Get My Best Tips For Passing Biology

Sign up for my newsletter and get my Free Guide!

053 Cardiac Output

Learn more about calculating cardiac output and how changing stroke volume and heart rate can increase or decrease its value.

Have fun!

Transcript of Today’s Episode

Hello and welcome to another episode of Interactive-Biology TV where we’re making Biology fun! My name is Leslie Samuel, and in this episode, Episode 53, I’m going to talk about the ‘Cardiac Output.’ I’m first going to talk about what it is and then, I’m going to talk about how to calculate it, and some of the things that are going to influence cardiac output. So, let’s get right into it.

Here, we’re looking at a picture of the heart. A diagram of the heart during systole, so it’s during contraction, ventricular contraction, and what’s happening here, is as the ventricles contract, the left ventricle is sending blood to the aorta which then goes to the rest of the body, the right ventricle of course, is sending the blood to the lungs so that, it can get oxygenated, come back to the heart and then, be sent to the rest of the body.

Now, we’re going to talk about cardiac output today so, let me write that here, ‘Cardiac Output.’ It kind of is exactly what it sounds like. Cardiac output is talking about the volume of blood that’s being ejected from the ventricles every minute. So, we’re talking about the amount of blood that’s being sent from the left ventricle to the rest of the body via the aorta, and also we’re talking about the amount of blood that’s being sent from the right ventricle to the lungs. You expect those to be the same or else that can lead to some other problems. That we’re not going to get into in this episode.

Right now, we are just going to try to look at how to calculate cardiac output. It’s a pretty simple formula and it involves two things that we’ve already looked at in previous episodes. Cardiac output is equal to SV, which is stroke volume, times HR, which is heart rate:

CO = SV x HR

Now, stroke volume tells you the amount of blood that’s ejected with each beat. So, we’re talking about milliliters of blood per beat, and then, with heart rate, we’re talking about how many times the heart is beating in one minute. So, we calculate that as beats per minute. So, stroke volume is the amount of blood ejected from the ventricles, let’s say the left ventricle in each beat, with each beat. And, the heart rate tells us how many times the heart is beating, how many times the ventricles are contracting in one minute. If we, multiply these out of course, if you apply some simple algebra, we’re going to be canceling out the beats, so, cardiac output is calculated in milliliters per minute – some pretty straightforward algebra there.

Now, let’s plug in some values. The average adult male has a stroke volume of approximately 70 millliters per beat and an average heart rate of 75 beats per minute. Now, if you want to calculate cardiac output, the amount of blood ejected from the ventricle each minute, cardiac output would be equal to 70 milliliters per beat times 75 beats per minute and that’s going to give us a value of 5,250 milliliters per minute. Of course, you can make that into 5.25 L per minute. So, this is the average adult male at rest, 5.25 L/min cardiac output. Now keep in mind that the average adult male has about 5L of blood in their body. So, every minute the heart is re-circulating pretty much all of the blood if you’re just at rest. All right, so the heart is doing a significant amount of work. It’s sending the blood to the muscles, that organs that need to get oxygen and the nutrients that come via the blood.

We know how to calculate cardiac output. Now, if you want to change cardiac output or if you want to influence cardiac output, it should be obvious that we can do that in three ways by influencing stroke volume, by influencing heart rate, or by influencing both of them. So, if you make a change, to the stroke volume or the heart rate, that of course, in turn is going to make a change to cardiac output.

Now, we’ve also looked at factors that are going to influence volume and heart rate. We’ve spoken about those factors in Episodes, I think it’s 46 and Episode 50. Episode 46 talks about how we can influence heart rate. Episode 50 talks about influencing stroke volume. You can always revisit those and see how that works.

When you’re exercising, you’re going to have a little bit of a different situation. You know when you’re starting to exercise and you’re doing some aerobic activity, your heart rate is going to increase, your cardiac output is also going to increase because you’re increasing stroke volume and your heart rate so, that’s going to give you some different values.

Let’s take an example where we’re trying to calculate cardiac output again. As usual, cardiac output is equal to stroke volume. We’re going to take that and multiply that by heart rate. Same exact situation.

