Correlation analysis of PRSA-based parameters during labor: a simulation study

During labor, a fetus might suffer considerable stress due to uterine contractions (UCs). Based on results obtained on a near-term pregnant sheep model, UCs mimicked as complete umbilical cord occlusions (UCOs) significantly activate vagal response, making the fetal inter-beat time interval (FRR) to display a sawtooth-like shape, which can be modeled using a pair of exponential functions (for the growing and decaying fronts, respectively). In addition, acceleration and deceleration capacities (AC/DC) and deceleration reserve (DR) computed through Phase-Rectified Signal Averaging (PRSA) technique proved to be sensitive to acid/base balance (for a wide range of their parameters T and s). In this preliminary study, we used a mathematical model linking UCOs and FRR response to investigate, using synthetic series, whether AC, DC, and DR are correlated with the time constants of the exponential models. Also we verified how this relation is affected by different values of the parameter T (with s = T). We found that DC and DR were strongly correlated with the time constant describing the increase of FRR after the onsets of UCOs in the range 5-11 (strongest correlation for DC was -0.87 at T = 8, while for DR -0.92 at T = 10, p < 0.05). AC was instead not significantly correlated with the decay time constant (likely to due the limited sample size available). This study motivates further investigations on PRSA related quantities and on the reasons behind their alterations during hypoxemia and metabolic acidosis.