Introduction
The main aim of autonomic system of is to maintain the optimal internal environment (Homeostasis) of the body. It governs various body functions which are normally carried out without conscious control.1
Numerous studies indicate a strong association between compromised ANS (e.g. decreased vagal activity or increased sympathetic activity) and sudden cardiac and non sudden cardiac death. Lifestyle modifications are also increasingly recognized as important factors in the treatment, prevention and rehabilitation of cardiovascular disorders. One highly popular and currently researched lifestyle modification is yoga. Regular Yoga practice has been postulated to help in prevention of disease, in particular, to streamline autonomic functions, specifically by modulating vagal efferents.2
Hence the present study was designed to know the effects of yoga on sympathetic nervous system.
Aims and Objectives
To evaluate the effects of yoga on sympathetic nervous system in yoga practitioners above the age group of 35 years.
To compare the results of sympathetic function tests in yoga practitioners with that of non yoga practitioners in the same age group.
Materials and Methods
An observational cross sectional study was carried out in 50 normal yoga practitioners and 50 normal non yoga practitioners above the age group of 35 years. Yoga practitioners were selected randomly from different yoga centers in Shimoga. Non yoga practitioners were selected randomly among non teaching staff of Shimoga institute of medical sciences, Shimoga. The ethical clearance for the study was obtained from the ethical committee.
Inclusion criteria
Study Group: Yoga practitioners attending yoga centers of both sex above the age group of 35 years in Shimoga.
Control Group: Non yoga practitioners of either sex above the age group of 35 years having similar exclusion criterias of study group will be selected from non teaching staff of SIMS Shimoga.
Exclusion criteria
Evidence of hypertension (BP > 140/90mmHg), known case of diabetes mellitus.
Subjects receiving drugs that are known to interfere with cardiac function such as beta blockers, sympathomimetic drugs, vasodilators and diuretics.
Associated disease or conditions known to affect autonomic function like Guillean Barre syndrome, Poliomyelitis, Diphtheria, Tuberculosis, Syphilis, Amyloidosis, Chronic renal failure and others.
Subjects with chronic history of alcohol intake and tobacco consumption in any form.
Subjects having cardiac and respiratory disorders.
Procedure
In each subject following physiological parameters were recorded.
Respiratory rate (cycles/minute)
Heart rate (Beats/minute)
Systolic and Diastolic blood pressure (mm of Hg) by using mercury sphygmomanometer.
In each subject following physiological parameters were recorded.
Respiratory rate (cycles/minute)
Heart rate (Beats/minute)
Systolic and Diastolic blood pressure (mm of Hg) by using mercury sphygmomanometer.
The sympathetic activity is assessed by
Blood pressure response to cold pressor test
Each subject was explained about the procedure and asked to sit comfortably in a chair and baseline BP was recorded. Then the subject was asked to immerse his hand in cold water maintained at 4-60 C, the BP was recorded at 30 sec intervals in the other arm for a period of 2 minutes.
Blood pressure response to sustained Hand grip exercise
Each subject was asked to sit comfortably in a chair. Initially the subject was asked to exert maximal hand grip strength on hand grip dynamometer with dominant hand. Then the subject was asked to exert 30% of maximal hand grip strength for 5 minutes (at least for 3 min) with dominant hand. Diastolic blood pressure was measured in the non-dominant hand at rest and at one minute intervals during hand grip. The maximum rise in diastolic BP (mm of Hg) during hand grip was noted.
Statistical analysis
Statistical analysis is done in consultation with statistician. All the data are entered in EPI INFO version 3.5.3 and analysis is done using SPSS software version 20.
All values are presented as Mean + Standard Deviation (Mean + SD). Comparison of mean values of parameters between Control and Study group is done by unpaired t test. Correlation between various autonomic function parameters
p Value >0.05 is taken as not significant.
p Value <0.05 is taken as significant.
p Value <0.01 is taken as highly significant.
p Value <0.001 is taken as very highly significant.3
Results
Table 1 Age (Years) of control and study Group :
Mean Age + SD of control Group- 41.38±4.208
Mean Age ± SD of study Group - 41.20±4.165
There is no significant variation in age of both Groups.
