Low Frequency Currents SRS
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This document provides an overview of low frequency currents used in electrotherapy. It discusses the history of electrotherapy including contributions from Galvani, Faraday, and others. It describes the main types of currents - direct current, alternating current, and pulsed current. Specific low frequency currents are explained such as faradic current, interrupted direct current, and TENS. The physiological effects and therapeutic indications of low frequency currents are outlined. Contraindications and precautions for electrotherapy are also reviewed.
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Low Frequency Currents SRS
- 2. Sreeraj S R AN INTRODUCTION Low Frequency Currents
- 3. Sreeraj S R What is electrotherapy? Medical therapy using electric currents. Also called electrotherapeutics1. Electrotherapy, also electro physical agents (EPA) are any forms of treatment or assessment conducted using an electro physical agent which can be applied externally to the human body2. http://www.thefreedictionary.com/electrotherapy Robertson V, Ward A, Low J, Reed A. Electrotherapy Explained. 4th edition. Elsevier; 2006. p. 2
- 4. Sreeraj S R History Electric fish for the treatment of gout in Greek and Roman times. By 1780, Luigi Galvani, an obstetrician and anatomist, University of Bologna, first observed the quick twitching of the muscle, produced by electricity in a nerve muscle preparation of the frog’s leg. As this type of electricity seemed quite distinct from electrostatic currents derived from frictional machines it was called Galvanic current. In honour of Luigi Galvani, the use of direct current in medicine is called Galvanism.
- 5. Sreeraj S R Johann G Kruger, professor of Medicine at Halle, Germany, published first book on medical electricity in 1743 entitled ‘Thoughts about the Electricity’. Christian G Kratzenstein published in 1745, was the first to use ‘Medical Electricity’ in its title. Richard Lovett of England, in 1756 treated numerous conditions with static shocks and published treatise recommending electrotherapy. John Wesley, inspired by Richard Lovett published his own experiences on the subject in 1759, in the book entitled ‘The Desideratum’.
- 6. Sreeraj S R History In the early 1800s, Michael Faraday laid the groundwork for the creation of alternating current (AC). The medical use of such current is called Faradism. The current was initially used for tightening and toning the muscles. In1965 Ronald Melzack and Patrick David Wall published their paper “Pain Mechanism: A New Theory” which revealed the benefits of electricity used as pain therapy to the people of today.
- 7. Sreeraj S R Types of Currents Mainly three types of currents used therapeutically: Direct current Alternating current Pulsed current.
- 8. Sreeraj S R Direct Current “Galvanic” can be used to describe DC Uninterrupted unidirectional flow of electrons Electrons travel from the cathode to the anode Example: Flashlight
- 9. Sreeraj S R Alternating current Bidirectional flow of electrons – direction & magnitude of flow reverses magnitude may not be equal on both sides of the baseline. AC possesses no true positive or negative pole. Electrons shuffle back & forth between the two electrodes as they take turn being + ve & - ve. Household electricity uses AC.
- 10. Sreeraj S R Alternating Current Amplitude: (peak value) – the maximal distance to which the wave rises above or below the baseline (only one side of the baseline) Peak-to-Peak Value: measured from the peak on the (+) side of the line to the peak on the (-) side of the line. Cycle Duration: measured from the originating point on the baseline to its terminating point; the amount of time required to complete one full cycle Hertz: number of cycles per second (1 MHz = 1 million cycles/second) Pattern – Sine Wave
- 11. Sreeraj S R Pulsed Current • Unidirectional or bi-directional flow • Usually 3 or more pulses grouped together • Pulses are interrupted • 3 Types of Waveforms • Monophasic • Biphasic • Polyphasic
- 12. Sreeraj S R Pulse Attributes A B C D F E B E A : Amplitude B : Phase Duration C : Pulse Duration D : Interpulse Interval E : Pulse Period F : Intrapulse Interval
- 13. Sreeraj S R Wave forms Rise and decay time Rise time is the time taken by pulse to reach maximum amplitude in each phase. Decay time is the time taken by pulse to return to neutral They are generally from ns to ms The more rapid the rise in amplitude the greater the nerve tissue excitability.
