physio behind "squat to stand"

[lisichka]

What is the physiology behind long systolic mumur increasing from squat to stand/or valsalva? indicating hypertrophic cardiomyopathy.
thank you.

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[spicedmanna]

What is the physiology behind long systolic mumur increasing from squat to stand/or valsalva? indicating hypertrophic cardiomyopathy.
thank you.

It's been a few months since I studied this and you know how information just vanishes when you don't refresh it, but I'll take a stab at it. Basically, you are talking about modulating (increasing or decreasing) preload in a heart that already has some degree of diastolic dysfunction as a result of the hypertrophy.

With hypertrophic obstructive cardiomyopathy (HOCM), there is an asymmetrical thickening of the intraventricular septum (IVS) and myofibril dysarray. This thickening of the septum which narrows the aortic outflow tract between the IVS and the anterior leaflet of the mitral valve (review heart anatomy). The myofibril dysarray predisposes to conduction issues, which can lead to deadly arrhythmias that are mainly responsible for the "sudden death," but that's another story.

Given the narrowing of the outflow tract, if you increase preload by squatting (think about it: if you squat, or lay down, or something like that, you are increasing venous return to the heart, consequently increasing preload), you are pushing more blood through the aortic outflow tract and basically easing some of the obstruction caused by the narrowing. Therefore, as a result, you should get a quieter murmur.

When you stand up or perform the Valsalva maneuver, you are effectively decreasing preload (from decreasing venous return to the heart) and thus pushing less blood through the narrow aortic outflow tract, which should exacerbate the obstruction and consequently make the murmur sound louder. Therefore, when you go from squatting (increased preload) to standing (decreased preload), you should hear the murmur go from quieter to louder.

Does that make sense? It's something like that. Take a look at Rapid Review Pathology, 2nd ed., pp. 192-194. That's basically what I reviewed and used as a reference to write this post.

Review the following concepts:

*Anatomy of the heart
*Venous Return
*Preload/Afterload
*Cardiac Output
*Cardiomyopathy
*Systolic vs. Diastolic Dysfunction

 

[lisichka]

great. thanks, Spicedmanna. will revisit the concept in rapid review.

 

[ChiDO]

great. thanks, Spicedmanna. will revisit the concept in rapid review.

Pg 187-188 in the 3rd edition for those of you wanting to find this as well