Date post: | 14-Jan-2016 |
Category: |
Documents |
Upload: | triston-holladay |
View: | 213 times |
Download: | 0 times |
Fetal Circulation
Fallot’ Project 2sd December 2009
Anatomical aspect of the fetal circulation
Role of the shunts and their regulation
Ductus arteriosusForamen ovaleDuctus veinosus
Fetal cardiac output / particularities of the fetal heart
Modification at birth of the fetal circulation
References
• Rudolph AM. Circ. Res. 1985; 57; 811-821
• 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 : 291-296.
FetalCirculation
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 resistancesShunt from RV and PA to the descending aorta
Regulation:Vasodilatation
Prostaglandin (PGE)Low PO2
VasoconstrictionIndomethacinEndothelin 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 1985
70%
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 factorsVasoactive substances: NO / PO2
Increasing of:pulmonary outflowleft venous return=> closure of the foramen ovale (Vieussens valve)
High PO2 => vasoconstriction of the D.A.
Oxygen saturations
65%50%
70%
35%