Abstract
Background:
The electroconductive value at acupoints of Ryodoraku theory, which is based on traditional East Asian medicine, pertains to the autonomic nervous system. Case series reported that acupuncture based on Ryodoraku theory lowers blood pressure in hypertensive patients. However, no epidemiological study has been conducted on the association between the electroconductivity and blood pressure. Therefore, this study examined the association between the electroconductive value at the acupoints and blood pressure in community-dwelling Japanese.
Materials and Methods:
The study participants were 451 men and 950 women aged 30–79 years old, who were not taking antihypertensive medication and who participated in the Toon Health Study from 2011 to 2015. Nationally licensed acupuncturists measured the electroconductive values at 24 acupoints in the hands (H1–6) and feet (F1–6) of participants using a Ryodoraku device. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured with an automatic sphygmomanometer after the participants had rested for 5 min. The association of the electroconductive value at each acupoint with SBP and DBP was examined using sex-specific multiple regression analysis after adjusting for age, body mass index, drinking status, smoking status, physical activity, and menopausal status.
Results:
In men, borderline significant positive association of the electroconductive values for F4 with SBP was found, and those for F1, F4, and F5 with DBP (p for trend <0.10). In women, significant positive association of the electroconductive values for H2 and F1 with SBP was found, and those for H1, H2, and H3 with DBP (p for trend <0.05).
Conclusions:
Increased electroconductive values at the acupoints were significantly or borderline significantly associated with the elevation of blood pressure in community-dwelling Japanese. Further longitudinal and interventional studies are needed to elucidate the causal relationship and therapeutic effect on hypertension.
Introduction
Hypertension is one of the most common diseases, and it significantly increases the risk of cardiovascular disease and mortality. 1 A recent study reported that the number of adults with raised blood pressure increased from 594 million in 1975 to 1.13 billion in 2015, 2 and the World Health Organization and United States Centers for Disease Control and Prevention launched the Global Heart Initiative in 2016 to achieve the global target of reducing the prevalence of hypertension by 25% by 2025.3,4 Thus, the prevention of hypertension is a global public health issue.
Recently, there has been a growing interest in acupuncture for lowering blood pressure, and the evidence on the effect of acupuncture treatment for hypertension has been accumulating in Asian countries as well as Western countries.5,6 Although the assessment of acupoint is important in the general clinical practice of acupuncture treatment, the assessment remains subjective and empirical. 7 Therefore, the objective assessment of acupoint is needed in clinical practice and research.
Ryodoraku theory was developed by Dr. Nakatani, who was a Japanese physiologist in the 1950s. 8 According to the theory, the electric current flow through the human skin differs according to the location on the body, and this phenomenon is reflected in the sympathetic nervous system.8–11 This difference in electroconductivity is also thought to be related to the 12 meridians and the acupoints in traditional East Asian medicine.8–11
Because the sympathetic nervous system plays an important role in the regulation of blood pressure,12,13 acupuncture treatment based on Ryodoraku theory has been used to treat hypertension. Several case series have reported that this treatment may lower and control blood pressure in hypertensive patients by improving electroconductive values,14,15 and mitigate their psychosomatic symptoms. These studies suggest that acupuncture treatment using the measurement of skin electroconductance could be useful as an alternative approach for treating hypertension.
However, the evidence on electroconductive value and blood pressure was sparse, and no observational studies have been conducted. Thus, the purpose of this cross-sectional study was to examine the association between electroconductive values measured based on Ryodoraku theory and blood pressure levels in community-dwelling Japanese.
