Differential effects of unilateral forced nostril breathing on baroreflex sensitivity and cardiovascular parameters in healthy young men: A cross-sectional study

Abstract

BACKGROUND:

Baroreflex sensitivity (BRS) is a crucial marker of autonomic cardiovascular control, and it is also a predictor of cardiovascular risk. Unilateral forced nostril breathing (UFNB) is one of the many types of pranayama, which are breathing techniques in Yoga. This type of breathing can influence autonomic function through hemispheric activation, yet its direct impact on BRS remains unexplored. To assess the immediate effects of left and right UFNB on BRS and cardiovascular parameters in healthy young adult men.

MATERIALS AND METHODS:

It is a cross-section study, which included 55 healthy adult men (mean age 25.67 ± 5.89 years). The participants underwent the standardized protocols for measuring BRS, blood pressure, and heart rate during baseline and the 2-minute interventions of left and right UFNB. BRS was measured using the sequence method with Finapres technology. Paired t-tests were used to compare the baseline and the postintervention values.

RESULTS:

Performing left UFNB significantly increased BRS by 19.6% (P < 0.001, d = 3.63), whereas the blood pressure and heart rate decreased (all P < 0.001), probably indicating profound activation of parasympathetic system. On the other hand, performing the right UFNB decreased BRS by 5.6% (P = 0.012, d = 0.35) and also increased blood pressure and heart rate (all P < 0.01), probably suggesting a sympathetic activation. Waist circumference correlated negatively with the baseline BRS values (r = −0.513, P < 0.001).

CONCLUSION:

Left UFNB produces substantial immediate improvements in BRS with parasympathetic enhancement, whereas right UFNB induces sympathetic activation. These findings suggest a potential therapeutic application for the use of UFNB in cardiovascular health management as a nonpharmacological intervention.

Introduction

Cardiovascular diseases remain one of the major causes of mortality in India, requiring effective preventive and therapeutic strategies for high-risk populations.[1] Baroreflex sensitivity (BRS) is a key marker of autonomic cardiovascular control. It has emerged as a crucial parameter in the understanding of cardiovascular health and disease progression.[2] BRS quantifies the effectiveness of heart rate modulation in response to blood pressure fluctuations, making it an important indicator of autonomic nervous system function.[3]

Impaired BRS has been identified as a significant predictor of adverse cardiovascular outcomes and a marker of cardiovascular disease risk, particularly in conditions such as hypertension, heart failure, and postmyocardial infarction.[4] Previous studies have shown that a reduction in BRS is associated with increased mortality risk and poorer prognosis in patients with cardiovascular disease.[5] Although pharmacological interventions have traditionally been the primary approach to improve BRS, there is a growing interest in nonpharmacological methods, particularly those derived from traditional practices such as Yoga, pranayama, and meditation.[6]

The nasal cycle is an ultradian rhythm characterized by alternating congestion and decongestion between the right and left nasal passages. It has been linked to autonomic nervous system function.[7] This physiological phenomenon demonstrates a remarkable connection to cerebral hemisphere activation by influencing the contralateral hemisphere.[8] Understanding this relationship has led to increased interest in yogic breathing techniques, particularly unilateral forced nostril breathing (UFNB).[9]

UFNB, also known as chandranadi pranayama (left) and suryanadi pranayama (right) in yogic practice, involves conscious breathing through one nostril while occluding the other.[10] This technique has been practiced for ages in traditional yoga practice in India and has recently gained scientific attention for its potential therapeutic applications with the advent of effective noninvasive instruments to measure cardiovascular parameters.[11]

Previous studies have shown that left UFNB tends to enhance parasympathetic activity, leading to decrease in heart rate and blood pressure,[12] while right UFNB causes increased sympathetic activity, resulting in elevated cardiovascular parameters.[13] These differential effects suggest a potential therapeutic application in conditions requiring specific autonomic modulation, such as hypertension and cardiovascular disorders, such as myocardial infarction.[14]

The relationship between body composition and cardiovascular parameters has been well established in the literature, with anthropometric measurements showing significant correlations with various cardiovascular indicators.[15] Studies have shown that central obesity, particularly the waist circumference, has strong association with cardiovascular risk factors.[16] Recent studies have also shown that anthropometric measurements may influence baroreflex function, suggesting a complex interaction between body composition and autonomic control even in healthy adults.[17]

Despite the growing body of evidence supporting the autonomic effects of UFNB, there is a significant gap in understanding its direct impact on BRS. Although previous studies have studied the effects of UFNB on heart rate variability and autonomic function test, not many studies have specifically investigated its influence on BRS. Given the clinical importance of BRS in cardiovascular health and the potential therapeutic applications of UFNB, this relationship warrants a detailed investigation.

