Introduction
The autonomic nervous system is the portion of nervous system that regulates most of the visceral functions of the body. This system helps to control arterial pressure, gastrointestinal motility, gastrointestinal secretion, urinary bladder emptying and many other activities.1
Cardiovascular functions are controlled by neural factors primarily concern with the Autonomic Nervous System (ANS), which plays a major role in maintaining and regulating cardiac functions, e.g. systolic and diastolic blood pressure (SBP and DBP) and heart rate (HR). Imbalances in these lead to cardiovascular disorders such as hypertension, ischaemia, infarction, etc. Yoga is considered a holistic practice generating a sense of well-being through its various actions on physiological systems in a seemingly complex, yet integrated manner.2
Hence the present study was designed to know the effects of yoga on parasympathetic nervous system.
Aims and Objectives
To evaluate the effects of yoga on parasympathetic nervous system in yoga practitioners above the age group of 35 years.
To compare the results of parasympathetic 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.
Heart rate response to Valsalva maneuver
Each subject was asked to sit comfortably. A nose clip was applied and subject was asked to blow through the mouth piece attached to the mercury manometer for 15 seconds maintaining a pressure of 40mm Hg. Throughout the manoeuvre ECG is recorded continuously and for 30 seconds after release of strain. A marker button was used to indicate the point at which the subject started to do the Valsalva maneuver and also marked the point where he stops.
Heart rate response to Valsalva maneuver is expressed as:
Heart rate response from standing to lying:
Each subject was asked to stand quietly and then lie down without help while a continuous electrocardiogram was made from 20 beats before to 60 beats after lying down. A marker button was used to indicate the point at which the subject started to lie down. The individual R-R intervals were measured with a ruler from the ECG and the results expressed as a ratio of the longest R-R interval during the five beats before lying down to the shortest R-R interval during the 10 beats after lying down (standing to lying ratio; S:L ratio).
Heart rate response from standing to lying was expressed as
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 significant3
Results
Table 1 Mean age distribution of subjects both in study group and control group.
Table 2 Sex distribution of subjects both in study group and control group.
Table 3 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 4 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 5 Tests to assess parasympathetic system functions in subjects both in study group and control group.
Heart Rate response to Valsalva maneuver in control and study Group:
Mean VR + SD of control Group- 1.51 ± 0.166
Mean VR+ SD of Study Group - 1.43 ± 0.972
There is significant (p=0.005) decrease in the Valsalva ratio (VR) of subjects in study Group compared to control Group.
Immediate heart rate response from standing to lying (30:15 ratio) in control and study Group:
Mean Ratio + SD of Control Group- 1.34 ± 0.122
Mean Ratio + SD of Study Group- 1.31 +0.162
There is insignificant (p=0.260) difference in the immediate heart rate response to lying between the study Group and control Group.
Table 1
| Age in years | Control group | Study group |
| 35-40 | 26 | 23 |
| 41-45 | 11 | 17 |
| 46-50 | 13 | 10 |
Age distribution of subjects in study and control group
Table 3
| 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/m2 ) | 23.90+1.66 | 23.18+1.13 | 0.013 |
Anthropometric measurements Mean ± SD of control and study group
Table 4
Physiological Parameters (Mean ± SD) of subjects in control and study group
Table 5
| Parameters | Control Group | Study Group | Level of significance |
| Valsalva Ratio | 1.51± 0.166 | 1.43 ± 0.97 | 0.005 |
| Immediate HR response from standing to lying (30:15) | 1.34 ± 0.122 | 1.31 +0.162 | 0.260 |
Tests to assess the function of parasympathetic system
Discussion
Heart rate response to Valsalva maneuver
A normal response to Valsalva maneuver is characterized by a decrease in the pulse pressure & tachycardia during strain & blood pressure overshoot & bradycardia following the strain.4 The Valsalva maneuver tests the integrity of both parasympathetic & sympathetic divisions of autonomic nervous system. The hemodynamic changes during the maneuver are mediated via baroreceptors. With parasympathetic affection, the baroreceptor mediated reflex bradycardia response to elevated blood pressure will be reduced.
In the present study the mean value of Valsalva ratio in Study Group is 1.43 ± 0.972 and that of control group is 1.51 ± 0.166 thus showed a significant (p<0.005) decrease in study group compared to control group.
Khadka R et al conducted a study on effect of yoga on cardiovascular autonomic reactivity in essential hypertensive patients. They divided the hypertensive group into two, one group practiced yoga and the other one is taken as control. They measured The Valsalva ratio, which is a marker of parasympathetic reactivity and baroreflex function, which was low before yoga was found to be increased after yogic practices, indicating increase in parasympathetic reactivity and baroreflex sensitivity.5 This study was conducted on hypertensive patients which might be the reason for change in the finding compared to our study.
Heart rate response to lying
Normally, when a subject lies down from a standing position, there is brief initial rise followed by a fall in heart rate. The initial rise is due to rapid decrease of vagal tone and latter fall is because of increase of vagal tone. This is seen in normal subjects and is more marked in young individuals. It is maximal at the 3rd or 4th beat after lying down and is followed by a decrease in heart rate beyond the resting level to reach a plateau around beats 25-30.
The mean Ratio + SD of Study Group is 1.31 +0.162 and mean Ratio + SD of Control Group is 1.34 ± 0.122 In the present study there is insignificant difference ( p>0.05) in standing to lying ratio between the study group and control group.
Our study is not in accordance with the study conducted previously by Naveen K Z et al.6
Conclusion
We conducted an observational cross-sectional study to evaluate the effect of yoga on autonomic nervous system in 100 normal healthy subjects (50 yoga practitioners and 50 non yoga practitioners in the age group of above 35 years). Observations from our study suggest that regular practice of yoga can bring significant improvement in the autonomic balance, respiratory performance and wellbeing. It can thus be concluded that these results would justify the incorporation of yoga as part of lifestyle in prevention of hyperreactivity to stress related disorders and age related cardiovascular complications.
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