Interferential Current Definition .
Interferential current is the production of low frequency current in the body tissue by the simultaneous application of two different medium frequency currents. As it is obtained as a result of interference of two different medium frequency currents, it is known as interferential current. Alternatively, Interferential current can be defined as the resultant current produced in the body tissue when two medium frequency alternating currents are applied simultaneously. This current is produced at the intersection of two medium frequency alternating currents.
Historically, in 1950, H Nemac for the first time suggested interferential current for therapeutic application. It is also called Russian current as Dr K M Kots first described its use in 1970, in Russian medical literature. Interferential current can be used for pain relief and acceleration of healing unlike TENS that is used only for pain relief. Present, research databases suggest that interferential current is more effective in chronic pain.
Characteristics of interferential current .
Here, we will discuss three fundamental things pertaining to interferential current. (You can recall them with ABC, where A is area of interference, B is beat frequency and C is current.)
Currents .
Two medium frequency currents are used to produce the interferential current . They are known as carrier waves as they do not produce muscle nerve stimulation and are just used to get greater depth of penetration and to produce interferential current. Out of two medium frequency currents the frequency of one current is fixed and it is 4,000 Hz.
The frequency of the other current lies in between 4,000 and 4,100 Hz, which is adjustable. When these currents cross each other, they will produce a third current at the point where they cross each other and this third current is known as interferential current.
Beat Frequency .
The frequency of the resultant current (third current produced due to crossing) is known as beat frequency. Beat frequency is equal to the difference between two medium frequency currents. It lies between 0 to 100 Hz. Beat frequency may be kept constant or varied rhythmically so as to prevent accommodation.
1. Constant beat frequency .
It is also called selective beat frequency. Different selective beat frequencies can be selected in between 0 and 100 Hz.
2. Variable beat frequency .
It is also called automatic beat frequency. Various variable beat frequencies can be used.
Beat frequency of zero to five hertz stimulate sympathetic nerves, 5 to 10 Hz stimulate parasympathetic nerves, 10 to 50 Hz stimulate motor nerves, 50 to 90 Hz produces sedative and spasmolytic effect and 90 to 100 Hz produces analgesic or pain relief effect. (Memory clue, SPM, SP social and preventive medicine’s special portion, where S is sympathetic, P is parasympathetic, M is motor nerves, S is spasmolytic, and P is pain relief).
Area of Interference .
Area of Interference is the area where interferential current is set-up. The pattern of the interferential area may be static or dynamic.
1. Static interference .
Here the area in which interferential current is setup-remains stationary. This area of static interference gives an appearance of a clove leaf as a result of the vector addition of two currents and it lies to 45º angles to the perpendicular lines from each electrode.
2. Dynamic area of 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. Current is varied from 50 to 100 percent. This dynamic area of interference is also called vector sweep, vector scan, rotating vector, etc.
Electrodes of interferential Therapy .
Various types of electrodes used for the application of interferential current include vacuum electrode, pad electrode, carbon impregnated/silicone rubber electrode, four field electrodes, two field double electrodes, quadripolar/four point probe electrode, labile electrode, etc.
Vacuum Electrode .
Vacuum electrode is like a rubber bell. Here, the electrode is kept at the base of the bell and wire or lead is connected at the narrow end. Generally, a soaked sponge or spontex is kept just below the electrode so as to achieve even contact to the skin and hence there is even conduction. These electrodes are held to the patient with negative pressure created by a vacuum pump. The magnitude of the vacuum should be adjusted so that, the least amount of suction is necessary to keep the electrodes on the skin otherwise, superficial bruising may occur. Vacuum electrodes are available in various sizes.
Vacuum can be adjusted so as to get constant or pulsed mode. When pulsed mode is used, additional effect of the massage can be obtained. Vacuum electrodes are excellent for treating flat smooth areas, where they can be applied easily and quickly. On bony areas such as shoulder and ankle, it is difficult to place the vacuum cup in correct position without deformation. The deformation squeezes the cup and the area enclosed by the rim is diminished. As a result of deformation, the two electrodes in a particular channel would not be of the same size and the circuit is unbalanced.
On hairy skin, it is difficult to get an airtight seal. In elderly patients, the skin is likely to be thin and papery, it presents difficulty with contact and bruises easily. Vacuum electrodes are considered unsafe for patients who are taking steroids, patients who are taking anticoagulation therapy, deep vein thrombosis, history of pulmonary embolism. This is again because of the likelihood of bruising and other complications.
Labile Electrodes .
Labile electrode is a special type of plate electrode, which is insulated on one side and is covered with sponge to provide contact. Two electrodes are used for the treatment purpose. The operator holds them in position while treating. During the treatment, these electrodes are moved over the patient’s skin. Usually one side of the electrode is insulated or operator puts on the gloves, so that current does not pass through the operator’s hand while applying the current through these electrodes to the patient.
Then operator secures them to his palms with velcro. It is helpful if foot control is available otherwise both the electrodes are first held by one hand while the other hand adjusts the current. Pads are moved in see-saw movement. It is useful in the treatment of muscular conditions and awkward areas.
Methods of Application .
Interferential current can be applied by means of bipolar, quadripolar, stereo-dynamic and labile method. In bipolar method, only two electrodes are used. It is said that in case of bipolar method, medium frequency currents are added inside the machine (pre-modulated) to produce low frequency output. This mode of treatment is sometimes known as electrokinesis.
