Hemodynamics

Question 1

What is flow?

Answer 1

The movement of fluid from a location to another

It measures how much fluid moves per unit of time

Question 2

What is another term used to describe flow?

Answer 2

Volume flow rate

Question 3

How are flow and velocity different?

Answer 3

Flow measures volume of fluid that moves per unit of time (liters/min)
Velocity measures speed of that fluid (distance/time)

Question 4

What is pulsatile flow?

Answer 4

It occurs when blood moves with variable velocity

Has high variability because of cardiac contraction and is often associated with high pressure and higher flow rate

Question 5

What vessels show pulsatile flow?

Answer 5

Arteries

Question 6

What is phasic flow?

Answer 6

It occurs when blood moves with variable velocity
It has variability when the vessel is compressed due to respiration, and is associated with lower pressure and lower flow rate

Question 7

What vessels show phasic flow?

Answer 7

Veins

Question 8

What is steady flow?

Answer 8

Flow that moves at a constant velocity or speed

Question 9

When is steady flow seen?

Answer 9

When patient holds their breath

Question 10

What is laminar flow?

Answer 10

When the flow streamlines are parallel and aligned

Can be plug or parabolic

Question 11

What is plug flow?

Answer 11

When all layers and blood vessels travel at an equal velocity

Question 12

What is parabolic flow?

Answer 12

When the flow is in the shape of a bullet

The center of the vessel holds the highest velocity

Question 13

What is the Reynolds number?

Answer 13

Unitless number that predicts whether flow will be turbulent or laminar

Question 14

What is turbulent flow?

Answer 14

When flow is chaotic and goes in many directions and speeds
Streamlines are obliterated and results in spectral broadening
Energy is lost when converted to sound or vibration

Question 15

What is turbulent flow associated with?

Answer 15

Cardiac and vascular pathologies and spectral broadening

Question 16

For Reynolds number, what is the threshold for predicting turbulent flow?

Answer 16

2000

Question 17

What is viscosity?

Answer 17

Thickness of a fluid
Comes from a fluid sticking to itself with internal friction
Increased viscosity - increased hematocrit and hemoglobin
Reduced viscosity - anemia

Question 18

What is stenosis?

Answer 18

Irregularity or narrowing of the lumen in a blood vessel
It can cause a change in flow direction, increased velocity in the narrowed area, turbulent flow after the stenosis, a pressure gradient, and loss of arterial flow pulsatility

Question 19

What happens to velocity of blood within a stenosis?

Answer 19

The velocity of flow increases within the stenosis, with the highest velocity occurring at the greatest narrowing

Question 20

What type of turbulence may be seen downstream from a stenosis?

Answer 20

Downstream from a stenosis, the turbulence is post-stenotic turbulence
The lumen extends more dramatically than it can be filled by streamlines of blood flow

Question 21

What is Bernoulli’s principle?

Answer 21

It describes the relationship between the pressure and velocity in a moving fluid
The sum of kinetic and pressure energy remains constant
Velocity increases as vessel narrows, while pressure decreases when vessel narrows

Question 22

What is Ohm’s law?

Answer 22

It states that movements of fluid through a tube and electrical current through a wire are similar
Voltage = current x resistance
Q = (change in P)/R

Question 23

How does the cross sectional shape of a vein change in high or low pressure situations?

Answer 23

The cross-sectional shape of a vein during higher pressure is large and round and during lower pressure (normal) is flattened in an hourglass shape

Question 24

What is Hydrostatic Pressure?

Answer 24

The weight of blood pressing on a vessel measured either above or below the level of the heart

Question 25

What is hydrostatic pressure in a supine patient?

Answer 25

It is 0 at all locations when the patient is supine

Question 26

What is the hydrostatic pressure at certain levels?

Answer 26

Head = -30 mmHg
Heart = 0 mmHg
Hands = 50 mmHg
Knees = 75 mmHg
Feet = 100 mmHg

Question 27

During inspiration what happens to venous flow from the legs?

Answer 27

During inspiration, venous flow from the legs decreases.

Question 28

During inspiration what happens to venous flow from the arms and abdomen to the heart?

Answer 28

During inspiration, venous return from the arms and abdomen to the heart increases.

Question 29

During expiration what happens to venous flow from the legs?

Answer 29

During expiration, venous flow from the legs increases.

Question 30

During expiration what happens to venous flow from the arms and abdomen to the heart?

Answer 30

During expiration, venous return from the arms and abdomen to the heart decreases

Question 31

What is a pressure gradient?

Answer 31

The difference or change in pressure from one location to another

Question 32

How is pressure gradient related to flow?

Answer 32

Pressure gradient = flow x resistance

It is directly related to flow because pressure gradient increasing will cause a flow increase