Prof. J.P.N. Mishra
The findings of the present study have very clearly shown a significant decline in the heart rate of experimental group of subjects, which were practicing the Yoga. Such significant changes were noticed at both three months & six months follow-up schedules. These findings depicting the positive effect of Yoga practice and are in accordance with the earlier studies.
Jyotsana et al (2001) studied the effect of yoga on cardiovascular system in subjects above forty years and they observed significant reduction in the heart rate in subjects practicing yoga. Although their observations were on similar line but in the subjects of higher age groups, whereas our findings, belong to adult group of subjects. They concluded that cardiovascular parameters alter with age but these alterations are shown in persons aging with yoga.
Raghuraj (1998) studied the effect of two selected yogic breathing techniques of heart rate virility (HRV). This study was conducted to evaluate the HRV in two yoga practices which have been previously reported to have opposite effects, viz, sympathetic stimulation (kapalabhati, breathing at high frequency, i.e., 2.0 Hz) and reduced sympathetic activity (nadisuddhi, alternate nostril breathing). The results showed a significant increase in low frequency (LF) power and LF/HF ratio while high frequency (HF) power was significantly lower following kapalabhati. There were no significant changes following nadisuddhi. The results suggest that kapalabhati modifies the autonomic status by increasing sympathetic activity with reduced vagal activity. The study also suggests that HRV is a more useful psychophysiological measure than heart rate alone.
Bhargava et. al. (1988) have shown that base line heart rate and blood pressure (Systolic and Diastolic) exhibited a tendency to decrease and both these autonomic parameters were significantly decreased at breaking point after pranayamic breathing. Although the GSR was recorded in all subjects the observations made were not conclusive. Thus Pranayama breathing exercises appear to alter autonomic responses to breath holding probably by increasing vagal tone and decreasing sympathetic discharges.
Telles et al (1993) determined whether yoga reduced heart rate and whether the reduction will be more after thirty days of yoga training. Two groups (yoga and control) were assessed on day one & day thirty during the intervening thirty days the yoga group received training in yoga technique while the control group carried out with their routine. Both the baseline heart rate of post follow-up heart rate were significantly lower in the yoga group on day thitry compared to day one. Our finding have also supported the trend of such changes.
Evaluating physiological responses to Hath yoga intervention of cardiovascular efficacy Funderburk (1977) observed significant reduction in heart rate blood pressure. Madanmohan et al (2004) assessed the impact of Hath yoga on heart rate & blood pressure and observed that even after short practice of Hath yoga heart rate came down significantly.
Meditation practice brings down serum Cortisol and total protein level along with systolic & diastolic blood pressure and heart rate. The percentage decrease in these parameters were up to 22% (Sudsunh et al, 1991)
Mishra and Shekhawat (2007) evaluated effect of Preksha meditation on cardiovascular response and lipid profile. Four weeks of Preksha meditation practice results in significant decrease in heart rate, blood pressure, total cholesterol, triglyceride, rate pulse pressure, mean pressure and increase in high density lipoprotein - total cholesterol ratio. Since rate pulse pressure is an index of myocardial oxygen consumption and load on the heart (Gobel et al, 1978), the authors concluded that Preksha meditation training decreases load on heart. A decrease in diastolic blood pressure along with heart rate have indicated reduction in sympathetic activity as reported by Ray at el (2001). Significant variation in spectral measurement of heart rate in experimental group of subjects practicing yoga could possibly due to variation in cardiac responsiveness to the change in vagal nerve traffic to the heart through parasympathetic channel (Singh at el, 1999). Goldberger at el (2003) have also postulated that heart rate variation increases with increasing vagal nerve traffic to the heart and then decreases with further increase in vagal tone. The findings of our study and another important scientific study conducted by Bijlani al el (2005) are in accordance with the results of Eradman at el (2002) who have concluded that a life style modification and stress management through yoga meditation leads to favorable cardiovascular response.
Strong sympathetic stimulation increases the heart rate four to five times and also the force with which heart muscle contracts there by increasing the cardiac output as much as two fold to three fold. Inhibition of the sympathetic nervous system can be used to decrease heart rate and strength of ventricular contraction. Strong parasympathetic vagal stimulation of the heart decreases the strength of heart contraction by as much 20-30%. In addition to that certain chemical compounds (hormones & cations) also influence the heart rate. Though the parasympathetic nervous system is exceedingly important for many other autonomic functions of the body, it plays only a minor role in regulation of the circulation. Its only really important effect is its control of heart rate through vagal nerve. (Guyton, 1982; Tortora at. el., 2006; Guyton, 1991).
