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The first is the foramen ovale (the valve present between them called eustachian valve) which shunts blood from the right atrium to the left atrium. The second is the ductus arteriosus which shunts blood from the pulmonary artery (which, after birth, carries blood from the right side of the heart to the lungs) to the descending aorta.
The blood pressure in the fetal aorta is approximately 30 mmHg at 20 weeks of gestation, and increases to ca 45 mmHg at 40 weeks of gestation. [16] The fetal pulse pressure is ca 20 mmHg at 20 weeks of gestation, increasing to ca 30 mmHg at 40 weeks of gestation. [16] The blood pressure decreases when passing through the placenta.
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]
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. Since the lungs now require a significant amount of blood flow, the vessels going to and from the lungs undergo dilation.
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.
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.
To diagnose a fetus with pulmonary hypertension, PVR must be higher than systemic vascular resistance, resulting in high afterload and decreased systemic blood flow. This causes a significant decrease in oxygen concentration, which clinically manifests as insufficient blood flow to the lower body, while there is adequate circulation to the head ...
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).