MVP vs MR squatting

[chromuffin]

Not quite sure how to explain how squatting makes MVP softer but MR louder. Any thoughts?

I understand squatting will increase afterload and SVR, preventing LV emptying. So more blood is in the LV. So then more pressure. But how does this not make the MVP louder? I would think this would push on the mitral valve and accentuate the sound like it does for MR. I think I read somewhere that this increased pressure will just sustain the MVP rather than actually causing ballooning?

Thanks

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[Rahas]

The MV prolapses because the papillary muscles + chordae tendinae are unable to hold it within the LV as it closes. Larger LV size means the papillary muscles + chordae tendinae get stretched (away from the MV), and hence prevent the prolapse. The trick is understanding the severity of MR depends on flow across the valve, but prolapse of the MV depends on LV cavity size. Also, the regurge associated with MVP will happen if and only if the valve prolapses (and not necessarily even then).

The other murmur dependent on cavity size is that of HCM.