Comparison of linear and non-linear heart rate variability indices between preterm infants at their theoretical term age and full term newborns

Abstract

Heart rate variability (HRV) enables non-invasive evaluation of cardiac autonomic activity. Preterm infants are known to have altered HRV characteristics that remain even when reaching their term age. Little is known about non-linear HRV measures between full term and preterm babies close to their theoretical full term. In this study, we calculated sample entropy, shape-describing parameters (skewness and kurtosis) and detrended fluctuation analysis coefficients α1 and α2 from RR time series of 16 very preterm babies (<32 weeks gestational age, “PT group”) measured at their theoretical term age. The values were compared to the values of nine full-term (>37 weeks, “FT group”) infants. Compared to the FT group, smaller values of sample entropy and lower values of α1 were found in the PT group. No difference in α2, kurtosis, or skewness was found. This indicates decrease in overall complexity of HR dynamics in the PT group. When various HRV indices, that included also non-linear indices, were projected to the principal component analysis space obtained from the FT group, a good separation between the PT and FT groups was found. The study was limited by a small sample but the results were in line with literature. The combinations of several HRV parameters can be of interest for future studies on the degree of ANS maturity.