Materials and Methods
Participants
This cross-sectional study was conducted as a part of the Toon Health Study, a prospective cohort study conducted in Toon City, Ehime Prefecture, Japan.16–18 The examination of electroconductive values was conducted for the participants in 2011, 2012, 2014, and 2015. In total, 1890 participants aged 30–84 years old were enrolled in the study from July 2011 to November 2015. Participants aged ≥80 years old (n = 52) were excluded, because older adults aged ≥80 years old often have multiple diseases including hypertension, 19 arteriosclerosis, 20 and renal disease, 20 and are highly affected by medication. 21
Participants without data on their electroconductive values (n = 4) were also excluded. Participants who were taking antihypertensive medication were also excluded (n = 433), because antihypertensive drugs (such as calcium antagonists, angiotensin-converting enzyme inhibitors, diuretic furosemides, and β-blockers) reduce blood pressure through sympathetic activity,22,23 which may affect the measurement of electroconductive values.8,23 In total, 1401 participants (451 men and 950 women) were eligible for the analysis.
The study protocol was approved by the institutional review board of Ehime University Graduate School of Medicine and the ethics committee of Juntendo University, and written informed consent was obtained from each study participant.
Measurement of electroconductive values at 24 acupoints selected based on Ryodoraku theory
The electroconductive values were measured at the 24 acupoints identified as representative measuring points (RMPs) in Ryodoraku theory.8–10 The RMPs are located in both hands (H1–6) and both feet (F1–6) (Fig. 1) and correspond to the 12 meridians in traditional East Asian medicine8–10 (Table 1). The procedure for measuring the electroconductive value for each RMP is shown in Figure 2. The electroconductive value at each RMP was measured with a participant in the sitting position, using a Ryodoraku device (Neurometer; MD-21; Marutakatechno, Shizuoka, Japan), by two nationally licensed acupuncturists in Japan who received training for measuring electroconductive value by the Ryodoraku theory.
RMPs in Ryodoraku theory. The RMPs H1–3 are located on the palm side of the wrist, and H4–6 are located on the back side of the wrist, on both left and right hands. The RMPs F1–3 are located on the inside of the foot, and F4–6 are located on the outside of the foot, on both left and right feet. RMPs, representative measuring points.
Flow figure for the measurement of electroconductive value.
The 12 Meridians Corresponding to the Representative Measuring Points
RMPs, representative measuring points.
A neurometer filled the ebonite cup (1 cm of inner diameter) of the tip of the electrode (minus) with moisturized cotton wool. A current of 200 μA with a voltage of 12 V was set. All participants were measured in the morning to control for diurnal variation in electroconductive values.24–26 The basic principle for measurement of electroconductive value is based on Ohm's law. The basic block diagram of the neurometer is shown in Supplementary Figure S1. A direct current (200 mA) with constant voltage (12 V) was passed between the two electrodes across the participant's skin surface, and any change in skin conductance was detected by a neurometer.
While the participant grips the electrode (plus) with his or her right hand, the electrode (minus) presses on the RMPs in a few seconds. The neurometer, which has an automated measurement terminal that applies constant force (60 g), was used to control for inter- and intraexaminer variability. The average of the two electroconductive values for each RMP was used (i.e., one value from each side), and also calculated the average value for H1–6 combined, F1–6 combined, and all RMPs combined. These values were divided into sex-specific quartiles.
Measurement of blood pressure
The procedure for measuring blood pressure is shown in Figure 3. First, participants waited for 5 min before measurement, and trained nurses measured the systolic blood pressure (SBP) and diastolic blood pressure (DBP) using an automatic sphygmomanometer (BP-103iII; OMRON Colin, Tokyo, Japan). Then, after controlling the participant's breathing for a few seconds, SBP and DBP were measured again. The mean of the two measurements was used for analysis.
Flow figure for the measurement of blood pressure.
Assessment of confounding factors
Height and weight were measured with the participants wearing no shoes and only light clothing. Body mass index (BMI) was calculated as weight (kg) divided by the square of height (m2). Trained dietitians interviewed the participants to assess their drinking status, smoking status, menopausal status (women only), and physical activity. As a measure of physical activity, metabolic equivalent of task (MET) values was assessed using the Japan Arteriosclerosis Longitudinal Study Physical Activity Questionnaire. 27 Physicians also asked participants whether they were taking antihypertensive medication.
