The efficacy evaluation of clinical trials of acupuncture is not only related to the randomization and blinding process, control group setting, and main endpoints but also closely associated with the acupuncture treatment procedure, including the selection and combination of acupoints, acupuncture methods, and treatment regimen. In particular, selections and combinations of acupoints according to the theory of meridians and acupoints as well as syndrome differentiation in TCM are of vital importance to the full realization of the therapeutic effects of acupuncture, which is a topic that has not been strictly studied in some randomized controlled clinical trials, leading to negative evaluations of acupuncture for asthma treatment. Thus, using data mining technology to analyze the effective acupoints in acupuncture clinical trials is helpful in improving the selection and combination of acupoints in clinical and experimental studies of acupuncture for asthma treatment.
In the 183 CCTs included in the analysis, a total of 8,746 patients with asthma received acupuncture treatment with an average clinical effective rate of 92 ± 6.71%. In parallel, clinical trials with an effective rate of more than 90% accounted for 83% of the total trials analyzed, indicating the significant therapeutic implications of treatment with acupuncture. Feishu (BL13) was the most frequently used acupoint in all of these clinical trials with a total frequency of 162. Also, this acupoint was in the most critical position of the complex acupoint correlation network, with the highest degree centrality (68), betweenness centrality (0.165), and closeness centrality (0.902). Feishu is an important acupoint for treating respiratory diseases, including asthma in TCM. It is the acupoint where the lung meridian Qi is infused into the back and is located in the projection area of the lung with the function of regulating lung meridian Qi. It has been demonstrated that acupuncture at Feishu inhibits acetylcholine synthesis and restores muscarinic acetylcholine receptor M2 expression in the lung of an asthma model [21]. Specifically, moxibustion at Feishu was shown to inhibit airway inflammatory responses in an asthmatic animal model [22]. Another of the most frequently used acupoints was found to be Dingchuan (EX-B1), with a total frequency of 106. Dingchuan is an extraordinary acupoint located on the back, 0.5 cun lateral to the side of Dazhui (GV14), and is located under the spinous process of the seventh cervical vertebra. Increased skin impedance has been found at the Dingchuan point in asthmatic patients when compared with healthy individuals [23]. Notably, Dazhui, the crossing point of three yang meridians and the Governor Vessel, is the third most frequently used acupoint for asthma, with the function of reinforcing the vital Qi to relieve asthmatic symptoms. Dingchuan and Dazhui are mainly located near the cervical sympathetic nerve trunk and the thoracic 1–4 sympathetic chain, where the sympathetic neurons that innervate the lungs and airways are distributed. Thus, acupuncturists will treat nearby acupoints at the same time as Dazhui and Dingchuan, like Dazhu (BL11) and the extraordinary acupoint, Chuanxi. Another key node in the acupoint correlation network is Fengmen (BL12), which has high degree centrality and closeness centrality. It is believed in TCM that this acupoint can regulate the flow of meridian Qi and can be used to dredge and activate the lung meridian, thereby treating pulmonary diseases.
In addition, the back-shu acupoints, including Feishu, Pishu (BL20), and Shenshu (BL23), are a type of specific acupoints commonly used in the treatment of asthma, accounting for 92% of the total frequency of acupoints. The back-shu acupoints are points on the back where the Qi and blood of respective zang-fu organs are infused. They are specifically located on either side of the vertebral column, in close proximity to the spinal dorsal root ganglia and within the innervation range of their respective zang-fu ganglia or the adjacent ganglion segments not exceeding the distance of more than two spinal ganglion segments. It has been reported that acupuncture at back-shu acupoints has an inhibitory effect on the uptake of neurotrophic factors, and the synthesis and release of substance P in dorsal root ganglia, resulting in the relief of airway neurogenic inflammation in asthma [24]. According to the TCM theory, the pathogenesis of asthma is closely linked to the aberrant functions of the lung, spleen, stomach, liver, kidney, and among other zang-fu organs. As mentioned in the Huangdi Neijing, “All the five zang organs and six fu organs make people cough and wheeze, not only the lung”. The Governor Vessel and the Conception Vessel travel along the posterior midline and anterior midline of the human body, respectively, and are closely connected to the above-mentioned zang-fu organs. At the same time, the energy Qi of these zang-fu organs is infused into the corresponding back-shu acupoints distributed on the Bladder Meridian of Foot Taiyang. Therefore, as our results show, the Bladder Meridian of Foot Taiyang, the Governor Vessel and Conception Vessel were found to be the most commonly selected meridians for asthma treatment in clinical practice.
