Patent ductus arteriosus is a heart condition in which the ductus arteriosus, which is a blood vessel that allows blood to bypass the baby's lungs before birth, fails to close after birth. During fetal development, the ductus arteriosus is a normal structure that allows blood to bypass circulation to the lungs. As the fetus does not use its lungs, because oxygen is provided through the mother’s placenta, flow from the right ventricle needs an outlet. The ductus provides this outlet, shunting flow from the left pulmonary artery to the aorta just beyond the origin of the artery to the left subclavian artery. After birth, the high levels of oxygen which it is exposed to causes it to close in most cases within 24 hours. When it does not close, it becomes a heart condition called Patent Ductus Arteriosus.
As the newborn takes its first breath, the lungs open and pulmonary vascular resistance decreases. After birth, the lungs release bradykinin to constrict the smooth muscle wall of the ductus arteriosus and reduce bloodflow through it as it narrows and completely closes, usually within the first few weeks of life. In normal newborns, the DA is substantially closed within 12–24 hours after birth, and is completely sealed after three weeks. The primary stimulus for the closure of the ductus is the increase in neonatal blood oxygen content. Withdrawal from maternal circulating prostaglandins also contributes to ductal closure. The residual scar tissue from the fibrotic remnants of DA, called the ligamentum arteriosum, remains in the normal adult heart.
Patent ductus arteriosus is common in newborn infant with persistent respiratory problems such as hypoxia, and has a high occurrence in premature children. In hypoxic newborns, too little oxygen reaches the lungs to produce sufficient levels of bradykinin and subsequent closing of the DA. Premature children are more likely to be hypoxic and thus have PDA because of their underdeveloped heart and lungs. A patent ductus arteriosus allows a portion of the oxygenated blood from the left heart to flow back to the lungs by flowing from the aorta (which has higher pressure) to the pulmonary artery. If this shunt is substantial, the neonate becomes short of breath: the additional fluid returning to the lungs increases lung pressure to the point that the neonate has greater difficulty inflating the lungs. This uses more calories than normal and often interferes with feeding in infancy.
Surgical Procedure to Close the Patent Ductus Arteriosus on Premature Baby, Performed by Dr. Redmond Burke MD