PATENT DUCTUS ARTERIOSUS

persistence of a channel that shunts blood between the pulmonary artery and the aorta. Normally, after birth, the pulmonary artery carries blood depleted of oxygen and laden with carbon dioxide from the right lower chamber of the heart to the lungs, where the excess carbon dioxide is removed from the blood and replaced with oxygen. Before birth the fetus depends upon its mother's circulation for this function and not on its own lungs. Consequently, most of the blood pumped into the pulmonary artery is shunted through the ductus arteriosus into the aorta for distribution into the general circulation. Normally at birth the ductus arteriosus constricts and closes, becoming a fibromuscular cord. Persistence of the open passage is a congenital defect that ordinarily causes no symptoms. It is diagnosed from characteristic abnormalities of the heart sounds. If the passageway is large, it can have serious effects, acting as a shunt that carries blood from the aorta into the pulmonary artery. This reversal of the shunt pathway occurs because, as a normal part of the changes from fetal to postnatal circulation, the blood pressure in the aorta rises greatly, while that in the pulmonary artery falls. As a consequence of this shunt, the blood may be routed two or three times from the left ventricle to the lungs before it follows its normal course into the systemic circulation. The left side of the heart is thus greatly overworked and becomes enlarged, and the lungs become congested and their network of blood vessels suffers damage from excessive blood pressure. As a result, the victim's body is deprived of adequate oxygen during exertionor, in extreme cases, even during rest. The oxygen deprivation is indicated by cyanosis (a bluish discoloration of the skin). Infants with patent ductus arteriosus can be treated with drugs that effectively close the shunt in many cases. If drug therapy is unsuccessful, the ductus can be tied off surgically.