WBR267

Author	[[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1] (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Embryology, MainCategory::Pathophysiology
Sub Category	SubCategory::Vascular
Prompt	[[Prompt::A 4-week-old female infant is brought to the emergency room for rapid breathing, diaphoresis, and difficulty feeding. The girl's past medical history is significant for preterm birth. Her mother mentions that ever since the girl was born, she has not been feeding well and there has been little weight gain. On physical examination, the infant has a hoarse cry with with evidence of bilateral basal crackles on pulmonary auscultation. Doppler echocardiogram demonstrates a significant left-to-right shunt. Which of the following statements is true about the infant’s underlying condition?]]
Answer A	AnswerA::The patency of the ductus arteriosus is primarily controlled by low fetal oxygen tension and the circulation of prostanoids produced from arachidonic acid metabolism.
Answer A Explanation	[[AnswerAExp::Oxygen-induced constriction of the ductus arteriosus fails in preterm infants potentially due to immaturity of oxygen-sensing receptors. Smooth muscle relaxation of the ductus arteriosus results from the activation of the G-coupled prostaglandin receptor EP4 by PGE2. Within 1– 5 days after a full-term birth, the ductus arteriosus closes as a result of increased oxygen tension and decreased circulating PGE2 and prostacyclins (PGI2).]]
Answer B	AnswerB::Oxygen-induced constriction of the ductus arteriosus fails in preterm infants potentially due to maturity of oxygen-sensing receptors
Answer B Explanation	AnswerBExp::Oxygen-induced constriction of the ductus arteriosus fails in preterm infants potentially due to immaturity (not maturity) of oxygen-sensing receptors.
Answer C	AnswerC::The ductus arteriosus is thought to derive from the embryonic left fourth aortic arch
Answer C Explanation	AnswerCExp::The ductus arteriosus is thought to derive from the embryonic left sixth (not fourth) aortic arch.
Answer D	AnswerD::Smooth muscle contraction of the ductus arteriosus results from the activation of the G-coupled prostaglandin receptor EP4 by PGF2
Answer D Explanation	AnswerDExp::Smooth muscle contraction of the ductus arteriosus results from the activation of the G-coupled prostaglandin receptor EP4 by PGE2 (not PGF2).
Answer E	AnswerE::Within 1 – 5 days after a full-term birth, the ductus arteriosus closes as a result of decreased oxygen tension and increased circulating PGE2 and prostacyclins (PGI2)
Answer E Explanation	AnswerEExp::Within 1 – 5 days after a full-term birth, the ductus arteriosus closes as a result of increased (not decreased) oxygen tension and decreased (not increased) circulating PGE2 and prostacyclins (PGI2).
Right Answer	RightAnswer::A
Explanation	[[Explanation::The patient is diagnosed with patent ductus arteriosus (PDA), which is characterized by significant postnatal left to right shunt. Pneumonia is a typical early manifestation of PDA, and PDA should be ruled out when infants are diagnosed with recurrent pneumonias shortly after birth. The ductus arteriosus (DA) is derived from the embryonic left sixth aortic arch. It connects the pulmonary artery to the aorta and it serves to shunt blood away from the lungs into the umbilical placental circulation, where gas exchange takes place. At birth, the closure of the DA is essential for postnatal adaptation. Its closure is initiated by an increase in oxygen and changes in both the pulmonary and systemic blood pressures. In full-term neonates, the DA typically closes within the first 5 days post-delivery. In preterm infants, however, failure of DA closure following birth is associated with an increased incidence of neonatal morbidity. The patency of the ductus arteriosus is primarily controlled by low fetal oxygen tension and the prostanoids in the blood produced from arachidonic acid metabolism. Oxygen-induced constriction of the ductus arteriosus fails in preterm infants potentially due to immaturity of oxygen-sensing receptors. Smooth muscle relaxation of the ductus arteriosus results from the activation of the G-coupled prostaglandin receptor EP4 by PGE2. Within 1 – 5 days after a full-term birth, the ductus arteriosus closes as a result of increased oxygen tension and decreased circulating PGE2 and prostacyclins (PGI2). Using either indomethacin or ibuprofen to trigger prostaglandin inhibition has been the standard of care to close the PDA in predisposed infants, who are particularly preterm. Surgical closure of the patent DA is often reserved to patients whose PDA fails to close following pharmacologic therapy. Educational Objective: Oxygen-induced constriction of the ductus arteriosus fails in preterm infants potentially due to immaturity of oxygen-sensing receptors. Smooth muscle relaxation of the ductus arteriosus results from the activation of the G-coupled prostaglandin receptor EP4 by PGE2. Within 1– 5 days after a full-term birth, the ductus arteriosus closes as a result of increased oxygen tension and decreased circulating PGE2 and prostacyclin (PGI2). References: Thebaud B, Lacaze-Mazmonteil T. Patent ductus arteriosus in premature infants: A never-closing act. Paediatr Child Health. 2010;15(5):267-70. ]]
Approved	Approved::Yes
Keyword	WBRKeyword::PDA, WBRKeyword::Patent ductus arteriosus
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::