Statistical analysis
Because of the sex differences in the electroconductive values at each RMP, sex-specific analysis was performed for all statistical analyses. To assess the differences between the sexes, the Student's t-test and Mann–Whitney U test were used for continuous variables, and the chi-squared test was used for discrete variables. The associations between the multivariable-adjusted mean SBP and DBP with the quartile of the electroconductive values for each RMP were calculated using analysis of covariance. Multiple regression analysis was performed to investigate the association of the median of each quartile range of the electroconductive values at each RMP with SBP and DBP.
Confounding factors were age (years), BMI (kg/m2), drinking status (y/n), smoking status (y/n), physical activity (METs·h/day), and menopausal status (y/n). All statistical analyses were conducted using the SAS statistical package, version 9.4 (SAS Institute, Cary, NC). All p-values for statistical tests were two tailed, and p < 0.05 was regarded as statistically significant.
Results
Table 2 gives the characteristics of the participants stratified according to sex. The proportion of men was 32.2%, the mean age was 57.6 years for men and 56.2 years for women. The SBP was 126.0 mmHg for men and 118.5 mmHg for women. The DBP was 79.4 mmHg for men and 71.6 mmHg for women. The mean SBP and DBP was significantly higher in men than in women. The median electroconductive values for each RMP were significantly higher in men than in women.
Sex-Specific Characteristics of Participants
Student's t-test.
chi-squared test.
Mann–Whitney U test.
DBP, diastolic blood pressure; IQR, interquartile range; MET, metabolic equivalent of task; SBP, systolic blood pressure; SD, standard deviation.
Table 3 gives the association of the electroconductive values at the RMPs with SBP and DBP in men. The borderline significant positive association of the electroconductive value for F4 with SBP was found, and those for F1, F4, and F5 with DBP (p for trend <0.10).
Multivariable Adjusted Means of Systolic Blood Pressure and Diastolic Blood Pressure According to the Quartiles of Representative Measuring Points in Men
Model 1: Adjusted for age. Model 2: Adjusted for age, body mass index, drinking status, smoking status, and physical activity.
RMPs, representative measuring points.
Table 4 gives the association of the electroconductive values at the RMPs with SBP and DBP in women. The significant positive association of the electroconductive values for H2 and F1 with SBP was found, and those for H1, H2, and H3 with DBP (p for trend <0.05). the borderline significant positive association of the electroconductive values for H1, H3, F3, and F4 with SBP was also found, and those for H6, F1, and F3 with DBP (p for trend <0.10).
Multivariable Adjusted Means of Systolic Blood Pressure and Diastolic Blood Pressure According to the Quartiles of Representative Measuring Points in Women
Model 1: Adjusted for age. Model 2: Adjusted for age, body mass index, drinking status, smoking status, physical activity, and menopausal status.
RMPs, representative measuring points.
The association of the electroconductive values at the RMPs with SBP and DBP was further examined, stratified by drinking status (Supplementary Table S1) and smoking status (Supplementary Table S2) in both sexes. The significant positive association between the electroconductive values and blood pressure was more evidently found among nondrinkers and nonsmokers compared with drinkers and smokers in both sexes.
Discussion
This cross-sectional study shows that elevated electroconductive values at the RMPs are significantly or borderline significantly associated with elevated blood pressure in community-dwelling Japanese, after adjusting for potential confounding factors. To the authors' knowledge, this is the first epidemiological study to show the association between electroconductive values at acupoints and blood pressure in the general population.
Several case series have suggested that acupuncture based on Ryodoraku theory is effective for decreasing and stabilizing blood pressure and mitigating psychosomatic complaints in hypertensive patients.14,15 Another study, involving 60 hypertensive patients and 67 healthy volunteers, showed that ultrasonic stimulation of the Zusanli acupoint (ST36) lowered their blood pressure and reduced the electroconductive values in both hands; furthermore, the reduction of blood pressure was more evident in the hypertensive patients than in the healthy volunteers. 28 These previous studies support the present findings, which reveal independent associations between blood pressure and the electroconductive values of the acupoints.
