Effects of different traditional Chinese exercises on pulmonary function in patients with stable chronic obstructive pulmonary disease: a network meta-analysis

Abstract

Objective

Traditional Chinese exercises (Taichi, Wuqinxi, Liuzijue, and Baduanjin) are considered effective alternative treatments for improving symptoms in the stable phase of COPD. However, the most effective exercise remains unknown. This study compared the effectiveness of different traditional Chinese exercises on pulmonary function in patients with stable chronic obstructive pulmonary disease (COPD) using a network meta-analysis.

Methods

From database establishment until September 2023, eligible randomized controlled trials (RCTs) were searched. Two reviewers performed the risk of bias assessment of the included studies using the Cochrane Collaboration tool, and the evidence level was suggested using the GRADE system.

Results

Fifty-seven studies comprising 4294 patients were included. The results of the network meta-analysis show that Baduanjin was most effective in improving the forced expiratory volume in the first second (FEV1). However, Liuzijue significantly improved the first–second forced vital capacity percentage of expected value (FEV1%) and the ratio of the forced expiratory volume in the first second to the forced vital capacity (FEV1/FVC). The probability ranking results indicated that Liuzijue was the most effective, followed by Baduanjin, Wuqinxi, and Taichi. Subgroup analysis in conjunction with intervention duration revealed that Liuzijue had a significant advantage over other interventions for improving FEV1, FEV1%, and FEV1/FVC within 6 months and improved FEV1% and FEV1/FVC for ≥ 6 months. Moreover, Subgroup analysis based on baseline pulmonary function revealed that Liuzijue had a significant advantage over other interventions for improving FEV1% within severe and moderate groups. Finally, Subgroup analysis based on the frequency of interventions showed that Liuzijue was still more effective in improving FEV1, FEV1%, and FEV1/FVC in the ≥ three times one week.

Conclusion

Liuzijue was more effective than Taichi, Wuqinxi, Liuzijue, and Baduanjin in improving pulmonary function in patients with stable COPD.

Introduction

Chronic obstructive pulmonary disease (COPD) is a heterogeneous lung disease characterized by chronic respiratory symptoms caused by abnormal airways and/or alveoli, leading to persistent and progressive airflow obstruction [1]. Moreover, COPD is associated with systemic manifestations and comorbid conditions, which may lead to extrapulmonary manifestations such as inflammation, heart failure, depression, osteoporosis, and lung cancer, reducing patients' quality of life and increasing their probability of death [2]. COPD has become a global public health problem owing to its increased mortality caused by the aging global population [3]. The World Health Organization (WHO) predicted that COPD would become the third leading cause of death worldwide by 2030 [4]. Therefore, the development of effective preventive and therapeutic strategies is essential.

Pulmonary rehabilitation treatments effectively improve symptoms during the stable phase of COPD [5, 6]. However, conventional treatments are heavy and monotonous, which reduces patient compliance [7]. Traditional Chinese exercises (Taichi, Wuqinxi, Liuzijue, and Baduanjin) are low- to moderate-intensity aerobic exercises with flexible and versatile forms. Relevant studies have confirmed the efficacy of these four traditional Chinese exercises in rehabilitating patients with stable COPD [8]. Existing studies have compared the effects of different traditional Chinese exercises on pulmonary function, exercise endurance, quality of life, and safety in patients with COPD [9,10,11]. However, these studies used only one indicator to compare the impact of traditional Chinese exercises on pulmonary function, and the sample sizes were relatively small, resulting in limited research results. Therefore, this study focused on patients with stable COPD and searched for randomized controlled trials (RCTs) in Taichi, Wuqinxi, Liuzijue, and Baduanjin. Based on the outcomes of the forced expiratory volume in the first second (FEV1), the first second forced vital capacity percentage of expected value (FEV1%), and the ratio of the forced expiratory volume in the first second to the forced vital capacity (FEV1/FVC), a network meta-analysis method was used to compare the effects of different traditional Chinese exercises on pulmonary function in stable COPD patients at a deeper level and provide practical evidence-based clinical support.

