What Is a Cardiac Output Equation?
Cardiac output, often denoted as CO, is the amount of blood ejected by the left ventricle into the aorta per minute (Martini et al., 2017, 680-681). It is conventionally expressed in liters of blood per minute and serves as a crucial indicator of heart function, representing the volume of blood entering the systemic circuit per minute.
The two key parameters that make up the cardiac output are:
- Stroke volume, in liters per heartbeat.
- Heart rate, in beats per minute.
The cardiac output, in liters per minute, can therefore be represented by:
Cardiac Output = Heart Rate × Stroke Volume
CO = HR × SV
This is the simplest formula for cardiac output, and many other alternative formulae exist that can consider various factors influencing heart rate or stroke volume.
While this formula may seem straightforward, it's essential to acknowledge the nuanced interplay of factors influencing heart rate, stroke volume, and, ultimately, cardiac output. Fortunately, our Cardiac Output Equation template can guide you in understanding the intricate dynamics at play.
How Does It Work?
Feel free to utilize this editable cardiac output formula, which can be digitally filled, printed, and completed by hand. Just follow these straightforward steps to ensure accurate cardiac output calculations every time:
Step 1: Enter the End-Diastolic Volume (EDV)
If you already have the stroke volume value, skip to step four and enter the stroke volume in the SV box of equation two. Otherwise, input the end-diastolic volume (EDV) in milliliters into the designated EDV box in equation one.
Step 2: Enter End-Systolic Volume (ESV)
Next, insert the milliliter end-systolic volume into the ESV box in equation one.
Step 3: Calculate Stroke Volume
Once you have the EDV and ESV filled in in equation one, subtract the ESV from the EDV to give you a value for stroke volume in milliliters.
Step 4. Copy the stroke volume into equation two (in liters)
Watch out for the units on this one! The next step is to copy the stroke volume value into the SV box in equation two but in liters.
Step 5: Enter Heart Rate
In equation two, input the heart rate value in beats per minute (bpm) into the HR box.
Step 5: Calculate Cardiac Output
The final step involves multiplying the stroke volume and heart rate, or the values in the HR and SV boxes in equation two. This computation will yield the cardiac output in liters per minute.
Cardiac Output Equation Example (sample)
An example problem involving cardiac output calculation from end-systolic volume (ESV), end-diastolic volume (EDV), and heart rate is given below:
Calculate the cardiac output for Marie, whose end-systolic volume is 45mL, end-diastolic volume is 120mL, and heart rate is 80 bpm.
You can download the example template here to show what the finished Cardiac Output Equation looks like for this specific example and see the value for Marie’s cardiac output.
When Would You Use This Equation?
There’s a variety of ways to calculate cardiac output, and while Fick’s equation is considered the gold standard, the best equation to use depends on your data and the technique you are using to obtain this data.
Any method that allows for measurement of the left ventricular volume at different phases of the cardiac cycle will allow for stroke volume calculation and, therefore, cardiac output calculation.
Cardiac MRI, echocardiography, or angiography can all be used with this simple cardiac output equation. While the Fick methods produce a more accurate and analytical result, imaging-based methods using this simple cardiac output equation produce an efficient estimate beneficial for tracking relative changes in cardiac output over time (Maleki et al., 2017, 183-184).
Professionals who may benefit from using this simple cardiac output equation in their working lives include:
- Cardiologists and cardiology trainees/students
- Medical and nursing students
- Medical Imaging Technologists
- Research Scientists and Students
What Do the Results Mean?
It's good to remember that when assessing a patient's cardiac health, relying on a single number doesn’t give the whole picture. Cardiac output is incredibly dynamic and can be influenced by various factors like exercise, hormones, or even body temperature. This means that each person will have their own unique baseline for heart function, and what's considered normal can vary widely.
A commonly cited stroke volume for a healthy adult hovers around 70mL per beat. Combined with a typical resting heart rate ranging from 60 to 80 beats per minute, you get a ballpark figure for 5 liters per minute cardiac output. However, these values are just averages, and individual values can fall anywhere within this spectrum.
If someone's cardiac output is lower than what's expected for a healthy individual, it could be a signal of an underlying heart condition like congestive heart failure or cardiomyopathy. Alternatively, a higher-than-expected cardiac output might be due to factors like hyperthyroidism, stress, or just the aftermath of a rigorous workout.
This underscores the importance of not taking a solitary cardiac output value at face value; it needs to be considered in the broader context to understand if there's an underlying health issue. So, the next time you look at cardiac output numbers, remember, it's not just about the digits—it's about the story they're telling in the context of a person's overall health.
Why Use Carepatron as Your Cardiac Output Equation App?
Heart disease is the leading cause of death for adults in the United States, according to the Centers for Disease Control and Prevention. Therefore, it will represent a significant proportion of the workload for medical practitioners, from general to emergency medicine practitioners.
Healthcare practitioners have a responsibility to their patients to provide the best course of treatment. However, due to the volume of administrative tasks frequently required, the time dedicated to the most important of a healthcare practitioner's job is often encroached upon by menial tasks.
Luckily, with Carepatron, you can get your precious time back with our smart software solutions designed to get you back to doing what you do best.
Carepatron is a comprehensive software suite that saves you time through smart practice management solutions. Offer your patients access to their own patient portal software to book appointments with you, see their results, or conduct telehealth appointments. Utilize our AI-powered smart medical dictation software or our library of helpful templates, such as this Cardiac Output Equation, to keep you working efficiently and elevate your practice to the next level.
Maleki, M., Alizadehasl, A., & Haghjoo, M. (Eds.). (2017). Practical Cardiology. Elsevier.
Martini, F., Ober, W., Nath, J., Bartholomew, E., & Petti, K. (2017). Visual Anatomy and Physiology. Pearson.
Young, D. B. (2010). Control of Cardiac Output. Morgan & Claypool Life Sciences.