Gorlin Formula Calculator
Calculate aortic valve area (AVA) and mitral valve area (MVA) using the Gorlin formula from cardiac output, heart rate, mean gradient, and ejection period. Free cardiology stenosis assessment tool.
About This Calculator
The Gorlin Formula Calculator computes cardiac valve area from hemodynamic parameters using the classic Gorlin equation, a foundational tool in cardiology for assessing valvular stenosis severity. Developed by Richard Gorlin and S. Gorlin in 1951, this hydraulic formula estimates the effective orifice area of stenotic cardiac valves — most commonly the aortic valve (AVA) and mitral valve (MVA) — using measurements obtained during cardiac catheterization.
The Gorlin formula for aortic valve area is: AVA = CO / (44.3 × HR × SEP × √ΔP), where CO is cardiac output in mL/min, HR is heart rate in bpm, SEP is systolic ejection period in seconds per beat, and ΔP is the mean pressure gradient across the valve in mmHg. For mitral valve area: MVA = CO / (37.7 × HR × DFP × √ΔP), using the diastolic filling period (DFP). The constants 44.3 and 37.7 are empirically derived discharge coefficients accounting for the geometric and flow characteristics of each valve.
Aortic stenosis grading follows the 2020 ACC/AHA guidelines: Normal AVA ≥ 3.0 cm², Mild 1.5-3.0 cm², Moderate 1.0-1.5 cm², Severe < 1.0 cm². Mitral stenosis grading: Normal MVA ≥ 4.0 cm², Mild 1.5-4.0 cm², Moderate 1.0-1.5 cm², Severe < 1.0 cm². A valve area below 1.0 cm² is considered critical and typically warrants intervention.
Limitations: The Gorlin formula may underestimate valve area in low-flow states (cardiac output below 2.5 L/min). In such cases, the continuity equation (AVA by Doppler echocardiography) is often preferred. The formula also assumes a constant discharge coefficient that may vary with valve morphology and flow rate. Concomitant aortic or mitral regurgitation can affect the accuracy of the gradient measurement.
Regional Notes
India: Rheumatic heart disease remains a leading cause of mitral stenosis in India, affecting younger populations. The Gorlin formula is used in Indian cardiac catheterization labs alongside echocardiography for pre-procedural planning of balloon mitral valvotomy and valve replacement surgery.
US & UK: In the US and UK, echocardiography (continuity equation) is the primary non-invasive method for valve area assessment. The Gorlin formula is typically reserved for cases where invasive hemodynamic assessment is needed, such as discrepancies between echocardiographic findings and clinical symptoms, or during cardiac catheterization prior to transcatheter aortic valve replacement (TAVR) or surgical valve replacement.
Frequently Asked Questions
What is the Gorlin formula?
The Gorlin formula is a hydraulic equation used to calculate cardiac valve area from hemodynamic parameters measured during cardiac catheterization. It computes aortic valve area (AVA) as CO / (44.3 × HR × SEP × √ΔP) and mitral valve area (MVA) as CO / (37.7 × HR × DFP × √ΔP), where CO is cardiac output in mL/min, HR is heart rate, SEP/DFP is systolic ejection or diastolic filling period in seconds per beat, and ΔP is the mean pressure gradient in mmHg.
How do you calculate aortic valve area using the Gorlin formula?
To calculate aortic valve area (AVA) with the Gorlin formula: AVA = CO / (44.3 × HR × SEP × √ΔP). First convert cardiac output from L/min to mL/min by multiplying by 1000. Measure heart rate (HR) in bpm, systolic ejection period (SEP) in seconds per beat, and mean pressure gradient (ΔP) in mmHg. A normal AVA is 3-4 cm². Values below 1.0 cm² indicate severe aortic stenosis.
What is the normal aortic valve area?
The normal aortic valve area (AVA) is 3 to 4 cm² in adults. Mild aortic stenosis is defined as AVA 1.5-3.0 cm², moderate stenosis as 1.0-1.5 cm², and severe stenosis as less than 1.0 cm². A critically stenotic aortic valve (AVA < 0.8 cm²) requires urgent intervention.
What is the normal mitral valve area?
The normal mitral valve area (MVA) is 4 to 6 cm² in adults. Mild mitral stenosis is defined as MVA 1.5-4.0 cm², moderate stenosis as 1.0-1.5 cm², and severe stenosis as less than 1.0 cm². The Gorlin formula uses a constant of 37.7 for mitral valve calculations instead of 44.3 for aortic.
What is the difference between the Gorlin formula and the continuity equation?
The Gorlin formula uses invasive hemodynamic data from cardiac catheterization (cardiac output, heart rate, pressure gradient, ejection period) to calculate valve area. The continuity equation uses echocardiographic Doppler measurements (LVOT diameter, velocity-time integrals) and is non-invasive. The Gorlin formula can underestimate valve area in low-flow states (CO < 2.5 L/min), where the continuity equation may be preferred.
What is the Gorlin constant for aortic and mitral valves?
The Gorlin constant is 44.3 for the aortic valve and 37.7 for the mitral valve. These empirical constants account for the different geometry and flow characteristics of each valve. The constant appears in the denominator of the formula: Valve Area = Cardiac Output / (Constant × Heart Rate × Filling/Ejection Period × √Mean Gradient).
What is valvular flow in the Gorlin formula?
Valvular flow is calculated as Cardiac Output (mL/min) divided by the product of Heart Rate (bpm) and the ejection or filling period (sec/beat). This gives the flow per second of valve opening in mL/s/beat. The Gorlin formula then divides this flow by the product of the valve-specific constant and the square root of the mean pressure gradient to obtain the valve area in cm².
What are the limitations of the Gorlin formula?
The Gorlin formula has several limitations: it underestimates valve area in low-flow states (CO below 2.5 L/min); it assumes a constant discharge coefficient that varies with flow and valve morphology; it may overestimate stenosis severity in patients with concomitant aortic regurgitation; it requires invasive catheterization; and it is sensitive to accurate measurement of the ejection period and mean gradient. The continuity equation is often preferred for echocardiographic assessment.