The nurse is conducting an admission assessment of an 11-month old infant with heart failure who is scheduled for repair of restenosis of coarctation of the aorta that was repaired 4 days after birth. Findings include blood pressure higher in the arms than the lower extremities, pounding brachial pulses, and slightly palpable femoral pulses. Which pathophysiologic mechanism supports these findings?

A. The aortic semilunar valve obstructs blood flow into the systemic circulation: Obstruction at the aortic valve (e.g., aortic stenosis) would affect blood flow from the left ventricle into the entire systemic circulation, not produce the characteristic difference between upper and lower extremities. Pounding brachial pulses with weak femoral pulses are more specific to coarctation. B. The lumen of the aorta reduces the volume of blood flow to the lower extremities: Coarctation of the aorta causes narrowing of a segment of the aorta. This narrowing increases resistance to blood flow beyond the constriction, reducing perfusion to the lower extremities while increasing pressure proximal to the stenosis. This explains the higher blood pressure in the arms, bounding brachial pulses, and diminished femoral pulses in the infant. C. The pulmonic valve prevents adequate blood volume into the pulmonary circulation: Pulmonic valve obstruction (pulmonary stenosis) affects right ventricular outflow and pulmonary blood flow, leading to cyanosis or right-sided heart failure signs. It does not cause the upper-to-lower extremity blood pressure gradient seen in coarctation of the aorta. D. An opening in the atrial septum causes a murmur due to a turbulent left to right shunt: An atrial septal defect results in a left-to-right shunt causing volume overload in the right heart and pulmonary circulation. It does not create a difference in upper versus lower extremity blood pressure or produce weak femoral pulses, making it unrelated to the findings in this infant.