- 14. Sreeraj S R Wave forms
- 15. Sreeraj S R Wave forms
- 16. Sreeraj S R Current Modulation
- 18. Sreeraj S R Types of LF Currents Pure faradic current Direct current: Constant direct current Interrupted direct current Faradic Type of current TENS
- 19. Sreeraj S R Faradic Current From Smart Bristow faradic coil Sinusoidal current First long duration low amplitude High intensity short duration waves Not used now Original Modern
- 20. Sreeraj S R Faradic type Current Short duration interrupted direct current Pulse duration 0.1 – 1 ms Frequencies 50 – 100 Hz Shorter duration used for stimulating innervated muscle
- 21. Sreeraj S R Modified Faradic Current Faradic currents are surged for treatment purposes. To produce a near normal tetanic type of contraction and relaxation The surges can be of various Duration Frequencies Wave forms
- 22. Sreeraj S R Modified Faradic Current The intensity of the successive impulses increases gradually. Surges can be adjusted from 2 to 5-second surge, continuously or by regularly selecting frequencies from 6 to 30 surges / minute. Rest period (pause duration) should be at least 2 to 3 times that of the pulse to give the muscle enough time to recover its normal state.
- 23. Sreeraj S R Interrupted Direct Current Interruption of unidirectional currents Frequency of up to 5 Hz. The equipment commonly provide duration of 0.01, 0.03, 0.1, 0.3, 1, 3, 10, 30, 100, 300 ms. Longer duration used for stimulating denervated muscle
- 24. Sreeraj S R Physiological Effects Effects on body tissues Stimulation of sensory nerves Stimulation of motor nerves Increasing metabolism Removal of waste products Stimulation of denervated muscle Chemical effects
- 25. Sreeraj S R Physiological Effects Effects on body tissues: Tissues contain fluid, thus ions so are good conductors. ex. muscles Epidermis has high resistance, thus is a bad conductor. So some media like water or conductive gel used to lower resistance Washing the area with soap and water lower resistance to some extend.
- 26. Sreeraj S R Physiological Effects Stimulation of sensory nerves Faradic current produces mild prickling sensation. IDC results in a stabbing or burning sensation ES produces slight erythema due to reflex vasodilatation.
- 27. Sreeraj S R Physiological Effects Stimulation of motor nerves Faradic current produces a tetanic contraction because of higher frequency rate. So they are surged to avoid muscle fatigue. Galvanic current produces a muscle twitch followed by relaxation.
- 28. Sreeraj S R Physiological Effects Increasing metabolism and Removal of waste products The contraction and relaxation of muscle causes pumping action on blood vessels. This results in increased supply of oxygen and nutrients Also aids in lymphatic and venous drainage. So removal of waste products
- 29. Sreeraj S R Physiological Effects Stimulation of denervated muscle Impulses of more than 1 ms required for this. Faradic current of more than 1 ms is not tolerable for the patient. IDC of sufficient intensity and duration is used for this.
- 30. Sreeraj S R Physiological Effects Chemical effects Chemical effects are produced at the electrode site resulting in chemical burns This risk is more in DC Using AC, depolarized DC and pulsing avoid this danger.
