Interferential Therapy: Difference between revisions

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== Acknowledgements  ==
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'''Original Editor '''- [http://www.electrotherapy.org/contact.htm Professor Tim Watson]


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== Introduction  ==
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<br>
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. <ref name="null" /><ref name=":0" />  


== Introduction &amp; IFT Production  ==
Medium frequency A+ Medium frequency B = low (therapeutic) frequency C Current


The basic principle of Interferential Therapy (IFT) is to utilise the strong physiologicaportable iftl effects of low frequency (&lt;250pps) electrical stimulation of nerves without the associated painful and somewhat unpleasant side effects sometimes associated with low frequency stim.
-But why using  2 medium frequency currents?


To produce low frequency effects at sufficient intensity at depth, patients can experience considerable discomfort in the superficial tissues (i.e. the skin). This is due to the impedance of the skin being inversely proportional to the frequency of the stimulation. In other words, the lower the stimulation frequency, the greater the impedance to the passage of the current &amp; so, more discomfort is experienced as the current is ‘pushed’ into the tissues against this barrier. The skin impedance at 50Hz is approximately 3200* whilst at 4000Hz it is reduced to approximately 40*. The result of applying a higher frequency is that it will pass more easily through the skin, requiring less electrical energy input to reach the deeper tissues &amp; giving rise to less discomfort.<br>
•Medium frequency currents is  associated with a lower skin resistance (impedance),thus more comfortable than low frequency currents.


The effects of tissue stimulation with these 'medium frequency' currents (medium frequency in electromedical terms is usually considered to be 1KHz-100KHz) has yet to be established. It is unlikely to do nothing at all, but in terms of current practice, little is known of its physiological effects. It is not capable of direct stimulation of nerve in the common context of such stimulation.  
•Using a medium frequency, a more tolerable penetration of current through the skin is possible.<ref name="null" /><ref name=":1">William E. Prentice. [https://vdoc.pub/download/therapeutic-modalities-in-rehabilitation-3rd-edition-therapeutic-modalities-for-physical-therapists-1ak2mabi02g8 Therapeutic modalities in rehabilitation]. 3rd Edition, McGraw-Hill Medical, 2017</ref>


Interferential therapy utilises two of these medium frequency currents, passed through the tissues simultaneously, where they are set up so that their paths cross &amp; they literally interfere with each other. This interference gives rise to an interference (beat frequency) which has the characteristics of low frequency stimulation – in effect the interference mimics a low frequency stimulation.  
== Characteristics of IFC ==
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.


The exact frequency of the resultant beat frequency can be controlled by the input frequencies. If for example, one current was at 4000Hz and its companion current at 3900Hz, the resultant beat frequency would be at 100Hz, carried on a medium frequency 3950Hz amplitude modulated 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).


By careful manipulation of the input currents it is possible to achieve any beat frequency that you might wish to use clinically. Modern machines usually offer frequencies of 1-150Hz, though some offer a choice of up to 250Hz or more. To a greater extent, the therapist does not have to concern themselves with the input frequencies, but simply with the appropriate beat frequency which is selected directly from the machine.  
•'''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.


The magnitude of the low frequency interference current is (in theory) approximately equivalent to the sum of the input amplitudes. It is difficult to show categorically that this is the case in the tissues but it is reasonable to suggest that the resultant current will be stronger than either of the 2 input currents.  
•'''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).<ref name=":1" /><ref name=":2">Val Robertson, Alex Ward, John Low John Low  Ann Reed, Electrotherapy Explained: Principles and Practice. 4th Edition. Butterworth-Heinemann,2006</ref>


The use of 2 pole I/F stimulation is made possible by electronic manipulation of the currents - the interference occurs within the machine instead of in the tissues. There is no known physiological difference between the effects of IFT produced with 2 or 4 electrode systems. The key difference is that with a 4 pole application the interference is generated in the tissues and with a 2 pole treatment, the current is ‘pre modulated’ i.e. the interference is generated within the machine unit.
== Amplitude Modulated Frequency (AMF) ==
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.<ref name=":2" />


Whichever way it is generated, the treatment effect is generated from low frequency stimulation, primarily involving the peripheral nerves. Low frequency nerve stimulation is physiologically effective (as with TENS and NMES) and this is the key to IFT intervention. <br>
== Beat Frequency ==
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.<ref name=":2" />


[http://www.electrotherapy.org/modalities/ift.htm Read more here .....]<br>
== Area of Interference ==
'''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.


== Frequency Sweep&nbsp;  ==
'''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.<ref name=":1" /><ref name=":3">Tim Watson, Electrotherapy: [https://pdf.wecabrio.com/electrotherapy-evidence-based-practice.pdf evidence-based practice. Physiotherapy essentials]. 12th edition, Churchill Livingstone,2008</ref>


Nerves will accommodate to a constant signal &amp; a sweep (or gradually changing frequency) is often used to overcome this problem. 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. The sweep range employed should be appropriate to the desired physiological effects (see below). It has been repeatedly demonstrated that ‘wide’ sweep ranges are ineffective in the clinical environment
== Base ==
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.<ref name=":2" /><ref name=":3" />


Note&nbsp;: Care needs to be taken when setting the sweep on a machine in that with some devices, the user sets the actual base and top frequencies (e.g. 10 and 25Hz) and with other machines the user sets the base frequency and then how much needs to be added for the sweep (e.g. 10 and 15Hz). sweep triangle sweep rectangle sweep trapezoidal (A) Triangular sweep pattern
== Spectrum ==
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.<ref name=":3" />


(B) Rectangular Sweep Pattern
== Sweep&nbsp;==


(C) Trapezoidal Sweep Pattern
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. 