The disadvantage of bipolar method of application is more sensory stimulation since there is more skin resistance for this output current as compared to classical interferential current and hence it gives unpleasant sensation to the patient. In stereo-dynamic systems, three pairs of electrodes are used and the machine provides three outputs. It reduces accommodation and provides three-dimensional interferential field.
In labile method, two labile electrodes are used for the treatment purpose and operator moves them during the treatment. The choice for electrode placement for interferential current application include area of pain, spinal nerve root, peripheral nerve, trigger point and acupuncture point.
Indications .
Interferential therapy is commonly used for the pain relief, relief of muscle spasm, improve the venous and lymphatic drainage, and re-education of deeply-situated muscles, which are not easily accessible with low frequency currents. Various conditions in which interferential current may be used are :
- Osteoarthritis .
- Ankylosing spondylitis .
- Spondylosis .
- Low back pain .
- Frozen shoulder .
- Chondromalacia .
- Stress incontinence .
- Nocturnal incontinence .
- Brachial neuralgia .
- Sciatica .
- Phantom pain .
- Buerger’s disease .
- Raynaud’s disease .
- Myalgia/ myositis .
- Edema following immobilization .
- Bronchial asthma .
- Bursitis .
- Tendonitis .
Contraindications and Precautions .
Interferential current is contraindicated in
- Patients with cardiac pacemaker .
- Advanced cardiac disease .
- Hypertension .
- Hypotension .
- Thrombosis .
- Recent Hemorrhage .
- Pregnancy .
- Neoplasm .
- Tuberculosis .
- Fever .
- Infection and active epiphyseal region .
It is believed that treatment of arterial diseases with interferential current could produce emboli, in acute phase of deep vein thrombosis, it is possible that thrombi could get dislodged or increase the inflammation of the vein, that is phlebitis. The treatment of an area of infection can cause aggravation of the symptoms, infection could spread, treatment of pelvic region with interferential current is not safe for fetus. Direct stimulation of tumor is contraindicated, but referred pain from tumor or metastasis can be treated with interferential current in hospices.
Maintain the suction level below that which causes damage or discomfort to the patient. Interferential apparatus must be kept at least six meters away from a short-wave diathermy machine, preferably in another room, otherwise circuit damage can occur or the patient may experience a sudden surge of current when the short-wave diathermy machine is turned off. To prevent interference from short-wave diathermy a filter circuit can be used in interferential therapy machine.
Dosimetry .
Interferential therapy can be applied for 10 to 20 minutes and if more than one area is to be treated, then total treatment time should not exceed 30 minutes, since it is believed that lengthy treatment causes tiredness towards the end of the day. Further, it is advised that interferential current treatment can be given for about 10 to 25 days, once a day basis.
Usually, the intensity, which produce a strong but comfortable prickling sensations without any discomfort is used. Alternatively, three times toleration (T T T Dose) can be used. Three T dose is used in treating localized condition that is tender and is to be an anesthetized.
Place the electrodes, increase the intensity so as to give intense prickling, once the intense prickling sensation is reduced, increase the intensity once again so as to get intense prickling and repeat the same once again so as to treat the area three times with strong prickling.
Therapeutic Effects of interferential current .
Therapeutic effects of interferential current include muscle contraction, increased blood flow, relief of spasm and pain relief.
Pain Relief .
Interferential current is commonly used for electroanalgesia in various musculoskeletal conditions. Interferential current is effective in cases of chronic pain with or without swelling but it is found to be less effective in post-traumatic pain in acute stage. The exact mechanism of pain relief by interferential current is not known. Pain relief may occur as a result of removal of irritant or pain substances.
Interferential current can stimulate autonomic nerves, which results in vasodilation and improved circulation. Improved circulation can remove the waste products or pain substances from the site of application. Alternatively, pain relief may be due to release of endorphins or due to activation of pain gate mechanism. Pain relief may also occur due to stimulation of reticular formation, blocking c fiber transmission and placebo effect.
Relief of Muscle Spasm .
Spasm is often associated with pain, unnatural movement and muscle strain. Relief of pain helps in breaking pain-spasm–pain cycle and hence interferential therapy can be used for the relief of muscle spasm.
Stimulation of Innervated Muscles .
Interferential current can stimulate deeply-situated muscles, as it is like a low frequency current. Stimulation with lower beat frequency such as 10 will result in a series of twitches, while stimulation with higher beat frequency like 50 will result in a titanic contraction. Selection of parameters that can result in combined muscle stimulation with an increase in blood flow can be helpful in the treatment of edema.
Effect on Edema .
Edema is the collection of fluid in interstitial space. Edema can be associated with swelling. Exudates in edema, may get organized and form adhesions and hence to prevent this, interferential current can be used. Interferential current causes vasodilation, increases venous, lymphatic flow, electroporation or increased permeability and pumping effect through muscle contraction that helps in accelerating physiologic mechanism for the absorption of the exudates. Hence, interferential current is preferred in the treatment of edema associated with traumatic and nontraumatic musculoskeletal conditions.
Increased Blood Circulation .
Interferential current affects the autonomic nervous system and an adequate beat frequency selection can cause stimulation of parasympathetic nervous system and thereby vasodilation and increased blood circulation. This therapeutic effect is useful in promoting healing and thereby it helps in restoration of function.
Advantages of Interferential Current .
Interferential current does not produce any sensorimotor irritation, metal is not contraindicated for interferential therapy and hence number of postoperative conditions can be treated with interferential therapy. Also, interferential current is useful in treating tissues at a greater depth. Owing to the frequency, the skin resistance is very less and current can be localized more effectively in specific areas.
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