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ElectricalPropertiesofAcupuncturePointsandMeridians:ASystematicReviewARTICLEinBIOELECTROMAGNETICSMAY2008ImpactFactor:1.86DOI:10.1002/bem.20403Source:PubMed
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ABioelectromagnetics 00:1^12 (2008)
Review
Electrical Properties of Acupuncture Pointsand Meridians:
ASystematic Review
Andrew C. Ahn,1,2,3* Agatha P. Colbert,4 Belinda J. Anderson,5
-rjan G. Martinsen,6,7
Richard Hammerschlag,8 Steve Cina,9 Peter M.Wayne,1 and Helene
M. Langevin10,11
1Division for Research and Education in Complementary
andIntegrativeMedical Therapies, HarvardMedical School, Boston,
Massachusetts
2Division of GeneralMedicine andPrimary Care, Beth Israel
DeaconessMedical Center,Boston, Massachusetts
3Center for Biomedical Engineering, Massachusetts Institute of
Technology,Cambridge, Massachusetts
4Helfgott Research Institute, National College of
NaturalMedicine, Portland, Oregon5Pacific College of
OrientalMedicine, NewYork, NewYork6Department of Physics,
University of Oslo, Oslo, Norway
7Department of Clinical andBiomedical Engineering,
Rikshospitalet, Oslo, Norway8Oregon College of OrientalMedicine,
Portland, Oregon
9NewEngland School ofAcupuncture,Watertown,
Massachusetts10Department of Neurology, University of Vermont,
Burlington,Vermont
11Department of Orthopaedics andRehabilitation, University of
Vermont,Burlington,Vermont
According to conventional wisdom within the acupuncture
community, acupuncture points andmeridians are special conduits for
electrical signals. This view gained popularity after
anecdotalreports and clinical studies asserted that these
anatomical structures are characterized by lowerelectrical
impedance compared to adjacent controls. To ascertain whether
evidence exists to support orrefute this claim, we conducted a
systematic review of studies directly evaluating the
electricalcharacteristics of acupuncture structures and appropriate
controls. We searched seven electronicdatabases until August 2007,
hand-searched references, and consulted technical experts. We
limitedthe review to primary data human studies published in
English. A quality scoring system wascreated and employed for this
review. A total of 16 articles representing 18 studies met
inclusioncriteria: 9 examining acupuncture points and 9 examining
meridians. Five out of 9 point studiesshowed positive association
between acupuncture points and lower electrical resistance
andimpedance, while 7 out of 9 meridian studies showed positive
association between acupuncturemeridians and lower electrical
impedance and higher capacitance. The studies were generally poorin
quality and limited by small sample size and multiple confounders.
Based on this review, theevidence does not conclusively support the
claim that acupuncture points or meridians areelectrically
distinguishable. However, the preliminary findings are suggestive
and offerfuture directions for research based on in-depth
interpretation of the data. Bioelectromagnetics00:112, 2008. 2008
Wiley-Liss, Inc.
Key words: impedance; resistance; capacitance; skin;
electrodermal
62008Wiley-Liss, Inc.BEM07-0187.R1(20403)
Grant sponsor: National Center for Complementary
AlternativeMedicine (NCCAM); Grant number: K23-AT003238.
*Correspondence to: Andrew C. Ahn, Harvard Medical
School,Division for Research and Education in Complementary
andIntegrative Medical Therapies, 401 Park Drive Suite
22A-West,Boston, MA 02215. E-mail: [email protected]
Received for review 12 October 2007; Final revision received
28November 2007
DOI 10.1002/bem.20403Published online in Wiley
InterScience(www.interscience.wiley.com).
