Interferential therapy employs medium frequency interferential currents used in 2 or 4-pole configurations to produce a low-frequency stimulation effect.
Prior to the introduction of interferential therapy in the mid 1950s, low-frequency stimulation (NMES) was used for pain relief, muscle re-education etc.
These currents, however, have the disadvantage that normal human skin has a relatively high impedance at such frequencies. In order to overcome the skin impedance, a larger voltage has to be used to achieve the desired current, resulting in a more uncomfortable treatment for the patient. In addition, the penetration depth of these currents is poor and in part is limited by the discomfort to the patient.
Interferential therapy overcomes the problem of skin impedance. At 50 Hz (faradic current) the impedance for a 100 cm2 of skin is approximately 3000 ohms. At 4000 Hz (medium frequency -medi-wave) the skin impedance of the same area is around 50 ohms. This means that a much lower voltage signal can be used to produce the desired current, resulting in less skin sensation and more comfortable treatment. This medium frequency is, however, well outside of the normal biological frequency range (0.1 to 250 Hz).
In order to produce the required stimulation, two medium frequencies are used. A constant frequency of, say, 4000 Hz is applied to one pair of electrodes and a slightly different frequency of say 3900 Hz is applied to the other pair. These two frequencies ‘interfere’ to produce an amplitude modulated medium frequency (beat frequency) in the tissue. The tissue responds to the cyclic rise and fall in the current intensity. It is the amplitude modulation frequency (AMF) that is within the normal biological frequency range and not the medium frequency (carrier).
Primo Interferential 960 features
•Touch screen technology
• Three carrier frequencies – 2kHz, 4kHz and 8kHz
• 0-100mA peak constant or 0-70/140V peak constant voltage, depending upon mode
• NMES Treatment protocols: Pain relief, Stimulate local blood flow, OA Knee, Chronic low back pain, Acute low back pain, Fibromyalgia, Postoperative knee pain, Stress incontinence, Urge incontinence.
• 2 independent output channels which allow 2 different treatments
• Operates in conjunction with EMS vacuum unit if required
• Easy wipe clean reducing the risk of cross-infection
• Mains powered as standard, optional battery available