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  #1  
Old 11-29-2011
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Vascular Increased blood velocity!

A patient complaining of chest pain with exercise is evaluated by cardiac catheterization. The left anterior descending (LAD) branch of the coronary artery is visualized but the contrast angiography is poor. A Doppler-tipped catheter is inserted and the blood velocity is observed to increase transiently from 10 cm/sec to 70 cm/sec and then decrease back to 10 cm/sec as the probe passes a particular location in the artery. What was the cause of these changes in velocity measurements?


A. A coronary artery aneurysm with a cross-sectional area 1/7th the size of the native artery
B. A coronary artery aneurysm with a cross-sectional area 7 times greater than the native artery
C. A coronary artery obstruction with a cross-sectional area 1/7th of the size of the native artery
D. A coronary artery obstruction with a cross-sectional area 7 times greater than the native artery
The correct
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Old 11-30-2011
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I am stumped
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Old 11-30-2011
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I say I pick B?

Something from somewhere tells me that if we apply a constriction to a uniform vessel, the flow across all parts will decrease by the same amount. The pressure upstream will increase whereas the pressure downstream decreases.

To explain an aneurysm by Laplace (Tension = pressure x Radius), as the radius increases, the tension must also increase.(a time bomb). This means we have the equation : flow x resistance = flow x resistance. left hand side is for aneurysm part, right hand side for normal part. Since the flow across the pathological part is increased by a factor of 7, we must divide the resistance of path part by 7. (so that both sides of equation are same.) Resistance of the aneurysm is one seventh the resistance of normal part. (Ermmm i think resistance is inversely proportional to cross section, so it means cross section of aneurysm must also be increased by a factor of 7.)

Now, a coronary artery obstruction with a cross-sectional area 1/7th of the size of the native artery might seem to be correct. But i think the smaller your pipe(stenotic part), the slower the water flows right?

Well, i am not sure i am right, i gotta admit thisis kinda convoluted

Please tell the correct amswer with explanation. TQ.
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Old 11-30-2011
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Its C atherosclerotic anguina stable anguina ! Simple crosssectional area decreses as there is atherosclerosis in that region !
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Quote:
Originally Posted by yasirsattar75 View Post
Its C atherosclerotic anguina stable anguina ! Simple crosssectional area decreses as there is atherosclerosis in that region !
hmm this seems more logical .....how could I have missed that?!? But i still don't know how the detection of increased flow works when the probe passed through the stenotic part?
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Quote:
Originally Posted by Daniel Wai View Post
hmm this seems more logical .....how could I have missed that?!? But i still don't know how the detection of increased flow works when the probe passed through the stenotic part?
Read question again u will get the idea probe has passed and at some area viscosity increased coz of atherscletosis and aftrr passing through it it decreases again ! Ok hope its clear !
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answer is C!!
A1 x V1 = A2 x V2

so if the velocity is increasing , area is decreasing!
its a UW concept!
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Quote:
Originally Posted by yasirsattar75 View Post
Read question again u will get the idea probe has passed and at some area viscosity increased coz of atherscletosis and aftrr passing through it it decreases again ! Ok hope its clear !
hey!!! how did ur exam go?!?!!
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Old 11-30-2011
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Yeah it was good it was doable sorry to write proper exam experience coz i have my med school exams in this month so it would b difficult for me to come online more at forums
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C is Answer.

low has increased 7-fold, indicating a decrease in cross-sectional area by a factor of 7. This would be caused by an obstruction, not an aneurysm.
Choice A is incorrect, because a coronary artery aneurysm would produce an increase in
cross-sectional area rather than a decrease.
Flow has increased 7-fold, indicating a decrease in vessel diameter, thus choices B and
D are incorrect.
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Quote:
Originally Posted by miss patho View Post
C is Answer.

low has increased 7-fold, indicating a decrease in cross-sectional area by a factor of 7. This would be caused by an obstruction, not an aneurysm.
Choice A is incorrect, because a coronary artery aneurysm would produce an increase in
cross-sectional area rather than a decrease.
Flow has increased 7-fold, indicating a decrease in vessel diameter, thus choices B and
D are incorrect.
Flow has not actually increased. Flow (theoretically anyway) is the same. What increased is the blood velocity.
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