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Heart Rate, Cardiac Output & Stroke Volume

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  • 0:31 Cardiac Output
  • 1:51 Heart Rate and Stroke Volume
  • 3:27 Clinical Importance
  • 3:57 Lesson Summary
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Lesson Transcript
Instructor
Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Expert Contributor
Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

The amount of blood your heart pumps is constantly changing to meet the needs of your body. In this lesson, you will learn how the heart maintains an adequate cardiac output, heart rate and stroke volume.

Circulatory System

There's a lot riding on the proper amount of blood being pumped by your heart with each heartbeat. A good, strong heart allows the proper amount of blood to flow through your body, which carries gases to your lungs and body tissues where they can be exchanged. It also delivers nutrients to the trillions of cells in your body and carries away cell waste. In this lesson, we will look at just how we calculate the amount of blood being pumped by your heart.

Cardiac Output

Cardiac output (CO) is the term used to show the amount of blood pumped per minute by each ventricle. When your body's at rest, your heart beats about 75 times per minute. Each time it pumps, it pushes out about 75 milliliters of blood, which is about a third of a cup - it's about the amount that you could hold in your cupped hand. When you multiply the number of heartbeats per minute times the amount of blood being pumped during each heartbeat, you get the cardiac output.

The average cardiac output of humans is 5.6 liters of blood per minute.
Cardiac Output

If we do the math using the examples above, we see that 75 heartbeats per minute times 75 milliliters of blood pumped during each heartbeat equals the average cardiac output of about 5.6 liters of blood pumped through your heart each minute. That's a lot of blood, and if you consider that large bottles of soda often come in 2 liter containers, that means that your heart pumps the contents of more than 2 and a half of these soda bottles every minute.

It's also interesting to consider that the total amount of blood in your body is usually between 5 and 6 liters; this means that your heart pumps the entire blood supply every minute. We've said it before, but it's true to say it again: the heart is quite a workaholic!

Heart Rate and Stroke Volume

What we have from the example just described is a formula for figuring out the amount of blood pumped per minute by each ventricle, what we call the cardiac output. So, let's look at this formula a little bit closer. Cardiac output equals the number of heartbeats per minute times the volume of blood pumped out of the ventricles with each heartbeat. When we look at this equation in cardiovascular physiology, we use the terms heart rate (HR) to describe the number of heartbeats per minute and stroke volume (SV) to describe the volume of blood pumped by the ventricles with each heartbeat. Therefore, our equation looks like this: CO = HR x SV.

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Additional Activities

Exercise and the Cardiovascular System

In this activity, students will get to measure their own heart rate, cardiac output and stroke volume before and after exercise to look at the impact of exercise on the cardiovascular system. Students should be able to move around to get their heart rate up for this activity. If they are unable to do so, an able-bodied adult can do the movement and students can be the "cardiologist" and take the measurements.

Directions

Now that you know about these important parameters of the cardiovascular system, we're going to find out how they work in our own bodies. In this activity, you will be measuring your heart rate and calculating the stoke volume and cardiac output while you are resting, then after you exercise for one minute. Then, we're going to answer some questions.

  1. Start by measuring your heart rate by taking your pulse after you've been sitting down resting for a while. Record this in the table below.
  2. Next, calculate your stroke volume by multiplying your heart rate by the amount of blood pumped with each beat, about 75mL on average. Record this in the table below.
  3. Next, calculate your cardiac output by multiplying the heart rate and the stroke volume. Record this in the table below.
  4. Next, it's time to exercise! Choose your favorite exercise, such as push ups, jumping jacks, or just dancing, and do it for one minute.
  5. Now, repeat steps 1-3 to determine your numbers after exercise.

ConditionHeart RateStroke VolumeCardiac Output
Before Exercise
After Exercise

Questions

  1. How is your cardiac output related to your heart rate?
  2. What happened to each of the three parameters after you exercised? Why do you think that is?
  3. Why is exercise good for the cardiovascular system and how does your data support that claim?
  4. How do you think different forms of heart disease might affect these parameters?

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