Nonlinear features of neonatal heart rate dynamics

The aim of this study was to investigate the short-term heart rate variability (HRV) as an index of the cardiac autonomic control development in healthy full-term neonates using various new complexity and irreversibility measures. HRV in 20 healthy full-term neonates was compared to HRV recorded in healthy young adults. Besides traditional time and frequency domain measures, we assessed HRV complexity measures including normalized complexity index (NCf), normalized unpredictability index (NUPf), pattern classification (OV%, 1 V%, 2LV%, 2UV%) and multiscale irreversibility indices (P%, G%, E). HRV magnitude was significantly decreased in the neonatal group compared to the adults. HR V complexity measures, i.e. indices NCf, NUPf and pattern indices 1 V%, 2LV%, were also significantly reduced. Pattern classification parameter OV% and Porta's irreversibility index P% showed significant increase in newborns compared to adults suggesting the shift in the sympathovagal balance of neonates towards sympathetic predominance. Moreover, surrogate data analysis of irreversibility indices revealed asymmetrical nature of the HRV series present already in the neonatal age suggesting the nonlinear nature of HR V dynamic even very shortly after birth.