Cardiovascular reactivity to stress in long-term yoga practitioners

ABSTRACT

Background:

Bhramari Pranayama yogic breathing is a very simple exercise of voluntary breathing which mitigates stress reactivity through autonomic modulation of heart rate.

Aim:

To study the effects of long-term practice of the yoga breathing exercise on cardiovascular reactivity to head-up tilt (HUT) test.

Methods:

All the participants were subjected to a 10-item yoga questionnaire. Based on Likert scale scoring, 32 subjects (group I) were selected as long-term yogic breathing practitioners, and autonomic function tests using heart rate variability (HRV) and a provocative stress test and HUT test were conducted. Cardiovascular parameters obtained were compared with controls who had never been engaged in any form of yoga (group II).

Results:

A highly significant decrease in values of both high (HF) and low frequency (LF) variables was observed in group II as compared to group I. However, a highly significant rise in LF/HF has been observed in group I compared to group I (P = 0.004), further indicating a greater withdrawal of vagal tone during the HUT test and also during recovery (P = 0.001).

Discussion:

The results and discussion of HRV analysis during provocative tests concluded that autonomic imbalance was present in the subjects who were not exposed to any form of yoga. Thus, it is advisable to practice yoga in any form regularly to mitigate the early onset of autonomic dysfunction.

Introduction

There are several benefits of yoga available in numerous literature, and practicing yoga regularly is essential to develop coping skills during stress. Bhramari Pranayama yogic breathing is a very simple exercise of voluntary breathing which mitigates stress reactivity through autonomic modulation of heart rate. One is supposed to sit comfortably in padmasana pose with his or her eyes closed, ears closed with index fingers, and deep breathing to be performed along with chanting during Bhramari pranayama. This has to be repeated five times which means five cycles daily, preferably in the morning between 7 and 7:30 am.[1,2,3,4]

Heart rate variability (HRV) is the variability in the interval between consecutive heartbeats or variability in the instantaneously calculated heart rates. It provides a dynamic window to the autonomic modulation of heart rate through parasympathetic and sympathetic nerves. Heart rate response to head-up tilt (HUT) is considered a useful tool for assessing sympathovagal imbalance in a person. To check for the integrity of the cardiovascular autonomic nervous system for autonomic reactivity, a few non-invasive provocative stress tests are used. Heart rate response to HUT is considered a useful tool for assessing sympathovagal imbalance in a person.[5,6,7]

Few studies have stated the role of yogic breathing exercises in cold pressor tests and electroencephalography (EEG) waves pattern, but there are no studies done to assess the cardiac autonomic control to provocative stress tests using HRV.[8,9,10] Thus, the objective of our research was to study the effects of the long-term practice of yoga breathing exercises on cardiovascular reactivity.

Materials and Methods

All procedures were approved by the Institutional Ethics Committee and Review Board based on the Declaration of Helsinki, and the study has been claimed as ‘exempted’ due to the non-invasive approach of our study.

The study comprises 86 men and women with years of regular slow yogic breathing practice (pranayama) recruited from the general community of Sharda University. All participants were aged between 30 and 45 years. Screening of the participants for long-term yoga practice was done by an online yoga questionnaire circulated across the population of Sharda University. The 10-item yoga questionnaire was systematically incorporated by the faculty experts engaged in the practice of yoga and medical education, along with the help of a previously published article in BMJ Open. It included the number of years of consistent practice in yoga, the rate of the importance of slow breathing if there is any improvement in mental and physical strength, and lifestyle changes, all rated on a five-point Likert scale (1 = not at all to 5 = very much). For the inclusion of participants in our study, strict criteria of an average Likert scale score of more than 4 were considered. Thus, based on the above criteria, only 32 participants (22 men and 10 women) could be considered for further study as stated in Table 1a and b. The reliability quotient for each item with Cronbach’s Alpha is 0.8.[11]

Table 1a.

