In the current study, we explored the use of five-phase acupoints in clinical trials and revealed characteristics of these acupoints using machine-learning methods. Among the five-phase acupoints, stream and sea acupoints were the most frequently used in the studies listed in the CDSR, whereas the well, spring, and river acupoints were relatively less commonly used. MDS and cluster analysis revealed that the LR3 (stream), ST36 (sea), GB34 (sea), BL60 (river), KI3 (stream), LI11 (sea), and HT7 (stream) acupoints exhibited their own characteristics based on distances representing the similarity between acupoint indications. These results suggest that stream and sea acupoints are more likely to exhibit unique properties, compared to the other acupoints.
The five-phase acupoints were not used equally to treat diseases. Kim et al. demonstrated clear differences in the prescription of five-phase acupoints by analyzing the selection of these acupoints in classic medical textbooks . They found that spring, stream, and sea acupoints were more commonly used compared to well acupoints . In the current study, data mining also revealed that stream and sea acupoints were more frequently used in clinical trials compared to other acupoints. The stream acupoints for the meridians of five visceral organs (liver, heart, spleen, lung, and kidney) are equivalent to the source acupoints of those meridians and are therefore regarded as sites where innate Qi remains and reveals the conditions of the visceral organ (e.g., deficiency or excess of visceral Qi). On the other hand, the stream acupoints for the meridians of six bowel organs are not considered the source acupoints for those meridians and are therefore less important for treating internal organs. We found that stream acupoints corresponding to the liver, heart, and kidney meridians exhibited distinguishing characteristics, whereas none of the stream acupoints for the six bowel organs were highlighted by the MDS analysis, suggesting that the stream acupoints for the five visceral organs are more likely to have acupoint-specific treatment effects. Based on the traditional theory, sea acupoints of meridians have been widely used for the treatment of problems in six bowel organs. We found that the sea acupoints for the stomach (ST3), gall bladder (GB34), and large intestine (LI11) were located far from the other acupoints on the MDS plot. The results for the stream acupoints for the five visceral organ meridians and the sea acupoints for the six bowel organ meridians may be indicative of acupoint-specific effects. On the other hand, the use of well acupoints to treat diseases was extremely limited in the present study. Traditionally, well acupoints are primarily used to treat acute diseases [19, 20], with indications limited to the induction of labor and brain injury in the current database. Given that the clinical trials covered only a small number of acute diseases, we cannot the rule out the possibility that the discrepancies in the usage rate of the five-phase acupoints may be related with the characteristics of the included diseases. Further studies examining a wider range of diseases will therefore be necessary to verify the different use patterns of the five-phase acupoints.
Clustering results in this study were as follows: the LR3 and ST36 acupoints were grouped in cluster 1; the LU5, BL40, ST41, BL60, SP9, LI11, and GB34 acupoints were grouped in cluster 2; the PC7, KI3, and HT7 acupoints were grouped in cluster 3; and other acupoints such as PC3, KI1, LU8, and LI3 were grouped in cluster 4. Of these locations, the LR3 (stream) and ST36 (sea) acupoints are representative of so-called major acupoints and have been widely used to treat many different conditions . The general effects of the major acupoints are explained by descending analgesia and central regulation [2, 22], and cluster 1 may represent acupoints that exhibit general efficacy for a wide variety of conditions. For cluster 2, the LU5 (sea), BL40 (sea), ST41 (river), BL60 (river), SP9 (sea), LI11 (sea), and GB34 (sea) acupoints are commonly used in diseases of the musculoskeletal system, nervous system, and injuries [23–26]. Cluster 2 included four sea acupoints and two river acupoints, suggesting that these acupoints may be related to diseases of the six bowel organs or corresponding meridians. On the other hand, PC7, KI3, and HT7 are all source acupoints of visceral organs including the heart, pericardium, and kidney, and these acupoints may be associated with the regulation of emotional reactions and problems related to visceral organs [27–30].
Five-phase acupoints are defined as the five acupoints of the meridians located below the elbow and knee areas in the limb extremities [5, 7]. Each of the five acupoints are allocated to one of five elements and manage the flow of Qi from the peripheral extremities to the heart [5, 31]. Among the various acupoints, practitioners select only a subset of acupoints that are relevant to the disease. It is therefore important to identify the most appropriate acupoints for the effective treatment of each disease. The current study revealed specific patterns of the five-phase acupoints from a clinical trial database. For instance, the GB41 (stream) and GB34 (sea) acupoints were more likely to be prescribed to treat various diseases within a given meridian (Fig. 3). As depicted in Fig. 3, starting from the spring acupoint, Qi is initially superficial and dynamic as it flows towards the heart, with the flow of Qi subsequently becoming wider and deeper. Therefore, superficial needling is sufficient to produce appropriate De-Qi sensations at spring acupoints, whereas deeper needling is needed for river and sea acupoints . Although the origin of five-phase acupoints was derived from the concept of Qi flow, we argue that we should not strictly adhere to the original meaning of the five-phase acupoints. Data-driven approaches will improve our understanding of the five-phase acupoints and lead to the establishment of new models of analysis and educational resources for acupoint characteristics.
Our study still has several limitations. First, the diseases analyzed in this study cannot fully represent the use of acupuncture under real-world conditions. However, the 30 diseases selected represents a large spectrum of diseases affecting the nervous system (6 studies), genitourinary system (5), digestive system (2), musculoskeletal system (2), circularity system (1), and respiratory system (1), as well as mental, behavioral, and neurodevelopment disorders (4) and other disorders . Further investigations examining a wider selection of diseases may reveal more clinically meaningful results. Second, this study presented the contents of the Acusynth database in an easily comprehensible plot, but more studies are needed to fully characterize the dimensions of the data. In this analysis, we identified which acupoints are clearly distinguishable from the other acupoints; however, we could not specify how and why those acupoints are located far from the other acupoints in the MDS plot. Further identification of factors that contribute to differences between acupoints will improve current approaches in the field of acupuncture studies.