What is the movement of fluid from one location to another?
Fluid moving with a variable velocity, that accelerates and decelerates; what is it?
What is fluid moving from one location to another that accelerates and decelerates from respiration called?
What type of flow pattern will be seen with normal physiological states?
Chaotic flow with many directions and speeds, whay type of flow is this?
Frictional loss occurs when one object rubs against another. Blood sliding across vessel walls would be considered what?
Know the Reynolds numbers
< 1500= laminar
What are the effects of stenosis?
change in flow direction
increased velocity as vessel narrows
turbulence downstream from the stenosis
pressure gradient across the stenosis
loss of pulsatility
What is hydrostatic pressure?
pressure related to the weight of blood pressing on a vessel measured at a height above or below heart level
Hydrostatic pressure in a supine patient with a blod pressure of 140mmHg
all measurement sites= 0mmHg
Hydrostatic pressure while standing upright in a patient with a blood pressure of 140mmHg:
ankle: level-far below heart level, hydrostatic pressure-100mmHg, measured pressure-240mmHg
knee: level-somewhat below heart, hydrostatic pressure-75mmHg, measured pressure-215mmHg
waist: level-slightly below heart, hydrostatic pressure-50mmHg, measured pressure-190mmHg
mid chest: level-heart level, hydrostatic pressure-0mmHg, measured pressure-140mmHg
top of head: level-above heart, hydrostatic presure--30mmHg, measured pressure-110mmHg
What does the Doppler shift provide information about?
measures the velocity of blood in the circulation
What is a positive Doppler shift?
blood moves towards transducer (arteries)
What is a negative Doppler shift?
blood moves away from transducer (veins)
What is the typical range of a Doppler shift?
20Hz to 20,000Hz (range of audible sound)
What is the phenomenon where high velocities appear as negative?
When the sample volume is deep, the PRF is what? Nyquist limit?
What are the 5 ways to eliminate aliasing?
adjust the scale to its maximum-increases Nyquist limit
select a new ultrasonic view with a shallower sample volume-increases Nyquist limit
select a lower frequency transducer-decreases Doppler shift
use baseline shift-aliasing remains but display more appealing
use continuous wave Doppler-never aliases, but range ambiguity
Know about large and small sample volumes. Which one will fill in on Doppler?
large spectral broading
What do the X and Y axis stand for on the Doppler spectrum?
Y=shift or velocity
What 2 things are related to Doppler spectrum?
amplitude of the reflected signal
number of blood cells creating the reflection
When we look at our Doppler Spectrums and we see our wave form, if you have a higher waveform, is a higher freq or lower freq being used?
What is Doppler shift inversely related to?
What is the basic Doppler system that simply identifies blood flow by the pressence of the frequency shift?
What is the Doppler effect?
What is the difference betwen speed and velocity?
speed measures distance
velocity measures magnitude and direction
Know about angles with Doppler:
when the angle between the direction of motion and sound is 0º or 180º, flow is parallel to the sound beam
the measured and true velocities are equal: Cosine 0º=1 (flow toward transducer), Cosine 180º=-1 (flow away from transducer)
Cosine 90º=0 (perpindicular/normal incidence can not measure Doppler shifts and velocities
What's a primary advantage for pulsed wave Doppler?
range resolution (being able to select the exact location where velocities are measured)
What's the primary advantage to continuous wave Doppler?
ability to accurately measure very high velocities
What kind of processing does bidirectional Doppler use?
Fast Fourier Transform (FFT) is used in what type of process?
used to process both pulsed and continuous wave Doppler signals
What type of velocities does color flow measure?
negative and positive shifts
slower and faster velocities
laminar and turbulent flow
What is autocorrelation?
a digital technique used to analyze color flow Doppler
What are the personal limitations to color flow imaging?
more time needed to aquire data
reduced frame rate
decreased temporal resolution
What is the area of interrogation in a Pulsed Doppler jam called?
What are the advantages and disadvantages of large Doppler packets?
more accurate velocity measurement, increased sensitivity to low flow
more time needed to aquire data, reduced frame rate, decreased temporal resolution
How do you measure low flow rates?
Know about inspiration:
diaphragm moves upward toward abdomen
thoracic pressure decreases
abdominal pressure increases
venous return to the heart increases
venous flow in legs decreases
Know about expiration:
diaphragm moves upward into thorax
thoracic pressure increases
abdominal pressure decreases
venous return to the heart decreases
venous flow in legs increases
When venous pressure is low, what is the volume of pressure in the veins?
What happens to the shape of veins when the venous pressure increases?
becomes more circular