How does inferential work?
Small amounts of electrical impulses are induced into the tissues in the vicinity of the injury. Where these waves intersect below the surface of the skin, low frequency stimulation is created. This prompts the body to secrete endorphins and other natural pain killers to help relieve pain
Benefits of interferential:
- Reduces pain sensation
- Increases blood circulation
- Soothes nerve irritation
- Decreases local swelling and edema
- Speeds the healing process
What will it feel like?
Patients will feel a slight tingling sensation like ants crawling
Pre-modulated interferential - both outputs of the unit provide a carrier frequency of 4000Hz, however, each output has the ability to premodulate or burst the frequency within the unit.
True interferential - One output of the unit is a constant 4000Hz while the second output frequency is adjustable from perhaps 4001Hz to as much as 4250Hz
While frequency ranges vary from manufacturer to manufacturer, basic therapy ranges are fairly consistent. Frequencies which vary from approximately 80Hz to 120Hz are considered most effective for acute pain while lower frequencies of perhaps 3Hz to 5Hz are preferred for the treatment of chronic pain. Some units feature a nerve block setting where both channels produce an output of 4000Hz to create an interferential nerve block to quickly block out acute pain. Most clinicians prefer a setting of 1 Hz to 150z for treating acute edema.
When treating acute pain with the 80Hz to 120Hz setting, interferential therapy will provide a release of enkephalin with a treatment time of 10 to 12 minutes. Chronic pain, however, requires 15 to 20 minutes of the 3Hz to 15Hz setting to provide relase of beta-endorphins. Nerve block techniques, 4000Hz, normally requires 10 minutes or more depending upon the size of the area being treated.
INTENSITY OF CURRENT
Interferential therapy provides a comfortable, soothing stimulation and should never be strong enough to cause any discomfort to the patient. Higher intensities should not be considered "better" as far as obtaining results. It is important to note that once the patients comfort level is established at the onset of therapy, the intensity should not be increased during the treatment. This could cause overstimulation of the tissue and even minor burns, particularly when treating with a unit that produces "true interferential" due to the Widensky inhibition effect.
CONTRAINDICATIONS AND PRECAUTIONS
Interferential therapy is considered a very safe modality when used properly for appropriate conditions. Most manufacturers list similar contraindications and precautions, most of which are the same as other electrotherapy devices. It is always recommened that the clinician review each manufacturers warnings prior to treatment with any device.
ELECTRODES, CONTACT, AND SAFETY
If carbon rubber electrodes are used, care should be taken to insure proper current flow. When conductive gels are used, the gel will create a glaze over the surface of the electrodes with long-term use. The glaze may prevent the flow of current over the entire electrode surface. Cleaning the electrode periodically with a mild soap and water and soft brush is recommended. It is not a good practice to use conducting mist sprays ain lieu of other conducting agents. This is due to the saline content of the sprays which has been shown to destroy the carbon content of the electrode, thus rendering the electrode useless.
The Original Concept of Inferential:
Interferential therapy was developed by Austrian physician, Dr. Hans Nemec, approximately in the 1950's. Dr. Nemec proposed that by crossing two slightly different medium frequency alternating currents within the tissue; a third frequency current of greater intensity is created in the deeper tissue. As an example, a frequency of 4000Hz interfering with another frequency of 4080Hz creates a third current of 80Hz. This is caused by the inphase and out of phase relationship of the two original currents as they alternate from positive to negative polarity. The third current, referred to as the "beat frequency" becomes the actual therapeutic frequency.
When considering the relative merits of these two methods, many clinicians have noted that while both create the interference effect, there may be a distinct advantage to the pre-modulated technique. Since the "true interferential" provides an uninterrupted, constant 4000Hz frequency to the tissue, a condition known as Widensky inhibition (depolarization of the nerve fibers) will occur beneath the electrodes. This will create numbness and what will be perceived by the patient as a reduction in the intensity of current. With pre-modulated interferential, however, since the current is being burst inside the unit itself, Widensky inhibition will not occur and a larger treatment area is established with the actual therapeutic frequency.