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- AuthorMelissa Bialowas
Melissa Bialowas has taught preschool through high school for over 20 years. She specializes in math, science, gifted and talented, and special education. She has a Master's Degree in Education from Western Governor's University and a Bachelor's Degree in Sociology from Southern Methodist University. She is a certified teacher in Texas as well as a trainer and mentor throughout the United States.
View bio - InstructorSheara Williamson
Sheara currently teaches undergraduate biology courses and has her doctorate in Kinesiology.
View bio
What is cardiac output? Learn to define cardiac output and how to calculate cardiac output. Learn the normal range and average values of cardiac output.Updated: 11/21/2023
Table of Contents
- What is Cardiac Output?
- Cardiac Output Normal Range
- Cardiac Output Formula
- How to Calculate Cardiac Output
- Measuring Cardiac Output
- Cardiac Index
- Lesson Summary
Frequently Asked Questions
How do you calculate stroke volume?
In order to calculate stroke volume, use the formula for cardiac output. Plug in the cardiac output and the heart rate and solve for the stroke volume using simple Algebra.
What is normal cardiac output?
In an adult at rest, the normal cardiac output ranges from 5-6 Liters per minute. This increases with exercise to much higher numbers so it is important the person is at rest during the cardiac output test.
How do you calculate cardiac output?
Cardiac output is measured by multiplying the heart rate by the stroke volume. The patient should be at rest when these measurements are collected.
Table of Contents
- What is Cardiac Output?
- Cardiac Output Normal Range
- Cardiac Output Formula
- How to Calculate Cardiac Output
- Measuring Cardiac Output
- Cardiac Index
- Lesson Summary
Cardiac output is the amount of blood the heart pumps in one minute. It is figured by multiplying the stroke volume and heart rate. The heart rate is the number of beats per minute. The stroke volume relies on contractility, preload, and afterload of the heart. Cardiac output is one of the key factors studied in hemodynamics, the study of the movement of blood inside the body.
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A heart that is healthy and has normal cardiac output pumps 5-6 liters of blood each minute when resting. If they are exercising, the body needs 3-4 times that amount because muscles require more oxygen when exerting force. This happens by increasing the heart rate and moving the blood quickly throughout the body. It could also increase the stroke volume by increasing the amount of blood filling the left ventricle before it pumps and pumping more forcefully. Ideally, the heart would increase both stroke volume and heart rate during exercise in order to achieve higher cardiac output. In the case of strenuous exercise, it can go as high as 25 liters per minute. Without the appropriate level of cardiac output, a person's blood pressure cannot be maintained. This can prevent the supply of oxygen-rich blood to vital organs.
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Cardiac output is measured in liters/minute. It can be determined by multiplying the stroke volume and the heart rate. The cardiac output formula is:
Cardiac output (CO) = Stroke Volume (SV) x Heart Rate (HR)
This can be used to figure any of the three variables when given the other two. If Dominick has a typical cardiac output of 5 liters (5,000 ml) and a pulse of 80 beats per minute, the stroke volume can be solved.
5000 = SV x 80
5000/80 = SV
SV = 62.5
Dominick's stroke volume is 62.5 which is in the normal range for adults (50-80 ml).
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In order to identify cardiac output, simply multiply heart rate and stroke volume. Here are some examples.
Jenny has a heart rate of 171 and a stroke volume of 90 ml. Multiply 171 times 90 to get 15,390 ml. This gives the cardiac output of 15.39 liters/minute. This is high for someone resting but reasonable for someone who is exercising.
Rob has a heart rate of 83 and a stroke volume of 48 ml. Multiply 83 times 48 to get 3,984 ml This gives the cardiac output of 3.984 liters/minute. This is low even for someone who is resting. Rob should consult a doctor.
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Doctors use different methods for measuring cardiac output. They each have pros and cons and different doctors have different preferences.
- Doppler ultrasound - This non-invasive ultrasound technique evaluates the movement of materials within the body. Doctors can see blood flow through arteries and veins.
The doppler is placed onto the neck where the carotid artery is located. The computer reads the sound waves that bounce back in order to get data and create a picture of the movement of the blood.
- Echocardiogram - This non-invasive technique requires placing electrodes on the chest in order to view heart size, shape, muscles, and valves.
This is one of the most popular and non-invasive techniques for measuring cardiac output.
- Pulmonary artery catheterization - This requires the insertion of a catheter into the pulmonary artery. The catheter gives direct, instant measurements of the pressures in the pulmonary artery, right atrium, right ventricle, and the filling pressure of the left atrium.
The heart catheter can be seen on an x-ray like this one from a 12-year-old patient.
