Electrical impedance along connective tissue planes associated with acupuncture meridians

Abstract

Background: Acupuncture points and meridians are commonly believed to possess unique electrical properties. The experimental support for this claim is limited given the technical and methodological shortcomings of prior studies. Recent studies indicate a correspondence between acupuncture meridians and connective tissue planes. We hypothesized that segments of acupuncture meridians that are associated with loose connective tissue planes (between muscles or between muscle and bone) visible by ultrasound have greater electrical conductance (less electrical impedance) than non-meridian, parallel control segments.

Methods: We used a four-electrode method to measure the electrical impedance along segments of the Pericardium and Spleen meridians and corresponding parallel control segments in 23 human subjects. Meridian segments were determined by palpation and proportional measurements. Connective tissue planes underlying those segments were imaged with an ultrasound scanner. Along each meridian segment, four gold-plated needles were inserted along a straight line and used as electrodes. A parallel series of four control needles were placed 0.8 cm medial to the meridian needles. For each set of four needles, a 3.3 kHz alternating (AC) constant amplitude current was introduced at three different amplitudes (20, 40, and 80 microAmps) to the outer two needles, while the voltage was measured between the inner two needles. Tissue impedance between the two inner needles was calculated based on Ohm's law (ratio of voltage to current intensity).

Results: At the Pericardium location, mean tissue impedance was significantly lower at meridian segments (70.4 +/- 5.7 Omega) compared with control segments (75.0 +/- 5.9 Omega) (p = 0.0003). At the Spleen location, mean impedance for meridian (67.8 +/- 6.8 Omega) and control segments (68.5 +/- 7.5 Omega) were not significantly different (p = 0.70).

Conclusion: Tissue impedance was on average lower along the Pericardium meridian, but not along the Spleen meridian, compared with their respective controls. Ultrasound imaging of meridian and control segments suggested that contact of the needle with connective tissue may explain the decrease in electrical impedance noted at the Pericardium meridian. Further studies are needed to determine whether tissue impedance is lower in (1) connective tissue in general compared with muscle and (2) meridian-associated vs. non meridian-associated connective tissue.

Figure 1

Block diagram of impedance meter. Through a rechargeable battery, a sine-wave alternating current is delivered to the outer two electrodes (a) and (d). A current sensor registers the amount of current delivered to the electrodes. The inner electrodes (b) and (c) are attached to the voltmeter which registers the electrical potential difference between them. The current and voltage readings may be recorded as time series through connections to a computer (BNC outputs).

Figure 2

Depiction of the Spleen and Pericardium meridians in relation to surface and sub-surface anatomical landmarks. 2 A, B: Cross sectional images of the right forearm as shown through ultrasound and gross anatomical cross section (obtained from the Visual Human Database). The Pericardium segment is located between the flexor carpi radialis and flexor digitorum superficialis muscles. 2 C, D: Cross sectional images of the right leg as shown through ultrasound and cadaveric cross section. The Spleen segment is located between the medial crest of the tibia and the flexor digitorum longus muscle. Blue arrows point to approximate sites where meridian and control needles were inserted.

Figure 3

Experimental setup. 3A- Holder placed on Pericardium meridian and control skin segments. Guide tubes indicate the location of needles on both segments. In this image, needles (a), (b), (c), and (d) are inserted along the control segment. Current is passed between electrodes (a) and (d) and voltage is measured between (b) and (c). 3B- Tissue impedance meter connected to laptop computer and to needle electrodes.

Figure 4

Tissue impedance measurements for individual subjects. The difference in impedance between control and meridian segments (Impedance difference) is shown for the Pericardium (A) and Spleen (B) meridian location.

Figure 5

Mean tissue impedance at Pericardium and Spleen meridian segments and at corresponding control segments. Bar graphs represent mean ± SE. * indicates p < 0.01.