Electrical impedance of acupuncture meridians: the relevance of subcutaneous collagenous bands

Abstract

Background: The scientific basis for acupuncture meridians is unknown. Past studies have suggested that acupuncture meridians are physiologically characterized by low electrical impedance and anatomically associated with connective tissue planes. We are interested in seeing whether acupuncture meridians are associated with lower electrical impedance and whether ultrasound-derived measures--specifically echogenic collagenous bands--can account for these impedance differences.

Methods/results: In 28 healthy subjects, we assessed electrical impedance of skin and underlying subcutaneous connective tissue using a four needle-electrode approach. The impedances were obtained at 10 kHz and 100 kHz frequencies and at three body sites - upper arm (Large Intestine meridian), thigh (Liver), and lower leg (Bladder). Meridian locations were determined by acupuncturists. Ultrasound images were obtained to characterize the anatomical features at each measured site. We found significantly reduced electrical impedance at the Large Intestine meridian compared to adjacent control for both frequencies. No significant decrease in impedance was found at the Liver or Bladder meridian. Greater subcutaneous echogenic densities were significantly associated with reduced impedances in both within-site (meridian vs. adjacent control) and between-site (arm vs. thigh vs. lower leg) analyses. This relationship remained significant in multivariable analyses which also accounted for gender, needle penetration depth, subcutaneous layer thickness, and other ultrasound-derived measures.

Conclusion/significance: Collagenous bands, represented by increased ultrasound echogenicity, are significantly associated with lower electrical impedance and may account for reduced impedances previously reported at acupuncture meridians. This finding may provide important insights into the nature of acupuncture meridians and the relevance of collagen in bioelectrical measurements.

Figure 1. Test Segments for the Three Meridians.

The location of the meridian are based on anatomical descriptions given in acupuncture text .

Figure 2. Challenges with Targeting Intermuscular Fascia.

(2A.) Ultrasound of upper arm. There are frequently no clear distinctive divisions between brachioradialis and biceps brachii muscles as shown in this ultrasound image. (2B.) Ultrasound of leg. The fascia between the sartorius and vastus medialis muscles have oblique depth angles.

Figure 3. Delineation of Tissue Layers and Zones.

(3A.) Ultrasound image. This longitudinal image of the thigh shows the subcutaneous and muscle layers. Echogenic bands (white bands) are seen in the subcutaneous layer. (3B.) Thresholded image. Thresholding the image delineates the echogenic bands in the dermal, SQ, and perimuscular zones.

Figure 4. Bivariable Relationships between Ultrasound-Derived Parameters and Impedance.

(4A.) Bivariable graphical plot: Impedance (100 kHz) vs. SQ Thickness. (4B.) Impedance (100 kHz) vs. Dermal Echogenic Area. (4C). Impedance (100 kHz) vs. SQ Zone Echogenic Density. (4D.) Impedance (100 kHz) vs. Perimuscular Echogenic Area.