Yoga questionnaire

Number of years of yoga practice

Number of hours of practice per week

My physical health has improved as a result of yoga

My mental health has improved as a result of yoga

I have changed my lifestyle as a result of yoga

My stress level has improved as a result of yoga

My flexibility has improved as a result of yoga

My concentration has improved as a result of yoga

My sleep has improved as a result of yoga

Rate the importance of slow breathing

Table 1b.

Workflow design

Healthy controls (n = 40) were recruited from the community who were not having any experience of any form with yoga or meditation. We excluded diagnosed hypertensive subjects, patients on medications, subjects who were diabetic or had any cardiovascular disease, who were on tobacco use or alcohol or using any psychopharmacologic drugs, and who were pregnant. After explaining the aim of this study to each participant in their own language, written informed consent was obtained from each subject of the study.

ECG analysis was performed. Each subject was asked to lie down on the couch and rest for 10 min. Following this, blood pressure was measured using an aneroid sphygmomanometer, and 12 lead ECG analysis was done by placing pregelled electrodes on the right arm, left arm, and left leg, and six precordial leads were placed on the chest of each subject. The ECG recording was done for 10 min.

Autonomic Function Tests

Basal Heart Rate Variability (HRV)

Using Powerlab 26T Polyrite D system, HRV was analyzed. Both time domain and frequency domain analyses were done and compared between the two groups of subjects. The sampling rate in our machine was 256 Hz. Filters used: For HRV, high filter-99 Hz, low filter-0.1 Hz. Screen speed: The screen speed was 30 mm/s.

Time domain parameters: mean of standard deviations of all NN intervals (SDNN), root mean square of successive differences between normal beats (RMSSD), and the mean number of times NN intervals exceed 50 ms (NN50)

Frequency domain parameters: low frequency (LF), high frequency (HF), and LF/HF ratio.

HRV During Head-Up Tilt Test (HUT)

Autonomic function tests were done in the physiology department. The whole procedure was explained in detail to each subject in his/her own language to allay any fear or apprehension. Subjects were comfortably laid down on a tilt table with foot plate support—a blood pressure cuff tied on the nondominant arm at rest. After resting for 10 min, subjects underwent passive HUT to 70° angle. HRV and BP were immediately recorded, followed by a recovery period of 5 min when the same hemodynamic parameters were recorded again.

Data Analysis

The statistical data analysis was performed using the software SPSS version 22.0. The analysis of the quantitative variables consisted of the calculation of the mean and standard deviation. An unpaired student t-test was used to compare independent groups. The level of significance was P < 0.05.

Results

Group I: Thirty-two subjects with a regular yogic breathing practice

Group II: Forty healthy age and sex-matched subjects with no experience in yoga

Basal Heart Rate Variability

The mean basal heart rate and HRV of both groups were compared in Table 2.

Table 2.

Time domain and frequency domain variables of basal heart rate variability in groups I and II

Parameter	Group I (mean±SD) n=32	Group II (mean±SD) n=40	P
SDNN (ms)	51.24±5.68	52.62±7.60	0.25
RMSSD	64.34±4.32	68.67±5.21	0.07
NN50	27.65±2.60	29.35±8.75	0.07
LF (nu)	46.75±2.68	48.86±5.52	0.10
HF (nu)	32.86±3.29	36.65±3.84	0.09
LF/HF	0.96±0.12	0.94±0.28	0.41

SDNN=Mean of standard deviations of all NN intervals, NN50=Mean number of times NN intervals exceed 50 ms, RMSSD=Root mean square of successive differences between normal beats, LF=Low frequency, HF=High frequency

Mean basal heart rate and RR intervals were within the normal range and comparable in the two groups. No statistical difference in the values of basal HR and RR was observed. The mean values of SDNN and NN50 were not significantly different in group II compared to group I. On comparison of frequency domain analysis of basal HRV, no significant difference was observed in all the frequency domain variables between the groups.

Head-Up Tilt Test (HUT) and HRV

The heart rate increased, and the R-R interval decreased in both groups during the HUT test; however, no significant difference was observed. The values of all the time domain variables during HUT were decreased. A highly significant decrease in RMSSD was observed in group II (P < 0.001), respectively, as compared to group I. The decreased values of time domain variables signify decreased vagal activity due to greater withdrawal of vagal tone and relative increase in sympathetic activity.

