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DMST 493 Vasc 2 > Arterial Hemodynamics > Flashcards

Arterial Hemodynamics Flashcards

1
Q

What is arterial hemodynamics?

A

Fluid dynamics that govern blood flow

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2
Q

What are two important aspects of arterial hemodynamics?

A
  1. Energy
  2. Pressure
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3
Q

In terms of hemodynamics what is the importance of pressure?

A

Pressure is the amount of force put on an artery at any point in time and measured in mmHg.

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4
Q

For blood to flow a _____ ______ must exist?

A

Pressure gradient

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5
Q

What is a pressure gradient?

A

A decrease in pressure from one area to the next and must be present for flow to occur

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6
Q

To preserve blood flow throughout the body, If there is an increase in resistance what must pressure gradient do?

A

It must also increase

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7
Q

What is the formula for Flow?

A

Q = (P1-P2)/R

Q = flow
P1-P2 pressure gradient
R = resistance

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8
Q

As blood flows from the heart to the ankles the ______ _______ increases. At the same time there is a decrease in ________ _________. As a result, the ______ ________ decreases from the aorta to the ankles allowing blood to flow from high to low pressure

A
  1. Systolic pressure
  2. Diastolic pressure
  3. mean pressure
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9
Q

Kinetic and potential energy combined provides what?

A

The energy for flow to occur

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10
Q

As kinetic energy increases potential energy does what?

A

Decreases and vice versa

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11
Q

What is kinetic energy (2%):

A

Energy of a moving entity

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12
Q

Kinetic energy in the bloodstream increases with demand for what?

A

Increased in flow volume

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13
Q

Potential energy (98%) is what?

A

Stored energy

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14
Q

What is the main form of energy in the vascular system and results from the pressure distending the vessels?

A

Potential energy

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15
Q

What is the formula for total energy?

A

Potential energy + kinetic energy

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16
Q

What is flow?

A

The amount of fluid traveling past a point in a given amount of time.

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17
Q

What is the units for flow?

A

Volume/time

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18
Q

What two fundamental fluid properties affect flow?

A
  1. Density
  2. Viscosity
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19
Q

What is density?

A

Mass per unit volume (g/ml).

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20
Q

What is the density of blood and is it constant?

A
  1. 1.05 g/ml
  2. It is constant
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21
Q

What is viscosity?

A
  1. Resistance to flow of a fluid in motion, or, how thick it is, its “stickiness”
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22
Q

What is the frictional forces that occur as the molecules of blood move against one another in the layers of flow? What is it measured in?

A
  1. Viscosity
  2. Measured in poise
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23
Q

What is the most important factor affecting viscosity?

A

The concentration of RBC’s and plasma protein

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24
Q

What is the difference between the two vessels?

A

Top one is low velocity and the bottom is high velocity

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25
Q

What is pressure? What is it measured in?

A
  1. The amount of force put on an artery at any point in time.
  2. Measured in mmHg
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26
Q

What is length?

A

Due to increased friction a longer tube contains more resistance than a smaller tube.

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27
Q

What happens to resistance when length increases?

A

Resistance also increases

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28
Q

What does radius have an affect on?

A

Arteriole radius has a large effect on resistance.

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29
Q

As a vessel diameter decreases, what happens to resistance?

A

Increases to the 4th power

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30
Q

What is resistance?

A

The force that must be overcome in order for flow to happen

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31
Q

What is resistance created by?

A

The friction of the blood against the arterial wall

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32
Q

With an increase in length or viscosity, resistance will do what?

A

Increase

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33
Q

With decrease in radius what happens to resistance?

A

Increases to the 4th power

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34
Q

Why is radius the most influential aspect of resistance?

A

A decrease in the radius increases resistance to the 4th power

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35
Q

If a vessel size decreases, resistance does what?

A

Increases dramatically

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36
Q

What is poisuilles law formula?

A

Q = Flow volume
N = viscosity
L = Length of vessel
R = Radius
P1-P2 = Pressure gradient

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37
Q

What does poiseuilles law define?

A

The relationship between pressure, volume, flow and resistance of fluid flowing through a cylinder tube model

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38
Q

What does poiseuilles law help us understand?

A

The relationship between pressure and blood flow

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39
Q

What is laminar flow?

A

Normal flow traveling through a vessel where the slowest flow is located near the vessel wall and the fastest flow is located in the center of the vessel

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40
Q

What is another name for Laminar flow?

A

Parabolic flow

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41
Q

In most vessels, blood moves in what kind or layers?