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Author Proof
ABACKGROUND
Despite hundreds of mechanistic and clinical studiesin
acupuncture, the fundamental tenets of acupuncturethe point and
meridianare poorly understood. ClassicChinese medical theory
recognizes about 361 points, saidto be located on 14 main meridians
connecting the body.The 14 main meridians are associated with
specific organsand serve as pathways for the flow of vital energy
or qi[Birch and Felt, 1999; Kaptchuk, 2002]. Within theacupuncture
community, it is a commonly held opinionthat these acupuncture
structures are special conduitsfor electrical signals [Brewitt,
1995]. This view gainedpopularity as early as the 1950s when
anecdotal reportsand clinical studies from China, Japan, France,
Germany,and the United States asserted that acupuncture points
andmeridians are distinguishable by their lower electricalimpedance
compared to adjacent controls [Royal andRoyal, 1991; Brewitt,
1995]. As this view gained traction,devices such as acupuncture
point locators and electro-diagnostic devices became commercially
available toscientifically assist the clinicians in diagnosis
andtreatment delivery.
The fundamental premise by which these deviceswere developed,
however, has always been viewed withconsiderable skepticism from
the conventional scien-tific community. Confounding factors, such
as skinmoisture, electrode pressure, stratum corneum thick-ness,
electrode polarization, and other factors have ledmany to assert
that the reportedly distinct electricalcharacteristics are
attributable to external factors and/orartifacts and not to the
acupuncture point or meridian.To this day, no systematic evaluation
of these studieshas been conducted.
This article aims to systematically review andsummarize the
studies evaluating the electrical propertiesof acupuncture points
and meridians. This review assesseswhether sufficient evidence can
support or refute the claimthat acupuncture structures are
electrically distinct. Tomaintain focus, we limited the review to
human studies.This review does not include studies that assess
theclinical significance of these electrical measures, focus onthe
temporal behavior of electrical measurements atacupuncture
structures alone, or offer theoretical explana-tion for this
reported association without empirical data.To make this review as
objective as possible, we createdand employed a scoring system to
characterize the qualityof the studies that met review
criteria.
EVIDENCE ACQUISITION
Search Strategy
We sought studies that evaluated the electricalproperties of
acupuncture points and meridians com-
pared to appropriate controls. We searched sevenelectronic
databases, including PubMed, CochraneLibrary Database,
AltHealthWatch (EBSCO Host),Allied and Complementary Database
(AMED), Biosis,EMBASE, and Scientific Citation Index Expanded
fordates ranging from the databases inception to August2007 for all
seven databases. We also searched theConference Paper Index and
Dissertation Citationbut found no useful citations or references in
thesetwo databases. Searches were limited to the Englishlanguage
due to translation challenges.
Titles, abstracts, and keyword lists of the sevenelectronic
databases were searched using the followingMeSH terms: acupuncture,
acupoint, and meridiancrossed with the terms: impedance,
resistance, conduc-tivity, conductance, admittance, susceptance,
potential,capacitive, capacitance, electropermeable,
electrophy-siologic, electrodermal, electrodiagnostic, and
electro-diagnosis. The MeSH terms were exploded to maximizeyield
and to capture all possible relevant studies. Welimited the search
to Human or English languagestudies, if such search options were
available. Wherepossible, related articles function was used to
identifyadditional references. We referred to popular acupunc-ture
texts to identify other potential studies, hand-searched all
relevant references from papers and texts,and contacted experts in
the field to identify anyadditional references.
Study Selection
For each database citation, we read the fullabstract to
determine whether acupuncture pointsor meridians were measured
electrically. Whenthe abstract lacked sufficient detail or was
simplyabsent, the full text article was acquired for
citationscontaining titles or abstracts indicating involvementof
electrical stimulation or device. Full text articlescontaining
primary data on electrical measures atpoints and/or meridians as
well as controls weremaintained in the review and further
evaluatedfor methodological quality. Controls were definedas (1)
areas not containing an acupuncture point ormeridian or (2) areas
within the vicinity of a pointor meridian. Based on the second
definition, studiescontaining only topographic profiles of
electricalmeasures around an acupuncture point were maintainedin
the review. Non-English publications and studieswith animals were
excluded. We did not includestudies that evaluated the clinical
significance ofelectrical measures, reported electrical
measurementswithout appropriate controls, or speculated on
themechanistic reasons for these electrical characteristicsat
acupuncture points or meridians without empiricaldata.
