• Cardiac output?(CO) is the term used to describe the volume of blood that is pumped by the heart (the left and right ventricle) per unit of time
• An average adult has a cardiac output of roughly 4.7 litres of blood per minute when at?rest
• Individuals who are?fitter?often have?higher cardiac outputs?due to having thicker and stronger ventricular muscles in their hearts
• Cardiac output?increases?when an individual is?exercising
  • This is so that the blood supply can match the increased metabolic demands of the cells
• The CO of an individual can be calculated using their?heart rate?and?stroke volume
• Heart rate?is the?number of times a heart beats per minute
  • This can also be described as the number of cardiac cycles per minute
• Stroke volume?is the?volume of blood pumped out of the left ventricle during one cardiac cycle

Graph showing the changes in the volume of the left ventricle within one cardiac cycle; this is the stroke volume

Calculating cardiac output

• Cardiac output is found by multiplying the heart rate by the stroke volume:

Cardiac output = heart rate x stroke volume

• The equation can be rearranged to find the heart rate and stroke volume if required:
  • Heart rate = cardiac output ÷ stroke volume
  • Stroke volume = cardiac output ÷ heart rate
• Cardiac output?is measured in?cm3?min-1
• Heart rate?is measured in?beats per min?(bpm)
• Stroke volume?is measured in?cm3

? Step 1: Find the heart rate

One cardiac cycle (atrial systole, ventricular systole and diastole) takes 1.2 seconds

To find the number of cardiac cycles completed in a minute, multiply by 60

60 x 1.2 = 72 bpm

Step 2: Insert relevant figures into the equation

Cardiac output = heart rate x stroke volume

Cardiac output = 72 x 75 = 5,400 cm3

Cardiac output =?5.40 dm3

Stroke volume = cardiac output ÷ heart rate

Stroke volume = 9,800 ÷ 110

Stroke volume =?89.09 cm3