Modified Bernoulli Equation
In most clinical situations the flow acceleration and viscous friction terms are ignored allowing the flow (pressure) gradient across a narrowed orifice to be determined from the convective flow acceleration term alone. If the flow velocity proximal to a narrowed orifice (V1) is < 1m/s then it is usually ignored as it provides no important effect on the result as compared to using the distal velocity (V2) alone.
Oh J, Seward JB, Tajik AJ.
The Echo Manual 3rd edition. Lippincott, Williams, Wilkins. 2007
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