Heart Rate, Stroke Volume and Cardiac Output
Cardiac output is stroke volume multiplied by heart rate, and breathing follows the same shape as tidal volume multiplied by breathing rate. Use both to compare a person at rest with the same person exercising.
What a learner can do afterwards
- Calculates cardiac output from a stroke volume and a pulse rate, with units on the answer.
- Rearranges the relation to find a missing quantity from the other two.
- Says which quantity changes most during exercise and why that helps the working muscles.
1 · Read
When you run your muscles need more oxygen carried by red cells, so the pump must move more blood each minute. Stroke volume is the blood one beat ejects, about 70 cm3 at rest. Heart rate is beats per minute. Cardiac output is the blood pumped per minute, in mL per minute or litres per minute.
Cardiac output equals stroke volume multiplied by heart rate. A stroke volume of 70 cm3, the same as 70 mL, with a pulse of 72 beats per minute gives 70 times 72, which is 5040 mL per minute. That is about 5 litres every minute.
You can rearrange the relation to find any missing quantity. Stroke volume equals cardiac output divided by heart rate. Heart rate equals cardiac output divided by stroke volume. During exercise the heart rate climbs most, with stroke volume rising too, so extra oxygen reaches the working muscles. Breathing mirrors this pattern, with tidal volume times breathing rate.
Let the units guide you. An answer in mL per minute comes from multiplying. An answer in mL or beats per minute comes from dividing. Always write the units down.
Output equals volume per beat times beats per minute, and exercise turns that dial up.
2 · Watch
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Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.