The pattern of the sweep makes a significant difference to the stimulation received by the patient. Most machines offer several sweep patterns, though there is very limited ‘evidence’ to justify some of these options. In the classic ‘triangular’ sweep pattern, the machine gradually changes from the base to the top frequency, usually over a time period of 6 seconds – though some machines offer 1 or 3 second options. In the example illustrated, the machine is set to sweep from 90 to 130Hz (figure A) employing a triangular sweep pattern. All frequencies between the base and top frequencies are delivered in equal proportion.  
Basically, there are three types of wave  modes commonly used.


Other patterns of sweep can be produced on many machines, for example a rectangular (or step) sweep. This produces a very different stimulation pattern in that the base and top frequencies are set, but the machine then ‘switches’ between these two specific frequencies rather than gradually changing from one to the other. The diagram (figure B) illustrates the effect of setting a 90 – 130Hz rectangular sweep.  
•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.  


There is a clear difference between these examples – even though the same ‘numbers’ are set. One will deliver a full range of stimulation frequencies between the set frequency levels and the other will switch from one frequency to the other. There are numerous other variations on this theme, and the ‘trapeziodal’ sweep is effectively a combination of these two.<br>
•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.


The only sweep pattern for which ‘evidence’ appears to exist is the triangular sweep. The others are perfectly safe to use, but whether they are clinically effective or not remains to be shown. <br>
•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.<ref name=":1" /><ref name=":2" />


[http://www.electrotherapy.org/modalities/ift.htm Read more on frequency sweep here .....]<br>
== Balance ==
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.<ref name=":2" />


== Physiological Effects &amp; Clinical Applications ==
== Therapeutic and Physiological effects ==


It has been suggested that IFT works in a ‘special way’ because it is ‘interferential’ as opposed to ‘normal’ stimulation. The evidence for this special effect is lacking and it is most likely that IFT is just another means by which peripheral nerves can be stimulated. It is rather a generic means of stimulation – the machine can be set up to act more like a TENS type device or can be set up to behave more like a muscle stimulator – by adjusting the stimulating (beat) frequency. It is often regarded (by patients) to be more acceptable as it generates less discomfort than some other forms of electrical stimulation.
''PAIN RELIEF  AND RELIEF OF MUSCLE SPASM''


The clinical application of IFT therapy is based on peripheral nerve stimulation (frequency) data, though it is important to note that much of this information has been generated from research with other modalities, and its transfer to IFT is assumed rather than proven. There is a lack of IFT specific research compared with other modalities (e.g. TENS).
''STIMULATION OF INNERVATED MUSCLES''


Selection of a wide frequency sweeps has been considered less efficient than a smaller selective range in that by treating with a frequency range of say 1-100Hz, the effective treatment frequencies can be covered, but only for a relatively small percentage of the total treatment time. Additionally, some parts of the range might be counterproductive for the primary aims of the treatment.
''EFFECT ON EDEMA/ SWELLING''


The are 4 main clinical applications for which IFT appears to be used: <br>
== Treatment Parameters  ==


*Pain relief <br>
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<ref name="null">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.[http://www.sciencedirect.com/science/article/pii/S0195670199906473/]</ref>).
*Muscle stimulation <br>
*Increased local blood flow <br>
*Reduction of oedema


In addition, claims are made for its role in stimulating healing and repair.  
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.  


As IFT acts primarily on the excitable (nerve) tissues, the strongest effects are likely to be those which are a direct result of such stimulation (i.e. pain relief and muscle stimulation). The other effects are more likely to be secondary consequences of these.  
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<ref name=":0">Ozcan J, Ward AR, Roberson VJ (2004). A comparison of true and premodulated interferential currents. Arch Phys Med Rehab. 85(3): 409-415.[http://www.sciencedirect.com/science/article/pii/S0003999303004787/]</ref>).  


[http://www.electrotherapy.org/modalities/ift.htm Read more on these physiological effects &amp; clinical applications here .....]<br>


== Treatment Parameters ==


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.
== References  ==


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 />


[http://www.electrotherapy.org/modalities/ift.htm Read more on treatment parameters here .....]<br>
  [[Category:Electrophysical]]

Latest revision as of 13:57, 20 September 2022

Original Editor - Professor Tim Watson

Top Contributors - Admin, Garima Gedamkar, Rachael Lowe, Chee Wee Tan, Sai Kripa, WikiSysop, Kim Jackson and Laura Ritchie  

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. [1][2]

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.

•Using a medium frequency, a more tolerable penetration of current through the skin is possible.[1][3]

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).[3][4]

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.[4]

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.[4]

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.[3][5]

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.[4][5]

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.[5]

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.[3][4]

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.[4]

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[1]).

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[2]).



References[edit | edit source]

  1. ↑ 1.0 1.1 1.2 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.[1]
  2. ↑ 2.0 2.1 Ozcan J, Ward AR, Roberson VJ (2004). A comparison of true and premodulated interferential currents. Arch Phys Med Rehab. 85(3): 409-415.[2]
  3. ↑ 3.0 3.1 3.2 3.3 William E. Prentice. Therapeutic modalities in rehabilitation. 3rd Edition, McGraw-Hill Medical, 2017
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Val Robertson, Alex Ward, John Low John Low  Ann Reed, Electrotherapy Explained: Principles and Practice. 4th Edition. Butterworth-Heinemann,2006
  5. ↑ 5.0 5.1 5.2 Tim Watson, Electrotherapy: evidence-based practice. Physiotherapy essentials. 12th edition, Churchill Livingstone,2008
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