Point-by-Point Response to Reviewer Comments

Introduction

tress, an inevitable aspect of modern lifestyles, is a major contributor to non-communicable diseases such as cardiovascular and psychosomatic disorders, necessitating effective interventions to mitigate its physiological and psychological impacts. The autonomic nervous system (ANS), which governs the body’s stress response through its sympathetic and parasympathetic divisions, is critical in maintaining homeostasis. Techniques such as Kriya Yoga, Kapalbhati, Anulom Vilom and Bhastrikriya, along with practices like exercise and brain entrainment, have been explored for their potential to modulate ANS activity and promote psychophysiological balance. A study by Patil Sarang and Shirley Telles explored the effects of Cyclic Meditation (CM) and Supine Rest (SR) on Heart Rate Variability (HRV), a marker of autonomic nervous system activity, in 42 male volunteers over two 35-minute sessions. CM, combining active yoga postures and guided relaxation, showed significant autonomic modulation, with increased heart rate and low-frequency (LF) HRV power. This indicated sympathetic activity during yoga postures and elevated high-frequency (HF) power, reflecting parasympathetic activity post-practice. In contrast, SR resulted in no significant autonomic changes^1,2. The findings suggest CM effectively enhances parasympathetic dominance and promotes relaxation, underscoring its potential for stress management and autonomic balance improvement^3,4. Khattab et al.⁵ Investigated the impact of Iyengar yoga on cardiac parasympathetic modulation in 11 healthy yoga practitioners (7 women and 4 men) who participated in five weekly 90-minute sessions, including two yoga and three placebo relaxation sessions. Using 24-hour Holter monitoring, they observed that HRV parameters linked to vagal tone, such as SDNNi and rMSSD, were significantly higher during yoga sessions than placebo sessions.

1. *Professor Dr Varun Malhotra, Additional Professor, Department of Physiology, AIIMS Bhopal, India; E-mail: varun.physiology@ aiimsbhopal.edu.in

2. Chanchal Suryawanshi, Yoga Instructor, AYUSH, AIIMS Bhopal, India

3. Francisco J Cidral-Filho, Scientific Officer, LaNEx, University of Southern Santa Catarina, Brazil, Integrative Wellbeing Institute, Windermere, Florida, USA, RE.L.PO.N. Research Laboratory of Posturology and Neuromodulation. Master’s Program in Posturology. University La Sapienza of Rome, Italy

4. Professor Dr Santosh Wakode, Professor & Head, Department of Physiology, AIIMS Bhopal, India

5. Dr Amy Thomas, Student, Department of Physiology, AIIMS Bhopal, India

6. Patrick K Porter, Quantum University, Honolulu, HI - USA

*for correspondence

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Additionally, increased mean RR intervals and overall HRV during yoga indicated enhanced parasympathetic activity. As a safe and practical approach, the study concludes that Iyengar yoga may improve autonomic balance and lower cardiac mortality risk, making it a valuable tool in cardiac rehabilitation programs⁶. The article “Stress and the Autonomic Nervous System: Implications of Yoga” by Udupa, Bhavanani and Ramanathan explores the relationship between modern stress, the autonomic nervous system (ANS) and yoga’s potential to enhance cardiovascular autonomic functions⁷. Stress, a key part of modern competitive life, fuels non-communicable diseases like heart disease and psychosomatic disorders, with amygdala hyperactivity raising cardiovascular risks⁸. The ANS, comprising the sympathetic and parasympathetic systems, maintains homeostasis, with the former driving “fight or flight” responses and the latter supporting “rest and digest” functions⁹. Cardiovascular autonomic control relies on the delicate balance of these systems, evaluated through tests like the Valsalva maneuver and HRV analysis, which provide valuable insights into autonomic function¹⁰. Yoga, an ancient Indian discipline, is emphasized for its ability to harmonize sympathetic and parasympathetic systems, promoting homeostasis. Practices such as pranayama (breathing exercises) and asanas (postures) enhance parasympathetic activity while reducing sympathetic overdrive, proving beneficial for hypertension, diabetes, and anxiety¹¹. Research demonstrates that chronic yoga lowers stress and improves autonomic regulation, although acute effects may vary. Notably, pranayama techniques like alternate nostril breathing are particularly effective in modulating autonomic responses. Stress is a prevalent concern in modern life, necessitating effective interventions to manage its physiological and psychological impacts. Various techniques, including Kriya Yoga, Kapalbhati, Anulom Vilom, Bhastrikriya, Chandra Nadi, Surya Nadi, exercise and brain entrainment, have been explored for their influence on stress indices. These methods are known to modulate autonomic nervous system activity and promote psychophysiological balance. However, scientific studies comparing their relative efficacy are limited. Each technique offers unique mechanisms for stress reduction, such as improving heart rate variability (HRV), enhancing parasympathetic activity, or altering brain wave patterns associated with relaxation. Our research systematically evaluates these techniques to identify the most effective method for reducing stress indices, providing evidence-based insights into their comparative benefits.

