Traditional views on neonatal pain neglected long neglected the neonates’ capability of feeling pain. Newborn infants experience at least one painful procedure during their first days of life, but with a lower gestational age, invasive procedures become more frequent and invasive. The modulation of the autonomic nervous system (ANS) is significantly changed during painful procedures. The analysis of the heart rate variability is shown to be a reliable tool in analyzing the ANS. In this study, the dynamic of the system has been examined by applying the Poincaré plot analysis, a primer of nonlinear methods used in the analysis of the ANS. The aim of this study is to assess the occurrence of changes in linear heart rate variability parameters, to determine the changes in the Poincaré plot indices and to evaluate the correlation between their differences in healthy newborns. The results have shown a significant increase in the heart rate, a reduction of the duration of RR intervals, and the square root of the mean squared differences between successive RR intervals (RMSSD), as well as a decrease in the short-term variability (SD1) of the Poincare plot. The results highlight the need for studying the application of nonlinear analyses of the HRV on the effects of pain on the ANS and its long-term effects on the infant.

Key words: autonomic nervous system, pain, poincare plot, nonlinear analysis, heart rate variability

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