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Ultrasound Physics > Fluid Dynamics and Hemodynamics > Flashcards

Fluid Dynamics and Hemodynamics Flashcards

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1
Q

Fluid dynemics

A

Study of fluid through a flow system

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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
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3
Q

Power

A

rate at which energy is transferred. Power describes how fast work is being performed (WATTS=joules/sec)

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4
Q

Work

A

the amount of energy transferred (AVERAGE POWER X TOTAL TIME) - JOULES

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5
Q

Energy

A

quantities such as mass energy, kinetic, potential, heat, radiation

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6
Q

Potential energy

A

energy which is stored which can be converted to other forms of energy

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7
Q

Energy

A

Must be concerved

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8
Q

Kinetic energy

A

Represents energy related to movement and is proportional to the velocity squared of the movement

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9
Q

Pressure

A

force per unit area

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10
Q

Volumetric Flow

A

– volume of fluid per time which moves past a point (Litres/min…etc.)

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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.

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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

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13
Q

Velcoity

A

speed with which a fluid moves in a specific direction

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14
Q

Viscosity

A

measure of the resistance of the fluid to flow due to the attraction of the molecules

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15
Q

Energy can occur from a

A

Higher to lower enrgy level

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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

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17
Q

Fundamental rule #1 of energy

A

Energy is always conserved – energy is never lost, only converted between forms

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18
Q

Energy within the cardiovascular system is

A

Converted back and forth between kinetic and potential energy

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19
Q

Pressure that represents force exerted on the vessel walls

A

Potential energy

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20
Q

force of flow direction in the vessels

A

Kinetic energy

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21
Q

Increase in blood velocity=

A

Increased kinetic energy and therefore decreased potential energy

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22
Q

As flow accelerates

A

Decrease in potential energy and an compsentory increase in kinetic energy

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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

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24
Q

hydrostatic pressure is a form of what

A

Potential energy

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25
Q

Hydrostatic pressure is what

A

is the pressure that results from the force of the fluid (gravity) which results from a column of fluid.

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26
Q

what is hydrostatic pressure proportional to

A

The hydrostatic pressure is proportional to the density of the fluid, the height of the fluid, and gravity

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27
Q

Any factors affecting weight will affect

A

hydrostatic pressure

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28
Q

A taller column will create higher/lower hydrostatic pressure

A

High hydrostatic pressure

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29
Q

A more dense fluid will create a higher/lower hydrostatic pressure

A

Higher hydrostatic pressure

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30
Q

clinically what affects hydrostatic pressure

A

Height and patient position

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31
Q

For normal density of blood, each inch of blood in a vertical column results in a pressure of….

A

2mmHG

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32
Q

Volumetric flow

A

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

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33
Q

Velcoity

A

Speed
Speed
Velocity, flow and pressure are all related
Can not assume that high flow represents a high velocity

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34
Q

Capactiance

A

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

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35
Q

Compliance

A

Is the measure of the ability to hold a change in volume per change in pressure

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36
Q

High compliance

A

implies that there is a large increase in volume for a small increase in pressure

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37
Q

Fluid viscoisty

A

Measure of the internal resistance of a fluid to flow

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38
Q

Fluid viscosity is caused by

A

Caused by molecular cohesive forces

Attraction of molecules

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39
Q

what does the resistance equation state

A

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

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40
Q

If the length increases

A

The resistance increases

More energy is required to transport the same flow in the longer pipeline

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41
Q

Resistance is inversely proportional to

A

Radius

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42
Q

Radius affects resistance faster then

A

Length

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43
Q

Radius is affected by

A

4th power

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44
Q

Resistance is inversely proportional to

A

r4

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45
Q

Resistance is proportional to

A

Viscosity

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46
Q

Higher viscosity results in

A

A higher resistance to flow

47
Q

Resistance equation

A

R=8ln/pir4

48
Q

Larger cross sectional area

A

Increases the volumetric flow

49
Q

Higher average spatial velocity increases

A

Volumetric flow

Increase in velocity increases flow

50
Q

Continuity (volumetric flow) equation

A

Q=v*area

51
Q

Assumption

A

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
Q

Pressure gradient is proportional to

A

Resistance

An increase in resistance results in an increase in pressure drop for fixed flow

53
Q

Pressure gradient is proportional to

A

Volumetric flow

For fixed resistance, higher flow results in an increase in the pressure gradient

54
Q

Simplified law of hemodynamics

A

P=Q*R

55
Q

Poiseuille’s law

A

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
Q

what is Poiseuille’s law

A

Q=Ppir4/8ln

57
Q

Poiseuille’s law can only function under certain conditions

A

The flow conduit is rigid and cylindrical tube
The flow is in a steady state, laminar flow
The fluid is Newtonian

58
Q

Bernoulli’s equation

A

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
Q

what does Bernoulli’s equation state

A

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
Q

What are some assumptions of Bernoulli’s equation

A
  • Rigid tube
  • no friction
  • steady, non pulsatile flow state
  • Non-viscous fluid
  • incompressible, inhomogeneous fluid
61
Q