- 31. Sreeraj S R Accommodation When a constant current flows nerve adapts itself to the current. Consequently the nerve no longer respond to the stimulus This is accommodation. A current rises or fall suddenly is more effective
- 32. Sreeraj S R Effects of nerve stimulation When a sensory nerve is stimulated Downward impulse has no effect Upward impulses appreciated when it reaches CNS. Long duration impulses produce uncomfortable stabbing sensation Short duration gives milder sensations When motor nerve stimulated Upward impulses do not pass Downward impulses cause muscle contraction Motor point causes maximum muscle stimulation
- 33. Sreeraj S R Effects of frequency of stimulation Increasing the frequency of stimuli shortens the period of relaxation Frequencies exceeding 20 Hz causes partial tetani, Frequencies exceeding 60 Hz causes tetanic contraction
- 34. Sreeraj S R Strength of contraction Depends on : The number of motor units activated Intensity of current Rate of change of current; slow rising currents causes accommodation
- 35. Sreeraj S R Indications Facilitation of muscle contraction inhibited by pain Muscle re-education Training a new muscle action Improvement of venous and lymphatic drainage Prevention and loosening of adhesions Nerve injury
- 36. Sreeraj S R Indications Facilitation of muscle contraction inhibited by pain Pain has an inhibitory effect on anterior horn cells. ES 1. reduces this inhibition 2. Facilitate transmission of voluntary impulses to the muscle and 3. Induce relaxation of its antagonists The procedure should be pain free, Otherwise this would inhibit the discharge from the AHC.
- 37. Sreeraj S R Indications Muscle re-education Inability to contract a muscle can be due to: Prolonged disuse Incorrect use Faradic stimulation may be used to restore the sense of movement.
- 38. Sreeraj S R Indications Training a new muscle action This could be in: Tendon transplant Reconstructive surgeries Faradic type current is used for this The patient is expected to assist with voluntary contraction
- 39. Sreeraj S R Indications Improvement of venous and lymphatic drainage The contraction and relaxation of muscle causes pumping action on blood vessels. A faradism under pressure is used to treat edema
- 40. Sreeraj S R Indications Prevention and loosening of adhesions Adhesions can be formed due to : Long standing effusions. improper muscle actions Faradic stimulation and adequate exercise loosens, stretches and prevent the adhesions.
- 41. Sreeraj S R Indications Nerve injury Seddon’s Classification: Neuropraxia: faradic current used to maintain the properties of muscle Axonotmesis: Short or Long duration current according to diagnostic responce Neurotmesis: start with faradic, but IDC after degeneration Wallerian degeneration
- 42. Sreeraj S R Contraindication Someone with a pacemaker Someone with a heart condition On head or neck of someone with epilepsy Someone with venous or arterial thrombosis or thrombophlebitis Cardiac pacemakers. Superficial metals. Near operating diathermy device
- 43. Sreeraj S R Contraindication On the eyes Using electrodes on infected skin Electrodes across the chest of a patient with cardiac disease Electrodes should not be placed near carotid artery in the anterolateral region of the neck. There is a potential risk that stimulation at this site might cause heart block by exciting the vagus nerve.
- 44. Sreeraj S R Precautions Areas of skin irritation, damage or lesions Areas with impaired sensation Over abdominal, lumbosacral or pelvic regions during pregnancy other than for labor/delivery Tissues vulnerable to hemorrhage or hematoma Extreme caution is needed with patients taking narcotic medication or who are known to have hyposensitive areas. Incompetent patients may not be able to manage the device and it must be kept out of reach of children.
- 45. Sreeraj S R 45 Thank You
- 46. Sreeraj S R Recommended Textbooks 1. Electrotherapy explained, 4th edition, Low & Reed 2. Clayton’s Electotherapy, Theory and Practice. Angela Forster. 9th Ed. 3. Clayton’s electrotherapy, 10th edition, Sheila Kitchen 4. Textbook of Electrotherapy, Jagmohan Singh. 5. Physical Agents in Rehabilitation, From Research to Practice, Michelle H. Cameron
- 47. Sreeraj S R Recommended Reference Books 1. Biophysical Basis of Electrotherapy, Alex J Ward 2. Handbook of practical electrotherapy, Pushpal Kumar Mitra, 3. Electrotherapy : Evidence Based Practice, Tim Watson 4. Principles and Practice of Electrotherapy. Joseph Kahn. 5. Thermal Agents in Rehabilitation. Susan L. Michlovitz. 6. Therapeutic modalities for physical therapists by William E Prentice 7. Clinical Electrotherapy by Roger Nelson, Dean Currier 8. Modalities for Therapeutic Intervention: Contemporary Perspectives in Rehabilitation by Susan Michlovitz, Thomas Nolan