Download Fetal circulation

Fetal Circulation
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
Fallot’ Project
2sd December 2009
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.
Ductus arteriosus
lungs
Fetal
Circulation
Foramen ovale
liver
aorta
Anatomic aspect
Ductus veinosus
(Arantius canal)
Umbilical vein
placenta
Placenta serves as the site
for gas exchange
Umbilical cord
Umbilical arteries
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
20%
SVC
70%
from Rudolph / Circ Res 1985
IVC
10%
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
50%
35%
70%
65%