Ch 1a + 1b Flashcards
What is pressure?
Driving force behind fluid flow
What is required in order for flow to occur?
A pressure difference
If the pressure difference is greater, will the flow rate be greater or poorer?
Greater, high pressure causing greater flow
(flow rate + pressure are directly proportional)
What is volumetric flow rate in a long straight tube determined by?
Pressure difference (gradient) + resistance to flow (viscosity)
If pressure difference increases, what happens to the volumetric flow rate?
It increases (b/c pressure + flow are directly proportional - they increase/decrease together)
If flow resistance increases, what happens to volumetric flow rate?
Decreases (b/c is harder for flow to travel)
What is the poise/viscosity of blood?
0.035 at 37 degrees C
(5x that of water)
What 3 factors affect flow resistance?
-Fluid viscosity/poise
-Tube length
-Tube radius (half of width)
If tube length increases, what happens to flow resistance?
It increases, length + resistance are directly proportional to each other
(b/c there is more surface area with a longer vessel for friction to occur, this causes resistance + lower flow rate)
What is plug flow a form of?
Laminar flow
Is the speed of fluid with plug flow constant or does it vary through the tube/vessel?
Is constant
When would plug flow occur?
At entrance/start of a tube or vessel
(ex. when LV pushes blood to ascending AO)
How do the streamlines appear with laminar flow?
Straight + parallel to each other (images shows flow going in same direction together)
Is laminar flow speed max at the beginning or center of a tube/vessel?
At center
Where is laminar flow speed at a minimum at in a tube/vessel?
At tube’s walls
What is parabolic flow a form of?
Laminar flow
Is the speed of fluid with parabolic flow constant or does it vary through the tube/vessel?
Varies, goes at different speeds
Where would we see parabolic flow in a tube/vessel?
In center of vessel, not at entrance like plug flow
The average flow speed across a vessel is equal to what?
One half the maximum flow speed (at the center)
What is disturbed flow a form of?
Laminar flow
What happens to the parallel streamlines with disturbed flow?
Altered from straight line form, no longer parallel
When would disturbed flow occur?
-At a stenosis (a narrowed vessel, ex. losing parallel shape due to going over top a hurdle like plaque)
-At a bifurcation
Do lanes of fluid still exist in disturbed flow?
Yes still organized, just no longer parallel to each other
Is turbulent flow a form of laminar flow?
Nope, it is NOT parallel, very chaotic directions
How do the streamlines appear with turbulent flow?
-Random with chaotic varying speeds + directions, flow going all over the place!
-No organization to it! Lanes not organized.
Is forward net flow still maintained in turbulent flow?
Yes
What is the continuity rule?
As a stenosis gets worse (vessel diameter decreases + narrows even more), flow speed will increase to try + maintain flow
What happens to flow once a vessel becomes occluded?
No flow present, completely blocked
Is blood created or destroyed as it flows through a vessel?
Neither
Should volumetric flow rate be constant proximal, within or distal to a stenosis?
Must be constant through all parts!
Does flow speed increase or decrease at a stenosis following the continuity rule + what occurs distal to it?
Increases at a stenosis to maintain flow continuity, turbulence can occur distally (chaotic flow)
What is the bernoulli effect?
-When pressure drops directly in the MIDDLE of a stenosis to a level less than before or after the stenosis
-A reduction in pressure associated with high flow speed at a stenosis
What is the rouleaux effect?
-A rouleaux are RBCs stuck together
-Can represent diseases, although is typically an incidental finding in healthy adults
What is poiseuille’s equation?
Volumetric flow rate (Q) = pressure difference (P) / viscosity (n)
Under line: anything that increases will decrease flow
Above line: anything that increases will increase flow
If diameter increases (vessel width), what happens to the flow rate?
Increases (b/c extra width allows more fluid to pass through causes less resistance)
If length increases, what happens to the flow rate?
Decreases (b/c more surface area + friction causing more resistance)
If viscosity increases, what happens to flow rate?
Decreases (b/c more resistance)
