Fetal Circulation Flashcards
Placenta function
provides gas exchange in the fetus
What are the vessels of the placenta?
2 umbilical arteries- deoxygenated blood from fetus to placenta
1 umbilical vein- returns oxygenated blood from placenta back to fetus
What are the three main fetal shunts?
Ductus Arteriosus
Foramen Ovale
Ductus Venosus
Fetal circulation changes at birth due to ____
loss of placenta as a source and establishment of lungs as the gas exchange unit
Parallel Circulation
Fetal Circulation shunts blood away from lungs
Both ventricles supply the systemic circulation
10-15% of blood from PA passes through ____
the lungs to reach LA, but the rest (90%) is shunted to to distal Ao via DA (the 10% which goes through lung goes back to LA via Pulmonary vein to LV to Ao to abdomen and lower extremities) then to internal iliac arteries, to 2 umbilical arteries then to placenta
Coming from placenta to 1 umbilical vein, 50% of blood to the IVC via ____
ductus venosus (DV connects L PV, to L HV), 50% through hepatic sinus to liver and enters IVC via HV
IVC blood enter LA during what percent of the cardiac cycle?
IVC blood enter LA during 80% of cardiac cycle. In 20% blood from IVC crosses TV into RV
Deoxygenated blood from head, neck, and upper extremities coming through SVC also ____
crosses tricuspid valve into RV
Most of the blood goes to which 3 large branches of aorta?
(brachiocephalic, left common carotid, and L subclavian to head, neck, UE. Preferential flow to coronary and cerebral circulation.
fetal lungs = ____
placenta = site of ____
Fetal lungs are collapsed
Placenta is sight of gaseous exchange
fetal hemoglobin
Fetal hemaglobin (HbF) – higher oxygen affinity – 2 𝛼 and 2 𝛾 globin chains
Although, Fetal Hgb has higher affinity for oxygen in such a low partial pressure environment of the fetal tissue it also readily unloads oxygen.
adult vs. fetal oxyhemoglobin dissociation curve
Hemodynamics and Oxygen Saturations of Term Fetus
Low O2 saturation in SVC
Higher O2 saturation in IVC
Patent ductus arteriosus (DA), foramen ovale (FO)
Collapsed lungs
High PVR
Hemodynamics and Oxygen Saturations during Transitional Circulation
DA and FO closing
Lower PVR
Increased AO O2 saturation
What closes several days after birth?
DA and FO closed
Ductus Arteriosus
Organ Bypassed: lungs
Changes after Birth: closure
Adult Remanent: Ligamentum Arteriosum
Foramen Ovale
Organ Bypassed: lungs
Changes after Birth: closure
Adult Remanent: Fossa Ovalis
Ductus Venosus
Organ Bypassed: liver
Changes after Birth: closure
Adult Remanent: Ligamentum Venosum
Umbilical Arteries
Changes after Birth: Obliteration
Adult Remanent: Medial Umbilical Ligaments
Umbilical Vein
Changes after Birth: Obliteration
Adult Remanent: Ligamentum Teres Hepatis
Foramen Ovale creates what kind of shunt? How?
Creates a R to L shunt in utero
The stream of blood from ductus venosus (DV) has higher velocity in IVC than the stream from the lower body and hepatic veins.
Facilitates delivery of higher oxygenated content blood across foramen ovale (FO) to Left atrium (LA) to LV then to 3 large branches of aorta
Describe the closure of the foramen ovale
In utero RAP> LAP
Inc in LAP causes closure of FO
Functional closure usually progresses to anatomical closure
May be patent in 30% of adults
May be patent in 50 % of children < 5 yrs old
Ductus Arteriosus creates what kind of shunt? How?
R to L shunt
90% of blood from Pulmonary artery shunted to distal Aorta via DA
In utero, patency by high levels of prostaglandins (prostacyclin (PGI2) and prostaglandin E1 (PGE1) due to the response to low oxygen tension relevant to hypoxia.
Describe the closure of the Ductus Arteriosus
Contraction of smooth muscle
Occurs within first day of life
↑Partial pressure of oxygen (PO2) and ↓ prostaglandins
Oxygen is dose-dependent ductal constrictor
NE and Epi may also have effect
Permanent Anatomical Closure
2-3 weeks of life in normal full-term neonate
Ductus Venosus provides _____
oxygenated blood from umbilical vein to bypass liver to IVC
50% of UV blood bypasses liver
Describe the closure of the Ductus Venosus
High oxygen tension which occurs after birth causes umbilical vessel constriction
Passive closure results from decrease in umbilical venous blood flow due to the severed connection between umbilical cord to placenta after birth
High levels of NE may also cause vasoconstriction
Functional closure by 1 week of life
Anatomic closure by 3 months
Fetal pulmonary vascular features
Low pulm BF secondary to high pulmonary vascular resistance (PVR)
Vasoconstriction
↓ PaO2
↓pH, leukotrienes
Potent Vasodilators of fetal pulmonary vessels
Ach, histamine, bradykinin, PGE1, PGE2, PGI2, prostaglandin D2, 𝛽 Adrenergic catecholamines (NE & Epi)
After Birth, _____ commences. Then what happens?
After Birth- ventilation commences
Reduced mechanical compression of small pulmonary vessels
↑bradykinin levels
↑PaO2 ↓PVR
↓PGE2 and prostacyclin levels
Consequently, ↑ in pulm BF to lungs results in ↑ pulmonary venous return to LA so ↑ in LV output and aorta receives more blood resulting in ↑ aortic BP
Myocardial Performance in Neonate
In utero
RV has CO of about 330 mL/kg/min
LV has CO of about 170 mL/kg/min
At Birth- Newborn
RV and LV CO is about 350 mL/kg/min
By 8-10 weeks of life
CO is about 150 mL/kg/min
How is myocardial performance different in Neonates?
Limited Preload Reserve
- Augmentation of stroke volume via Frank-Starling mechanism is limited compared to adult
Reduced Contractile Capacity
- Neonatal cardiac cells contain more water and fewer contractile elements than mature myocardium
Reduced Ventricular Compliance
-Deficiency of elastic elements
Incomplete autonomic innervation
- Sympathetic innervation is underdeveloped
- Parasympathetic, however, is fully functional at birth
Immature Myocardial metabolism
May be protective
Oxygen Consumption (infant, child, adult)
Infant: 6-8 mL/kg/min
Child: 4-6 mL/kg/min
Adult: 2-3 mL/kg/min
Cardiac Output (neonate, infant, adult)
Neonate: 350 mL/kg/min
Infant: 150 mL/kg/min
Adult: 75 mL/kg/min
Blood Volume for different age groups
Premature: 90-100 mL/kg
Newborn (<1 month): 80-90 mL/kg
Infants (3 mo to 3 yrs): 75-80 mL/kg
Children older than 6 yrs: 65-70 mL/kg
Adults: 65-70 mL/kg
