Knowledge mapping of acupoint sensitization and acupoint specificity: a bibliometric analysis

Objective

The relationship between acupoint sensitization and acupoint specificity is a topic of significant interest in acupuncture research. Numerous clinical studies have demonstrated that needling pain sensitive acupoints yields superior therapeutic outcomes compared to traditional acupoints, particularly in the context of pain disorders. However, there is a lack of bibliometric analysis in acupuncture area. Therefore, the objective of this study is to offer a comprehensive overview of the knowledge structure and research hotspots pertaining to acupoint sensitization and acupoint specificity.

Methods

The search for publications pertaining to acupoint sensitization and acupoint specificity was conducted in the Web of Science Core Collection (WoSCC) database from its inception until August 11, 2023. Subsequently, bibliometric analyses were carried out using VOSviewer, CiteSpace, R software (Bibliometrix package), and GraphPad Prism software.

Results

This study includes 4,940 articles from 72 countries, with China and the United States being the leading countries. The number of publications related to acupoint sensitization and specificity has been increasing annually. Major research institutions involved in this field include the Shanghai University of Traditional Chinese Medicine, Kyung Hee University, Beijing University of Chinese Medicine, Chinese Academy of Chinese Medical Sciences, and China Medical University, among others. "Evidence-based Complementary and Alternative Medicine" is the most popular journal in acupuncture field, and "PAIN" is the most co-cited journal. Publications are contributed by 20,325 authors from all over the world, with Wu Huangan, Fang Jianqiao, Lin Yi-Wen, Liu Huirong, and Chen Rixin having published the most articles. Han Ji-Sheng is the most cited author in this research area. The main directions include the study of temperature specificity of acupoints, the diagnosis of acupoint sensitization diseases, and the study of the mechanism of acupoint sensitization. The most listed keywords in recent years are "TRPV1," "signaling pathway," and "diagnosis."

Conclusion

This is the first bibliometric study to comprehensively summarize research trends and advances in acupoint sensitization and acupoint specificity, and the information highlights recent research preliminary and main directions that serve as a reference for acupoint sensitization and acupoint specificity research.

Skin Temperature of Acupoints in Health and Primary Dysmenorrhea Patients: A Systematic Review and Meta-Analysis

Objective

Dysmenorrhea is a common clinical condition and some studies shown that the skin temperature of some acupoints changes in primary dysmenorrhea (PD) patients. This study aimed to evaluate the changes in skin temperature at specific acupoints in PD patients and healthy subjects.

Methods

The literature for assessing skin temperature at acupoints in PD patients and healthy subjects was searched in eight databases. The literatures obtained from the search was independently screened by two authors, and the quality of the included articles was evaluated using the consensus checklist of the Thermographic Imaging in Sports and Exercise Medicine (TISEM) and the Newcastle-Ottawa Scale (NOS) scale. The skin temperature of the relevant acupoints or the difference between the left and right acupoints of the same name was used as the outcome during any period of menstruation. Finally, the meta-analysis was performed using RevMan 5.4.1 software to evaluate the changes in skin temperature in the related acupoints.

Results

Seven eligible studies were included, which included 328 patients with PD and 279 healthy subjects. The results of the meta-analysis revealed a significant difference in skin temperature around the Sanyinjiao (SP6)(MD: 0.04, 95% CI: 0.00, 0.08), Xuehai (SP 10)(MD: -0.07, 95% CI:-0.11, -0.02) and Taixi (KI 3)(MD: 0.06, 95% CI:0.01, 0.11) acupoints between PD and healthy subjects. PD patients also showed a difference in skin temperature at the Taixi (KI 3)(MD: 0.14, 95% CI:0.04, 0.24), Shuiquan (KI 5)(MD: 0.11, 95% CI: 0.03,0.19), Taichong (LR 3)(MD: -0.10, 95% CI: -0.19,-0.01), Diji (SP 8)(MD: -0.09, 95% CI: -0.16, -0.01), and Xuehai (SP 10)(MD: -0.14, 95% CI: -0.23, -0.06) acupoint areas at different times of menstruation compared to that of healthy subjects, as revealed by the subgroup analysis.

