Correlation between average acceleration and deceleration capacity of fetal heart rate and biomarkers of acid-base status in a vivo sheep model

INTRODUCTION: Fetal heart rate variability (fHRV) is an indirect index of fetal wellbeing and autonomous nervous system (ANS) integrity. Fetal monitoring methods in labor are widely based on fHRV analysis but fail in early detection of hypoxia and acidemia. We explored the relation among two measures of ANS regulation, fHR Average Acceleration and Deceleration Capacities (AAC and ADC), computed by Phase-Rectified Signal Averaging (PRSA) method, and biomarkers of fetal acidemia, i.e. pH, Lactate (L) and Base Excess (BE). METHODS: In an in-vivo near-term fetal sheep model (n=9) repetitive umbilical cord occlusions (UCO) were applied for 1 min every 2.5 min as follows: mild partial UCO for 1 h; moderate partial UCO for 1h; and complete UCO x 1-2 h, until arterial pH<7.00. Arterial blood samples were collected at baseline, every 20 min during the UCO series, and at 1 h of recovery. Fetal ECG was recorded. AAC/ADC were computed for each phase of the protocol. Pearson correlation coefficient (r) was determined between AAC/ADC and biomarkers at T=3 (T determines the periodicities detected by PRSA). RESULTS: A significant correlation between AAC/ADC and biomarkers was found (0.45<|r|<0.8, p<0.05). The largest correlation was found between ADC and pH (r=-0.79; p<0.05). The table shows the r values between AAC/ADC and biomarkers. pH L BE ADC -0.79 * 0.55 * -0.72 * AAC 0.75 * -0.57 * 0.69 * Table 1: r between AAC/ADC and biomarkers (* p<0.05). CONCLUSIONS: This is the first in vivo evaluation of the correlation between AAC/ADC and acid-base status biomarkers computed by PRSA analysis of fHR. Our findings suggest that worsening acid-base status has an impact on AAC and ADC of fHR. This finding puts the grounds for future clinical studies.