Expiration tends to intensify left-sided murmurs by increasing which preload?

• A. Expirat ion increases left atrial preload, intensifying left-sided murmurs
• B. Expirat ion decreases left atrial preload
• C. Expirat ion increases right atrial preload
• D. Expirat ion has no effect on left-sided murmurs

Answer: (A)

The main idea is that what you breathe in and out changes how much blood returns to the heart on the left side, so left-sided murmurs get louder when preload to the left heart increases. Expiration raises intrathoracic pressure, which reduces venous return to the right heart and shifts more blood toward the pulmonary circulation—this increases pulmonary venous return to the left atrium. That boosts left atrial preload, leading to greater left ventricular filling. With more volume in the left ventricle, the flow across left-sided valves (like the mitral or aortic valve) can produce a louder murmur, especially if there’s regurgitation or stenosis. In contrast, inspiration raises right-sided preload and tends to reduce left-sided filling, so right-sided murmurs are louder with inspiration and left-sided murmurs tend to soften. So expiration intensifies left-sided murmurs by increasing left atrial preload.