Ma Shu-ya (马舒雅), Pan Li-jia (潘丽佳), Liu Jun (刘君), She Yan-fen (佘延芬)

Hebei University of Chinese Medicine, Shijiazhuang 050091, China

Abstract

Keywords: Acupuncture Points; Meridian Acupoint Detection; Biophysical Properties; Meridian Imbalance; Meridian Imbalance Test; Meridian Acupoint Diagnosis; Review

Acupuncture points are special parts where the qi from the meridians and Zang-fu organs is infused to the body surface. They are the reaction points of diseases and also acupuncture sites, and their state is closely related to changes in qi and blood within Zang-fu organs[1]. As early as the era of theHuang Di Nei Jing(Yellow Emperor’s Classic of Internal Medicine), it was recognized that acupuncture points could reflect the physiological and pathological state of the human body and could be used for clinical diagnosis.

With the development of detection methods and technologies such as biophysics, scholars across the world, in their search for objective evidence of meridian body trajectories and meridian sensory transmission,have applied biophysical methods to the meridian circulation lines, finding that meridians have different properties from non-meridians, including electrical properties, thermal properties, optical properties,acoustic conduction properties, magnetic properties,and isotope migration phenomena along the meridians.Currently, the electrical and thermal properties are most studied, which can be used clinically in diagnosis,point selection and positioning, and reflecting the acupuncture efficacy[2].

In the pathological state, qi, blood, and Zang-fu organs are in a state of imbalance between yin and yang.The biophysical properties of the meridian points, as reaction points on the body surface, change accordingly and also become imbalanced, and this imbalance is manifested not only between meridian and non-meridian points[3-4], but also between the left and right namesake points[5]. There is no uniform standard for calculating and determining this imbalance. We searched and collected the literatures on the imbalance of biophysical properties of meridian points between January 1, 2005 and March 1, 2020 in China National Knowledge Infrastructure (CNKI), Wanfang Academic Journal Full-text Database (Wanfang), Chongqing VIP Database (CQVIP) and PubMed database, and then analyzed and summarized the applied methods for calculating the imbalance degree in the biophysical properties of meridian points, in order to provide a reference for studying the biophysical properties of meridian points.

1 Imbalance Degree Calculation Methods

1.1 Direct comparison between measurements of the left and right namesake points

Direct comparison between measurements of the left and right namesake points is more commonly used,and we speculate that it is related to the fact that this method can directly reflect the changes in the biophysical properties of meridian points. In the healthy state, imbalances can occur between the left and right namesake points in different physiological cycles. By observing the changes in the resistance values of the Yuan-Primary points, Xi-Cleft points, crossing points and nonspecific points of the three yin meridians of foot in normal female university students at different menstrual cycles, a study found an imbalance in the resistance values beyween the left and right sides of Taichong (LR 3), Taibai (SP 3), Taixi (KI 3), Diji (SP 8),Sanyinjiao (SP 6), Zhongdu (LR 6) and Shuiquan (KI 5)[6].This method can also be applied in the disease state. A study selected 20 points and directly compared the temperatures of the left and right namesaked points,and the results showed that 8 points including Kongzui(LU 6), Taiyuan (LU 9), Wenliu (LI 7), Pianli (LI 6), Hegu(LI 4), Yinlingquan (SP 9), Gongsun (SP 4) and Taibai(SP 3) in patients with allergic rhinitis showed a leftright imbalance in temperature[7]. In another study, the resistance values of 6 points including Xinshu (BL 15),Neiguan (PC 6), Jueyinshu (BL 14), Danzhong (CV 17),Zusanli (ST 36) and Geshu (BL 17) in patients with coronary artery disease were measured and compared between the left and right sides. Statistical tests revealed that the resistance values of Xinshu (BL 15),Neiguan (PC 6) and Jueyinshu (BL 14) showed an imbalance[8]. This calculation has also been used in studies comparing changes in the measurements of meridian points before and after acupuncture, and the results showed that the imbalance between the left and right namesake points was reduced and even disappeared after treatment[9-10].

