In Vivo Visualization of the Pericardium Meridian with Fluorescent Dyes

Abstract

The anatomical basis of acupuncture meridians continues to be enigmatic. Although much attention has been placed on potential correlations with inter/intramuscular fascia or lower electrical impedance, animal studies performed in the past 40 years have shown that tracer dyes-specifically Tc-99m pertechnetate-injected at strategic skin points generate linear migrations closely aligning with acupuncture meridians. To evaluate whether this phenomenon is also observable in humans, we injected two fluorescent dyes-fluorescein sodium and indocyanine green (ICG)-into the dermal layer both at acupuncture points (PC5, PC6, and PC7) and a nonacupoint control. Fifteen healthy volunteers were enrolled in this study. Of the 19 trials of fluorescein injected at PC6, 15 (79%) were associated with slow diffusion of the dye proximally along a path matching closely with the pericardium meridian. Furthermore, the dye emerged and coalesced proximally at exactly acupoint PC3. Injections of ICG at the acupoints PC5, PC6, or PC7 showed a similar trajectory close to the injection site but diverged when migrating proximally, failing converge on acupoint PC3. Injections of either dye at an adjacent PC6-control did not generate any notable linear pathway. Both ultrasound imaging and vein-locating device did not reveal any corresponding vessels (arterial or venous) at the visualized tracer pathway but did demonstrate correlations with intermuscular fascia.

Figure 1

Development of fluorescent lines. Migration of fluorescein from PC6 with respect to time after injection (hour: minute) as shown in right lower corners. In series (a), migration was rapid, while in series (b), migration was slower. In (a), a clear line was observed as early as 10 minutes, peaked at 60 minutes, then diminished thereafter. Of note, in (b), fluorescence at PC3 preceded appearance of the linear path between PC3 and PC4.

Figure 2

Variations in fluorescein migratory paths. Examples are provided to reveal variations in dye migrations. (a, b) Fluorescent signals were strong and quickly formed linear trajectories. Additional collateral lines were observed accompanying the main meridian-associated line. (c, d) Intermittent, broken lines formed along PC meridian within 30 minutes after injection. (e) Dye was also visualized in blood vessels. (f) Linear paths formed slowly 1 hour after injection and was weakly visible; nevertheless, PC3 appeared approximately 40 minutes before the linear path could be visualized. Similarly, in other cases, only PC3 fluoresced, while no linear path was observed (not included here). (g, h) No linear trajectories or point fluorescence at PC3 was seen.

Figure 3

Injection of fluorescein in nonacupoint (PC6 control). Fluorescein injected at a nonmeridian point did not produce a linear pathway, even 90 minutes after injection.

Figure 4

ICG migratory path after injection at PC5. After injection of ICG at PC5 (a), fluorescent line develops and is imaged here at 2.5, 5, and 18 hours (c–e). Five hours after injection, fluorescent lines are observed in both the forearm and upper arm (d). The fluorescent line was traced with a pen (b), passing by PC4 and PC3. Eighteen hours after injection, the fluorescence on the upper arm is still visible (e). The photo and video were taken with a mobile phone with long-pass filter above 780 nm.

Figure 5

ICG fluorescent line 24 hours after injection at PC6 (a). The fluorescent line was traced and compared with acupoints PC5, PC4, and PC3, marked before injection (b) (black dots). These points and traced line closely approximated each other.

Figure 6

ICG fluorescent line after injection at PC7 (a). One hour after injection, the fluorescent line appears as shown in (b). Sixteen hours later, it is weaker (c). After 24.5 hours, the line in (d) was traced and compared with acupoints (e). PC5, PC4, and PC3, marked as pink cross, closely approximated to the red traced line.

Figure 7

Fluorescent path covisualized with vein-imaging. (a) Fluorescence imaging only after fluorescein injection in PC6. (c) Vein Finder imaging only. (b) Overlay of both florescent line and vein-imaging revealing no clear overlap between the fluorescent pathway and visible vasculature.

Figure 8

: Transverse ultrasound imaging of fluorescent line. As shown in upper images, metal wire was overlaid on the fluorescent line and fixed in place with a rectangular ultrasound gel pad. Transverse images were obtained as the ultrasound probe followed the course of the metallic wire from PC6 toward PC3. The metal wire is seen as an echogenic white dot (white arrow in left lower picture), casting a B-scan shadow. Color Doppler signal was only seen at the end of scanning (near elbow PC3) but not directly under the metallic wire.