The Electrocardiogram is composite record of action potential produced by all the heart muscle fibers during each heartbeat. Three clearly recognizable wave appear with each heartbeat. Those are P-wave, QRS complex & T wave.
The QRS complex represents rapid ventricular depolarization and T- wave indicates ventricular repolarization. Heart functions are manifested in the form of these waves and measuring the time span between the waves, called intervals or segments, gives the clear picture of the state of heart function. The S-T segment, which begins at the end of the S wave & ends at the beginning of T wave, represents the time when the ventricular fibers are depolarized during the plateau form of the action potential. The elevated S-T segment denotes acute myocardial infarction and depression in the S-T segment denotes the insufficiency of oxygen. Reduction in S-T segment denotes the strengthful and rhythmic depolarization followed by repolarization.
In the present study the author have observed reduction in S-T segment in the experimental group of subjects. This finding was supported by Stancak (1991). Satyanarayana (1992), while evaluating the effect of Shanti Kriya on certain psycho-physiological parameters, have also observed reduction in S-T segment.
Duren at el (2008) have stated that regular physical activity had the greatest influence on pulse wave velocity calculated from electrocardiogram. Similar results were also reported by Tanaka at el (2004), who found 20-35% reduction in S-T segment in middle aged men & women after relaxation exercise.
QT interval is measured from starting of Q wave to end of T wave which also includes S-T segment. This interval represents ventricular depolarization and repolarization. It is purely an indicator of ventricular function, the ventricles receive sympathetic nerves only, and thus QT internal is an indicator of sympathetic functions. Any change in the S-T segment as such represents the change in autonomic function. Our findings show a decrease in S-T segment, which thereby indicate a decrease in sympathetic activity and parasympathetic dominance.
Similar results were reported by Soichiro et al (1996). Ventricular depolarization and repolarization varies with changes in heart rate (Marques et al, 1997). The altered interval, if any is corrected over time by using Bazett's formula. Heart rate adjusted QT interval and S-T segment predicts mortality in certain pathological conditions including coronary heart disease, nephropathy and autonomic neuropathy (Landstedt et al, 1999). An increase may also be associated with an imbalance of sympathetic nervous system. A decrease in S-T segment suggests a stable balance in sympathetic 8c parasympathetic activation, rather parasympathetic dominance (Ewing et al, 1996 8c Parisi et al, 1999). Also there may occur a shift towards parasympathetic relative dominance as observed by decrease in heart rate (Patel, 1975). Our results are in conformity with these findings. This may be due to improved vagal tone after selected slow relaxative asanas and meditation. Changes in heart rate and respiration accompanying a meditation practice are intended to alter the state of mind alone (Wallace and Benson, 1972). It has been seen that certain yogies can alter the patterns of their cardiovascular functions, voluntarily create arterial fibrillation or stop their heart at their will (Kuvalyananada, 1968).
Duren at el (2008) has stated that regular physical activity had the greatest influence on pulse wave velocity calculated from electrocardiogram. Similar results were also reported by Tanaka at el (2004), who found 20-35% reduction in S-T segment in middle aged men 8c women after relaxation exercise.
Ventricular depolarization and repolarization varies with changes in heart rate (Marques et al, 1997). Heart rate adjusted RRIV and QT/QS2 ratio predicts mortality in certain pathological conditions including coronary heart disease, nephropathy and autonomic neuropathy (Landstedt et al, 1999). An increase may also be associated with an imbalance of sympathetic nervous system. A decrease in QT/QS2 ratio suggests a stable balance in sympathetic 8c parasympathetic activation, rather parasympathetic dominance (Ewing et al, 1996 8c Parisi et al, 1999). Also there may occur a shift towards parasympathetic relative dominance as observed by decrease in heart rate (Patel, 1975).
Our results are in conformity with the findings of several studies of the same field. This may be due to improved vagal tone after selected slow breathing in pranayama. Changes in heart rate and respiration accompanying a swas preksha practice are intended to alter the state of mind alone (Wallace and Benson, 1972). It has been seen that certain yogies can alter the patterns of their cardiovascular functions, voluntarily create arterial fibrillation or stop their heart at their will (Kuvalyananada, 1968). Other type of voluntary alteration of heart rate such as tachicardia, bradicardia, reduction of P-wave amplitude, achieving T-wave amplitude more than that of R-wave and arterial flutters have also been recorded (Talukdar, 1996).
These observations suggest that our practice module causes a shift in the autonomic equilibrium to the parasympathetic side. This inference is again supported by Dang et al (1999), in their findings, which they have stated in reference to certain other yogic practices.
