The heart rate variability (HRV) of preterm neonates undergoing a polysomnography is analysed in relation to the occurrence of abnormal cardiorespiratory events on one hand and the type of sleep stages on the other hand. The goal of the study is to examine the difference in sleep stage for neonates with and without abnormal cardiorespiratory events, based only on the heart rate recordings during periods without abnormal events. To quantify HRV, the numerical noise titration technique is used, which is a highly sensitive test for deterministic chaos and a relative measure for tracking chaos of a noise-contaminated signal in short data segments.
The methodology for calculating this HRV parameter is adapted to neonatal heart rate data. HRV is calculated for 30 preterm neonates, divided in three groups according to the occurrence of abnormal events during the polysomnographies and the eventual home monitoring. The results show that periods of non-REM (non rapid eye movement) sleep have lower noise limit values and can be distinguished significantly from periods of REM (rapid eye movement) sleep and from the total recording period. The presence of abnormal events does not influence this finding.
This recently developed technique offers many possibilities for further studies since the NL parameter has a strong discriminating character for classification in different pathologies such as sudden infant death syndrome (SIDS) and asphyxia.