Conclusion

Primary dysmenorrhea patients showed some differences in the skin temperature of the special acupoints are as Sanyinjiao (SP6), Diji (SP 8), Xuehai (SP 10), Shuiquan (KI 5), Taichong (LR 3), and Taixi (KI 3) compared with healthy subjects.

Registration Number

CRD42022381387.

An infrared thermographic analysis of the sensitization acupoints of women with primary dysmenorrhea

OBJECTIVE

To explore the sensitization acupoints of women with primary dysmenorrhea (PD) by comparing infrared radiation temperatures between acupoints and non-acupoints.

METHODS

We tested 10 acupoints of every woman with PD and healthy subjects on premenstrual, menstrual, and postmenstrual days using an infrared imaging device. The primary outcome was the absolute value of body surface temperature difference (AVTD) between the left and right sides of the same testing point.

RESULTS

A total of 58 PD patients and 57 healthy volunteers completed the test from May 2016 to May 2017. Compared with the healthy group, we observed a significant reduction and increase in the AVTD in Taichong (LR3) and Sanyinjiao (SP6), respectively, during menstrual days in the PD group (= 0.01; = 0.04); while during postmenstrual days, all AVTDs of Shuiquan (KI5), Diji (SP8), and Xuehai (SP10) were diminished in the PD group (= 0.01; = 0.03; = 0.01, respectively). No significant differences in AVTD were detected at any other points or testing times.

CONCLUSIONS

Compared with the healthy group, the AVTDs of Taichong (LR3), Sanyinjiao (SP6), Shuiquan (KI5), Diji (SP8), and Xuehai (SP10) at menstruation-relevant points of PD patients were sensitized, providing a reference for the selection of acupoints in the treatment of PD.

[Sensory and sympathetic nerves are involved in the changes of skin temperature, blood infusion and inflammatory cytokines of cutaneous tissue in the sensitized area of colitis rats]

OBJECTIVE

To investigate the changes of skin temperature, blood infusion and inflammatory cytokines of cutaneous tissue in the sensitized area of colitis model rats, as well as the relationship between sensory and sympathetic nerves and the formation of sensitized area, and to initially reveal the partial physical-chemical characteristics of the sensitized area in the colitis model rats.

METHODS

Thirty-five male SD rats were randomly divided into a control group (n=10), a model group (n=18) and a guanethidine group (n=7). 5% dextran sulfate sodium (DSS) was adopted for 6-day free drinking to establish colitis model in the model group and the guanethidine group. On day 6 and 7, in the guanethidine group, guanethidine solution (30 mg/kg) was injected intraperitoneally for sympathetic block. On day 7, after injection of evans blue (EB) solution, the EB extravasation areas on the body surface were observed to investigate the distribution and physical-chemical characteristics of the sensitized area. The control area was set up, 0.5 cm away from the sensitized area, and with the same nerve segment innervation. Disease activity index (DAI) score of rats was compared between the normal group and the model group, and the morphological changes in the colon tissue were investigated with HE method. Using infrared thermal imaging technology and laser speckle flow imaging technology, skin temperature and blood infusion were determined in the sensitized area and the control area of the rats in the model group. Immunofluorescence technique was adopted to observe the expression levels of the positive nerve fibers of substance P (SP), calcitonin gene-related peptide (CGRP) and tyrosine hydroxylase (TH), and the correlation with blood vessels; as well as the expression levels of SP positive nerve fibers/tryptase⁺ mast cells, and tryptase⁺ mast cells/5-hydroxytryptamine (5-HT) in skin tissue in the sensitized area and the control area of the rats in the model group. MSD multi-level factorial method and ELISA were applied to determine the contents of pro-inflammatory and anti-inflammatory cytokines (e.g. TNF-α, IL-1β, IL-6, IL-4 and IL-10) and anti-inflammatory substance corticosterone (CORT).

