Valvular Heart Disease USMLE Step 1 Practice Question
A 65-year-old man presents for a routine physical examination. He is asymptomatic and denies dyspnea, orthopnea, or palpitations. Vital signs: heart rate 78/min, blood pressure 142/88 mm Hg, respiratory rate 16/min, oxygen saturation 98% on room air. On cardiac auscultation, a holosystolic murmur is heard best at the left lower sternal border (4th-5th intercostal space). The murmur increases in intensity during inspiration and decreases during expiration. Which of the following physiologic mechanisms best explains the increase in murmur intensity during inspiration?
Answer choices
- ADecreased intrathoracic pressure increases venous return to the right heartCorrect answer
- BIncreased pulmonary vascular capacitance reduces right ventricular afterload
- CNegative intrathoracic pressure decreases left ventricular preload
- DIncreased sympathetic tone enhances right ventricular contractility
- EPositive airway pressure reduces systemic vascular resistance
- FIncreased intrapulmonary pressure compresses the left atrium
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