2 Ahn et al.
Bioelectromagnetics
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AFull-text articles were further screened with a
predetermined set of scoring criteria and eliminated ifthey
scored less than three out of the possible tenpoints. This strategy
was employed based on theassumption that poor quality studies would
unlikelycontribute meaningfully to our understanding ofacupuncture
points and meridians.
Development and Application of theScoring Instrument
To assess study quality in a manner that minimizessubjective, a
set of scoring criteria was created forthis review. The criteria
were developed by a multi-disciplinary panel of five experts,
representing therelevant disciplines of acupuncture,
biomedicine,electrophysiology, biophysics, electrical
engineering,and survey methodology. Each panelist first produceda
list of items he/she considered important forevaluating electrical
characteristics at acupuncturesites. The items were combined into
one large listand resent to all panelists for reevaluation. Items
withlow face validity were eliminated by consensus, withthe
understanding that the instrument should becomprehensive yet
flexible enough to account forstudy diversity. The items were
presented in a yes/no/partial format to minimize subjectivity.
Based on panelists feedback, a preliminaryscoring instrument was
created and subsequentlytested on selected articles by three
academic clini-cianstwo of whom were not on the panel of
experts.Problems in clarity and/or applicability of eachitem were
identified, and wording was modified toaddress these concerns. The
panelists categorized theitems into ten domains: subjects and
settings, siteselection, controls, electrode, confounding
variables,instruments, electrical input, measurements, blinding,and
result/statistical analysis. Each domain has a valueof one point,
yielding a total of ten points for the scoringsystem. The final
instrument was resent to panelistsfor final approval. (The final
scoring instrument can beviewed at http://osher.
hms.harvard.edu/pu_general_pub.asp.)
Two physicians (AA and AC) with backgrounds inacupuncture and
electrophysiology independentlyreviewed and scored the qualifying
studies. Thesereviewers were not blinded to the study title or
authorsnames. Each item within the scoring criterion wasdiscussed
until a final agreement was reached. For thoseitems where an
agreement could not be reached, a thirdparty evaluator was involved
to achieve consensus.Relevant data were extracted from the studies
andaggregated in tabular form.
EVIDENCE SYNTHESIS
Selection Results
From 1663 citations, we identified 320 withpotential relevance
to this review (see Fig. 1). Afterobtaining and reading the full
texts, we identified50 articles that actively measured electrical
parametersat the skin. Of these articles, 10 were excluded due
tolack of a control [Nakatani, 1956, 1986; Nakatani andYamashita,
1977; Motoyama et al., 1984; Motoyama,1986; Ionescutirgoviste et
al., 1987; Cho and Chun,1994; Comunetti et al., 1995; Cheng et al.,
2000; Fanget al., 2004]; 16 were excluded due to poor quality
asdefined by a quality score of less than three out ofpossible ten
points [Bergsmann and Woolley-Hart,1973; Noordergraaf and Silage,
1973; Brown et al.,1974; Ghaznavi, 1974; Roppel and Mitchell,
1975;Becker, 1976; Shenberger, 1977; Eory, 1984; Zhu et al.,1984;
Croley, 1986; Nansel and Jansen, 1988; Zhu et al.,1988; Chen, 1996;
Eickhorn and Schimmel, 1999; Luet al., 1999; Halek, 2000]; and 6
were excluded for usingelectrical parameters to initially define
acupuncturepoints or meridians [Wulfson and Warren, 1976;Prokhorov
et al., 2000a,b, 2006; Lee et al., 2003; Zhanget al., 2004].