RESULTS

Sensitization occurred at the T₁₂-S₁ segments of the colitis model rats, especially at L₂-L₅ segments. Compared with the normal group, DAI score was increased in the rats of the model group (P<0.05), and the colonic mucosal damage was obvious, with the epithelial cells disordered, even disappeared, crypt destructed, submucosal edema and a large number of inflammatory cells infiltrated. In comparison with the control area, the skin temperature and blood infusion were increased in the sensitized area of the model group (P<0.05, P<0.01); as well as the expression levels of the positive nerve fibers of SP, CGRP and TH of skin tissue (P<0.05), which was specially distributed in peripheral vessels, the expression levels of SP positive nerve fibers/tryptase⁺ mast cells, and tryptase⁺ mast cells/5-HT of the skin tissue were all expanded (P<0.05) in the sensitized area of the model group. Compared with the model group, the number of sensitized areas was reduced in the guanethidine group (P<0.05). In comparison with the control area of the model group, in the sensitized area, the contents of pro-inflammatory cytokines, e.g. TNF-α, IL-1β and IL-6, and the anti-inflammatory substance CORT of skin tissue were all increased (P<0.05); and the contents of IL-6 and TNF-α were negatively correlated with CORT (P<0.05).

CONCLUSION

The sensitized areas on the body surface of colitis rats are mainly distributed in the L₂-L₅ segments. Sensory and sympathetic nerves are involved in the acupoint sensitization, and the sensitized areas may have the dynamic changes in pro-inflammatory and anti-inflammatory substances.

Skin Temperature of Acupoints in Health and Disease: A Systematic Review

Introduction: Despite substantial progress made in the field of acupuncture research, the existence and specificity of acupoints remain controversial. In recent years, the concept of acupoint sensitization has emerged as a theoretical framework for understanding acupoints as dynamic functional entities that are sensitized in pathological conditions. Based on this premise, some have claimed that specific acupoints are thermally distinct between healthy and clinical populations, but no systematic review has been conducted to synthesize and evaluate the quality of studies supporting such claims. In this review, we provide a summary and quality assessment of the existing literature addressing the question of whether changes in skin temperature at specific acupoints are indicative of pathological conditions. Methods: A systematic literature search was performed in PubMed, EMBASE, and AltHealthWatch (EBSCO Host), by combining variations of search terms relevant to acupoints and temperature. The search was limited to the English language, and publication dates ranged from database inception to December 2020. Two authors independently screened all resulting abstracts and subsequently read full-text articles for eligibility. Information on study design, sample, acupoints, parameters of skin temperature assessments, and main findings were extracted from included studies. Quality of the thermal sensing methodology was evaluated using a thermal assessment checklist, adapted from the Thermographic Imaging in Sports and Exercise Medicine (TISEM) consensus checklist, and a modified Newcastle-Ottawa Scale (NOS) for case-control studies. Results: The search strategy yielded a total of 1771 studies, of which 10 articles met the eligibility criteria. Eight studies compared skin temperature at acupoints in healthy versus clinical populations, and two studies assessed within-subject changes in temperature of acupoints in relation to changes in health status. There were seven clinical conditions examined in the included studies: chronic bronchial asthma, chronic hepatitis, hyperplasia of mammary glands, infertility, intracranial hypertension, obesity, and primary dysmenorrhea. There were numerous methodological quality issues related to skin temperature measurements. Eight studies with case-control designs reported significant differences between healthy and clinical populations in temperature at certain acupoints. Two studies with pre-post designs reported that changes in health-disease status could be associated with changes in temperature at specific acupoints. Conclusion: A review of the available literature suggests that certain acupoints may be thermally distinct between healthy and unhealthy states. However, given the methodological limitations and heterogeneity across included studies, no definitive conclusion could be drawn as to whether changes in skin temperature at specific acupoints are indicative of pathological conditions.

[Discussion of novel mode of acupuncture and moxibustion based on identifying the acupoint sensitization]

On the base of the paradigms of clinical studies on modern moxibustion by identifying the acupoint sensitization, the records of ancient literature in successive dynasties were collected on "identifying the sensitization" of acupoints in acupuncture. In association with acupoint detection of acupuncture recorded in current textbooks, a novel concept, "exerting acupuncture by identifying the acupoint sensitization" is proposed. Acupoint sensitization is the common initial link of effect achieved by both acupuncture and moxibustion. Hence, on the basis of the routine acupoint selection by differentiating syndrome, the state of acupoint must be considerably emphasized in either acupuncture or moxibustion. The clinical curative effect may be improved by selecting the sensitized points and identifying sensitization. This novel mode of diagnosis and treatment focuses on identifying acupoint sensitization by unifying acupuncture with moxibustion and in coincidence with the modern clinical characteristics of either acupuncture or moxibustion.

