Electroacupuncture analgesia: A review of neurophysiological and clinical evidence on ideal parameters

Background
Electroacupuncture (EA) is widely used for painful conditions. EA is used with or without needles, and on traditional acupoints or motor or trigger points. Electrical stimulation used varies in frequency, intensity, pulse duration and size of electrodes. So far, no consistent understanding of the ideal parameters of EA is available.

Objectives

1. To identify the role of each parameter in EA by reviewing neurophysiological and clinical studies; and
2. To provide background for searching for the ideal set of parameters.

Results
Frequency of EA is associated with the types of endogenous opioid peptides released. Alternating frequency (2/15 Hz or 2/100 Hz) may enhance the analgesic effect and reduce the risk of opioid tolerance (Han et al 1991). With a fixed frequency, EA at strong but tolerable levels induced stronger and long-lasting analgesia than EA with low intensity (Want et al 1997). Pulse width of 2-5 msec induces longer-term analgesia. Electrodes with small sizes are more likely to produce analgesia in relatively deep tissue. For reliving pain in the deep muscle, EA with needles should be used (Ishimaru et al 1995).

Conclusions
Future studies should investigate whether traditional acupoints are the "ingredient" of ideal parameters. The following areas should be investigated

1. A comparison of analgesia induced by acupoints selected according to TCM theory versus those selected according to neural anatomy;
2. A comparison of analgesia induced by traditional acupoints, but not trigger or motor points versus those acupoints that are also trigger or motor points.