An Introduction to Interferential Current Therapy

Foreword

1. Electrotherapy

2. Interferential Current
2.1  Advantages of interferential currents
2.2  Amplitude modulation - possible frequency settings
2.3  The principle of interference
2.4  Automatic vector

3. Effects of Interferential Currents
3.1  Effects of constant frequencies
3.2  Effects of rhythmic frequencies

4. Indication and Contra-indication

5. Selection of Dosage

6. Types of Electrodes
6.1  Plate electrodes
6.2  Suction electrodes
6.3  Pad electrodes

*  Please Note *
The following information was obtained through an extensive review and translation of published text books and is intended for reference purposes only.  The authors and owners of this website are not responsible for any errors, omissions or claims contained herein.

Foreword

As a result of its positive effects and its versatility in application, interferential current therapy has become an established modality in physical medicine.  Besides the proven therapeutic results, it is the easy application technique of suction or pad electrodes that makes this form of treatment so popular.  

The following report contains the most important theoretical and practical aspects of interferential current therapy condensed into an intelligible form for the reader to put the information into immediate practical use. 

1. Electrotherapy

The different types of electrical current used in electrotherapy are divided into two groups according to their effects

• Direct  (DC or galvanic) and
• Alternating (AC)

The noticeable effects for the patient will be the characteristic sensation of current flow or of occurring muscle contractions.  The stimulation currents furthermore are grouped into currents of low frequencies (LF) and medium frequencies (MF)

Low-frequency (LF) stimulation currents:
When using frequencies in a range below 1000 Hz, nerves and muscle fibers are able to follow this rhythm and respond to each single current pulse.
Ex.: TENS, Faradic, Pulsed Galvanic, Diadynamic Currents

Medium frequency (MF) stimulation currents:
When using frequencies in the range of approximately 1000 Hz up to 100,000 Hz it becomes impossible for excitable structures to react to every single pulse Only the summation of a number of pulses achieves a single depolarization response (Gildemeister Summation Effect).

Interferential current is an alternating current of approximately 4000 Hz. Therefore, it belongs into the group of medium-frequency stimulation currents.

2. Interferential Current

2.1 - Advantages of Interferential currents as compared to other stimulating currents

• Low current sensation - intensive depth effect
  Because it is an alternating current of medium frequency, the interferential current overcomes the skin resistance more easily than low-frequency DC-currents and penetrates the tissue to greater depth while the patient's sensory discomfort is markedly reduced
  
  
• Simple electrode application
  The polarity of electrodes is of no importance since stimulation is effected at both poles with equal intensity, in contrast to the low-frequency DC-currents This simplifies the treatment considerably
  
  
• No risk of burns
  Application of Direct Currents, (DC) effects an accumulation of ions under the electrodes whereas the constantly changing polarity of the interferential currents eliminates the production of yes and acids This not only makes inter­ferential currents safer to use but also enables treatment of patients with implant
  
  
• No uncomfortable sensations
  Electrodes can be relocated during interferential and AMF-current treatment without first turning the intensity down since this will cause the patient no unpleasant shock effects as would be the case with low-frequency currents

2 - Amplitude modulation of medium-frequency currents

When applying alternating currents of medium frequency at a constant intensity for a longer period of time the stimulation effect eventually diminishes (Wedensky inhibition) Interrupting the current flow or modulating the amplitude* between the preset value and 0 continuously prevents this decrease in stimulation effect.

* amplitude = maximum level during one cycle, peak value of an alternating current

The body primarily responds to the rate of this amplitude modulation, i.e. the number per second of the increase and decrease of the current intensity. Therefore the repetition rate of amplitude modulation per second represents the actual “stimulation frequency" of MF currents

In order to adjust the treatment parameters to the individual clinical requirements of the patient, the operator can select from a wide variety of "stimulation frequencies" and "frequency programs".

 The following frequency settings are possible:

• Constant frequencies:
  In mode "Selective" any frequency from 0 to 100 Hz (250 Hz) can be selected as a constant, during the entire treatment time invariable stimulation frequency

• Cycle Duration
  Some units are provided with a control marked "Cycle Duration" that allows adjustment of the speed of frequency alterations in case of rhythmic frequencies. In other models the speed of frequency alteration is preset to a fixed rate.

• Rhythmic frequencies:
  In this mode the selected interferential or stimulation frequency is continuously altered within a pre-selected range.

