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 painEdema reductionMuscle spasm reductionReducing joint contracturesMinimizing disuse/ atrophyFacilitating tissue healingStrengthening muscleFacilitating fracture healing
4 Contraindications of Electrotherapy Cardiac disabilityPacemakersPregnancyMenstruation (over abdomen, lumbar or pelvic region)Cancerous lesionsSite of infectionExposed metal implantsNerve Sensitivity
5 Terms of electricityElectrical current: the flow of energy between two pointsNeedsA driving force (voltage)some material which will conduct the electricityAmper: 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 pointsNegative pole an area of high electron concentration (Cathode)Positive pole and area of low electron concentration (Anode)
7 ChargeAn 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 attractLike charges repelallow the drug to be “driven”Reduce edema/blood
9 Charge: FactorsMembranes rest at a “resting potential” which is an electrical balance of charges. This balance must be disrupted to achieve muscle firingMuscle depolarization is difficult to achieve with physical therapy modalitiesNerve depolarization occurs very easily with PT modalities
10 Terms of electricityInsulators: materials and tissues which deter the passage of energySemiconductors: both insulators and conductors. These materials will conduct better in one direction than the otherRate: How fast the energy travels. This depends on two factors: the voltage (the driving force) and the resistance.
11 Terms of electricityVoltage: electromotive force or potential difference between the two polesVoltage: an electromotive force, a driving force. Two modality classification are:Hi Volt: greater than VLo Volt: less than V
12 Terms of electricityResistance: the opposition to flow of current. Factors affecting resistance:Material compositionLength (greater length yields greater resistance)Temperature (increased temperature, increase resistance)
13 Clinical application of Electricity: minimizing the resistance Reduce the skin-electrode resistanceMinimize air-electrode interfaceKeep electrode clean of oils, etc.Clean the skill on oils, etc.Use the shortest pathway for energy flowUse the largest electrode that will selectively stimulate the target tissuesIf resistance increases, more voltage will be needed to get the same current flow
14 Clinical application of Electricity: Temperature RelationshipAn increase in temperature increases resistance to current flowApplicabilityPreheating 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 flowApplication: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 sameExcitable TissuesNervesMuscle fibersblood cellscell membranesNon-excitable tissuesBoneCartilageTendonsLigamentsCurrent 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 otherWatt= 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 possibleremember the all or none response and the Arndt-Schultz Principle
19 Simulation ParameterPulse 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 depolarizationSlow rise: the nerve accommodates to stimulus and a action potential is not elicitedGood 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 timeDo not assume the lower the frequency the longer the pulse durationLow 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 lineDC indicated that the energy travels only in the positive or on in the negative directionDCAC
23 Stimulation Parameter: Waveforms; the path of the energy. May be smooth (sine) spiked, square,, continuous etc.Method to direct currentPeaked - sharperSign - 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 occur1:1 Raito fatigues muscle rapidly1:5 ratio less fatigue1:7 no fatigue (passive muscle exercise)
25 Stimulation Parameter: Average current (also called Root Mean Square)the “average” intensityFactors effective the average current:pulse amplitudepulse durationwaveform (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 DensityThe 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 durationThe higher the capacitance the longer before a response. Body tissues have different capacitance. From least to most:Nerve (will fire first, if healthy)Muscle fiberMuscle 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 intensityThe onset of stimulation must be rapid enough that tissue accommodation is preventedThe lower the capacitance the less the charge can be storedIf 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 occurThe 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 = twitch10 pps = summation25-30 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 circulationThe 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 circuitThe body becomes the conductorMonophasic application requires one negative electrode and one positive electrodeThe strongest stimulation is where the current exists the bodyElectrodes 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 densityGenerally 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 electrodeA multitude of placement techniques may be used to create the clinical and physiological effects you desire
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