Methods

This study employed a within-subjects crossover design to evaluate the acute effects of yogic and non-yogic interventions on stress indices. Thirty (30) healthy volunteers underwent all eight interventions (Kriya Yoga, Kapalbhati, Anulom Vilom, Exercise, Brain Entrainment, Bhastrikriya, Chandra Nadi and Surya Nadi) in a randomized sequence. Sessions were separated by a 48-hour washout period to minimize carryover effects. This interventional study was conducted at the Department of Physiology, All India Institute of Medical Sciences (AIIMS), Bhopal from 2019 to 2025, after obtaining ethical approval from the Institutional Human Ethics Committee (IHEC-LOP/2021/IM0427 dated: 26/10/2021, IM0425 dated 27/10/2021 and IM0179 dated 26/08/2018).

Based on a medium effect size (Cohen’s d = 0.5), a significance level of 0.05 and 80.0% statistical power, the sample size required for the study was 30 participants.

The inclusion criteria required individuals to be between 18 and 45 years of age, with no history of chronic diseases such as cardiovascular, respiratory, or neurological conditions and no recent acute illnesses within the past four weeks. Exclusion criteria included a diagnosis of lung diseases such as asthma or chronic obstructive pulmonary disease (COPD), spinal deformities that could affect posture, pregnancy and regular use of medications known to influence autonomic function, such as beta-blockers.

All participants provided written informed consent. The study duration was from 2021-2025.

Participants were trained in each yoga technique by certified instructors prior to data collection. Practices such as Kriya Yoga-Slow Deep Breathing, Kapalbhati, Anulom Vilom, Bhastrikriya and Nostril Breathing were demonstrated to participants just before the intervention to ensure proper understanding and execution. Similarly, the exercise and brain entrainment protocols were also demonstrated immediately before their implementation and no prior experience was required.

To control for confounding variables, all sessions were conducted in a pre-meal state, with participants fasting for at least two hours prior to the intervention. The room temperature was maintained within a thermoneutral range of 22-24°C to ensure environmental consistency. Participants were instructed to wear loose, comfortable clothing and to abstain from caffeine and alcohol for 24 hours before each session.

Participants were allowed 10 minutes to rest before data collection and were dressed comfortably. The room temperature was comfortable, and all recordings were done in a quiet environment. The Neural Check Spinal Energy system (BrainTap® Inc., New Bern, NC) measured stress levels using a digital neurodynamic analyzer. This device adheres to cardiac interval measurement standards set by the European Society of Cardiology and the North American Society of Electrophysiology¹². It provides real-time monitoring of functional state indices by analyzing heart rate data derived from an electrocardiogram (ECG). The device measures the vitals in 5 minutes. Using water or gel, two electrodes were placed on the wrists, and baseline recordings were obtained over five minutes. ECG data were recorded during meditation using the Neural Chek system.

