Fetal and Neonatal Circulation RR Flashcards
Where does fetal gas exchange occur?
The placenta
What are the 2 main reasons for high resistance to blood flow in the fetal lungs?
Hypoxic vasoconstriction and crushed vessels due to the lungs not being inflated
What are the four unique shunts in the fetal circulation?
Ductus Arteriosus
Ductus Venosus
Foramen Ovale
Placenta
What is meant by the combined cardiac output in the fetal heart?
The sum of the outputs of both the left and right ventricles
What percent of fetal blood flow is diverted through the placenta?
50%
What are the major cadiopulmonary adjustments at/after birth?
1 Loss of placental circulation requires newborn to breath on its own.
2 Dramatic increase in pulmonary blood flow
3 Closrue of ductus venosus, foramen ovale, and ductus arteriosus
What triggers the first breath? (conventional thought)
hypoxia, hypercapnia, tactile stimuli, and cold skin
What are the three reasons that pulmonary vascular resistance falls at birth?
1 Pulmonary vessels are no longer crushed as the lung inflates
2 Breathing causes increase PO2 which causes vasodilation
3 Local prostaglandins cause vasodilation
What are the four essential functions of the adult organs that the placenta performs?
Lungs, Kidney, Liver, GI
What lies in the intervillous space? What supplies this space? what drains this space?
Maternal blood is trapped in the intervillous space. Maternal spiral arteries feed blood into this space. Maternal veins drain this space
Why is O2 saturation in the umbilical vein higher than that in the maternal vein if the partial pressure of O2 is the same in both?
Fetal blood has a higher percentage of fetal hemoglobin which has a higher affinity for oxygen, also fetal relative CO is higher.
What does closure of the placental circulation do to peripheral resistance and the pressure in the aorta?
causes PVR to double and pressure in the aorta and left ventricle to increase
Describe the changes that take place after birth that lead to the closure of the foramen ovale?
Increase pulmonary flow causes increased venous return to the left atrium and decreased right atrial pressure. The reversal in pressure caused the foramen ovale to close and a permanent seal forms in a few months or years.
What is possible mechanism for closure of ductus venosus? What does it become? What is it called if it fails to close?
Possibly increase PO2 and reduced prostaglandins cause the smooth muscle to contract. It closes within 3 hrs after birth. Failure of closure creates a portosystemic shunt
What are the mechanisms for closure of the ductus arteriosus? What are symptoms that can be caused by a patent ductus arteriosus?
Increased PO2 and decreased prostaglandins as well as bradykinin from the lung. A patent ductus arteriosus can cause pulmonary hypertension and possible CHF and arrythmias