In using a hierarchical clustering algorithm, 39 acupoints with a frequency greater than 2 were clustered into five major clusters (Fig. 5) signifying the main treatment principles and concepts of “facilitating the flow of the lung Qi, tonifying spleen and kidney, treating both the symptoms and root causes”. TCM distinguishes two general patterns of asthma, an “excess” pattern and a “deficiency” pattern. The former corresponds to an acute asthma attack caused by the obstruction of lung Qi due to external pathogenic factor invasion, with symptoms such as chest tightness, severe shortness of breath, wheezing, and fever. The “deficiency” pattern occurs in chronic asthma caused by excessive phlegm resulting from weakened spleen and kidney, the two main zang organs responsible for the processing of body liquids. Patients with a “deficiency” pattern complain of wheezing, sweating, and general lassitude with cold hands and feet. In clinic, most patients present with “deficiency-excess complication”, of which the impaired functions of the spleen and kidney are root causes. Based on the general principle of “treating both the symptoms and root causes”, TCM emphasizes dispelling pathogenic factors and protecting the lungs to treat symptoms, as well as tonifying the spleen and kidney to treat root causes in the treatment of asthma. Thus, acupoint Cluster 1, Feishu and Dingchuan; Cluster 2, Lieque (LU7) and Yuji (LU7); and Cluster 3, Dazhui and Fengmen, were selected to dispel exogenous pathogenic factors, alleviate fever, depress the upward reversal of lung Qi, and strengthen the function of the lung to command Qi and control respiration. Acupoint Cluster 4, Pishu and Shenshu, are used to nourish and tonify the spleen and kidneys, help the kidneys grasp and keep the air (Qi) down, and improve the transportation and transformation of body fluid to reduce the production of phlegm. Meanwhile, Cluster 5, including Danzhong (CV17), Tiantu (CV22), Gaohuang (BL43), Zusanli (ST36), and Fenglong (ST40), were selected to relax the chest, regulate Qi and descend the adverse flow of Qi, and dissolve phlegm stagnation in the lungs.
In clinical practice, acupuncturists usually combine more than one acupoint targeting the symptoms and pathogenesis of diseases to enhance the synergy between them and improve the therapeutic effect of acupuncture. In this study, we identified the two most commonly used acupoint combinations in asthma treatment by using an association rule mining techniques (Fig. 6c). One of the most popular acupoint combination was found to be Pishu, Shenshu, Feishu, and Dingchuan. Pishu and Shenshu, two back-shu acupoints that regulate the functions of the spleen and kidney, are used together in asthma treatment because, as mentioned above, TCM believes that the deficiency of the spleen and kidney is an important aetiology of persistent and recurrent asthma attacks. It has been shown that acupuncture at Pishu can increase the percentage of CD4+ lymphocytes and decrease the percentage of CD8+ lymphocytes and, in parallel, increase the production of IL-4 and reduce that of IFN-γ in rats with chronic fatigue [25]. Moxibustion therapy on Shenshu and Zusanli was found to significantly increase the number of Treg cells and decreased the number of Th17 cells in a mouse model, thereby suppressing collagen-induced arthritis in the mice [26]. These results indicate that acupuncture at Pishu and Shenshu tends to be effective in regulating immune balance, which is considered to be important for alleviating the airway inflammation caused by asthma. The combination of Feishu, Dingchuan, and these two acupoints not only can relieve the airway hyperresponsiveness and dyspnea during an asthma attack but can also inhibit the airway inflammatory response stemming from chronic asthma. The other most commonly used acupoint combination was found to be Feishu, Dazhui, and Fengmen, also known as “Three-acupoint and Five-needle therapy” in China. It represents a summary of Professor Shao’s clinical experience in treating asthma for years and is used to improve the pulmonary function, strengthen the body’s constitution, and prevent the recurrence of asthma. Our previous clinical study indicated that the total efficacy rate of “Three-acupoint and Five-needle therapy” in the treatment of allergic asthma was 85% [10]. After treatment, the serum levels of total immunoglobin E (IgE) and the IL-2R+ T lymphocyte and eosinophil counts in the peripheral blood were significantly decreased. The production of soluble IgA and total IgA in the saliva and nasal secretions of asthma patients was also remarkably decreased [10]. Moreover, proteomic analysis revealed that acupuncture at Feishu, Dazhui, and Fengmen down-regulated the expression of pro-inflammatory proteins (e.g., S100A8, RAGE, and S100A11) and up-regulated the expression of anti-inflammatory proteins (e.g., CC10, ANXA5, and sRAGE) in the lungs of an asthma model [11]. Further experimental studies demonstrated that the combination of these three acupoints reduced CD4+ IL-17A+ cell numbers and increased CD4+ Foxp3+ cell numbers in the bronchoalveolar lavage fluid [27], and inhibited the recruitment of pulmonary group 2 innate lymphoid cells (ILC2s) in ovalbumin-induced asthma [28]. Both the theory of TCM and relevant results from modern molecular biological research have provided rationale for the priority use of the acupoint combination of Pishu, Shenshu, Feishu, and Dingchuan as well as the combination of Feishu, Dashui, and Fengmen in asthma treatment.
There are several limitations in this study that should be considered. First, the methodological quality of the included studies was relatively low due to the inadequate concealment of the allocations and incomplete outcome data in addition to the fact that fully double-blinding is extremely difficult to achieve for acupuncture treatments. More rigorous randomized controlled trials (RCTs) of acupuncture for asthma will be needed in the future to improve the quality of evidence. Second, the effectiveness of the acupoint prescription in each study was not adequately considered, which was mainly due to unclear control group settings and efficacy evaluation criteria; moreover, this information was not available in some studies. The future well-designed studies with an appropriate control group and efficacy evaluation criteria will enable the extraction of acupoint prescriptions with definite effectiveness. Third, since this current study focuses on the main acupoints in the acupuncture treatment of asthma, data regarding the selection and combination of adjunct acupoints prescribed based on syndrome differentiation was not extracted for analysis. Such data could be further mined in future studies to discover more comprehensive acupoint selection patterns based on TCM syndrome differentiation theory.