Volume 1, Issue 2 , Pages 91-96, December 2008
Changes in Electrical Skin Resistance at Gallbladder 34 (GB34)
Article Outline
- Abstract
- 1.. Introduction
- 2.. Materials and Methods
- 3.. Results
- 4.. Discussion
- 5.. Conclusion
- Acknowledgments
- References
- Copyright
Abstract
Objective
Electrodermal screening is widely used in the acupuncture community for point location, diagnosis and therapy. However the underlying theory that electrical skin resistance (ESR) of an area corresponding to an acupuncture point (AP) is lower than ESR of the surrounding areas is yet to be proven. The objective of this study was to evaluate and quantify the phenomenon of ESR changes at the Gallbladder 34 (GB34) Acupuncture Point (AP).
Materials and Methods
In this single-blinded study GB34 was measured bilaterally in 43 healthy volunteers. Electrical skin resistance measurements (ESRMs) were performed with a specially designed array consisting of 64 (8 × 8) electrodes on an area of 6 × 6 cm. Then the electrodes corresponding to the AP were identified and compared with those of the surrounding electrodes with Wilcoxon rank sum test. Values for p of less than 0.05 were considered statistically significant.
Results
Eighty-one ESRMs were evaluated. ESR was significantly different from the surrounding skin area in 27 (33.3%) cases with 15 (18.5%) points showing a lower and 12 (14.1%) points showing a higher ESR.
Conclusion
This shows that ESR changes at APs exist in one third of the measured points, a very low rate for a postulation that forms the basis of various diagnosis and therapy systems.
Key words: acupuncture , electrodermal testing , skin impedance
1. Introduction
It is a common theory in Traditional Chinese Medicine (TCM) that electrical skin resistance (ESR) of areas corresponding to meridians and acupuncture points is lower than ESR of the surrounding areas [1, 2, 3, 4, 5]. Numerous devices for acupuncture point (AP) location and entire diagnosis and treatment systems based upon this theory have been developed and are widely used in the clinical practice of alternative and complementary medicine today.
The first reports describing this phenomenon were published in the 1950s [6, 7]. Until now, the evidence for a physiological basis of the claimed theory has been lacking, even though many investigators have tried to develop different methods of electrical skin resistance measurements (ESRMs) [8, 9, 10, 11]. A review article published earlier this year found as many as 320 articles referring to this topic. Most of them are anecdotal reports and of poor quality. Only eighteen studies met the criteria for further evaluation, where nine studies evaluated ESR at AP, and nine studies evaluated meridians. Their results are controversial [12]. These findings give cause for concern about the validity of ESRM devices and raise the need for significant research, taking into account that devices are widely used in clinical TCM practice today.
The reason for the lack of scientific evidence can be found in deficiencies in study design and statistical analysis as well as in the complexity of the measuring procedure itself. There are various factors [13, 14] known to influence ESRM results (Figure 1) and in order to obtain valid measurements, these factors have to be eliminated as far as possible.
Figure 1.
Factors that influence ESRM results. These factors should be taken into account and need to be eliminated if ESRMs are to produce valid results.
Most devices for ESRM consist of a single electrode (of varying size) placed at the tip of a pen shaped device, which is pressed manually against the skin by the examiner [8, 11, 15]. It is known that variation of pressure, angle or duration of the measurement can significantly influence the results. Furthermore, repeatedly pressing the electrode tip into the skin or scratching over the skin surface may result in hyperemia and superficial abrasions of the stratum corneum layer that increase electrical conductivity.
Therefore the first step in objectively evaluating ESR changes at APs was to develop a device for ESRM that eliminates the most important interference factors and creates equal conditions for all measured skin points.
We used a newly designed ESRM array consisting of 8 × 8 electrodes on a square plastic foil of 6 × 6 cm. Its design overcomes the most common problems in ESRMS [14]. The 64 electrodes are measured almost simultaneously within 1 second and the environmental conditions can thus be assumed to be the same for all electrodes. Furthermore, the measured resistance values are only compared to the values of the other electrodes of one single measurement (AP vs. non-AP). This method of evaluation allows only yes/no statements about ESR changes at the measured point, but it is necessary to ensure a valid evaluation in which disturbing factors eliminate themselves. Another source of irritation is eliminated by the AP localization performed by an investigator who was not involved in the measuring process and blinded regarding the measurement results. Using this procedure we found a method of objectively evaluating and quantifying differences in ESR at APs.
