
Current Density
The amount of charge per unit area. This is usually relative to the size of the electrode. Density will be greater with a small electrode, but also the small electrode offers more resistance.

27. Capacitance:
The ability of tissue (or other material) to store electricity. For a given current intensity and pulse duration
The higher the capacitance the longer before a response. Body tissues have different capacitance. From least to most:
Nerve (will fire first, if healthy)
Muscle fiber
Muscle tissue

28. Capacitance:
Increase intensity (with decrease pulse duration) is needed to stimulate tissues with a higher capacitance.
Muscle membrane has 10x the capacitance of nerve

29. Factors effecting the clinical application of electricity
Factors effecting the clinical application of electricity Rise Time: the time to peak intensity
The onset of stimulation must be rapid enough that tissue accommodation is prevented
The lower the capacitance the less the charge can be stored
If a stimulus is applied too slowly, it is dispersed

30. Factors effecting the clinical application of electricity
An increase in the diameter of a nerve decreased it’s capacitance and it will respond more quickly. Thus, large nerves will respond more quickly than small nerves.
Denervated muscles will require a long rise time to allow accommodation of sensory nerves. Best source for denervated muscle stimulation is continuous current DC

31. Factors effecting the clinical application of electricity:
Ramp: A group of waveforms may be ramped (surge function) which is an increase of intensity over time.
The rise time is of the specific waveform and is intrinsic to the machine.

32. Law of DuBois Reymond:
The amplitude of the individual stimulus must be high enough so that depolarization of the membrane will occur.
The rate of change of voltage must be sufficiently rapid so that accommodation does not occur
The duration of the individual stimulus must be long enough so that the time course of the latent period (capacitance), action potential, and recovery can take place

33. Muscle Contractions Are described according to the pulse width
1 pps = twitch
10 pps = summation
25-30 pps = tetanus (most fibers will reach tetany by 50 pps)

34. Frequency selection: 100Hz - pain relief 50-60 Hz = muscle contraction
1-50 Hz = increased circulation
The higher the frequency (Hz) the more quickly the muscle will fatigue

35. Electrodes used in clinical application of current:
Electrodes used in clinical application of current: At least two electrodes are required to complete the circuit
The body becomes the conductor
Monophasic application requires one negative electrode and one positive electrode
The strongest stimulation is where the current exists the body
Electrodes placed close together will give a superficial stimulation and be of high density

36. Electrodes used in clinical application of current:
Electrodes spaced far apart will penetrate more deeply with less current density
Generally the larger the electrode the less density. If a large “dispersive” pad is creating muscle contractions there may be areas of high current concentration and other areas relatively inactive, thus functionally reducing the total size of the electrode
A multitude of placement techniques may be used to create the clinical and physiological effects you desire

37. General E-Stim Parameters

38. E-Stim for Pain Control: typical Settings