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Cardiac Output: Definition, Formula, Calculation & Normal Range

Cardiac Output: Definition, Formula, Calculation & Normal Range
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  • 0:00 What Is Cardiac Output?
  • 1:42 What's the Normal Range?
  • 2:55 Measuring Cardiac Output
  • 4:15 A Sample Calculation
  • 5:20 Lesson Summary
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Lesson Transcript
Instructor: Sheara Williamson

Sheara currently teaches undergraduate biology courses and has her doctorate in Kinesiology.

Medical professionals need to be able to quantify how efficient your heart works, which involves understanding cardiac output. This lesson will look at what cardiac output is, how it is calculated and why it is important.

What Is Cardiac Output?

Cardiologists and other medical professionals study the heart and how it functions so they can determine whether a patient is healthy or not. They begin by seeking to understand how well a person's heart distributes blood while they are resting. Once they have that baseline information, doctors are generally better able to recognize anything out of the ordinary. One way to measure the heart function is to check cardiac output, looking at how much blood gets pumped out of it every minute, which tells doctors how efficiently a heart is doing it's job.

Cardiac output is the product of two variables, stroke volume and heart rate. The first variable, stroke volume, is a measure of the volume of blood that is pushed out of the ventricles (the large muscular chambers of the heart) with every beat. In other words, its the amount of blood pushed out every time the heart beats. Echocardiography is often used to calculate the stroke volume. Just as doctors perform sonograms to monitor and measure a growing fetus, the echocardiogram provides a way for doctors to view and measure the heart. The other variable, heart rate, is simply the number of times your heart beats each minute.

One reason to determine someone's cardiac output would be to monitor their cardiovascular function over time. Sometimes a cardiologist may need to calculate cardiac output to provide patients with information about how efficiently their hearts are pumping blood and delivering oxygen rich blood. Changes in cardiac output over months or years could indicate a change in the heart's ability to pump blood. It is important to first determine how well (or not) a person's heart pumps blood while they are at rest.

What's the Normal Range?

So far, we know that cardiac output is the amount of blood that is moved out of the heart each minute. On average, a healthy adult's heart will pump 5 L every minute, meaning the average cardiac output (or CO) is approximately 5 L/min. Now, the typical adult has approximately 5 L of total blood volume. That means that every minute, while average Joe is sitting at his desk, his heart circulates his entire blood volume. That's a lot of work for an organ that's only the size of your fist.

We have to remember that every person is different, so some people may have a cardiac output that is a little higher or lower than what is considered average. For example, a larger person, say an NBA player, will have a larger cardiac output than a smaller person, such as a gymnast. This is why it is so important to first find out what a person's resting or baseline cardiac output is.

It is expected that the workload of your heart will increase when your physical workload increases. Think about how your heart beats faster and stronger when you start running. You can actually feel it working harder. It's not uncommon for cardiac output to increase 5-fold when you exercise, especially if you're working hard.

Measuring Cardiac Output

Let's take a look at out how we can figure cardiac output.

We can use this simple calculation to figure out cardiac output:

Cardiac Output = Stroke Volume * Heart Rate, which is written CO = SV * HR.

Remember, there are two variables that are used to determine the cardiac output. Those are the stroke volume and heart rate.

To determine the cardiac output, we first need to know the stroke volume and heart rate. Heart rate can be easily determined by feeling or palpating the pulse rate on your wrist or neck. In a doctor's office or laboratory, heart rate may be determined by attaching electrodes to the patient's chest and recording the electrical activity. Normal resting heart rate generally ranges between 60 and 100 beats per minute.

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