Interferential Units Explained

Interferential current (IFC): is characterized by the crossing of two electrical medium, independent frequencies that work together to effectively stimulate large impulse fibers. These frequencies interfere with the transmission of pain messages at the spinal cord level. Because of the frequency, the Interferential wave meets low impedance when crossing the skin to enter the underlying tissue. This deep tissue penetration can be adjusted to stimulate parasympathetic nerve fibers for increased blood flow. Interferential Stimulation differs from TENS because it allows a deeper penetration of the tissue with more comfort (compliance) and increased circulation.

Difference between TENS and Interferential - article from the Journal of American Physical Therapy Association (PDF version)

 Interferential current is essentially a deeper form of TENS. In essence, IFC modulates a high frequency (4000 Hz) carrier waveform with the same signal produced by a TENS unit. The high frequency carrier waveform penetrates the skin more deeply than a regular TENS unit, with less user discomfort for a given level of stimulation. Deep in the tissues, the carrier waveform is cancelled out, resulting in a TENS-like signal deep under the skin.

TENS and muscle stimulators use discrete electrical pulses delivered at low frequencies of 2-160 Hz per second. However, Interferential stimulators use a fixed carrier frequency of 4,000 Hz per second and also a second adjustable frequency of 4,001-4,400 Hz per second. When the fixed and adjustable frequencies combine (heterodyne), they produce the desired signal frequency (Interference frequency). 

Interferential stimulation is concentrated at the point of intersection between the electrodes. This concentration occurs deep in the tissues as well as at the surface of the skin. Conventional TENS and Neuromuscular stimulators deliver most of the stimulation directly under the electrodes. Thus, with Interferential Stimulators, current reaches to greater depths and over a larger volume of tissue than other forms of electrical therapy. When current is applied to the skin, capacitive skin resistance decreases as pulse frequency increases.' For example, at a frequency of 4,000 Hz (Interferential unit) capacitive skin resistance is eighty (80) times lower than with a frequency of 50 Hz (in the TENS range). Thus, Interferential current crosses the skin with greater ease and with less stimulation of cutaneous nociceptors allowing greater patient comfort during electrical stimulation. 

In addition, because medium-frequency (Interferential) current is tolerated better by the skin, the dosage can be increased, thus improving the ability of the Interferential current to permeate tissues and allowing easier access to deep structures. This explains why Interferential current may be most suitable for treating patients with deep pain, for promoting osteogenesis in delayed and nonunion fractures and in pseudothrosis, for stimulating deep skeletal muscle to augment the muscle pump mechanism in venous insufficiency, and for depressing the activity of certain cervical and lumbosacral sympathetic ganglia in patients with increased arterial constrictor tone.

Since Interferential Therapy has been in use for many years, its effectiveness is well documented. Studies have shown that patients using Interferential Therapy after surgery develop fewer post-op complications than those relying solely on narcotics for pain relief. Interferential stimulation does not cause respiratory depression. Interferential Therapy aids in circulation, increasing the recovery time for patients. Multiple treatments at home or work will typically speed the patient's recovery and allow earlier resumption of their normal lifestyle.

Although the thought of electrical impulses being sent into the body may seem frightening at first, all you really feel is a slight vibrating sensation. Unlike many drugs, Interferential devices have no known side effects.

Individuals with a pacemaker or patients who are pregnant should not use an Interferential device. Consult your doctor or clinician first.

Will an Interferential device work for me?
Interferential Therapy has been used extensively for managing post-surgical, post-traumatic acute pain, edema and inflammation reduction. It has been used successfully for a wide variety of procedures such as:

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