Arterial Hemodynamics Flashcards
1
Q
What is arterial hemodynamics?
A
Fluid dynamics that govern blood flow
2
Q
What are two important aspects of arterial hemodynamics?
A
- Energy
- Pressure
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.
4
Q
For blood to flow a _____ ______ must exist?
A
Pressure gradient
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
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
7
Q
What is the formula for Flow?
A
Q = (P1-P2)/R
Q = flow
P1-P2 pressure gradient
R = resistance
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
- Systolic pressure
- Diastolic pressure
- mean pressure
9
Q
Kinetic and potential energy combined provides what?
A
The energy for flow to occur
10
Q
As kinetic energy increases potential energy does what?
A
Decreases and vice versa
11
Q
What is kinetic energy (2%):
A
Energy of a moving entity
12
Q
Kinetic energy in the bloodstream increases with demand for what?
A
Increased in flow volume
13
Q
Potential energy (98%) is what?
A
Stored energy
14
Q
What is the main form of energy in the vascular system and results from the pressure distending the vessels?
A
Potential energy
15
Q
What is the formula for total energy?
A
Potential energy + kinetic energy
16
Q
What is flow?
A
The amount of fluid traveling past a point in a given amount of time.
17
Q
What is the units for flow?
A
Volume/time
18
Q
What two fundamental fluid properties affect flow?
A
- Density
- Viscosity
19
Q
What is density?
A
Mass per unit volume (g/ml).
20
Q
What is the density of blood and is it constant?
A
- 1.05 g/ml
- It is constant
21
Q
What is viscosity?
A
- Resistance to flow of a fluid in motion, or, how thick it is, its “stickiness”
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
- Viscosity
- Measured in poise
23
Q
What is the most important factor affecting viscosity?
A
The concentration of RBC’s and plasma protein
24
Q
What is the difference between the two vessels?
A
Top one is low velocity and the bottom is high velocity
25
What is pressure? What is it measured in?
1. The amount of force put on an artery at any point in time.
2. Measured in mmHg
26
What is length?
Due to increased friction a longer tube contains more resistance than a smaller tube.
27
What happens to resistance when length increases?
Resistance also increases
28
What does radius have an affect on?
Arteriole radius has a large effect on resistance.
29
As a vessel diameter decreases, what happens to resistance?
Increases to the 4th power
30
What is resistance?
The force that must be overcome in order for flow to happen
31
What is resistance created by?
The friction of the blood against the arterial wall
32
With an increase in length or viscosity, resistance will do what?
Increase
33
With decrease in radius what happens to resistance?
Increases to the 4th power
34
Why is radius the most influential aspect of resistance?
A decrease in the radius increases resistance to the 4th power
35
If a vessel size decreases, resistance does what?
Increases dramatically
36
What is poisuilles law formula?
Q = Flow volume
N = viscosity
L = Length of vessel
R = Radius
P1-P2 = Pressure gradient
37
What does poiseuilles law define?
The relationship between pressure, volume, flow and resistance of fluid flowing through a cylinder tube model
38
What does poiseuilles law help us understand?
The relationship between pressure and blood flow
39
What is laminar flow?
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
40
What is another name for Laminar flow?
Parabolic flow
41
In most vessels, blood moves in what kind or layers?
Concentric layers or laminae
42
Each concentric layer travels at what kind of velocity?
A different velocity with the fastest in the center. This creates a normal spectral doppler with a clear window
43
For a laminar flow, the mean velocity is what?
Half of the maximum/ peak velocity which is measured in the center of the vessel
44
What is blunt flow?
Uniform flow across a vessel
45
What is another name for blunt for?
Plug flow
46
When does blunt flow occur?
During systole in larger vessels, sometimes occurs at arterial branch origins
47
What are some examples of places that blunt flow is seen?
Aorta
48
What is non-laminar flow?
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
Occasionally laminar flow can be altered into what?
A mixed blood flow pattern containing both forward and backward components
50
The area where the lamina reach zero- velocity is referred to as what? And is known as what?
1. Boundary layer separation
2. Transition zone
51
Where do we see non-laminar flow?
At carotid bifurcation and distal to a stenosis
52
Where does flow separation occur?
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
Flow separation is considered what type of flow variation?
Normal
54
What is turbulence?
Chaotic flow where fluid is exiting a tight spot and entering an enlarged space
55
During turbulence space is filled by what?
Fluid moving in eddies and whirls and is much more disordered than disturbed flow
56
Turbulence develops more easily in what kind of vessels?
Larger vessels with high flow volume
57
Velocity pattern typically has a _______ appearance and is associated with ________ ________
1. Feathered
2. Spectral broadening
58
The _______ _________ predicts when turbulence will occur and will increase as _________ increase and decreases as _________ Increases
1. Reynolds number
2. Velocity
3. Viscosity
59
Turbulence occurs with the Reynolds number meets or exceeds what number?
