What is the cardiac response during deceleration? An experimental study using a fetal sheep model

Abstract

Introduction

The study aim was to describe fetal cardiovascular physiology during cord compressions that mimicked uterine contractions.

Method

For this experimental study in a near-term fetal sheep model, an impedance measurement probe was surgically inserted into the fetal left ventricle to enable pressure and volume measurements. An axillary arterial catheter was used for gasometric sampling. The protocol involved mimicking contractions using umbilical cord occlusion (UCO) with six complete 1-min UCO every 10 min. During these occlusions, cardiac parameters, including dynamic (i.e. pressure–volume curve), hemodynamic, and gasometric parameters were recorded.

Results

Five fetuses were included. At 10s after the start of UCO, heart rate fell by 26.1%, left-ventricular end-diastolic volume by 14,6%, end-systolic volume by 4,8%, and left-ventricular output by 69.7%. Simultaneously, end-diastolic pressure rose by 8,8% and end-systolic pressure by 15.1%. There was an increase in pCO2 (+8%) and a parallel decrease in partial pressure of oxygen (pO2, −20%) during the first 10s, while arterial pH remained stable. Pressure–volume curve analysis revealed a decrease in volume and flow, with preservation of systolic function and decline of diastolic function, followed by an increase in volume and a decrease in contractility.

Conclusion

This study shows cardiac adaptation to UCO, with an initial increased systemic pressure with transient decrease of the left ventricle volumes and systemic cardiac output. Otherwise, cardiac systolic function was preserved during the first part of the UCO, followed by a slow decrease during the second part. Nevertheless, diastolic cardiac dysfunction was observed at the early UCO stage. This cardiac adaptation highlights the multiple physiological mechanisms involved in fetal deceleration during labor.