A newborn has a wide pulse pressure, bounding peripheral pulses, and a continuous machinery murmur. The wide pulse pressure in this condition results from:
- A Diastolic runoff of blood from the aorta into the pulmonary artery through the patent ductus ✓
- B Increased stroke volume secondary to bradycardia
- C Elevated diastolic pressure caused by increased systemic vascular resistance
- D Systolic hypertension from aortic coarctation proximal to the ductus
Correct answer: A. Diastolic runoff of blood from the aorta into the pulmonary artery through the patent ductus
Explanation
When the ductus remains open beyond the neonatal period, aortic pressure exceeds pulmonary arterial pressure throughout the cardiac cycle, so blood flows from aorta to pulmonary artery even in diastole. This diastolic runoff lowers diastolic pressure while the compensatory increase in stroke volume raises systolic pressure, producing the wide pulse pressure and bounding pulses. Systemic resistance is not elevated, and coarctation is a separate lesion that does not explain the continuous murmur.
Reference: Nelson Textbook of Pediatrics, 22nd ed.
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