CO = SV x HR

But, okay, I’m showing ladies here exercising but, we’re going to stick with the example for the calculations, we’re going to stick with males, and we’re going to see during moderate exercise, the stroke volume might increase to a point of let’s say about 100 mL/beat, and let’s say the heart rate increases before it was 75 and let’s say we have, let’s go with a 100 because that’s easy to calculate, a hundred beats per minute (100 beats/min). So, we have more of an intense situation, it’s not a very stressful situation but, you’re doing some exercise. So, that’s going to influence cardiac output of course. Cardiac output is going to be equal to:

CO = 100 mL/beat x 100 beats/minute

Giving us a cardiac output of 10 L/min. So, by doing a little bit of exercise, we’ve almost doubled the cardiac output. In other words, your blood is being pumped throughout your body twice in that minute with moderate exercise.

As you exercise and you train, hopefully we’re doing this on a regular basis, hopefully, like three times a week, **hint, hint, hint** but, as you’re doing this more regularly, there are going to be some adaptations that happen. One of the main adaptations is that your stroke volume increase, (I’m just going to put an up arrow here showing that your stroke volume increases). In other words, everytime that your heart pumps, it pumps more blood than the average untrained individual.

What that can do in turn is that can actually cause a lower resting heart rate. All right, so, a trained person on average has a lower heart rate than an untrained person. However, they’re still able to get the same cardiac output. In other words, your heart is becoming more efficient at pumping the blood. Everytime it contracts the ventricles, it’s sending a significant amount more than the untrained person and you can achieve the same effect if not even a better effect with less work.

So, the take home message there I guess you could say is, do like this ladies, get into the gym and start doing some exercise. That’s always good and it’s going to pay off in the long run.

That’s not what I intended to teach but, hey it’s something that’s good for us to learn. That’s pretty much it for this episode. As usual, you can visit the website at Interactive-Biology.com for more Biology resources and a bunch of other resources that we’re adding there. We’re adding quizzes and we have just added a brand new Biology community where you can ask questions, get answers, give input. Join the community and make the community stronger and much more fun.

Thank you for watching this episode and I’ll see you on the next one.

The following two tabs change content below.
Leslie Samuel is the creator of Interactive Biology. His mission is to use this site to Make Biology fun for people all over the world.

Tags: , , , , , , ,


Leave An AWESOME Comment

42 Responses to “053 Cardiac Output”

  1. Mohammed Anjum September 5, 2011 at 11:09 pm #

    YOU ARE AMAZING!!! YOU SHOULD BE THE NEW TEACHER FOR KAPLAN!!! OR MAKE A BOOK FOLLOWING THE STEP 1!!

    • Lrsamuel September 6, 2011 at 7:14 am #

      Well thank you very much Mohammed :)

      I appreciate the compliment. You should check out my Study Guide.

  2. AHM391 January 11, 2012 at 12:24 am #

    thank you very very much

  3. burnettracer January 22, 2012 at 12:28 am #

    your videos are wonderful!! what a wonderful way to spend a Saturday night. ;). You should do some Intro to Chem videos.

  4. burnettracer January 22, 2012 at 5:28 am #

    your videos are wonderful!! what a wonderful way to spend a Saturday night. ;). You should do some Intro to Chem videos.

  5. xxTaKe2xx January 29, 2012 at 10:53 am #

    Not only informative, but also very neatly designed. Love it.

  6. xxTaKe2xx January 29, 2012 at 3:53 pm #

    Not only informative, but also very neatly designed. Love it.

  7. Rachel March 1, 2012 at 7:45 pm #

    Absoutely love your lectures Lesley – I am at Uni training to be a Nurse (UK). Thanks for all your help!

  8. MegaDreamOo March 10, 2012 at 2:52 am #

    Man ur star
    Nigga + biology = real love !!!!

  9. MegaDreamOo March 10, 2012 at 7:52 am #

    Man ur star
    Nigga + biology = real love !!!!

  10. MrJany82 March 20, 2012 at 5:33 pm #

    you make biology so easy, thank you so and more strenght to your elbow.

  11. MrJany82 March 20, 2012 at 5:33 pm #

    you make biology so easy, thank you so and more strenght to your elbow.

  12. MrJany82 March 20, 2012 at 9:33 pm #

    you make biology so easy, thank you so and more strenght to your elbow.

  13. Masalamuffin March 22, 2012 at 2:11 am #

    These videos are extremely helpful could you please make some videos which compare veins, arteries and capillaries and also more videos to do with ventilation perfusion relationsips
    Id really appreciate it :)

  14. Masalamuffin March 22, 2012 at 6:11 am #

    These videos are extremely helpful could you please make some videos which compare veins, arteries and capillaries and also more videos to do with ventilation perfusion relationsips
    Id really appreciate it :)

  15. Naomi May 12, 2012 at 4:09 am #

    Thank you, this is really helpful.
    If I ask questions, will you do tutorials on the subjects I ask about?
    i have so many questions

    • Leslie Samuel May 13, 2012 at 6:19 pm #

      Unfortunately not. I can no longer take individual requests due to time limitations. I make videos as I need them for the classes I teach, and make them publicly available with the hopes that they can help others.

