II. Physiology: Fetus
- Fetal gas exchange occurs at the placenta (not the lung)
- Ductus venosus
- Carries oxygenated blood from the placenta
- Delivers to the inferior vena cava via the umbilical vein
- Mixes with deoxygenated blood returning from the lower extremity
- Pulmonary arteries
- Returns blood from the descending aorta to the placenta to be re-oxygenated
- Ductus venosus
- Fetal right ventricular output
- Right to left shunt, bypassing the lungs (60% of flow)
- Increased pulmonary vascular resistance
- Ductus arteriosus
- Foramen ovale
- Pulmonary system (40% of flow)
- Alveoli are filled with amniotic fluid and result in minimal gas diffusion
- Right to left shunt, bypassing the lungs (60% of flow)
III. Physiology: Birth Transition from Fetal Circulation
- Alveolar fluid is replaced with air on initial ventilations
- Critical first step that leads to reduced pulmonary vascular resistance
- Results in an increase in PaO2 with an associated decreased in pulmonary vascular resistance
- Negative intrathoracic pressure increases
- Initiated with uterine contractions and travel through the birth canal
- First few breaths add to the negative intrathoracic pressure
- Increased pulmonary perfusion
- Results from less resistance to flow through pulmonary system than through fetal shunts
- Increased Systemic Vascular Resistance following delivery
- Flow reverses in the ductus arteriosus (now traveling aorta to pulmonary artery)
- Closure of shunts (last steps in transition)
- Ductus arteriosus closes within hours to days (unless Patent Ductus Arteriosus)
- Foramen ovale closes last
- Results from increased left atrial flow and pressure
-
Myocardium changes
- Right ventricle wall thins
- Left ventricle wall hypertrophies
IV. Resources
- Cove Point Foundation - Congenital Heart Disease
V. References
- Joseph and Webb (2015) Crit Dec Emerg Med 29(1): 10-8
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Related Studies
| Definition (MSH) | The circulation of blood through the fetus, umbilical cord and placenta on the fetal side. |
| Concepts | Organ or Tissue Function (T042) |
| MSH | D021041 |
| English | CIRC FETOPLACENTAL, FETAL PLACENTAL CIRC, FETOPLACENTAL CIRC, fetoplacental circulation, fetal-placental circulation, Circulation, Fetal-Placental, Circulation, Fetoplacental, Circulations, Fetal-Placental, Circulations, Fetoplacental, Fetal Placental Circulation, Fetal-Placental Circulation, Fetal-Placental Circulations, Fetoplacental Circulations, Fetoplacental Circulation |
| Czech | fetoplacentární oběh |
| French | Circulation foetoplacentaire, Circulation foeto-placentaire |
| German | Fetoplazentarer Kreislauf, Kreislauf, fetoplazentarer |
| Italian | Circolazione fetoplacentare |
| Norwegian | Føtoplacentar sirkulasjon |
| Dutch | Circulatie, foetoplacentaire, Foetoplacentaire circulatie |
| Portuguese | Circulação Fetoplacentária |
| Spanish | Circulación Fetoplacentaria |
