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At birth, when the lungs become functional, the pulmonary vascular pressure decreases and the left atrial pressure exceeds that of the right. This forces the septum primum against the septum secundum, functionally closing the foramen ovale. In time the septa eventually fuse, leaving a remnant of the foramen ovale, the fossa ovalis.
A flap of tissue called the septum primum acts as a valve over the foramen ovale during that time. After birth, the introduction of air into the lungs causes the pressure in the pulmonary circulatory system to drop. This change in pressure pushes the septum primum against the atrial septum, closing the foramen. [1]
At birth, there is a reversal in the pressure gradient between the atria, resulting in functional closure of the valve of the foramen ovale. Permanent anatomical closure of the foramen ovale occurs with time in normal infants. Inappropriate failure of closure of the foramen ovale results in patent foramen ovale.
Atrial septal defect (ASD) is a congenital heart defect in which blood flows between the atria (upper chambers) of the heart.Some flow is a normal condition both pre-birth and immediately post-birth via the foramen ovale; however, when this does not naturally close after birth it is referred to as a patent (open) foramen ovale (PFO).
When the pressure in the left atrium exceeds the pressure in the right atrium, the foramen ovale begins to close and limits the blood flow between the left and right atrium. While the eustachian valve persists in adult life, it essentially does not have a specific function after the gestational period.
Foramen ovale. The foramen ovale is an opening in the greater wing of the sphenoid bone. [1] The foramen ovale is one of two cranial foramina in the greater wing, the other being the foramen spinosum. [2]: 771 The foramen ovale is posterolateral to the foramen rotundum and anteromedial to the foramen spinosum.
Once a baby is born, blood should flow through the lungs, which now function to provide oxygen to the blood. The foramen secundum and foramen ovale act as a shunt where blood bypasses the lungs and does not become oxygenated. To provide proper blood flow as a newborn, the foramen secundum and foramen ovale must close at birth.
Although closure of a patent foramen ovale or atrial septal defect theoretically removes the pathway for an arterial embolus to enter venous circulation and cause a paradoxical embolism, data suggests that closing intracardiac shunts is no more effective than medical management alone in preventing strokes. [2]