European Journal of Cardiovascular Medicine

The segment of nervous system which employ at subliminal level known as autonomic nervous system (ANS),  it regulates various task  of the internal organs, including the  pumping activity by the heart, movements of the gastrointestinal tract, and secretion by various  body  glands.^[1]

The regulation of important body function such as blood pressure (BP), heart rate, temperature, respiration, gastrointestinal, bladder, and sexual function is dealt by the autonomic nervous system and its dysfunction lead to many diseases. ^[1] The good mental health and control and development of mind can be taken care of by practicing Yoga. ^[2]

In India, yoga is being practiced to maintain health and to get spiritual peace since a long time. It is believed that yoga practice is helpful to maintain good health. Some studies support this concept. A small number of clinical research studies  have suggested that improvement of  glycemic control can be achieved by yoga and hyperglycemia has been a main cause of compromised autonomic functions. ^[3,4]

Any activity that uses large muscle groups, and can be sustained continuously and is rhythmic in nature termed as aerobic exercise. It increases the need for oxygen.^[5]

The autonomic system is affected widely by exercise. During exercise heart and stroke volume are increased to compensate more blood supply needed in exercising muscles. The shielding and restorative effects of long term exercise training are linked to the effect on the autonomic nervous system.^[6]

The welfare of physical exercise in respect  to  hemodynamic, hormonal, metabolic, neurological and respiratory function enhancement  has been brought out in previous literature. ^[7]

Small number of  studies have found the effect of yoga training – pranayama and aerobic exercise on autonomic function tests in North India.  There is scarcity of data on  comparing  the effect of yoga and aerobic exercise training on autonomic functions. Therefore, this study was planned  to compare the effects of comprehensive yogic breathing program (kapalbhati  and anulom- vilom) and aerobic exercise on autonomic functions in healthy individuals.

The present study was performed  in the Department of  Physiology of tertiary care centre of north India. The research  was aimed to compare the effects of yoga and aerobic exercise training on autonomic functions.

Non- randomized comparative study.

Study   Duration:  1 June 2019 to 30 November 2020

Source Of Data

  The research was  carried out  in individuals of 30-50 age group, doing yoga (anulom-vilom and kapalbhati) and aerobic exercise fast walking and cycling.

Sample Size

Total 150 subjects were enrolled   in the study. The participants of study were split into in three groups, Yoga group, Aerobic Exercise group and Control group. Each group comprised of 50 subjects.

Sampling Technique: Purposive sampling technique was used for the study group and controls.

Ethical Consent

The institutional ethical clearance committee gave his approval before inception of the study. Informed written consent (in both English and Hindi) was taken from all the study subjects before beginning of the study.

Selection Criteria  of study Population  

Participants of age group 30-50 years of   both sexes, who were doing yoga and aerobic exercise  for   3 month  and  Individuals of  age group 30-50 years of  both sexes, who were not doing any  yoga or aerobic exercise were included in the study. Those participants  suffering from any disease like diabetes, hypertension or any chronic illness or autonomic disorders or any endocrinal, cardiovascular and neurological disorders or musculoskeletal abnormality  were excluded . Participants who did not give consent for study and Substance abusing like alcohol, cannabis etc.and pregnant female were also excluded from the study.

Parameters

General and Cardiovascular Parameters: Age, Sex, Heart Rate (HR) in beats per minute. and Systolic and Diastolic Blood Pressure in mm Hg.

       Autonomic Function Tests 

    Tests for  Sympathetic Functions

• Cold pressure test
• Sustained handgrip test

Tests for Parasympathetic Functions

• Deep breathing test,
• Valsalva maneuver test,
• Lying to standing test.

