The document discusses the fetal circulatory system, highlighting the role of the placenta and various shunts in blood flow and oxygen exchange. It also covers the transition to postnatal circulation, including the closure of the ductus venosus and changes in pulmonary blood flow, and factors affecting the ductus arteriosus. Additionally, it notes the implications of pulmonary conditions and high altitude on circulation and potential heart failure in infants.

2.  The placenta provides the exchange of
gases and nutrients in the fetus.

3. Four Shunts :
1. The Placenta – 55% of ventricular output and has
the lowest vascular resistance in the fetus.
2. SVC – 15%
3. IVC – 70%
4. The highest partial pressure of oxygen (PaO2) is
found in umbilical vein – 32 mmHg
5. Brain and coronary arteries – receive blood with
higher oxygen saturation PaO2 of 24 mmHg

5.  Lungs receive 15% of combined ventricular
output.
 RV > LV
 RV- 55% LV – 45%

6.  Fetal C.O directly proportional to HR
 Low compliance of Fetal Heart .

7.  Primary change – Shift of blood flow from
placenta to lungs for oxygenation.
 Establishment of Pulmonary circulation

8.  Increase in SVR
 Cessation of blood flow in the umbilical
vein
 Closure of Ductus Venosus

9.  Reduction in PVR
 Increase in Pulmonary blood flow
 Fall in PA Pressure
 Functional closure of foramen ovale
 Increase in LA pressure
 Decrease RA pressure
 Closure of PDA

11. 1.Hypoxia and /or altitude
2. RDS or Congenital Pneumonia
3. Metabolic Acidosis
4. Increased pulmonary artery pressure
secondary to VSD or PDA
5. Increased pressure in the left atrium or
pulmonary vein.

12.  Infants with large VSD may not develop
CHF while living at high altitude, but
develop CHF at sea level.
 In RDS, increase in PaO2 dilates
pulmonary vasculature  resulting in CHF
as baby improves
 CHF does not develop in VSD till 6 to 8
weeks of age or older due to high PA
pressure directly transmitted through LV
pressure.

13.  Functional Closure  10 to 15 hours after
birth by constriction of the medial smooth
muscle in the ductus.
 Anatomic Closure  2 to 3 weeks
permanent changes in the endothelium and
subintimal layers of the ductus.
 Oxygen, PGE2 levels, and maturity of
newborn, acetylcholine and bradykinin are
important factors in the closure of the
ductus.

14.  Strongest stimulus for constriction of the
ductal smooth muscle  postnatal
increase in PaO2 from 25 mmHg to 50
mmHg
 Ductal tissue is less responsive to the
oxygenation changes in premature infant
due to immature ductus and smooth
muscles in the media of ductus.
 High levels of PGE2 in preterm infants.

15.  Decrease in PGE2 levels after birth 
constriction of the ductus
 Constricting effects by indomethacin and
the dilator effects of PGE2 &
Prostaglandin I2 > for premature babies
 Aspirin use in mother  Constricts the
ductus during fetal life  can cause
PPHN.

16.  Increased PGE2
 Reduced arterial PaO2
 Birth Asphyxia
 Hypoxia due to pulmonary diseases
 High altitude

17. PA constricted by
 O2 and Metabolic acidosis
 Epinephrine
 Nor-epinephrine
PA dilated by
 Vagal stimulation
 Isoproterenol
 Bradykinin

18.  Rate at which PVR falls
 Responsiveness of the ductus arteriosus
to oxygen
 High circulating levels of PGE2
 Early onset of a large left to right shunt
and CHF