Therefore the aim of this study was to evaluate differences in electrical skin resistance between the AP Gallbladder 34 (GB34)–the so called Meeting Point for tendons and muscles and known as an important AP in TCM.
2. Materials and Methods
2.1. Participants
Volunteers, aged between 18 and 40 years (mean age 26.3 years) were recruited on the campus of the Ludwig-Maximilians University. All volunteers signed an informed consent form before participation. The study was approved by the Ethics committee of the University of Munich.
Inclusion criteria were general good health, age 18–40 years and the ability to understand and sign an informed consent form. Exclusion criteria were pregnancy, current use of medication and acute or chronic medical problems of any kind. Skin irritations, acupuncture or transcutaneous electrical nerve stimulation (TENS) treatment on the measured acupuncture points in the 4 weeks before participation also led to exclusion.
2.2. Setting and procedures
The study was carried out in a standardized setting in the Multidisciplinary Pain Unit of the Ludwig-Maximilians University, Munich, Germany. Subjects were advised to rest for 15 minutes before measurements were taken. If necessary, shaving of the skin in male subjects was performed on the evening before measurement.
2.3. Instruments
The electrical skin resistance measurement array was specially designed and fabricated for the purpose of this study [16]. It consists of a field of 64 electrodes on a flexible plastic foil surface of 6 × 6 cm with a distance of 8 mm between the centers of each electrode.
The electrodes were scanned rapidly one after the other against a reference electrode which was held firmly in one of the participants' hands during ESRMs. The whole array was scanned almost simultaneously within 1 second, with an average scanning time of 15 milliseconds/electrode. Electrical skin resistance was indicated in arbitrary units for each of the measuring electrodes. Figure 2 shows the array for ESRMs and a screenshot of the ESRM software.
Figure 2.
Electrical skin resistance measurements (ESRMs): (A) ESRM array consisting of 64 electrodes on a 6 × 6 cm square plastic foil. (B) Screenshot of ESRM analyzing software, ESR values are indicated in colors and arbitrary units.
The current used was direct current (DC) with a max flow of 20 μA and a mean voltage of 4.8 V. These technical details correspond approximately to other commercially available standard devices for skin resistance measurement. The array has been approved by the German Technical Inspection Authority for Security.
2.4. Electrical skin resistance measurements
ESRMs were performed in a single-blinded setting. An investigator (not experienced in acupuncture) placed the array on the skin area cranioventral of the fibular head. The head of the fibula was dorsally palpated in order to avoid manipulation in the measured skin area. An evenly distributed fixation pressure of the array was achieved with a pad of medical gel that was placed upon the array and fixed with a standard blood pressure cuff with a pressure of 10 mmHg. The ESR measuring process was started and terminated after 30 seconds. The exact localization of the array was ink marked on the skin area. The localization of GB34 was performed after termination of the measuring process by an independent investigator with good experience in acupuncture. The AP was marked on the skin. An array template was used to match array electrodes and marked APs. A square of 3 × 3 electrodes surrounding the detected electrode was assumed to correspond to the AP. The ESR values of these nine electrodes were compared with the other 55 electrodes of the array.
2.5. Acupuncture point
GB34 was selected for electrical skin resistance measurement. This AP is located in the depression ventral and distal of the head of the fibula [17]. GB34 was selected because of its importance as a Meeting Point for tendons and muscles. It is commonly used in clinical practice. Symptoms associated with the external course of the Gallbladder meridian (Foot Shao Yang) include temporal headache, pain along the channel in the hip region, leg or foot, lateral chest pain, hypochondriac discomfort and alternating chills and fever [17]. Hence, GB34 was chosen for clinical relevance as well as its location on the lower leg that allows fixation of the array with a steady pressure.
2.6. Statistical analysis
Statistical analysis was performed with Microsoft Excel and SPSS. Changes in ESR were evaluated with Wilcoxon rank sum test. An area of 3 × 3 electrodes around the located point was defined as the acupuncture point. These nine electrodes were compared to the rest of the electrodes on the array. Electrodes corresponding to the nearby AP ST36 were excluded from evaluation. ESRMs were further excluded if the AP was located too far on the edge of the measured area and the reduced number of electrodes could therefore reduce the validity of the evaluation. Values for p of less than 0.05 were considered as statistically significant. A false discovery rate was used as an adjustment for multiple testing.
