Calculate Cardiac Output Using Feo2

What is Cardiac Output Calculation Using FEO2?

The calculation of cardiac output using FEO2 (Fraction of Expired Oxygen) is an application of the Fick principle. The Fick principle is a foundational concept in physiology that states the total uptake of a substance by the body’s tissues is equal to the blood flow multiplied by the difference in the substance’s concentration between arterial and venous blood. When oxygen is used as the substance, this principle allows us to calculate the total blood flow pumped by the heart per minute, which is the cardiac output (CO).

This specific method uses respiratory gas analysis, including FEO2, to determine the body’s total oxygen consumption (V̇O₂). By measuring how much oxygen is inhaled versus how much is exhaled, we can calculate the exact amount consumed by the body’s metabolic processes. This V̇O₂ value is the numerator in the Fick equation. The denominator is the arteriovenous oxygen difference (CaO₂ – CvO₂), which represents how much oxygen is extracted by the tissues from each unit of blood. This method, while requiring several inputs, is considered a highly accurate way to determine cardiac output.

Cardiac Output Formula and Explanation

The core of this calculation lies in two main formulas that work together. First, we determine oxygen consumption, and then we use that to find cardiac output.

1. Oxygen Consumption (V̇O₂) Formula

This formula calculates how much oxygen your body uses based on the air you breathe in and out.

V̇O₂ (mL/min) = V̇E (L/min) * (FiO₂/100 - FEO₂/100) * 1000

2. Cardiac Output (CO) Formula

This is the classic Fick equation, which uses the calculated V̇O₂.

CO (L/min) = V̇O₂ (mL/min) / ((CaO₂ - CvO₂) * 10)

The multiplication by 10 in the denominator is a crucial unit conversion to change the arteriovenous difference from mL/dL to mL/L, ensuring the final cardiac output is in the standard unit of Liters per minute (L/min).

Table of Variables
Variable	Meaning	Unit	Typical Range (Resting)
CO	Cardiac Output	L/min	4.0 – 8.0
V̇O₂	Oxygen Consumption	mL/min	200 – 300
V̇E	Minute Ventilation	L/min	5 – 8
FiO₂	Fraction of Inspired Oxygen	%	20.93 (Room Air)
FEO₂	Fraction of Expired Oxygen	%	16 – 17
CaO₂	Arterial Oxygen Content	mL/dL	17 – 20
CvO₂	Mixed Venous Oxygen Content	mL/dL	12 – 15

Practical Examples

Example 1: A Healthy Adult at Rest

Consider a person at rest with stable vitals.

Inputs: V̇E = 6 L/min, FiO₂ = 20.93%, FEO₂ = 16.5%, CaO₂ = 20 mL/dL, CvO₂ = 15 mL/dL
V̇O₂ Calculation: 6 * (0.2093 – 0.165) * 1000 = 265.8 mL/min
CO Calculation: 265.8 / ((20 – 15) * 10) = 5.32 L/min
Result: A cardiac output of 5.32 L/min is well within the normal resting range.

Example 2: An Individual During Moderate Exercise

During exercise, metabolic demand increases dramatically.

Inputs: V̇E = 40 L/min, FiO₂ = 20.93%, FEO₂ = 17.0% (efficiency improves), CaO₂ = 20 mL/dL, CvO₂ = 8 mL/dL (more O2 extracted)
V̇O₂ Calculation: 40 * (0.2093 – 0.170) * 1000 = 1572 mL/min
CO Calculation: 1572 / ((20 – 8) * 10) = 13.1 L/min
Result: The cardiac output increases to 13.1 L/min to meet the body’s heightened need for oxygenated blood. For more on exercise effects, consider using a Oxygen Consumption Calculator.

How to Use This calculate cardiac output using feo2 Calculator

Follow these steps to get an accurate estimation:

Enter Minute Ventilation (V̇E): This value is typically measured with a spirometer. Enter the volume in Liters per minute.
Enter Inspired and Expired O₂ (FiO₂ & FEO₂): FiO₂ is 20.93% for room air but can be different with supplemental oxygen. FEO₂ is measured from collected exhaled gas.
Enter Blood Oxygen Content (CaO₂ & CvO₂): These values are obtained from arterial and mixed venous blood gas analysis, respectively. The mixed venous sample must be taken from a pulmonary artery catheter for true accuracy.
Review Results: The calculator will instantly provide the total Oxygen Consumption (V̇O₂) and the final Cardiac Output (CO). The results are also displayed on a chart for easy visualization. For a related measurement, you can use a Ejection Fraction Calculator to assess heart efficiency.

