Pressor effect of electroacupuncture on hemorrhagic hypotension

Neiguan (PC-6) is a traditional acupoint in each forearm and overlies the trunk of the median nerve. Previous studies show that electroacupuncture (EA) at the Neiguan acupoint could improve not only myocardial ischemic dysfunction by inducing a depressor response but also recover hemorrhagic hypotension by inducing a pressor response. However, their physiological mechanisms are not yet elucidated. We investigated the pressor effect of Neiguan EA and its mechanism by focusing on left ventricular (LV) performance in a canine hemorrhagic hypotension model. We hemorrhaged 36 anesthetized and thoracotomized mongrel dogs and decreased LV end-systolic pressure (ESP) to similar to70 mmHg (35% decrease). We obtained LV pressure-volume (P-V) data with a micromanometer catheter and a conductance catheter. One-hour Neiguan EA significantly recovered the decreased ESP, end-diastolic volume, and stroke volume by 32+/-13%, 27+/-13%, and 39+/-17%, respectively (P<0.05), without changing heart rate and the slope of the end-systolic P-V relation. Neiguan EA inhibited a hemorrhage-induced increase in plasma catecholamines. However, vecuronium (neuromuscular blocking agent) administration abolished the antihypotension effect of Neiguan EA. Furthermore, Neiguan EA was much more effective than a nonacupoint thigh EA. We conclude that Neiguan EA achieved the antihypotension effect by improving LV filling of the hemorrhage-depressed LV performance despite the inhibition of the hemorrhage-increased plasma catecholamines. This pressor effect seemed to accompany an increased venous return by Neiguan EA-increased vasomotor tone and muscle pump. This study demonstrated a scientific basis for the therapeutic efficacy of acupuncture in the treatment of hemorrhagic hypotension and shock.