Fetal Circulation Fallot’ Project 2 sd December 2009 Anatomical aspect of the fetal circulation Role of the shunts and their regulation Ductus arteriosus Foramen ovale Ductus veinosus Fetal cardiac output / particularities of the fetal heart Modification at birth of the fetal circulation

References Rudolph AM. Circ. Res. 1985; 57; Kiserud T and Rasmussen S. Ultrasound Obstet Gynecol 2001; 17: 119–124 Jouannic J.-M, Fermont L, Brodaty G, Bonnet D, Daffos F. J Gynecol Obstet Biol Reprod 2004 ; 33 :

Fetal Circulation lungs liver placenta aorta Ductus arteriosus Foramen ovale Umbilical vein Umbilical arteries Ductus veinosus (Arantius canal) Umbilical cord Anatomic aspect Placenta serves as the site for gas exchange

Role of the shunts Orientate oxygenated blood flow to the supra-aortic parts (brain / heart) Umbilical Vein -> DV -> IVC -> RA -> FO -> LA -> LV -> ascending aorta Orientate deoxygenated blood flow to the infra-aortic parts toward the placenta IVC -> RA -> RV -> PA -> DA -> descending aorta

Role of the foramen ovale Preferential flow from the IVC and from the right hepatic vein (anterior part of the IVC) to the right ventricle (less or deoxygenated blood flow) Preferential flow from the ductus veinosus (U.V.) and from the left hepatic vein (posterior part of the IVC) to the foramen ovale then to the left ventricle (oxygenated blood flow) Orientate oxygenated blood flow to the supra-aortic parts (brain / heart) Hypothesis : the streamlining of flows in the inferior vena cava « Anatomical canal » into the RA (Eustachian valve) helps direct the flow into the LA via FO Difference of the velocities between the two flows. Kiserud T. Fetal venous circulation — an update on hemodynamics. J Perinat Med 2000; 28: 90-6.

Role of the ductus arteriosus High pulmonary vascular resistances Shunt from RV and PA to the descending aorta Regulation: Vasodilatation Prostaglandin (PGE) Low PO2 Vasoconstriction Indomethacin Endothelin 1 (<= smooth muscular cells / endothelium) High PO2 (at birth)

Role of the ductus veinosus 50% of the blood flow coming from the umbilical vein bypasses the liver and goes directly to the left ventricle through the foramen ovale (70% in case of hypoxemia or hypovolemia) The O2 extraction by the liver is weak: only 15% Importance of the flow’s regulation in case of decreasing of the pressure into the umbilical vein: prostagladins, CO, adrenergic system,… i.e.: when umbilical venous return is progressively reduced the percentage of umbilical venous blood passing through the ductus venosus increases progressively 40% 5%

Fetal cardiac output (425ml/mn/kg) The factors that influence cardiac output are heart rate, filling pressure or preload, compliance of the ventricles, resistance against which the ventricles eject, or afterload, and myocardial contractility. Fetal myocardial compliance – Lower possibility to increase the stroke volume after increasing of the preload than in an adult heart (less compliant) Fetal myocardial contractility – Difficulty to support stroke volume after increasing of the postload

Percentages of combined ventricular output ejected by each ventricle from Rudolph / Circ Res % 20% 10% SVC IVC

Modification of the fetal circulation Pulmonary output => Only 10% of the combined output At birth : Importante decreasing of the pulmonary resistances: Mechanical factors Vasoactive substances: NO / PO2 Increasing of: pulmonary outflow left venous return => closure of the foramen ovale (Vieussens valve) High PO2 => vasoconstriction of the D.A.

Oxygen saturations 65% 50% 70% 35%