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Old 09-17-2007, 06:10 AM   #1
Matt DeMinico
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Determinants of Cardiac Output (how it all really works)

There has been some discussion in the past about how exactly the heart works, what determines cardiac output, etc, especially with regards to how we approach the cooldown after an intense WOD.

I knew there was a good video out there, but I couldn't remember where it was, I recently found it on my computer, and wanted to link it for everyone here at CF. Basically, it shows how the heart works, under what conditions the heart will (and won't) pump, and determinants of how much flow it will generate based on changing certain variables.

Basically, the heart is a non-sucking pump, it relies on input pressure to fill itself (if it "sucked" blood into itself, then the slightest restriction on the venous side (veins, or the input side) would cause a loss of pressure on "half" of your circulatory system, and if that presure was great enough, would cause veins to collapse). Similarly, if there's not enough pressure to fill the input side of the heart, it can't pump at all.

The video linked below is a good intro, and I haven't gotten a chance to read through the whole 2nd link (it's a lot of detailed info in book form). But one good paragraph in there that has me wanting to dig deeper is this:

One can calculate cardiac output in the same way as in the urinary bladder example: by multiplying stroke rate times stroke volume. Also, just as in that example, while stroke rate multiplied by stroke volume measures the amount of output, those variables are not determinants of that output. The heart, by filling passively, pumps out blood at a rate determined by the rate of blood coming to it. Given that the heart is a pump that produces the flow but has a flow rate determined by extra-cardiac factors, let us examine those factors that determine circulation rate.

(W/F safe)

Last edited by Matt DeMinico : 09-17-2007 at 06:18 AM.
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