Reference ranges of gender- and age-related heart rate variability parameters in Russian children

To obtain reference ranges for heart rate variability (HRV) parameters in healthy children, taking into account their gender and age. The study included the results of testing 22,468 children ranging 5.5-12.5 years of age. The data were grouped by age and gender. The analysis of HRV parameters was carried out according to the standards described in existing guidelines. It was based on a 5-min rhythmogram obtained from a standard 12-lead electrocardiogram (ECG). The following characteristics of the temporal and spectral analyses of HRV were studied: standard deviation of NN intervals (SDNN), power in the low-frequency band of the HRV spectrum (LF), low-frequency power as mean percentage of total power (TP) of HRV spectrum (LF%), power in the high-frequency band of the HRV spectrum (HF), high-frequency power as mean percentage of TP of HRV spectrum (HF%), power in the very-low-frequency band of HRV (VLF), and LF/HF ratio. The values of SDNN, LF, HF, HF% and TP increased with age, reaching a peak at 8 and 9 years of age. It is notable that the values of SDNN, LF and TP were significantly lower in girls in each age group. The values of LF% and LF/HF decreased with age, with a peak decrease at 8 and 9 years of age, followed by a moderate increase or stabilization. The values of LF% and LF/HF did not differ statistically significantly between boys and girls. The VLF parameter exhibited a clear trend of growth with age and had higher values in boys of each age group. The correlation between HRV and heart rate (HR) was statistically significant. The correlation graphs had similar curves in both gender groups and both age groups. The parameters of the total HRV, as well as the activity of the parasympathetic nervous system (PNS), exhibited similar growth trends with age, with a peak increase in their values at 8 and 9 years of age. HR, as well as the activity of the sympathetic nervous system (SNS), decreased with age. Gender differences also followed a consistent pattern: parameters characterizing the activity of the peripheral nervous system were significantly higher in boys than in girls across all age groups.