Presentation on theme: "Dip. Diab.DCA, Dip. Software statistics"— Presentation transcript:
1Dip. Diab.DCA, Dip. Software statistics Fetal circulationDr. S. ParthasarathyMD., DA., DNB, MD (Acu),Dip. Diab.DCA, Dip. Software statisticsPhD (physio)Mahatma gandhi medical college and research institute, puducherry, India
2What are the needs of the CVS ?? Give oxygen to tissuesGive metabolic nutrients to tissues
6Essence The entire cardiac output cannot go to the lungs Hence we have shunts in the circulationBut adequate oxygen supply has also be thereAfter delivery, lungs take over, shunts disappearThe foramen ovale, ductus arteriosus, and ductus venosus
7Some changes take place That is transitional circulationWord is important – transitional !!!If it is permanent – think of preterm, critically ill neonate or congenital cardiac illness
8Special charactersParallel arrangement of two main arterial systems and their respective ventricles.But series in adultsMixing of venous return and preferential streaming.High resistance, low flow of pulmonary circulation.Low resistance and high flow of placental circulation.Presence of shunts
9The pathway Deoxygenated blood of fetus Descending aorta Umbilical arteries PlacentaIntervillous spaces gas exchange oxygenated blood
13From the IVC, it bypasses the right atrium through foramen ovale to Left atrium
14StreamingEustechian valve helps to direct the IVC blood to cross the foramen ovale to left atriumThe lower margin of septum secundum [crista dividens] helps to direct the left posterior stream to preferentially across the foramen ovale.Posterior and left stream of IVC blood carries oxygenated blood while anterior and right stream carries poorly oxygenated bloodSVC blood is directed across the TV to right ventricle
15Left atrium to left ventricle through mitral valve LV to ascending aortaSupplies oxygenated blood to three main arteriesMixes with ductus arteriosus blood
23RV vs LVThe RV receives about 65% of the venous return and the LV about 35%.Thus, in the shunt dependent circulation of the fetus, the situation is much more complex and cardiac output must be defined in different terms.Hence CVO = combined ventricular output45 % to placenta 8 % to lungs
24The big three high hemoglobin (16gm%) fetal haemoglobin high CVO help maintain oxygen delivery in the fetus despite low oxygen partial pressures
27TransitionGas exchange function is transferred from placenta to the lungs.Shunts closureSeparation of systemic and pulmonary circulations.LV output must increaseIncreased metabolism to maintain body temperature
28What is done Placenta removed Cord clamped Baby cries and lung starts to inspire
29Cord clamped and placenta removed The umbilical vessels are reactive and constrict in response to longitudinal stretch and the increase in blood PO2.Obviously external clamping of the cord will augment this process.Placenta removedNo flow through ductus venosus
30The ductus venosus closes passively 3–10 days after birth.
32Lungs expandAt birth, after expansion of the lungs, there is a dramatic fall in PVR and an 8–10-fold increase in pulmonary blood flow.Expansion stimulation of stretch receptors vasodilationNot oxygen , even any gas
34Initial closure of the foramen ovale occurs within minutes to hours of birth. Anatomical closure occurs later via tissue proliferation.Ductus venosus is closed FO closed , what nextDuctus arteriosus
35Concomitant with the drop in PVR, the shunt at the level of the DA becomes bi-directional. The exact mechanism of ductal closure is not knownincreased PO2 in neonatal blood- direct constriction of smooth muscle within the duct.concentrations of PGE2, produced in the placenta, fall rapidly after birth, causes ductal constriction.
40By then-- why we should know about fetal circulation Take for example – A case of truncus or transposition of vessels come for other surgery – It should be known to us that Ductus arteriosus should be kept patent –Yes they need shuntsWe can start PGE1 infusionsCongenital diaphragmatic hernia – PVR has not come down – What should be done to make fit !!