Heart rate, stroke volume and cardiac outputSpec 8.12
- Heart rate
- The number of times the heart beats per minute (bpm).
- Stroke volume
- The volume of blood pumped out of the heart in each beat, in cm³.
- Cardiac output
- The volume of blood pumped out of the heart per minute, in cm³ per minute.
Calculating cardiac output
A person has a resting heart rate of 70 beats per minute and a stroke volume of 75 cm³. Calculate the cardiac output.
- cardiac output = stroke volume × heart rate
- cardiac output = 75 × 70 = 5250
Answer: 5250 cm³ per minute
You may be asked to rearrange the equation. Stroke volume = cardiac output ÷ heart rate. Heart rate = cardiac output ÷ stroke volume.
You can measure heart rate by taking a pulse for a set time, for example counting beats in 30 seconds and doubling. A suggested practical is to investigate the short-term effect of exercise on heart rate and breathing rate, which both increase to supply more oxygen to the working muscles.
Quick check
Which vessel carries oxygenated blood from the lungs to the heart?
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The pulmonary vein.
Why is the wall of the left ventricle thicker than the wall of the right ventricle?
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It pumps blood around the whole body, which needs a higher pressure than pumping blood to the lungs.
What is the job of the valves in the heart?
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To prevent backflow and keep blood flowing in one direction.
State the equation for cardiac output.
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Cardiac output = stroke volume × heart rate.