Doppler studies can detect the relative increase in flow velocity seen in the jet of flow within the stenosis itself. The severity of the obstruction can be estimated by comparing the higher velocity within the stenotic area with the lower velocities obtained immediately proximal to the obstructing lesion. Provided that the proximal velocity is not abnormally high, a modified Bernoulli equation can be used to estimate the peak pressure drop across the stenosis.


peak gradient in mm Hg = difference in pressure =

= 4 * (((peak velocity in stenotic area in m/sec) ^2) - ((velocity below obstruction) ^2))


If the velocity below the obstruction is < 1 m/s, the equation can be simplified to


peak gradient in mm Hg = difference in pressure =

= 4 * ((peak velocity in stenotic area in m/s) ^2)



• The pressure gradient across any stenosis varies not only directly with the severity of the stenosis itself but also with the rate of flow through it. Thus, if the flow is reduced due to decreased cardiac output, then the resulting flow decrease will decrease the pressure gradient across stenosis independent of the severity of the stenosis. If the flow is increased, then the pressure gradient can be high even with mild stenosis.

• Doppler-determined peak pressure gradients exceeding 70 mm Hg generally denote clinically important aortic stenosis.

• Doppler estimates of peak aortic gradients are usually 30% higher than those measured by cardiac catheterization.


To read more or access our algorithms and calculators, please log in or register.