Cardiac Autonomic Dysfunction in Diabetic Highlander and Lowlander Populations of Nepal Assessed by Heart Rate Variability

Introduction Diabetes mellitus is associated with cardiac autonomic dysfunction (CAD) and enhanced cardiovascular risk. High-altitude dwellers exhibit physiological adaptations that may regulate autonomic function. The present study aims to compare cardiac autonomic function in diabetic highlanders vs diabetic lowlanders of Nepal using heart rate variability (HRV). Methods A cross-sectional study was performed on a total of 128 patients with type 2 diabetes mellitus (T2DM), including 64 native highlanders residing above 2500 m (Phaplu, Solukhumbu district, Nepal) and 64 native lowlanders below 500 m (Biratnagar, Morang District, Nepal). HRV was measured using standard electrocardiography (ECG) under baseline resting state. Time- and frequency-domain HRV indices including age, gender, duration of diabetes, and HbA1c were recorded and analyzed. Comparative statistical analysis was conducted using independent t tests and Mann-Whitney U tests. Results In time-domain HRV parameters, diabetic highlanders showed significantly higher SDNN (88.9 [48.5–97.2] ms vs 28.7 [20.2–43.1] ms; P < .001) and increased RMSSD (64.9 [35.1–92.3] ms vs 21.6 [14.3–38.3] ms; P < .001) compared to lowlanders. Likewise, in frequency-domain HRV analysis, as compared to diabetic lowlanders, diabetic highlanders revealed significantly increased HF power (317.6 [96.5–869.2] ms 2 vs 86.1 [29.7–314.0] ms 2 ; P < .001) and lower LF/HF ratio (0.4 [0.2–1.1] vs 1.2 [0.9–3.4]; P < .001) demonstrating relatively better autonomic balance. Conclusion Highlanders with T2DM exhibit relatively preserved cardiac autonomic balance compared to diabetic lowlanders, indicating that chronic exposure to high altitude influences diabetes-related autonomic dysfunction. These findings highlight the importance of considering geographical and environmental factors during management and risk assessment of diabetic individuals in Nepal.