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Rivolta, Massimo W.; Stampalija, Tamara; Casati, Daniela; Richardson, Bryan S.; Ross, Michael G.; Frasch, Martin G.; Bauer, Axel; Ferrazzi, Enrico and Sassi, Roberto (2014): Acceleration and Deceleration Capacity of Fetal Heart Rate in an In-Vivo Sheep Model.
In: PLOS ONE 9(8), e104193 [PDF, 784kB]


Background: Fetal heart rate (FHR) variability is an indirect index of fetal autonomic nervous system (ANS) integrity. FHR variability analysis in labor fails to detect early hypoxia and acidemia. Phase-rectified signal averaging (PRSA) is a new method of complex biological signals analysis that is more resistant to non-stationarities, signal loss and artifacts. It quantifies the average cardiac acceleration and deceleration (AC/DC) capacity. Objective: The aims of the study were: (1) to investigate AC/DC in ovine fetuses exposed to acute hypoxic-acidemic insult; (2) to explore the relation between AC/DC and acid-base balance; and (3) to evaluate the influence of FHR decelerations and specific PRSA parameters on AC/DC computation. Methods: Repetitive umbilical cord occlusions (UCOs) were applied in 9 pregnant near-term sheep to obtain three phases of MILD, MODERATE, and SEVERE hypoxic-acidemic insult. Acid-base balance was sampled and fetal ECGs continuously recorded. AC/DC were calculated: (1) for a spectrum of T values (T= 1 divided by 50 beats; the parameter limits the range of oscillations detected by PRSA); (2) on entire series of fetal RR intervals or on "stable'' series that excluded FHR decelerations caused by UCOs. Results: AC and DC progressively increased with UCOs phases (MILD vs. MODERATE and MODERATE vs. SEVERE, p < 0.05 for DC T = 2-5, and AC T = 1-3). The time evolution of AC/DC correlated to acid-base balance (0.4 < vertical bar rho vertical bar < 0.9, p < 0.05) with the highest D r D for 2 <= T <= 7. PRSA was not independent from FHR decelerations caused by UCOs. Conclusions: This is the first in-vivo evaluation of PRSA on FHR analysis. In the presence of acute hypoxic-acidemia we found increasing values of AC/DC suggesting an activation of ANS. This correlation was strongest on time scale dominated by parasympathetic modulations. We identified the best performing T parameters (3 <= T <= 5),and found that AC/DC computation is not independent from FHR decelerations. These findings establish the basis for future clinical studies.

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