Physics 2 Test Ch 18, 19, 20 Flashcards
What kind of flow is moving with a variable velocity from cardiac contractions?
Pulsatile Flow
pg 286
What kind of flow is moving with a variable velocity from respirations?
Phasic Flow
pg 286
What is laminar flow?
Flow streamlines are alined and parallel. Characterized by layers of blood that travel at individual speeds. Laminar flow patters are commonly found in normal physiologic States. Two types of flow are plug(all layers of blood travel at the same velocity). Parabolic (bullet shaped with velocity highest in the center)
Pg 287
What is chaotic flow?
Turbulence
pg 288
What are frictional losses?
Viscous(thickness), frictional (heat), inertial(tendency of fluid to resist changes in velocity)
Occurs when flow energy is converted to heat as one object rubs against another.
pg 290/291
What is the Reynolds number for turbulent flow?
Greater than 2000
pg 288
What are the effects of a stenosis?
Change in flow direction increased velocity as vessel narrows turbulence downstream from the stenosis pressure gradient across the stenosis loss of pulsatility pg 292
What is hydrostatic pressure in a supine position?
All parts of the body are at the same level as the heart so… The hydrostatic pressure is zero.
Pg 297
What is hydrostatic pressure in a standing position?
Finger in air -50 Heart 0 Waist 50 Knee 75 Ankle 100
What is coaptation?
When you can compress the vein.
When you breath in, what happens to the pressure in the legs, abdomen, and chest?
Inspiration
Diaphragm moves downward Thoracic pressure decreases Abdominal pressure increases Venous return to the heart increases Venous flow in legs decreases
pg 301
When you breath out, what is happening to the pressure of the legs, abdomen, and chest?
Expiration
Diaphragm moves upward Thoracic pressure increases Abdominal pressure decreases Venous return to the heart decreases Venous flow in legs increases pg 301
What is a positive Doppler shift?
When blood moves toward the transducer. The reflected frequency is higher than the transmitted frequency.
Pg 304
What is a negative Doppler shift?
When blood moves away from transducer. The reflected frequency is lower than transmitted frequency.
pg 304
What information does a Doppler shift tell us?
the velocity of blood cells in circulation (venous going away or arterial coming toward).
Doppler shift is directly related to frequency of transmitted sound.
pg 303
What is the normal Doppler shift range in diagnostic imaging
20 Hz and 20kHz
audible range
pg 338
What is aliasing?
Most common error with Doppler. Very high velocities in one direction are incorrectly displayed as going in the opposite direction.Wrap around appearance.
pg 315
The phenomenon where high velocities appear in the opposite direction
pg 338
When the sample volume is deep, PRF is _____ and the Nyquist limit is _____.
low / low
pg 317
What are the 5 ways to eliminate the effects of aliasing?
Adjust scale to maximum Select a new view with shallower volume Lower frequency Change the base line Use a continuous wave Doppler pg 319
The sample volume should always be at 2 mm; however if you are using a larger gate the Doppler will look different, will it be larger or smaller?
larger (aliasing)
pg 317
What is the y-axis on the Doppler spectrum?
velocity
pg 307
What is the x-axis on the Doppler spectrum?
time
pg 307
What are the gray shades on the Doppler spectrum related to?
Amplitude of the reflected signal.
Number of blood cells creating the reflection.
pg 324
A higher frequency transducer creates a Doppler spectrum that is _____.
High, because they are directly related
p. 308
Doppler shift is inversely related to _____.
Propagation speed
pg 306
What kind of processing is used in bidirectional Doppler?
Phased quadrature
P.311
What is the difference between speed and velocity?
Speed is magnitude 50 mph
velocity is magnitude plus direction 50 mph to the south
pg 305
What kind of Doppler shift will be recorded at a 90 degree angle?
No Doppler shift
pg 338
Higher frequency transducers will produce a Doppler shift that is _____ than a lower frequency transducer.
higher
Doppler shift is directly related to frequency of transducer.
pg 308
What is the primary advantage for pulsed wave?
Being able to see the exact location where the velocity is being measured. Range resolution, range specificity, and freedom from range ambiguity.
pg 314
What is the primary advantage of continuous wave?
Accurately measuring very high velocities
pg 312
What is Fast Fourier Transform?
A digital system used to process both pulsed and continuous wave Doppler signals. 2 advantages are exceedingly accurate and displays all individual velocity components that make up the complex reflected signal. It distinguishes laminar from turbulent flow.
Laminar flow well cleaned windows.
Turbulent flow broadening spectrum and filled in windows.
pg 336
What is Autocorrelation?
A digital system that is used to analyze color flow Doppler. This process is less accurate but faster to perform than FFT.
pg 337
What is color Doppler looking for?
It provides us with the direction of flow. Color Doppler gives us mean velocity were as pulsed and continuous wave measure the peak velocity.
pg 325
What are we measuring with continuous wave Doppler?
We are measuring all the moving blood cells in the overlap region.
High velocities
pg 312
What is a limitation for color Doppler?
creates aliasing?
What are Doppler packets?
With color multiple U/S pulses are used to accurately determine blood velocities. 2 advantages of larger packets are more accurate velocity measurement and increased sensitivity to low flow. 3 disadvantages are more time needed to acquire data, reduced time frame, and decreased temporal resolution.
pg 332
What is sensitive to low flow states?
Power Doppler
pg 333
What is the movement of one fluid from one location to another referred to as?
energy gradient
pg 289
Possibly velocity Pg. 285
What is the shape of the venous structure at high pressure?
circle
pg 295
What is the shape of the venous structure at intermediate pressure?
oval
pg 295
What is the shape of the venous structure at low pressure?
hourglass
pg 295
