Immediately after birth, what happens to pulmonary vascular resistance and how does it affect the ductus arteriosus?

• A. Pulmonary vascular resistance decreases; the ductus arteriosus constricts
• B. Pulmonary vascular resistance stays the same; the ductus arteriosus remains open
• C. Pulmonary vascular resistance increases; the ductus arteriosus constricts
• D. Pulmonary vascular resistance increases; the ductus arteriosus stays open

Answer: (A)

Immediately after birth, the lungs expand and oxygen levels rise, causing pulmonary vascular resistance to fall. This drop in resistance allows more blood to flow through the lungs and, along with higher oxygen and lower placental prostaglandins, prompts the ductus arteriosus to constrict. The ductus arteriosus constriction closes the fetal shunt, redirecting blood to the lungs for oxygenation. In short, pulmonary vascular resistance decreases and the ductus arteriosus constricts, leading to functional closure soon after birth.