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Cardiac output
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Cardiac output is simply how much blood the heart pumps in one minute. It comes from multiplying two things: heart rate, which is how many times the heart beats in that minute, and stroke volume, which is how much blood it ejects with each beat. Two dials for the same flow: how often it beats and how much it ejects each time.
The second dial has a mechanism of its own. Stroke volume depends on three factors: preload, which is how much blood filled the ventricle before it contracted; contractility, which is how forcefully the muscle squeezes; and afterload, which is how much resistance it has to overcome to push the blood out.
All of this exists to keep up with the oxygen the body needs: changes in cardiac output are proportional to changes in that demand. At rest it is usually five or six liters per minute, and in elite athletes during exercise it goes above thirty-five.
In brief
Cardiac output is the blood the heart pumps per minute, and it is heart rate multiplied by stroke volume.
Two dials for the same flow: how often it beats and how much it ejects each time.
Stroke volume is the blood ejected with each beat and depends on preload, contractility and afterload.
That is why output tracks oxygen demand: five or six liters per minute at rest, and more than thirty-five in elite athletes during exercise.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Cardiac Output, StatPearlsPublished
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