electrical properties of paths on the human body described by Chinese Medicine (i.e., meridians) [1]. The specific points of interest (acupuncture points) are described as being one millimeter in diameter. The electrical characteristics of the acupuncture meridians have been extensively studied since the 1950s to establish their existence by scientific methods [2]-[3]. To date, the bioelectric properties of acupuncture points are not clearly understood. For example, many discrepancies and inconsistencies appear in the literature concerning skin impedance on the acupuncture points [4]. The change in impedance at acupuncture points is reportedly anywhere from 1/2 to 1/20 of the impedance of the surrounding skin. These low impedance points are thought to be the result of sensory and motor nerves emerging from deep tissue to superficial layers of the skin (see fig.1) [5]. It is by now generally accepted that both meridian and acupuncture points have lower electrical resistance or impedance than nearby surrounding points. Small electrical potentials can be recorded on the skin at the terminal points of acupuntcure meridians and the results are replicable under controlled experimental conditions [6]-[7]. As a results of these potentials, the current produced ranges from a few to several hundred nanoamperes, which can be recorded by an external measuring device. The electromotive force producing these endogenous currents results from electrical potentials at the acupuncture points on the skin and is a function of the internal resistance of the point.

Figure 1. An acupuncture point seen as the result of sensory and motor nerves emerging from deep tissue to superficial layers of the skin

Figure 2 shows a typical behaviour of the electric resistance on an acupuncture point. The resistance is a function of the cutaneous region, skin humidity and pressure of the measurement electrode. The arrow points out the strong decrease of resistance in the point of acupuncture. The ordinate reflects the resistance in ohms, the abscissa the run of the electrode on the cutaneous surface. Most of research on electroacupuncture has been based on skin resistance and feeding in external currents [8]-[9]. All of these instruments use an external voltage source to measure the skin conductance and the measurement can be easily influenced and disrupted by many factors, making it difficult to achieve reliable and replicable results. Moreover, feeding the point with an external current in order to measure the internal resistance constitutes an interference from a physiological point of view and the exact effect on the human organism of applying external invasive currents of even a few μA to acupuncture points are not know. Thus, any method permitting readings to be taken in nanoamperes at acupuncture points without feeding in addictional external current would be diagnostically useful. Figure 3 shows the schematic representation of current measurement without use of an external generator[10].

Figure 2. Electrical resistance of the acupuncture point

A pointed electrode placed on an acupuncture point acquires the current and a ground reference electrode with a large surface area rests on the subject’s forearm. This measurement is able to detect the current emitted by the acupuncture point when it is short circuited on the instrument, but some experiences has pointed out the scarce reliability and inadequacy of this kind of measurement technique due to unavoidable error components.

 

Figure 3. Schematic representation of current measurement without use of an external voltage source.

The main purpose of this study was to improve such measurement technique using a new non-ivasive biopotential electrode designed to solve most of the above measurement problems. Our experience has confirmed the presence of electrical potentials of several millivolts (between few mV and 500 mV) that can be detected on the surface of the skin at acupuncture points. The body’s conductivity determines the amount of current produced by electromotive force resulting from differences in these tiny potentials and if current can be measured in a replicable manner, free of external interference, the result could be potentially useful for medical diagnostics. Considering the internal resistance of the points, the generated short circuit dc currents are expected to fall in the range of 10nA to 5000 nA.