|Year : 2012 | Volume
| Issue : 6 | Page : 276-277
Tai Chi improves natural harmony in autonomic function
Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital and National Taiwan University, College of Medicine, Taipei, Taiwan
|Date of Web Publication||14-Jun-2012|
Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital and National Taiwan University, College of Medicine, Taipei
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Lan C. Tai Chi improves natural harmony in autonomic function. North Am J Med Sci 2012;4:276-7
Regular exercise improves physical capacity and quality of life in healthy individuals and patients with chronic disease. However, the major limitation of exercise participation lies in pathological abnormalities and limited accessibility. Chinese mind-body exercises, such as Tai chi, are easily accessible and have potential benefits for health promotion. Previous studies have shown that Tai chi is beneficial to aerobic capacity, muscular strength, microcirculation, and some cardiovascular risk factors. Furthermore, Tai chi appears to be safe and effective for patients with acute myocardial infarction (AMI), those who underwent a coronary artery bypass grafting surgery or had congestive heart failure. 
The interplay of sympathetic and vagal outputs of the central autonomic network through sinoatrial node produces beat-to-beat heart rate variability (HRV), and cardiac vagal function can be evaluated by spectral HRV analysis. Cardiac vagal modulation decreased in various pathological conditions, such as AMI and heart failure, and decreased HRV was found to be associated with poor clinical outcome. Low-frequency (LF) and high-frequency (HF) spectral HRV components are distinguished in a spectrum calculated from short-term recordings of heart beats, and LF and HF power may be measured in normalized units. Vagal activity is the major contributor to the HF component, and LF reflects both sympathetic activity and vagal activity. The LF/HF ratio is considered to mirror sympathovagal balance or to reflect the sympathetic modulations.
Exercise training may significantly increase HRV, and deep breathing has been shown to affect the depolarization of the sinus node and increase vagal outflow. Tai chi is an exercise integrating diaphragmatic breathing into body motions, and hence may increase HRV and has the potential benefits to better cardiovascular health. There are three studies that reported the effect of Tai chi to HRV in healthy subjects. ,, Väänänen et al.  reported that HRV increases immediately after Tai chi exercise in young and old male healthy subjects. Lu et al.  reported that Tai chi practitioners displayed higher HRV than the sedentary controls, which implied that Tai chi might enhance the vagal modulation and tilt the sympathovagal balance toward decreased sympathetic modulation. In a recent study, Audette and colleagues  reported that Tai chi training in sedentary women displayed increased HF power, representing increased vagal activity, and decreased LF power, representing decreased sympathetic activity in the Tai chi group. Although these studies showed positive effect to HRV, they usually recruited a small number of subjects and did not control the breathing rate.
In this issue of the Journal, Figueroa and colleagues  reported that they measured the autonomic responses (HRV and BP variability) and rate pressure product (RPP) for a Tai chi group and nontrained sedentary controls at rest and at two stressor phases (hand gripping and standing). The Tai chi group practiced classical Yang Tai chi for a minimum of 2 h/week and at least 6 months of training. Each training session consisted of 40 min of Tai chi practice, which comprised 108 movements. The respiratory rate was controlled at 12 breaths/min during the measurement of the autonomic variables to prevent the influence of breathing depth and frequency on HRV. The Tai chi group maintained a greater HF component at rest and during the isometric grip stressor phase, which indicated increased vagal outflow. Additionally, sympathetic outflow and RPP were significantly lower in the Tai chi group at rest, during the isometric grip and standing stressor phases. The results imply that the Tai chi group is more efficient in myocardial oxygen utilization during resting and pathological stress, and the autonomic responses favored parasympathetic outflow.
Furthermore, Figueroa and colleagues also found that LF modulation of systolic blood pressure (BP) variability, a noninvasive marker of sympathetic vasomotor modulation, was significantly lower at rest, during the isometric contraction and standing for the Tai chi group. Although increased variability of BP has been reported to be associated with higher incidence or mortality of cardiovascular disease, there is conflicting evidence whether BP variability can predict future cardiovascular events. More research is needed to substantiate the effect of exercise training to BP variability.
Although this study showed potential benefits of Tai chi to the autonomic function, its design is cross-sectional and the number of subjects is relatively small. To demonstrate the benefits of Tai chi to autonomic function, further longitudinal studies recruiting more subjects are needed. In addition, although increased parasympathetic flow shows benefits in some cardiac patients, whether it shows similar cardiaovascular benefits in healthy people remains to be elucidated.
| References|| |
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|2.||Väänänen J, Xusheng S, Wang S, Laitinen T, Pekkarinen H, Länsimies E. Taichiquan acutely increases heart rate variability. Clin Physiol Funct Imaging 2002;22:2-3. |
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