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?

1. A)Inspiration decreases intrathoracic pressure, increasing venous return to the right atrium and right ventricular stroke volumeGABARITO
2. B)Inspiration increases pulmonary vascular resistance, causing increased right ventricular afterload and flow across the tricuspid valve
3. C)Inspiration decreases left ventricular compliance, causing compensatory right ventricular dilation
4. D)Inspiration increases systemic vascular resistance, shunting more blood toward the right heart chambers
5. E)Inspiration increases left ventricular stroke volume through increased pulmonary venous return