Neuroscience Research Institute, Beijing Medical University Beijing, China
The ancient acupuncture technique of manual needling has largely been modified by electrical stimulation administered via needles inserted into the tissue (electroacupuncture, EA), or even via electrodes applied on the skin over the acupoints. In this case, the parameters of the electrical stimulation become one of the most important characters determining the effectiveness of the treatment. The electrical parameters of EA consist at least of frequency and intensity. The intensity of electrical stimulation can only be varied in a relatively narrow range, i.e., higher than the excitation threshold and lower than the nociceptive level. Since we do not intend to induce frank pain, the C fiber is not the target of EA stimulation. Therefore a pulse width of less than 1 ms is preferable. T A13 fibers and part of the A f ibers are identified by most researchers to be responsible for De-Chi (needle sensation). For this reason, a pulse width of 0.3 to 0.6 ms is commonly used. Under this condition, a current intensity of 2-10 mA is preferable for EA, and 8-15 mA for stamp-sized skin electrodes. For normal subject or in acute pain patients, a higher intensity usually produces a stronger analgesic effect. However, in chronic pain status, a moderate rather than strong stimulation produces better analgesic effect.
Compared to the intensity, the frequency of stimulation seems to be of wider variability and more importance. According to our study, the endogenous opioid peptides (enkephalins, endorphins and dynorphins) in the CNS can be readily released by peripheral stimulation of identified frequencies. Low frequency (i.e., 2 Hz) is apt to accelerate the release of enkephalins and 13-endorphin in the brain, whereas the high frequency stimulation 9100 Hz in human and rat, and 30 Hz in rabbit) are more effective in accelerating the release of dynorphin in the spinal cord. Based on the results of a series of careful study we have come to the conclusion that the best parameter for pain control is a dense-and-disperse (DD) mode of stimulation where 2 Hz is alternating with 100 Hz, each lasting for 3 seconds. Under this special parameter, all 3 kinds of opioid peptides are released simultaneously, thus producing a synergistic analgesic effect. This has been shown not only in rats but also in humans. A constant current output device entitled Han’s Acupoint Nerve Stimulator (HANS) has been developed. While DD mode stimulation produces best results in pain control and treatment of heroin addiction, patients with muscle spasm caused by spinal injury were best treated with 100 Hz stimulation that selectively releases dynorphin, resulting in a suppression of anterior horn neuron and amelioration of muscle spasm. Supported by National Natural Science Foundation of China and a grant from NIDA, USA.