Immediately after birth, the neonatal ductus arteriosus begins to close. Which is the most important physiological stimulus triggering functional closure within the first hours of life?

• A Rise in left atrial pressure causing mechanical compression of the ductus
• B Surge in circulating catecholamines stimulating ductal smooth muscle contraction
• C Fall in circulating prostaglandin E2 and rise in arterial PO2 ✓
• D Cord clamping raising systemic vascular resistance and reversing ductal shunt

Explanation

Functional closure of the ductus arteriosus occurs within 10–15 hours of birth in term neonates and is triggered by two simultaneous changes: (1) the rise in arterial PO2 as the lungs inflate and gas exchange begins — oxygen directly constricts ductal smooth muscle via inhibition of voltage-gated K+ channels and increased Rho-kinase activity; and (2) the fall in circulating PGE2 as placental production ceases and pulmonary vasculature (which metabolizes PGE2) is now perfused. Permanent anatomical closure takes 2–3 weeks as the ductus becomes the ligamentum arteriosum.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.