| Summary & Conclusion: In this randomized control study on 60 male patients undergoing CABG, the components of HRV power spectrum showed a significant decrease in VLF, LF, and HF in both the groups, decrease of LF/HF in yoga and increase in control group were observed. The heart rate increased significantly in both the groups.
The LF band of the HRV spectrum corresponds to sympathetic activity, the HF band of HRV spectrum corresponds to parasympathetic activity. The balance between the sympathetic and parasympathetic activity is indicated by LF /HF ratio. VLF band reflects the humoral factors affecting the HRV.
The observation of decreased sympathetic tone after YRT seems to validate objectively with the observations made by Huttan et al [3] who demonstrated increased calm scores after foot massage and guided relaxation technique in a similar setting.
In both the groups significant reduction in sympathetic tone has been observed with no significant difference between the groups. This indicates the recovery from the surgical stress. Since the pre-operative sympathetic tone was very high as seen by high LF power values and high LF/HF ratio (4.19) which is much greater than in a balanced autonomic status of normal people (LF/HF=0.5 [12]).
Although the complementary effect of YRT in restoring the sympathetic tone is not shown in the values of LF it is shown in LF/HF ratios. LF/HF ratio is an indication of autonomic balance. LF/HF ratio< 0.5 indicates of low sympathetic activity and > 0.5 indicates the high sympathetic activity [12]. Reduction of LF/HF ratio in this study after YRT may indicate recovery of autonomic balance in contrast to control group which showed a significant increase of LF/HF ratio. Thus YRT introduced in the first post –operative week, may help in faster restoration of autonomic balance.
With the reduction in LF spectrum after YRT one would expect a reduction in heart rate. Where as we observed a significant rise in heart rate. Observations in the changes in Heart rate showed greater increase in heart rate in control group (28bts/min) than YRT group (21bts/min). Since there is reduction in sympathetic tone (LF) the increase in the heart rate could be either due to decreased parasympathetic tone or humoral factors. In this case since the VLF band is reduced in both yoga and control group the increase in the heart rate may not be the effect of any local humoral factors. Hence it is most likely to be due decreased vagal tone as seen by decreased in the HF component.
In view of the fact that LF has significantly reduced with increase in HR we may conclude that this increase in HR is due to reduction of parasympathetic tone that is well known to occur in critically ill patients or patients with significant cardiac disease (Winchell et al [13]).
Several studies on autonomic function have been studied in normal healthy volunteers after yogic practices. After guided relaxation the power of LF component is reduced and increase in HF power value. The result suggests that reduced sympathetic activity after yoga based guided relaxation [14].
Observations on HRV after CABG by Bryniarski L et al [15] showed that cardiac rehabilitation speeds up the improvement in time domain HRV and frequency parameters after long term observations. Thus addition of yoga in cardiac rehabilitation in first post-operative week may hasten the recovery in frequency domain parameters of HRV. |