Slow deep breathing

Participants practiced slow deep breathing (SDB) while seated comfortably. Their posture included a straight spine, relaxed shoulders, a slightly drawn abdomen and a chin parallel to the ground. Participants focused on the point between their eyebrows during the 10-minute SDB session, following a 15-count nasal inhale, breathe hold and exhale rhythm. If 15 counts were difficult, the count was reduced to a comfortable level. The breathing rate was 2-4 breaths per minute, pacing at approximately two counts per second.

Kapalbhati pranayama

Under the guidance of a qualified yoga instructor, participants practiced kapalbhati pranayama while seated comfortably with a straight spine, relaxed shoulders and the abdomen drawn in. This practice involved deep inhalation followed by forceful exhalation, facilitated by rapid diaphragm and abdominal muscle movements. Due to its high intensity and risks like pneumothorax, the session was restricted to five minutes. Participants were cautioned to perform this practice only under expert supervision.

Right and Left Nostril Breathing: Surya Nadi and Chandra Nadi Pranayama

Volunteers rested for at least 10 minutes before data collection and wore comfortable clothing. The room temperature was maintained at a thermoneutral range, and silence was ensured during the sessions. Breathing exercises were performed pre-meal, with participants advised against prolonged breath-holding to reduce organ pressure.

Surya Nadi pranayama involves right-nostril breathing with specific counts (25-12-25 at 2 counts/sec), while Chandra Nadi uses left-nostril breathing with identical timing. Variations include Surya and Chandra anuloma viloma (right/left-nostril inhale-exhale cycles).

Exercise protocol

Participants rested for 5 minutes for baseline recordings followed by 5-10 minutes of warm-up. They then performed stationary cycling at a mild intensity (30.0-50.0% of their maximum heart rate) for five minutes, stopping if discomfort or a sudden heart rate increase occurred. Spinal energy was recorded during the resting phase, every five minutes during the 20-minute exercise, and recovery.

Alternate nostril breathing

During alternate nostril breathing (ANB), participants maintained an upright posture. Their gaze was directed between their eyebrows. The session consisted of 5 minutes baseline rest and 5 minutes of ANB, involving inhaling through one nostril, holding (6-12 counts), and exhaling through the other. The nostrils were alternated for each cycle. Breathing was paced at 2 counts/second, with inhalation and exhalation lasting up to 25 counts each.

Data were tested for normality and found to follow a parametric distribution. Results are expressed as Mean ±SD. Using GraphPad software, paired t-tests were conducted to compare stress Index parameters between resting and during interventions.

Parameters

Stress index

Stress index is used in heart rate variability (HRV) analysis to assess the autonomic nervous system’s (ANS) response to stress. The Stress Index is derived from RR intervals measured by ECG. The stress index is calculated based on the distribution and variability of these intervals.

Calculation steps: A) Obtain RR Intervals: Measure RR intervals from ECG data. These represent the time (in milliseconds) between consecutive R-peaks on the ECG waveform; B) Build a Histogram of RR Intervals: “Histogram of RR intervals (ms) versus frequency”; C) Apply Baevsky's Stress Index Formula:

The Stress Index is derived using the formula:

Stress Index = AMo² / (Mo × MxDMn)

[AMo: Amplitude (percentage) of the mode, i.e., the most frequent value of RR intervals; Mo: Mode, i.e., the most frequent RR interval value (milliseconds); MxDMn: The difference between the maximum and minimum RR intervals represents variability].

D) Interpret the stress index: i) A higher stress index indicates increased sympathetic nervous system activation, reflecting stress and ii) A lower stress index signifies parasympathetic dominance, representing relaxation⁷.

Results

Table I: Stress index values before and during various manoeuvres with p value

Study/Group	Mean (Before) ±SD	Mean (During) ±SD	n	p Value
Kriya Yoga	109.53±52.96	31.28±20.15	30	<0.0001
Kapalbhati	165.19±113.87	234.05±107.51	30	0.0098
Anulom Vilom	183.45±87.30	80.70±49.42	30	0.0001
Exercise	146.15±80.01	270.8±116.03	30	<0.0001
Brain entrainment	263.44±72.66	134.72±92.24	30	<0.0001
Bhastrikriya	119.21±30.33	109.32±43.44	30	0.3530
Chandra Nadi	136.33±129.55	42.10±20.25	30	0.0015
Surya Nadi	102.65±59.00	36.90±15.77	30	<0.0001

