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Old 08-17-2011
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Vascular 50% Stenosis and coronary blood flow

49 years old woman with coronary artery disease undergo coronary artery angiography that shows a 50% decrease in the lumen of the left anterior descending coronary artery. for any arterior venous pressure gradient, the flow through this artery (comparing to the normal) will decrease by a facor of which of the following:

A- 2
B- 4
C- 8
D- 16
E- 32
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Old 08-17-2011
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Default

D) 16

R=(1/r^4) of the vessel wall

i.e)(1/2)^4 =1/16
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Old 08-17-2011
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Default ans is 16

flow is directly proportional to r^4 and change in pressure and inversly proportional to viscosity and length of the vessel.

now radius of the vessel has become r/2 because of the 50% reduction in luminal diameter.

so flow is (r/2)^4= 16
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Old 08-17-2011
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49 years old woman with coronary artery disease undergo coronary artery angiography that shows a 50% decrease in the lumen of the left anterior descending coronary artery. for any arterior venous pressure gradient, the flow through this artery (comparing to the normal) will decrease by a facor of which of the following:

A- 2
B- 4
C- 8
D- 16
E- 32
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  #5  
Old 08-17-2011
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Default yes, but

yes, if that was all it happened, yes
but in reality the small arterioles in the territory supplied by the stenotic artery would dilate (due to local mediators) thus compensating for the stenosis mentioned in the stem of this question (at least under resting conditions). Remember that small arterioles account for most vascular resistance.
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Old 08-18-2011
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Default correct answer DD

good job guys!

if radius is decreased by half, the resistance increases 16 folds.
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  #7  
Old 08-23-2011
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this is nmbe question too!
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Cardiovascular-, Physiology-

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