M2&3: Arterial Hemody. & Doppler Flashcards
Movement of blood from 1 point to another requires what 2 conditions
1 pathway
2 pressure/energy gradient
total energy contained in moving fluid includes what 3 things
pressure or potential energy
kinetic energy
gravitational energy (hydrostatic pressure)
what type of energy is thr primary energy present in blood flow
pressure or potential energy
what is the primary pressure source in the body?
this same organ creates an energy gradient for blood to flow
heart
what 2 things dictate the volume of blood leaving the heart
blood pressure
peripheral resistance
when the arterial walls expand due to an increased blood volume, this creates what type of energy w/in the vessel
PE
what happens to blood volume, diameter and pressure in arteries during diastole
all decrease
what does bernoullis principle explain
explains the maintenance of energy during the movement of fluid (total energy = Pe + Ke)
describe bernoulli’s principle as it applies to a stenosis
a decrease in vessel diameter will result in a pressure drop and an increase in velocity through that area to maintain volume flow rate…
how does an decrease in pressure effect velocity
increases it
as the angle of insonation increases, what happens to the doppler shift
it gets smaller
why is the angle of insonation so important for doppler
it effects the velocity reading so will make calculations incorrect if its inaccurate (greater than 60)… and the angle increases so does the % error for velocity
what is the nyquist limit
what happens if its exceeded
the limit reached when the RBC velocities are faster than the machines ability to sample
it is equal to 1/2 the PRF… if half the PRF is EXCEEDED than aliasing will occur b/c RBCs arent being sampled fast enough
what are the 5 ways to correct for aliasing
which are acceptable to use?
- move the baseline
- increase the PRF/scale
- increase the doppler angle
- lower the operating frequency
- change to CW
1 and 2
where is the CW doppler SV found? what is it called
at the intersection of the transmitted and received beam… called the zone of sensitivity
with CW, how do we compensate for the fact that angle correct is not possible
you must get parallel to flow
what does the doppler spectral tracing represent
the range of doppler shift frequencies produced from each RBC that passed through the SV
what are the characteristics of high pulsatility/resitance waveforms
- sharp up stroke
- reversal or absent diastolic flow
more ‘pulstile’
in which vessels do we commonly see high resistance waveforms?
arteries of the extremities…. body parts that are now vital to life
e.g. CFA
what are the characteristics of low pulsatility/resistance waveforms
- broad systolic peak
- forward flow through diastole… this diastolic part tells us that the vessel is supplying a vital organ/area
eg. ICA, renal arteries, etc
what are the characteristics of moderate pulsatility/resistance waveforms
- tall, narrow, sharp systolic peaks
- forward flow through diastole
in which vessels do we commonly see moderate resistance waveforms?
vessels that feed both high and low resistance vascular beds
e.g. CCA (splits into ICA and ECA)
what is the formula for pulsatility index
PI = PSV - Furthest point from PSV / Mean V
what is the formula for resistive index
RI = PSV - EDV / PSV
what is the systolic/diastolic ratio formula
PSV / EDV
what is spectral broadening
what does it indicate
the vertical thickening of the spectral tracing or envelope
indicates that there is a greater range of velocities w/in the SV
what can cause spectral broadening
disturbances in flow: bifurcations, anastomoses, curves in vessels
pathology in arteries = plaque
what is autocorrelation
produces the colour doppler and represents the mean velocity
what vessels control vascular resistance of blood flow
arterioles
if the size of a vessel is constant, will a smaller or large vessel diameter produce slow flow
smaller = slower
IF SIZE IS CONSTANT
but if theres a stenosis, then thinner means faster velocity
describe blunt/plug flow, where is it seen?
uniform flow… flow pattern that has almost all RBCs travelling at the same velocity
-seen during systole in large vessels like the AO and at some arterial branch origins
describe laminar parabolic flow, where is it seen?
flow pattern where the RBCs move in concentric layers (or laminae) w/ all different velocities, the fastest velocity are at the centre…
‘NORMAL’ flow, called parabolic due to its velocity profile
-most common flow pattern in normal arteries
describe jet flow, where is it seen?
flow pattern seen at areas of significant reduction in vessel diameter… e.g. stenosis
describe non-laminar/disturbed flow, where is it seen?
normal flow pattern that occurs at bifurcations, or sudden widening of vessels…. mixed blood flow pattern
- may see spectral broadening and/or reversal along the walls
- norm flow reestablished ~3 cm after disruption
-eg carotid bulb
describe turbulent flow, where is it seen?
- flow velocities and direction vary greatly., fluid is exiting a tight spot and entering a larger space
- fluid moves in eddies and whirls, more disordered than disturbed flow
flow pattern that is seen just past a stenosis, or can develop in larger vessels w/ high flow volume that dont have a stenosis
what type of spectral waveform would you get w/ turbulent flow
is turbulent flow normal?
- spectral broadening since there are many velocities, and feathering
- not normal except near the heart
what does a Reynolds number (RN) predict
can predict onset of turbulence in a vessel
having an RN greater than, or equal to, what value indicates turbulence?
2000
describe the changes of pressure experienced at a stenosis
at a stenosis theres a pressure drop in order to accommodate the acceleration of blood through the stenosis… after the stenosis blood decelerates
describe the changes of PE experienced at a stenosis
PE is converted to KE when it enters the stenosis and then is converted pack to PE after the stenosis
what is tradus parvus
why does it occur
the drop in acceleration time and peak systolic velocity of arterial flow after a stenosis…..
