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Impedance analysis of acupuncture points and pathways
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2011 J. Phys.: Conf. Ser. 329 012034
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Impedance analysis of acupuncture points and pathways
Michal Teplan1, Marek Kukučka2, Alena Ondrejkovičová3
1Institute of Measurement Science, Slovak Academy of Sciences, Dúbravská cesta 9,
84104 Bratislava, Slovakia
2Department of radio electronics, Faculty of Electrical Engineering and Information
TechnologySlovak University of Technology, Ilkovičova 3, 81219 Bratislava,
Slovakia
3Liming, Mýtna 5, 81107 Bratislava, Slovakia
E-mail: michal.teplan@savba.sk
Abstract. Investigation of impedance characteristics of acupuncture points from acoustic to
radio frequency range is addressed. Discernment and localization of acupuncture points in
initial single subject study was unsuccessfully attempted by impedance map technique. Vector
impedance analyses determined possible resonant zones in MHz region.
1. Introduction
In acupuncture and related fields it is assumed that there are special pathways in the body called
meridians which are connected to main body systems, such as cardio-vascular, respiratory, digestive,
etc. In this concept the pathways are exposed to the surface of human body in so called acupuncture
points localized on skin surface. Although use of acupuncture is relatively well established in Western
medicine as a complementary diagnostic and therapeutic tool, its physical and medical
characterization is still largely unknown.
According to Zhang [1] within human body there is an invisible dissipative structure of EM field
which in mainly composed of an interference patterns of standing waves in the resonance cavity of
human body under the condition of permanent support of energy in an open system. This invisible
structure may correspond to some extent to the mysterious acupuncture system and is closely related
to different modalities of energetic medicine.
With noninvasive skin measurements typical values of impedance are around the range 100 k Ω
and capacitive elements around fractions of μF. Some of the previous studies showed that electrical
characteristics like impedance and capacitance at acupuncture points may show distinct values in
comparison to values obtained from surrounding non-acupuncture points. Acupuncture sites were
found to possess lower impedance and higher capacitance. However, some studies found no
distinction from surrounding tissues. According to the review by Ahn et al. [2] preliminary evidence
supports these findings however it is still impossible to determine whether acupuncture structures
possess distinct electrical characteristics until better quality studies are performed.
9th International Fr¨
ohlich’s Symposium IOP Publishing
Journal of Physics: Conference Series 329 (2011) 012034 doi:10.1088/1742-6596/329/1/012034
Published under licence by IOP Publishing Ltd
1
Segments of human body may be modelled by electrical circuits. Complex electronic
circuitry consists of conductors, capacitors and inductances. Resistive component reflects
mainly proportion of liquids comprised in the tissue together with liquid properties of current
conductance depending on concentration of different ions. Capacitive component reveals
integrity of cell membranes. Phase angle is in bioelectrical impedance analysis used as an indicator
for disease, hydration and nutritional status. Better overall health status should correspond with higher
phase angle. Fukumoto [3] suggested a new approach for acupuncture point determination by
constructing a ratio of imaginary and real part of complex impedance.
Within wide frequency range it may be beneficial to focus on the question whether
resonant behavior may occur in systems of interest. Focus is directed to frequency windows
with values of impedance modulus and/or phase angle different from values at surrounding
frequencies. Basic resonance phenomena is often demonstrated on simple serial RLC circuits
where inductance component is vitally needed in order to compensate capacitive part. Resonance
should occur when phase angle vanishes. In biological systems inductance appears to play no
significant role. However, also circuits with only resistive and capacitive components may possess
resonant behaviour. Reichmanis et al. showed in [4] such an example: Infinite transmission line
consisting of elements built from serial resistance with another resistance in parallel with capacitance
(figure 7, model B) and terminated by its characteristic impedance.
