Fetal Circulation

Question 1

Placenta function

Answer 1

provides gas exchange in the fetus

Question 2

What are the vessels of the placenta?

Answer 2

2 umbilical arteries- deoxygenated blood from fetus to placenta

1 umbilical vein- returns oxygenated blood from placenta back to fetus

Question 3

What are the three main fetal shunts?

Answer 3

Ductus Arteriosus
Foramen Ovale
Ductus Venosus

Question 4

Fetal circulation changes at birth due to ____

Answer 4

loss of placenta as a source and establishment of lungs as the gas exchange unit

Question 5

Parallel Circulation

Answer 5

Fetal Circulation shunts blood away from lungs
Both ventricles supply the systemic circulation

Question 6

10-15% of blood from PA passes through ____

Answer 6

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

Question 7

Coming from placenta to 1 umbilical vein, 50% of blood to the IVC via ____

Answer 7

ductus venosus (DV connects L PV, to L HV), 50% through hepatic sinus to liver and enters IVC via HV

Question 8

IVC blood enter LA during what percent of the cardiac cycle?

Answer 8

IVC blood enter LA during 80% of cardiac cycle. In 20% blood from IVC crosses TV into RV

Question 9

Deoxygenated blood from head, neck, and upper extremities coming through SVC also ____

Answer 9

crosses tricuspid valve into RV

Question 10

Most of the blood goes to which 3 large branches of aorta?

Answer 10

(brachiocephalic, left common carotid, and L subclavian to head, neck, UE. Preferential flow to coronary and cerebral circulation.

Question 11

fetal lungs = ____
placenta = site of ____

Answer 11

Fetal lungs are collapsed
Placenta is sight of gaseous exchange

Question 12

fetal hemoglobin

Answer 12

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.

Question 13

adult vs. fetal oxyhemoglobin dissociation curve

Answer 13

Question 14

Hemodynamics and Oxygen Saturations of Term Fetus

Answer 14

Low O2 saturation in SVC
Higher O2 saturation in IVC
Patent ductus arteriosus (DA), foramen ovale (FO)
Collapsed lungs
High PVR

Question 15

Hemodynamics and Oxygen Saturations during Transitional Circulation

Answer 15

DA and FO closing
Lower PVR
Increased AO O2 saturation

Question 16

What closes several days after birth?

Answer 16

DA and FO closed

Question 17

Ductus Arteriosus

Answer 17

Organ Bypassed: lungs
Changes after Birth: closure
Adult Remanent: Ligamentum Arteriosum

Question 18

Foramen Ovale

Answer 18

Organ Bypassed: lungs
Changes after Birth: closure
Adult Remanent: Fossa Ovalis

Question 19

Ductus Venosus

Answer 19

Organ Bypassed: liver
Changes after Birth: closure
Adult Remanent: Ligamentum Venosum

Question 20

Umbilical Arteries

Answer 20

Changes after Birth: Obliteration
Adult Remanent: Medial Umbilical Ligaments

Question 21

Umbilical Vein

Answer 21

Changes after Birth: Obliteration
Adult Remanent: Ligamentum Teres Hepatis

Question 22

Foramen Ovale creates what kind of shunt? How?

Answer 22

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

Question 23

Describe the closure of the foramen ovale

Answer 23

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

Question 24

Ductus Arteriosus creates what kind of shunt? How?

Answer 24

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.

Question 25

Describe the closure of the Ductus Arteriosus

Answer 25

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

Question 26

Ductus Venosus provides _____

Answer 26

oxygenated blood from umbilical vein to bypass liver to IVC 50% of UV blood bypasses liver

Question 27

Describe the closure of the Ductus Venosus

Answer 27

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

Question 28

Fetal pulmonary vascular features

Answer 28

Low pulm BF secondary to high pulmonary vascular resistance (PVR) Vasoconstriction ↓ PaO2 ↓pH, leukotrienes

Question 29

Potent Vasodilators of fetal pulmonary vessels

Answer 29

Ach, histamine, bradykinin, PGE1, PGE2, PGI2, prostaglandin D2, 𝛽 Adrenergic catecholamines (NE & Epi)

Question 30

After Birth, _____ commences. Then what happens?

Answer 30

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

Question 31

Myocardial Performance in Neonate

Answer 31

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

Question 32

How is myocardial performance different in Neonates?

Answer 32

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

Question 33

Oxygen Consumption (infant, child, adult)

Answer 33

Infant: 6-8 mL/kg/min Child: 4-6 mL/kg/min Adult: 2-3 mL/kg/min

Question 34

Cardiac Output (neonate, infant, adult)

Answer 34

Neonate: 350 mL/kg/min Infant: 150 mL/kg/min Adult: 75 mL/kg/min

Question 35

Blood Volume for different age groups

Answer 35

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