This study aims to examine the immediate effects of right and left UFNB on BRS in healthy young men. In addition, it also seeks to explore the relationships between anthropometric measurements and baseline cardiovascular parameters, including BRS, systolic blood pressure (SBP), and diastolic blood pressure (DBP). Understanding these relationships and the potential modulatory effects of UFNB on BRS could provide valuable insights for developing nonpharmacological interventions in cardiovascular health management.

This study is relevant given the increasing trend in integrative approaches to cardiovascular health and the growing evidence supporting the effectiveness of yogic or guided breathing practices in autonomic modulation. The findings could have significant implications for both preventive healthcare and therapeutic interventions, particularly in conditions where autonomic dysfunction plays a crucial role in diseases such as diabetes.

Materials and Methods

Study design and setting

This was a cross-sectional study conducted in the cardiovascular laboratory of Department of Physiology, JIPMER, Puducherry. Environmental conditions were controlled throughout the experimental protocol to ensure standardization and reliability of measurements. All measurements were scheduled between 8:00 AM and 10:00 AM. Participants were instructed to maintain a minimum 4-hour fasting period before testing to control for potential postprandial effects on cardiovascular function.

Study participants and sampling

Fifty-five healthy male volunteers between the ages of 18 and 40 years who consented to the study were recruited by a convenience sampling. Participants were excluded from the study if they had smoking history; alcohol intake >3 drinks/week; presence of deviated nasal septum; active upper respiratory infection at the time of testing, regular practice of meditation or yoga, and professional athletes; or any chronic medical conditions such as diabetes mellitus and hypertension.

Data collection tool and technique

The weight of the participants was measured using a digital weighing scale with accuracy to the nearest 100 gm, in minimal clothing, with the subject standing in the centre of the scale without support and with the weight distributed evenly on both feet. Height was measured by a calibrated stadiometer on hard and level ground with the subject standing upright with feet together, the back in contact with the stadiometer, and the head in the Frankfort plane. A nonstretchable tape was used for measuring waist circumference at the midpoint between the lower costal (10^th rib) border and the iliac crest at the end of a gentle, normal expiration with abdomen muscles relaxed with the subject standing and with forearms crossed over the thorax. Hip circumference was measured at the widest portion of the buttocks with the subject standing and forearms crossed over the thorax, gluteal muscles relaxed, and feet together.

The experimental protocol followed a sequence designed to capture both baseline values and intervention responses. Initially, participants underwent a 20-minute acclimatization period in a supine position to establish cardiovascular stability. After acclimatization, baseline measurements were recorded for 10 minutes under resting conditions. The first intervention was left UFNB performed for 2 minutes. This was followed by a 10-minute postintervention measurement period. A 15-minute washout period was then implemented to ensure return to baseline conditions. Subsequently, participants performed right UFNB for 2 minutes, followed by another 10-minute postintervention measurement period.

Noninvasive BRS was measured by using the Finapres (Finapres Medical Systems, the Netherlands). BRS was calculated using the sequence method, which analyses the relationship between continuous blood pressure measurements and RR intervals. This method used specific criteria to ensure efficient analysis: sequences were required to have a minimum length of 3 beats, with a correlation coefficient threshold of 0.85 to ensure strong linear relationships. Blood pressure ramps were identified using a threshold of 1 mmHg, while RR interval changes were detected using a threshold of 4 ms. These parameters were selected based on established protocols in cardiovascular research and were consistently applied across all analysis periods.

Throughout the protocol, the participants maintained a supine position on a comfortable examination bed, with the head elevated at a 30-degree angle to optimize comfort while maintaining standardized posture. All measurements were conducted in a quiet environment to minimize external influences on cardiovascular parameters. The sequence of interventions (left UFNB followed by right UFNB) was maintained consistently across all participants to ensure standardization of the protocol.

