Cardiac output

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Cardiac output is the amount of volume ejected by the heart, usually expressed as the volume of blood pumped into the circulation in one minute. It can be factored into stroke volume x heart rate:

C.O. = H.R. x S.V.

At rest, a typical heart rate is 70 beats per minute, and a typical stroke volume is 70ml (approx. 1ml/kg of body weight). Therefore a typical cardiac output is about 4900ml/min or 5 litres/min.

It can be seen that an increase in cardiac output can be produced by either an increase in heart rate (tachycardia), an increase in stroke volume, or both.

As circulating blood volume is about 5 litres, the cardiac output (at rest) is such that the entire circulating volume is pumped through the heart every minute.

Measuring Cardiac Output