Taking pulse, calculating blood flows

The pulse

The simplest way of checking heart rate is to measure your pulse. As the heart beats, a pulse can be felt in locations where an artery passes over a solid structure, such as bone. Locations include wrist, neck and upper arm.

The pulse rate is expressed in beats per minute.

An illustration of taking the pulse rate from wrist

To measure your pulse rate, count the number of beats in a set period of time, eg 30 seconds, or a minute.

In healthy people, generally, the lower the resting pulse rate, the fitter they are.

Pulse rates increase during and after exercise, as more oxygen must be provided to the muscles, and carbon dioxide removed.

Flow rates of blood

Scanning techniques such as MRI can be used to measure blood flow in the body.

The blood flow from the heart is called cardiac output. It is the volume of blood pumped by the heart per minute. Stroke volume is the volume of blood pumped out of the heart per minute.

curriculum-key-fact
Cardiac output in cm3 per minute = heart rate in beats per minute × stroke volume in cm3 per beat.

An increase in heart rate or stroke volume will increase cardiac output.

So, if a person has a resting heart rate of 70 beats per minute and a resting stroke volume of 75 cm3 per beat, the cardiac output for this person at rest is:

Cardiac output in cm3 per minute = 70 × 75 = 5250 cm3 per minute.

Question

An athlete is exercising. If their maximum heart rate is 130 beats per minute, and stroke volume is 150 cm3, what is their cardiac output in dm3?

Answer:

19.5 dm3

Calculation:

Cardiac output in cm3 per minute = heart rate in beats per minute × stroke volume in cm3 per beat.

Cardiac output in cm3 per minute = 130 × 150 = 19 500 cm3 per minute = 19.5 dm3 per minute.

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