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# Interferential therapy

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Interferential therapy, IFT, IFC, physiotherapy

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### Interferential therapy

1. 1. Sreeraj S R
2. 2. Sreeraj S R DEFINITION Developed by Dr. Hans Nemec of Vienna, Austria in the early 1950’s It may be described as the transcutaneous application of alternating medium frequency electrical currents, amplitude modulated at low frequency for therapeutic purposes. 2
3. 3. Sreeraj S R Why IFT?.. MF currents associated with a lower skin resistance (impedance), more comfortable than low frequency currents more tolerable penetration of current through the skin is possible 3
4. 4. Sreeraj S R SKIN IMPEDANCE The word impedance comes from the Latin impedire meaning to prevent, to stop from going on. Impedance signifies the resistance of a conductor when an electric current passes. Conventionally speaking, the term resistance refers to the obstacle to the direct current, and it is represented by the letter R. The terms impedance refers to the obstacle to the alternating current and it is represented by the letter Z. Impedance Z, as resistance R, is expressed in ohms. 4
5. 5. Sreeraj S R SKIN IMPEDANCE SKIN IMPEDANCE is calculated as Z = ½ π f C Where, Z = skin resistance f = frequency in Hertz (Hz) C = capacitance of skin in microfarads From above formula, skin impedance is inversely proportional to frequency and capacitance of the skin. Capacitance of the skin cannot be changed; hence by increasing the frequency the skin impedance can be lowered. 5
6. 6. Sreeraj S R SKIN IMPEDANCE It is assumed that a capacitance of 1 microfarad. For a 50-Hz alternating current we obtain: Z = 1/2π x 50x 10-6 = 3200 Ω For a 4,000-Hz alternating current this means: Z = 1/2π x 4000x 10-6 = 39,8 Ω 6
7. 7. Sreeraj S R PRINCIPLE The principle of IFT is to pass two Medium Frequency Alternating Currents which are slightly out of phase, through the tissues, where the currents intersect to produce a low frequency effect. 7
8. 8. Sreeraj S R 8
9. 9. Sreeraj S R Principles of wave interference: Combined Effects Constructive, Destructive, & Continuous Constructive interference: when two sinusoidal waves that are exactly in phase or one, two or three wavelengths out of phase, the waves supplement each other in constructive interference + = 9
10. 10. Sreeraj S R Principles of wave interference: Combined Effects Destructive interference: when the two waves are different by 1/2 a wavelength (of any multiple) the result is cancellation of both waves + = 10
11. 11. Sreeraj S R Principles of wave interference: Combined Effects Continuous Interference: Two waves slightly out of phase collide and form a single wave with progressively increasing and decreasing amplitude = + 11
12. 12. Sreeraj S R WORKING In the interferential therapy method, two medium- frequency alternating currents that interact with each other are used. One of the alternating currents has a fixed frequency of 4,000 Hz while the frequency of the other alternating current can be set between 4,000 and 4,250 Hz. The superimposition of one alternating current on the other is called interference 12
13. 13. Sreeraj S R WORKING The frequency of the new medium-frequency alternating current can be calculated as follows: f1 + f2 /2 where Example: f1 = 4,000 Hz f2 = 4,150Hz f1 + 1/2Δf = 4,000 + 75 = 4,075 Hz (Resultant Carrying Frequency) 13
14. 14. Sreeraj S R WORKING The frequency with which the amplitude varies is referred to as the amplitude modulation frequency (AMF). In interferential therapy the AMF (treatment frequency) corresponds to frequencies which are used in low-frequency electrotherapy. The AMF has a value of f1 – f2 14
15. 15. Sreeraj S R WORKING The AMF has a value of f1 – f2 Example: f1 = 4,000 Hz f2 = 4,150 Hz f 1 - f2 = 4,000 - 4,150 = 150 Hz (AMF or treatment frequency) 15
16. 16. Sreeraj S R Amplitude Modulation Frequency 16 4000 Hz 4150 Hz 150 Hz
17. 17. Sreeraj S R 17
18. 18. Sreeraj S R 18 4000 Hz 3900 Hz
19. 19. Sreeraj S R Why Amplitude modulation? Synchronous depolarization Asynchronous depolarization Gildemeister effect/summation principle Wedensky inhibition 19
20. 20. Sreeraj S R SWEEP The principle of using the sweep is that the machine is set to automatically vary the effective stimulation frequency using either pre-set or user set sweep ranges. Such sweep prevents accommodation of nerves. Example: An AMF of 20 Hz is set and a 50 Hz spectrum is added. The current begins with an AMF of 20 Hz and passes successively through all frequencies up to 70 Hz, after which it decreases gradually to 20 Hz. This process is repeated automatically. 20
21. 21. Sreeraj S R Triangular sweep pattern Rectangular Sweep Pattern Trapezoidal Sweep Pattern 21
22. 22. Sreeraj S R 22
23. 23. Sreeraj S R Vector Scan 23
