The Effect of Ex-vivo Gravid Uterine Support on Umbilical Vessel Flow Velocities and Ductus Arteriosus Patency

Abstract

PurposeFetal lamb artificial womb (AW) models rely on perfusion delivered via extracorporeal membrane oxygenation (ECMO) through umbilical or central vessel cannulation. Ductus arteriosus (DA) patency is paramount to fetal survival but may be disrupted by physiological stress and ECMO support. Existing AW models without the placenta use prostaglandin infusion to maintain DA patency, risking side effects like dysrhythmias, edema, or hypotension. We aim to investigate DA patency in an ex-vivo sheep model of gravid uterine support and quantify placental regulation of umbilical vessel flow with extrauterine flow variations. MethodsAn ex-vivo placental perfusion model was employed with bilateral uterine artery and vein cannulation. To maintain adequate flow, there is frequent manual titration of pump revolutions per minute, altering the blood pressure delivered to the uterus. Ultrasound measurements were obtained before laparotomy and on ECMO to document shunt patency and umbilical vessel and DA flow velocities; velocities were compared with students paired t-tests. ResultsSix of eleven sheep had ultrasounds obtained on full ECMO support. There was no difference in peak average velocity through the ductus before or after ECMO cannulation (p=0.26; CI -0.41 - 0.13), umbilical vein peak velocity (p=0.78; CI -0.08 - 0.10), or umbilical artery peak velocity (p=0.73; CI -0.17 - 0.13). ConclusionWhile perfusing a gravid uterus via the uterine vessels, we demonstrate a patent fetal DA and relatively constant umbilical vein flow velocities despite fluctuations in the ECMO pressure delivery to the uterus. The placenta therefore maintains regulation of umbilical vein blood flow velocity, facilitating physiologic shunt patency.