B2.17 Calculating cardiac output

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Cardiac output is the volume of blood pumped out by the heart in a given time, usually one minute.

It is calculated using two values:

• heart rate

• stroke volume.

B2.17 Calculating cardiac output

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Heart rate is the number of contractions of the heart in a given time, usually given per minute.

Average resting heart rate for an adult is around 70 bpm (beats per minute).

Children and some people who are ill have a higher resting heart rate significantly higher than 70 bpm.

In the short-term, activity and stress increase heart rate. Exercise training over a long period usually decreases the resting heart rate.

B2.17 Calculating cardiac output

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Stroke volume is the volume of blood pumped out by the heart by one ventricle during each contraction.

Average resting stroke volume is around 70 cm3 for an adult man.

Women have a smaller average resting stroke volume because they have smaller bodies and smaller hearts.

B2.17 Calculating cardiac output

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Disease of the heart and blood vessels may decrease stroke volume.

Activity usually increases stroke volume a little during the period of exercise.

Exercise training over a long period usually decreases the resting stroke volume.

B2.17 Calculating cardiac output

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Cardiac output is calculated as:

• heart rate × stroke volume

So the resting cardiac output for an average adult man is:

• 70 bpm × 72 cm3

= 5040 cm3/minute

= c. 5 dm3/minute

B2.17 Calculating cardiac output

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In a healthy but untrained man, during vigorous exercise, heart rate increased to 160 bpm and stroke volume increased to 120 cm3.

Calculate the cardiac output for a man during vigorous exercise.

B2.17 Calculating cardiac output

© Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original.

In a healthy but untrained man, during vigorous exercise, heart rate increased to 160 bpm and stroke volume increased to 120 cm3.

Calculate the cardiac output for a man during vigorous exercise.

160 × 120

= 19 200 cm3/min

= about 19 dm3/min

B2.17 Calculating cardiac output

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A trained athlete has a resting heart rate of 54 bpm and aresting stroke volume of 110 cm3.

Calculate the cardiac output for a trained athlete.

B2.17 Calculating cardiac output

© Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original.

A trained athlete has a resting heart rate of 54 bpm and aresting stroke volume of 110 cm3.

Calculate the cardiac output for a trained athlete.

55 × 100

= 5500 cm3/min

= 5.5 dm3/min