Sixteen articles representing 18 studieswere maintained in the
review and evaluated in detail.Nine studies evaluated the
acupuncture point [Reich-manis et al., 1975, 1976; Hyvarinen and
Karlsson, 1977;McCarroll and Rowley, 1979; Poon et al., 1980;
Falket al., 2000; Pearson et al., 2007], while the other
nineevaluated the acupuncture meridian [Reichmanis et al.,1977a,b,
1979; Hu et al., 1992; Zhang et al., 1999a;Martinsen et al., 2001;
Johng et al., 2002; Lee et al.,2003; Ahn et al., 2005].
Acupuncture Points: Data Summary
Most studies evaluating the acupuncture pointswere of poor
quality and published in journals withlow citation index (see Table
1). All studies testedthe hypothesis that acupuncture points are
areas oflower resistance or impedance. Overall, the samplesizes
were small (mean N 13), and study participantswere mostly healthy.
DC or low frequency currentswere commonly used and thus electrical
resistanceor conductance was the parameter most
frequentlyevaluated. In four cases, the choice of controls
wasinadequately justified and could have easily influencedthe
outcome [Reichmanis et al., 1975, 1976; Falk et al.,2000; Pearson
et al., 2007]. All studies employed amonopolar electrode
arrangement with a smaller activeelectrode over the point(s) of
interest and a largerreference electrode frequently held in the
hand by thestudy participant. In addition, the studies tended to
limit
Properties of Acupuncture Points andMeridians 3
Bioelectromagnetics
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Author Proof
Atheir evaluation to the upper extremities. Only threestudies
evaluated acupoints not located on the armsand evaluated points on
the ear and forehead aswell [Hyvarinen and Karlsson, 1977; Falk et
al., 2000;Pearson et al., 2007].While five out of nine studies
showed a positiveassociation between acupuncture points and
decreasedelectrical impedance/resistance, the higher qualitystudies
showed little to no association. Pearson et al.sstudy [2007], the
highest rated study, used two devicesone with a DC current and the
other with a 100 Hz ACcurrentto determine the resistance/impedance
at an(1) acupuncture point, (2) non-acupuncture point locatedon a
meridian, and (3) a non-acupuncture point not on ameridian. These
three points were identified on severalbody sites that included the
palm (PC8), forehead(GB14), and fourth finger (TW1). Only acupoint
GB14showed any significant differencewith the
non-meridian/non-acupuncture control and, furthermore, this
differ-ence was seen only with the 100 Hz device. The
meridianpoints, on the other hand, demonstrated significant (ornear
significant) decrease in electrical impedancecompared to the
non-meridian control in all three bodysites with the exception of
the DC resistance at acupointPC8.
In evaluating acupuncture points, two generalstrategies were
taken. One strategy was to firstidentify the acupuncture
point/control and then meas-
ure the electrical resistance or conductance [McCarrolland
Rowley, 1979; Pearson et al., 2007]. The otherstrategy was to scan
or survey the skin to identifylow resistance areas and subsequently
see if theareas coincided with acupuncture points [Hyvarinenand
Karlsson, 1977]. The studies that resorted tothe latter method
tended to have more positiveresults than those taking the former
approach. Thisimplies that the inappropriate or inaccurate
identifica-tion of points might have contributed to the
discrepantfindings.
The techniques applied in these studies wereremarkably diverse,
particularly with respect to probetype. Reichmanis in 1975 wheeled
a circular steelelectrode 0.2 cm in diameter along the meridian
andcontrol line [Reichmanis et al., 1975], whereas Reich-manis in
1976 used a 6 6 array of 2 mm diameter steelelectrodes to produce a
topographic representation ofelectrical conductance [Reichmanis et
al., 1976]. Incontrast, Hyvarinen used two concentric
electrodesa0.5 mm diameter inner electrode and a 2.5 mm
diameterouter ring electrode that served as a control [Hyvarinenand
Karlsson, 1977], while Poon et al. [1980] used anadhesive,
conducting tape with high voltage intensities.This diversity in
techniques accounts for why the resultsare neither readily
comparable between studies norgeneralizable to all low-impedance
points and controlson the human body.
Fig. 1. Study flow.
4 Ahn et al.
Bioelectromagnetics
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