Methods

The systematic review was performed in accordance with the guidelines for the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA 2020 statement) [12]. This study was registered with the International Platform of Registered Systematic Review and Meta-analysis Protocols (INPLASY) under the registration number INPLASY202330117 (registration date: March 29, 2023).

Eligibility criteria

Inclusion criteria

The inclusion criteria were set based on participants, intervention, comparison, outcomes, and study design (PICOS) strategy. Participants (P): Patients with COPD diagnosed according to the 2020 revised version of the Global Initiative for the Diagnosis, Management, and Prevention of Chronic Obstructive Lung Disease [13] and in the stable phase, without psychiatric disorders or cognitive impairment, aged 18–90 years, with no restriction on sex. (I) Patients participated in only one of the four traditional Chinese exercises: Taichi, Wuqinxi, Liuzijue, and Baduanjin. Comparison (C): The conventional treatment group received medication and health guidance. Outcomes (O): The primary outcome measures assessed pulmonary function, including FEV1, FEV1%, FEV1/FVC, and adverse events. Study design (S): randomized controlled trials (RCTs). The PICOS strategy is presented in Table S1.

Exclusion criteria

The exclusion criteria adopted in the present study are as follows: (1) duplicate publications; (2) full text not available through relevant databases or other means; (3) non-randomized designs; (4) lack of relevant outcome indicators; (5) concurrent medication therapy during the intervention.

Search strategy

Randomized controlled trials on traditional Chinese health-preservation exercises for patients with COPD in Embase, Scoups, Opengrey, PubMed, Web of Science, The Cochrane Library, CNKI, Wanfang, and CSTJ databases were systematically searched, and the search time was controlled from the time of library construction to September 2023. The PICOS strategy [14] was used to structure the bibliographic search as follows: Participants (P) = patients with COPD; Intervention (I) = Taichi, Wuqinxi, Liuzijue, and Baduanjin; Comparison (C) = conventional treatment; and Outcome (O) = FEV1, FEV1%, and FEV1/FVC. Study design (S): RCTs. The languages were restricted to English or Chinese. The search strategy used a combination of subject terms and free words. Specific search terms included Taichi, Qigong, Baduanjin, Wuqinxi, Liuzijue, and Chronic Obstructive Pulmonary Disease. Subsequently, a second search was conducted on the references included in the study to identify other relevant studies. The detailed search strategies are listed in Table S2.

Study selection and data extraction

Two reviewers performed an initial screening of the retrieved results. First, Endnote X9 software was used to delete duplicate data. The titles and abstracts were read to identify studies that met the inclusion criteria. Subsequently, the full text was reviewed to determine the final inclusion criteria. Second, the data were extracted from the included studies and collected using an Excel spreadsheet. Extracted data included the first author's name, nationality, year of publication, sample size, age, intervention, outcome indicators, and intervention length. The studies were reevaluated for disagreements; unresolved disagreements were resolved through a group discussion.

Risk of bias assessment and GRADE

The methodological quality of the included studies was evaluated by two reviewers using the Cochrane Collaboration's Risk of Bias Tool 2.0 [15]. Several domains were evaluated, including the randomization process, deviations from intended interventions, missing outcome data, measurement of the outcome, and selection of the reported results. Additionally, we assessed evidence using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach. The risk of bias, consistency, accuracy, indirectness, and possibility of publication bias were evaluated. The evidence level was classified as high, moderate, low, or very low. Disagreements were resolved through collective discussions among the study team.

Statistical analysis

Network meta-analysis

Stata 14.0 and GeMTC 0.14.3 were used for statistical analysis and graphical plotting. The outcome measures were continuous variables and were assessed using the same instrument; therefore, the weighted mean difference (WMD) and 95% confidence interval (CI) were taken as the effect sizes. Statistical analysis was performed using GeMTC 0.14.3, using four chains for simulation and setting the number of iterations to 50 000, with the first 20 000 iterations used for annealing. Cumulative ranking probability plots were constructed to rank the efficacy of the interventions. Stata 14.0 was used to construct the network evidence diagram. The points in the network evidence diagram represent interventions; a larger dot represents a larger sample size of the included studies; the solid line connecting two points represents the direct connection between two interventions; and the thicker the solid line, the greater the number of studies between the two interventions.

