Lecture 4 Flashcards
how does blood flow?
from high to low pressures
a difference in pressure gradients causes what?
blood flow
the greater the difference the more flow
what is cardiac output?
amount of blood entering the arteries per minute. Increased volume increases blood pressure.
normal: 5L/min
what is peripheral resistance
amount of blood in the arterial circulation. If the peripheral resistance increases, the amount of blood in the arteries increases.
how does the diameter of arterioles effect peripheral resistance
higher peripheral resistance in the constricted state.
There is a decrease in peripheral resistance in the dilated state.
viscosity of blood
increase viscosity increases resistancee
poiseuilles law
Q= volume flow p1-p2= pressure gradient r=radius to 4th power L=length of tube V=viscosity
What happens if you increase the Pressure Gradient and the Radius
remains the same?
The Greater the Pressure Gradient the Greater the Flow
what happens to the volume flow in a hemodynamically
significant stenosis?
Velocities increase at the site of the stenosis, X. The volume flow should remain the same because of the increased pressure gradient.
pulsatile flow
arterial flow
flow and velocities change during the cardaic cycle
laminar flow
Arterial flow travels in laminar fashion in the arteries. It travels in concentric layers with the fastest flow in the center stream
The slowest flow along the wall is the boundary layer.
what is this image of?
Disturbed flow (spectral broadening) profile due to plaque
what is this image of?
Increased flow velocities due to stenosis. Spectral broadening also is present.
total fluid energy equation
PE + KE + energy losses
potential energy
blood pressure
kinetic energy
blood flow
energy loss
heat
viscous losses
friction between the formed elements of the blood. Effected by the diameter of the lumen.
Inertial losses
due to acceleration and deceleration of the pulsatile flow and direction changes.
bernoullis equation
Q= volume flow V= velocity A= area of tube
what does bernoullis principle describe?
Describes the pressure drop that occurs in a stenosis.
The higher the velocity, the lower the pressure.
what is the energy gradient through a stenosis
decrease in potential energy
increase in kinetic energy
energy loss due to heat
As the diameter reduction of an arterial stenosis increases…
the pressure gradient increases.
50% to 70% stenosis
Volume flow remains the same as the velocities increase.
70 % or more stenosis
Increased velocities no longer compensate for the volume flow. This is a hemodynamically significant stenosis.
pre stenotic spectral
post stenotic spectral
distal to stenosis spectral
As flow exits a stenosis, the velocities decrease and bi-directional flow occurs due to boundary layer separation.
tardus parvus
spectral at the site of the stenosis
Increase in peak systolic velocity (psv), end diastolic velocity (edv)
the greater the stenosis what happens in end diastole
decreases
increase in resistance to flow depending upon grade of stenosis
what is the boundary layer
is the slowest blood flow along the wall of the artery
is separates from the wall of the artery
sudden decrease in diameter
what are the inertial loss due to stenosis
direction change as flow direction narrows and broadens
turbulence at the entrance and exit
what causes the increase to resistance to flow
- Stenosis
- Surface roughness
- Curvature and tortuosity of the vessel
- Noncircular vessel cross section
- Vortices, eddies, reversal of flow (turbulence)
what type of flow do you see in the carotid bulb?
flow reversal
how can you tell the difference between the ICA and ECA
the ICA has a larger proximal diameter after bifurcation
how is the flow around a curve in a vessel?
tuburlent
