Flashcards in Lesson 20 (Part 2) Deck (34)
Where is pulsatile flow observed?
What happens to the pressure and speed of blood as the heart beats?
They increase then decrease
What do we observe in compliant vessels? (2)
1. Added forward flow
2. Reversal of flow
Expansion and contraction of non-rigid vessels during systole and diastole
Added forward flow
What happens to the vessel during systole?
What happens to the vessel during diastole?
- resulting in extended flow without driving pressure from heart
What does pulsatile flow also have?
What happens to pulsatile flow in the aorta during diastole?
Blood doesn’t flow back, because aortic valve closes
What happens to pulsatile flow in the distal circulation during diastole?
In some locations, when pressure decreases and vessel contracts
- there will be reversal of flow especially with no valves to prevent back flow
What happens to speed at the stenosis?
It goes up
- eg) garden hose
Why does speed go up at the stenosis?
To keep volumetric flow rate (Q) constant at all 3 regions
- before, at and after stenosis
Trying to keep Q constant all the time in all locations
- need to compensate to keep it as even as possible
What is the formula for the continuity rule?
Q = V(average) x A
Q = volumetric flow rate (mL/s)
V = average velocity (cm/s)
A = cross sectional area (cm^2)
What is volumetric flow rate for a short segment?
If area decreases by 2x, what happens to the speed?
It increases by 2
What happens to the volumetric flow rate if area decreases by 2?
It stays the same
- complies with the continuity rule
What percentage does the vessels resistance begin to increase?
What happens at 75%? (2)
1. Q starts going down
- eventually becoming 0 (occlusion)
2. V keeps going up
- compensates for decrease in A
- goes down near occlusion
What can velocity determine?
The severity of the disease
What is distance to stenosis?
What is the sound produced by stenosis?
What happens to the area if the radius goes down by 2x?
It goes down by 4
- pie r^2
What happens to the velocity if the radius goes down by 2x?
It goes up by 4
What do you use the formula Q=VxA?
In short segments
- usually stenosis
When do you use the formulas Q=deltaP pie d^4/128Ln?
In long strait tubes
What happens when speed goes up?
Pressure goes down
- indirectly proportional
Decrease in pressure in regions of high flow speed
- at stenosis
What happens to pressure before stenosis?
Pressure goes up to push blood through stenosis