A highly significant decrease in values of both HF and LF variables was observed in group II as compared to group 1. However, a highly significant rise in LF/HF has been observed in group II compared to group I (P = 0.004), further indicating a greater withdrawal of vagal tone during the HUT test and also during recovery (P = 0.001).

The above findings of HRV are depicted in Figures 1-3.

Figure 1.

Comparison of time domain variables (mean number of times NN intervals exceed 50 ms & root mean square of successive differences between normal beats) during head-up tilt

Figure 3.

Comparison of low frequency/high frequency during the head-up tilt recovery phase in groups I and II

Figure 2.

Comparison of low frequency/high frequency ratio during head-up tilt

Discussion

The observations of the present study were consistent with the study conducted in a recent paper stating that heart rate is an important variable regulating health. An enhanced sympathetic activity promotes responses that prepare the body for strenuous physical activity in an emergency or stressful situation by the release of adrenergic agents that increase heart rate, the force of myocardial contraction, and vasoconstriction. On the other hand, parasympathetic activity dominates under resting, relaxed and nonthreatening circumstances; therefore, parasympathetic activity or vagal tone is cardioprotective by its opposing action.[12]

In the present study on the comparison of frequency domain variables of basal HRV of group II with group I, no statistical difference in mean values of LF (nu), HF (nu), and LF/HF ratio were observed. These findings were suggestive of the balanced tone of both the divisions of ANS in both groups under resting conditions. These observations were consistent with the studies by Östh J et al.[13] who reported that LF/HF is a better predictor of the relative level of sympathetic and parasympathetic influence.

The above findings of time domain variables of HRV in the prospective study are in accordance with studies by Sharma evaluated cardiac autonomic control by analyzing HRV using the HUT model and reported that tilt from 10°–70°, there was a significant decrease in all the parasympathetic indicators (SDNN, RMSSD, and NN50). Brown studied autonomic cardiovascular control during passive HUT by analyzing HRV and reported reduced HRV. The observations of the present study denoted that during the stress test (HUT), there was a greater withdrawal of parasympathetic input to the heart. Hence, there was a relatively over-sympathetic activity due to sympathovagal imbalance.[14,15]

The HRV analysis of frequency domain variables was in accordance with the studies of Koukam et al. Since LF (nu) is the marker of sympathetic activity and parasympathetic activity, HF (nu) is the marker of parasympathetic activity, therefore during HUT, significantly less increase in LF band variables and less value of HF variables in group II indicated less increase in sympathetic activity as well as a decrease in parasympathetic activity. From these observations during HUT, it can be concluded that in subjects with no exposure to any form of regular yoga practice, there is a greater withdrawal of parasympathetic activity along with less increase in sympathetic activity.[15,16]

Significantly raised values of the LF/HF ratio are also suggestive of altered sympathovagal balance. The above findings of HRV in this study further suggested greater withdrawal of vagal tone and persistent overdrive of sympathetic activity due to sympathovagal imbalance, resulting in delayed recovery from stress. These findings were in accordance with the studies of Grubb BP and Kenny.[17]

Conclusion

The results and discussion of HRV analysis during provocative tests concluded that autonomic imbalance was present in the subjects who were not exposed to any form of yoga. Thus, the practice of yoga not only calms our mind and reduces stress but also helps to maintain good sympathovagal balance to combat different physical and mental stressors in life.

Limitations

The study included only one type of yoga to eliminate any bias and maintain uniformity while analyzing, yet further studies can be done with other yoga practices.

Ethics statement

The studies involving human participants were reviewed and approved by the School of Medical Sciences & Research, Sharda University, Greater Noida, India. The participants provided their written informed consent to participate in this study.

Author contributions

All authors contributed to the manuscript revision and read and approved the submitted version. AB contributed to the conception and design of the study. SK conducted the data analysis.

Declaration of patient consent

The authors certify that they have obtained written informed consent forms from all participants.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.