[Revealing characteristics and rules of acupoint sensitization phenomena: based on knee osteoarthritis]

OBJECTIVE

To explore the characteristics and rules of acupoint sensitization phenomena based on knee osteoarthritis (KOA), one of the clinical dominant diseases of acupuncture-moxibustion.

METHODS

In combination with literature and expert experiences, the acupoints with the highest use frequency in treatment of KOA were screened, e.g. Heding (EX-LE 2), Liangqiu (ST 34), Mingmen (GV 4), Neixiyan (EX-LE 4), Ququan (LR 8) and Dubi (ST 35). In 814 patients with KOA and 217 healthy subjects, the acupoint temperature, mechanic pain threshold and pressure pain threshold were detected separately. Using machine learning method, the sensitization was judged at each acupoint.

RESULTS

Compared with healthy subjects, the acupoint temperature was increased and the mechanic pain threshold and pressure pain threshold were reduced in KOA patients (P<0.05). Besides, the cut-off value was presented to distinguish whether the acupoint was sensitized or not. The results of machine learning showed that the highest prediction accuracy of acupoint sensitization was 86.7% (Shenshu [BL 23]) and the lowest one was 73.9% (Heding [EX LE 2]). The prediction accuracy at the third clinical stage trial was higher, the highest was 93.3% (Ququan [LR 8]) in KOA patients.

CONCLUSION

It is confirmed that the acupoint sensitization reflects the characteristics of disease and is correlative with the conditions of illness, which may provide the reference for the auxiliary diagnosis and condition assessment of KOA.

[On the acupoint and its specificity]

Although acupuncture has spanned thousands of years in the history of traditional medicine, still some basic questions are not clarified. Acupuncture is the theory based on long time medical practice of the ancient sage, combined with objectivesymptom and medical expertise from diseases, and being applied for the instruction in clinic. In this way, acupoint is discovered by doctors in the practice of disease treatment other than a natural occurrence in the healthy population. And acupoint specificity is attached to the target organ involved in pathological condition. In our opinion, acupoint originates from somatic referred area reactive to visceral disorders. And accordingly, referred hyperesthesia of the somatic area is phenomenon of acupoint sensitization. Acupoint is the situ having health code formed in the biological evolution. Corresponding acupoint of a given organ is the alarmer for the state of health, and also is the trigger for self-healing where acupuncture can work as a gating-button. Therefore, acupoint must be accompanied with diseases in that it is reinforced by, relayed on, responsive to and neutralize by the pathological course. In conclusion, acupoint cannot exist without the disease. In another word, acupoint will be unshown, or be functionally hidden, under physiological condition.

[Clinical observation on distribution characteristics and rules of pain sensitivity points on body surface in patients with knee osteoarthritis]

OBJECTIVE

To observe the distribution characteristics and rules of pain sensitivity points on body surface in patients with knee osteoarthritis (KOA).

METHODS

A total of 916 patients with KOA were selected in this study, the pain sensitivity points of local site of knee joint were probed by thumb palpation. Tape was used to measure the distance between the pain sensitivity points and the most nearby acupoints. The Wagner tenderness measuring instrument was used to measure the tenderness threshold of pain sensitivity points.

RESULTS

A total of 3618 pain sensitivity points were probed, among them, 3338 pain sensitivity points were sensitized. The minimum sensitization degree was 1.00, the maximum sensitization degree was 3.39, while the average sensitization degree was (2.16±0.60). Pain sensitivity points were distributed 0.37-1.73 cun around the acupoints, the average distance was (1.26±0.20) cun. Most of the pain sensitivity points (48.7%) were around Yingu (KI 10), Ququan (LR 8) and Xuehai (SP 10). The number and sensitization degree of pain sensitivity points were associated with McGill pain questionnaire score of patients with KOA (P<0.001).

CONCLUSION

The pain sensitivity points of patients with KOA may be the expansion effect of acupoint areas in the disease states, pain sensitivity points are more likely to appear on the medial side of knee joint.

[Correlation between referred pain distribution and acupoint sensitization in patients with intestinal diseases]

OBJECTIVE

To observe the correlation between referred pain distribution and acupoint sensitization in patients with intestinal diseases.

