- #1

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Now my doubt is that why does pressure decrease? When the velocity of blood flow increases inside the artery?

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- #1

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Now my doubt is that why does pressure decrease? When the velocity of blood flow increases inside the artery?

- #2

bigfooted

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So if the velocity goes up (because for instance the flow-through area of the artery is decreasing), the dynamic pressure goes up and therefore the static pressure goes down.

There is a derivation based on conservation of energy here:

http://en.wikipedia.org/wiki/Bernoulli's_principle#Derivations_of_Bernoulli_equation

- #3

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Can you give me the theoretical reason for it?

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Chestermiller

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If you have a literature reference for this explanation, please provide it.

- #6

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I don't know a reference. I just wanted to give some intuition as to why there was a trade off between pressure and flow velocity squared.If you have a literature reference for this explanation, please provide it.

constant energy =~ V

The references I have seen seemed more rigorous, but less intuitive to me.

- #7

Chestermiller

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The reason I asked for a reference is that this doesn't seem correct (to me). The Bernoulli equation, which is what Bigfoot was alluding to in post #2 and you were alluding to in this quote, is based on Newton's 2nd law. If the velocity is higher downstream than upstream, the pressure must be higher upstream than downstream in order to accelerate the fluid. (This, of course, neglects viscous drag).I don't know a reference. I just wanted to give some intuition as to why there was a trade off between pressure and flow velocity squared.

constant energy =~ V_{total}^{2}= V_{toward wall}^{2}+ V_{parallel to wall}^{2}=~ Pressure + 1/2 ρ V_{parallel to wall}^{2}

The references I have seen seemed more rigorous, but less intuitive to me.

Chet

- #8

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I agree. I must have said something confusing in my earlier post if I implied the opposite. And your way of looking at it may be the most intuitive of all.If the velocity is higher downstream than upstream, the pressure must be higher upstream than downstream in order to accelerate the fluid.

To continue your logic: If the velocity slows down farther downstream, there must be some higher pressure downstream that slowed it down. So the trade-off between flow velocity and pressure is intuitive in all cases.

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