Fluid Dynamics and Hemodynamics Flashcards
1
Q
Fluid dynemics
A
Study of fluid through a flow system
2
Q
what are some variables associated with fluid dynamics
A
Power Work Energy Potential/kinetic energy Pressure Volumetric flow Resistance Capacitance Compliance Velocity Viscosity
3
Q
Power
A
rate at which energy is transferred. Power describes how fast work is being performed (WATTS=joules/sec)
4
Q
Work
A
the amount of energy transferred (AVERAGE POWER X TOTAL TIME) - JOULES
5
Q
Energy
A
quantities such as mass energy, kinetic, potential, heat, radiation
6
Q
Potential energy
A
energy which is stored which can be converted to other forms of energy
7
Q
Energy
A
Must be concerved
8
Q
Kinetic energy
A
Represents energy related to movement and is proportional to the velocity squared of the movement
9
Q
Pressure
A
force per unit area
10
Q
Volumetric Flow
A
– volume of fluid per time which moves past a point (Litres/min…etc.)
11
Q
Resistance
A
ratio of the pressure drop across a vessel per volumetric. Measured of the impediment that must be overcome for flow to occur.
12
Q
Capacitance
A
the ability to hold a change in volume per change in tome (dv/dt) V is volume and t is time
13
Q
Velcoity
A
speed with which a fluid moves in a specific direction
14
Q
Viscosity
A
measure of the resistance of the fluid to flow due to the attraction of the molecules
15
Q
Energy can occur from a
A
Higher to lower enrgy level
16
Q
Energy is converted from what to what in ultrasound?
A
Electropotential energy is converted into acoustic mechanical energy and transmitted into the body – absorption is mainly the conversion of the acoustic energy into heat energy
Reflected waves are then converted back into electropotential energy
17
Q
Fundamental rule #1 of energy
A
Energy is always conserved – energy is never lost, only converted between forms
18
Q
Energy within the cardiovascular system is
A
Converted back and forth between kinetic and potential energy
19
Q
Pressure that represents force exerted on the vessel walls
A
Potential energy
20
Q
force of flow direction in the vessels
A
Kinetic energy
21
Q
Increase in blood velocity=
A
Increased kinetic energy and therefore decreased potential energy
22
Q
As flow accelerates
A
Decrease in potential energy and an compsentory increase in kinetic energy
23
Q
Key concept Kinetic/potential energy
A
If we make the assumption that little or no energy is lost to heat, conservation of energy requires that a change in kinetic energy must equal a change in potential energy.
Since kinetic energy is related to velocity and since velocity can be measured by Doppler, a change in potential energy (pressure) can be determined by performing Doppler
24
Q
hydrostatic pressure is a form of what
A
Potential energy
25
Hydrostatic pressure is what
is the pressure that results from the force of the fluid (gravity) which results from a column of fluid.
26
what is hydrostatic pressure proportional to
The hydrostatic pressure is proportional to the density of the fluid, the height of the fluid, and gravity
27
Any factors affecting weight will affect
hydrostatic pressure
28
A taller column will create higher/lower hydrostatic pressure
High hydrostatic pressure
29
A more dense fluid will create a higher/lower hydrostatic pressure
Higher hydrostatic pressure
30
clinically what affects hydrostatic pressure
Height and patient position
31
For normal density of blood, each inch of blood in a vertical column results in a pressure of....
