Valvular Heart Disease USMLE Step 1 Practice Question
A 65-year-old man with a history of myocardial infarction 2 years ago presents for follow-up evaluation. He reports no dyspnea, orthopnea, or lower extremity edema. Vital signs are: heart rate 82/min, blood pressure 145/90 mm Hg, respiratory rate 16/min. On cardiac auscultation, a holosystolic (pansystolic) 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 best explains why this murmur increases in intensity with inspiration?
Answer choices
- AInspiration decreases intrathoracic pressure, increasing venous return to the right atrium and right ventricular stroke volumeCorrect answer
- BInspiration increases pulmonary vascular resistance, causing increased right ventricular afterload and flow across the tricuspid valve
- CInspiration decreases left ventricular compliance, causing compensatory right ventricular dilation
- DInspiration increases systemic vascular resistance, shunting more blood toward the right heart chambers
- EInspiration increases left ventricular stroke volume through increased pulmonary venous return
- FInspiration decreases right ventricular contractility, allowing greater regurgitant flow across the tricuspid valve
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