Table 2 Anthropometric measurements of subjects both in study group and control group.
Height (cms) of control and study Group :
Mean + SD of control Group- 164.34± 7.320 cms
Mean ± SD of study Group - 164.60± 7.972 cms
There is no significant (p=0.865) difference in the height of the subjects between the study Group and control Group.
Weight (Kg) of control and study Group:
Mean + SD of control Group- 64.88±8.86
Mean ± SD of study Group - 62.92±6.379
There is no significant (p=0.208) difference in the weight of the subjects between the study Group and control Group.
BMI (kg/m2) of control and study Group:
Mean + SD of control Group - 23.90 + 1.66
Mean ± SD of study Group - 23.18 + 1.13
There is significant (p=0.013) difference in the BMI of subjects between the study Group and control Group.
Table 3 Physiological parameters of subjects both in study group and control group.
Resting Pulse Rate (beats/min) of control and study Group:
Mean + SD of control Group- 72.82±3.486
Mean ± SD of study group- 70.64±3.286
There is highly significant (p=0.002) decrease in the Resting Pulse Rate of subjects in study Group compared to control Group.
Resting Respiratory Rate (cycles/min) of control and study Group:
Mean + SD of control Group- 14.04±1.603
Mean ± SD of study group - 13.02±1.491
There is a highly significant (p=0.001) **decrease in the Resting Respiratory Rate of subjects in study Group compared to control Group.
Resting Systolic Blood Pressure (mm of Hg) of control and study Group:
Mean + SD of control Group- 123.48±5.108
Mean ± SD of study group - 122.00±4.081
There is insignificant (p=0.113) decrease in the Resting SBP of subjects in study Group compared to non yogic Group.
Resting Diastolic Blood Pressure (mm of Hg) of control and study Group:
Mean + SD of control Group- 82.44±4.006
Mean ± SD of study group- 80.28±3.104
There is highly significant (p=0.003) decrease in the Resting Diastolic Blood Pressure of subjects in study Group compared to control Group.
Table 4,Table 5 Tests to assess sympathetic system functions in subjects both in study group and control group.
Blood pressure response to cold pressor test (increase in SBP in mm Hg) in control and study Group:
Mean SBP + SD of control Group- 15.44 ± 3.63
Mean SBP + SD of study Group- 12.9 ± 2.97
There is significant (p=0.000) increase in the blood pressure (SBP) response to cold pressor test in control Group compared to study group.
Blood pressure response to cold pressor test (increase in DBP in mm Hg) in control and study Group:
Mean DBP + SD of control Group- 13.04 ± 3.136
Mean DBP + SD of study Group- 11.20 ± 3.05
There is significant (p=0.004) increase in the blood pressure (DBP) response to cold pressor test in control Group compared to study Group.
Blood pressure response to sustained hand grip (increase in SBP in mm Hg) in control and study Group:
Mean SBP + SD of control Group - 13.4 ± 3.31
Mean SBP + SD of study Group- 10.8 ± 3.61
There is significant (p=0.000) increase in the blood pressure (SBP) to sustained hand grip exercise in control Group compared to study Group.
Blood pressure response to sustained hand grip (increase in DBP in mm Hg) in control and study Group:
Mean DBP + SD of control Group - 10.4 ± 3.32
Mean DBP + SD of study Group- 8.7 ± 3.40
There is significant (p=0.012) increase in the blood pressure response to sustained hand grip in control Group compared to study Group.
Table 1
| Parameter | Control Group | Study Group | Level of significance |
| Age (Years) | 41.38±4.208 | 41.20±4.165 | p= 0.830 |
Age (Mean + SD) of control and study Group
Table 2
| Parameters | Control Group | Study Group | Level of significance |
| Height (cms) | 164.34±7.320 | 164.60±7.972 | 0.865 |
| Weight (Kg) | 64.88±8.86 | 62.92±6.379 | 0.208 |
| BMI ( kg/m 2) | 23.90 + 1.66 | 23.18 + 1.13 | 0.013 |
Anthropometric measurements Mean ± SD of control and study group
Table 3
Physiological Parameters (Mean ± SD) of subjects in control and study group.
