Original Editor - Professor Tim Watson
Introduction[edit | edit source]
Interferential therapy (IFT) is introduced by Dr. Nemec in the early 1950’s.He wanted to overcome the problems of discomfort caused by low-frequency currents, while maintaining their claimed therapeutic effect. It remained disappear until 1970s, when work on pain mechanism by Melzack/Wall showed that pain could be reduced by stimulating primary afferent neurons. The transcutaneous application of alternating medium-frequency electrical currents are applied to the body in such a manner to produce amplitude modulated low frequency current within in the body for therapeutic purposes. It is the production of low frequency current in the body tissue by the simultaneous application of two different medium frequency currents. As the low frequency current is the result of interference of two different medium frequency currents, it is named as – interferential current. 
Medium frequency A+ Medium frequency B = low (therapeutic) frequency C Current
-But why using 2 medium frequency currents?
•Medium frequency currents is associated with a lower skin resistance (impedance),thus more comfortable than low frequency currents.
Characteristics of IFC[edit | edit source]
Two medium frequency currents are used to produce the interferential current. They are known as carrier waves as they don't produce muscle or nerve stimulation and are used just used to get the greater depth of penetration and to produce interferential current.
•Current A: f1 -this current is set on the machine, thus called “intrinsic/carrier frequency”, usually at 4000 Hz (2 000Hz and 6000Hz also available).
•Current B: f2 -same amplitude, but slightly higher frequency; therapist sets this one. f2 would be variable from 4001 Hz to 4150 Hz -it is better to have f2 “swing” within a range of frequencies because it limits accommodation and habituation to current.
•F = f2 - f1 ,the amplitude of F (Current C) is NOT constant. This is called as beat frequency current C. F = f2 - f1 ranges from 1 Hz to 150 Hz (the frequency swing is also referred to as spectrum or sweep).
Amplitude Modulated Frequency (AMF)[edit | edit source]
The frequency with which the amplitude of current is modulated is called Amplitude Modulated Frequency (AMF). In interferential current, the resulting current formed due to the intersection of the two carriers has its amplitude modulated at the frequency which is the difference between the 2 carrier frequencies.
Beat Frequency[edit | edit source]
The frequency of the resultant current is known as the beat frequency. Beat frequency is equal to the difference between two medium frequency currents. It may be kept constant or varied rhythmically so as to prevent accommodation. Constant beat frequency is also called as the selective beat frequency.
Area of Interference[edit | edit source]
Static Interference: The area in which interferential current is set-up remains stationary. This area of static interference gives an appearance of clove leaf as a result of vector addition of two currents and it lies at 45º angles to the perpendicular lines from each electrode.
Dynamic Interference: It is possible to move the area in which interference current is developed in a to and fro manner through 45º.It is obtained by varying the current intensity in suitable manner. This dynamic area of interference is also called as vector sweep, vector scan, rotating vector etc. The available vector scans are 45, 90, 360° C.
Base[edit | edit source]
This denotes the starting point of the waveform or the frequency from the neutral level, i.e. if the base is set at 10 Hz the waveform or the frequency cycle starts from 10 Hz reaches the required peak and travels down. It now maintains a steady flow of current or a pause and again starts from the 10 Hz zone to complete the next consecutive cycle.
Spectrum[edit | edit source]
This denotes the required peak level reach of the waveform or the frequency range from the base, i.e. if the spectrum is set at 60 Hz and the base being 10 Hz, the cycle starts from the base of 10 Hz travels and reaches the maximum peak level of 60 Hz and again travels down . The use of spectrum has the advantage that the tissues does not adapt to a certain frequency and accommodation property is prevented. Thus, the given treatment can be performed for a longer period and repeated more often.
Sweep [edit | edit source]
This denotes the flow of the frequency from a present lowest level to the highest level, which is selected by base and spectrum, i.e., if the user needs a frequency sweep between 10 and 60 Hz the base level is present at 10 Hz and the spectrum level is present at 50 Hz where the frequency sweep is 10 to 60 Hz. The advantage of this being, depending upon the stage of the patients condition the wave type can be adjusted and the accommodation property of the tissues can be altered.
Basically, there are three types of wave modes commonly used.
•Mode-1: This is a rectangular waveform mode where the frequency remains at the base level for 1 sec. This form has a very aggressive effect and so much recommendations for chronic conditions.
•Mode-2: This is a trapezoidal waveform mode where the frequency remain at the base level for 5 sec. This form is much milder and tolerated best by the patients easily with sub acute conditions.
•Mode-3: This is a triangular waveform mode where the frequency reaches from base to spectrum within 6 sec., This form is very mildest and tolerated best by the patients easily with acute conditions.
Balance[edit | edit source]
Electric current applied through the skin depends on the conditions of the electrode, sponge and the skin. Hence, when the 2 currents are applied there may be unequal current passing through each circuit due to the unequal resistance countered. In order to compensate this situation the current in both channels can be equalized using this balance.
Therapeutic and Physiological effects[edit | edit source]
PAIN RELIEF AND RELIEF OF MUSCLE SPASM
STIMULATION OF INNERVATED MUSCLES
EFFECT ON EDEMA/ SWELLING
Treatment Parameters[edit | edit source]
Stimulation can be applied using pad electrodes and sponge covers (which when wet provide a reasonable conductive part), though electroconductive get is an effective alternative. The sponges should be thoroughly wet to ensure even current distribution. Self adhesive pad electrodes are also available (similar to the newer TENS electrodes) and make the IFT application easier in the view of many practitioners. The suction electrode application method has been in use for several years, and whilst it is useful, especially for larger body areas like the shoulder girdle, trunk, hip, knee, it does not appear to provide any therapeutic advantage over pad electrodes (in other words, the suction component of the treatment does not appear to have a measurable therapeutic effect. Care should be taken with regards maintenance of electrodes, electrode covers and associated infection risks (Lambert et al 2000).
Whichever electrode system is employed, electrode positioning should ensure adequate coverage of the area for stimulation. Using larger electrodes will minimise patient discomfort whilst small, closely spaced electrodes increase the risk of superficial tissue irritation and possible damage / skin burn.
The bipolar (2 pole) application method is perfectly acceptable, and there is no physiological difference in treatment outcome despite several anecdotal stories to the contrary. Recent research evidence supports the benefit of 2 pole application (e.g. Ozcan et al 2004).
References[edit | edit source]
- Lambert I, Tebbs SE, Hill D, Moss HA, Davies AJ, Elliott TSJ (2000). Interferential therapy machines as possible vehicles for cross-infection. J Hosp Infect. 44(1), 59-64.
- Ozcan J, Ward AR, Roberson VJ (2004). A comparison of true and premodulated interferential currents. Arch Phys Med Rehab. 85(3): 409-415.
- William E. Prentice. Therapeutic modalities in rehabilitation. 3rd Edition, McGraw-Hill Medical, 2017
- Val Robertson, Alex Ward, John Low John Low Ann Reed, Electrotherapy Explained: Principles and Practice. 4th Edition. Butterworth-Heinemann,2006
- Tim Watson, Electrotherapy: evidence-based practice. Physiotherapy essentials. 12th edition, Churchill Livingstone,2008