Heart Rate Variability and Baroreflex Sensitivity Among Young Adults with Normal and Increased Neck Circumference and Their Correlation with Anthropometric Indices

Background: Neck circumference (NC) is an emerging surrogate marker for upper-body adiposity, associated with elevated cardiometabolic risk. Cardiac autonomic indices, such as heart rate variability (HRV) and baroreflex sensitivity (BRS), are established prognosticators of cardiovascular disease (CVD) risk. While various anthropometric parameters have been linked to CVD risk, the specific association between increased NC and CVD risk remains unexplored. Methodology: This cross-sectional study enrolled 63 healthy young adult males. Participants were categorized into two groups: Group 1 (normal NC, ≤ 35.5 cm) and Group 2 (increased NC, > 35.5 cm). Their anthropometric variables BMI, waist-hip ratio (WHR), A body shape index (ABSI), abdominal volume index (AVI), conicity index (CI), body roundness index (BRI), body adiposity index (BAI), were calculated using standard formulae. A 5-minute lead-II ECG was recorded to assess short-term HRV, and BRS was measured using a Finometer. Results: Significant differences were observed in high-frequency power (HF) (P<0.05), low- frequency normalized units (LFnu) (P=0.006), and LF/HF ratio (P=0.006) between the groups. Root mean square of successive differences (RMSSD) was significantly correlated with BMI (P=0.022), AVI (P=0.009), BRI (P=0.026), and NC (P=0.020). LF/HF ratio was significantly correlated with BMI (P=0.012), WHR (P=0.011), AVI (P=0.008), BRI (P=0.012), and NC (P=0.001). BRS showed a significant correlation with NC (P=0.037). NC (R²=0.25) and AVI (R²=0.25) showed a strong association with the LF/HF ratio compared to BMI, WHR, and BRI. Conclusion: NC could predict 25% of the variance in LF/HF ratio. Hence, NC may be considered a practical adjunctive screening measure for cardiovascular risk stratification in large-scale epidemiological studies, potentially outperforming other anthropometric measures.