A mixed-design ANOVA was conducted to examine the effects of different conditions (Kriya yoga, Kapalbhati,…..) and time (before & during the condition ) on the Stress Index

The analysis revealed a significant main effect of different conditions, F(7, 160) = 20.041, p= <0.001, η² = 0.467. During Kapalbhati & exercise conditions, the stress index was increased as compared to before the condition; all the other conditions show a decreased stress index

There was also a significant main effect of time, F(1, 160) = 27.811, p = <0.001, η² = 0.148, with participants showing a significant difference in stress index during the condition compared to before the condition.

Furthermore, the interaction between condition and time was significant, F (1, 7) = 23.301, p = <0.001, η² = 0.505. Post hoc comparisons between different conditions are as per Table.

Table II: Post-hoc Comparisons between Conditions

Comparison	Mean difference	SE	t-value	Cohen’s d	p value
Kriya vs. AunVil	-68.452	19.374	-3.533	-0.901	0.007
Kriya vs. KapBht	-137.762	19.374	-7.111	-1.814	<0.001
Kriya vs. Exercise	-146.595	19.374	-7.567	-1.930	<0.001
Kriya vs. BT	-141.024	19.374	-7.279	-1.857	<0.001
AunVil vs. KapBht	-69.310	19.374	-3.577	-0.913	0.006
AunVil vs. Exercise	-78.143	19.374	-4.033	-1.029	0.001
AunVil vs. BT	-72.571	19.374	-3.746	-0.956	0.004
AunVil vs. SU	60.548	19.374	3.125	0.797	0.025
KapBht vs. BH	85.286	19.374	4.402	1.123	<0.001
KapBht vs. CH	110.405	19.374	5.699	1.454	<0.001
KapBht vs. SU	129.857	19.374	6.703	1.710	<0.001
Exercise vs. BH	94.119	19.374	4.858	1.239	<0.001
Exercise vs. CH	119.238	19.374	6.155	1.570	<0.001
Exercise vs. SU	138.690	19.374	7.159	1.826	<0.001
BT vs. BH	88.548	19.374	4.570	1.166	<0.001
BT vs. CH	113.667	19.374	5.867	1.497	<0.001
BT vs. SU	133.119	19.374	6.871	1.753	<0.001

Note: indicates statistical significance (p<0.05). Only statistically significant comparisons are shown. P values are adjusted using Holm's method for multiple comparisons. SE = Standard Error; Kriya: Kriya Yoga; AunVil: Anulom Vilom; KapBht: Kapalabhati; Exercise: Physical Exercise; BT: Brain Entrainment; SU: Suryanadi; CH: Chandranadi and BH: Bhastrika.

Figure 1 Figure 2 Figure 3

Figure 4 Figure 5

Figure 6

Figures 1, 2, 3, 4, 5 and 6: The stress index values demonstrated significant changes across various maneuvers, highlighting their impact on physiological responses

The stress index values demonstrated significant changes across various maneuvers, highlighting their impact on physiological responses. During Kriya Yoga, a 71.45% reduction in stress index was observed, reflecting its calming effect. In contrast, Kapalbhatti led to a 41.66% increase, suggesting heightened physiological activation. Anulom Vilom induced a notable 56.01% reduction, underscoring its relaxing influence. Exercise caused an 85.33% increase, indicating elevated stress levels due to physical exertion. Brain entrainment yielded a 48.86% reduction in stress index, signifying improved neural and physiological synchronization. Bhastrikriya resulted in a modest 8.30% reduction, showing limited impact compared to other techniques. Chandra Nadi produced a 69.14% reduction, while Surya Nadi reduced the stress index by 64.06%, emphasizing the calming effects of these pranayama practices. These findings reveal the diverse physiological effects of different interventions on stress index levels.

