Cardiac output is calculated by multiplying stroke volume by heart rate.
Cardiac output (CO) is a vital measurement in understanding how well your heart is functioning. It represents the volume of blood your heart pumps per minute, typically measured in liters per minute (L/min). Understanding how to calculate it is key for healthcare professionals and those interested in cardiovascular health.
The Cardiac Output Equation
The core formula for calculating cardiac output is straightforward:
Cardiac Output (CO) = Stroke Volume (SV) x Heart Rate (HR)
Where:
- Stroke Volume (SV): The amount of blood ejected by the heart with each beat (measured in mL/beat).
- Heart Rate (HR): The number of times the heart beats per minute (measured in beats/min).
Step-by-Step Calculation
Here's how to calculate cardiac output:
- Determine Stroke Volume: This usually requires specialized equipment like an echocardiogram or cardiac catheterization to measure directly. Estimation techniques can also be used.
- Determine Heart Rate: This can be easily measured by taking your pulse or using an electrocardiogram (ECG).
- Multiply: Multiply the stroke volume by the heart rate.
Example
Let's say someone has a stroke volume of 70 mL/beat and a heart rate of 72 beats/min.
CO = 70 mL/beat x 72 beats/min = 5040 mL/min
To convert to liters per minute, divide by 1000:
CO = 5040 mL/min / 1000 mL/L = 5.04 L/min
Therefore, the cardiac output is 5.04 L/min.
Factors Affecting Cardiac Output
Several factors can influence cardiac output, including:
- Heart Rate: A faster heart rate generally increases cardiac output, up to a certain point.
- Stroke Volume: Factors that affect stroke volume include:
- Preload: The amount of stretch on the heart muscle before contraction.
- Afterload: The resistance the heart must overcome to pump blood.
- Contractility: The force of the heart's contraction.
Importance of Cardiac Output
Cardiac output is a crucial indicator of cardiovascular health. Low cardiac output can lead to symptoms such as fatigue, shortness of breath, and dizziness. Conditions like heart failure can significantly reduce cardiac output.
