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In about 25% of adults the foramen ovale does not close completely, but remains as a small patent foramen ovale ("PFO"). [5] In most of these individuals, the PFO causes no problems and remains undetected throughout life.
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]
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).
patent foramen ovale – a hole between the atrial chambers of the heart in the fetus is normally closed by a flap with the first breaths at birth. In about 20% of adults the flap does not completely seal, however, allowing blood through the hole when coughing or during activities that raise chest pressure.
The septum primum, a septum which grows down to separate the primitive atrium into the left atrium and right atrium, grows in size over the course of heart development.The primary interatrial foramen is the gap between the septum primum and the septum intermedium, which gets progressively smaller until it closes.
The left atrium now has higher pressure than the right atrium causing the foramen ovale to close. Within the first 10 minutes of birth, blood begins to flow left-to-right through the ductus arteriosus. This causes a significant increase in output of the left ventricle and increase in stroke volume.
The increased pressure causes a rupture of the cranial dura mater, leading to a CSF leak and intracranial hypotension. [46] [47] Patients with a nude nerve root, where the root sleeve is absent, are at increased risk for developing recurrent CSF leaks. [48] Lumbar disc herniation has been reported to cause CSF leaks in at least one case. [49]
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.