Table 4
| Blood pressure response to cold pressor test | Control Group | Study Group | Level of significance |
| SBP | 15.44 ± 3.63 | 12.9 ± 2.97 | 0.000 |
| DBP | 13.04 ± 3.136 | 11.20 ± 3.05 | 0.004 |
Blood pressure response to cold pressor test (increase in SBP and DBP)
Table 5
| Blood pressure response to hand grip exercise | Control Group | Study Group | Level of significance |
| SBP | 13.4 ± 3.31 | 10.8 ± 3.61 | 0.000 |
| DBP | 10.4 ± 3.32 | 8.7 ± 3.40 | 0.012 |
Blood pressure response to sustained hand grip (increase in SBP and DBP)
Discussion
Blood pressure response to cold pressor test
Under conditions of stress of physical or psychological origin, there is activation of sympathetic nervous system. The cold pressor response which consist of placing the hand into cold water acts as a painful stimulus and has been used to study the autonomic response of different individuals. The afferent fibers for this response are the pain fibers which are stimulated by placing the hand in cold water and the efferent fibers are sympathetic fibers. The response of 15-20 mm Hg increase in systolic BP and diastolic BP by 10 mmHg is considered as normal response to cold pressor test.
In our study there is significant decrease in SBP (p=0.000) and DBP (0.004) in study group compared to control group.
Similar to our study, Kiran et al performed a study on the influence of raja yoga meditation on cold pressor response. The purpose of the study was to compare the rise in the mean value of SBP and DBP in acute stressful conditions in Rajayoga meditators and non meditators by performing CPT. They found rise in mean value of SBP and DBP to be 6.32 ± 2.41 and 6.0 ± 2.65 respectively in meditators whereas non meditators showed increase in the mean value of SBP and DBP to be 13.88 ± 3.95 and 13.66 ± 3.35. There was significant(p=0.001) difference between the two groups. Meditation is believed to gradually diminish sympathetic dominance, resulting in better balance between the sympathetic & the parasympathetic, resulting in greater autonomic stability.
Regular practice of Rajyoga meditation does have a relaxing effect on the mind and body and decreases the blood pressure response to acute stress and pain. By modifying the state of anxiety, meditation reduces stress induced sympathetic over activity.4
Blood pressure response to sustained hand grip
In our study there is significant difference in the blood pressure response SBP (p=0.000) and DBP (p=0.012) to sustained hand grip exercise between the yogic Group and non yogic Group.
Blood pressure response to Sustained Hand Grip appear to be more sensitive parameters to detect autonomic function amongst the two Sympathetic function tests.
Similar to our study Khadka R et al studied the effect of yoga on cardiovascular autonomic reactivity in essential hypertensive patients. In their study 14 essential hypertensive patients, who were on salt.reduction and similar antihypertensive were randomized into two groups; control (n=7; age 42.2±11.9 years) and yoga (n=7; age 44.9±10.8 years). The yoga group practiced yoga for ½ h/d, 6 d/week for 6 weeks. The control group did not practice any type of yogic exercises or relaxation techniques. They concluded significant reduction in SBP was found after yogic practices in response to hand grip exercise.5
Similar to our study Kiran et al concluded that during hand grip test the mean value of changes in systolic and diastolic blood pressures in meditators are 13.12 ± 3.57mmHg and 11.96 ± 2.98 resp while in non meditators20.24 ± 4.83 and 17.20 ± 3.90 resp. The values are highly significant (P<0.001).6
Reduction in the blood pressure indicates a shift in the balancing components of autonomic nervous system towards the parasympathetic activity. This modulation of autonomic nervous system activity might have been brought about through the conditioning effect of yoga on autonomic functions.
Conclusion
With increased awareness and interest in health, one should adopt the non-pharmacological methods like Yoga exercise, meditation and lifestyle modification to control the modifiable risk factors responsible for cardiovascular morbidity and mortality. It can be concluded that Yogic techniques may affect the autonomic activity significantly blunting the sympathetic discharge and might help in reducing psychosomatic disorders.
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