24. 24. Sreeraj S R INSTRUMENTATION AMF PARAMETER To choose the basic value of the LF modulation that is desired. SPECTRUM PARAMETER to set the range of variation in the AMF value that is desired; for ex. AMF at 100Hz and spectrum at 50Hz will give an AMF variation from 100hz up to 150Hz and back to 100Hz. SWEEP TIME PARAMETER sets the time period for the AMF to change from base to peak frequency. Faster sweep is used for less painful stimulation and for strong muscle contraction or sensory input, sweep must be slow, to ensure aggressive stimulation. 24
25. 25. Sreeraj S R INSTRUMENTATION… CONTOUR PARAMETER sets the rate of change of the AMF from the base to peak frequency. ROTATION PARAMETER is applicable in case of vector currents only and sets the rate of rotation and the direction change of the AMF field within the tissues. 25
26. 26. Sreeraj S R APPLICATION Methods of applications are: 1. Static interference 2. Dynamic interference 3. Bipolar interference 26
27. 27. Sreeraj S R STATIC INTERFERENCE Here the area in which IFT is set up remains stationary. This area of static interference gives an appearance of ‘clover leaf ’. It lies to 45°angles to the perpendicular lines from each electrode. 27
28. 28. Sreeraj S R DYNAMIC INTERFERENCE This is moving the area of interference current in a to and fro manner through 45°. It is obtained by varying the current intensity from 50 to 100%. The dynamic area of interference is also called as vector sweep, vector scan, rotating vector, etc. 28
29. 29. Sreeraj S R BIPOLAR INTERFERENCE Here pre-modulated IFT are applied through 2 surface electrodes. IFT is generated inside the equipment and is delivered to the patient through 2 electrodes. Useful for smaller areas. 29
30. 30. Sreeraj S R PHYSIOLOGICAL EFFECTS This depends upon: 1. Magnitude of current 2. Type of mode used i.e. Rhythmic or constant 3. The frequency range used 4. Accuracy of electrode positioning 30
31. 31. Sreeraj S R PHYSIO.EFFECTS (CONT…) Main clinical applications are : 1. Pain relief 2. Muscle stimulation 3. Increased local blood flow 4. Reduction of edema 31
32. 32. Sreeraj S R PAIN RELIEF Believed that this may be achieved by stimulation of the reticular formation at frequencies of 10-25Hz or by blocking ‘c’ fiber transmission at > 50Hz. 32
33. 33. Sreeraj S R MUSCLE STIMULATION For patients who can not generate useful voluntary contraction, IFT may be beneficial. Most effective motor nerve stimulation range is between 10-25Hz When employing IFT it is possible to continue to stimulate the muscle beyond its point of fatigue. Some machines employ a ‘surged’ mode to overcome this. 33
34. 34. Sreeraj S R BLOOD FLOW Experimentation demonstrated vascular changes at 10-25Hz. Effects of blood flow is believed to be due to: 1. Effects of suction electrodes on tissues 2. Effects of muscle stimulation on circulation. 3. Deep tissue penetration stimulates parasympathetic nerve fibers for increased blood flow. 34
35. 35. Sreeraj S R OEDEMA Local muscle contraction combined with its local vascular changes encourages the reabsorbtion of tissue fluid. The use of suction electrodes may also be beneficial. 35
36. 36. Sreeraj S R CONTRAINDICATIONS 1. Cardiac pacemaker 2. Advanced cardiac disease 3. Hypertension 4. Thrombosis 5. Hemorrhage 6. Pregnancy 7. Neoplasm 8. T b 9. Fever 10. Infections 11. The eyes 12. Skin disorders 13. Epiphyseal region in children 36
37. 37. Sreeraj S R PRECAUTIONS IFT apparatus must be at least 6 meters away from SWD machine Patients with febrile conditions Epileptic patients Over anterior chest wall Position suction electrode below the level of damage or discomfort. 37
38. 38. Sreeraj S R Placement of electrodes 38
39. 39. Sreeraj S R Types of Electrodes Plate Vacuum Pen 39
40. 40. Sreeraj S R Plate Electrodes Made of conducting rubber which are comfortable and long lasting larger plates electrodes give more comfortable treatment and deeper effect Smaller electrodes are used for a localized effect, but this effect is more superficial Attached to the patient by means of straps to assure a good contact and greater tolerance of treatment
41. 41. Sreeraj S R
42. 42. Sreeraj S R Vacuum Electrodes made from a vacuum unit plug into a rubber suction cup connected to a machine capable of producing a vacuum, suction should not be constant because it can be uncomfortable and causes bruising wet sponges are placed in the cups and moisten the edges of the cups for better adherence, excellent for treating flat smooth areas for example back or a plump knee not indicated for treatment of the hairy areas because can’t get an airtight seal
43. 43. Sreeraj S R
44. 44. Sreeraj S R Electrode positioning 44
45. 45. Sreeraj S R ELBOW 45
46. 46. Sreeraj S R KNEE 46
47. 47. Sreeraj S R NECK 47
48. 48. Sreeraj S R SHOULDER 48
49. 49. Sreeraj S R LOWER BACK 49
50. 50. Sreeraj S R 50 Thank You