What effect explains the pressure drop that occurs before a stenosis to allow acceleration into the constriction and deceleration afterward?

• A. Bernoulli effect
• B. Poiseuille effect
• C. Venturi effect
• D. Reynolds effect

Answer: (A)

In fluid flow, velocity and pressure trade energy along a streamline according to Bernoulli’s principle: as velocity increases, pressure decreases. When blood approaches a stenosis, the lumen narrows, so the flow must speed up to get through the constricted area. That acceleration comes with a drop in pressure just ahead of and within the narrowed segment. After the constriction, the velocity reduces and the pressure climbs again, causing deceleration downstream. This pattern—pressure lowering as velocity rises to push through the constriction and pressure recovery afterward—fits Bernoulli’s relationship between speed and pressure. The other ideas aren’t describing this local velocity–pressure exchange as directly: Poiseuille relates to overall laminar flow in a long, straight tube and viscosity effects; Reynolds is about the tendency toward laminar or turbulent flow; the Venturi effect is a specific application of Bernoulli in a constricted tube, but the general concept at play here is Bernoulli.