Study of Tai Chi Chuan for Cardiovascular Disease Provides Little Guidance
Abstract & Commentary
By Dónal P. O'Mathùna, PhD, Senior Lecturer in Ethics, Decision-Making & Evidence, School of Nursing and Human Sciences, Dublin City University, Ireland. Dr. O'Mathùna reports no financial relationships relevant to this field of study.
Synopsis: A prospective before and after study examined the impact of Yang-style Tai Chi Chuan on cardiac parameters. Significant improvements were found for fasting glucose, blood pressure, and body weight. A subgroup analysis found that those who engaged in 80% or more of the sessions had some improvement in cardiovascular parameters. However, limitations in the study design and reporting weakened the strength of any recommendations based on the study's findings.
Source: Huang Y-T, et al. Adhering to a Tai Chi Chuan exercise program improves vascular resistance and cardiac function. Int J Gerontolog 2011;5:150-154.
Tai Chi Chuan is an ancient Asian form of exercise and relaxation. A number of different types of Tai Chi Chuan are practiced, but there is insufficient evidence to determine if the styles have clinical relevance. The most popular form is the Yang style, which was used in this study. Participants slowly go through a series of movements while controlling their breathing. Although the movements are relatively slow, Tai Chi has been classified as a moderately intense form of aerobic exercise. For this reason, and because of its low intensity, it has been recommended for older people.
Previous research suggested that Tai Chi may have beneficial effects on cardiovascular disease.1 The study reported here evaluated the effect of Tai Chi on markers of cardiac function and was conducted in Taipei, Taiwan. Participants were recruited from a Tai Chi club at a hospital in the city. All subjects exercised at least three times per week prior to the study, but the report did not state what form of exercise they undertook. Participants were free from cardiovascular disease, hypertension, hyperlipidemia, diabetes or other serious disease. None of the subjects was overweight (mean body mass index 23.4 kg/m2), 70% were female, and the mean age was 62.3 years.
The report stated that 122 subjects were recruited and 83 completed pre- and post-test measurements. All subjects participated in a Yang style Tai Chi program consisting of 24 movements carried out over 1 hour. Subjects practiced Tai Chi three times a week for 5 months. No control group was involved. Analyses were conducted on the 83 subjects who completed the measurements.
Outcomes were measured before and after the 5-month program. Blood analyses were conducted to measure fasting glucose, total cholesterol, LDL-cholesterol, triglyceride, C-reactive protein, and uric acid levels. Vascular resistance and vascular compliance were measured with a Dynapulse 200 M monitor (which uses a noninvasive cuff to measure arterial pulsation signals; details are published elsewhere.2).
After 5 months of Tai Chi, significant reductions (all P < 0.01) were found in body weight (0.6 kg), systolic (8 mm Hg) and diastolic blood pressure (6 mm Hg), and fasting glucose (4.7 mg/dL). No significant changes were found for pulse pressure, heart rate, or other biochemistry levels. Of the 12 cardiovascular parameters measured by the Dynapulse monitor, only systemic vascular resistance (SVR) was significantly lowered.
The data from the study were further analyzed according to two subgroups: an adherent group (who attended more than 80% of the Tai Chi sessions) and a non-adherent group (attended < 80%). It was not mentioned if this subgroup analysis was planned prior to the study. The adherent group contained 33 subjects with 34 in the non-adherent group. No explanation was provided regarding why the two groups contained 16 fewer subjects than the total who completed the study.
The two subgroups did not differ significantly at baseline. After the 5-month Tai Chi program, the adherent group had significantly lower triglyceride levels than the non-adherent group. No other biochemistry levels differed significantly. Regarding cardiovascular parameters, the adherent group had significantly more improvement in left ventricular contractility, cardiac output, cardiac index, stroke volume, and SVR (all P < 0.01). The non-adherent group had significantly better brachial artery compliance (P = 0.02).
The authors acknowledged that their study had limitations; a relatively small number of subjects was involved, and only indirect measures of cardiac performance were measured. The subjects were already involved in a Tai Chi club and may have been engaged in other health-promoting activities compared to the general population. The reasons for non-adherence were not explored. Other confounding factors were not examined. They concluded that "longitudinal studies over several years are required to determine the effects of TCC [Tai Chi Chuan] on these clinically important outcomes."
This study is of limited value in evaluating the effectiveness of Tai Chi on cardiovascular disease. The lack of a comparison group means that confounding factors cannot be ruled out as contributory factors to any changes. No power analysis was reported to demonstrate how many subjects were needed in the study. The report did not discuss the factors contributing to the changing numbers of subjects in the various stages of analysis: why 122 subjects were recruited, complete data were reported for 83 subjects, and then only 67 subjects were included in the subgroup analysis.
Another limitation not discussed in the report was the contribution of multiple hypothesis testing.3 When statistical significance is set at P = 0.05, there is a 1 in 20 chance of getting a false positive. The chance of obtaining a false positive result increases with each additional outcome tested. For example, with five outcomes, the calculated chance of a false positive is almost 1 in 4.3 The study measured numerous outcomes without a priori selection of primary and secondary outcomes. A statistical test (like the Bonferonni Correction) should have been conducted to take account of the problems with multiple hypothesis testing. In addition, it was not clear if the subgroup analysis was planned prior to conducting the study, or if it was developed after the initial analysis including all subjects revealed few significant improvements.
Overall, the design of the study without a control group introduced serious limitations in its attempt to evaluate the effectiveness of Tai Chi. The use of multiple outcome measures and the sub-group analysis introduced further limitations. A number of important factors were not described in the article reporting the study.
A systematic review was previously conducted of Tai Chi for patients with cardiovascular disease or risk factors for cardiovascular disease.1 This review included many studies published in Chinese which previously had not been examined in English reviews. The review found some evidence of benefit, but concluded that the literature was limited. Given this, the reviewers concluded that Tai Chi may be a reasonable adjunct to conventional care, especially for those who are unwilling or unable to engage in other forms of physical activity. However, more rigorous research is needed to provide clearer evidence of its effectiveness.
1. Yeh GY, et al. Tai chi exercise for patients with cardiovascular conditions and risk factors: a systematic review. J Cardiopulm Rehabil Prev 2009;29:152-160.
2. Brinton TJ, et al. Development and validation of a noninvasive method to determine arterial pressure and vascular compliance. Am J Cardiol 1997;80:323-330.
3. O'Mathùna DP, et al. Critically appraising quantitative evidence. In: Evidence-Based Practice in Nursing and Healthcare: A Guide to Best Practice, 2nd ed. Ed. Melnyk B, Fineout-Overholt E. Philadelphia: Lippincott Williams & Wilkins, 2010; 81-134.