1. Dip. Diab.DCA, Dip. Software statistics
Fetal circulation
Dr. S. Parthasarathy
MD., DA., DNB, MD (Acu),
Dip. Diab.DCA, Dip. Software statistics
PhD (physio)
Mahatma gandhi medical college and research institute, puducherry, India

2. What are the needs of the CVS ??
Give oxygen to tissues
Give metabolic nutrients to tissues

3. Fetus to neonate

4. Placenta to lungs

5. Fetus

6. Essence The entire cardiac output cannot go to the lungs
Hence we have shunts in the circulation
But adequate oxygen supply has also be there
After delivery, lungs take over, shunts disappear
The foramen ovale, ductus arteriosus, and ductus venosus

7. Some changes take place
That is transitional circulation
Word is important – transitional !!!
If it is permanent – think of preterm, critically ill neonate or congenital cardiac illness

8. Special characters
Parallel arrangement of two main arterial systems and their respective ventricles.
But series in adults
Mixing of venous return and preferential streaming.
High resistance, low flow of pulmonary circulation.
Low resistance and high flow of placental circulation.
Presence of shunts

9. The pathway Deoxygenated blood of fetus Descending aorta
Umbilical arteries Placenta
Intervillous spaces gas exchange oxygenated blood

11. Then what happens Umbilical vein
Preferably through ductus venosus to IVC
Streaming
Liver bypassed

13. From the IVC, it bypasses the right atrium through foramen ovale to Left atrium

14. Streaming
Eustechian valve helps to direct the IVC blood to cross the foramen ovale to left atrium
The 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 blood
SVC blood is directed across the TV to right ventricle

15. Left atrium to left ventricle through mitral valve
LV to ascending aorta
Supplies oxygenated blood to three main arteries
Mixes with ductus arteriosus blood

17. most highly oxygenated blood is delivered to
the myocardium and brain.

18. The pathway
Deoxygenated blood from the SVC and part of IVC enter Right atrium,
Tricuspid valve
Right ventricle
Pulmonary artery
Then lungs ?? No
But through ductus arteriosus to descending aorta

20. Left to right (blue)
And
Right to left shunt (Pink)
follows

21. SVC and IVC

22. 60 50 65
80 %
25%

23. RV vs LV
The 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 output
45 % to placenta 8 % to lungs

24. The big three high hemoglobin (16gm%) fetal haemoglobin high CVO
help maintain oxygen delivery in the fetus despite low oxygen partial pressures

25. HbF
Normal Hb

26. The transition from fetus to neonate

27. Transition
Gas exchange function is transferred from placenta to the lungs.
Shunts closure
Separation of systemic and pulmonary circulations.
LV output must increase
Increased metabolism to maintain body temperature

28. What is done Placenta removed Cord clamped
Baby cries and lung starts to inspire

29. Cord 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 removed
No flow through ductus venosus

30. The ductus venosus closes passively 3–10 days after birth.

31. Placenta (low resistance) cut off, SVR increases

32. Lungs expand
At 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 vasodilation
Not oxygen , even any gas

33. LA flow increase – RA flow decrease FO closes

34. Initial 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 next
Ductus arteriosus

35. Concomitant with the drop in PVR, the shunt at the level of the DA becomes bi-directional.
The exact mechanism of ductal closure is not known
increased 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.

36. PVR change

37. Ductus arteriosus Functional closure by 96 hours
anatomical closure via endothelial and fibrous tissue proliferation later
Hemoglobin
HbF becomes adult Hb – better oxygen delivery

38. Cardiac output Term fetus -- CVO = 400 ml / kg/min.
Neonate CVO = upto 400 ml / kg/min.
Upto 4.0 litres / sq. metre
Necessary for increased metabolic demands
LV and RV outputs equalize

39. Persistent fetal circulation

40. By 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 shunts
We can start PGE1 infusions
Congenital diaphragmatic hernia – PVR has not come down – What should be done to make fit !!

41. Thank you all