Principles of Electrical Currents

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

17. 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

18. 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

19. 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)

20. 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)

21. 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

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

23. 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)

24. 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)

25. 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.

26. 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

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

28. 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

29. 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

30. 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.

31. 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

32. Muscle Contractions & Frequency • 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) • 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

33. 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

34. 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

35. 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

36. General E-Stim Parameters

37. E-Stim for Pain Control: typical Settings

38. High Volt Pulsed Stimulation

39. CURRENT CONCEPTSEVIDENCE BASED • ES increased 20% verses control (no activity) demonstrating that ES “can alter the blood flow in muscle being stimulated” Currier et all 1996 • Currier et al 1988: Similar study but 15% • Bettany et al 1990: Edema formation in frogs decreased with HVPC 10 minutes after the trauma

40. CURRENT CONCEPTSEVIDENCE BASED • Walker et al 1988: HVS at a pulse rate of 30 Hz and intensities to evoke 10% - 20% MVC did not increase blood flow to the popliteal artery. The exercise group demonstrated 30% increase • Von Schroeder et al 1991: Femoral venous flow shown to increase greatest with passive SLR elevation, then CPM, active ankle dorsiflexion, manual calf compression and passive dorsiflexion

41. HVPS • The application of monophasic current with a known polarity • typically a twin-peaked waveform • duration of 5 - 260 msec • Wide variety of uses: • muscle reeducation (requires 150V) • nerve stimulation (requires 150V) • edema reduction • pain control

42. Physiological response can be excitatory and non-excitatory Excitatory Peripheral nerve stimulation for pain modulation (sensory, motor and pain fibers) Promote circulation: inhibits sympathetic nervous system activity, muscle pumping and endogenous vasodilatation Non-Excitatory (cellular level) Protein synthesis Mobilization of blood proteins Bacteriocyte affects (by increased CT micro-circulation there is a reabsorption of the interstitial fluids) Clinical Application:

43. General Background • Early in history HVS was called EGS, then HVGS, then HVPS • Current qualifications to be considered HVS • Must have twin peak monophasic current • Must have 100 or 150 volts (up to 500 V)

44. Precautions Stimulation may cause unwanted tension on muscle fibers Muscle fatigue if insufficient duty cycle Improper electrodes can burn or irritate Intense stim may result in muscle spasm or soreness Contraindications Cardiac disability Pacemakers Pregnancy Menstruation Cancerous lesion Infection Metal implants Nerve sensitivity Indications past slide HVPS

45. Treatment Duration • General - 15-30 minutes repeated as often as needed • Pain reduction - sensory 30 minutes with 30 minute rest between tx

46. Current Parameters • greater than 100-150 V • usually provides up to 500 V • high peak, low average current • strength duration curve = short pulse duration required higher intensity for a response • high peak intensities (watts) allow a deeper penetration with less superficial stimulation

47. Pulse Rate: ranges from 1-120 pps varies according to the desire clinical application Current Pulse Charge related to an excess or deficiency of negatively charged particles associated with the beneficial or harmful responses (thermal, chemical, physical) Modulations intrapulse spacing duty cycle: reciprocal mode usually 1:1 ratio ramped or surged cycles Clinical Considerations: always reset intensity after use (safety) electrode arrangements may be mono or bipolar units usually have a hand held probe for local (point) stimulation most units have an intensity balance control Current Parameters

48. Application Techniques • Monopolar: 2 unequal sized electrodes. Smaller is generally over the treatment site and the large serves as a dispersive pad, usually located proximal to the treatment area • Bipolar: two electrodes of equal size, both are over or near the treatment site • Water immersion - used for irregularly shaped areas • Probes: one hand-held active lead • advantages: can locate and treat small triggers • disadvantages: one on one treatment requires full attention of the trainer

49. Electrodes • Material • carbon impregnated silicone electrodes are recommended but will develop hot spots with repeated use • you want conductive durable and flexible material • tin with overlying sponge has a decreased conformity and reduced conductivity

50. Electrodes • Size • based on size of target area • current density is important. The smaller the electrode size the greater the density