Release time：2022-12-09 17:00
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I. Overview
Transcutaneous electrical nerve stimulation therapy (peripheral nerve fiber electrical stimulation therapy) is an electrotherapy method that treats pain by inputting a specific low-frequency pulse current into the human body through the skin. This is an electrotherapy that emerged in the 1970s and has achieved good results in pain relief, so it has been widely used clinically (especially in the United States).
II. Physical properties
The difference between TENS therapy and traditional nerve stimulation therapy is that traditional electrical stimulation mainly stimulates motor fibers, while TENS is designed to stimulate sensory fibers. For this reason, TENS instruments must meet the following conditions:
1. High frequency: mostly between 2 and 160Hz, which belongs to the low frequency range.
2. Short pulse - or shorter: Generally, the pulse width is between 9 and 350μs. If the pulse is too wide, the fibers that transmit pain will be activated, and the ionization under the plate will increase. However, for those with more fat tissue, the pulse can be wider.
3. Appropriate intensity: Use a subthreshold intensity that makes the patient feel comfortable and does not cause muscle contraction. In this way, TENS can selectively stimulate the response of sensory, afferent nerve fibers without triggering the response of motor, efferent nerve fibers.
4. The current shape isn't uniform. Currently, the following waveforms are commonly used:
(1) Symmetrical bidirectional square wave;
(2) Medium or high frequency current modulated by unidirectional square wave;
(3) Symmetrical bidirectional pulse;
(4) Unidirectional square wave;
(5) Another asymmetric bidirectional pulse.
III. Therapeutic mechanism
There are several hypotheses:
1. Gate control hypothesis
It is believed that TENS is a kind of stimulation that excites coarse fibers. The excitation of coarse fibers closes the gate of pain input, thereby relieving pain symptoms. Electrophysiological experiments have shown that square waves with a frequency of about 100 Hz and a wave width of 0.1 ms are more suitable for exciting coarse fibers.
2. Endogenous morphine-like substance release hypothesis
A certain low-frequency pulse current stimulation may activate endogenous morphine-producing neurons in the brain, causing the release of endogenous morphine-like polypeptides and producing analgesic effects. Some people have proved through experiments that: when the electrode area of 24cm2 is placed on the outer side of the middle 1/3 of the right leg, the β-endorphin content in the cerebrospinal fluid of the lumbar puncture increases significantly when the square wave, width 0.2ms, frequency 40-60Hz, current intensity 40-80mA, is used for stimulation for 20-45 minutes. It is believed that the endorphin is released into the cerebrospinal fluid due to electrical stimulation, resulting in a temporary and significant relief of pain.
3. Promote local blood circulation: In addition to analgesia, TENS also promotes local blood circulation. After treatment, the local skin temperature rises by 1-2.5℃.
IV. Equipment and treatment methods
1. Instruments: All low-frequency pulse electrotherapy machines with t rise, t width, t fall and f that can be adjusted arbitrarily can be used. L64-2 polymorphic wave therapy machine can be used for this treatment.
Electrode: Lead plate and pad are the same as direct current therapy. Electrodes with a diameter of 2-3cm are commonly used.
2. The following are the common methods of electrode placement:
(1) Place at special points, i.e. trigger points, acupuncture points and motor points. Because the skin resistance of these special points is low, there is a high-density input to the central nervous system. These points are effective places to place electrodes.
(2) Place at the same segment as the lesion, because electrical stimulation can cause the release of endorphins in the same segment and relieve pain.
(3) Place at the superior cervical ganglion (on both sides of the C2 transverse process under the mastoid) or pass the current through the skull, both of which can achieve a good analgesic effect.
3. The choice of frequency is mostly based on the patient's feeling that it can relieve symptoms. Chronic pain is suitable for 14-60Hz; postoperative pain is suitable for 50-150Hz; herpes pain is suitable for 15-180Hz; pain after peripheral nerve injury is suitable for 30-120Hz, etc. It is generally recommended that patients choose the frequency they think is appropriate. Most patients are suitable for a stimulation frequency of 100Hz and a t width of 0.1-0.3ms.
4. Current intensity is suitable for causing obvious tremor without causing pain. Generally 15-30 mA, depending on the tolerance of the disease.
5. Treatment time: 2-3 minutes for treating causalgia. Generally 20 minutes, but can be as long as 1 hour or several hours.
V. Main indications and contraindications
1. Indications: headache, migraine, neuralgia, causalgia, phantom limb pain, joint pain, abdominal pain, postoperative pain, labor pain, cancer pain, etc.
In short, TENS is effective for acute, chronic and neuropathic pain, and the efficacy of short-term treatment is higher than that of long-term treatment.
2. Contraindications
(1). Patients with pacemakers. Especially those with on-demand pacemakers should be more careful because the current of TENS can easily interfere with the pacemaker's pace.
(2). Stimulate the carotid sinus.
(3). The waist and lower abdomen of women in early pregnancy.
(4). Patients with local sensory loss and electrical allergy.
This article comes from: Transcuataneous electrical nerve stimulation