Assessment of Heart Rate Variability in 4–6 Year-Old Children in Contrast Hardening

The article presents the results of assessing the features of heart rate variability (HRV) in children of senior preschool age (4–6 years old) who are engaged in contrast hardening according to a specially developed technique (T.A. Fisher, S.S. Kolyvanova, and E.L. Dremina, patent RU2744024C2, July 9, 2019) in a preschool educational institution. Significantly higher statistical indicators evaluating the overall autonomic tone (SDNN, RMSSD, рNN50, and CV) were revealed in children involved in contrast hardening compared to the control group. Evaluation of statistical, spectral parameters of heart rate variability (HRV) in the hardening group indicated the predominance of parasympathetic influences on heart rate and a shift in the autonomic balance towards parasympathicotonia. This was expressed in a significant decrease in vegetative rhythm index (VRI), an increase in high-frequency (HF) indicators, and a decrease in the LF/HF index in children of the hardening group compared with the control.