A

Concentric layers or laminae

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42
Q

Each concentric layer travels at what kind of velocity?

A

A different velocity with the fastest in the center. This creates a normal spectral doppler with a clear window

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43
Q

For a laminar flow, the mean velocity is what?

A

Half of the maximum/ peak velocity which is measured in the center of the vessel

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44
Q

What is blunt flow?

A

Uniform flow across a vessel

45
Q

What is another name for blunt for?

A

Plug flow

46
Q

When does blunt flow occur?

A

During systole in larger vessels, sometimes occurs at arterial branch origins

47
Q

What are some examples of places that blunt flow is seen?

A

Aorta

48
Q

What is non-laminar flow?

A

When in normal and abnormal conditions laminar flow can be disrupted and once it is altered the velocity profile is not re-established for approximately 3 cm

49
Q

Occasionally laminar flow can be altered into what?

A

A mixed blood flow pattern containing both forward and backward components

50
Q

The area where the lamina reach zero- velocity is referred to as what? And is known as what?

A
  1. Boundary layer separation
  2. Transition zone
51
Q

Where do we see non-laminar flow?

A

At carotid bifurcation and distal to a stenosis

52
Q

Where does flow separation occur?

A
  1. When there is a sudden widening of a vessel
  2. Fluid separate to fill the newly opened area, causing flow reversal along the wall
53
Q

Flow separation is considered what type of flow variation?

A

Normal

54
Q

What is turbulence?

A

Chaotic flow where fluid is exiting a tight spot and entering an enlarged space

55
Q

During turbulence space is filled by what?

A

Fluid moving in eddies and whirls and is much more disordered than disturbed flow

56
Q

Turbulence develops more easily in what kind of vessels?

A

Larger vessels with high flow volume

57
Q

Velocity pattern typically has a _______ appearance and is associated with ________ ________

A
  1. Feathered
  2. Spectral broadening
58
Q

The _______ _________ predicts when turbulence will occur and will increase as _________ increase and decreases as _________ Increases

A
  1. Reynolds number
  2. Velocity
  3. Viscosity
59
Q

Turbulence occurs with the Reynolds number meets or exceeds what number?

A

2000

60
Q

What is the Reynolds number formula?

A
61
Q

At the branch the layers become disrupted and will show a ___________ flow pattern?

A

Disturbed

62
Q

Flow patterns may differ depending on what?

A

The angle and size of the vessel

63
Q

A larger angle will result in what?

A

A greater flow disturbance

64
Q

At bifurcations of normal vessels what happens to pressure?

A

There is a small pressure drop

65
Q

In arteries with significant disease there is most often what?

A

Disturbed flow

66
Q

What is a helical flow pattern?

A

When blood moves around a curve, fluid in the center moves outward and is replaced by the slower flow located near the arterial wall.

67
Q

On a curve, fluid flows faster where?

A

On the outside and flow may appear reversed on the inside as the fluid fills the inner void from the outward shift

68
Q

What does Bernoulli’s principles explain?

A

The maintenance or balance of energy in the movement of fluid

69
Q

What does bernoulli’s principle describe?

A

The relationship between area, velocity, and pressure at a stenosis

70
Q

To preserve energy, a velocity increase leads to what

A

A corresponding decrease in pressure

71
Q

When fluids flow from one point to another, its total energy does what?

A

Remains constant assuming flow is stable and there are no frictional energy losses

72
Q

Within a stenosis, velocity and pressure are related how?

A

Inversely

73
Q

What is bernoullis equation?

A
74
Q

What does this image demonstrate?

A

Bernoulli effect

75
Q

According to Bernoulli’s principle, there will be a _______ ________ at the ___________ to the stenosis because the high velocity flow state is needed to maintain the flow volume

A
  1. Pressure drop
  2. Entrance
76
Q

At the _______, __________ may be seen due to the jet entering the wider lumen

A
  1. Exit
  2. Turbulence
77
Q

Immediately __________________ the ________ ___________ due to the increased lumen size resulting in an _____________.

A
  1. Distal to the exit
  2. Velocity decreases
  3. Increase in pressure
78
Q

Energy loss due to friction and viscosity will vary according to what?

A
  1. Length of the stenosis
  2. Whether there are tandem stenosis
  3. Surface contour of the plaque
79
Q

Plaque alters pressure and flow at the site of what?

A

The lesion, but significant reduction in cross- sectional diameter has to occur before hemodynamic changes are noted distally

80
Q

The velocity and pressure proximal to a stenosis are used as what?

A

The baseline

81
Q

Within the stenosis, the velocity is what? What is the pressure?

