Normative Heart Rate Variability Parameters Across Age and Gender in Healthy Adults from an Apex Tertiary Care Centre in Southern India.

Background: Autonomic regulation of the heart is commonly assessed using heart rate variability (HRV), which reflects beat-to-beat fluctuations in heart rate. Time- and frequency-domain HRV indices are known to vary with age, sex and environmental influences. However, existing reference values are largely derived from Western populations, underscoring the need for region-specific normative HRV data. Purpose: This study aimed to develop comprehensive, region-specific reference values for HRV and to examine age- and gender-related differences in HRV indices in a predominantly South Indian population. Methods: This cross-sectional observational study recruited 272 healthy adults aged 18-80 years, predominantly from South India. Five-minute resting ECG recordings were obtained for HRV analysis. Standard time- and frequency-domain HRV parameters were calculated. Data normality was assessed prior to analysis. Baseline comparisons were performed across gender and across three predefined age groups, followed by appropriate post hoc analysis. A prior power analysis was also conducted. Results: Data from 249 healthy individuals were included in the final analysis. Normative reference values for time- and frequency-domain HRV parameters were established. Males exhibited lower resting heart rate and higher LF/HF ratio, whereas females demonstrated significantly higher root mean square of successive difference and percentage of successive RR intervals differing from the previous interval by more than 50 ms. Age-wise analysis revealed a more pronounced decline in mean RR interval beyond 30 years of age. Compared with individuals younger than 30 years, those older than 30 years showed significant reductions in HRV-particularly in time-domain parameters and frequency-domain indices. Conclusion: This study provides 5-min HRV reference data for healthy adults from a predominantly South Indian population. Both age and gender independently influenced HRV indices, with an age-related decline in overall HRV and higher vagal tone observed in women compared to men. The observed deviations from international Task Force reference values suggest population-specific influences, potentially related to ethnicity, lifestyle and environmental factors. We advocate the generation of region-specific HRV data sets by different centres to get a holistic picture of region- and population-specific variations in HRV.