In the physiological state, the electrical and thermal properties of the left and right namesake points are symmetrical[11-12]but not exactly equal. The temperature difference between the left and right namesake meridian points can be up to 0.5 ℃[13], and the temperature difference between the left and right sides varies in different points. Some studies have suggested that meridian points are lateralized, and that left-right laterality in the human body is objective[14].Just as theSu Wen(Essential Questions) states that ‘the right ear and eye are not as clear as the left...and the left hand and foot are not as strong as the right’. Direct comparison of the measured biophysical properties of the left and right namesake points does not take into account the influence that the meridian points themselves are lateralized and the measured values are not exactly equal, and thus it is easy to attribute the imbalance in the physiological state to the imbalance produced by the pathological state.

1.2 Difference method

The strength of the difference method is that it reduces the errors caused by the environment(temperature, humidity) and the measuring instruments[15], mainly including the following two methods.

1.2.1 Comparing the difference in the measured values between the left and right namesake points

In the healthy state, the body surface temperature around the meridian points is more susceptible to the room temperature than the temperature difference between the two sides of the namesake points, which has been confirmed by a relevant study[16]. This study was conducted on the first day of menstruation with continuous dynamic detection of body surface temperature around each test point for 60 min, and room temperature and humidity were recorded once every 10 min. After analysis, it was found that the temperature difference between the namesake points on the two sides was not easily affected by room temperature and humidity, while the body surface temperature was easily affected by room temperature,which provided certain basis for adopting the difference method (temperature difference between the namesake points on the two sides) in the disease state.Therefore, this method is more commonly applied to calculating the imbalance degree in the biophysical properties in the disease state. A study measured the temperature of 13 pairs of namesake points on the left and right sides of face in patients with Bell palsy, and found that the temperature difference was more than 1.5 ℃, and the more severe the paralysis, the greater the temperature difference[17]. A study took infrared thermograms of the back of patients with unilateral lung disease, and calculated the temperature difference between the left and right Feishu (BL 13). The results showed that the maximum temperature difference could be between 0.5 ℃ and 0.8 ℃, and the average temperature difference was 0.3-0.5 ℃, thus indicating that the elevated skin temperature of Feishu (BL 13) in patients with unilateral lung disease showed asymmetric characteristics between the left and right sides[18]. With treatment and recovery, this asymmetry will gradually decrease or even disappear. A study found that the temperature difference between the left and right sides of acupuncture points commonly used for treating facial palsy was between 0.25 ℃ and 0.50 ℃.The overall temperature of the face showed low temperature on the affected side and high temperature on the healthy side. After recovery, the temperature difference between the left and right sides of acupuncture points on the face was mostly close to that in healthy individuals[19].

1.2.2 Comparing the difference in the measured values between the left and right points and the reference point

The reference point is mostly selected from the midline of the body, such as Danzhong (CV 17) and Yintang (GV 29). This method is mostly used for calculating the imbalance degree in the disease state. A study used ‘relative temperature’ [Infrared temperature of the meridian point - Temperature of the control point(Danzhong, CV 17) on the chest and abdomen] as the ending indicator, and found the temperature imbalance between the left and right namesake points in patients with stomachache by comparing the mean relative temperatures of the bilateral points[20-21]. A study found an imbalance between the left and right namesake points in patients with asthma[22-23]and coronary heart disease[24]by calculating the ‘temperature change value’[Temperature of acupuncture points - Temperature of Yintang (GV 29)], and comparing the average temperature change values of the left and right namesake points.

The temperature value of the control point Yintang(GV 29) is more stable so that the temperature value of each point was subtracted from the temperature value of the control point during statistical analysis[25], which can remove the differences caused by the individual temperatures. It has been demonstrated that the ambient temperature has an effect on the temperature and resistance measurements of the meridian points[16,26]so that some studies have used the method of the initial temperature minusing the background temperature (ambient temperature) in order to calculate the calibration temperature during the experiments, and this data was reorganized into measurements as a final indicator for analysis[27]. Thus,the effect of ambient temperature on the measured temperature can be partially eliminated by subtracting the reference value from the measured values on the left and right sides respectively. Similarly, it can be speculated that the effects of the detection apparatus[28-29], ambient humidity[30], skin contamination[31], and experiment time[32]on the measured values can also be reduced to a certain extent by this method, thus improving the accuracy of the measured values. However, just as the method of directly comparing the measured values on the two sides, this method does not take into account the fact that the meridian points themselves are lateralized and the measured values are not exactly equal in the calculation process.

