2. ο The placenta provides the exchange of
gases and nutrients in the fetus.
3. Four Shunts :
1. The Placenta β 55% of ventricular output and has
the lowest vascular resistance in the fetus.
2. SVC β 15%
3. IVC β 70%
4. The highest partial pressure of oxygen (PaO2) is
found in umbilical vein β 32 mmHg
5. Brain and coronary arteries β receive blood with
higher oxygen saturation PaO2 of 24 mmHg
6. ο Fetal C.O directly proportional to HR
ο Low compliance of Fetal Heart .
7. ο Primary change β Shift of blood flow from
placenta to lungs for oxygenation.
ο Establishment of Pulmonary circulation
8. ο Increase in SVR
ο Cessation of blood flow in the umbilical
vein
ο Closure of Ductus Venosus
9. ο Reduction in PVR
ο Increase in Pulmonary blood flow
ο Fall in PA Pressure
ο Functional closure of foramen ovale
ο Increase in LA pressure
ο Decrease RA pressure
ο Closure of PDA
10.
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. ο Infants with large VSD may not develop
CHF while living at high altitude, but
develop CHF at sea level.
ο In RDS, increase in PaO2 dilates
pulmonary vasculature ο resulting in CHF
as baby improves
ο 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. ο Functional Closure ο 10 to 15 hours after
birth by constriction of the medial smooth
muscle in the ductus.
ο Anatomic Closure ο 2 to 3 weeks
permanent changes in the endothelium and
subintimal layers of the ductus.
ο Oxygen, PGE2 levels, and maturity of
newborn, acetylcholine and bradykinin are
important factors in the closure of the
ductus.
14. ο Strongest stimulus for constriction of the
ductal smooth muscle ο postnatal
increase in PaO2 from 25 mmHg to 50
mmHg
ο Ductal tissue is less responsive to the
oxygenation changes in premature infant
due to immature ductus and smooth
muscles in the media of ductus.
ο High levels of PGE2 in preterm infants.
15. ο Decrease in PGE2 levels after birth ο
constriction of the ductus
ο Constricting effects by indomethacin and
the dilator effects of PGE2 &
Prostaglandin I2 > for premature babies
ο Aspirin use in mother ο Constricts the
ductus during fetal life ο can cause
PPHN.
16. ο Increased PGE2
ο Reduced arterial PaO2
ο Birth Asphyxia
ο Hypoxia due to pulmonary diseases
ο High altitude
17. PA constricted by
ο O2 and Metabolic acidosis
ο Epinephrine
ο Nor-epinephrine
PA dilated by
ο Vagal stimulation
ο Isoproterenol
ο Bradykinin
18. ο Rate at which PVR falls
ο Responsiveness of the ductus arteriosus
to oxygen
ο High circulating levels of PGE2
ο Early onset of a large left to right shunt
and CHF