Biomedical engineering meets acupuncture - development of a miniaturized 48-channel skin impedance measurement system for needle and laser acupuncture
© Litscher and Wang; licensee BioMed Central Ltd. 2010
Received: 13 September 2010
Accepted: 23 November 2010
Published: 23 November 2010
Due to controversially discussed results in scientific literature concerning changes of electrical skin impedance before and during acupuncture a new measurement system has been developed.
The prototype measures and analyzes the electrical skin impedance computer-based and simultaneously in 48 channels within a 2.5×3.5 cm matrix. Preliminary measurements in one person were performed using metal needle and violet laser (405 nm) acupuncture at the acupoint Kongzui (LU6). The new system is an improvement on devices previously developed by other researchers for this purpose.
Skin impedance in the immediate surroundings of the acupoint was lowered reproducibly following needle stimulation and also violet laser stimulation.
A new instrumentation for skin impedance measurements is presented. The following hypotheses suggested by our results will have to be tested in further studies: Needle acupuncture causes significant, specific local changes of electrical skin impedance parameters. Optical stimulation (violet laser) at an acupoint causes direct electrical biosignal changes.
The autonomic nervous system plays a key role in basic acupuncture research . There are several studies evaluating the electrical properties of acupuncture points and meridians . For the first time we are able to investigate possible acupuncture-specific changes in the activity of the autonomic nervous system using a newly developed prototype which measures and analyzes the electric skin impedance computer-based and simultaneously in 48 spots within a 2.5×3.5 cm matrix.
A review of scientific literature on the topic yields 320 publications dealing with electrical skin impedance measurements. Considering only those using methods of evidence-based medicine, this number is reduced to 18 relevant studies . These can be divided into acupuncture studies (n = 9) and so-called 'meridian studies' (n = 9). Five of the acupuncture studies found a lowered skin impedance in the area of an acupuncture point, four studies yielded contrary results.
Because of the controversially discussed results of existing studies, a new multi-channel skin impedance measurement system was developed at the TCM (Traditional Chinese Medicine) Research Center at the Medical University of Graz. This system was designed to supply objective data for the first time, taking into consideration the previously existing technical limitations. The present manuscript introduces the new measurement system and contains first problem-oriented, forward-looking results on needle and laser acupuncture.
Relevant previous work by other authors has to be pointed out: The publication by Becker et al.  laid the original foundation for our miniaturized 48-channel-system. More recently, the research group of Wiegele et al.  designed and the research group of Kramer et al.  tested a similar device. The device designed by Wiegele et al., however, did not have a spatial resolution as precise as the one presented in this paper, but is an important forerunner of this system.
Does the skin resistance show differences between acupoints and the surrounding area already in resting state?
Does needle acupuncture and needle stimulation result in any significant local changes of electrical skin resistance?
Does violet laser acupuncture alter skin resistance?
Results and Discussion
As mentioned in the background section, there are some already existing important systems. Already in 1976, Becker et al.  have performed very interesting measurements with a system based on the same idea (multi-channel recordings). However, the data are not directly comparable because they used different materials, different inter-electrode distances and also a different recording procedure. They first investigated the skin with a meridian scanning probe (1-channel system) and then with the 36-channel system. One of the main disadvantages of this previously developed system was that investigations can only be performed in the resting period, but not during acupuncture stimulation. With our system, it is possible for the first time to continuously and simultaneously monitor a region of interest (around the acupoint) even during the insertion of a metal needle or the activation/deactivation of a laser for acupuncture.
The previously existing limitations of electrodermal impedance measurements were the measurement area (point selectors with a tip only, representing a hand-held 1-channel system) and related problems (pressure, angle) and also too few registration sites (in most cases only punctual measurements, no multi-channel systems)[7, 8]. In contrast to our electrode configuration (electrode diameter 0.9 mm), the electrodes of the system of Colbert et al.  have a diameter of 4 mm and are fixed separately at the body surface with an elastic adhesive or cloth wrist band. "Confounding factors, such as skin moisture, electrode pressure, stratum corneum thickness, electrode polarization and other factors, have led many to assert that the reportedly distinct electrical characteristics are attributable to external factors and/or artifacts and not to the acupuncture point or meridian" . The newly developed system allows for the first time simultaneous and continuous, acupuncture-relevant multi-channel measurements using appropriate analysis methods. As we have only performed measurements in one subject, further measurements in a great number of healthy volunteers are absolutely necessary.
The present paper is principally a demonstration of a new instrumentation. In addition, the preliminary results suggest hypotheses listed below (i - iii) which will be tested by further studies:
(i) Skin resistance within a distance of 2.5×3 cm from an acupoint shows distinct differences already in resting state. These variations and their connections with different acupoints have to be clarified in extensive studies;
(ii) Needle insertion and manual needle stimulation cause significant, specific and local changes of electrical skin resistance parameters;
(iii) It is noteworthy that also acupuncture stimulation using a violet ('blue') laser (405 nm; 110 mW, 500 μm) can alter skin resistance significantly, specifically and locally.
The latter result (iii) could be the first proof in acupuncture research that optical stimulation (violet laser) at an acupoint causes a direct electrical biosignal change at a distance of < 3 mm. This fact alone might yield answers to important core questions in acupuncture (meridian and/or placebo research), be it for further basic or clinical acupuncture research.
The author wants to thank Mr. Gebhard Raich for the innovative development work; Ms. Tao Huang, MD, (China Academy of Chinese Medical Sciences, Beijing/China and TCM Research Center Graz) for performing acupuncture and Ms. Ingrid Gaischek, MSc, for the help in manuscript and figure preparation. The work was carried out within the project 'Bioengineering and clinical assessment of high-tech acupuncture - A Sino-Austrian research pilot study' (Austrian Ministries of Health and of Science and Research and the Eurasia-Pacific Uninet) and was supported by the Science Department of the City of Graz.
The Austrian Society for Controlled Acupuncture (OGKA) has awarded the scientific work described in this paper with the OGKA Scientific Award 2010 for TCM Basic Research (award ceremony on Sep 25, 2010).
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