Ethical consideration

This study was approved by the Institutional Human Ethics committee (Project No. JIP/IEC/2016/29/955), and the National Ethical Guidelines for Biomedical and Health Research 2017 Declaration by the Indian Council of Medical Research were followed throughout the study.

Statistical analysis method

Statistical analyses were performed using SPSS 21.0 (IBM Corp., Armonk, NY, USA) software. The Shapiro–Wilk test was performed to check for data normality. All normally distributed data were represented as mean and standard deviation. Paired sample t-tests were conducted to compare the cardiovascular parameters (BRS, SBP, DBP, and HR) between the baseline and postintervention measurements for both the left and right nostril breathing. Effect sizes were calculated using Cohen d to quantify the magnitude of changes. Percentage changes from baseline were computed to assess the clinical significance of the interventions. The relationships between anthropometric measurements and baseline cardiovascular parameters were evaluated using Pearson correlation coefficient. P < 0.05 was considered statistically significant.

Results

Table 1 presents the baseline characteristics of the study population, showing that participants with age range of 18–39, with normal body mass index (BMI) and waist-to-hip ratio, indicating generally healthy adults with normal anthropometric parameters.

Table 1.

Demographic and anthropometric characteristics of study population (n=55)

Variable		Mean±SD
Age (years)		25.67±5.89
Height (m)		1.72±0.06
Weight (kg)		70.84±12.46
BMI (kg/m²)		23.86±3.91
Waist circumference (cm)		78.92±9.41
Hip circumference (cm)		85.39±10.02
Waist-to-hip ratio		0.93±0.03

BMI=Body mass index; SD=Standard deviation

Table 2 presents the paired sample t-test results comparing both the left and right nostril breathing with the baseline values. Left nostril breathing in the above results shows that there is a significant parasympathetic dominance, as evidenced by decreases in systolic blood pressure, diastolic blood pressure, and heart rate (P < 0.001), accompanied by an enhancement in BRS (P < 0.001). By contrast, the right nostril breathing had a sympathetic response pattern, showing significant increases in systolic blood pressure, diastolic blood pressure, and heart rate (P < 0.01), along with a reduction in BRS (P = 0.012). These findings suggest that left nostril breathing promotes cardiovascular relaxation, while right nostril breathing induces cardiovascular activation, indicating the differential effects of unilateral nostril breathing on autonomic regulation.

Table 2.

Comparison of cardiovascular parameters of unilateral left nostril and unilateral right nostril with baseline breathing

Parameter		Phase		Mean±SD		t		P
BRS (ms/mmHg)		Baseline		16.73±2.11		-		-
		LNB		20.01±2.34		−26.899		<0.001
		RNB		15.80±1.89		2.610		0.012
SBP (mmHg)		Baseline		119.52±9.12		-		-
		LNB		115.41±8.89		10.134		<0.001
		RNB		122.07±10.23		−4.813		<0.001
DBP (mmHg)		Baseline		76.45±8.34		-		-
		LNB		72.76±7.89		11.390		<0.001
		RNB		77.50±8.56		−2.668		0.010
HR (bpm)		Baseline		77.23±4.56		-		-
		LNB		74.33±4.23		6.847		<0.001
		RNB		81.00±4.89		−7.252		<0.001

SBP=Systolic blood pressure; DBP=Diastolic blood pressure; HR=Heart rate; SD=Standard deviation

Table 3 presents the changes using effect sizes and percentage changes. The percentage changes reveal that left nostril breathing had the most substantial impact on BRS (+19.6%) compared with other parameters. Effect size analysis and percentage changes revealed varying changes of impact for different physiological parameters during unilateral nostril breathing. Left nostril breathing exhibited pronounced impact observed in BRS (d = 3.63) and diastolic blood pressure (d = 1.54). Notably, BRS showed the largest percentage increase (+19.6%) during left nostril breathing compared with other cardiovascular parameters. Right nostril breathing, while also effective, demonstrated its strongest influence on heart rate (d = 0.98). These effect sizes indicate that left nostril breathing had a more substantial overall impact on cardiovascular parameters compared with right nostril breathing, with particularly strong effects on autonomic regulatory mechanisms as reflected by the pronounced changes in BRS.

Table 3.