Inconsistency test and Potential Scale Reduced Factor (PSRF) parameters

The inconsistency between direct and indirect evidence was tested using the nodal partitioning method, and p > 0.05 indicated that the inconsistency was not significant. Using the PSRF to assess the model, the convergence between the included studies was indicated by the PSRF; when the PSRF was close to 1, it indicated good convergence. High-confidence level results can be obtained using consistency model analysis.

Subgroup analysis

Subgroup analysis was performed according to the duration of the interventions、frequency of interventions and baseline pulmonary function of COPD patients used in the included studies.

Sensitivity analysis

Sensitivity analysis was performed by excluding studies with a sample size of less than 30 and articles exhibiting a high risk of bias and lacking methodological rigor.

Publication bias

Funnel plots were used to assess whether there was a small-sample effect or publication bias in the included studies.

Results

Search results

This process is illustrated in Fig. 1. A total of 1813 studies were initially obtained by searching the relevant databases, and 936 studies were obtained after eliminating duplicates using Endnote X9. Titles and abstracts were read to obtain 108 studies that met the requirements, and 57 studies were finally identified for inclusion after reading the full text.

Fig. 1

Flowchart of the study selection process

The basic characteristics of the included studies are presented in Table S3. A total of 57 studies were included, all RCTs in English and Chinese, including 4294 patients aged between 40 and 88 years. Among them, 19 studies reported Taichi, 5 studies reported Wuqinxi, 14 studies reported Liuzijue, and 19 studies reported Baduanjin. We have presented the references of the included literature in the supplementary materials.

Risk of bias assessment and GRADE

The results of the risk of bias assessment of the included studies are shown in Figures S1. Among them, most studies were assessed as having “some concerns or low risk,” with only six studies being at a high risk of bias. The main source of the high risk was potential bias due to the selection of the reported results. In addition, three studies had a high risk of bias owing to the randomization process. These issues may be partly due to the lack of published protocol analysis plans in the study or a lack of clarity in the randomized reporting methods. Other sources of concern were potential deviations from the intervention measures described and concerns about the risks in the outcome measures.

The GRADE results are presented in Table S4. For FEV1, the quality of evidence ranged from low to moderate. Regarding the FEV1%, the quality of evidence ranged from low to moderate. Regarding the FEV1/FVC ratio, the quality of evidence ranged from very low to moderate. Owing to the potential risk of bias in the inclusion of studies in terms of randomization, allocation concealment, and blinding methods, downgrading was achieved. Moreover, the sample size included in the study was small, and the confidence interval was large, leading to downgrading.

Evaluation of safety

Only one study reported that patients experienced mild chest tightness and shortness of breath during treatment, which was relieved after a few minutes of rest [16]. In addition, no adverse reactions were reported in other studies.

Inconsistency test and PSRF parameters

The outcome indicators of this study were based on the indirect comparison of conventional treatment groups with each exercise group, and the lack of direct comparison between the exercise groups did not constitute a closed loop; therefore, an inconsistency test was not required [17]. In addition, the PSRF parameter for each indicator was equal to or close to 1, indicating good convergence and high reliability of the study results.

Network meta-analysis

A network evidence diagram for each indicator is shown in Fig. 2. The results of the network meta-analysis are shown in Fig. 3. A total of 57 studies were included, with five interventions. The dots in the diagram represent interventions; larger dots represent larger sample sizes of the included studies; a solid line connecting two dots indicates a direct link between two interventions; the thicker solid line represents a more significant number of studies between the two interventions.

Fig. 2

Network evidence diagram. CT = conventional treatment

Fig. 3

Network meta-analysis results. CT = conventional treatment

FEV1

In terms of FEV1, 35 studies with 2769 patients were included. The results showed that Baduanjin was superior in improving FEV1 compared to the control group, and the difference was statistically significant (WMD = -0.27, 95% CI [0.40, 0.14], p < 0.05). Moreover, Baduanjin was superior to Taichi (WMD = -0.19, 95% CI[-0.36,-0.02], p < 0.05), Wuqinxi (WMD = -0.09, 95% CI [0.17, 0.33], p < 0.05), and Liuzijue (WMD = -0.03, 95% CI[-0.18,-0.23], p < 0.05), indicating that Baduanjin was better than the other interventions at improving FEV1.