Experiment  Protocol

All the participants were subjected to detailed history and clinical examination . The study participants were described in short  about the experimental procedure. The procedure was  done in a quiet room. The study participants were instructed not to take any food after 10:00 pm on the previous night and avoid any  physical or mental stress, or any medicine that can  affect  central nervous system. They also told to have a good sleep at night before the day of examination. After the individuals had been briefed regarding the methodology and purpose of study, willingness to participate in the study was sought. After obtaining relevant history, autonomic functions were tested as following^-[8,9]

1. Sustained Handgrip Test- Sustained hand grip causes a rise in HR & BP.

Procedure- Study Participants were asked to hold hand grip dynamometer upto maximum tensiondeveloped.  Then 30% of maximum tension was sustained for 5 minutes. HR & BP recorded before & after holding hand grip dynamometer at 30 sec.

2. Cold Pressure Test- The reason of sympathetic system stimulation is physical or mental stress, when hand is dived in cold water it  acts as pain stimulus and lead to rise in blood pressure.

Procedure- Subject was seated at stool and procedure explained.  Person was asked to immerse the hand in water maintain at 4-6 degree. BP was measured at 30 sec. upto 2 minutes.

3. Valsalva Maneuver- Valsalva maneuver is forced expiration against closed glottis. This straining, associated with change in HR & BP. It has 4 phases-

Phase 1- Onset of strain. There is transient rise in BP without any change in HR due to an increased intrathoracic pressure.

Phase 2- Occurs during straining. Initially BP decreases. It inhibits the baroreceptors producing tachycardia and vasoconstriction. As a result BP returns to normal and HR increases.

Phase 3- It occurs following the release of strain which result in the transient decrease of BP without any change in HR.

Phase 4- Occurs in further cessation of strain. The BP slowly rises to reach above baseline level secondary to peripheral vasoconstriction called overshoot phenomenon. This stimulates baroreceptors producing bradycardia and drop in BP to normal level.

Procedure – Every subject was trained to perform a standardized VM. The procedure was explained, history of fainting attack was asked, ill fitting dentures were removed and then the subjects were made to practice the same. Subjects were asked to exhale into a mouthpiece connected to a mercury manometer, and to maintain an expiratory pressure of 40 mmHg for approximately 10 s. After training, every individual was able to perform the maneuver well. Participants were given a short break of at least 3 min between every 2 VMs. Each individual performed the maneuver a total of 3 times. During the ‘Valsalva Maneuver’ and 30 seconds after of  this maneuver, recording of ECG was done  in supine position in standard limb lead II. To get a final reading average of such three reading were calculated.

 The ‘Valsalva Ratio’ was calculated as under:

Valsalva ratio = Maximum RR distance after Valsalva Maneuver / Minimum RR distance during  Valsalva Maneuver

• Deep Breathing Test- The variation of HR with respiration is called Sinus Arrhythmia. Inspiration increases HR whereas expiration decreases HR.

Procedure- Subject was asked to lie supine quietly . Baseline ECG was recorded. Participant was instructed to breathe slow and deep (6 breaths/minute). HR was measured during inspiration and expiration. 6 longest R-R intervals and 6 shortest R-R intervals were selected. E / I ratio was calculated.

• Lying to Standing Test- When an individual changes its posture from lies down to a standing position, first a rise in Heart rate which is followed by to return baseline HR.

Procedure- Participant   was asked to lie down in supine position comfortably. After 5 minutes of rest, ECG was recorded. 30 beats in lying position; continue when subject change position from lying to standing 15 beats taken in standing position. 30:15 RR ratio was calculated.

Yoga

All subjects underwent 3 months of supervised kapalbhati and anulom-vilom  for 5 days a week and each session lasted for 20 minutes. Yoga started with 10 minutes of slow breathing exercise, Anulom-Vilom followed by 5 minutes of rest; then 1 minute fast breathing exercise, Kapalbhati followed by 2 of minutes rest and 4 cycles of   Kapalbhati exercise were completed in one day of yoga.

Aerobic Exercise

Aerobic exercise consisted of 20-30 minutes of cycling or fast   walking  aerobic exercise was also performed 5 days in a week.

Statistical Analysis

Data were expressed as Mean ± SD. Unpaired Student’s t- test   was used for differences between the study group and control group. A two tailed test (P<0.05) was considered statistically significant. MS excel and Software Package for Statistical Analysis IBM SPSS version 20.0.were used for statistical analysis.

