Abstract
Phase Entropy (PhEn) was recently introduced for evaluating the nonlinear features of physiological time series. PhEn has been demonstrated to be a robust approach in comparison to other entropy-based methods to achieve this goal. In this context, the present study aimed to analyze the nonlinear features of raw electrohysterogram (EHG) time series collected from women at the third trimester of pregnancy (TT) and later during term active parturition (P) by PhEn. We collected 10-min longitudinal transabdominal recordings of 24 low-risk pregnant women at TT (from 35 to 38 weeks of pregnancy) and P (>39 weeks of pregnancy). We computed the second-order difference plots (SODPs) for the TT and P stages, and we evaluated the PhEn by modifying the k value, a coarse-graining parameter. Our results pointed out that PhEn in TT is characterized by a higher likelihood of manifesting nonlinear dynamics compared to the P condition. However, both conditions maintain percentages of nonlinear series higher than 66%. We conclude that the nonlinear features appear to be retained for both stages of pregnancy despite the uterine and cervical reorganization process that occurs in the transition from the third trimester to parturition.
Highlights
Over the last few years, entropy measures have emerged to study the time series from physiological systems such as the cardiovascular, the muscular, and the nervous system, as well as the female reproductive system [1]
We hypothesized that the Phase Entropy (PhEn) in the EHG time series differs between the third trimester of pregnancy and term active parturition owing to the uterine and cervical reorganization processes that occur in the transition from the third trimester to parturition
The second-order difference plots (SODPs) of P (Figure 3d) exhibits a wider distribution of scatter points over the SODP of P (Figure 3d) exhibits a wider distribution of scatter points over the whole phase space in the whole phase space in comparison to trimester of pregnancy (TT), which shows a dense concentration of scatter points comparison to TT, which shows a dense concentration of scatter points around the origin (Figure 3b)
Summary
Over the last few years, entropy measures have emerged to study the time series from physiological systems such as the cardiovascular, the muscular, and the nervous system, as well as the female reproductive system [1]. The time series of EHG show intermittent bursts of action potentials associated with uterine contractions and basal activity when the uterus is at rest. Changes in the dynamics of EHG between term low-risk parturient and non-parturient women have rarely been explored by using diverse entropy approaches [7,10,11]. Authors highlight the necessity of finding suitable measures that characterize electrohysterographic time series generated by the uterine activity during parturition [12]
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