METHODS

In clinical research, 443 patients from 8 hospitals were recruited, including the outpatients and inpatients of Crohn's disease (n=143), ulcerative colitis (n=108), chronic appendicitis (n=87) and other intestinal diseases (n=105). The site with tenderness on the body surface and the morphological changes of local skin were observed and recorded in the patients. Using a sensory tenderness instrument, the pain threshold at the sensitization point was measured in 60 patients with ulcerative colitis. In animal experiment, SD rats were used and divided into a enteritis group (n=8), in which the enteritis model were established, and a control group (n=3), in which no any intervention was given. After the injection of Evans blue (EB) at caudal vein, the blue exudation points on the body surface were observed and the distribution rule was analyzed statistically.

RESULTS

The referred pain on the body surface in the patients with intestinal diseases was mainly located in the lower abdomen (93.9%, 416/443), the lumbar region (70.9%, 314/443) and the lower legs (33.0%, 146/443). The diameter of tenderness region was 1.5 to 2.5 cm. Compared with the region without sensitization, the pain threshold of the sensitization point in the patients with ulcerative colitis was reduced significantly (P<0.001). The referred pain on the body surface in the patients with appendicitis was located in the right lower abdomen (97.7%, 85/87), the waist and back (54.0%, 47/87) and the right lower limbs on the medial side (71.3%, 62/87). The tenderness region was 1 to 2 cm in diameter and was irregular in form. After modeling of enteritis in the rats, the EB exudation points were visible from T₁₂ to L₂.

CONCLUSION

Intestinal diseases induce referred pain on the body surface where is the same as or adjacent to the location of the spinal segment corresponding to the affected intestinal section. These sensitization regions are related to the locations of acupoints.

Lack of association between acupoint sensitization and microcirculatory structural changes in a mouse model of knee osteoarthritis: A pilot study

As a stimulating point in acupuncture, acupoint has unique microcirculatory features, and its dynamics vary greatly depending on health status. Acupoint sensitization is defined as the transformation of an acupoint from a "silenced status" (healthy) to an "activated status" (disease). Our previous study demonstrated that acupoint sensitization is associated with an increase in the level of local blood perfusion. However, the structural changes in microcirculation during acupoint sensitization have yet to be elucidated because the high-resolution microcirculation imaging of acupoints has been difficult to obtain. In this study, the structural changes in microcirculation at the Zusanli (ST36), Yanglingquan (GB34) and nonacupoint sites on days 0, 7 and 21 were dynamically observed during acupoint sensitization in an experimental knee osteoarthritis mouse model by using optical-resolution photoacoustic microscopy. The results showed that no significant differences in microvessel density, the distribution of vessel diameters or vascular tortuosity were observed at the GB34, ST36 or nonacupoint sites among days 0, 7 and 21. We proposed that acupoint sensitization may not be associated with the structural changes in microcirculation and that the microcirculatory changes during acupoint sensitization are more likely to be functional. The functional characteristics of the sensitized acupoints warrant further investigation.

Acupoint Sensitization is Associated with Increased Excitability and Hyperpolarization-Activated Current (Ih) in C- But Not Aδ-Type Neurons

Under pathological conditions, acupoint sensitization is the phenomenon of acupoints transforming from the stable state to the dynamic state. Evidences suggest that hyperpolarization-activated current (I_h), conducted by the hyperpolarization-activated/cyclic nucleotide-gated (HCN) channel, greatly contributes to the peripheral and central sensitization. However, the role of the I_h current in acupoint sensitization has not been explained. In the present study, changes in excitability, I_h density and the HCN channel of dorsal root ganglion (DRG) nociceptive neurons were examined in the later phase of knee osteoarthritis (KOA) rats. To investigate the neuronal specificity of acupoint sensitization, retrograde dyes were injected into the acupoints ST35 and GB37. The results showed that acupoint sensitization occurred in bilateral ST35 but not GB37 acupoints. The excitability and I_h density of C- but not A_δ-type neurons innervating ST35 acupoint increased in bilateral L5 DRG of acupoint sensitized rats than that of sham rats. No obvious changes were found in the excitability or I_h density of C- and A_δ-type neurons innervating the GB37 acupoint in the bilateral L5 DRG. HCN channel subtype 2 (HCN2) expression levels significantly increased after acupoint sensitization. Furthermore, ZD7288, an HCN current (I_h) blocker, attenuated the acupoint sensitization of the ST35 acupoint. Taken together, our findings suggest that the increased excitability of C- but not A_δ-type neurons and the upregulation of I_h/HCN2 channels contribute to the formation of acupoint sensitization.