2mmHG
32
Volumetric flow
Flow is defined as the amount or volume of a quantity which moves past a point per unit time
Doppler does not measure FLOW, it measures velocity
33
Velcoity
Speed
Speed
Velocity, flow and pressure are all related
Can not assume that high flow represents a high velocity
34
Capactiance
Capacitance is defined as a change in volume per time. Is a measure of the ability to hold a change in volume per change in time
35
Compliance
Is the measure of the ability to hold a change in volume per change in pressure
36
High compliance
implies that there is a large increase in volume for a small increase in pressure
37
Fluid viscoisty
Measure of the internal resistance of a fluid to flow
38
Fluid viscosity is caused by
Caused by molecular cohesive forces
| Attraction of molecules
39
what does the resistance equation state
States that the resistance is directly proportional to the vessel length and the fluid viscosity and inversely proportional to the radius of the vessel to the 4th power
40
If the length increases
The resistance increases
| More energy is required to transport the same flow in the longer pipeline
41
Resistance is inversely proportional to
Radius
42
Radius affects resistance faster then
Length
43
Radius is affected by
4th power
44
Resistance is inversely proportional to
r4
45
Resistance is proportional to
Viscosity
46
Higher viscosity results in
A higher resistance to flow
47
Resistance equation
R=8ln/pir4
48
Larger cross sectional area
Increases the volumetric flow
49
Higher average spatial velocity increases
Volumetric flow
| Increase in velocity increases flow
50
Continuity (volumetric flow) equation
Q=v*area
51
Assumption
We know that flow only occurs from a higher to lower energy state
One for of energy is pressure exertion on a wall
If we assume no other energy it is fair to say that this higher pressure region to a lower pressure region would create flow against a resistive pathway
52
Pressure gradient is proportional to
Resistance
| An increase in resistance results in an increase in pressure drop for fixed flow
53
Pressure gradient is proportional to
Volumetric flow
| For fixed resistance, higher flow results in an increase in the pressure gradient
54
Simplified law of hemodynamics
P=Q*R
55
Poiseuille's law
Is the same law as the simplified law, but written in terms of the volumetric flw (Q) and with a direct substitution for resistance
56
what is Poiseuille's law
Q=Ppir4/8ln
57
Poiseuille's law can only function under certain conditions
The flow conduit is rigid and cylindrical tube
The flow is in a steady state, laminar flow
The fluid is Newtonian
58
Bernoulli's equation
Is derived directly from the conservation of energy theorem
Since energy must be conserved in a closed system, the sum if the energy at point 1 must be equal to the energy at point 2
By grouping the pressure terms on one side of the equation, the kinetic energy terms on the other, the expression becomes Bernouli’s
59
what does Bernoulli's equation state
For a closed system, assuming no energy lose to heat (friction on walls), the energy at point 1 musy qual the energy at point 2
60
What are some assumptions of Bernoulli's equation
- Rigid tube
- no friction
- steady, non pulsatile flow state
- Non-viscous fluid
- incompressible, inhomogeneous fluid
61
Bernoulli's equation
Takes into account major sources of energy interacting to create flow
62
What are rigid tube flow asusmptions
- Flow conduit is a rigid tube
- surface of the tube is smooth with no irregulates
- fluid is Newtonian (homogeneous with constant viscosity)
- compressible fluid
- there is no energy lost to heat
- flow state is steady
63
flow is affected by what
Changes in a cross sectional area
64
Decreasing area
Causes acceleration and a blunting of parabolic laminar flow
65
Increasing area
flow disturbances can occur (turbulence) as a mechanism of reducing kinetic energy
66
Steady flow
Steady flow is constant in volumetric flow
67
Pulsatile flow
- Volumetric flow is dynamic with time
| - dynamic pressure is generated by heart, blood flow
68
Laminar flow
- Well behaved manner and uniform direction
| - Fluid moves in concentric rings with no crossing of ring boundaries
69
Plug Flow
laminar flow that occurs from an acceleration component such as early systole or ascending branch of aorta
70
Parabolic flow
velocity profile across vessel shaped like parabola, arterial flow in straight, unchanging arteries, venous flow
71
Disturbed flow
disturbed flow in any deviation from laminar flow
72
Turbulent flow
fluid is not uniform and is random or chaotic. Occurs distal to stenosis or narrowing
73
Entrance effects
change in velocity profile into a vessel of a reduced caliber. Since the caliber has decreased in area, the velocity must increase (accelerate).
74
Exit effects
change in velocity profile exiting a vessel of a smaller diameter. Velocity must decrease to maintain constant flow. Inertia is dissipated by chaotic or turbulent flow
75
Reynolds number
Indicates the likelihood of turbulence occurring
| A higher Reynold’s number implies a greater likelihood of turbulence occurring
76
In hemodynamics what is removed
Basic assumptions (Rigid, cylindrical tube, steady, laminar flow, Newtonian fluid) as they do not hold true for blood flow
77
Driving pressure in hemodynamics
Is dynamic (blood flow is pulsatile)
78
what is the principal parameter measured by Doppler
Velocity
79
Time variant velocity signal from doppler is reliant on...