Figure 7: Stress index before and during maneuvers

Discussion

Kriya Yoga

Numerous examples in the science of Kriya Yoga demonstrate the mathematically precise relationship between a person's breathing rate and their various states of consciousness. When an individual’s mind is deeply engrossed - such as during an intense intellectual debate or while performing an exceptionally delicate or challenging physical task- their breathing naturally becomes very slow. This focused absorption of the mind is directly linked to a slower breathing rate. Conversely, the breath inevitably becomes rapid or irregular during fear, desire, anger, or other harmful emotional disturbances. For instance, while humans typically breathe 18 times per minute, a restless monkey breathes 32 times per minute. In contrast, animals known for their longevity- such as elephants, tortoises, and snakes- breathe slower than humans. A notable example is the giant sea turtle, which lives for up to 300 years and breathes only four times per minute³. This study explores the acute effects of slow deep breathing (SDB) with equal counts of inhalation, breath holding, and exhalation on heart rate variability (HRV) in 30 healthy Kriya Yoga practitioners with 10-20 years of experience⁵. Participants performed SDB with a respiratory rate of fewer than 4 breaths per minute, involving 15 counts each for inhalation, holding, and exhalation, for 5 minutes. The analysis of ECG recordings using the Neural Chek HRV system revealed significant increases in HRV time domain parameters such as SDNN and RMSSD, indicating improved autonomic regulation and parasympathetic activity. LF power increased markedly in the frequency domain, suggesting parasympathetic modulation during slower respiratory rates. In contrast, HF power decreased and the LF/HF ratio increased significantly, reflecting a shift in autonomic balance. Heart rate showed a significant reduction, highlighting the calming effect of SDB on the cardiovascular system. The observed changes were attributed to enhanced baroreflex sensitivity, respiratory modulation, and transient excitation of autonomic centres. The findings suggest that regular practice of SDB may serve as a non-pharmacological intervention to improve cardiovascular autonomic regulation and overall cardiovascular health

Kaplabhati

The study found that during the kapalbhati breathing exercise, there is a clear withdrawal of parasympathetic activity and an increase in sympathetic activation, similar to physical exercise^13,14,15. As noted by the authors: "Kapalbhati is initially energizing, cleansing, and heating. The finding of a prospective open-label pilot study suggests that during fast breathing, as in kapalbhati pranayama, parasympathetic withdrawal occurs¹⁶”. The stress response during the exercise was evidenced by: i) Increased heart rate and sympathetic activation, ii) Decreased parasympathetic markers (RMSSD, HF ratio), iii) Increased LF/HF ratio indicating sympathetic dominance and iv) Changes similar to those seen during physical exercise. The author’s state: “The changes of HRV during Kapalbhati are similar to that of physical exercise, and the cardiovascular improvement during kapalbhati is excessive but not correlated with the intensity of exercise^17”. However, this stress response appears temporary, with parasympathetic activity increasing after the kapalbhati ends. This makes kapalbhati potentially beneficial for those unable to exercise regularly, as “A person unwilling or unable to exercise may receive similar benefits to physical exercise if he practices kapalbhati pranayama¹⁷”.

Anulom Vilom Pranayam

The study demonstrates that AVP (alternate nostril breathing) helps reduce stress by modulating both cardiac and neural oscillations¹⁸. During AVP practice, researchers observed increased heart rate variability (HRV) parameters and beneficial changes in brain wave patterns¹⁹. The practice leads to a balanced autonomic state where parasympathetic and sympathetic activities reach equilibrium, resulting in a calm yet alert mental state²⁰.

The key findings show that AVP: i) Increases overall heart rate variability while maintaining a steady heart rate¹³; ii) Enhances alpha, beta, and gamma brain waves, indicating improved focus and relaxation²¹; iii) Creates a physiological state conducive to stress reduction through balanced autonomic function²² and vi) Generates inhibitory signals through slow breathing that help synchronize neural elements²³.

As the authors note: “Pranayama practice naturally slows breathing, which calms the heart^18” and “Yogic practices shift the autonomic nervous system balance from primarily sympathetic to parasympathetic, by directly enhancing parasympathetic output, possibly through vagal stimulation¹⁸”.