…. the stenosis detracts from the pressure gradient that was created by the heart
does tardus parvus indicate proximal or distal stenosis
Proximal (to where your scanning)
what type of spectral trace will you get if you’re scanning proximal to a stenosis
you’ll have increased pusatility, a smaller peak velocity and you’ll lose diastole because blood cant get through the stenosis as easily
if your SV is too large, the spectral waveform that you get may mimic the waveform of what type of pathology
post stenotic turbulence
what is the name for the area where the lamina reach zero velocity
when would this be see
site of boundary layer separation known as the transition zone
carotid bulb and distal to a stenosis
what flow pattern is associated w/ the site of boundary layer separation (known as the transition zone)
non-laminar/disturbed
how will the ‘zero velocity’ area appear w/ colour doppler
black/no flow
will vessels that dive at a steeper angle show a greater flow disturbance
yes
in norm vessels, how does the pressure change at a site of bifurcation
small drop
what type of flow pattern dose curved vessels produce
helical flow
describe how the velocity of blood changes when it passes a curve
fluid on the outside flows faster and fluid on the inside may appear reversed
what does volume flow (Q) refer to
amount of fluid traveling past a point in a given time
to preserve flow in the body, if theres an increase in resistance, what happens to the pressure gradient
it must increase
modified poiseuille
Q = (P1 - P2)/Resistance
what does poiseuilles law explain
defines the relationship b/w pressure, volume flow rate and resistance of fluid flowing through a cylinder tube
complete poiseuille equation
most dominant factor
Q = pie (P1-P2) r^4 / 8Ln
radius is the most dominant factor, as radius decreases, resistance increases to the 4th power
define viscosity (n)
how is it measured
resistance to flow of a fluid, or how thick a substance is… generates frictional forces
measured in poise
most important factor effecting viscosity
[ ] of RBCs (hematocrit) and plasma protein
does a longer tube provide more or less resistance
more, due to increased friction
relationship b/w resistance and length
direct
relationship b/w resistance and radius
inverse
why is there a discrepancy b/w poiseuilles law and the continuity rule
P: based on a long single tube
C: only concerned w/ a short part of the vessel that has a stenosis
what is the continuity rule?
what does it explain
it says: in the presence of a stenosis, the volume of flow must remain constant proximal to, at, and distal to the stenosis
it explains why we get a ‘jet’ when we have a stenosis… the velocity of blood must increase in a stenosis in order to keep the volume flow constant
if the diameter of a stenosis is 1/2 of the vessel, what happens to the velocity of blood flow in this area
the velocity will double to maintain volume flow rate
why is there turbulent flow post stenosis
b/c of the increased velocity through the stenosis and sudden increase in size of the vessel radius right after
Energy loss due to friction and viscosity will depend on what 3 things
length of stenosis
tandem stenosis (multiple)
surface contour of plaque
when will hemodynamic changes be notes distal to a stenosis
only if theres a significant reduction in cross sectional area… where as hemodynamic changes will always be seen at the site of stenosis regardless
define doppler effect
a perceived change in pitch due motion of the source of sound or the observer….
difference b/w the transmitted freq and received freq
when a source of sound is moving towards you, will the pitch be higher or lower
higher
when a source of sound is moving away from you, will the pitch be higher or lower
lower
What will the waveform proximal to a stenosis look
Increased pulsatility (high resistance) Loss of diastolic flow Decreased PSV velocity Reversal if stenosis is really bad thumping in systole in stenosis is severe
What will the waveform in a stenotic jet look like
Increased velocities, up to 80% diameter reduction, then more than that, velocity will decrease
EDV very increased w/ severe stenosis
If velocity doubles in a stenosis what does this mean for the diameter of the vessel
It’s a 50% reduction of diameter of the vessel
What will the waveform distal to a stenosis look
Immediately past the stenosis = turbulent flow w/ reversal, flow separation, vortices, eddy currents (eg post stenotic turbulence)
what colour artifact may you see at a stenosis
visible bruit (caused by soft tissue vibrations due to a sever stenosis)
further distal to a significant stenosis, what waveform will you see
tardus parvus (slow to peak/slower acceleration time and lower velocities) because the flow after the stenosis is not as effected by the hearts pressure gradient
what are tandem lesions
multiple stenosis in the same vessel
how do tandem lesions effect energy and blood volume
greater loss of energy and volume… first stenosis will have the highest energy and velocities, then drops off for the second stenosis
review drawing at end of hemodynamics notes
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doppler shift is defined as…
different b/w transmitted and received frequencies
the method used to measure the doppler shift is based on which principle
wave interference
what is beat frequency
the sum of the transmited and received frequencies which will vary slight from one another
are there many different frequencies contained in a beat frequency
yes
doppler formula
doppler shift = 2 (Fo x V x cos theda) / C
know the relationships
what is high PRF mode
what can it cause
when the machine sends out another pulse before the first one has returned… can cause range ambiguity
what is range ambiguity
when the machine doesnt know what depth the echoes are being returned from due to high PRF, and it will show misrepresented echoes on the tracing.
through what process is spectral doppler created
fast fourier transformation
is spectral doppler quantitative
yes
how does fast fourier transformation work
takes the complex beat frequency and separates it out into its individual wave components… each wave is the result of a refection of a moving blood cell in the SV
is there range resolution w/ CW
no
velocities in CW comes from which area / where is the SV area for CW
zone of sensitivity
what happens to the ring time of the doppler elements when we increase the size of the PW SV
how does this effect SPL
increases ring time and increases SPL…. we need a longer SPL for doppler
RT would decrease if we made the SV smaller
how does SV size effect spectral broadening
larger = more broadening small = less broadening
how does power doppler detect flow
uses the amplitude of the returning doppler signals to detect flow (instead of doppler shift) which makes it very sensitive
is power doppler independent of angle
yes