 EXAMPLE
When selecting the program 0 Hz - 10 Hz, the stimulation frequency is continuously altered from 0 Hz through 1, 2, 3 etc. up to 10 Hz and back again through 9.6.7.... 0 Hz

NOTE
The choice of the proper frequency or range of frequencies depends upon the actual clinical requirement of the patient and is discussed in section "Effects of interferential Current".

2.3  The principle of interference

The electrical generator of an interferential therapy unit does not actually deliver an amplitude modulated current via the leads and electrodes to the patient The unit produces in two separate circuits sinusoidal currents of medium frequency and constant amplitude By crossing two currents in the region of the body to be treated their superimposition results in an amplitude-modulated MF current This newly and endogenously generated current is named interferential current after the physical principle of interference

Advantage of the interference principle:
The skin under the four electrodes is exposed only to un-modulated medium-frequency currents having little, and as treatment progresses, no stimulating effects However, in the current crossing area the modulation creates the highly stimulating interferential current in the deeper layers of the body tissue

2.4  Automatic Sweep “Dynamic”

3. Effects of Interferential Currents

• The physiological effects on the tissue depend on the following factors:
  -  Frequency selected
  -  Use of constant frequency or rhythmic frequency swing
  -  Intensity of current used
  -  Accuracy of electrode placement and type and size of electrode selected
  -  Accuracy of localization of the lesion to be treated 
  -  Underlying pathophysiology in relation to the desired effect
  
  Interferential current stimulation causes a variety of reactions, which may have functional interrelations.  Generally, interferential currents stimulate the vegetative, sensory and motor nerves and bring about the following responses:
  
  
• Hyperemia
  Together with hyper-metabolism, increased absorption, higher antiphlogistic and bactericidal properties of the permeated tissue.
  
  

• Analgesia
  Which might be attributed in part to the hyperemia and its secondary effects but also to the superposition of stimulations (gate-control effect).
  
  

• Effects on musculature
  By direct stimulation of the respective organ using a suitable electrode technique or by the cutivisceral reflex arc
  
  

• Effects on inner organs
  Either by reducing the tone of strained muscles or by stimulating the muscular tonus, allowing contractions of exactly predictable intensity and desired intervals.

The selection of a suitable constant frequency or rhythmic frequency swing enables the therapist to achieve the desired effects when treating a specific medical indication.

3.1  Effects of constant Interferential frequencies

• High frequencies between 80 - 100 Hz (100 - 250 Hz)
  Depression and inhibition of the sympathetic system causing Analgesia and hyperemia. These frequencies are used predominantly in cases of acute pain or in preventive therapy.
  
  

• Low frequencies between 0 - 10 Hz (0 - 25 Hz)
  Stimulation of the sympathetic nervous system, strong stimulation of the motor nerves resulting in single contractions, and vegetative stimulations. This frequency is used to treat muscular atrophy. The stimulation of denervated muscles by means of interferential currents is not possible.

3.2  Effects of rhythmic Interferential frequencies

They are of particular importance since the continuously changing frequency eliminates almost totally a possible habituation or adaptation commonly experienced when using constant frequencies over a long period.

• 80 to l00Hz (100 - 250 Hz)
  Corresponds to the effects of individual frequencies in this range.  The basic effect is analgesic and also vasodilatory. Selection of the 80 to 100 Hz (100 - 250 Hz) frequency swing is recommended particularly in the treatment of neuralgic types of pain like migraine and brachial neuralgia.
  
  
• 0 to 2, 3 or 5 Hz
  Single contractions of the muscles and vegetative stimulation
  
  
• 0 to 10Hz (0 - 25 Hz)
  This frequency spectrum stimulates the sympathetic nervous system like the constant frequencies in this range. Muscular action starts with slow individual contractions changing over to palmospasms and returning to single contractions again.
  
  
• 0 to 100 Hz (0 - 250 Hz)
  This rhythmic frequency range covers all excitable structures of the tissue within the preset time of one cycle. It causes excitation and sedation in alternating sequence. Currents of this frequency provide an active hyperemia at the surface and in deeper tissues, accelerate the resorption of edema and hematoma, improve the cell metabolism and normalize the tissue tonus.

4. a) Indications
Treatment of a wide range of medical indications and conditions is possible because of the variety of effects produced by interferential currents. Interferential current therapy is a well-proven treatment method for:

• Pain
  Treatment of the cause and the referred pain pathway has marked analgesic effects for pain of sympathetic origin such as causalgia, reflex sympathetic dystrophy, migraine and neuralgia
  
  
• Diseases of the locomotor system
  (bones, joints, capsules, ligaments, muscles, etc.)
  
  a) trauma-induced:
  distortions, contusions, conditions following luxations and fractures, overstretched muscles.
  b)  degenerative:
  arthrosis, humeroscapular periarthritis, chondrosis and osteochondrosis of the spine, myalgia like lumbago and torticollis, muscular atrophy, epicondylitis.
  
