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4.1.3 Description Current Waveforms

4.1.3.1 4 Pole Interferential Currents

With the interferential current type a medium frequency carrier frequency is used to pass the low

frequency stimulation (beat) frequency through the skin. The relatively low resistance of the skin to the

carrier frequency contributes to the patient comfort that is often associated with this current type.

Interferential currents are all AC currents without any residual DC components. Several variations of the

interferential current type are known, of which the following are available in the 4-series:

4.1.3.1.1 Classical Interferential

With this therapy method four electrodes are used and two non modulated currents are

generated. The frequency of one channel is fixed at the carrier frequency, while the other channel

has a variable frequency, based on the Beat frequency and Frequency Modulation settings.

Interference occurs where the two currents intersect in the tissue. The modulation depth (which

determines the current amplitude of the stimulation) depends on the direction of the currents, and

can vary from 0 to 100%. 100% modulation depth only occurs at the diagonals (and hence at the

intersection) of the two currents. This is of course a theoretical situation, based on the

assumption that the tissue is homogeneous. In reality, the tissue is heterogeneous, so that the

current balance between the two channels has to be used to obtain the 100% modulation depth

(Fig. 1). The current balance can also be used to compensate for differences in sensation

occurring under the electrodes.

Modulation depth is only 100% at

the diagonals.

4.1.3.1.2 Isoplanar Vector

The isoplanar vector technique is intended to increase the area where effective stimulation

occurs. Amplitude modulation occurs in the equipment and a special phase relation between the

two channels ensures a 100% modulation depth between the four electrodes in all positions.

Modulation depth is 100% over the entire treatment area.

The advantage of this method is that the positioning of the four electrodes to effectively treat the

affected tissue is less critical. The sensation of the Isoplanar vector mode is soft and equally

divided over the treatment area.

Enraf Nonius Sonopuls 490 Operating Instructions

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