At birth, the first breath of a neonate triggers closure of the foramen ovale. Which sequence of hemodynamic events is the CORRECT mechanism?

• A Lung expansion → decreased pulmonary vascular resistance → increased pulmonary blood flow → increased left atrial pressure → functional closure of foramen ovale ✓
• B Umbilical cord clamping → increased systemic vascular resistance → reversed aortic-to-pulmonary pressure gradient → closure of ductus arteriosus before foramen ovale
• C Pulmonary vasoconstriction at first breath → increased right atrial pressure → pressure-driven opening of foramen ovale
• D Decreased left atrial pressure → passive closure of foramen ovale by reduced hydrostatic force

Explanation

With the first breath, lungs inflate and hypoxic pulmonary vasoconstriction (present in utero) is relieved. Pulmonary vascular resistance falls dramatically, pulmonary blood flow increases massively, returning large volumes to the left atrium. Left atrial pressure rises above right atrial pressure, functionally pushing the flap of the foramen ovale against the septum secundum — achieving functional closure. Cord clamping (option B) increases SVR and contributes but is not the primary mechanism for foramen ovale closure. Options C and D have the pressure gradients reversed.

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

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Written and medically reviewed by the StethoPrep medical team.