Valve Area Calculator

The Gorlin equation, published by Richard Gorlin and Sidney Gorlin in 1951, was the original method for converting cardiac catheterization pressure and flow measurements into an actual valve orifice area, and a version of it is still used today alongside modern echocardiographic methods. The core idea is that flow through a fixed orifice relates to the pressure gradient driving that flow -- a smaller, more stenotic orifice needs a larger pressure gradient to push the same amount of blood through it, so measuring flow and gradient together lets you back-calculate the effective orifice area. This calculator computes flow across the valve from cardiac output, heart rate, and the relevant time period (systolic ejection period for the aortic valve, diastolic filling period for the mitral valve, since that is when each valve is actually open and conducting flow), then divides by an empirical constant times the square root of the mean pressure gradient. The constant differs by valve because the underlying discharge coefficient -- how efficiently flow actually passes through the anatomic orifice compared to an idealized opening -- differs between the two valves: 44.3 for the aortic valve, and 37.7 for the mitral valve (the 1972 Cohen-Gorlin revision, using a 0.85 discharge coefficient for the mitral valve rather than the original 0.7). For aortic stenosis, a calculated valve area above 2.0 cm² is considered normal, 1.5-2.0 cm² mild, 1.0-1.5 cm² moderate, and below 1.0 cm² severe.

Mitral stenosis grading follows the ACC/AHA 2020 valvular heart disease guideline: valve area above 2.5 cm² is not considered hemodynamically significant, 2.0-2.5 cm² mild, 1.5-2.0 cm² moderate, and 1.5 cm² or below severe (with 1.0 cm² or below further classified as very severe). Note that these bands describe the degree of narrowing relative to when stenosis becomes hemodynamically meaningful, not the mitral valve's true undiseased anatomic size, which is considerably larger (roughly 4-6 cm²). This calculator also reports a velocity derived from the simplified Bernoulli equation (v = √(ΔP/4)) using the same mean pressure gradient entered above. Because it is derived from the *mean* gradient rather than a directly measured Doppler *peak* velocity, it reads meaningfully lower than a true peak velocity at the same severity and should not be compared directly against peak-velocity severity cutoffs (such as the ≥4.0 m/s threshold used for severe aortic stenosis) -- ΔP = 4v² is the standard relationship used at the bedside to convert a Doppler-measured velocity into a pressure gradient, or vice versa, but a true peak-velocity estimate requires the peak instantaneous gradient, not the mean.