A

Velocity is high and pressure is low

82
Q

Since the are within a stenosis is smaller and the flow must be maintained, the velocity must do what? And the velocity does this what happens to the pressure?

A
  1. Velocity must increase
  2. Pressure decreases since the total energy must remain the same
83
Q

Factors within a stenosis that cause hemodynamic changes are what?

A
  1. Length and diameter of narrowed segment
  2. Surface roughness
  3. Surface irregularity and shape of lesion
  4. Ratio of normal vessel diameter to a narrowed segment
  5. Collateral circulation
  6. Pressure gradient
  7. Peripheral resistance distal to stenosis
84
Q

What happens proximal to a stenosis?

A
  1. Increased pulsatility
  2. Narrow, sharp peak
  3. Low PSV due to decreased flow
  4. Laminar flow
  5. “Thumping” in systole if stenosis very severe
85
Q

What does this image demonstrate?

A

Hemodynamic characteristics proximal to a stenosis

86
Q

What happens at a stenotic jet (zone)?

A
  1. Increased velocities not necessarily isolated to the stenotic segment
  2. PSV increases to 80% diameter reduction then decreases
  3. EDV is markedly increased with >70% stenosis
87
Q

What happens distal to a stenosis?

A
  1. Immediately past the stenosis the flow stream spreads out and flow reversal, flow separations, vortices and eddy currents are seen
  2. Energy is given up as heat
  3. Maximum flow disturbance is seen within 1 cm of a stenosis and a visible bruit may be seen
  4. Dampened or tardus parvus waveform is seen
  5. Stenotic jets are seen in the stenotic segment and may also occur just proximal or distal to a stenosis
88
Q

What type of flow is seen here?

A

Tardus parvus

89
Q

What are tandem lesions in terms of energy and volume?

A

Greater loss of energy and volume

90
Q

For a tandem lesion, The first stenosis will have a ________ _________ energy and will produce _______ _________ than the second stenosis as it will have _________ _________ _________.

A
  1. Greater incoming energy
  2. Higher velocities
  3. Decreased incoming energy
91
Q

Velocities vary with what?

A
  1. From patient to patient
  2. Throughout the circulatory system
  3. Dependent on the hemodynamic conditions at a given time
92
Q

Doppler velocity waveforms patterns offer?

A

Information for what is occurring at the sample site as well as proximal and distal

93
Q

In its normal resting state, each artery has its own what?

A

Velocity waveform pattern that is characterized as being high resistance or low resistance

94
Q

In disease states velocity flow patterns may do what?

A

Change and other characteristics of the waveform may present

95
Q

What is low resistance?

A

Constant forward flow in systole and diastole with a diastolic component well above the baseline

96
Q

The increased diastolic component of low resistance indicates what?

A

That the vessel supplying an area (vascular bed) that demands constant blood flow (highly vascular)

97
Q

What does this image demonstrate?

A

Low resistance

98
Q

What are some example of low resistance flow structures?

A
  1. ICA
  2. Vertebral arteries
  3. Renal arteries
  4. Splenic artery
  5. Post prandial mesenteric artery
  6. Celiac artery
  7. Hepatic artery
99
Q

What does high resistance mean?

A

Sharp upstroke, with low to absent diastolic flow and is described as having more “pulsatility” in the waveform pattern

100
Q

The decreased diastolic component of high resistant waveforms indicate what?

A

That the vessel is supplying an area (vascular bed) that does not require constant forward flow and is highly resistant

101
Q

What are some examples of high resistant structures?

A
  1. ECA
  2. Upper/ Lower extremity peripheral vasculature
  3. Pre- Prandial mesenteric artery
102
Q

What does pulsatility mean?

A

Flow in the arterial system contains alternating phases of acceleration and deceleration due to the pulsatile pumping activity of the heart

103
Q

Pulsatility alterations are displayed with what?

A

Doppler ultrasound as a waveform which has low, moderate or high pulpability features, and are high or low resistance

104
Q

What type of flow pattern is this an image of?

A

High resistance flow

105
Q

What does a low pulsatility doppler waveform look like?

A

Broak systolic peak and forward flow throughout diastole

106
Q

What does a moderate pulsatility waveform look like on doppler?

A

Tall, sharp peak and little diastolic flow

107
Q

What does high pulsatility look like?

A
  1. Narrow systolic peak
  2. Flow reversal in early diastole
  3. Little or absent late diastolic flow
108
Q

Label the image from left to right

A
  1. Low
  2. Moderate
  3. High

DMST 493 Vasc 2 (9 decks)

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