  
• Circulatory disorders
  a) Functional type:
  Raynaud's disease, migraine, acrocyanosis.
  b)  Organic type:
  arterial sclerosis, endo-angutis obliterans, varicosis, conditions following frostbites and burns.
  
  
• Disturbances of the nervous system
  Neuralgia like ischialgia, trigeminal neuralgia brachialgia, etc.
  neuritis
  radiculopathy
  herpes zoster
  and faradisable paralysis

Disorders of inner organs
Obstipation or other functional disorders of inner organs.

4. b) Contra-Indications

-  Interferential current therapy must not be used in cases of:
-  highly inflamed or feverish infections
-  pregnancy
-  patients with cardiac pacemakers
-  malignant tumors
-  spastic paralysis
-  skin lesions in the area of treatment like skin injuries
-  varicous and atrophic degenerated skin
-  arterial disease, deep vein thrombosis, thrombo-phlebitis
-  danger of hemorrhage

5. Selection of Dosage

Dosage is the most important factor in therapy and, therefore, has to be determined individually.  To find the optimum dose for a particular patient, the therapist should observe the patient's response to the treatment and subsequently vary the stimulating parameters where required.

Stimulation Parameters of Interferential Current Therapy

• Intensity:
  The intensity adjustment is not based primarily on the mA reading of the meter but has to be made rather in accordance with the resulting sensations.  In general, acute cases are treated with lower current intensity (barely noticeable), and chronic cases with higher intensities (clearly noticeable).  However, there should be no continuous strong muscle contraction (tetany), and the current intensity must always be kept below the individual tolerance threshold of the patient
  
  
• Treatment Time:
  The duration of a typical treatment session is between approximately 6 to 8 minutes, using shorter durations in acute cases and longer durations in chronic cases.

When using suction electrodes the treatment time usually is shorter because of the added suction massage effect than when using plate or pad electrodes.

• Treatment intervals:
  As with all other methods of physical therapy, acute conditions require daily treatment and often 2 treatment sessions a day, while chronic conditions are treated 2 to 3 times per week.
  
  
• Number of sessions:
  In acute cases short treatment series (approx. 6 sessions) often can bring the desired results, while chronic cases usually require a larger number of treatments (approx. 10 sessions).

Notes:
As long as the patient's response is not known always use low dosage in the initial treatment even when treating chronic cases.  Acute pain may be treated successfully using high intensities (gate-control effect).

6. Types of Electrodes

Interferential therapy requires four electrodes since two current circuits are applied simultaneously.  The current may be introduced via plate electrodes, pad electrodes and suction electrodes.

6.1 Plate electrodes

This type consists of metal or rubber plates which are covered by well moistened sponge pockets. The electrodes are fixed to the skin of the patient by means of straps. Alternatively, the electrodes may also be held in position by small sand bags or the body weight of the patient.

The electrode pockets have a thicker and a thinner wall. Always place the thicker wall to the skin.

Plate electrodes with sponge pockets are available in various sizes.

It is good practice to wet the electrode rim prior to electrode application and to use only moderately moist (not dripping wet) sponges.

Two sizes of suction electrodes with sponges are available. The standard size has a diameter of 90 mm and the smaller one has 65 mm diameter.

Most of the modern machines have the vacuum producing pump system built into the interferential therapy unit. A choice of either a constant or an interrupted suction mode is available. The interrupted mode produces a rhythmically increasing and de­creasing "suction pulsation" or "suction wave", and results in a considerable increase in blood and lymph flow in the tissue under the suction elec­trodes. This effect, combined with the electrical stimulation effect, achieves therapeutic results in a much shorter treatment time than the use of plate or pad electrodes. With a glass or acrylic suction applicator a suction wave therapy can be carried out giving similar therapeutic re­sults as connective tissue massage (CTM). No electrical current is applied in this mode. Application of suction electrodes over varicose veins, open wounds and areas of disturbed capillary function is contra-indicated.

6.3  Pad electrodes
Pad electrodes, made of a soft special rubber, are available in different shapes and sizes. They are especially helpful where use of suction electrodes is not indicated or possible, and where plate electrodes are difficult to apply. Typical areas of pad electrode application are neck, face, hands and ankle.

NOTE: Never use pad electrodes for impulse current application since the padding could lead to burns.