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Vascular 2 > M2&3: Arterial Hemody. & Doppler > Flashcards

M2&3: Arterial Hemody. & Doppler Flashcards

1
Q

Movement of blood from 1 point to another requires what 2 conditions

A

1 pathway

2 pressure/energy gradient

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2
Q

total energy contained in moving fluid includes what 3 things

A

pressure or potential energy
kinetic energy
gravitational energy (hydrostatic pressure)

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3
Q

what type of energy is thr primary energy present in blood flow

A

pressure or potential energy

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4
Q

what is the primary pressure source in the body?

this same organ creates an energy gradient for blood to flow

A

heart

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5
Q

what 2 things dictate the volume of blood leaving the heart

A

blood pressure

peripheral resistance

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6
Q

when the arterial walls expand due to an increased blood volume, this creates what type of energy w/in the vessel

A

PE

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7
Q

what happens to blood volume, diameter and pressure in arteries during diastole

A

all decrease

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8
Q

what does bernoullis principle explain

A

explains the maintenance of energy during the movement of fluid (total energy = Pe + Ke)

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9
Q

describe bernoulli’s principle as it applies to a stenosis

A

a decrease in vessel diameter will result in a pressure drop and an increase in velocity through that area to maintain volume flow rate…

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10
Q

how does an decrease in pressure effect velocity

A

increases it

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11
Q

as the angle of insonation increases, what happens to the doppler shift

A

it gets smaller

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12
Q

why is the angle of insonation so important for doppler

A

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

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13
Q

what is the nyquist limit

what happens if its exceeded

A

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

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14
Q

what are the 5 ways to correct for aliasing

which are acceptable to use?

A
  1. move the baseline
  2. increase the PRF/scale
  3. increase the doppler angle
  4. lower the operating frequency
  5. change to CW

1 and 2

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15
Q

where is the CW doppler SV found? what is it called

A

at the intersection of the transmitted and received beam… called the zone of sensitivity

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16
Q

with CW, how do we compensate for the fact that angle correct is not possible

A

you must get parallel to flow

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17
Q

what does the doppler spectral tracing represent

A

the range of doppler shift frequencies produced from each RBC that passed through the SV

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18
Q

what are the characteristics of high pulsatility/resitance waveforms

A
  • sharp up stroke
  • reversal or absent diastolic flow

more ‘pulstile’

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19
Q

in which vessels do we commonly see high resistance waveforms?

A

arteries of the extremities…. body parts that are now vital to life

e.g. CFA

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20
Q

what are the characteristics of low pulsatility/resistance waveforms

A
  • 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

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21
Q

what are the characteristics of moderate pulsatility/resistance waveforms

A
  • tall, narrow, sharp systolic peaks

- forward flow through diastole

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22
Q

in which vessels do we commonly see moderate resistance waveforms?

A

vessels that feed both high and low resistance vascular beds

e.g. CCA (splits into ICA and ECA)

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23
Q

what is the formula for pulsatility index

A

PI = PSV - Furthest point from PSV / Mean V

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24
Q

what is the formula for resistive index

A

RI = PSV - EDV / PSV

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25
Q

what is the systolic/diastolic ratio formula

A

PSV / EDV

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26
Q

what is spectral broadening

what does it indicate

A

the vertical thickening of the spectral tracing or envelope

indicates that there is a greater range of velocities w/in the SV

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27
Q

what can cause spectral broadening

A

disturbances in flow: bifurcations, anastomoses, curves in vessels

pathology in arteries = plaque

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28
Q

what is autocorrelation

A

produces the colour doppler and represents the mean velocity

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29
Q

what vessels control vascular resistance of blood flow

A

arterioles

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30
Q

if the size of a vessel is constant, will a smaller or large vessel diameter produce slow flow

A

smaller = slower

IF SIZE IS CONSTANT

but if theres a stenosis, then thinner means faster velocity

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31
Q

describe blunt/plug flow, where is it seen?

A

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

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32
Q

describe laminar parabolic flow, where is it seen?

A

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

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33
Q

describe jet flow, where is it seen?

A

flow pattern seen at areas of significant reduction in vessel diameter… e.g. stenosis

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34
Q

describe non-laminar/disturbed flow, where is it seen?

A

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

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35
Q

describe turbulent flow, where is it seen?

A
  • 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

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36
Q

what type of spectral waveform would you get w/ turbulent flow
is turbulent flow normal?

A
  1. spectral broadening since there are many velocities, and feathering
  2. not normal except near the heart
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37
Q

what does a Reynolds number (RN) predict

A

can predict onset of turbulence in a vessel

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38
Q

having an RN greater than, or equal to, what value indicates turbulence?

A

2000

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39
Q

describe the changes of pressure experienced at a stenosis

A

at a stenosis theres a pressure drop in order to accommodate the acceleration of blood through the stenosis… after the stenosis blood decelerates

40
Q

describe the changes of PE experienced at a stenosis

A

PE is converted to KE when it enters the stenosis and then is converted pack to PE after the stenosis

41
Q

what is tradus parvus

why does it occur

A

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

42
Q

does tardus parvus indicate proximal or distal stenosis

A

Proximal (to where your scanning)

43
Q

what type of spectral trace will you get if you’re scanning proximal to a stenosis

A

you’ll have increased pusatility, a smaller peak velocity and you’ll lose diastole because blood cant get through the stenosis as easily

44
Q

if your SV is too large, the spectral waveform that you get may mimic the waveform of what type of pathology

A

post stenotic turbulence

45
Q

what is the name for the area where the lamina reach zero velocity

when would this be see

A

site of boundary layer separation known as the transition zone

carotid bulb and distal to a stenosis

46
Q

what flow pattern is associated w/ the site of boundary layer separation (known as the transition zone)

A

non-laminar/disturbed

47
Q

how will the ‘zero velocity’ area appear w/ colour doppler

A

black/no flow

48
Q

will vessels that dive at a steeper angle show a greater flow disturbance

A

yes

49
Q

in norm vessels, how does the pressure change at a site of bifurcation

A

small drop

50
Q

what type of flow pattern dose curved vessels produce

A

helical flow

51
Q

describe how the velocity of blood changes when it passes a curve

A

fluid on the outside flows faster and fluid on the inside may appear reversed

52
Q

what does volume flow (Q) refer to

A

amount of fluid traveling past a point in a given time

53
Q

to preserve flow in the body, if theres an increase in resistance, what happens to the pressure gradient

A

it must increase

54
Q

modified poiseuille

A

Q = (P1 - P2)/Resistance

55
Q

what does poiseuilles law explain

A

defines the relationship b/w pressure, volume flow rate and resistance of fluid flowing through a cylinder tube

56
Q

complete poiseuille equation

most dominant factor

A

Q = pie (P1-P2) r^4 / 8Ln

radius is the most dominant factor, as radius decreases, resistance increases to the 4th power

57
Q

define viscosity (n)

how is it measured

A

resistance to flow of a fluid, or how thick a substance is… generates frictional forces

measured in poise

58
Q

most important factor effecting viscosity

A

[ ] of RBCs (hematocrit) and plasma protein

59
Q

does a longer tube provide more or less resistance

A

more, due to increased friction

60
Q

relationship b/w resistance and length

A

direct

61
Q

relationship b/w resistance and radius

A

inverse

62
Q

why is there a discrepancy b/w poiseuilles law and the continuity rule

A

P: based on a long single tube
C: only concerned w/ a short part of the vessel that has a stenosis

63
Q

what is the continuity rule?

what does it explain

A

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

64
Q

if the diameter of a stenosis is 1/2 of the vessel, what happens to the velocity of blood flow in this area

A

the velocity will double to maintain volume flow rate

65
Q

why is there turbulent flow post stenosis

A

b/c of the increased velocity through the stenosis and sudden increase in size of the vessel radius right after

66
Q

Energy loss due to friction and viscosity will depend on what 3 things

A

length of stenosis
tandem stenosis (multiple)
surface contour of plaque

67
Q

when will hemodynamic changes be notes distal to a stenosis

A

only if theres a significant reduction in cross sectional area… where as hemodynamic changes will always be seen at the site of stenosis regardless

68
Q

define doppler effect

A

a perceived change in pitch due motion of the source of sound or the observer….
difference b/w the transmitted freq and received freq

69
Q

when a source of sound is moving towards you, will the pitch be higher or lower

A

higher

70
Q

when a source of sound is moving away from you, will the pitch be higher or lower

A

lower

71
Q

What will the waveform proximal to a stenosis look

A 
Increased pulsatility (high resistance)
Loss of diastolic flow
Decreased PSV velocity
Reversal if stenosis is really bad
thumping in systole in stenosis is severe
72
Q

What will the waveform in a stenotic jet look like

A

Increased velocities, up to 80% diameter reduction, then more than that, velocity will decrease
EDV very increased w/ severe stenosis

73
Q

If velocity doubles in a stenosis what does this mean for the diameter of the vessel

A

It’s a 50% reduction of diameter of the vessel

74
Q

What will the waveform distal to a stenosis look

A

Immediately past the stenosis = turbulent flow w/ reversal, flow separation, vortices, eddy currents (eg post stenotic turbulence)

75
Q

what colour artifact may you see at a stenosis

A

visible bruit (caused by soft tissue vibrations due to a sever stenosis)

76
Q

further distal to a significant stenosis, what waveform will you see

A

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

77
Q

what are tandem lesions

A

multiple stenosis in the same vessel

78
Q

how do tandem lesions effect energy and blood volume

A

greater loss of energy and volume… first stenosis will have the highest energy and velocities, then drops off for the second stenosis

79
Q

review drawing at end of hemodynamics notes

A

/

80
Q

doppler shift is defined as…

A

different b/w transmitted and received frequencies

81
Q

the method used to measure the doppler shift is based on which principle

A

wave interference

82
Q

what is beat frequency

A

the sum of the transmited and received frequencies which will vary slight from one another

83
Q

are there many different frequencies contained in a beat frequency

A

yes

84
Q

doppler formula

A

doppler shift = 2 (Fo x V x cos theda) / C

know the relationships

85
Q

what is high PRF mode

what can it cause

A

when the machine sends out another pulse before the first one has returned… can cause range ambiguity

86
Q

what is range ambiguity

A

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.

87
Q

through what process is spectral doppler created

A

fast fourier transformation

88
Q

is spectral doppler quantitative

A

yes

89
Q

how does fast fourier transformation work

A

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

90
Q

is there range resolution w/ CW

A

no

91
Q

velocities in CW comes from which area / where is the SV area for CW

A

zone of sensitivity

92
Q

what happens to the ring time of the doppler elements when we increase the size of the PW SV

how does this effect SPL

A

increases ring time and increases SPL…. we need a longer SPL for doppler

RT would decrease if we made the SV smaller

93
Q

how does SV size effect spectral broadening

A 
larger = more broadening
small = less broadening
94
Q

how does power doppler detect flow

A

uses the amplitude of the returning doppler signals to detect flow (instead of doppler shift) which makes it very sensitive

95
Q

is power doppler independent of angle

A

yes

Vascular 2 (6 decks)

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