Adaptation of circulation in newborns.

1. Big picture

Adaptation of circulation in newborns means the rapid cardiovascular transition from placenta-based fetal circulation to lung-based postnatal circulation.

The examiner wants you to understand this sequence:

First breath + cord clamping
→ pulmonary vascular resistance falls
→ systemic vascular resistance rises
→ pulmonary blood flow increases
→ left atrial pressure rises
→ foramen ovale functionally closes
→ ductus arteriosus constricts
→ neonatal circulation becomes “adult type”

Clinically, this topic is important because failure of normal transition causes:

• persistent pulmonary hypertension of the newborn (PPHN)
• persistent ductus arteriosus (PDA)
• cyanosis
• shock after ductal closure in duct-dependent congenital heart disease
• differential saturation between upper and lower body

---