This study suggested a significant positive association between the electroconductive values and blood pressures. However, the authors were unable to identify which RMPs are specifically associated with elevated blood pressure. Previous case series reported elevated electroconductive values for H3, F1, F2, F3, and F4 among patients with hypertension.9,14,15 Some RMPs were consistent with the results of this study, whereas others were not. Although the reason for this discrepancy was unclear, one potential reason was the difference in population; that is, these previous studies were conducted on hypertensive patients, whereas this study was conducted on the general population without hypertensive medication.
Therefore, further epidemiological evidence on the association between electroconductive values on acupoints and blood pressure in the clinical and general population is required to identify which RMPs are associated with elevated blood pressure. Moreover, this evidence will contribute to establishing an objective evaluation of acupoints, developing a therapeutic method based on electroconductive values, and improving the licensed acupuncturist's ability to educate patients on acupuncture treatment for hypertensive patients.
Regarding the electrical characteristics of meridian and acupoints, recent studies revealed that connective tissue is an important part of the anatomic substrate of meridians,29,30 and lower electrical impedance values were observed at the meridian-related connective tissue compared with adjacent muscle controls. 31 In addition, although there are no definitive conclusions regarding the electrical characteristics of acupoints, a systematic review has reported that acupoints were areas of lower impedance. 32 Therefore, acupoints and meridians may have a lower electrical impedance than the surrounding tissue. The findings of this epidemiological study, which showed that increased electroconductive values were significantly associated with the elevation of blood pressure at several RMPs, which are representative of the 12 meridians were consistent with those previous studies, and may support the claim that meridians and acupoints are electrically distinguishable.
In this study, the associations between electroconductive values and blood pressures were more clearly observed in women than in men. The reason for these sex differences was unclear, but there are two potential reasons. One is that the sample size was smaller for men (n = 451) than for women (n = 950), and this may not have been sufficient to detect all associations between electroconductive values and blood pressure. The other reason is that the drinking and smoking status of the participants may have confounded the association between sympathetic nervous activity and blood pressure.33,34
In this study population, the proportions of current drinkers and smokers were higher in men than in women. The associations between electroconductive values and blood pressure after stratification by drinking and smoking status were examined (Supplementary Tables S1 and S2). Despite the relatively small sample size in men, significant associations were more evident among nondrinkers and nonsmokers than among current drinkers and smokers. Therefore, current drinkers and smokers in men might mask the associations between the electroconductive values and blood pressure.
Although the mechanism underlying the association between electroconductive activity and blood pressure is unclear, sympathetic nervous activity may play an important role. Electroconductive activity on the human skin is affected by sympathetic nervous activity.35,36 Upon activation of the sympathetic nerves, cells in the skin epidermis are depolarized, and its permeability to intracellular ions (e.g., Na+ and K+) is enhanced. This may allow current to flow more easily through the skin.8,10 With respect to blood pressure, activation of the sympathetic nervous system raises the blood pressure by constricting blood vessels and increasing heart rate and myocardial contractility.12,37
Furthermore, recent studies have provided more evidence on the mechanism of skin conductance and sympathetic nerve activity. In vivo studies in rat models have demonstrated that nitric oxide (NO) content and neuronal NO expression are consistently higher in acupoints associated with low electric resistance.