```
Cardiac Output
Pulse Pressure
Mean Arterial Pressure (MAP)
Peripheral Resistance
Venovasmator Tone
```
80
Pressure is ______in the human body
Dynamic
81
Arteries are _____ and therefore not ______for flow
elastic rigid conduits for flow
82
why is elasticity important
- allows aorta to be capacitive
- Capacitance of aorta allows energy to be stored in walls to provide energy to propel blood during diastole
- Run off from the capacitive aorta through the resistive arterioles and capillaries reduces pulsatility, improving heart efficiency
83
Because of vessel compliance....
A change in pressure results in a change in cross sectional area and hence an increase in the capacity for flow volume (Vasodilation and vasoconstriction)
84
When pressure is applied to the vessel wall this creates....
A larger cross sectional areas of the vessel and greater volume of flow
85
As walls stretch in a vessel
Electricity decreaceases
86
Significant distention of walls does what
Decreases compliance at a point
87
simplified pressure volume relationship
Expresses the rate of change in pressure is proportional to the rate of change in volume
88
There is a _____range over which small increases in ______result in large increases in _______
Large, pressure, volume
89
At both low and high ends the rate of volume with increases pressure is slower/faster than in the middle
Slower
90
Initial filling requires an increase in ______before stretching and the rate can then become constant
pressure
91
Once vessel is stretched out, the ability to hold volume _______
Decreases
92
Non compliant vessles
At lower pressures the relationship is linear but at higher pressures, an increase in pressure=no increase in volume
93
Series resistance
effective (overall) resistance is the sum of the resistances of each component
94
Parallel resistance
overall resistance is more complicated
| inverse effective resistance is calculated as the sum of individual inverse resistances
95
Effective resistance decreases/increases with increasing parallel vessels
Decreases
96
Effective resistance for a single larger dimeter vessel is much more/less than for a parallel combination
less
97
Amount of energy lost by transporting blood over a rough vessel is.....
greater than the energy lost transporting over smooth surfaces
98
kinetic energy is lost to ____
heat through the friction from both external interaction of fluid with the walls and internal interaction related to viscosity
99
Energy losses _____with decreasing vessel size as a result of increased frictional and viscous energy loss
increase
100
Varying vessel sizes is a principal mechanism in controlling the ______ throughout the arterial system
Effective resistance
101
Why is control of resistance important
To control pressure decrease as well as regulate volumetric flow
102
Resistance ________in progression from the low resistance the aorta to the high resistance of the arterioles
Decreases
103
effective resistance of the capillaries is high but
lower then arterioles because of the sheer number of capillaries
104
Velocity of the flow is controlled primarily by....
The varying total cross sectional area of the vessels
105
For a fixed volume as the area _______ the velocity _______
increases, decreases
106
Pressure in the venous system
Low
107
Venous system is referred to as the
Capacitive or reservoir component of the cardiovascular system
108
The venous pressure gradient is.....
Small, the capacitance of the veins creates a reservoir where it can stay until a gradient exists for return
blood loss situations draw from the venous reservoir
109
Where is most of the blood volume
Veins and venules
110
Calf muscle pump
The calf muscle pump helps overcome the effect of gravity to aid with venous return for a patient in the standing position. By muscle contraction, the venous volume is ratcheted back toward the right heart through a series of valves which open and close with muscle contraction.
111
what is transmural pressure
measure of the difference of the pressure inside the vessel (intravascular pressure) relative to the pressure outside the vessel (tissue pressure). Note that the transmural pressure is always referenced from the inside of the vessel to the outside of the vessel.
112
With increased intravascular pressure
tissue pressure is lower
113
Critical stenosis
When the disease becomes critical, the amount of energy lost to frictional and viscous effects become so severe, that volume is not maintained across the lesion. As depicted below, a point is reached at which there is a narrow stream of flow at a high velocity with most of the flow traveling at a relatively low velocity (“string flow”).
