Ductus arteriosus

In the developing fetus, the ductus arteriosus (DA) is a shunt connecting the pulmonary artery to the aortic arch that allows most of the blood from the right ventricle to bypass the fetus' fluid-filled lungs. During fetal development, this shunt protects the lungs from being overworked and allows the right ventricle to strengthen. There are two other fetal shunts, the ductus venosus and the foramen ovale.

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Eponym

The ductus arteriosus is sometimes called the ductus Botalli, after Leonardo Botallo, although the discovery should have been attributed to Giulio Cesare Aranzi, to whom (less commonly) the ductus venosus is named.^[1]

Closure at birth

When the newborn takes its very first breath, pulmonary vascular resistance falls due to physical opening of the pulmonary capillaries and attenuation of intrauterine hypoxic pulmonary vasoconstriction. Decreased pulmonary vascular resistance increases pulmonary blood flow while pulmonary vascular pressure falls below aortic pressure. At the same time, the lungs release bradykinin (vasodilator) and falling prostaglandin levels cause constriction of the smooth muscle in wall of the DA, reducing flow. Bradykinin works by acting on eNOS to increase NO produced, thus inducing vasodilatation. ACE breaks down bradykinin and therefore, ACE inhibitors aid in prolonging the action of vasodilatation by bradykinin. Additionally, because of reduced pulmonary resistance, more blood flows from the pulmonary arteries to the lungs and thus the lungs deliver more oxygenated blood to the left heart. This further increases aortic pressure so that flow in DA may transiently reverse.

Usually, the DA begins to close when breathing is established, and is completely sealed after four to ten days. A cord-like vestige of the DA, called the ligamentum arteriosum, remains to connect the exterior of the left pulmonary artery to the exterior of the aortic arch.

When the ligamentum arteriosum forms it traps the left branch of the recurrent left vagus nerve in the thorax.

Patent ductus arteriosus

Main article: Patent ductus arteriosus

Failure of a child's DA to close after birth results in a condition called patent ductus arteriosus and the generation of a left-to-right shunt. If left uncorrected, patency leads to pulmonary hypertension and possibly congestive heart failure and cardiac arrhythmias. Closure may be induced with a drug class known as NSAIDs such as indomethacin or ibuprofen because these drugs inhibit prostaglandin synthesis. Prostaglandins are responsible for maintaining the ductus arteriosus.

References

1. ^ doctor/264 at Who Named It