  16. Beth May 16, 2012 at 9:22 am #

    Thank you very much, you made cardiac cycle easier to understand.
    FANTASTIC TEACHER !!!

    • Leslie Samuel May 16, 2012 at 9:27 pm #

      You are very much welcome. Glad to know that the videos are helping you :)

  17. Aida Walker June 11, 2012 at 5:46 pm #

    Wish this site was available when I was in nursing school. Now that I teach Basic ECG interpretation, I send my students to yiou for positive re-enforcement.

    Your wording is clear, the material is relevant not over whelming, your video/pictures are very helpful. Keep up the great work,

    A. Walker, RN

  18. vikassahu01 June 30, 2012 at 5:00 pm #

    @msfbwng yes i mean it. it was really hard when I first started working out and my muscles were going nowhere at all. Listen really I encourage you set aside just 10 minutes and make up your mind for yourself. The video describing the method is here -> bit.ly/Ks5n0B?=ehsgtf

  19. vikassahu01 June 30, 2012 at 5:00 pm #

    @msfbwng yes i mean it. it was really hard when I first started working out and my muscles were going nowhere at all. Listen really I encourage you set aside just 10 minutes and make up your mind for yourself. The video describing the method is here -> bit.ly/Ks5n0B?=ehsgtf

  20. vikassahu01 June 30, 2012 at 5:00 pm #

    @msfbwng yes i mean it. it was really hard when I first started working out and my muscles were going nowhere at all. Listen really I encourage you set aside just 10 minutes and make up your mind for yourself. The video describing the method is here -> bit.ly/Ks5n0B?=ehsgtf

  21. smarie4real August 9, 2012 at 3:08 pm #

    Thanks for the video… Very helpful!

  22. ramiltor September 21, 2012 at 5:24 pm #

    If you like the videos subscribe to the channel and view the videos through there so these guys get paid.

  23. shafiramed October 24, 2012 at 9:50 pm #

    Doesn’t slower heart rate also increase the stroke volume? Is that what makes trained person to have the same cardiac output at rest with the untrained person?

  24. mrCLICKman November 14, 2012 at 4:10 pm #

    those ladies in the background keep going at it!

  25. raedalqahtani8 November 20, 2012 at 1:11 am #

    Keep up proffesor :-)

  26. Tanaz89 December 20, 2012 at 6:10 pm #

    thanks alot.

  27. Tanaz89 December 20, 2012 at 6:10 pm #

    ur videos are very useful

  28. Tanaz89 December 20, 2012 at 6:10 pm #

    keep it up

  29. 0113slimshady January 4, 2013 at 2:49 am #

    Legend

  30. Whoopi Goldburg March 29, 2013 at 11:32 am #

    my stroke volume and heart rate are going up just from keeping up with those ladies doing that for an hour….. damn

  31. MissReba88 April 15, 2013 at 7:54 pm #

    Cadiac output is represented by Q, they do this so not to confuse with carbon monoxide

  32. SycShadow April 23, 2013 at 4:30 pm #

    Watched all your videos in this playlist and moving on as a major help :D
    but can’t get over how neat you writing is :L

  33. SycShadow April 23, 2013 at 4:30 pm #

    Watched all your videos in this playlist and moving on as a major help :D
    but can’t get over how neat you writing is :L

  34. ReinaDelAcordeon June 23, 2013 at 10:28 am #

    Thank you so much for your help. Every video you upload is extremely helpful. Thank you! I am forever a subscriber for you.

  35. Walid Shams Amar July 30, 2013 at 9:08 am #

    Thanks

  36. Carlos Romero August 23, 2013 at 12:13 am #

    Do the stroke volume and cardiac output change with a valves that regurgitate?

  37. Denise September 3, 2013 at 7:28 pm #

    I am a nursing student in my last semester of cardiology. I would just like to thank you for your time in making these exceptional videos. They are so informative and I wish I had found them a year and a half ago when I started school. Many many thanks!

  38. Paula Bartolome September 15, 2013 at 7:41 pm #

    what happens to the preload, afterload, and contractility in stroke volume?

  39. Camellia Sultan September 23, 2013 at 5:36 am #

    loved the last past about the exercise effect on heart ..
    u r a great mentor THANK YOU