Electrical impedance along connective tissue planes associated with acupuncture meridians

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Electrical impedance along connective tissue planes associated with acupuncture meridians
Received: 14 October 2004
Accepted: 9 May 2005
Published: 9 May 2005
Andrew C Ahn1 , Junru Wu2 , Gary J Badger3 , Richard Hammerschlag4 and Helene M Langevin5
BMC Complementary and Alternative Medicine 2005
BioMed Central

1Division for Research and Education in Complementary and Integrative Medical Therapies, Harvard Medical School, Boston, MA, USA
2Departments of Physics, University of Vermont, Burlington, VT, USA
3Department of Medical Biostatistics, University of Vermont, Burlington, VT, USA
4Research Department, Oregon College of Oriental Medicine, Portland OR, USA
5Department of Neurology, University of Vermont, Burlington, VT, USA

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 μAmps) 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 Ω) compared with control segments (75.0 ± 5.9 Ω) (p = 0.0003). At the Spleen location, mean impedance for meridian (67.8 ± 6.8 Ω) and control segments (68.5 ± 7.5 Ω) 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.

Background
In classic Chinese medicine theory, acupuncture meridians represent channels through which energy or "meridian qi" flows. Acupuncture points, traditionally located along these meridians, embody needling sites where the flow of qi may be affected. Acupuncture points and meridians are at the core of traditional acupuncture practice, yet anatomical and physiological explanations for these concepts remain elusive.

One widespread, yet controversial, explanation for acupuncture meridians involves electrical activity. In the acupuncture community, it is widely believed that acupuncture points and meridians are endowed with unique electrical properties. This constitutes the underlying assumption behind the use of electrical point locators commonly used in clinical practice and research. The experimental evidence in support of this practice, however, has been equivocal to date. Prior studies have reported that acupuncture points possess increased electrical conductivity compared to non-acupuncture points, and proposed that acupuncture meridians act as conduits for electrical current [1-16]. These studies, in general, were limited by small sample sizes, poor research design and procedural descriptions, and/or lack of rigorous statistical analyses. In addition, most studies used surface electrodes which may cause confounding by various factors including pressure, skin moisture, electrode contact and abrasion of the stratum corneum. For these reasons, the associations between acupuncture points or meridians and certain electrical properties have remained controversial.

Another proposed explanation for acupuncture points and meridians involves connective tissue. Recent studies have shown that acupuncture points exhibit a different biomechanical response to needling compared with non-acupuncture points [17], that this biomechanical response involves connective tissue [18,19], and that the network formed by acupuncture meridians may correspond to the body-wide network formed by connective tissue [20]. While the physiologic significance of this anatomical association is at present unclear, some researchers have proposed that the collagen content within connective tissue imparts electrical conductive properties [21,22]. These authors also suggested that connective tissue may act as the medium through which electrical communications travel within the acupuncture meridian network.

The goal of this study was to combine ultrasound evaluation and tissue impedance measurements to examine the electrical properties of connective tissue planes associated with meridians. We hypothesized that electrical impedance (which is inversely proportional to electrical conductivity) is lower along two acupuncture meridians associated with loose connective tissue planes (between muscles or between muscle and bone) visible by ultrasound, compared with non-meridians. In order to overcome the limitations associated with prior electrodermal studies, we used gold-plated acupuncture needles inserted into the tissues instead of surface electrodes and used a four-electrode technique with digital data acquisition to measure tissue electrical impedance. In this technique, four electrodes are placed in a straight line, a constant amplitude alternating (AC) current is passed between the two outer electrodes while voltage is measured between the two inner electrodes, and electrical impedance is calculated as the ratio of current to voltage amplitudes.

© 2005 Ahn et al; licensee BioMed Central Ltd.
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