Effect sizes and clinical significance

Parameter		Comparison		Cohen’s d		Percentage change
BRS		Baseline versus LNB		3.63		+19.6
		Baseline versus RNB		0.35		−5.6
SBP		Baseline versus LNB		1.37		−3.4
		Baseline versus RNB		0.65		+2.1
DBP		Baseline versus LNB		1.54		−4.8
		Baseline versus RNB		0.36		+1.4
HR		Baseline versus LNB		0.92		−3.7
		Baseline versus RNB		0.98		+4.9

SBP=Systolic blood pressure; DBP=Diastolic blood pressure; HR=Heart rate; BRS=Baroreflex sensitivity

Table 4 demonstrates the associations between cardiovascular parameters and anthropometric measurements BRS demonstrated significant negative correlations with all anthropometric variables, with the strongest inverse relationship observed with waist circumference (r = −0.513, P < 0.001), suggesting that increased central adiposity is particularly associated with reduced baroreflex function. Systolic blood pressure exhibited positive correlations across all anthropometric measurements, with waist circumference showing the strongest association (r = 0.589, P < 0.001). Diastolic blood pressure followed a similar pattern to systolic blood pressure, with slightly lower correlation coefficients. These findings indicate that central obesity, as measured by waist circumference, has the strongest relationship with cardiovascular parameters, showing an inverse association with BRS and a positive associations with blood pressure measures. The relationships across different anthropometric measurements underscore the significant impact of body composition on cardiovascular regulation even in normal range of BMI and waist circumference.

Table 4.

Association of anthropometric parameter with cardiovascular parameter

Anthropometric measurements		Basal BRS		Basal SBP		Basal DBP
BMI		r=−0.482** P<0.001		r=0.567** P<0.001		r=0.534** P<0.001
Waist circumference		r=−0.513** P<0.001		r=0.589** P<0.001		r=0.548** P<0.001
Hip circumference		r=−0.437* P=0.001		r=0.492** P<0.001		r=0.463** P<0.001
Waist-to-hip ratio		r=−0.394* P=0.003		r=0.436* P=0.001		r=0.401* P=0.002

r: Pearson correlation coefficient; **Correlation is significant at the 0.01 level (two-tailed); *Correlation is significant at the 0.05 level (two-tailed). SBP=Systolic blood pressure; DBP=Diastolic blood pressure; BRS=Baroreflex sensitivity; BMI=Body mass index

Discussion

This study provides the first comprehensive evidence demonstrating the differential effects of UFNB on BRS and cardiovascular parameters in healthy young men. Our findings reveal distinct autonomic responses to left and right UFNB, with left UFNB showing particularly more pronounced effects on cardiovascular regulation, contributing to the growing body of evidence supporting breathing-based interventions for cardiovascular health.

The increase in BRS after left UFNB (+19.6%), accompanied by decreases in blood pressure and heart rate, demonstrates the shift toward parasympathetic dominance. The magnitude of this effect (Cohen d = 3.63) indicates a powerful influence of left UFNB on autonomic cardiovascular control. Our results are consistent with the previous researches demonstrating the parasympathetic effects of left nostril breathing techniques. Bhavanani et al. demonstrated that left nostril breathing reduced heart rate and blood pressure while increasing parasympathetic activity as measured by HRV parameters, with effect sizes comparable with our observations.[18] Similarly, Raghuraj et al. reported significant immediate decreases in systolic pressure and heart rate during left nostril breathing, accompanied by improved HRV parameters indicating parasympathetic dominance.[19] A recent study by Kalaivani et al. in hypertensive patients showed immediate effects of alternate nostril breathing on cardiovascular parameters,[20] supporting our findings in healthy population.

By contrast, right UFNB produced opposite effects, characterized by increased blood pressure and heart rate, with a slight reduction in BRS (−5.6%). This pattern suggests sympathetic activation, consistent with the earlier studies showing hemispheric lateralization of autonomic control. Jahan et al. found that right nostril breathing increased sympathetic activity, while left nostril breathing enhanced parasympathetic tone, as evidenced by changes in HRV parameters and cardiovascular measures.[6] Malhotra et al. showed SDNN decreases during RNB pranayama and SDNN increases during LNB pranayama, although these changes were not statistically significant in regular yoga practitioners.[21] More recently, Mallick and Prakash demonstrated that left nostril breathing improved the high-frequency component of HRV, while the right nostril breathing increased the LF/HF ratio, supporting the hemisphere-specific autonomic effects.[22]