FEV1%

In terms of FEV1%, 45 studies with 3371 patients were included. The results showed that Liuzijue was superior in improving FEV1% compared to the control group, and the difference was statistically significant ([WMD = -8.60, 95% CI [(-11.16, -5.92], p < 0.05). Moreover, Liuzijue was superior to Taichi (WMD = -6.07, 95% CI [-9.70, -2.38], p < 0.05), Wuqinxi (WMD = -5.73, 95% CI [-10.41, -0.72], p < 0.05), and Baduanjin (WMD = -3.56, 95% CI [-7.01, 0.03], p < 0.05), indicating that Liuzijue was better than the other interventions for improving FEV1%.

FEV1/FVC

In terms of FEV1/FVC, 41 studies with 2700 patients were included. The results showed that Liuzijue was superior in improving FEV1/FVC compared with that of the control group, and the difference was statistically significant (WMD = -7.35, 95% CI [-10.02, -4.51], p < 0.05). Moreover, Liuzijue was superior to Taichi (WMD = -3.89, 95% CI [-7.58, 0.02], p < 0.05), Wuqinxi (WMD = -0.96, 95% CI [-5.89, 4.39], p < 0.05), and Baduanjin (WMD = -3.42, 95% CI [-7.15, 0.45], p < 0.05, which indicated that Liuzijue was better than the other interventions for improving FEV1/FVC.

Cumulative probability ranking

The results of the cumulative probability ranking are shown in Fig. 4.

Fig. 4

Cumulative probability ranking. CT = conventional treatment

The results for FEV1 were ranked from highest to lowest and divided into five ranks: from 1 to 5. The ranking results were as follows: Baduanjin > Liuzijue > Wuqinxi > Taichi > conventional treatment.

Similarly, the FEV1% results were ranked from highest to lowest and categorized into five levels: from level 1 to 5. The specific results were as follows: Liuzijue > Baduanjin > Wuqinxi > Taichi > conventional treatment.

For FEV1/FVC, the results were ranked from highest to lowest and divided into five levels, from 1 to 5. The specific ranking results were as follows: Liuzijue > Wuqinxi > Baduanjin > Taichi > conventional treatment.

Subgroup analysis

Considering that differences in intervention time might have affected the study results, subgroup analyses were performed based on different intervention durations. Two subgroups were established: the duration of intervention < 6 months group and the duration of intervention ˃ 6 months group. The results are summarized in Supplementary Table S5. In the duration of intervention < 6 months group, Liuzijue showed superior results than the conventional treatment in improving FEV1. Moreover, Liuzijue was more effective than Baduanjin, Wuqinxi, and Taichi. In contrast, in the duration of intervention ≥ 6 months group, Baduanjin exhibited superior results than the conventional treatment in improving FEV1 and was more effective than Liuzijue, Wuqinxi, and Taichi. Based on the cumulative probability ranking results (Figure S2A, B), Liuzijue had better outcomes when the duration of intervention was < 6 months, whereas Baduanjin was considered superior for interventions lasting ≥ 6 months.In the duration of intervention < 6 months group, the results showed that improved FEV1% was observed with Liuzijue than the conventional treatment, and more effective Baduanjin, Wuqinxi, and Taichi. In addition, in the duration of intervention ≥ 6 months group, the results showed that Liuzijue was also better than conventional treatment and was superior to Baduanjin, Wuqinxi, and Taichi. The results of the cumulative probability ranking (Figure S2C, D) showed that Liuzijue was more effective in improving FEV1%. In the duration of intervention < 6 months group, the results showed that Liuzijue was superior to conventional treatment in improving FEV1/FVC, and was also superior to Baduanjin, Wuqinxi, and Taichi. In addition, in the duration of intervention ≥ 6 months group, the results showed that Liuzijue was also better than conventional treatment and was superior to Baduanjin, Wuqinxi, and Taichi. The results of the cumulative probability ranking (Figure S2E, F) showed that Liuzijue was the best option for improving FEV1/FVC.