Total 150 participants were selected for this study. Participants were equally distributed in three groups -Yoga group (n = 50), Aerobic Exercise group (n = 50) and control group (n = 50). Details of participants such as age, gender, vital parameters and findings of autonomic function test were collected. All participants were aged between 30 to 50 years with 40.5±6.9yrs as the mean age of all participants. There were a total of 112 males and 38 females in the study.

Among Yoga group (n=50), most common age group was   46 – 50 years age (42%), followed by 30 – 35 years (22%). Among Aerobic Exercise group (n=50), most common age group was   30 – 35 years age (36%), followed by 46 – 50 years (30%). Among Control group (n=50), more than one-fourth of the participants (28%) were 30 – 35 years age, followed by (24%) in other age group. The relationship of age group among all three group was statistically non-significant (p>0.05).

Among Yoga group (n=50), 80% were males and 20% of the participants were females. Among Aerobic Exercise group and Control group (72%) were males and 28% participants were females in each group. The relationship of gender among all three group was statistically non-significant (p>0.05).

Mean values of baseline Systolic BP was higher in Control group (123.8 ± 4.7 mmHg), compared to Aerobic Exercise group (121.4±3.8 mmHg) and Yoga group (119.2±4.8). Comparison of baseline Systolic BP was done by one way ANOVA test   in all three group was statistically significant (p<0.05). 

Mean values of baseline Diastolic BP was higher in control group (78.8±2.9 mmHg), compared to Aerobic Exercise group (76.6±3.1 mmHg) and Yoga group (76.4±5 mmHg). By applying one-way ANOVA test comparison of baseline Diastolic BP in all three group was statistically significant (p<0.05). (Table 1)

After doing handgrip test mean values of Systolic BP were significantly lower (p<0.05), while Diastolic BP and heart rate were significantly higher in Yoga group compared to Control group (p<0.05). However, increase in systolic and diastolic BP compared to baseline BP was significantly higher (p<0.05) in Yoga group as compared to Control group.

Mean values of Systolic BP and Heart rate were significantly higher (p<0.05), while Diastolic BP were non-significantly higher (p>0.05) in Aerobic Exercise group compared to Control group. However, increase in systolic and diastolic BP compared to baseline BP was significantly higher (p<0.05) in Aerobic exercise group as compared to Control group. (Table 2)

After doing handgrip test, mean values of Systolic BP were significantly lower (p<0.05) and Diastolic BP were significantly higher (p<0.05) in Yoga group compared to Aerobic exercise group. However, there was non-significantly higher levels of heart rate among Yoga group compared to Aerobic Exercise group (p>0.05).Though, increase in systolic BP as per baseline was significantly lower (p<0.05) and increase in diastolic BP as per baseline was significantly higher (p<0.05) in Yoga group as compared to Aerobic exercise group.

This research   was aimed to compare the effects of yogic practice-Pranayama (anulom- vilom and kapalbhati) and Aerobic exercises on autonomic functions.

Heart rate (HR) was recorded   in yoga group (post 3 months of yoga training ), Aerobic exercise group (after three months aerobic exercise training) and  control group. Baseline HR was non-significantly lower (p>0.05) in Yoga groups (77.5±3.5 per minute) and Aerobic exercise group (77.7± 5.3 per minute) as compared to control group (79.6 ± 4.5 per minute). Our study was in agreement with the study of Arto J. Hautala et al (2003), where they found a significant decrease in heart rate after aerobic training.^[10] Similar findings were observed by Athokpam Mirabai et al (2017) Sonika Choudhary et al (2018)   in their studies.^[11,12]   Previous study  showed that Yoga practice lead to  non- significant reduction in heart rate and it is attributed to increased vagal tone and decreased sympathetic activity. ^[13,14]

We recorded Blood Pressure   in yoga group (post 3 months of yoga training ), Aerobic exercise group (after three months aerobic exercise training) & control group. We observed baseline systolic blood pressure was significantly lower within normal limit in Yoga group (119.2 ± 4.8 mmHg) and Aerobic Exercise group (121.4±3.8 mmHg) as compared to Control group (123.8±4.8 mmHg). Mean values of baseline Diastolic BP were significantly lower but within normal limits in Aerobic Exercise group (76.6± 3.1 mmHg ) and Yoga group (76.4±5 mmHg ) as compared to Control group (78.8± 2.9 mmHg ).

