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Ultrasound Physics > 16 Hemodynamics > Flashcards

16 Hemodynamics Flashcards

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1
Q

What is flow?

A

Movement of fluid from one location to another

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2
Q

What is steady flow?

A

Fluid moving at a constant speed or velocity

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3
Q

What is pulsatile and phasic flow?

A

Fluid moving at a variable velocity

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4
Q

What is the difference between pulsatile vs phasic flow?

A

Pulsatile - arterial, cardiac contraction, high rate, higher P
Phasic - venous, respiration, low rate, lower P

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5
Q

What is the difference between flow and velocity?

A

Flow - volume, how much?, vol/time (L/min)

Velocity - speed, how fast?, distance/time (m/s)

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6
Q

What is laminar flow?

A

Flow streamlines that are layered, aligned, and parallel

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7
Q

What are the different patterns for laminar flow?

A

Plug or parabolic

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8
Q

What is turbulent flow?

A

Chaotic flow in many directions and speeds

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9
Q

What is turbulent flow associated with?

A

CV pathology and increased velocities (stenoses)

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10
Q

What is flow energy converted to in turbulent flow?

A

Sound - murmurs, bruits

Vibration - thrill

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11
Q

What can turbulent be identified as?

A

Spectral broadening

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12
Q

What is a vortex?

A

A swirling pattern of rotational flow

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13
Q

What are eddy currents?

A

Turbulent flow

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14
Q

What is Reynold’s Number?

A

A unitless number indicating whether flow is laminar or turbulent
2000 = turbulent

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15
Q

What is the energy gradient?

A

When total fluid energy at one location differs from the total fluid energy at another location

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16
Q

What is kinetic energy?

A

Motion energy associated with object’s speed and mass

17
Q

What is pressure energy?

A

Form of potential or stored energy that has the ability to perform work

18
Q

What are 3 forms of energy loss?

A

Frictional loss
Viscous loss
Inertial loss

19
Q

What is friction?

A

Conversion of other forms of energy into heat

20
Q

What is viscosity?

A

Thickness of a fluid

Units = Poise

21
Q

What is inertia?

A

Tendency of fluid to resist changes in its velocity

22
Q

What does stenosis cause?

A 
Change in flow direction
Increased velocity, highest at max narrowing
Turbulent flow at exit
Pressure gradient
Loss of pulsatility
23
Q

What are the factors that determine resistance?

A

Radius of lumen
Length
Viscosity of fluid

24
Q

What is Bernoulli’s Principle?

A 
Law of Conservation of Energy
At the most narrowed location - 
Velocity is highest
Kinetic energy is highest
Pressure energy is lowest
25
Q

What is hydrostatic pressure?

A

Weight of blood pressing on the vessel from heart level to point of measurement

26
Q

What is the equation for measured pressure?

A

Pressure measured = circulatory P + hydrostatic P

27
Q

How is hydrostatic pressure above and below the heart?

A

Above - negative

Below - positive

28
Q

What is hydrostatic pressure in a supine patient?

A

Zero at all locations

29
Q

What are different measurements of hydrostatic pressure in a standing patient?

A

-50mmHg - fingertip with hand above head
-30mmHg - at head
0mmHg - at heart
75mmHg - at knee
100mmHg - at ankle

30
Q

What is coaptation?

A

Vessel collapse - when opposing vessels walls touch each other

31
Q

Why does respiration have a profound effect on venous flow?

A

Venous system is a low pressure system

Muscles producing respiration change pressures in the thorax and abdomen

32
Q

How is venous flow phasic flow?

A

Pressures in the 2 compartments (abdomen and thorax) vary with inspiration and expiration, and venous flow varies as well

33
Q

What occurs during inspiration?

A

Diaphragm descends into the abdominal cavity
P in the abdomen increases - venous flow in legs decrease
Pressure in thorax decreases - venous return to heart increases

34
Q

What occurs during expiration?

A

Diaphragm ascends into the thorax
P in abdomen decreases - venous flow in legs increases
P in thorax increases - venous return to heart decreases

Ultrasound Physics (20 decks)

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