Bernoulli’s equation

A

Takes into account major sources of energy interacting to create flow

62
Q

What are rigid tube flow asusmptions

A
  • 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
Q

flow is affected by what

A

Changes in a cross sectional area

64
Q

Decreasing area

A

Causes acceleration and a blunting of parabolic laminar flow

65
Q

Increasing area

A

flow disturbances can occur (turbulence) as a mechanism of reducing kinetic energy

66
Q

Steady flow

A

Steady flow is constant in volumetric flow

67
Q

Pulsatile flow

A
  • Volumetric flow is dynamic with time

- dynamic pressure is generated by heart, blood flow

68
Q

Laminar flow

A
  • Well behaved manner and uniform direction

- Fluid moves in concentric rings with no crossing of ring boundaries

69
Q

Plug Flow

A

laminar flow that occurs from an acceleration component such as early systole or ascending branch of aorta

70
Q

Parabolic flow

A

velocity profile across vessel shaped like parabola, arterial flow in straight, unchanging arteries, venous flow

71
Q

Disturbed flow

A

disturbed flow in any deviation from laminar flow

72
Q

Turbulent flow

A

fluid is not uniform and is random or chaotic. Occurs distal to stenosis or narrowing

73
Q

Entrance effects

A

change in velocity profile into a vessel of a reduced caliber. Since the caliber has decreased in area, the velocity must increase (accelerate).

74
Q

Exit effects

A

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
Q

Reynolds number

A

Indicates the likelihood of turbulence occurring

A higher Reynold’s number implies a greater likelihood of turbulence occurring

76
Q

In hemodynamics what is removed

A

Basic assumptions (Rigid, cylindrical tube, steady, laminar flow, Newtonian fluid) as they do not hold true for blood flow

77
Q

Driving pressure in hemodynamics

A

Is dynamic (blood flow is pulsatile)

78
Q

what is the principal parameter measured by Doppler

A

Velocity

79
Q

Time variant velocity signal from doppler is reliant on…

A 
Cardiac Output
Pulse Pressure
Mean Arterial Pressure (MAP)
Peripheral Resistance
Venovasmator Tone
80
Q

Pressure is ______in the human body

A

Dynamic

81
Q

Arteries are _____ and therefore not ______for flow

A

elastic rigid conduits for flow

82
Q

why is elasticity important

A
  • 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
Q

Because of vessel compliance….

A

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
Q

When pressure is applied to the vessel wall this creates….

A

A larger cross sectional areas of the vessel and greater volume of flow

85
Q

As walls stretch in a vessel

A

Electricity decreaceases

86
Q

Significant distention of walls does what

A

Decreases compliance at a point

87
Q

simplified pressure volume relationship

A

Expresses the rate of change in pressure is proportional to the rate of change in volume

88
Q

There is a _____range over which small increases in ______result in large increases in _______

A

Large, pressure, volume

89
Q

At both low and high ends the rate of volume with increases pressure is slower/faster than in the middle

A

Slower

90
Q

Initial filling requires an increase in ______before stretching and the rate can then become constant

A

pressure

91
Q

Once vessel is stretched out, the ability to hold volume _______

A

Decreases

92
Q

Non compliant vessles

A

At lower pressures the relationship is linear but at higher pressures, an increase in pressure=no increase in volume

93
Q

Series resistance

A

effective (overall) resistance is the sum of the resistances of each component

94
Q

Parallel resistance

A

overall resistance is more complicated

inverse effective resistance is calculated as the sum of individual inverse resistances

95
Q

Effective resistance decreases/increases with increasing parallel vessels

A

Decreases

96
Q

Effective resistance for a single larger dimeter vessel is much more/less than for a parallel combination

A

less

97
Q

Amount of energy lost by transporting blood over a rough vessel is…..

A

greater than the energy lost transporting over smooth surfaces

98
Q

kinetic energy is lost to ____

A

heat through the friction from both external interaction of fluid with the walls and internal interaction related to viscosity

99
Q

Energy losses _____with decreasing vessel size as a result of increased frictional and viscous energy loss

A

increase

100
Q

Varying vessel sizes is a principal mechanism in controlling the ______ throughout the arterial system

A

Effective resistance

101
Q

Why is control of resistance important

A

To control pressure decrease as well as regulate volumetric flow

102
Q

Resistance ________in progression from the low resistance the aorta to the high resistance of the arterioles

A

Decreases

103
Q

effective resistance of the capillaries is high but

A

lower then arterioles because of the sheer number of capillaries

104
Q

Velocity of the flow is controlled primarily by….

A

The varying total cross sectional area of the vessels

105
Q

For a fixed volume as the area _______ the velocity _______

A

increases, decreases

106
Q

Pressure in the venous system

A

Low

107
Q

Venous system is referred to as the

A

Capacitive or reservoir component of the cardiovascular system

108
Q

The venous pressure gradient is…..

A

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
Q

Where is most of the blood volume

A

Veins and venules

110
Q

Calf muscle pump

A

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
Q

what is transmural pressure

A

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
Q

With increased intravascular pressure

A

tissue pressure is lower

113
Q

Critical stenosis

A

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”).

Ultrasound Physics (10 decks)

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