1.3 Ratio method

1.3.1 Comparing the ratio between the measured values

When applying this method, some studies compared the ratio between the measurements of the namesake points on the left and right sides, and some studies compared the ratio between the measurements of the left and right points and the reference point.

This method is mostly used for the calculation of imbalance degree in the disease state and after treatment. A study measured the resistance values of the left and right meridian points in patients with primary dysmenorrhea to calculate the ‘imbalance rate’with the formula ‘Left resistance value ÷ Right resistance value’, and the results showed that the imbalance rate of resistance was significantly higher in the group of patients with primary dysmenorrhea compared with the normal group[33]. Another study also applied this formula to calculate the imbalance degree by specifying a resistance ratio of more than (1.0±0.2)between the left and right sides[34]. The researchers measured the body surface infrared temperature around bilateral points and both axillae to calculate the‘relative temperature’ of each point with the formula‘Point temperature ÷ Ipsilateral axillary temperature’.And then performed statistical analysis using infrared temperature and relative temperature as indicators,and found that the relative temperature of Riyue (GB 24)in patients with chronic cholecystitis was significantly different and showed a higher figure on the right side than on the left side[35]. A study used ‘infrared relative temperature’ [Point infrared temperature ÷ Danzhong(CV 17) infrared temperature] as a calculation method,and showed that the relative temperature changes on the right side of Qimen (LR 14), Riyue (GB 24) and Bulang (KI 22) were more sensitive than on the left side during chronic hepatitis B virus infection[36]. With treatment, this imbalance decreased. One study specified Imbalance degree = Left resistance value ÷Right resistance value, and found that resistance imbalance of bilateral Shenshu (BL 23), Ciliao (BL 32)and Gongsun (SP 4) was more significant in patients with primary dysmenorrhea before treatment compared with the normal group, and decreased significantly and returned to normal levels after treatment[37].

The outcome indicators of this method are relative numbers, and thus the effect of the unit of measurement can be eliminated when performing statistical analysis. However, there is a variation in the implementation of this method in terms of which site's measurements should be selected as the denominator,and how to determine the denominator should be considered in future studies.

1.3.2 Comparing the difference (or the absolute value of the difference) between the left and right namesake points divided by the measured value on one side

Some studies fixed the denominator in their calculations[38], and some studies took the larger[39-40]or the average[41-42]measurement of both sides as the denominator.

Changes in the physiological cycle of healthy women may cause changes in the imbalance degree of meridian points. A study used the ‘skin resistance imbalance degree’ [(Skin resistance at the left probe point - Skin resistance at the right probe point) ÷ The higher skin resistance] as the calculation method, and specified that a resistance imbalance degree of 0 represents a perfect balance between the left and right, while 1 represented the greatest imbalance. The results found that there was a difference in the resistance imbalance degree between Sanyinjiao (SP 6) and Taichong (LR 3)before menstruation compared with the first day of menstruation, and it was inferred that Sanyinjiao (SP 6)and Taichong (LR 3) might reflect the normal menstrual flow of female college students[39]. This formula is also used for the calculation of imbalance rate in the disease state. One study found that the resistance imbalance degree of Sanyinjiao (SP 6) was significantly higher than that of Xuanzhong (GB 39) in patients with dysmenorrhea due to cold and damp stagnation on the first day of menstruation[40]. The denominator in the imbalance degree equation, however, differs in disease states. One study used the ‘resistance imbalance degree of the namesake points’ [(Left resistance - Right resistance) ÷ Left resistance] as a method of calculation and found a statistical difference in the resistance imbalance degree of Diji (SP 8) between the left and right sides of the dysmenorrhea group on the first day of menstruation and the third day after the end of menstruation, thus tentatively speculating that Diji (SP 8)might be a response point for primary dysmenorrhea[38].This method is also used to compare the differences before and after treatment. Studies measured the temperature of the namesake points on the healthy side and the affected side in patients with peripheral facial palsy and specified[41-42]that Asymmetry coefficient = (Healthy side measurement - Affected side measurement) ÷ Average of both sides. It found that the asymmetry coefficient of points on both sides of patients with facial palsy gradually decreased with the recovery and the increasing number of acupuncture treatment.

This method is a combination of the left-right difference method and the left-right ratio method,which partly eliminates the influence of environmental factors and measurement units. And all studies in the application of this method have chosen the absolute value to avoid the influence of mixed positive and negative values on the calculation results. However,there is no unified standard on how to determine the size of imbalance degree, which should be considered when using this method.

