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Discussion Starter #1
A 49 YO woman with CAD undergoes coronary arteriography that shows a 50% decrease in the lumen of the LAD. For any arteriovenous pressure gradient, the flow thru this artery (compared with normal) wall decrease by a factor of which of the following?

a) 2
b) 4
c) 8
d) 16
e) 32

need explanation of equation please?
 

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Poiseulle's law is

and Flow = ΔP/resistance
so the factor of change in ΔP (1/r^4 in this case) is the same as that in Flow
, by the transitivity of multiplication.
Okay, I said that badly...:eek:
The italicized part should say "Flow is Q in the equation, so the factor of change in Flow is the inverse of that in ΔP (1/r^4 in this case) = r^4 = 1/16. So, as aktorque said, the flow would decrease by a factor of 16."
Hope that's clearer, and sorry for the bad explanation before!
 

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Mondoshawan is right. this is another way to look at it;

Resistance = (8 x viscosity x length)/ radius^4
Resistance = Pressure change/Flow

If radius reduces by 1/2, then resistance increases by 16. (inverse proportnl)
If resistance increases by 16,then Flow reduces by 16.(inversely proportional)

for questions like this, Goljan said, just remember '16', the boards wont go beyond that.
hope this helps.
 
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