Physics 1 Module 7 & 8

Question 1

What is the Doppler shift formula?

Answer 1

Doppler shift = 2fo x V x Cos(-) / c

Question 2

Why use the lowest possible frequency when performing doppler?

Answer 2

Reduce attenuation (esp. absorption)

Question 3

What happens to velocity as angle of insonation increases?

Answer 3

Increased percent error for velocity

Question 4

RBC velocities faster than the machine’s ability to sample

Answer 4

Aliasing/nyquist limit exceeded

Question 5

Nyquist limit =

Answer 5

1/2PRF

Question 6

What are the 5 ways to correct for aliasing?

Answer 6

1. Move the baseline *
2. Increase the scale/PRF/velocity range *
3. Increase doppler angle
4. Lower frequency
5. Change to CW

Question 7

What determines the sample volume?

Answer 7

1. Beam width
2. Gate length
3. Length of the emitted pulse (SPL. We want longer SPL with doppler b/c longer interaction with RBCs and shorter with 2D)

Question 8

How does a smaller gate length affect the spectral display?

Answer 8

Improves it

Question 9

What is the minimum number of cycles/pulse required for doppler?

Answer 9

4

Question 10

Where is the sample volume found for CW?

Answer 10

Zone of sensitivity where the transmitted and received beam intersect

Question 11

What are the axes on a spectral tracing?

Answer 11

X time
Y velocity
Z power/RBC density

Question 12

Mathematical technique that separates the individual doppler shifts from the complex beat frequency

Answer 12

Fast Fourier Transform (FFT)

Question 13

Tall, narrow, sharp systolic peaks with reversed or absent diastolic flow

Answer 13

High pulsatility/resistance

Question 14

Broad systolic peaks, forward flow through diastole

Answer 14

Low pulsatility/resistance

Question 15

Tall, narrow, sharp systolic peaks with forward flow through diastole

Answer 15

Moderate resistance/pulsatility

Question 16

Vertical thickening of the spectral trace or envelope

Answer 16

Spectral broadening

Question 17

What happens to flow rate if the pressure gradient increases?

Answer 17

It increases

Question 18

What happens to volume flow rate if the resistance to flow increases?

Answer 18

It decreases

Question 19

What does Poiseuille’s Law describe?

Answer 19

The relationship between pressure and flow

Question 20

What happens to flow velocity when there is an increase in tube length or increase in viscosity?

Answer 20

It decreases

Question 21

What happens to flow when there is a decrease in the diameter?

Answer 21

A large decrease in flow

Question 22

All RBCs travelling at the same velocity, usually seen at the opening of large vessels (Aorta)

Answer 22

Plug flow

Question 23

Most common flow pattern in normal arteries, the middle RBCs moving faster than the ones near the wall.

Answer 23

Laminar/parabolic flow

Question 24

Seen when there is a significant reduction in the vessel diameter (stenosis)

Answer 24

Jet flow

Question 25

Can occur naturally in the presence of vessel tapering, curvatures, bifurcations, etc.

Answer 25

Disturbed flow

Question 26

The type of flow you see past a stenosis

Answer 26

Turbulent flow

Question 27

What is the Reynolds number?

Answer 27

> 2000

Question 28

Why does blood velocity increase in a stenosis?

Answer 28

The volume of flow must remain constant proximal to, within, and distal to the stenosis

Question 29

If the diameter of a stenosis is 1/2 of the normal vessel, what is the velocity within it?

Answer 29

Doubled

Question 30

Not only is volume flow rate maintained, but the energy within a fluid system is kept in balance as well.

Answer 30

Bernoulli’s Principle

Question 31

Decreased acceleration time and PSV after a stenosis

Answer 31

Tardus parvus

Question 32

Continued forward flow in the aorta during diastole due to the elasticity of the vessel walls

Answer 32

Windkessel effect

Question 33

What happens to flow when the pressure wave along the walls of the vessel reaches the end of the arterial system? Why?

Answer 33

Flow reversal because the pressure wave moves faster than the blood flowing within and it gets reflected when it reaches the end

Question 34

What explains how the body maintains a constant flow rate in the presence of disease.

Answer 34

The continuity rule.