Aim of the initial part of our study was to prepare methodology for several types of impedance
measurements in order to study resonant behaviour of acupuncture system. Our investigation was
focused on critical assessment of electrical properties of single acupuncture points and properties of
meridians measured between two acupuncture points of the same meridian. In the first step we
attempted to localize acupuncture points from impedance modulus maps. Then followed investigation
of electrical properties of acupuncture system by vector impedance analysis in acoustic and
radiofrequency range.
2. Methods
All data were measured from single healthy subject (corresponding author, male, 36 years old).
Acupuncture points were chosen according to their accessibility – left arm, diversity of acupuncture
pathways and significance regarded to therapeutic use in acupuncture medical system. The following
points were used: Large intestine LI-4 and LI-11, heart HT-3 and HT-7, lungs LU-5and LU-7,
pericardum PC-6 and PC-3, and triple warmer TW-3, TW-8, and TW-9. Experienced clinical
acupuncturist localized all the points and afterwards they were labeled by marker and photographed.
Control points were taken several centimeters apart from acupuncture points, namely in LI-4 and HT-3
area.
For the first part, impedance maps were measured with a grid of 64 brass telescopic needle
electrodes (figure 1). Their telescopic tips maintained balanced pressure across measured area with
side lenght 17.5 mm. Distance between neighbouring tips was 2.5 mm. Monopolar arrangement was
applied with clamp reference electrode on the opposite arm (surface 6 cm2). Frequency of probing
current was 1 kHz. Unique recording system was controlled from Matlab environment via USB port.
Prototype comprised microprocessor (Atmel ATmega16) with serial port and eight A/D converters
with 10-bit resolution. The device measured voltage difference between active and passive electrodes
based on spike detectors. Consequently, off-line transformation from voltage into impedance was
performed based on interpolation of voltage data corresponding to known resistances.
For the second and the third experimental setup adhesive disposable Ag/AgCl ECG electrodes
(Ambu Blue Sensor P) with measuring area 154 mm2 and PUR sponge with highly conductive wet gel
were used (figure 2). Electrode polarization effect was minimized by Ag/AgCl coating [5]. These
active electrodes were placed on acupuncture point of the left arm.
9th International Fr¨
ohlich’s Symposium IOP Publishing
Journal of Physics: Conference Series 329 (2011) 012034 doi:10.1088/1742-6596/329/1/012034
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Figure 1: Brass needle electrodes with telescopic tips.
Figure 2: Adhesive disposable Ag/AgCl ECG electrodes.
3. Results and discussion
3.1. Impedance maps
We have found only one study depicting impedance/conductance maps of acupuncture point. Becker
et al. [6] found higher conductance in the centre of acupuncture point surrounded by roughly circular
equiconductance pattern (figure 3).
9th International Fr¨
ohlich’s Symposium IOP Publishing
Journal of Physics: Conference Series 329 (2011) 012034 doi:10.1088/1742-6596/329/1/012034
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Figure 3: Sample of conductance map on acupuncture point LI-4 from study of Becker et al. [6].
Impedance maps from 11 acupuncture points did not consistently support any map structure
with similar characteristics and pattern. In most of the cases distinctive minima surrounded by
circular patterns were not found. In many maps there was no isolated depression in impedance
modulus (figure 4). To show one of the most resembling map, there is local extreme in a form of
minima at the upper left picture of figure 4 with certain indication of surrounding pattern. Control
maps showed similar structures: irregular extremities spread across the measured skin surface,
often with considerable variations within mm distance: Readings from neighbouring electrode
sites differed up to the one order of magnitude. We found that repeatability of the same map was
valid only under very restricted conditions – with immediate repetition and without removing the
electrode grid from the skin. As a next step we plan to localize acupuncture points more precisely
into the centre of the map and test different pressure levels of telescopic needles.
9th International Fr¨
ohlich’s Symposium IOP Publishing
Journal of Physics: Conference Series 329 (2011) 012034 doi:10.1088/1742-6596/329/1/012034
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Figure 4: Sample of impedance maps of acupuncture points LI-4 and TW-3. Lower left: control
point. Lower right: 3D plot.
