Control of Cardiac Output Quiz

See Cardiac Output. Cardiac output (E) equals heart rate multiplied by stroke volume. It is the volume pumped by one ventricle per minute, so multiplying beats per minute by millilitres per beat gives millilitres per minute. Stroke volume is the difference between end-diastolic volume, the filled volume before contraction, and end-systolic volume, the blood remaining after ejection. Increasing rate or stroke volume raises output if the other factor is unchanged. In a real heart the factors interact: a very rapid rate can reduce filling time and stroke volume, so a faster pulse does not guarantee more blood flow.

Systolic minus diastolic pressure (B) is pulse pressure, a pressure difference rather than a volume per minute. C gives the amount ejected with one beat, so heart rate is still needed to turn it into output. The load opposing ejection (D) is afterload, which can alter how much blood leaves a ventricle but is not a measure of flow itself. A is end-systolic volume, the blood left behind; subtracting it from the starting filled volume gives stroke volume, not cardiac output without the rate.