Why does expiration increase left preload? : r/Cardiology

A subreddit covering the evolving evidence base in cardiology and cardiothoracic surgery. This subreddit is for medical professionals only. DO NOT ASK FOR MEDICAL ADVICE OR OPINION. Why does expiration increase left preload? ^^ I've tried to look this up so many times. I understand why inspiration increases venous return to the right side of the heart and can increase right-sided murmurs, but why is the opposite true for the left side of the heart? Why do most left sided murmurs increase on expiration? Some things say it's just because expiration lowers lung volume, brining the heart closer to the chest wall. I've also heard people say it somehow squeezes pulm veins (increasing return to left atrium). Do we actually know? Thx in advance! Increased intrathoracic pressure causes lungs to collapse and squeeze the blood out of them to the left side of the heart, thus increasing preload : ) The physiology is actually really beautiful. Think about the flow throughout the body purely as a fun

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