Flashcards in Physics Test Ch. 18, 19, 20 Deck (52)
What is flow?
Also called volume flow rate
Indicates the volume of blood moving during a particular time. Measurements answer the question "how much?"
Units: volume divided by time; L/min
What is velocity?
Indicates the speed or swiftness of a fluid moving from one location to another. Answers the question "how fast?"
Units: distance divided by time; cm/s
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?
Depends upon whether the measurement is made above or below heart level.
Top of head: -30 mmHg
Heart: 0 mmHg
Waist: 50 mmHg
Knee: 75 mmHg
Ankle: 100 mmHg
Reynold's number predicts..
whether flow is laminar or turbulent
What is the Reynold's number for laminar flow?
Less than 1,500
Pressure related to the weight of blood pressing on a vessel measured at a height above or below heart level
When you breath in, what happens to the pressure in the legs, abdomen, and chest?
-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?
-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
Speed vs. Velocity
Speed: which is purely a magnitude, indicates the distance that a red blood cell moves in 1 second. Units- cm/s
Velocity: defined by a magnitude and a direction. example- think of velocity as an arrow, where the length of the arrow indicates its magnitude, and the angle at which the arrow points indicates the direction.
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
When the sample volume is shallow, PRF is ____ and the Nyquist limit is ____.
What are the 5 ways to eliminate the effects of aliasing?
-Adjust scale to maximum
-Select a new view with shallower volume
-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
Less aliasing vs. More aliasing
-slower blood velocity
-lower frequency transducer
-shallow gate (high PRF)
-faster blood velocity
-higher frequency transducer
-deep gate (low PRF)
What is the y-axis on the Doppler spectrum?
velocity pg 307
What is the x-axis on the Doppler spectrum?
time pg 307