magdaramirez
Forum Newbie
Topics: 2
Posts: 3
|
Hello out there,
I am studying vascular resistance, and is driving me nuts ,
It says that , the vessel resistance is directly proportional to the length of the vessel and viscosity of the blood. And inversely proportional to the radius to the four power, in other words
if L and viscosity increases then R increases.
If radius increases to the four power then resistance decreases to the four power?
Then here is the question
A men with atherosclerosis coronary artery that is 50%. The maximal blood flow to this artery is reduce by? a)1/2; b)1/4; c) 1/8; d)1/16; e) 1/32
The answer is 1/16, why? It says that the radio is reduce in one half, the resistance is multiplied by 16. where the 16 is come from? 50% =1/2 = 1/ (2)(2)(2)(2)
Magda
|
| ruthiea04
Forum Newbie
Topics: 0
Posts: 2
|
yeah resistance is directly proportional to the length of the vessel and the viscosity but it is inversely proportional to the 4th power of the vessel radius. So in this case the radius of these man's artery decreased by 1/2 causing flow to decrease by 1/ (2 into 2 into 2 into 2) = 1/16... and consequently resistance also increases by a factor of 16 (2 to the fourth power).
i think thats what it is.. pls correct if i"m wrong
|
| bengiz
Forum Newbie
Topics: 0
Posts: 4
|
That is right.It should not be forgotten that the Most Important Factor that determines a Vessel's Resistance is its Radius,although other factors like Length and Viscosity are included.Remember that the Length of a Vessel can not be affected in normal circumstances, but changing the Radius of the vessel,either by Physiological or Pathological means significantly affects the Resistance in the vessel.In your question, the athersclerotic Plaque that caused a 50% reduction(1/2) in the Radius of the Vessel will increase the Resistance by 16 fold.In a Similar question,if you are asked to choose a suitable Stent for this Patient you better choose the one with the Largest radius.
|
| littledoc
Forum Elite
Topics: 9
Posts: 340
|
R=vl/4th power of r. so if radius is reduced to 1/2, resistance will increase by 16 fold. & flowQ=P difference/R. so by increasing resistance to 16 fold flow decreases & becomes 1/16 of original.
___________________
"slow & steady wins the race!"
|
|
| |
| | | | |