2000
60
What is the Reynolds number formula?
61
At the branch the layers become disrupted and will show a ___________ flow pattern?
Disturbed
62
Flow patterns may differ depending on what?
The angle and size of the vessel
63
A larger angle will result in what?
A greater flow disturbance
64
At bifurcations of normal vessels what happens to pressure?
There is a small pressure drop
65
In arteries with significant disease there is most often what?
Disturbed flow
66
What is a helical flow pattern?
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
On a curve, fluid flows faster where?
On the outside and flow may appear reversed on the inside as the fluid fills the inner void from the outward shift
68
What does Bernoulli's principles explain?
The maintenance or balance of energy in the movement of fluid
69
What does bernoulli's principle describe?
The relationship between area, velocity, and pressure at a stenosis
70
To preserve energy, a velocity increase leads to what
A corresponding decrease in pressure
71
When fluids flow from one point to another, its total energy does what?
Remains constant assuming flow is stable and there are no frictional energy losses
72
Within a stenosis, velocity and pressure are related how?
Inversely
73
What is bernoullis equation?
74
What does this image demonstrate?
Bernoulli effect
75
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
1. Pressure drop
2. Entrance
76
At the _______, __________ may be seen due to the jet entering the wider lumen
1. Exit
2. Turbulence
77
Immediately __________________ the ________ ___________ due to the increased lumen size resulting in an _____________.
1. Distal to the exit
2. Velocity decreases
3. Increase in pressure
78
Energy loss due to friction and viscosity will vary according to what?
1. Length of the stenosis
2. Whether there are tandem stenosis
3. Surface contour of the plaque
79
Plaque alters pressure and flow at the site of what?
The lesion, but significant reduction in cross- sectional diameter has to occur before hemodynamic changes are noted distally
80
The velocity and pressure proximal to a stenosis are used as what?
The baseline
81
Within the stenosis, the velocity is what? What is the pressure?
Velocity is high and pressure is low
82
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?
1. Velocity must increase
2. Pressure decreases since the total energy must remain the same
83
Factors within a stenosis that cause hemodynamic changes are what?
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
What happens proximal to a stenosis?
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
What does this image demonstrate?
Hemodynamic characteristics proximal to a stenosis
86
What happens at a stenotic jet (zone)?
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
What happens distal to a stenosis?
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
What type of flow is seen here?
Tardus parvus
89
What are tandem lesions in terms of energy and volume?
Greater loss of energy and volume
90
For a tandem lesion, The first stenosis will have a ________ _________ energy and will produce _______ _________ than the second stenosis as it will have _________ _________ _________.
1. Greater incoming energy
2. Higher velocities
3. Decreased incoming energy
91
Velocities vary with what?
1. From patient to patient
2. Throughout the circulatory system
3. Dependent on the hemodynamic conditions at a given time
92
Doppler velocity waveforms patterns offer?
Information for what is occurring at the sample site as well as proximal and distal
93
In its normal resting state, each artery has its own what?
Velocity waveform pattern that is characterized as being high resistance or low resistance
94
In disease states velocity flow patterns may do what?
Change and other characteristics of the waveform may present
95
What is low resistance?
Constant forward flow in systole and diastole with a diastolic component well above the baseline
96
The increased diastolic component of low resistance indicates what?
That the vessel supplying an area (vascular bed) that demands constant blood flow (highly vascular)
97
What does this image demonstrate?
Low resistance
98
What are some example of low resistance flow structures?
1. ICA
2. Vertebral arteries
3. Renal arteries
4. Splenic artery
5. Post prandial mesenteric artery
6. Celiac artery
7. Hepatic artery
99
What does high resistance mean?
Sharp upstroke, with low to absent diastolic flow and is described as having more "pulsatility" in the waveform pattern
100
The decreased diastolic component of high resistant waveforms indicate what?
That the vessel is supplying an area (vascular bed) that does not require constant forward flow and is highly resistant
101
What are some examples of high resistant structures?
1. ECA
2. Upper/ Lower extremity peripheral vasculature
3. Pre- Prandial mesenteric artery
102
What does pulsatility mean?
Flow in the arterial system contains alternating phases of acceleration and deceleration due to the pulsatile pumping activity of the heart
103
Pulsatility alterations are displayed with what?
Doppler ultrasound as a waveform which has low, moderate or high pulpability features, and are high or low resistance
104
What type of flow pattern is this an image of?
High resistance flow
105
What does a low pulsatility doppler waveform look like?
Broak systolic peak and forward flow throughout diastole
106
What does a moderate pulsatility waveform look like on doppler?
Tall, sharp peak and little diastolic flow
107
What does high pulsatility look like?
1. Narrow systolic peak
2. Flow reversal in early diastole
3. Little or absent late diastolic flow
108
Label the image from left to right
1. Low
2. Moderate
3. High