In this study baseline SBP & DBP of yoga group and aerobic exercise group was decreased within normal limits as compared to control group. It was concordant with results obtained by  previous studies as well where they found significant decrease in systolic and diastolic BP after practicing yoga. ^[11,15,16]

After doing handgrip test, increase in systolic and diastolic BP as compared to baseline BP was significantly higher (p<0.05) within normal limit in Yoga group compared to Control group. It was discordant with the results obtained by Athokpam Mirabai et al (2017)  where they found an increase in SBP (ΔSBP)  and a decrease in DBP (ΔDBP) after the yoga practice. ^[11] This may be due to the short duration of yoga of 3 months which was not adequate enough to cause changes in the sensitivity of barometers to affect this parameter.

Cold pressor  test is the sympathetic stimulation by pain produced by cold water. We recorded our observations after Cold pressure test and found that the increase in systolic and diastolic BP as compared to baseline BP, within normal limit, was significantly higher (p<0.05), in Yoga group as compared to Control group. Our findings did not corroborate with the results obtained by Sonika Choudhary et al (2018), where, they found a significant decrease in ΔSBP and ΔDBP in response to cold pressure test after 3 months of Yoga training.^[12] This may be due to the fact that the yoga training in their study consisted of  asanas and pranayama including anulom – vilom and kapalbhati and studied the pre and post yoga training changes in the same group, in contrast to our study where the yoga group participants performed only Pranayama consisting of anulom-vilom ( slow breathing) and kapalbhati ( fast breathing) exercises and the findings were compared with a control group. However, our results were concordant with the observation obtained by Monika Maurya et al 2008 where they observed an increase in systolic and diastolic BP in response to Cold Pressor test after 3 months of slow breathing practice like anulom-vilom in hypertensive patients.^[17]

We also observed that after doing Cold  pressor  test (CPT), increase in systolic and diastolic BP, as compared to baseline BP, was significantly higher (p<0.05) in Aerobic Exercise group as compared to Control group.

However on comparing the effects of CPT between Yoga and aerobic group, we found that the increase in systolic BP as per baseline BP was significantly higher (p<0.05) in Yoga group as compared to the aerobic exercise group. This may be due to the fact that the baseline BP was lower in the Yoga group and was recorded at the end of 3 months of yoga training consisting of slow and fast breathing exercises. We have observed an increase in sympathetic activity which may be due to the effect of fast breathing exercise on autonomic functions as fast breathing leads to sympathetic activation.^[18]

 After doing Deep breathing test, mean values of Heart Rate during expiration was significantly lower (p<0.05) and E/I ratio was significantly higher (p<0.05) in Yoga groups as compared to Control group. It was concordant with result obtained by Sonika Choudhary et al (2018), Monika Mourya et al (2009) and  Pal GK et al (2004), where there was a significant rise in E/I ratio after yoga practice.^[12,17,19]

After doing Deep breathing test, mean values of E/I ratio was significantly higher in Aerobic exercise group as compared to Control group (p<0.05).  Improvement in autonomic functions after aerobic exercise group was due to generalized positive effect of aerobic exercise on the body.

Also on comparing the effect of  DBT between Yoga and Aerobic exercise group we found that heart rate during expiration was significantly lower in the yoga group (p<0.05). Deep breathing test is a test of parasympathetic functions. A rise in E/I ratio indicates an increase in vagal activity.

During inspiration,sympathetic activity increases and  vagal activity decreases and.^[20] Therefore, the heart rate rises during inspiration and decreases during expiration. The difference in heart rate in different phases of respiration is called as sinus arrhythmia. Yoga improves parasympathetic parameters. But E/I ratio was also found to be increased in aerobic exercise group.