The differential effects can be explained by the anatomical and functional asymmetry in the autonomic cardiac control, where the right vagal stimulation produces greater cardiac deceleration compared with the left vagal stimulation. These changes observed in cardiovascular parameters can be attributed to the underlying physiological mechanisms such as the nasal-cerebral axis. UFNB activates the contralateral cerebral hemisphere through trigeminal nerve stimulation, leading to differential autonomic outflow patterns. This hemispheric activation is supported by research showing increased EEG activity in the contralateral hemisphere during unilateral nostril breathing.[7,18]

Emerging evidences suggest that with minimal prerequisite training, slow deep breathing around 0.10 Hz can acutely enhance cardiovagal BRS in humans.[23] This supports our findings and suggests that the breathing interventions can be rapidly implemented with immediate cardiovascular benefits. The respiratory–cardiovascular coupling likely plays a role through mechanical effects on venous return and chemical effects through blood gas changes.

The clinical implications of these findings are significant and align with current cardiovascular disease prevention strategies. Slow breathing reduces blood pressure and enhances BRS in hypertensive patients, with effects appearing potentially beneficial in the management of hypertension.[24] The substantial increase in BRS after left UFNB suggests potential therapeutic applications in conditions characterized by reduced BRS, such as hypertension and autonomic dysfunction.

A comprehensive study by Singh et al. on alternate nostril breathing in healthy young adults found modulation of cardio–respiratory and autonomic functions,[12] while Sharma et al. demonstrated specific cardiac effects of slow and fast nostril breathing on stress and cardiovascular parameters.[14] These studies collectively support the physiological basis for our observed effects.

Our findings regarding anthropometric correlations provide additional insights into the relationship between body composition and autonomic function. The strong negative correlation between waist circumference and BRS (r = −0.513, P < 0.001) suggests that central adiposity may influence autonomic cardiovascular control, even within normal BMI ranges. This relationship likely reflects the complex interaction between metabolic factors and autonomic regulation, consistent with emerging evidence linking body composition to cardiovascular risk through autonomic pathways.[25] The association between anthropometric indices and cardiovascular parameters in terms of BRS, blood pressure, and heart rate suggests that body composition influences autonomic function through multiple pathways. This finding has implications for risk assessment and preventive strategies in cardiovascular health management. Current secondary prevention guidelines emphasize lifestyle interventions alongside pharmacological treatments to reduce cardiovascular events and mortality.

Limitations of the study were involving only healthy young male participants, which restricts the generalizability of findings to other populations, including female participants, older adults, and individuals with cardiovascular diseases. The cross-sectional design limits our ability to establish causality between UFNB interventions and the observed cardiovascular changes. Third, only immediate effects were assessed, and the long-term effects and sustainability of these cardiovascular need to be evaluated in the future study.

Conclusion

Left UFNB produces substantial immediate improvements in BRS with parasympathetic enhancement, while right UFNB induces sympathetic activation. These findings align with contemporary evidence-based approaches to cardiovascular health promotion and suggest significant potential for integrating UFNB interventions into comprehensive cardiovascular prevention programs.

The cost-effectiveness, accessibility, and immediate beneficial effects of left UFNB will make it particularly suitable for population-level interventions, supporting global health initiatives aimed at reducing cardiovascular disease burden. Future research should investigate long-term effects and clinical applications in specific patient populations, particularly in the context of current cardiovascular disease prevention guidelines and health policy frameworks.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

AI policy

The conceptual framework figure was developed with assistance from Claude Sonnet 4 (Anthropic) for generating the Mermaid diagram code, which was subsequently rendered using the Mermaid Live Editor. The theoretical content and framework design were author-directed.

Ethical approval

This study was approved by the Institutional Human Ethics Committee, JIPMER, Puducherry (Project No. JIP/IEC/2016/29/955). The study was conducted in accordance with the National Ethical Guidelines for Biomedical and Health Research 2017 by the Indian Council of Medical Research (ICMR). which is already mentioned in the methodology under ethical consideration.

Author contributions

MC: Conceptualization, study design, data collection, statistical analysis, and manuscript writing. VKS: Supervision, critical review, and manuscript editing. AR: Data analysis, interpretation of results, manuscript review, and editing. All authors read and approved the final manuscript.

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.