Comparison of heart rate variability in normotensive and newly detected hypertensive adults in a tertiary care hospital, Mysuru, Karnataka

Abstract

Background and objectives

Autonomic dysfunction plays a key role in blood pressure regulation, and heart rate variability (HRV) is a sensitive non-invasive marker of autonomic function. This study aimed to compare HRV among newly detected hypertensive and normotensive adults and to examine the association of HRV parameters with blood pressure levels.

Methods

This hospital-based case–control study included 52 participants (26 hypertensives and 26 normotensives). Time-domain HRV parameters, standard deviation of all normal-to-normal RR intervals (SDNN), and root mean square of successive differences (RMSSD) and frequency-domain parameters, low frequency (LF), high frequency (HF), and LF/HF ratio, were derived from electrocardiographic recordings. HRV parameters were compared between normotensive and hypertensive groups. Correlation with blood pressure and LF/HF was assessed using Spearman’s correlation, and logistic regression was used to examine the independent association between HRV and blood pressure parameters. Significance was set at 5% (P< 0.05).

Results

Time-domain measures of HRV among hypertensives had lower SDNN [28.16 (21.75–39.50) ms², P=0.020], and lower RMSSD [16.88 (11.79–25.51) ms², P=0.003]. In the frequency domain, hypertensive individuals showed significantly lower HF [102.25 (53.73–209.75), P<0.001], and the LF/HF ratio was significantly higher [1.94 (1.60–3.19), P< 0.001]. LF/HF ratio correlated positively with systolic (rₛ=0.49) and diastolic blood pressure (rₛ= 0.50), both P<0.001. Multinomial logistic regression shows that higher systolic blood pressure was significantly associated with increased odds of sympathetic dominance [Odds ratio (OR) 1.09, 95% Confidence interval (CI) (1.04-1.15), P<0.001].

Interpretation and conclusions

Newly detected hypertensive adults demonstrated reduced parasympathetic activity and increased sympathetic dominance, with the LF/HF ratio showing a significant positive association with systolic and diastolic blood pressure and independently predicted hypertension.

Hypertension is a leading preventable cause of cardiovascular morbidity and mortality worldwide, with a substantial proportion of affected individuals remaining undiagnosed.^1,2 Autonomic nervous system dysregulation plays a central role in blood pressure control, and heart rate variability (HRV) is a sensitive, non-invasive marker of sympatho-vagal balance.^3,4 Reduced HRV, reflecting sympathetic predominance and diminished parasympathetic activity, has been consistently reported in hypertensive individuals and is associated with adverse cardiovascular outcomes.⁵ This study aimed to assess and compare HRV between newly detected hypertensive and normotensive adults and to correlate the parameters of the time and frequency domain of HRV with the severity of hypertension.

Methods

Study design

This was an observational, hospital-based case–control study was conducted by the department of Community Medicine, JSS Medical College, JSS AHER, Mysuru, Karnataka, India, over the period of September 2025 to October 2025, in a tertiary care outpatient setting after obtaining the Institutional Ethics Committee approval.

Sample size

The sample size was calculated based on the Shah et al⁶ study reporting a large effect size (0.8) for HRV differences between normotensive and hypertensive adults, yielding a minimum of 52 participants (26 per group). Adults aged ≥18 year with newly diagnosed hypertension (Systolic blood pressure (SBP ≥140 mmHg and/or diastolic blood pressure (DBP) ≥90 mmHg)⁷ and not on antihypertensive therapy were included. Participants with cardiovascular disease, arrhythmias, chronic systemic illness, or recent surgery were excluded. Age and gender were matched to select the controls. Convenience purposive sampling was used.

Data collection

After obtaining written informed consent, sociodemographic characteristics and lifestyle history were recorded using a structured questionnaire. Blood pressure was measured in the sitting position on the right arm after a 15-min rest using a validated, fully automated Omron HEM 7124 device. Measurements were taken by the first author (MBBS trainee). Two readings were recorded 5 min apart, and the average of the two readings was considered the final value. Height was measured using a calibrated Prestige HM007 stadiometer, and weight was measured using an Omron HN289 digital weighing scale. Body mass index was calculated using standard methods.⁸ Heart rate variability was assessed according to the Task Force guidelines of the European Society of Cardiology, the North American Society of Pacing Electrophysiology,⁹ using a 10-min lead II electrocardiographic recording, following 15 min of supine rest in a temperature-controlled environment. Time-domain parameters (standard deviation of all normal-to-normal RR intervals (SDNN), and root mean square of successive differences (RMSSD)) and frequency-domain parameters (low frequency (LF), high frequency (HF), and LF/HF ratio were analysed using AD Instruments PowerLab and LabChart software. All the equipment were calibrated regularly, and data entry was double-checked for accuracy.

