interferential therapy

Sreeraj S R

Sreeraj S R

DEFINITION

�Developed by Dr. Hans Nemec of Vienna,Austria in the early 1950’s

� It may be described as the transcutaneousapplication of alternating mediumfrequency electrical currents, amplitudemodulated at low frequency for therapeuticpurposes.

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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

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SKIN IMPEDANCE

� The word impedance comes from the Latin impediremeaning 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.

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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.

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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

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PRINCIPLE

�The principle of IFT is to pass two MediumFrequency Alternating Currents which areslightly out of phase, through the tissues,where the currents intersect to produce alow frequency effect.

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Principles of wave interference: Combined Effects

� Constructive, Destructive, & Continuous

� Constructive interference: when two sinusoidal wavesthat are exactly in phase or one, two or threewavelengths out of phase, the waves supplement eachother in constructive interference

+=

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Principles of wave interference: Combined Effects

� Destructive interference: when the two waves aredifferent by 1/2 a wavelength (of any multiple) theresult is cancellation of both waves

+ =

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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

=+

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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

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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)

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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

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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)

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Amplitude Modulation Frequency

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4000 Hz

4150 Hz

150 Hz

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4000 Hz

3900 Hz

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Why Amplitude modulation?

� Synchronous depolarization

� Asynchronous depolarization

� Gildemeister effect/summation principle

� Wedensky inhibition

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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 passessuccessively through all frequencies up to 70 Hz, after which it decreases gradually to 20 Hz.

� This process is repeated automatically.20

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Triangular sweep pattern Rectangular Sweep Pattern

Trapezoidal Sweep Pattern21

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Vector Scan

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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

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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.

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APPLICATION

� Methods of applications are:

1. Static interference

2. Dynamic interference

3. Bipolar interference

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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.

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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.

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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.

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PHYSIOLOGICAL EFFECTS

� This depends upon:

1. Magnitude of current

2. Type of mode used i.e. Rhythmic orconstant

3. The frequency range used

4. Accuracy of electrode positioning

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PHYSIO.EFFECTS (CONT…)

Main clinical applications are :

1. Pain relief

2. Muscle stimulation

3. Increased local blood flow

4. Reduction of edema

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PAIN RELIEF

�Believed that this may be achieved bystimulation of the reticular formation atfrequencies of 10-25Hz or by blocking ‘c’fiber transmission at > 50Hz.

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MUSCLE STIMULATION

�For patients who can not generate usefulvoluntary contraction, IFT may bebeneficial.

�Most effective motor nerve stimulationrange is between 10-25Hz

�When employing IFT it is possible tocontinue to stimulate the muscle beyond itspoint of fatigue. Some machines employ a‘surged’ mode to overcome this.

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BLOOD FLOW

� Experimentation demonstrated vascularchanges 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 stimulatesparasympathetic nerve fibers for increasedblood flow.

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OEDEMA

�Local muscle contraction combined with itslocal vascular changes encourages thereabsorbtion of tissue fluid.

�The use of suction electrodes may also bebeneficial.

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CONTRAINDICATIONS1. Cardiac pacemaker2. Advanced cardiac disease3. Hypertension4. Thrombosis5. Hemorrhage6. Pregnancy7. Neoplasm8. T b9. Fever10. Infections11. The eyes12. Skin disorders13. Epiphyseal region in children

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PRECAUTIONS

� IFT apparatus must be at least 6 metersaway from SWD machine

�Patients with febrile conditions

�Epileptic patients

�Over anterior chest wall

�Position suction electrode below the level ofdamage or discomfort.

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Placement of electrodes

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Types of Electrodes� Plate

� Vacuum

� Pen

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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

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Sreeraj S R

Vacuum Electrodes � made from a vacuum unit plug into a rubber suction

cup connected to a machine capable of producing avacuum,

� suction should not be constant because it can beuncomfortable and causes bruising

� wet sponges are placed in the cups and moisten theedges of the cups for better adherence,

� excellent for treating flat smooth areas for exampleback or a plump knee

� not indicated for treatment of the hairy areas becausecan’t get an airtight seal

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Sreeraj S R

Electrode positioning

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ELBOW

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KNEE

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NECK

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SHOULDER

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LOWER BACK

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Thank You