Furthermore, subgroup analyses were performed according to the different baseline pulmonary functions (level of airway obstruction) of the COPD patients in the study, considering that the different baseline pulmonary functions could have a significant impact on the results of the study. Two subgroups were created based on the Global Strategy for Prevention, Diagnosis and Management of COPD: 2024 Report's classification of the severity of COPD patients: the moderate group and the severe group [18]. The results are summarized in Supplementary Table S6. In the moderate group, Liuzijue showed superior results than the conventional treatment in improving FEV1%. Moreover, Liuzijue was more effective than Baduanjin, Wuqinxi, and Taichi. In the severe group, the results showed that Liuzijue was also better than conventional treatment and was superior to Baduanjin, Wuqinxi, and Taichi. The results of the cumulative probability ranking (Table S7) showed that Liuzijue was more effective in improving FEV1%.

Finally, considering that the frequency of interventions might have affected the study results, subgroup analyses were performed based on the frequency of interventions. One subgroup was established: the frequency of intervention ≥ three times a week group. The results are summarized in Supplementary Table S8. In the frequency of intervention ≥ three times a week group, Liuzijue showed superior results than the conventional treatment in improving FEV1, FEV1% and FEV1/FVC. Moreover, Liuzijue was more effective than Baduanjin, Wuqinxi, and Taichi. The results of the cumulative probability ranking (Table S9) showed that Liuzijue was more effective in improving FEV1, FEV1% and FEV1/FVC.

Sensitivity analysis

Sensitivity analyses were performed by removing studies with sample sizes less than 30 and articles exhibiting a high risk of bias and lacking methodological rigor to verify the robustness of our results.

The results of the pairwise comparisons (Table S10, S11) and cumulative probability ranking (Figure S3, Table S12) were not significantly different from the overall results. Therefore, we conclude that our results are stable and reliable.

Publication bias

As shown in Fig. 5, owing to the small sample size and publication bias, the study findings need to be carefully explained.

Fig. 5

Funnel plot

Discussion

The Joint ACCP/AACVPR Evidence-Based Clinical Practice Guidelines for Pulmonary Rehabilitation [19] state that effective pulmonary rehabilitation measures can slow down the rate of decline in pulmonary function in patients with COPD. The level of pulmonary function is not only a reflection of the gas exchange function of COPD patients but also an objective indicator for evaluating the severity of the disease [20, 21]. In the clinical efficacy observation of COPD, three indicators, FEV1, FEV1%, and FEV1/FVC, are commonly used to reflect the pulmonary function status of patients [22,23,24,25]. The results showed that traditional Chinese exercises were effective in improving pulmonary function.Consistent with the results of a previous study, the Baduanjin and Liuzijue groups showed a significant improvement in FEV1 and FEV1% than that of the conventional treatment group [26]. The three sections of Baduanjin, "Two hands hold up the sky to manage the three jiao, left and right open the bow like shooting eagles, and regulate the spleen and stomach with a single lift," included respiratory muscle exercises along with meditation and adjusting breathing rhythm, which had the most apparent effect on the pulmonary rehabilitation of patients with COPD [27]. Baduanjin promotes air exchange efficiency by increasing the strength of the respiratory muscles, thereby reducing the amount of residual pulmonary air and alleviating the decline in pulmonary function [28]. The Liuzijue breathing method in interventions for patients with COPD improves pulmonary function by improving abdominal muscle tone and increasing the amplitude of their diaphragmatic ascending and descending movements, thus enhancing their respiratory muscle strength [29, 30]. Although the effect values in the Taichi and Wuqinxi groups were higher than those in the conventional treatment group, the difference was not statistically significant. As only five studies on interventions for patients with COPD in Wuqinxi were included in the literature, the effectiveness of Wuqinxi for COPD patients with COPD needs to be further demonstrated.