Statistical analysis

Data were entered in Microsoft Excel and analysed using Jamovi version 2.3.28, free open-source software, from Sydney, Australia Data normality was assessed using the Shapiro–Wilk test and Q–Q plots and was found to be non-normal (P<0.001). The Mann-Whitney U test was used to compare the HRV parameters between normotensive and hypertensive groups, and the correlation between HRV parameters and SBP was assessed using Spearman’s rank correlation. Binary logistic regression and multivariate regression were performed to examine the independent association between HRV and blood pressure parameters. Significance was set at 5% (P< 0.05) with a 95% confidence interval (CI).

Results

A total of 52 participants were included, comprising 26 hypertensives and 26 normotensive controls. The mean age was 39.2±8.77 y in hypertensives and 36.5±8.21 y in normotensives. The mean systolic and diastolic blood pressures among hypertensives were 147±7 mmHg and 98±5 mmHg, respectively, compared with 117±3 mmHg and 77±4 mmHg in normotensives. Anthropometric and lifestyle variables are summarised in Table I.

Table I.

Distribution of respondents’ sociodemographic and anthropometric variables

Sociodemographic variables	Hypertensives (N=26); n (%)	Normotensives (N=26); n (%)
Age (y)
<40	14 (54)	14 (54)
>40	12 (46)	12 (46)
Gender
Female	5 (19)	4 (15)
Male	21 (81)	22 (85)
Marital status
Single	9 (35)	12 (46)
Married	17 (65)	14 (54)
Socioeconomic class
Lower class	18 (69)	10 (38)
Lower middle	3 (12)	0 (0)
Upper middle class	2 (8)	11 (42)
Upper class	3 (12)	5 (19)
Physical activity
Yes	17 (65)	20 (77)
No	9 (35)	6 (23)
BMI classification
Normal	5 (19)	13 (50)
Overweight	7 (27)	2 (8)
Obese	14 (54)	11 (42)
Waist-to-hip ratio
Normal	4 (15)	10 (38)
Increased	22 (85)	16 (62)

Distribution and comparison of HRV parameters are shown in Table II. Spearman’s rank correlation analysis demonstrated a statistically significant positive correlation between LF/HF ratio and systolic blood pressure (rₛ=0.49; P<0.001) as well as diastolic blood pressure (rₛ=0.50; P<0.001).

Table II.

Comparison of heart rate variability parameters with hypertensives and normotensives

Heart rate variability parameters	Hypertensives(N=26) Median (Q1–Q3)	Normotensives(N=26) Median (Q1–Q3)	P value
Low frequency (LF) (ms2)	225.05 (115.75 – 353.23)	312.70 (190.72 – 823.45)	0.076
High frequency (HF) (ms2)	102.25 (53.73 – 209.75)	487.15 (167.60 – 1060.20)	<0.001*
Low frequency/High frequency (LF/HF)	1.94 (1.60 – 3.19)	0.91 (0.62 – 1.19)	<0.001*
Standard deviation of normal-to-normal RR intervals (SDNN) (ms2)	28.16 (21.75 – 39.50)	41.20 (25.06 – 59.66)	0.020*
Root mean square of successive differences (RMSSD) (ms2)	16.88 (11.79 – 25.51)	29.09 (18.77 – 49.34)	0.003*

^*Level of significance at P<0.05

Binary logistic regression analysis showed that a higher LF/HF ratio was significantly associated with hypertensives [Odds ratio (OR)=0.06, 95% CI: 0.01–0.34, P< 0.001]. Multinomial logistic regression shows that higher systolic blood pressure was significantly associated with increased odds of sympathetic dominance [OR 1.09, 95% CI (1.04-1.15) P< 0.001].

Discussion

This study was designed to compare heart rate variability (HRV) among normotensive and hypertensive Indian adults. The findings demonstrate a significant reduction in HRV among hypertensives compared with normotensives, characterised by lower SDNN and RMSSD values and a higher LF/HF ratio. HF power was significantly reduced in hypertensive individuals, and the LF/HF ratio showed a significant positive correlation with both systolic and diastolic blood pressure. These findings indicate progressive autonomic imbalance with rising blood pressure.

