Venturi Effect and Blood Flow

[kryptonxenon]

Hey guys! From what I understand the venturi effect only applies to ideal fluids and it states that a fluid's pressure decreases in a constricted region.

However, if you have have plaque buildup in an artery the pressure will increase. Is this because blood is not an ideal fluid? It would be great if someone could expound on this!

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[betterfuture]

I'm going to go ahead and give this a shot and hopefully, someone can correct me if I am wrong.

Well from Poiseuille's law we know,

Q = (pi*r^4*delta P)/(8*viscosity*L)

• Q is the flow rate
• r is the blood vessel radius
• delta P is the change in pressure along the blood vessel

We see that as the radius decreases, it causes a significant change in the pressure because delta P is inversely proportional to the fourth power of the radius. Hence why as plaque builds up, the radius decreases and Pressure increases.

I am going to assume that blood does not follow the continuity equation because flow rate can change throughout the body and the Bernoulli equation assumes the tube is rigid and does not allow for changes in the flow of fluid. Blood, however, travels through arteries which are elastic so the shape of the blood vessels change. So in other words, blood is not an ideal fluid.

 

[kryptonxenon]

Thank you @betterfuture! That makes sense to me.