Heart Rate Variability in Taiwanese Obese Children

Abstract

Objective: The primary purpose of the present community-based study was to investigate early changes in cardiac autonomic function in obese children. Materials and Methods: A survey of juvenile obesity in Hualien in eastern Taiwan was performed in 2002. A total of 1,724 adolescents who were 12 or 13 years old were recruited. The overall prevalences of normal weight, overweight and obese adolescents were 71.5% 13.1%, and 15.4%, respectively. A stratified random sampling scheme was performed. We selected 100, 50 and 75 subjects from the above-mentioned three groups, and invited them to join this study. Totally, 170 students (normal-weight: overweight: obese=81:34:55) participated in this study. They received blood checks and a heart rate variability (HRV) examination. The homeostasis model assessment of insulin resistance (HOMA-IR) was used to evaluate insulin sensitivity. Results: Compared with the normal-weight group, the obese children had significantly elevated body mass indexes (BMI), HOMA-IR, and systolic and diastolic blood pressure levels. In addition, compared to their normal weight counterparts, obese children had significantly reduced high-frequency power (HF) but elevated low-frequency power in normalized units (LF%), and elevated ratios of low-frequency power to high-frequency power (LF/HF ratio). Further analyses revealed that compared with the normal weight counterparts; obese boys had significantly reduced HF but elevated LF % and LF/HF ratios. Among obese girls, the HF was reduced significantly, and LF% and the LF/HF ratio were increased, though not significantly. In stepwise multiple regression analysis, the BMI and heart rate were negatively associated with the HF component and positively associated with the LF/HF ratio and LF%. For every 1kg/m^2 increment in the BMI, the LF/HF ratio and LF% components of HRV increased ln(0.02) and 0.42% respectively, while HF decreased 0.03 ln(ms^2). Boys had a higher LF/HF ratio and LF% than girls. Conclusions: The obese boys and girls had increased insulin resistance and changes in autonomic nervous function that included reduced parasympathetic control and obese boys had elevated sympathovagal modulation. Gender-related autonomic differences, such as girls having lower sympathetic modulations of HRV, were also noted.