Exercise

The study demonstrates that mild-intensity stationary cycling exercise leads to significant autonomic modulation, mainly showing increased sympathetic activity and decreased parasympathetic control. As Malhotra et al. note, “During exercise, various cardiovascular adjustments take place in the body. Exercise transitions from parasympathetic to sympathetic control with increasing intensity^24”. The research found significant changes in heart rate variability (HRV) parameters during exercise, indicating increased physiological stress. Time domain parameters (SDNN, pNN50, and RMSDD) showed a significant decrease during exercise compared to resting values, demonstrating reduced parasympathetic activity. High-frequency power, which indicates parasympathetic activity, decreased during exercise, while there was a shift toward sympathetic dominance^25,26. The study also revealed that in untrained individuals, recovery from exercise-induced stress is slower, as “the HRV recovery is delayed, and maybe because the study participants are not trained athletes and require more time to recover from exercise²⁴.

Brain entrainment

The study found that brainwave entrainment (BWE) using audio-visual stimulation can effectively induce relaxation while maintaining alertness²⁷. During BWE sessions that included guided slow deep breathing (SDB), participants showed increased alpha waves (indicating relaxation) alongside increased gamma and beta activity (indicating focus and alertness). The BWE intervention also positively affected heart rate variability (HRV), suggesting improved autonomic nervous system regulation.

Specifically, the study demonstrated that BWE with SDB: i) Increased HRV parameters indicate better stress regulation²⁷; ii) Enhanced alpha brain wave activity is associated with relaxed alertness²⁸; iii) Improved parasympathetic nervous system activation through increased Low Frequency (LF) power²⁹ and iv) Reduced heart rate from 85 to 82 bpm, suggesting a calming effect³⁰.

As quoted from the paper: “Slow breathing during BWE increases baroreceptor sensitivity^31,32. When blood pressure increases, the baroreceptor reflex increases vagal and decreases sympathetic outflow to the SA and atrioventricular node. This helps to decrease the heart rate, as seen in our study from 85 bpm to 82 bpm²⁷”

Bhastrikriya

This study examined the acute effects of Bhastrika pranayama on 20 regular yoga practitioners, focusing on heart rate variability (HRV) and brain wave patterns³³. The research found that fast-paced Bhastrika leads to increased sympathetic activity and altered brain wave patterns, suggesting potential stress-modulating effects^34,35.

“Pranayama improves HRV via parasympathetic activation, stress hormone reduction and GABAergic amygdala inhibition³⁶”.

The practice was found to modify brain wave patterns, with increases in delta waves and decreases in beta, theta, alpha, and gamma waves, indicating altered states of consciousness. Recent research has shown that “practicing Bhastrika pranayama for four weeks could reduce anxiety and enhance positive emotions^12”.

While fast-paced Bhastrika (>60 breaths/minute) increases sympathetic activity³⁷, similar to exercise, slower-paced Bhastrika (6 breaths/minute) activates the parasympathetic nervous system¹⁷, promoting relaxation. The study suggests that Bhastrika could be an effective tool for stress management³⁸, though further research is needed to understand its long-term benefits fully.

Right nostril breathing (RNB) and left nostril breathing (LNB)

The study examined the immediate autonomic changes during RNB and LNB in 20 regular yoga practitioners. Both breathing techniques calmed the heart and reduced stress by: i) Significantly decreasing heart rate during practice (from ~72 to ~69 bpm for both techniques)³⁹; ii) Increasing heart rate variability parameters (SDNN and RMSSD), indicating better autonomic regulation³⁹ and iii) Increasing parasympathetic activity during slow breathing (<7 breaths/min)³⁹.

While ancient texts suggest LNB has more cooling/calming effects, and RNB has more energizing effects, this acute study found statistically similar immediate effects from both techniques on heart rate variability and stress reduction³⁹. The authors note that longer-term studies may be needed to validate traditional distinctions between the techniques.

