Eustachian valve是上下腔静脉瓣？

Eustachian valve是上下腔静脉瓣？as the 是多余的吗？

In utero, the pulmonary arteries have high vascular resistance while there is low systemic vascular resistance. The majority of oxygenated blood from the placenta enters the right heart and is shunted across the Eustachian valve to the left atrium to supply the brain, heart and upper body with relatively highly oxygenated blood. Immediately after birth the inflation of the lungs with the first few breaths causes a drop in the resistance to pulmonary blood. The majority of blood flow is now circulated through the lungs which replaces the placenta as the as the organ of gas exchange. The subsequent increase in left atrial blood flow from the pulmonary veins increases left atrial pressure and functionally closes the foramen ovale [8]. With these anatomic and flow changes the right heart and pulmonary artery pressures fall. In a healthy neonate the mean pulmonary artery pressure approaches 50% of mean systemic pressure by the end of day one of life, and should drop to the normal adult level by two weeks of age [9]. In the case of a neonate with a congenital diaphragmatic hernia the normal fall in pulmonary artery pressure may not occur and the degree of persistent pulmonary hypertension as a result of the defect will become apparent in the first few days of life.