3.2. Impedance in acoustic frequency range
For impedance measurement in acoustic frequency range Tesla BM 595 RLCG meter was used.
Copper reference electrode in a shape of cylinder was placed under the right thigh. Supported
frequency range was 100 – 20 000 Hz.
No distinction of acupuncture points from control points was obtained. On the contrary to
expectations (e.g. [7]), control points had not higher impedance modulus (figure 5) in comparison to
acupuncture points. While in impedance modulus all the curves were slightly decreasing, phase angle
curves (figure 6) did not exhibit monotonous behaviour for most of the cases.
9th International Fr¨
ohlich’s Symposium IOP Publishing
Journal of Physics: Conference Series 329 (2011) 012034 doi:10.1088/1742-6596/329/1/012034
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Figure 5: Impedance modulus dependance on frequency in acoustic frequency range. Black color
holds for control points. Note the only meridian at the bottom of the legend.
Figure 6: Phase angle in acoustic frequency range. Black color holds for control points. Note the
only meridian at the bottom of the legend.
From obtained data it is possible to fit impedance |Z(f)| according to simple circuit models depicted
in figure 7. Johng et al. [7] succesfully fitted their data according to model from scheme A of figure 7.
Resulted estimates of one resistive and two capacitive components represented electrical elements
based on skin layers: epidermis on the surface with dry tissue of stratum corneum (parallel R with C)
together with serial R representing dermis. Their estimates agreed with distinction of acupuncture
points as to be sites with smaller resistance and larger capacitance.
102103104105
1
10
100
frequency [Hz]
impedance [k ]
control1
control1
control2
control3
LI4
LI4
TW3
HT7
LU7
PC3
LI11
LI11
TW8
TW9
LI4-LI11
102103104105
10
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20
5
frequency [Hz]
phase angle [°]
control1
control1
control2
control3
LI4
LI4
TW3
HT7
LU7
PC3
LI11
LI11
TW8
TW9
LI4-LI11
9th International Fr¨
ohlich’s Symposium IOP Publishing
Journal of Physics: Conference Series 329 (2011) 012034 doi:10.1088/1742-6596/329/1/012034
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Figure 7: Electrical equivalent circuits from [2]: Model A was proposed by Johng et al. [7], model
B by Rosendal [8].
Preliminary fitting of our data based on models from figure 7 was not appropriate, as the regression
error was too large. In the next step we plan to build more complex model with more circuit elements.
Also, relatively large surface of active electrode (1.5 cm2) could cause that the largest current density
flowed at electrodes’ periphery and thus could avoid active points.
3.3. Impedance in radio frequency range
Depth of penetration into the skin is determined by AC frequency of measurement. Direct and low-
frequency currents penetrates mainly only into the epidermis dominated by the dead stratum corneum.
Moreover, at low frequencies (typically below several hundred kilohertz), the conductivity of the
tissue is dominated by conduction in the electrolytes in the extracellular space. In order to investigate
properties of deeper tissue structures and intracellular space as well, experimental setup with radio
frequency impedance analyzer was prepared.
At radio frequencies, the tissue exhibits the beta dispersion, centered in the range 0.1 to 10 MHz,
due to the charging of cell membranes through the intracellular and extracellular media. Above the
beta dispersion, the cell membranes have negligible impedance, and the current passes through both
the extracellular and intracellular media. On the other hand ionic flow is diminishing as relatively
heavy ions are not able to adjust to rapid change of current direction.
Tomco TE1000 radio frequency impedance analyzer was applied with ECG active electrodes
placed at acupuncture points and copper cylinder reference electrode hold in the right palm. The
measurements were realized in the electromagnetically shielded room. Frequency from 0.5 – 150 MHz
range was scanned with 1.5 MHz step.
The variations in impedance values across the whole frequency range were at the level of 1-2
orders of the magnitude (figure 8). Observed lower impedance zones around 50 and 70 MHz could
point to the zone with improved information transmission in the studied tissues. Moreover, both zones
bear another distinct property - zero phase angle (figure 9). These are the characteristics of resonant
behaviour. Resonant properties may be demonstrated by either negative or positive impedance peaks.