HRV, a sensitive non-invasive marker of autonomic nervous system function, showed consistent deterioration with increasing blood pressure in the present study. These results are supported by the study by Natarajan et al¹⁰, Shah et al⁶, which reported significantly reduced HF, SDNN, and RMSSD among hypertensive individuals, along with significantly increased LF and LF/HF ratio, reflecting increased sympathetic activity and reduced vagal tone. Similarly, He et al⁵ demonstrated that an increased LF/HF ratio, indicating sympathetic overactivity, was positively associated with both systolic and diastolic blood pressure, while RMSSD, representing parasympathetic activity, was significantly higher in normotensives The association between hypertension and autonomic dysfunction is further supported by the review by Valensi¹¹, a study which highlights sympathetic overactivity and reduced parasympathetic activity as common consequences of modern lifestyle changes, including sedentary behaviour, reduced physical activity, obesity, and adverse metabolic factors. These contributors were also more prevalent among hypertensive individuals in the present study, reinforcing their role in HRV disruption. The clinical significance of reduced HRV is well documented. Hillebrand et al¹² reported that low HRV is associated with a 32–45% increased risk of first cardiovascular events in individuals without known cardiovascular disease, and that a 1% increase in SDNN corresponds to a 1% reduction in the risk of fatal or non-fatal cardiovascular events. Similarly, Goldenberg et al¹³ showed that low HRV was independently associated with a two-fold increased likelihood of myocardial ischaemia, and that incorporating HRV into traditional coronary artery disease risk assessment significantly improved predictive accuracy. The inclusion of a homogeneous population of newly detected hypertensive individuals minimised confounding by comorbidities and antihypertensive medications, although the small sample size limits generalisability. Overall, newly detected hypertension was associated with early autonomic dysfunction characterised by reduced parasympathetic activity and increased sympathetic dominance. HRV, particularly the LF/HF ratio, may serve as a useful non-invasive marker for early identification of autonomic imbalance and highlights the importance of early lifestyle-based interventions to reduce cardiovascular risk.

शोध-संदेश

मैसूरु के एक बड़े अस्पताल में किए गए इस अध्ययन में पाया गया कि नए पहचाने गए उच्च रक्तचाप (हाइपरटेंशन) वाले वयस्कों में स्वायत्त तंत्रिका तंत्र का संतुलन प्रभावित होता है, जिसमें पैरासिम्पेथेटिक गतिविधि कम तथा सिम्पेथेटिक गतिविधि अधिक होती है। LF/HF अनुपात हृदयगति में परिवर्तन की सम्भावना को मापने का एक पैमाना है जो शरीर के तनाव (stress) और आराम (relaxation) के स्तर को दर्शाता है। अध्ययन में पाया गया कि जिन लोगों का LF/HF अनुपात अधिक था, उनमें रक्तचाप का स्तर भी अधिक पाया गया। यह मानक उच्च रक्तचाप का स्वतंत्र पूर्वानुमानक (independent predictor) हो सकता है। उच्च रक्तचाप की प्रारंभिक पहचान और जोखिम के आकलन में यह मानक सहायक हो सकते हैं।

Author contributions

VG, MB, MSM, CM, UB, VSS: Study concepts and design; VG, YA, MSM, CM, UB, VSS: Literature search; VG, YA, VV, UB, VSS: Data extraction/collection; VG, YA, MB, VV, MSM, CM: Data analysis; VG, YA, MB, UB, VSS: Manuscript writing; MB, VV: Critical revision; MB, VG: Guarantor author. All authors have read and approved the final printed version of the manuscript.

Financial support and sponsorship

The study received funding support from the Indian Council of Medical Research (ICMR), New Delhi, for the Short-Term Studentship (STS) programme (STS Reference no.: STS2024-3Y-04444) awarded to first author (VG), under the guidance of corresponding author (MB).

Conflicts of Interest

None.

Use of Artificial Intelligence (AI)-Assisted Technology for manuscript preparation

The authors confirm that there was use of AI-assisted Grammarly tool for language editing and grammatical refinement, which was reviewed by the authors. Images or figures are not generated using AI tools in this manuscript.