Consistent with the findings of previous studies, all traditional Chinese exercises were better than the conventional treatment in improving FEV1/FVC [10]. Traditional Chinese exercises are low- to medium-intensity aerobic exercises that are conducive to improving the oxygen-carrying and oxygen-transporting capacity of pulmonary capillaries, which in turn leads to the diastole of alveolar capillaries, improves the efficiency of air exchange, and ultimately enhances the pulmonary function of patients [9]. Conversely, traditional Chinese exercise emphasizes "breath regulation,” breathing training, and body movement synchronization, during the exercise process. Breath adjustment" is based on lip contraction and abdominal breathing, which effectively contract the respiratory muscles and increase alveolar ventilation and tidal volume, thereby improving the patient's ventilation and ventilation function and relieving the symptoms of dyspnea [11].

The cumulative probability ranking revealed that Baduanjin was most effective in improving FEV1, followed by Liuzijue. Liuzijue was most effective in improving FEV1% and FEV1/FVC. However, considering the small effect sizes and statistically insignificant differences in the two-by-two comparisons of the results between the Baduanjin and Liuzijue groups in improving FEV1, coupled with the cumulative probability ranking of the subgroup analysis based on baseline pulmonary function and duration of interventions showed that Liuzijue was the best intervention. Further exploration of this result of the cumulative probability ranking of improving FEV1 is still needed through studies with larger sample sizes. Contrary to the findings of a previous study that reported the effectiveness of Wuqinxi in improving FEV1/FVC, this study demonstrated the efficacy of Liuzijue regarding FEV1% and the FEV1/FVC. [10]. This could possibly be attributed to the inclusion of more studies in our review. However, based on this result, Li et al. concluded that Wuqinxi was the best intervention for improving pulmonary function. Furthermore, after evaluating more indicators and conducting a comprehensive analysis, we concluded that Liuzijue was the best intervention for improving pulmonary function. Liuzijue results in a slower respiratory rate and greater respiratory depth during exercise, allowing the respiratory muscles to be fully exercised and relieving respiratory muscle fatigue [29]. Liuzijue is a traditional Chinese exercise with moderate difficulty and a suitable load, emphasizing the use of six-character sounds combined with body movements to stimulate the movement of the visceral meridians [31]. Essentially, Liuzijue is a respiratory muscle exercise that combines lip contraction and fully reverses abdominal breathing to exercise the respiratory muscles and diaphragm. The lungs and thorax need to be expanded to improve ventilation, thereby preventing the premature collapse of small airways, improving pulmonary ventilation, and delaying the deterioration of pulmonary function in patients with COPD [30]. Traditional Chinese exercises such as Liuzijue are a great alternative complementary therapy for pulmonary rehabilitation that can be implemented without the limitations of time, equipment, and space, thereby improving the accessibility of pulmonary rehabilitation [11]. However, most current research has focused on the effects of traditional Chinese exercises. Therefore, future studies investigating the doses and mechanisms of different traditional Chinese exercises are warranted.

Our study had certain limitations. First, only Chinese and English databases were searched, which might have contributed to language bias. Meanwhile, the limited number of studies did not allow for subgroup analyses of studies in which the frequency of interventions was less than three times a week and where baseline pulmonary function was mild and very severe, so further attention should be paid to this issue in future studies. Second, owing to the large age range of the patients included in the study, we could not conduct a subgroup analysis based on age. These limitations should be considered when selecting effective treatments in clinical practice. In addition, due to the insufficient number of outcome indicators included in the study, other pulmonary function criteria and clinical outcomes were not analyzed, such as transfer factors and exercise capacity. Finally, although the network meta-analysis in this study revealed that Liuzijue is the best intervention for improving pulmonary function in patients with stable COPD, the results still need treated with caution given the small number of included studies and the potential risk of bias across the included studies.

The strengths of this study included the following: the PRISMA reporting guidelines, obtaining evidence from RCTs, and registration at INPLASY to improve transparency. The most effective traditional Chinese exercise for improving pulmonary function in patients with stable COPD was determined through a network meta-analysis, providing a valuable reference for clinical application.

Conclusion

Based on current evidence, Liuzijue is the best intervention for improving pulmonary function in patients with stable COPD. Owing to the uneven methodological quality and small sample size of the included literature, this study requires further validation from more high-quality, large-sample RCTs.