Lesson 20 (Part 2) Flashcards
Where is pulsatile flow observed?
In arteries
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)
- Added forward flow
2. Reversal of flow
Compliance
Expansion and contraction of non-rigid vessels during systole and diastole
Widkessel effect
Added forward flow
What happens to the vessel during systole?
It expands
What happens to the vessel during diastole?
It contracts
- resulting in extended flow without driving pressure from heart
What does pulsatile flow also have?
Flow reversal
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
Continuity rule
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?
Constant
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?
75%
What happens at 75%? (2)
- Q starts going down
- eventually becoming 0 (occlusion) - 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?
Turbulence
What is the sound produced by stenosis?
Brute
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
Bernoulli effect
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
What happens to pressure at stenosis?
Pressure goes down to maintain energy
- pressure energy = flow energy
What happens to pressure after stenosis?
Pressure energy is the same as flow energy
Where is pressure the slowest?
At the stenosis
Where is flow the slowest?
Before and after stenosis
Where is volumetric flow rate the lowest?
It will be the same throughout
