Electrical Stimulation Currents

1. Electrical Stimulation Currents Therapeutic Modalities Chapter 5

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

3. Electromagnetic Radiations • Other Forms Of Radiation Other Than Visible Light May Be Produced When An Electrical Force Is Applied

4. Infrared Spectrum Red Orange Yellow Green Blue Violet Ultraviolet

5. Electromagnetic Radiations • In Addition, Other Forms Of Radiation Beyond Infrared And Ultraviolet Regions May Be Produced When An Electrical Force Is Applied • These Radiations Have Different Wavelengths And Frequencies Than Those In The Visible Light Spectrum

6. Collectively The Various Types Of Radiation Form The Electromagnetic Spectrum

7. Electromagnetic Spectrum Longest Wavelength Lowest Frequency Electrical Stimulating Currents Commercial Radio and Television Shortwave Diathermy Microwave Diathermy Infrared { LASER Visible Light Ultraviolet Shortest Wavelength Highest Frequency Ionizing Radiation

8. Wavelength And Frequency • Wavelength-Distance Between Peak Of One Wave and Peak of the Next Wave • Frequency-Number Of Wave Oscillations Or Vibrations Per Second (Hz, CPS, PPS) • Velocity=Wavelngth X Frequency

9. Electromagnetic Radiations Share Similar Physical Characteristics • Produced When Sufficient Electrical Or Chemical Forces Are Applied To Any Material • Travel Readily Through Space At An Equal Velocity (300,000,000 meters/sec) • Direction Of Travel Is Always In A Straight Line

10. Electromagnetic Radiations Share Similar Physical Characteristics • When Contacting Biological Tissues May Be…

11. Electromagnetic Radiations Share Similar Physical Characteristics • When Contacting Biological Tissues May Be… • Reflected

12. Electromagnetic Radiations Share Similar Physical Characteristics • When Contacting Biological Tissues May Be… • Reflected • Transmitted

13. Electromagnetic Radiations Share Similar Physical Characteristics • When Contacting Biological Tissues May Be… • Reflected • Transmitted • Refracted

14. Electromagnetic Radiations Share Similar Physical Characteristics • When Contacting Biological Tissues May Be… • Reflected • Transmitted • Refracted • Absorbed

15. Laws Governing The Effects of Electromagnetic Radiations • Arndt-Schultz Principle • No Changes Or Reactions Can Occur In The Tissues Unless The Amount Of Energy Absorbed Is Sufficient To Stimulate The Absorbing Tissues

16. Laws Governing The Effects of Electromagnetic Radiations • Law Of Grotthus-Draper • If The Energy Is Not Absorbed It Must Be Transmitted To The Deeper Tissues • The Greater The Amount Absorbed The Less Transmitted and Thus The Less Penetration

17. Laws Governing The Effects of Electromagnetic Radiations • Cosine Law • The Smaller The Angle Between The Propagating Radiation And The Right Angle, The Less Radiation Reflected And The Greater The Absorption Source Source

18. Laws Governing The Effects of Electromagnetic Radiations • Inverse Square Law • The Intensity Of The Radiation Striking A Surface Varies Inversely With The Square Of The Distance From The Source Source 1 Inch 2 Inch

19. Electromagnetic Modalities • The Majority of Therapeutic Modalities Used By Athletic Trainers Emit A Type Of Energy With Wavelengths And Frequencies That Can Be Classified As Electromagnetic Radiations

20. Electromagnetic Modalities Include... • Electrical Stimulating Currents • Shortwave And Microwave Diathermy • Infrared Modalities • Thermotherapy • Cryotherapy • Ultraviolet Radiation Therapy • Low-Power Lasers • Magnet Therapy

22. 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

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

24. 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

25. 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: an area of low electron concentration (Anode)

26. Charge • An imbalance in energy. The charge of a solution has significance when attempting to “drive” medicinal drugs topically via iontophoresis and in attempting to artificially fire a denervated muscle

27. 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

28. 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

29. 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.

30. 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 100-150 V • Lo Volt: less than 100-150 V

31. 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)

32. Clinical application of Electricity: minimizing the resistance • Reduce the skin-electrode resistance • Minimize air-electrode interface • Keep electrode clean of oils, etc. • Clean the skin of 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

33. 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

34. 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

35. 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 Clinical Application of Electricity: Material of Circuit

36. 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

37. Simulation Parameter • Pulse duration: the length of time the electrical flow is “on” ( on vs off time) 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

38. 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 reeducation with assisted contraction - ramping (shock of current is reduced)

39. 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 ot 100K Hz (Interferential, Russian stim LVGS) • High Frequency: above 100K Hz (TENS, HVGS, diathermies)

40. 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

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

42. 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)

43. Stimulation Parameter: • Average current (also called Root Mean Square) • the “average” intensity • Factors effecting 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)

44. 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.

45. 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

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

47. 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

48. 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

49. 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.

50. 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