Mechanism of action

To elucidate the mechanisms underlying the observed changes in stress index during the various maneuvers, let’s explore the potential physiological and neurophysiological processes involved:

A) Kriya Yoga: i) Mechanism: Kriya Yoga is known for its slow, rhythmic breathing patterns and meditative focus, which activate the parasympathetic nervous system (PNS)⁶. This reduces sympathetic activity, leading to lower heart rate and blood pressure and a significant decrease in the stress index (71.45% reduction); and ii) These practices boost vagal tone while reducing cortisol.

B) Kapalbhati: i) Mechanism: Kapalbhati involves rapid, forceful exhalations that stimulate sympathetic activity. This can lead to heightened alertness and arousal, reflected in the increased stress index (41.66% increase) and ii) Neurophysiology: Rapid breathing increases oxygen supply to the brain but can also trigger mild hyperventilation, raising physiological stress markers temporarily.

C) Anulom Vilom (Alternate Nostril Breathing): i) Mechanism: This practice promotes balance between the sympathetic and parasympathetic systems, favoring relaxation and stress reduction. The significant 56.01% reduction in stress index suggests improved autonomic regulation; and ii) Neurophysiology: Alternating nostril breathing is thought to synchronize brain hemispheres and enhance parasympathetic dominance, reducing stress markers.

D) Exercise: i) Mechanism: Physical activity increases metabolic demand, activating the sympathetic nervous system. The rise in the stress index (85.33%) is a normal response to elevated cardiac output and oxygen delivery demands during exertion; and ii) Neurophysiology: Exercise-induced catecholamine increases (e.g., adrenaline) elevate heart rate and blood pressure. Long-term exercise, however, enhances autonomic flexibility and stress resilience.

E) Brain Entrainment: i) Mechanism: Brain entrainment techniques, such as binaural beats or neurofeedback, modulate brainwave activity to induce relaxation or focus. The observed 48.86% reduction in stress index indicates a shift toward parasympathetic dominance; and ii) Neurophysiology: Alpha and theta wave enhancement during brain entrainment is associated with reduced stress and improved emotional regulation.

F) Bhastrikriya: i) Mechanism: Similar to Kapalbhati, Bhastrikriya involves forceful breathing, but the effect on the stress index (8.30% reduction) suggests a milder impact on sympathetic activation; and ii) Neurophysiology: The mixed breathing pattern may trigger a transient increase in sympathetic activity, followed by enhanced parasympathetic recovery.

G) Chandra Nadi (Left Nostril Breathing): i) Mechanism: Chandra Nadi's breathing, focused on the left nostril, is linked to parasympathetic activation. The 69.14% reduction in the stress index underscores its calming effects: and ii) Neurophysiology: Left nostril breathing increases vagal activity, lowering heart rate and blood pressure and reducing stress.

H) Surya Nadi (Right Nostril Breathing): Mechanism: Surya Nadi breathing, targeting the right nostril, tends to stimulate the sympathetic nervous system, but its 64.06% reduction in stress index suggests a post-practice parasympathetic rebound; and ii) Neurophysiology: The transient sympathetic activation may prime the body for enhanced parasympathetic recovery, reducing overall stress markers.

These mechanisms illustrate the dynamic interaction between the autonomic nervous system, respiratory control centers and neuroendocrine responses during these maneuvers. Each practice uniquely modulates stress markers based on the sympathetic and parasympathetic activation balance.

Conclusion

In conclusion, the efficacy of stress-reduction techniques varies based on their physiological impact. Heating pranayamas such as Kapalbhati and fast-paced Bhastrikriya, along with exercise, were found to increase the stress index during the maneuver, making them unsuitable for individuals with conditions like hypertension. In contrast, cooling pranayamas-including Anulom Vilom, Kriya Yoga, Chandra Nadi, right-nostril breathing, and slow-paced Bhastrikriya- along with brain entrainment techniques, demonstrated a calming effect on the mind. These methods are particularly beneficial for stress management in individuals with hypertension or other stress-exacerbating conditions. The findings highlight the importance of tailoring stress-reduction practices to individual health profiles and underscore the need for further research to refine their therapeutic applications.

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