Depressor effect on blood pressure and flow elicited by electroacupuncture in normal subjects

Abstract

To clarify the effect of electroacupuncture (Ea) on the activity of the cardiovascular system in normal individuals, hemodynamic parameters including arterial blood pressure (BP), finger blood flow (FBF) and heart rate (HR) as well as paravertebral temperature (PVT) were non-invasively recorded under Ea stimulation. Surface stimulation electrode was placed on the Hoku point (Li-4). Square wave pulses (0.05 ms) were applied from a stimulator with a stimulation frequency of 2 Hz (3 min). The stimulation intensity was five times of sensory threshold. BP and FBF were decreased (68.5±6.0%, P<0.01 and 96.8±1.1%, P<0.01 of control, respectively, n=7) while HR and PVT were increased significantly (115.0±5.1 of control, P<0.05 and 0.054±0.004 degree C, P<0.01, respectively, n=7) during Ea treatment. The results suggested an inhibition in sympathetic outflow, which induced vasodilatation of systemic arteriole and decrease in BP and FBF were elicited by Ea stimulation.

Introduction

Acupuncture has been used in China to treat various diseases for more than 2000 years. It is an effective means to control various types of pain, and has been recognized by National Institutes of Health (NIH) of the United States as potentially useful for a variety of chronic pain conditions or for patients in whom conventional treatments are ineffective. Because there are almost no adverse effects associated with acupuncture in the general population, it is a reasonable choice for some patients with chronic pain.

Acupuncture is theorized to have local, segmental and central pain-mediating effects involving the somatic–autonomic reflex Sato and Schmidt, 1973, Sato et al., 1997, Andersson et al., 1973, Kimura et al., 1995. Researchers exploring the physiological mechanism underlying acupuncture suggested that acupuncture might modulate nerve activity influencing visceral function via somato–sympathetic reflexes Koizumi et al., 1980, Sato et al., 1993, Tsuchiya et al., 1991.

Many animal studies concentrated upon the effect of acupuncture on cardiovascular system, but the results were divergent. For example, Ohsawa et al. (1995) reported that depressor effect on blood pressure (BP) was elicited by acupuncture in anesthetized rats. On the other hand, Sato et al. (1993) investigated the effect of acupuncture in anesthetized rats and suggested pressor effect on BP was induced. Such contradiction in these results may arise from the fact that the parameters employed in each experiment were different. In these two experiments, the manual twist of needle was used with a frequency of about 2 Hz or so, but intensity was difficult to determine. In the present study, electroacupuncture (Ea), which stimulates the acupoints via electric current, was employed. Since the stimulating parameters, which include frequency, intensity and duration of Ea, can be easily quantified, the experiment results can be compared and further analyzed, both qualitatively and quantitatively.

The neural mechanism underlying Ea on BP in animals was investigated by various groups Liao et al., 2002, Lin and Fu, 2000, Lin et al., 1998, Ting et al., 2002. In their study, sympathetic nerve activity was altered by Ea to induce a therapeutic effect. On the other hand, Averill et al. (2000) investigated the parameters of autonomic nervous system in response to acupuncture in spinal cord injury patients. In their report, all the parameters remained stable after treatment, indicating that acupuncture has no effect on the autonomic nervous system in human subjects. However, in their study, only the data before and after treatment was recorded and compared, and the therapeutic effect during the stimulation session has not been elucidated.

To clarify whether depressor effect in human subjects can be elicited during Ea or not, and study the possible mechanism for its therapeutic effect, hemodynamic parameters—including BP, heart rate (HR) and finger blood flow (FBF)—were continuously recorded non-invasively under Ea stimulation, since increase in skin temperature of the trunk can be used as an indicator of paralysis in sympathetic tone during spinal anesthesia (Chamberlain and Chamberlain, 1986). Paravertebral temperature (PVT) was also recorded in the present study to serve as a non-invasive index of sympathetic activity.