3. Results
The acupuncture point GB34 was measured on both sides in 43 healthy volunteers. Five measurements were excluded because of insufficient AP localization (AP on the edge of the array). Eighty-one ESRMs were evaluated regarding electrical skin resistance changes at acupuncture points. ESR values in general varied broadly between no impedance (=high conductance) and no conductance (=high impedance) at all. This variation was not only found inter-individually, but also among the 60 measuring electrodes. Figure 3, Figure 4 show the distribution of ESR values at exemplary measurements of GB34 with significantly lower ESR.
Figure 3.
Graphical presentation of ESR at GB34: an example of a measurement with significantly lower electrical skin resistance (p = 0.0048). The areas of the AP G834 and the nearby ST36 are indicated by circles. ESR is indicated in color: low ESR values are blue and high ESR values are red.
Figure 4.
Graphical presentation of ESR at GB34: an example of a measurement with significantly lower electrical skin resistance (p = 0.0048). The areas of the AP GB34 and the nearby ST36 are indicated by circles. Differences in ESR are shown by level curves.
In contrast to the popular postulation that ESR at acupuncture points is lower than ESR of the surrounding areas, we found measurements of the GB34 AP that had no significantly different ESR at all. We also found some measurements that had a significantly higher electrical skin resistance at the acupuncture point GB34.
We evaluated a total of 81 acupuncture point measurements of GB34. For each single measurement it was tested whether there was a statistically significantly changed ESR at the AP-location (p < 0.05). According to this result the measurements were classified as “no ESR changes” and “significant ESR changes” which were further divided into “lower ESR” and “higher ESR”. Next the percentage of each class was calculated. Twenty-seven (33.3%) of the initial 81 ESRMs showed an ESR at the AP that was significantly different from the surrounding skin area with 15 (18.5%) points showing a lower and 12 (14.8%) a higher skin resistance than the surroundings (Figure 5).
Figure 5.
Results of electrical skin resistance measurements (ESRMs): 81 ESRMs were evaluated. 15 showed a significantly lower and 12 a significantly higher ESR than the surrounding areas.
4. Discussion
Many investigators have so far tried to evaluate ESR changes at APs. Nevertheless the phenomenon has never before been quantified under the exclusion of the most relevant influencing factors. To our knowledge our results describe for the first time that ESR at APs can not only be lower compared with the surrounding skin areas but also higher.
We found that there generally is a strong variation within the measured ESRM values-not only between subjects, but also between each single array electrodes of one measurement. This finding is in accordance with the results of other researchers [9, 10, 11, 18, 19].
The main objective of this study was to evaluate differences in electrical skin resistance between an acupuncture point and the surrounding area. Valid results were achieved by minimizing the most common disturbances in skin impedance testing and by creating stable testing conditions and reducing possible interferences to a minimum. Still there are limitations: the distance between the electrodes on the array is rather big and thus the array images can only give a general idea of the ESR of the measured area. Employing an array with more electrodes on the same area would help to evaluate small local ESR changes. We only investigated ESR changes at one single AP and only in healthy volunteers. An investigation of a selection of different APs and a comparison of the ESR status in different illnesses could help to further enlighten the phenomenon of ESR potentials at APs.
Nevertheless our findings show that there are changes in ESR at approximately one third of our measurements at GB34. These findings suggest that there is a significant physiological basis for the claimed theory of ESR differences at APs and therefore strengthen the theory that acupuncture points may have a specific physiological or anatomical basis. However, the results outlined here raise considerable doubt about the validity of widely used diagnosis and therapy systems, as we did not find differences in skin resistance in about 70% of measurements in healthy subjects.
5. Conclusion
In this study we found that electrical skin resistance (ESR) at acupuncture points can not only be lower but also higher compared to the surrounding area. We found significant changes in ESR at the acupuncture point GB34 in a total 33.3% of measurements. In our opinion this suggests that a basic principle of the claimed theory does actually exist. Based on our results it seems to be worthwhile to examine the electrical skin resistance at acupuncture points in patients with certain symptoms traditionally connected to certain APs.
Acknowledgments
We thank Prof. Dr. Florian Kolb and Dr. Dieter F. Kutz, Department of Physiological Genomics, Institute of Physiology, University of Munich, Germany for technical assistance.
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GrantThis study was supported by the German Medical Acupuncture Association (DÄGfA).
PII: S2005-2901(09)60028-5
doi:10.1016/S2005-2901(09)60028-5
© 2008 Korean Pharmacopuncture Institute. Published by Elsevier Inc. All rights reserved.
Volume 1, Issue 2 , Pages 91-96, December 2008
