❤️ Doppler Echo Cardiac Output Calculator
Calculate cardiac output using Doppler echocardiography. Measure stroke volume from the LVOT diameter and velocity-time integral (VTI), then compute cardiac output and cardiac index.
📊 Cardiac Output Results
What Is Cardiac Output?
Cardiac output (CO) is the volume of blood pumped by the heart per minute. It is one of the most important hemodynamic parameters, reflecting the heart's ability to meet the body's metabolic demands.
A normal cardiac output at rest is typically 4 to 8 L/min. When indexed to body surface area, the normal cardiac index ranges from 2.5 to 4.0 L/min/m².
How Does Doppler Echocardiography Measure Cardiac Output?
Doppler echocardiography allows non-invasive estimation of cardiac output by measuring blood flow through the left ventricular outflow tract (LVOT). The calculation involves three steps:
Step 1: Calculate LVOT Cross-Sectional Area (CSA)
The LVOT diameter is measured from the parasternal long-axis view, then the area is calculated assuming a circular cross-section:
Step 2: Calculate Stroke Volume (SV)
The velocity-time integral (VTI) is obtained by tracing the pulsed wave Doppler signal at the LVOT. It represents the distance blood travels per heartbeat:
Normal stroke volume is typically 60–100 mL.
Step 3: Calculate Cardiac Output (CO)
Multiply stroke volume by heart rate to get cardiac output:
Cardiac Index (CI)
The cardiac index normalizes cardiac output to body size:
Where BSA is the body surface area in m². This is typically estimated using the Du Bois formula:
Normal Values
| Parameter | Normal Range | Unit |
|---|---|---|
| LVOT Diameter | 1.8 – 2.2 | cm |
| LVOT VTI | 18 – 22 | cm |
| Stroke Volume | 60 – 100 | mL |
| Cardiac Output | 4.0 – 8.0 | L/min |
| Cardiac Index | 2.5 – 4.0 | L/min/m² |
Clinical Significance
Doppler-derived cardiac output is used extensively in clinical practice to:
- Assess ventricular function — a low cardiac output may indicate heart failure or cardiogenic shock
- Monitor hemodynamics — serial measurements help track response to medications or mechanical support
- Evaluate valvular disease — particularly helpful in assessing severity of aortic stenosis
- Guide fluid management — useful in intensive care settings for optimizing fluid/pressor therapy
Frequently Asked Questions
Why is the LVOT assumed circular?
While the LVOT is slightly elliptical in reality, assuming a circular geometry using a single diameter measurement provides a clinically acceptable and reproducible estimate. 3D echocardiography can measure the true cross-sectional area directly.
What does low cardiac output mean?
A cardiac output below 4 L/min or cardiac index below 2.2 L/min/m² suggests low cardiac output state, which may be seen in heart failure, cardiogenic shock, or severe hypovolemia. Clinical context is essential for interpretation.
How accurate is Doppler cardiac output?
Doppler echocardiography correlates well with thermodilution and other invasive methods when measurements are performed carefully. Key sources of error include inaccurate LVOT diameter measurement (small errors are squared in the CSA calculation) and poor Doppler signal quality.