A common problem with electrotherapy (or transcutaneous electrical nerve stimulation, abbreviated TENS) is that the low-frequency current can cause discomfort when it enters the affected area through the skin.
Interference Current (IFC): This type of stimulation is characterized by the crossover of two dielectrics with independent frequencies, which work together to effectively stimulate large pulse fibers. These frequencies interfere with the transmission of pain information at the spinal cord level.
Due to its frequency, the interfering wave encounters low impedance when penetrating the skin and entering the underlying tissues. This deep tissue penetration can be modulated to stimulate parasympathetic nerve fibers, thereby increasing blood flow.
Interference stimulation differs from TENS because it allows for deeper tissue penetration, greater comfort (compliance), and increased circulation.
Interference current is essentially a deeper form of TENS. Essentially, IFC uses the same signal generated by a TENS unit to modulate a high-frequency (4000 Hz) carrier waveform. This high-frequency carrier waveform penetrates the skin more deeply than a regular TENS unit, resulting in less discomfort for the user at a given level of stimulation. Deep within the tissue, the carrier waveform is canceled out, thus generating a TENS-like signal deep within the skin.
IFC devices may be useful for patients whose TENS has not yet been relieved.
Interferential electrical stimulation (TENS) is a unique way to effectively deliver therapeutic frequencies to tissues. Traditional TENS and neuromuscular stimulators use discrete electrical pulses delivered at low frequencies of 2–160 Hz.
However, the interference stimulator uses a fixed carrier frequency of 4,000 Hz and a second adjustable frequency of 4,001–4,400 Hz. When the fixed and adjustable frequencies are combined (heterodyne), they produce the desired signal frequency (interference frequency).
The interfering stimulus is concentrated at the intersection between the electrodes. This concentration occurs both deep within the tissue and on the skin surface.
Traditional TENS and neuromuscular stimulators deliver most of the stimulation directly under the electrodes. Therefore, compared to other forms of electrotherapy, using interferential stimulators allows current to be infused to greater depths and larger tissue volumes. When current is applied to the skin, capacitive skin resistance decreases with increasing pulse frequency. For example, at a frequency of 4,000 Hz (interferential unit), capacitive skin resistance is eighty (80) times lower than at 50 Hz (within the TENS range).
Therefore, interfering currents pass through the skin more easily and stimulate the skin's nociceptors less, thus allowing for greater patient comfort during electrical stimulation.
Furthermore, since the skin is more tolerant to intermediate frequency (interference) currents, the dosage can be increased to enhance the ability of the interference current to penetrate tissues and more easily reach deeper structures.
This explains why interfering currents may be best suited for treating patients with deep pain, promoting bone formation in delayed fractures and nonunion fractures, as well as pseudoarthrosis, stimulating deep skeletal muscles to enhance the muscle pump mechanism in venous insufficiency, and inhibiting the increased tension of active arterial constrictors in certain areas, thereby increasing the cervical and lumbosacral sympathetic ganglia in patients.
Benefits : IFC interference therapy has been used for many years and its effectiveness has been well proven.
Studies have shown that patients who receive interferential therapy after surgery experience fewer postoperative complications compared to those who rely solely on anesthetics for pain relief. Interferential stimulation does not cause respiratory depression.
Interference therapy can improve blood circulation and increase a patient's recovery time. Multiple treatments at home or at work often accelerate recovery and allow patients to return to a normal lifestyle sooner.
Common uses: before and after orthopedic surgery, joint injuries, cumulative trauma disorders, improving circulation, and pain control for various causes.
Interference therapy is used for pain relief, treatment of circulatory disorders, range of motion, edema, swelling, and muscle spasms. Post-operatively, patients will use the device three times a day for 15 minutes each time for 14-30 days.
IFC treatment is usually provided by professional physical therapy clinics. The advantage is that it is performed by professionals and the rehabilitation and pain relief effects are faster and more ideal.
Inheritance Medical has introduced the IFC pain relief machine from PMT (Pain Management Technology) in the United States. It is a home-use, easy-to-operate IFC interference therapy device. 
PMT is an innovator in advanced medical and therapeutic devices. For the past 20 years, PMT has been a leading medical device manufacturer in the United States. With the support of Dr. Norman W. Lefkovitz, MD, Chair of the Department of Neurology, St. Thomas Hospital, and the city of Akron, Ohio, PMT's staff are trained and kept abreast of emerging medical device technologies.