2 Analysis and Prospect

There is low uniformity in the calculation of imbalance degree in studies of biophysical properties of meridian points, which has limited the application and promotion of biophysical properties of meridian points.We propose the following three recommendations for reference and correction.

2.1 Introducing mathematical methods to reduce variability in calculation methods

The methods for calculating the imbalance degree in the biophysical properties of meridian points are diverse without uniformity. Different conclusions may be reached with different calculation methods for the same measurement target, thus causing problems for the application and promotion of research results.There are no studies comparing the same measurement data by different imbalance degree calculation methods,and therefore, it is impossible to determine which calculation method can truly reflect the changes in the biophysical properties of the meridian acupoints while minimizing the influencing factors during the experiment. Some researchers have suggested that this problem can be solved by mathematical thinking,determining for each meridian point its own membership function and setting up a dynamic correction rule in the future calculation[43]. This rule will bring the measured values of the biophysical properties of meridian points into the function, and if the obtained results cannot be returned to the normal reference range by the correction rule, it indicates an imbalance in the corresponding meridian point, thus providing a solution to the determination of the imbalance degree of the meridian points.

In addition, researchers can systematically organize,share and improve the results already obtained through multidisciplinary cooperation, and develop a unified method that can better control the complex factors and make the research method more easily to obtain consensus, so as to promote the clinical application and promotion of previous research results.

2.2 Multidisciplinary and multi-industry cooperation to reduce the variability of detection instruments

In terms of the thermal properties of meridian points,the detection instruments are basically infrared thermographic cameras[44]. With the increasing understanding of the electrical properties of meridian points and the emergence of new research techniques and methods, the research on the electrical detection instruments has achieved a lot in the stability of the instruments, the measurement area expands as well as the measurement time, and realized visualization and automation schemes[45], but the uniformity of instrument application is still relatively low. These also suggest that in future research, multi-disciplinary and multi-industry cooperation is needed to develop resistance detection instruments that can meet different research needs and have more accurate measurement values, in order to improve the promotion of accurate resistance detection instruments in the future research process and facilitate research results to better guide scientific research and clinical practice.

2.3 Establishing a health data model with a given range of reference values

In the majority of studies on the biophysical properties of meridian points, the imbalance degree of meridian points in healthy subjects is regarded as a control value for the imbalance of the patient's meridian points, but previous findings suggested a correlation between the biophysical properties of meridian points and age[46], gender[47], and individual constitutions[48]. The same healthy subjects, applying different study methods, have different ranges of measured values[49]. Therefore, we recommend that in the future, healthy subjects should be recruited through cooperation, and the normal reference range of biophysical properties of commonly used meridian points should be obtained by considering age, gender and constitution, thus building up a corresponding data model of healthy individual. Therefore, when conducting disease studies, it can be compared with the corresponding data model of healthy individuals to discover which points are subject to imbalance and to determine the size of imbalance degree. This will not only facilitate the application of biophysical properties of meridian points in scientific research and clinical treatment, but also reduce research costs and improve the economic and social benefits of research.

3 Discussion

The results of this study indicate that the uniformity of current methods for calculating the imbalance degree in the biophysical properties of meridian points is relatively low, and each method has certain strengths and flaws. Therefore, in order to make the biophysical properties of meridian points more valuable in disease diagnosis and treatment, it is of significance to improve the reproducibility and reliability of the methods for calculating the imbalance degree of meridian points,and this is a key point to be emphasized in future studies. The accuracy of the measurement results of the imbalance degree of meridian points directly affects the accuracy of clinical diagnosis and treatment, which requires us to improve the scientific nature of the imbalance degree calculation methods. The improvement of scientificity requires multidisciplinary cooperation in calculation methods, detection instruments, and health data models to achieve scientific conclusions with wider applicability and experimental results with higher generalization, so that the scientific and clinical value of the biophysical properties of meridian points can be fully utilized.

Conflict of Interest

The authors declare that there is no potential conflict of interest in this article.

Acknowledgments

This work was supported by General Projects of National Natural Science Foundation of China (国家自然科学基金面上项目, No. 81473773, No. 81573884); Youth Project of National Natural Science Foundation of China (国家自然科学基金青年项目, No. 81603542).

Received: 29 October 2020/Accepted: 7 December 2020