[The sensitization phenomenon of acupoint and biological significances]

In the pathological conditions, the human body induces somatic sensory exchanges and takes neurogenic inflammatory reactions according to referred visceral organ. Acupoint possesses both diagnosing and treating functions according to the acupuncture theory. The sensitization of acupoint refers to a pathophysiological dynamic change which is manifested predominately as a neurogenic inflammatory reaction in the specific area(s) of the body surface under pathological conditions. Furthermore, the process of acupoint from "silent" (physiological status) to "active" (pathological status) is generally represented by the dynamic changes of acupoint location, size and physicochemical environment. These responses of acupoint sensitization simultaneously activate self-healing system in the body and eventually induce the curative effects.

[Distribution of algesia sensitized acupoints in the patients of intestinal cancer]

OBJECTIVE

To judge whether algesia sensitization of some acupoints is existed and whether the acupoint algesia sensitization area is expanded in the patients of intestinal cancer.

METHODS

Totally, 30 patients of intestinal cancer and 30 healthy subjects were included. The electronic Von Fray was used to determine the pressure-pain thresholds at 13 acupoints relevant with gastrointestinal disorders and the reference points at the sites 1 cun and 2 cun lateral to those points as well as the sites at the corresponding nerve segments. Compared with the pressure-pain thresholds at the reference points of the different segments, the relative value was calculated. The changes were analyzed in the pressure-pain thresholds at the relevant acupoints on the body surface in the patients of intestinal cancer as compared with the relative pressure-pain thresholds in the healthy volunteers.

RESULTS

The pressure-pain thresholds at Zusanli (ST 36), Shangjuxu (ST 37), Xiajuxu (ST 39), Quchi (LI 11) and Dachangshu (BL 25) in the patients of intestinal cancer were all significantly reduced as compared with those of the healthy subjects (P<0.05, P<0.01, P<0.001). At the non-acupoint sites 1 cun and 2 cun lateral to those acupoints as well as at the sites of the same segments, the pressure-pain thresholds were reduced significantly as compared with the control group (P<0.05, P<0.01, P<0.001). Particularly, the sensitization zone of Yinlingquan (SP 9) focused on the acupoint, the site 1 cun lateral to it as well as the non-acupoint sites of the same segments (P<0.01, P<0.001).

CONCLUSION

The acupoint sensitization is displayed at Zusanli (ST 36), Shangjuxu (ST 37), Xiajuxu (ST 39), Quchi (LI 11), Dachangshu (BL 25) and Yinlingquan (SP 9) and the sensitization area is expended in the patients of intestinal cancer.

[Review on skin temperature of acupoints]

We retrieve and analyze the articles on body surface temperature of acupoints in the recent 50 years. Surface temperatures have been compared between acupoints and nonacupoints, and among acupoints in different states. The impacts of interventions for acupoint temperature are explored, including acupuncture,moxibustion and cupping, etc. We summarize the features and the rules of acupoint skin temperature. It is considered that there exists distribution rule for healthy people's acupoint skin temperature. That means acupoints have higher surface temperature than nonacupoints. In the same meridian the nearer acupoints close to the head and trunk, the higher the temperature is. The difference in symmetrical acupoints temperatures between the left and right side is about 0.5℃. In the different meridians the skin temperatures of adjacent acpoints are similar. The changes of acupoint's skin temperature in illness can be used as the auxiliary diagnosis. Acupuncture, moxibustion and cupping can produce acupoints stimulating, metabolism improving, yin-yang balance, acupoint temperature regulating. Thus,diseases are relieved. The specificity and regularity that acupoint's skin temperature presents may be one of the manifestations of the acupoint specificity, also it is an important starting point of the research on acupoint sensitization. The further studies should consider different diseases and modern biological engineering techniques, so that more rules of acupoints temperature can be found by more sensitive and objective temperature measurements as well as experimental and the mathematical models.