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Constant stroke volume (LV and RV)

Why must stroke volume for each ventricle be the same?
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I understand that if central venous pressure increases then the RV end diastolic volume (and hence pressure) increases so by Starling's Mechanism the contractility of the RV increases.
This will increase LV- end diastolic pressure too so LV stroke volume increase.

WHAT I DON'T GET is why this means LV and RV stroke volume must be the same. For example, in heart failure the LV EDP may increase enormously to maintain the stroke volume. I do not understand why this happens. Please could you explain?
Thank you

Reply 1

Hype en Ecosse

Well, in reality, you'll struggle to ever measure the stroke volumes from each ventricle as exactly the same. But generally, they'll be in the same ballpark. But you'll rarely measure exactly the same to the millilitre. You might end up with something like 69ml and 71ml, or 70.5ml and 70ml. Things like that. This difference can be more exaggerated in heart failure where cardiac output of the failing side decreases.

They're generally the same because the preloads and afterloads of each system are related to each other. The right ventricle doesn't function independent of the influence of the left ventricle, and vice versa. I'm not sure, but I think that LVEDP increases simply due to either the decreased ejection fraction (it has more leftover to fill, so LVEDP becomes raised and SV increases via Frank-Starling) or through the decreased compliance of the ventricle as in diastolic dysfunction (smaller volume of ventricle => higher pressure).

Edit: just found this, which explains the increases behind LVEDP (preload) well. :smile: