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Vascular 1 > C3&4 Hemodynamics and Doppler > Flashcards

C3&4 Hemodynamics and Doppler Flashcards

1
Q

what are the 2 primary functions of the venous sys?

A

Return blood from capillaries to the heart

Act as a reservoir to maintain homeostasis

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2
Q

what % of blood is in veins?

A

80%

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3
Q

what is needed for blood to flow?

A

pressure or energy gradient (flow from high press to low)

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4
Q

when does blood lose press after it leaves the heart?

A

as it flows through high resistance vessels

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5
Q

what is the press at the level of the venules and capillaries?

A

15mmHg

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6
Q

whats hydrostatic press?

and how is it measured?

A

the weight of a column of blood or gravitational pressure, measured from the heart to a point of press

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7
Q

whats the primary factor in determining intravascular pressure? and how does this fact effect venous return?

A

hydrostatic press

impedes venous return

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8
Q

whats the hydrostatic pressure in a supine and standing position?

A

supine: 15mmHg because all body parts on the same level as the RA
standing: 110mmHg at ankles because gravity resists blood flow from the legs to the heart
(veins in leg dilate and blood pools)

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9
Q

whats the press at the RA?

A

0mmHg

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10
Q

which part of the body is pressure highest?

A

lower part

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11
Q

if you raise your arms above your head, what happens to hydrostatic press? and what type of value will it have

A

it lowers and becomes negative (because hydrostatic pressure is relative to the RA)

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12
Q

what causes hypotension and what does hypotension cause?

A

standing in one position for too long

you will faint

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13
Q

whats the hydrostatic press when your walking?

A

25mmHg

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14
Q

what are the mechanisms for venous return?

A 
cardiac function
respiration
muscle contraction
press gradient
valves
compliance
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15
Q

what type of pressure is responsible for the expand/contract on veins?

A

the intramural/intraluminal and interstitial pressure

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16
Q

what does compliance permit?

A

large increase in venous flow without significant increase in venous pressure

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17
Q

how does higher volumes and pressures effect compliance?

A

they decrease it

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18
Q

which have more compliance, veins or arteries?

A

veins

arteries have greater elasticity

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19
Q

whats transmural press and does it effect the shaped of the vein?

A

difference between intraluminal (inner) and interstitial (outer) pressures

yes, determines the cross sectional shape of the vein

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20
Q

whats intraluminal pressure (ILP)?

A

press within the vein (will increase will higher blood volume)
higher ILP = rounder vein

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21
Q

how are intraluminal and transmural press related?

A

directly

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22
Q

whats interstitial pressure (ISP)?

A

press outside of the vein

higher ISP = collapsed vein

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23
Q

describe the effects of high vs los transmural press

A

high: vein wall will become circular and distend
low: vein wall collapses and is elliptical shaped

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24
Q

how does valsalva maneuver effect the venous system? and flow?

A

it increases the press in both the upper and lower extremity veins

flow should stop or diminish in upper and lower body (flat waveform)
NO REVERSAL

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25
Q

what creates dynamic pressure?

A

contraction of heart

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26
Q

4 parts of venous wave

A
  1. atrial systole
  2. systolic wave
  3. atrial diastole
  4. diastolic wave
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27
Q

when are the two periods of increased venous flow during the cardiac cycle?

A 
ventricular systole
When AV (MV and TV) valves open
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28
Q

describe what happens to press and volume in the atria during ventricular systole

A

volume increases
press decreases

this lowers venous pressure because theres increased flow into the RA

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29
Q

does respiration have a greater effect on the upper or lower extremities?

A

lower

because upper is closer to heart (its more pulsatile)

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30
Q

does respiration have the same effect on venous flow when standing?

A

no, it has less

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31
Q

does expiration increase of decrease venous flow?

A

expiration increases venous flow

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32
Q

how does muscle contraction effect venous press?

A

it decreases it

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33
Q

where does flow most often occur when the muscles are relaxed?

A

in perforators from the superficial to deep veins

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34
Q

whats the venous heart?

A

calf muscle

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35
Q

which calf muscle are the most efficient of the pumps?

A

gastroc and soleus muscles

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36
Q

how much venous blood is ejected during 1 contraction?

A

40-60% of the veins volume (generates 200mmHg)

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37
Q

what is ambulatory venous hypertension and what causes it?

what does it cause?

A

abnormally high venous press when standing, caused by dysfunctional valves

Cause PRIMARY varicose veins and edema

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38
Q

does muscles contraction help blood return to the heart with ambulatory venous hypertension?

A

no, it expels blood in all different directions

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39
Q

which vessel is a common site for an UE valve?

A

jugular vein

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40
Q

where is the venous valve sinus?
what is its size compared to the vein?
what pathology is comply found here?

A

the are between the valve leaflet and the intimal wall

wider than the vein

thrombosis due to stagnent flow

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41
Q

are valves more commonly found in superficial or deep veins?

A

superficial

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42
Q

which vessel has the greatest # of valves

A

GSV (then LSV and calf veins)… # lower as you move up the leg

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43
Q

whats the Doppler effect?

A

-perceived change in frequency due to motion of the source or the observer
(motion of the source is the motion of the RBCs)
-the difference between transmitted ad received frequency

44
Q

how does the echo frequency change if the RBCs are moving towards the transducer?

A

echo frequency is larger (antegrade flow, + flow)

45
Q

how does the echo frequency change if the RBCs are moving away from the transducer?

A

echo frequency is smaller (retrograde flow, - flow)

46
Q

what are the 3 methods we use to detect and analyze the doppler shifts?

A

color flow
spectral flow
audible sound

47
Q

whats the doppler shift equation?

A

Doppler shift freq = 2(operating freq) x velocity x cos0/c
OR
Doppler shift freq = returned freq - operating freq

48
Q

whats the most influential factor that effects the doppler shift freq?

A

angle of insonation

49
Q

whats the ideal angle of intonation and what do we use?

A

ideal: 0
used: 60, its reproducible and has a low margin of error

50
Q

why is an angle of 90 bad?

A

cos 90 is zero so no doppler shift can be detected

51
Q

what happens when we increase the angle?

A

larger margin of error and changes the velocity reading significantly

52
Q

is angle important when assessing venous flow? do we use velocities?

A

no and no

53
Q

differences between CW and PW?

A

CW:

  • 2 elements, one rings and one listens constantly
  • no image
  • no specific sampling depth
  • no aliasing

PW:

  • 1 element, fires and then listens
  • image
  • can specify depth and region
  • aliasing occurs
54
Q

what factor limits out ability to sample at higher velocities?

A

PRF

55
Q

what causes aliasing?

A

when PRF is too low…. we aren’t sampling fast enough

56
Q

whats the nyquist limit?

A

1/2 of the PRF, if exceeded, aliasing will occur because red blood cell velocities are travelling faster than our ability to sample

57
Q

what is the fast Fourier transformation

A

separates out the individual frequencies from the doppler shift frequencies and then displays them as a spectral trace

58
Q

in what 3 axises are the spectral trace displayed?

A

x: time
y: velocity
z: power/brightness

59
Q

what does the z axis depend on?

A

the number of RBCs passing through the sample area

60
Q

what the function of quadrature detection?

A

it processes the signal as a + or – value depending on the direction of flow relative to the transducer

61
Q

what are the 6 components of a waveform?

A
  1. peak systole
  2. diacritic notch - early diastole flow reversal signifies closing of AO valve
  3. end diastole - lowest point
  4. envelope - white line that shows the various frequencies passing through the sample, brightness determined by # of RBCs
  5. window - clear area below envelope
  6. spectral broadening - thickness of white line
62
Q

definition of pulsatility (for arteries)

is pulsatility qualitative or quantitative?

A

relationship of peak to minimum velocities over the mean velocity of the cycle

can be both

63
Q

definition of resistance (for arteries)

A

relationship of peak systolic velocity to end diastolic velocity

64
Q

describe high and low resistance waveforms

A

low: will always have forward flow through diastole
high: has reversal of flow during diastole

65
Q

what structures have low resistance flow?

A

organs we cant live without

brain, liver, kidneys

66
Q

how are pulsatility and resistance related?

A

directly

67
Q

describe laminar parabolic flow

what type of spectral waveform does it produce?

A

blood moves in concentric layers with the fastest velocity in the centre and the slowest in the periphery
…. profiles include parabolic and plug/blunt

very thin envelope

68
Q

whats the avg velocity of laminar parabolic flow?

A

1/2 the maximum velocity

69
Q

what factors effect laminar flow?

A

velocity
diameter of vessel
curves, branches

70
Q

describe disturbed pattern flow

what causes it and is it considered normal?

A

forward flow with a variety of velocities and directions
caused by friction and E loss

considered normal

71
Q

describe turbulent flow

what causes it and is it considered normal?

A

no linear flow with many different velocities and directions

caused by a stenosis
abnormal except near the heart

72
Q

if spectral gains are too high what can occur?

A

false spectral broadening, background noise or mirror image

73
Q

with antegrade flow, if the baseline is too high, what can this cause?

A

aliasing

74
Q

whats the purpose of a wall filter?

A

eliminates low level echos

75
Q

what are the 2 types of color?

A

colour doppler and power doppler

76
Q

what does power doppler measure and what does it depend on?

what are its advantages and disadvantages?

A
  • measures the strength of the signal rather than doppler shift
  • based of # of RBCs
Pros:
no aliasing
more sensitive
not angle dependant
less blooming

Cons:
slow frame rate
cant determine direction

77
Q

what is power doppler commonly used to asses?

A

small vessels
tissue flow
slow flow

78
Q

how do stationary reflectors and moving reflectors appear with colour doppler?

A

stationary: grey scale
moving: colour

79
Q

what does colour doppler represent?

A

mean frequency shift

…. also, movement of RBCs based on direction and velocity

80
Q

whats autocorrelation?

A

process that uses 6-20 pulses per scan line to give information about received echos

81
Q

how does the lightness of the colour relate to frequency?

A

lighter: higher freq and vice versa

82
Q

what info does colour doppler provide?

A 
provides info about:
direction
Mean frequency
power or amplitude
variance
83
Q

is colour dopp qualitative or quantitative?

A

qualitative

84
Q

how does colour effect PRF and frame rate?

A

lowers PRF and frame rate which degrades the 2D image

85
Q

does height of the colour box effect frame rate?

A

no, only width (narrower= higher frame rate)

86
Q

what are the 3 types of maps?

A

shifting hue: different colours represent different frequencies (most common)

changing shade (saturation): the same colour saturated with white… more white saturation = higher frequency

variance maps: ability to tag certain frequencies

87
Q

how are speed of flow and PRF related?

A

directly

faster flow= higher PRF

88
Q

what occurs if PRF is too high?

A

range ambiguity

flow will not be detected and vessel will fill poorly

89
Q

where is the baseline found for colour doppler

A

in the middle of the colour map, can be changed to accommodate more red or blue

90
Q

whats another term for power doppler?

A

angio

91
Q

list the common colour artifacts and describe them

A

mirror image artifact: when a false duplication of a structure occurs

blooming/bleeding

colour flash: occurs when adjacent motion causes colour to flash outside of the vessel

aliasing: PRF is too low

visible bruit: soft tissue vibration near an area of high flow
(indirect sign of severe blockage)

92
Q

what would happen to the received frequency if the transmitted frequency was halved?

A

received frequency would also be halved…. because the received frequency is directly proportional to the transmitted frequency

93
Q

what process generates the Color Doppler image?

A

autocorrelation

94
Q

if we want a high frame rate when scanning with colour doppler, should your scan line density be high or low?

A

LOW

95
Q

what type of flow (low, med or high resistance) will have a waveform thats removed from the baseline?

A

low resistance

96
Q

Why does colour Doppler degrade the 2D image?

A

Because it lowers the PRF

97
Q

In what vessels do mirror image artifacts commonly occur?

A

Subclavian artery, due to the lungs

98
Q

What is threshold with reference to colour gains?

A

The gain level just before blooming occurs

99
Q

How does depth effect our ability to detect flow?

A

It impedes it

100
Q

When using colour Doppler, which area is the area that contains the scan lines?

A

The colour box

101
Q

Valves in perforating veins direct flow in which direction?

A

Superficial to deep veins

102
Q

At rest with no muscle activity, what is the main function of veins?

A

Act as venous reservoirs

103
Q

Why might some reversal happen at the venae cava/atrial junction?

A

Because there’s no valves between the IVC/SVC and the R atria

104
Q

What is capacitance?

A

The veins ability to adapt to changes in blood volume

105
Q

When you increase or decrease the colour scale, what are you actually changing?

A

PRF

106
Q

What’s the function of colour priority?

A

Let’s you choose if you want to give priority to colour or grey scale

107
Q

As you increase the angle of insonation how does it effect the Doppler shift frequency

A

Makes it smaller

Vascular 1 (5 decks)

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