Differences in the Asymmetry of Beat-to-Beat Fetal Heart Rate Accelerations and Decelerations at Preterm and Term Active Labor

Figures

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  Figure 1. Description of the Phase-Rectified Signal Averaging (PRSA) algorithm and of the generation of the ADC, AAC, and DR indices. The transabdominal ECG signals are processed to obtain the fetal beat-to-beat R-R time series. The first step of the PRSA algorithm is the selection of the anchor points; in the figure, the anchor points for decelerations are marked with red points, and the anchor points for accelerations are marked with blue points; the selection of the anchor points depends on the parameter T. The second part of the algorithm is the choice of a time window covering each anchor point; this window measures 2L. The next step of the algorithm is a phase-rectification; then, all the time windows are aligned and averaged with respect to the anchor points. This process provides the PRSA signal. The ADC and AAC values are the central point of the signal. Finally, DR values are calculated by the sum of AAC and ADC.

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  Figure 2. Examples of Phase-Rectified Signal Averaging (PRSA) curves (T = 50, s = 10) of fetal heart rate for the average acceleration capacity (AAC) and average deceleration capacity (ADC) in Preterm and Term active labor. (a) PRSA-AAC curve for Term; (b) PRSA-AAC curve for Preterm; (c) PRSA-ADC curve for Term and (d) PRSA-ADC curve for Preterm. A reduction of the central part of the ADC and AAC curve in Preterm can be observed.

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  Figure 3. Error bar (mean ± SEM) of multiscale asymmetry indices of fetal beat-to-beat R-R intervals time series using (a) Porta (PI%); (b) Guzik (GI%); and (c) Ehlers (EI) at lags τ = 1–10 for Preterm and Term groups. * p < 0.05 between Term and Preterm (unpaired t-test or Mann–Whitney test).