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#1
08-17-2011
 USMLE Forums Addict Steps History: CK Only Posts: 105 Threads: 19 Thanked 69 Times in 32 Posts Reputation: 79
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
 The above post was thanked by: drgsarunprasath (08-17-2011), jahn77 (08-17-2011)

#2
08-17-2011
 USMLE Forums Scout Steps History: Not yet Posts: 99 Threads: 29 Thanked 89 Times in 37 Posts Reputation: 99

D) 16

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

i.e)(1/2)^4 =1/16
 The above post was thanked by: jahn77 (08-17-2011)
#3
08-17-2011
 USMLE Forums Scout Steps History: Not yet Posts: 29 Threads: 2 Thanked 15 Times in 13 Posts Reputation: 25
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
#4
08-17-2011
 Guest Steps History: 1+CK+CS Posts: 441 Threads: 153 Thanked 394 Times in 211 Posts Reputation: 417

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
#5
08-17-2011
 USMLE Forums Scout Steps History: 1+CK+CS Posts: 69 Threads: 4 Thanked 76 Times in 21 Posts
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.
#6
08-18-2011
 USMLE Forums Addict Steps History: CK Only Posts: 105 Threads: 19 Thanked 69 Times in 32 Posts Reputation: 79

good job guys!

if radius is decreased by half, the resistance increases 16 folds.
#7
08-23-2011
 USMLE Forums Addict Steps History: Not yet Posts: 189 Threads: 17 Thanked 95 Times in 58 Posts Reputation: 105

this is nmbe question too!
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 Tags Cardiovascular-, Physiology-

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