CVT 100 #7 Physics PP Flow Behavior Flashcards
Laminar blood flow:
moving in concentric layersLaminar flow is orderly,undisturbed flow.
Two configurations of laminar flow:
- Parabolic profile 2. Plug or blunt profile
Spectral Doppler from internal carotid artery:
Systolic upstroke has very narrow range of velocities (plug) Diastolic component has wider range of velocities (parabolic)
Parabolic flow profile: Velocity highest in center…
Velocity highest in center,dropping off toward walls
Parabolic flow profile: Peak velocity is twice…
Peak velocity is twice the mean velocity
Parabolic flow profile: Velocity at walls is…
Velocity at walls is (theoretically) zero
Plug flow profile: Velocities are the same…
Velocities are the same almost all the way across the lumen (Wall drag still slows down the outer layers)
Parabolic flow profile:
All the time in steady flow Throughout cardiac cycle in small arteries (< 3 mm) During diastole in larger arteries
Plug flow profile:
Systole in larger arteries (> 3 mm) Also, entrances to branches, entrance to stenosis
Disorderly flow:Turbulence
Breakdown of laminar, orderly character of flow Many velocities, many directions Chaotic flow character
Turbulence in the heartcauses
a murmur
Turbulence in the vascular systemcauses
a bruit (broo-ee) (French word for “noise”)
A cardiac murmur during systole is…
Systolic cardiac murmurcan be normal. (“functional murmur”)
A cardiac murmur during diastole is…
Diastolic murmuris never normal.
Factors that increase the likelihood of turbulence:
the Reynolds number Dimensionless number predicting likely onset of turbulence
“Flow disturbance”suggests some degree of
interaction of the laminae (layers)in laminar flow
Turbulence is the extremeof flow disturbance:
many velocities, many directions.
Loss of laminar flow due to metal pin at top, creating “vortex streets”—… The degree of disturbance depends on several factors in the Reynolds equation, Coming soon.
the semi-orderly disturbance downstream.
Basilar artery joins the… then bifurcates into… There is little mixing of the flow from right and left vertebrals within the basilar artery.
Basilar artery joins the two vertebral arteries, then bifurcates into right and left posterior cerebral arteries. There is little mixing of the flow from right and left vertebrals within the basilar artery.
There is little mixing of the flow from____________ within the basilar artery.
right and left vertebrals
The Reynolds equation: V= p= d= n=
Re = Vpd ——- n V = velocity p = density d = diameter n = viscosity
If velocity,density, or diameteris increased,
the likelihood of turbulence is increased.
Bigger diameter—>
—>more room for un-laminar flow to get started(walls help to stabilize flow)
Higher density—>
—>more particles to bump together and disturb flow
Higher velocity—>
—>more chance for particles to bump together, layers to interact,and disturb flow
Flow in aorta can get somewhat turbulent in an
exercising person—bigger diameterand faster velocities(due to stronger LV contractions—remember?)
Viscosity is internal friction created by
molecular attraction,creating a tendency to resist motion.
If viscosity is increased,the likelihood of turbulenceis…
decreased. (Molasses vs. waterin the upper Kern River)
What happens to Reynolds number if viscosity is cut in half?
Re = Vpd = (2) (2) (2) —> (2) (2) (2) ——- ————– ————- n (2) (1) Inversely proportional: Re is doubled. (More likelihood of turbulence)
What happens to Reynolds number if velocity is doubled?
Re = Vpd = (2) (2) (2) —> (4) (2) (2) ——- ———— ————- n (2) (2) Directly proportional: Re is doubled. (More likelihood of turbulence)
Stenosis:
Reduction of area causes increased velocity within stenosis(in arteries, usually the result of plaque)
Proximal to stenosis:
Laminar flow, normal pressure
Within stenosis:
Increased velocity, lower pressure against walls
Distal to stenosis:
Turbulence and decreased velocity depending on severity of stenosis (along with decreased pressure and decreased flow distally if the stenosis is “critical”)
Also: Waveforms distally will manifest ____ _____ ______ due to stenosis, depending on the severity.
loss of energy
Note:Two separate phenomena The pressure drop WITHIN a stenosis is due to… The pressure drop DISTAL to a critical stenosis is due to…
Bernoulli effect (high velocity over the surface);it is local. the loss of energy created by the stenosis; it shows up everywhere beyond the stenosis
Bernoulli effect, it’s time to meet Daniel Bernoulli (1700-1782)Discovered that …
Discovered that pressure in a flowing fluid is lowest where the speed is greatest. (Blow over top of paper) This keeps airplanes up in the air.
Air has farther to travel over top of wing, so has to go faster. Faster flow over top—>
—> lower pressure Higher pressure pushes up
The boomerang:
the Bernoulli effect makes it fly,and gyroscopic precession makes it go in a circle (return)
The frightening Bernoulli equation
E = 1/2 d v2 + dgh + P — V The important thing: v and P are inversely proportional, since energy must remain the same.(dgh is gravitational potential energy)
Real-life application:Modified Bernoulli equation
P1-P2 = 4 (V2) Finds pressure gradient across a cardiac valve in mmHgbased on velocity in m/sec
If velocity = 200 cm/sec= 2 m/sec
∆P = 4 (22) = 4 ( 4 ) = 16 mmHg pressure gradient across the valve
If velocity is 3 m/sec
∆P = 4 (32) = 36 mmHg gradientacross the valve (Again, stenosis causes loss of energy distally depending on severity of narrowing.)
Velocity in an aortic valve is5.2 m/sec What is the pressure gradientacross the valve?
solve
Another real-life implication: Greatly increased velocities within an arterial stenosis can help to disrupt the surface of the plaque and promote embolic activity.
(“Bernoulli effect sucking on the plaque.”)
