Cardiac output

Cardiac Output is the volume of blood that is ejected by the heart from the left ventricle into the aorta or from the right ventricle into the pulmonary artery in one minute. It is a key indicator of the heart's function and health.

Definition

Cardiac output is typically measured in liters per minute (L/min). It is calculated by multiplying the stroke volume (the amount of blood ejected by the heart in one heartbeat) by the heart rate (the number of heartbeats per minute). The formula is as follows:

Cardiac Output = Stroke Volume x Heart Rate

Factors Affecting Cardiac Output

Several factors can affect cardiac output, including:

• Preload: The volume of blood in the ventricles at the end of diastole (just before contraction). An increase in preload can increase stroke volume and thus cardiac output.
• Afterload: The resistance that the heart must overcome to eject blood. An increase in afterload can decrease stroke volume and thus cardiac output.
• Contractility: The strength of the heart's contraction. An increase in contractility can increase stroke volume and thus cardiac output.
• Heart rate: The number of heartbeats per minute. An increase in heart rate can increase cardiac output.

Clinical Significance

Cardiac output is a crucial measure in the diagnosis and management of many cardiovascular diseases, including heart failure, hypertension, and shock. A low cardiac output can indicate heart failure, while a high cardiac output can indicate conditions such as thyrotoxicosis or anemia.

Measurement

Cardiac output can be measured using several methods, including:

• Echocardiography: This non-invasive method uses ultrasound to measure the volume of blood ejected by the heart in each beat, and the heart rate.
• Cardiac catheterization: This invasive method involves inserting a catheter into the heart to measure pressures and flows, which can be used to calculate cardiac output.
• Pulse contour analysis: This method uses a sensor to measure the shape of the arterial pulse wave, which can be used to estimate cardiac output.

See Also

• Stroke volume
• Heart rate
• Ejection fraction
• Cardiac index