Different acupuncture subsystems differ from each other in resonant frequency around 50 MHz up to
10 MHz. A few another null angle zones appeared in the figure 8 while not binding to impedance
extremities.
9th International Fr¨
ohlich’s Symposium IOP Publishing
Journal of Physics: Conference Series 329 (2011) 012034 doi:10.1088/1742-6596/329/1/012034
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Figure 8: Impedance modulus for acupuncture (colored) and control (black) points. Note the only
meridian at the bottom of the legend.
Figure 9: Phase angle for acupuncture (colored) and control (black) points. Note the only meridian
at the bottom of the legend.
Acupuncture in comparison to control points seems to exhibit higher variations in impedance. Also,
the main impedance minima at 50 MHz is for acupuncture points shifted to higher frequencies. The
same holds for null angle characterizing resonant frequency around 50 MHz. The only acupuncture
pathway measured between two acupuncture points exhibits distinct behaviour: sharper extremities
and higher number of zero phase crossing.
Overall, the preliminary results require more data accumulation and further analysis. Experiences
with measurement techniques confirm the fact that results may be heavily dependent on some of the
50 100 150
102
103
104
frequency [MHz]
impedance [k ]
control1
control2
control3
LI4
TW3
HT7
LU7
PC3
LI11
TW8
TW9
LI4-LI11
50 100 150
-80
-60
-40
-20
0
20
40
frequency [MHz]
phase angle [°]
control1
control2
control3
LI4
TW3
HT7
LU7
PC3
LI11
TW8
TW9
LI4-LI11
9th International Fr¨
ohlich’s Symposium IOP Publishing
Journal of Physics: Conference Series 329 (2011) 012034 doi:10.1088/1742-6596/329/1/012034
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following measurement characteristics: skin surface, presence of sweat glands, electrode geometry and
polarizability, contact pressure, time fluctuation of electrical properties, etc.
Impedance analysis of acupuncture system deserves further attention along the need for improved
understanding of physical mechanisms behind basic functioning of this relatively broadly used
medical modality.
4. Acknowledgement
This work was supported by Slovak Grant Agency for Science (grant VEGA No 2/0210/10 and
1/0285/09).
References
[1] Zhang CL 2002 Skin resistance vs. body conductivity Frontier Perspectives 15-25
[2] Ahn AC, Colbert AP, Anderson BJ, Martinsen OG, Hammerschlag R, Cina S, Wayne PM and
Langevin HM 2008 Electrical properties of acupuncture points and meridians: a systematic
review Bioelectromagnetics 29 4 245-256
[3] Fukumoto T and Akiyama H 2010 Acupuncture point position evaluating apparatus US Patent
7,818,054
[4] Reichmanis M, Marino AA and Becker RO 1977 Laplace plane analysis of transient impedance
between acupuncture points Li-4 and Li-12 IEEE Trans. Biomedical Engineering 4 402-405
[5] Ahn A C and Martinsen O. G. 2007 Electrical characterization of acupuncture points: technical
issues and challenges The journal of alternative and complementary medicine 13 8 817-824
[6] Becker RO, Reichmanis M, Marino AA and Spadaro JA 1976 Electrophysiological correlates of
acupuncture points and meridians Psychoenergetic Systems 1 106 195-212
[7] Johng HM, Cho JH, Shin HS, Sah KS, Koo, TH, Choi SY, Koo HS and Park MS 2002
Frequency dependence of impedances at the acupuncture point Quze (PC3) Eng. Medicine
and Biology Magazine IEEE 21 2 33-36
[8] Rosendal T 1944 Further Studies on the Conducting Properties of Human Skin to Direct and
Alterting Current Acta Physiologica Scandinavica 8 2-3 183-202
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ohlich’s Symposium IOP Publishing
Journal of Physics: Conference Series 329 (2011) 012034 doi:10.1088/1742-6596/329/1/012034
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