WEILAI Online Academic assistant
WEILAI Online Academic assistant
Back to 课程

Biology_Alevel_Ocr

0% Complete
0/0 Steps
  1. 4-1-communicable-diseases-disease-prevention-and-the-immune-system
    16 主题
  2. 4-2-biodiversity
    10 主题
  3. 4-3-classification-and-evolution
    15 主题
  4. 5-1-communication-and-homeostasis
    4 主题
  5. 5-2-excretion
    10 主题
  6. 5-3-neuronal-communication
    9 主题
  7. 5-4-hormonal-communication
    4 主题
  8. 5-5-plant-and-animal-responses
    16 主题
  9. 5-6-photosynthesis
    10 主题
  10. 5-7-respiration
    14 主题
  11. 6-1-cellular-control
    7 主题
  12. 6-2-patterns-of-inheritance
    13 主题
  13. 6-3-manipulating-genomes
    11 主题
  14. 6-4-cloning-and-biotechnology
    14 主题
  15. 6-5-ecosystems
    7 主题
  16. 6-6-populations-and-sustainability
    6 主题
  17. 1-1-practical-skills-written-assessment
    7 主题
  18. 1-2-practical-skills-endorsement-assessment
    16 主题
  19. 2-1-cell-structure
    9 主题
  20. 2-2-biological-molecules
    17 主题
  21. 2-3-nucleotides-and-nucleic-acids
    8 主题
  22. 2-4-enzymes
    9 主题
  23. 2-5-biological-membranes
    9 主题
  24. 2-6-cell-division-cell-diversity-and-cellular-organisation
    11 主题
  25. 3-1-exchange-surfaces
    7 主题
  26. 3-2-transport-in-animals
    12 主题
  27. 3-3-transport-in-plants
    11 主题
课 Progress
0% Complete

Calculating cardiac output

  • Cardiac output (CO) is the term used to describe the volume of blood that is pumped by the heart 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 = number of times a heart beats per minute

      • This can also be described as the number of cardiac cycles per minute

    • Stroke volume = the volume of blood pumped out of the heart during one cardiac cycle

Graph showing left ventricle volume over time. Stroke volume marked between 60 and 120 cm³. Time on x-axis, volume in cm³ on y-axis.
Stroke volume is the volume of blood that leaves the heart per cardiac cycle; here the stroke volume of the left ventricle can be determined from the graph

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, so:

    • heart rate = cardiac output ÷ stroke volume

    • stroke volume = cardiac output ÷ heart rate

Worked Example

It took a woman 1 second to complete a single cardiac cycle. Her stroke volume was measured at 73 cm3.

Calculate the cardiac output. Give your answer in dm3 per minute.

Answer:

Step 1: find the heart rate

  • 1 cardiac cycle takes 1 second

  • 1 minute = 60 seconds

  • 60 x 1 = 60 bpm

Step 2: insert relevant figures into the equation

Cardiac output = heart rate x stroke volume

  • Cardiac output = 60 x 73 = 4 380 cm3 per minute

Step 3: convert to dm3

  • 1 dm3 = 1000 cm3

  • 4 380 ÷ 1000 = 4.38

  • CO = 4.38 dm3 per minute

Examiner Tips and Tricks

While this has not been demonstrated above, it can be useful to convert all the figures found in the question into the units required before starting your working; this way you are less likely to forget to do it later on!

Most cardiac cycle graphs show the changes in pressure in the left ventricle, left atrium and aorta. Remember that in order to work out the stroke volume you need to know the change in volume, not the change in pressure!