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. An opening in the atrial septum causes a murmur due to a turbulent left to right shunt: An atrial septal defect causes a murmur and left-to-right shunt but does not explain the differential blood pressures or pulses between upper and lower extremities. B. The pulmonic valve prevents adequate blood volume into the pulmonary circulation: Pulmonic valve obstruction affects pulmonary blood flow, not systemic perfusion or the blood pressure differences seen in coarctation of the aorta. C. The aortic semilunar valve obstructs blood flow into the systemic circulation: Obstruction at the aortic valve (e.g., aortic stenosis) impairs outflow from the left ventricle but would affect all systemic blood flow equally rather than producing higher pressures in the upper extremities compared with the lower extremities. D. The lumen of the aorta reduces the volume of blood flow to the lower extremities: Narrowing of the aortic lumen distal to the branches supplying the upper extremities causes elevated blood pressure and strong pulses in the arms and diminished pulses and perfusion to the lower extremities.