What causes the ductus arteriosus in a full-term infant to functionally close within the first day of life?

The functional closure of the ductus arteriosus in a full-term infant within the first day of life is primarily attributed to increased pressure in the aorta. After birth, as the infant takes its first breaths, blood flow to the lungs significantly increases. This increase in pulmonary blood flow causes the left side of the heart to pump more vigorously, resulting in an elevation of pressure in the aorta.

This higher pressure in the aorta compared to the pulmonary artery encourages the closure of the ductus arteriosus, which normally shunts blood from the pulmonary artery to the aorta while the fetus is still in utero. The change in pressure dynamics effectively causes the ductus to constrict and eventually close off, transitioning to more normal circulatory physiology.

Although increased blood flow to the lungs is an important factor in the process, it is the resultant increase in aortic pressure that plays a crucial role in the functional closure of the ductus arteriosus. Lower oxygen levels in the blood typically do not contribute positively to the closure; in fact, higher oxygen levels post-delivery promote closure. Decreased pressure in systemic circulation does not align with the physiological changes affecting the ductus arteriosus either.