The ductus carries blood from the pulmonary artery to the aorta during fetal life, whereas its persistence produces an aorta-to-pulmonary artery shunt.
Direction and continuity of flow
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Before the fetal lungs begin functioning, most pulmonary artery blood passes through the ductus into the aorta.
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With persistent ductus arteriosus, aortic pressure exceeds pulmonary artery pressure throughout the cardiac cycle, producing a continuous aorta-to-pulmonary artery shunt.
Volume load and pulmonary consequences
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Shunt volume depends on ductal size. As much as 50% of left ventricular output may recirculate through the lungs, increasing cardiac work.
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A large left-to-right shunt in infancy may considerably increase pulmonary artery pressure and sometimes cause progressive pulmonary vascular damage.