Release time：2024-04-26 16:43
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1. No electrolytic effect
Medium frequency current is a sinusoidal alternating current. Because it is alternating current, there is no distinction between positive and negative poles when it acts. It also does not produce electrolytic effect, so it is easy to operate when used, and the electrodes are general (lead plate and a layer of flannel).
2. Reduce tissue resistance and increase the depth of action
The body tissue is equivalent to a small capacitor. The capacitive reactance displayed by alternating current can be expressed by XC=1/2πfc. From the formula, it can be seen that the higher f, the smaller XC. Therefore, medium frequency current can overcome the body tissue resistance and achieve a greater depth of action.
3. Excitatory effect on body tissue
Medium frequency current cannot cause excitement in a single cycle. Since mammalian motor nerves have an absolute refractory period after each excitement, which lasts about 1ms, in order to make each stimulus cause excitement, the frequency cannot be greater than 1KHz. For this reason, the frequency below 1000Hz is defined as low frequency current. The frequency of medium-frequency current is between 1KHz and 100KHz. It can no longer cause excitement every time it is stimulated. It needs the continuous action of multiple stimulations to cause excitement. This is the so-called comprehensive effect of medium-frequency electrical stimulation.
4. Characteristics of medium-frequency electricity on neuromuscular stimulation
The stimulation of the sensory nerves of the skin by medium-frequency current causes a comfortable vibration (uncomfortable restraint when the intensity is high). This stimulation will not cause the excitement of pain fibers. Therefore, when medium-frequency current acts, a larger current intensity can be used to cause deep muscles to contract strongly, but it will not cause burning and stinging sensations under the electrodes. At present, it is believed that low-frequency induced current can only excite normal nerves and muscles, while medium-frequency alternating current (especially those with a frequency of 6000Hz) may still excite degenerated nerves and muscles. Some people have proposed that when the medium-frequency current of 6000-8000Hz acts, there is a clear separation between the muscle contraction threshold and the pain threshold, that is, within this frequency, the muscles can contract strongly without causing pain.
5. Physiological characteristics of medium frequency current modulated by low frequency
Although medium frequency current with constant amplitude has the above advantages, it is easy for the human body to adapt to it because its amplitude does not change. At present, low frequency (0-150Hz) current has been used to modulate medium frequency current in clinical practice, so that the amplitude of medium frequency current changes with the frequency of low frequency current (Figure 4.1.1). Therefore, this current has the characteristics of both low and medium frequency currents, and it is not easy for the human body to adapt to it because of the constant changes in its waveform, amplitude, frequency, and modulation amplitude. At present, this type of current used in clinical practice includes interference current and modulated medium frequency current. The rectified pulsed medium frequency current can also be used for drug ion introduction treatment.
Different physiological effects occur due to different frequencies of modulated current.
For motor nerves and muscles
1~10Hz: can cause muscle contraction
25~50Hz: can cause muscle contraction
100Hz: can cause muscle contraction to weaken or disappear
For sensory nerves
50Hz: obvious tremor
100Hz: pain relief
For blood vessels
1~20Hz: increase blood vessel tension
50~100Hz: dilate blood vessels
For autonomic nerves
4~10Hz: excite sympathetic nerves
20~40Hz: excite vagus nerves
100~150Hz: inhibit sympathetic nerves