Key Factors That Affect Cardiac Output

Several physiological factors can influence cardiac output. Understanding them provides context to the numbers.

Heart Rate: A faster heart rate directly increases cardiac output, assuming stroke volume is constant.
Stroke Volume: The amount of blood pumped per beat. This is influenced by contractility (heart muscle strength), preload (ventricular filling), and afterload (resistance the heart pumps against). A higher stroke volume increases CO. A tool like our Stroke Volume Calculator can provide more insight.
Metabolic Rate: Higher metabolic activity (e.g., during exercise, fever, or stress) increases the body’s oxygen demand (V̇O₂), which in turn requires a higher cardiac output to supply it.
Blood Volume and Hemoglobin: Hypovolemia (low blood volume) reduces preload and therefore cardiac output. Anemia (low hemoglobin) reduces the blood’s oxygen-carrying capacity, requiring the heart to pump more blood to deliver the same amount of oxygen.
Systemic Vascular Resistance (SVR): High blood pressure or constricted arteries increase afterload, making it harder for the heart to eject blood, which can lower cardiac output. Our Systemic Vascular Resistance Calculator is a useful resource for this.
Age and Fitness Level: Athletes typically have a lower resting heart rate but a higher stroke volume, resulting in a very efficient cardiac output. CO generally declines with age.

Frequently Asked Questions (FAQ)

What is a normal cardiac output?: At rest, a normal cardiac output for an adult is between 4.0 and 8.0 liters per minute. This can increase to over 30 L/min in elite athletes during peak exertion.
Why is the Fick method considered a gold standard?: Because it is based on a direct measurement of the body’s total oxygen consumption and oxygen extraction, it has fewer assumptions than other methods like thermodilution, making it highly accurate when performed correctly.
Can I measure these values at home?: No. This calculation is for educational purposes and clinical settings. Measuring V̇E, FEO₂, CaO₂, and CvO₂ requires specialized medical equipment, including blood gas analysis and spirometry.
What does a low cardiac output signify?: A low cardiac output can indicate heart failure, shock, hypovolemia, or other serious cardiovascular conditions where the heart is unable to meet the body’s metabolic demands.
What does a high cardiac output signify?: A high cardiac output is normal during exercise. At rest, it can be a sign of certain conditions like sepsis, severe anemia, or hyperthyroidism, where the body’s demand for oxygen is abnormally high.
How does FiO₂ affect the calculation?: The FiO₂ is critical for calculating V̇O₂. If a patient is on supplemental oxygen, using the standard 20.93% for room air will lead to a highly inaccurate V̇O₂ and CO calculation.
What is the difference between CaO₂ and CvO₂?: CaO₂ is the oxygen content in blood leaving the lungs (arterial), which is typically high. CvO₂ is the oxygen content in blood returning to the heart after delivering oxygen to the tissues (venous), which is lower. The difference shows how much oxygen the body used. For more on blood pressure, see our Mean Arterial Pressure Calculator.
Is this calculator a substitute for medical advice?: Absolutely not. This tool is for informational and educational purposes only. The results should not be used for self-diagnosis or to replace professional medical evaluation and advice.

Related Tools and Internal Resources

Explore other calculators that provide insight into cardiovascular health and metabolic function:

Stroke Volume Calculator: Determine the volume of blood pumped from one ventricle of the heart with each beat.
Mean Arterial Pressure Calculator: Calculate the average arterial pressure during a single cardiac cycle.
Ejection Fraction Calculator: A key measurement of heart function.
Systemic Vascular Resistance Calculator: Assess the resistance the heart must overcome to pump blood.
Oxygen Consumption Calculator: Focus specifically on calculating V̇O₂ from respiratory gases.
Basal Metabolic Rate Calculator: Estimate your body’s baseline energy expenditure.

Cardiac Output Calculator (from FEO2)

Results Visualization