This is an interesting finding of our study and we have observed the positive effect of aerobic exercise on autonomic functions. Our findings are concordant with Christian Alex et al who published a study in 2013 to see aerobic exercise and strength training effects on cardiovascular sympathetic functions in healthy adults.^[21] They reported that aerobic exercise training reduced the cardiovascular sympathetic indices. Also, Chung-yin Hsu et al in their, study found that exercise training has positive  effects on decreasing  autonomic dysfunction in CHF.^[22]  However, further research must be done after taking into account the duration and intensity of aerobic exercise..

Before doing  Valsalva test, mean values of Baseline Systolic & Diastolic BP were significantly lower (p<0.05), while after Valsalva test systolic BP was significantly lower (p<0.05) and diastolic BP was non-significantly higher (p>0.05) in Yoga groups compared to Control group (p<0.05). Though Valsalva ratio was significantly higher in Yoga groups compared to Control group (p<0.05). It was concordant with result obtained by Monika Maury et al (2009),Sonika Chaudhary et al (2018), where there was an increase in Valsalva ratio after yoga practice. ^[12]

 After doing Valsalva test increase in systolic& diastolic BP compared to baseline and Valsalva ratio was significantly higher (p<0.05) in Aerobic Exercise group as compared to Control group.

However, no significant difference was observed on comparing the findings of Valsalva test and Valsalva ratio between yoga & aerobic exercise group.

During and after valsalva maneuver,  changes occur in  sympathetic vasomotor activity and  in the cardiac vagal efferent  as a consequence of  stimulation of aortic arch baroreceptors and carotid sinus and other intrathoracic stretch receptors.^{[ 23]}  It is justified that Valsalva ratio is a test of parasympathetic functions and it was found to be increased in yoga group in our study however we also observed an increase in Valsalva ratio in the aerobic exercise group which indicates that aerobic exercise training may increase PNS activity.

This is an interesting finding in our study which is in accordance with Goldsmith et al  who reported that exercise training may increase PNS activity. ^[24] But various other studied have reported conflicting results therefore further investigations are required to understand the effect of aerobic exercises on autonomic functions.

In Lying position, mean values of Systolic & Diastolic BP were significantly lower (p<0.05), but in standing position mean values of Systolic & Diastolic BP was non-significantly higher(p>0.05) in Yoga group as compared to Control group. Though by changing position from Lying to standing decrease in systolic& Diastolic BP was significantly lower (p<0.05) in Yoga group, as compared  to Control group. However, no significant difference in 30:15 RR ratio was observed between yoga & aerobic exercise group.

Our findings were discordant with the results obtained by Monika Mourya et al (2009) where they found an increase in 30:15 R-R ratio in the slow breathing practice group as compared to fast breathing practice.

In Lying position, mean values of Systolic & Diastolic BP were significantly lower (p<0.05), but in standing position mean values of Systolic & Diastolic BP were non-significantly higher(p>0.05) in Yoga groups as compared to Aerobic exercise group. Though by changing position from Lying to standing decrease in systolic & Diastolic BP was significantly lower (p<0.05) in Yoga group, as compared to Aerobic exercise group. However, no significant difference in 30:15 R-R ratio was observed between yoga and aerobic exercise group. This may be due to short duration of yoga and exercise in our study.

Three months of   yoga training has lead to decrease in the baseline Heart rate, Systolic blood pressure &   Diastolic blood pressure within normal limit which is a potential beneficial effect of yoga on cardiac autonomic function. Three months of aerobic exercise training may increase Parasympathetic nervous system activity. However the present findings should be confirmed & further explored in future studies with longer duration of training program & in various populations before generalization of result. Both   Yoga   and  aerobic  exercise training have lead to improvement in autonomic functions. Fast breathing yoga exercise stimulates sympathetic activation. Measurement of autonomic functions may be important in designing training programs for individuals. More experimental work is required to elucidate the link between cardiovascular autonomic functions and yoga & aerobic exercise training.

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