- Transcutaneous - This non-invasive technique starts with an injection of a chemical that can be viewed and measured as it moves through the bloodstream. This allows for understanding how quickly it moves and where it is located.
- Transesophageal echocardiogram - This technique inserts a probe down the esophagus to perform an echocardiogram. The esophagus is close to the heart and the sound waves do not go through bone, muscle, or skin so it is more detailed than a traditional echocardiogram.
In this test the echocardiogram is placed closer to the heart by inserting it into the esophagus.
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The cardiac index is the relationship, or proportion, of cardiac output to body surface area. It is measured in liters per minute per square meter {eq}(L/min/m^2) {/eq}.
The formula is {eq}CI = \frac{CO}{BSA} = \frac{SV*HR}{BSA} {/eq}
CI - cardiac index
BSA - body surface area
SV - stroke volume
HR - heart rate
A normal cardiac index, when a person is at rest, would be within the range of 2.6 - 4.2 {eq}L/min/m^2 {/eq}. This is a measurement often used in critical care patients and cardiac intensive care. It is not typically used in everyday medical practices.
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Cardiac output is a measurement of both the amount of blood moving through the heart and how quickly it is moving. Cardiac output (CO) is measured by multiplying two numbers together: heart rate (HR) and stroke volume (SV). Heart rate is the number of beats per minute when a person is at rest. The stroke volume is a measure of how much blood the heart is taking in and pushing out within each beat. The formula for determining cardiac output is CO = HR x SV. Normal cardiac output for an adult at rest is anywhere from 5-6 Liters/minute when the person is at rest. This increases as the person exercises and the heart beats fasters and takes in larger amounts of blood with each pump.
Cardiac output can be measured in a number of different ways. Most doctors use non-invasive techniques like an echocardiogram or doppler ultrasound. In emergency situations or when there is concern about heart disease or failure, more invasive techniques are used including placing the echocardiogram into the esophagus and placing a diagnostic catheter into the arteries directly. In critical care units sometimes the cardiac index is measured. This takes the cardiac output measurement and divides it by the body surface area in order to find the efficiency of the heart in getting blood throughout the body.
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Video Transcript
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.
Stroke volume requires more invasive techniques than required for determining heart rate. An example of a common method used is echocardiography or an ultrasound of the heart. Trained medical professionals evaluate images or look at the heart beating in real time in order to measure the volume of blood pushed out of the ventricles. Stroke volume averages between 60 and 80 mL each time the heart beats. So now that we know the normal ranges for heart rate and stroke volume, how can we figure out what the normal range for cardiac output is? Let's put it all together.
A Sample Calculation
While Mike is sitting in biology class doodling in his notebook, his heart is busy keeping blood moving through all of his blood vessels throughout his body. His heart rate is 70 beats per minute, and his stroke volume is 70 mL each beat. So how do we figure out how hard his heart is working? It's simple! We only have to multiply his heart rate by his stroke volume. Remember our formula: CO = SV x HR.
So, we take Mike's stroke volume and multiply it by his heart rate, or CO = 70 mL per beat x 70 beats per minute, or CO = 4900 mL/minute.
More often than not, CO is expressed in L/minute. Since there are 1000 mL in 1 L, we can multiply our result 4900 mL by .001 to move the decimal place to the left three times and express our result as 4.9 L/minute. Got it? Mike's cardiac output is 4.9 L/minute.
Lesson Summary
So let's review. One of the measures cardiologists use to check heart health is cardiac output, which is a measure of how many liters of blood are circulated through the chambers of the heart per minute. Cardiac output is the product of two variables, stroke volume and heart beat. Heartbeat is simply a count of the number of times a heart beats per minute. Stroke volume is the amount of blood circulated by the heart with each beat. The formula for this is expressed as CO = SV x HR.
A healthy heart should circulate your entire blood supply, which is around 5L each minute. This figure will vary based on a person's size and activity level.
Cardiac Output: Key Terms
- Cardiac Output: a measurement of how many liters of blood are passing through the chambers of the heart per minute
- Heart Rate: number of beats of the heart per minute
- Stroke Volume: measure of the volume of blood pushed out through the ventricles per heartbeat
- Normal Resting Heart Rate : normal number of heartbeats per minute while the body is at rest; generally 60-100 beats/minute
- Echocardiogram: medical tool to view and measure the heart
Learning Outcomes
When this lesson is over, students should be able to:
- Describe cardiac output
- Discuss the variables involved in determining cardiac output
- Identify the importance of checking cardiac output
- Recall and use the formula for determining cardiac output
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