Increased pain threshold following electroacupuncture: analgesia is induced mainly in meridian acupuncture points

Pain thresholds were determined before and after electroacupuncture of the dorsal aspect acupuncture points (AP) of the hand and non acupuncture points (NAP) located 15 mm from the traditional acupuncture points to assess changes in pain threshold thus provoked. Methods. in eight volunteers the pain threshold of specific points was determined before and after acupuncture in the Hegu point (L.I. 4), at the back of the hand. A pressure dolorimeter was used to evaluate pain threshold at the Yangxi (L.I. 5) and Quchi (L.I. 11) points and at sites 15 mm from them. The effects on pain threshold were also measured at Yingxiang (L.I. 20) on both sides. Results. Before electrostimulation there were no significant differences among the pain thresholds in both AP and NAP. After electrostimulation of the Yangxi point, pain threshold raised from 5.20 kg/sq.cm to 9.20 kg/sq.cm (p<0.01); acupuncture at Quchi caused the threshold to increase from 5.36 kg/sq.cm to 9.20 kg/sq.cm (p<0.01) and Yingxiang stimulation changed threshold from 2.63 kg/sq.cm to 3.83 kg/sq.cm (p<0.051) at the point on the same side and from 2.26 kg/sq.cm to 3.90 kg/sq.cm (p<0.05) in the opposite side. Before electroacupuncture the pain thresholds at all the tested sites were not statistically different (p>0.1). After electrostimulation the pain threshold increased 77% at L.I. 5 but went up just 9% and 6% 15 mm from L.I. 5 (p<0.01); threshold increased by 70% at L.I. 11 but only by 6% and 7% (p<0.01) 15 mm from L.I. 11. Conclusions. The pain threshold increased significantly in all tested sites after electroacupuncture but the analgesic effect was predominant in those points lying along the acupuncture meridians.