Corpus: Ductus arteriosus

The ductus arteriosus is a vascular connection between the aorta and the pulmonary trunk that exists in the foetal circulation and normally obliterates after birth.

The ductus arteriosus develops from the left 6th gill arch artery. Before birth, it is a physiological short-circuit connection (shunt) that bypasses the pulmonary circulation. As the foetal lungs are not yet ventilated in utero, significant pulmonary perfusion would be uneconomical for the foetus. The lack of ventilation of the lungs leads to hypoxic vasoconstriction, which greatly increases the resistance to flow in the pulmonary arteries. The majority of the blood (> 90 % of cardiac output) therefore flows from the pulmonary trunk via the ductus arteriosus into the aorta.^[1] Only a small proportion of the blood flows through the pulmonary capillaries and via the pulmonary veins back to the left atrium.

The ductus arteriosus is kept open prenatally primarily by high levels of prostaglandin E₂ (PGE₂). PGE₂ is formed in the smooth muscle cells of the wall of the ductus arteriosus and in the placenta.^[1]

Normally, the ductus arteriosus begins to close successively when the child starts breathing after birth. Various factors play a role in this:

• Ventilation of the lungs causes the pulmonary arteries to widen and the resistance to flow decreases. This changes the pressure conditions, resulting in a reversal of flow in the ductus arteriosus. The blood from the pulmonary trunk increasingly flows into the pulmonary circulation.
• After birth, the oxygen content in the blood increases and the PGE₂ level decreases, as the placenta ceases to be a PGE₂ producer and PGE₂ is broken down in the increasingly perfused lungs. Both promote the contraction of the smooth muscles in the ductus and lead to a functional closure of the ductus arteriosus within about 3 days after birth^[1]
• Due to an intimal proliferation in the first year of life, the ductus arteriosus closes permanently. What remains is a thin strand of connective tissue, the ligamentum arteriosum.

The lack of closure of the ductus arteriosus after birth is referred to as a persistent ductus arteriosus (ductus arteriosus Botalli apertus). Among other things, this is part of the Gregg triad, the characteristic constellation of symptoms in the full picture of rubella embryopathy.

The ductus arteriosus can be kept open temporarily by the prostaglandin E1 derivative alprostadil. This is indicated, for example, in some cyanotic congenital heart defects.