Relationship Between Deceleration Morphology and Phase Rectified Signal Averaging-Based Parameters During Labor

Abstract

During labor, uterine contractions trigger the response of the autonomic nervous system (ANS) of the fetus, producing sawtooth-like decelerations in the fetal heart rate (FHR) series. Under chronic hypoxia, ANS is known to regulate FHR differently with respect to healthy fetuses. In this study, we hypothesized that such different ANS regulation might also lead to a change in the FHR deceleration morphology. The hypothesis was tested in an animal model comprising nine normoxic and five chronically hypoxic fetuses that underwent a protocol of umbilical cord occlusions (UCOs). Deceleration morphologies in the fetal inter-beat time interval (FRR) series were modeled using a trapezoid with four parameters, i.e., baseline b, deceleration depth a, UCO response time τu and recovery time τr. Comparing normoxic and hypoxic sheep, we found a clear difference for τu (24.8±9.4 vs. 39.8±9.7 s; p < 0.05), a (268.1±109.5 vs. 373.0±46.0 ms; p < 0.1) and Δτ = τu − τr (13.2±6.9 vs. 23.9±7.5 s; p < 0.05). Therefore, the animal model supported the hypothesis that hypoxic fetuses have a longer response time τu and larger asymmetry Δτ as a response to UCOs. Assessing these morphological parameters during labor is challenging due to non-stationarity, phase desynchronization and noise. For this reason, in the second part of the study, we quantified whether acceleration capacity (AC), deceleration capacity (DC), and deceleration reserve (DR), computed through Phase-Rectified Signal Averaging (PRSA, known to be robust to noise), were correlated with the morphological parameters. DC, AC and DR were correlated with τu, τr and Δτ for a wide range of the PRSA parameter T (Pearson's correlation ρ > 0.8, p < 0.05). In conclusion, deceleration morphologies have been found to differ between normoxic and hypoxic sheep fetuses during UCOs. The same difference can be assessed through PRSA based parameters, further motivating future investigations on the translational potential of this methodology on human data.

Dissecting the contributions of the peripheral chemoreflex and myocardial hypoxia to fetal heart rate decelerations in near‐term fetal sheep

“…Thus, deepening decelerations are likely to reflect worsening myocardial hypoxia in parallel with worsening hypotension. Overall, these findings support the continued development of measures that quantify the frequency, duration and, crucially, the depth of decelerations, including total deceleration area and deceleration capacity (Beguin et al, 1975;Cahill et al, 2012Cahill et al, , 2018Furukawa et al, 2019;Georgieva et al, 2017Georgieva et al, , 2021Gyllencreutz et al, 2021;Lear et al, 2023;Martí Gamboa et al, 2017;Rivolta et al, 2014Rivolta et al, , 2021Tournaire et al, 1976). These represent the best predictors of the risk of hypoxia-ischaemia currently under investigation.…”

Fetal heart rate responses in chronic hypoxaemia with superimposed repeated hypoxaemia consistent with early labour: a controlled study in fetal sheep

“…21 This difference likely in part reflects the use of initial partial rather than complete UCOs and milder pre-existing hypoxaemia (defined as baseline S a O 2 <55%, versus mean 27.5 ± 3.6% in the present study). 21 In the present study, the morphology of decelerations in the hypoxaemic group visually appear to be more 'U-shaped' than the 'V-shape' in the normoxic group. Of interest, lower FHR at 30 seonds of UCO correlated with min-MAP (Figure 1B), suggesting that cardiovascular compromise is associated with faster decelerations even if the final nadir is not different.…”

“…In contrast, a recent report slowing of FHR decelerations in fetal sheep with mild chronic hypoxaemia. 21 This difference likely in part reflects the use of initial partial rather than complete UCOs and milder pre-existing hypoxaemia (defined as baseline S a O 2 <55%, versus mean 27.5 ± 3.6% in the present study). 21 In the present study, the morphology of decelerations in the hypoxaemic group visually appear to be more 'U-shaped' than the 'V-shape' in the normoxic group.…”

“…In recent animal studies, DA and DC predicted fetal hypotension 19 and acidemia. [19][20][21] Hypotension is the key determinant of neural injury [22][23][24] and therefore its relation with hypotension 19 provides physiological support for the utility of DA and DC. Their practical implementation requires defined thresholds for intervention.…”

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

“…Emerging evidence has even suggested that DR may be considered to measure the fetal heart rate's asymmetry, providing more precise monitoring of the ANS dynamics even when there is a lack of data and noise [16,17]. Asymmetry is a fundamental characteristic of non-equilibrium systems [18]; hence, this property is expected to be present and has been documented in physiological systems [19].…”