38
The strength of this study was a large sample size from the general population and adjusted for potential confounding factors. However, several limitations related to the study design are acknowledged. First, since this study used a cross-sectional design, no causal relationships could be confirmed. Second, the effect of measurement bias should be considered. Blood pressure and electroconductive values exhibit circadian variation.24–26 However, in this study, all measurements were performed in the morning, so the effects of the circadian rhythm were minimized. In addition, the level of proficiency of the examiner in measuring electroconductive values is important, and differences between examiners would lead to examiner bias.43,44 All electroconductive values were measured by two examiners in this study, and these examiners were trained nationally licensed acupuncturists. In addition, they used neurometers that had an automated measurement terminal that applied constant force. Furthermore, a previous study reported that the electrical measurement of acupoints is affected by various factors (skin dryness, skin thickness, size of the sensing electrode, pressure applied to the electrode, interelectrode distance, room temperature, and humidity). 32 Although electroconductive values was measured based on the protocol of the Ryodoraku theory, data on skin dryness, skin thickness, room temperature, and humidity were not collected; hence, these factors could not be considered in this study with regard to the association between electroconductive values and blood pressure. In particular, room temperature and humidity may strongly affect participants' skin conditions, and controlling these factors is important for the measurement of skin conductance. However, this study was conducted as a part of a community health checkup, and skin conductance was measured in a community health center. Therefore, the room temperature and humidity could not be controlled rigidly, as measured in a laboratory space. In addition, because electroconductive values at the nonacupoints and nonmeridian areas as controls were not measured, the difference in electric properties between acupoints and controls could not be verified in this study. Further studies are needed to elucidate the association between electroconductive values at acupoints and blood pressure, using standardized methods and protocols for the measurement of skin electroconductance. 45 Third, although the authors showed that the increased electroconductive value on some RMPs was significantly associated with the elevated blood pressures, they could not identify which RMP was associated with blood pressure. Therefore, the possibility that the results of this study were due to chance cannot be ruled out. Further studies are needed to identify which RMPs are specifically associated with blood pressure. Fourth, although participants taking antihypertensive medication were excluded and adjusted for various possible confounding factors, there may have been residual confounders, such as drugs, that affected their autonomic nervous systems. 46 Further studies are needed to address these issues. Finally, despite the large sample size in this study, the participants were recruited on a voluntary basis, so the representativeness of this study population cannot be guaranteed and generalizing these findings to other populations should be made with caution.
Recently, the evidence on the effect of acupuncture treatment for hypertension has been accumulating.5,6 However, the assessment of acupoint remains subjective and empirical, and the objective assessment of acupoint is required to establish further evidence. 6 In Ryodoraku theory, the skin electroconductivity is thought to represent the condition of acupoints, and the association between the electroconductive values at the RMPs and blood pressure was demonstrated. Therefore, the result of this study could be helpful for establishing the evidence on the prevention for hypertension in Traditional East Asian medicine.
Conclusions
In this study, electroconductive values were positively associated with blood pressure in community-dwelling Japanese, after adjusting for potential confounding factors. Further longitudinal and interventional studies are needed to elucidate the causal relationship and therapeutic effect of acupuncture treatment using the measurement of skin electroconductance on hypertension.
Footnotes
Authors' Contributions
M.O. analyzed the data and drafted the article. I.S., K.M., and T.T. designed and coordinated the study and obtained funding. K.T., I.S., and K.M. collected the data. K.T. provided technical assistance with data analysis. K.T., I.S., K.M., D.Y., and T.T. critically revised the article. T.T. is a guarantor for this study.
Acknowledgments
The authors are grateful to the staff at Ehime Prefectural Central Hospital Acupuncture and Moxibustion Care Unit, East Asian Traditional Medicine. They also thank the staff and participants of the Toon Health Study and the municipal authorities, officers, and health professionals of Toon City for their valuable contributions.
Author Disclosure Statement
No competing financial interests exist.
Funding Information
This study was supported in part by Grants-in-Aid for Scientific Research (Grants-in-Aid for Research B, No. 22390134 for 2010–2012 and No. 25293142 for 2013–2015, and Grant-in-Aid for Early-Career Scientists, No. 19K16991 for 2019–2022) from the Ministry of Education, Culture, Sports, Science and Technology of Japan, and Health, and in part by Labor Sciences Research Grants (Comprehensive Research on Lifestyle-Related Diseases including cardiovascular diseases and diabetes mellitus, No. 201021038A for 2010–2012) from the Ministry of Health, Welfare, and Labor, Japan.
Abbreviations Used
References
Supplementary Material
Please find the following supplemental material available below.
For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.
For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.
