Module 4 Physics Flashcards
What is the average flow speed across a laminar parabolic flow vessel?
It is one half of the max flow speed (at the centre)
What is the entrance affect?
this is when we see plug flow - typically when we are entering a larger artery into a smaller radius or ascending aorta
When does turbulent flow occur
In an area of stenosis or bifurcation
What does a waveform of turbulent fllow look like
ragged edges and SB
What is the Windkissel effect?
During systole, the LV contracts pushing blood into the aorta and larger arteries causing expansion of walls with increased pressure, then when diastole occurs the LV relaxes and release ith elastic recoil of the arteries allowing for blood to push through during diastole too
What type of arteries perform the windkissel effect?
aorta and larger arteries because they have more elastic components to stretch and recoil
Kinetic energy formula”
velocity squared
What is hydrostatic pressure?
it is the force of fluid, proportional to the density of fluid, height of fluid and gravity
Hydrostatic pressure formula
density x gravity x height
What is the resistance equation
8ln/pier^4
n - viscosity
r- radius
What is the flow equation?
Q = pressure difference / resistence
BP equation
CO x TPR
Where is the highest pressure in the body?
left ventricle 100 mmHg
Which have lower pressures? Arteries or veins?
Veins - arterial side is higher because of the pumping of heart
Where is the lowest pressure in the body
the right atrium 0mmHG
Most energy loss happens where?
at the capillaires
What is Poiseuilles Equation
Q = change in pressures x pie x r^4 / 8 x l x n
What is the continuity rule
flow rate must remian constant regardless so if area changes velocity must change and vise sersa
Q = v x area
this is why in a stenosis (decrease area) the velociuty increases
Where are the highest velocities typically
just beyond the point of max narrowing
What is the bernouilli effect
increase in flow speed = decrease in pressure
What is the Doppler Effect?
The Doppler Effect is a change in frequency due to change in wavelength from a change in motion
Wavelength formula
wavelength = c/f
Increasing wavelength will ___ frequency?
decrease freq
What causes the best change in frequency with Doppler imaging?
when the angle is 0 deg
What is the Doppler Shift (DS)?
A measure of doppler effect - how much the frequency has changed
it is the difference between transmitted vs recieved frequency
DS = F recieved - F transmitted
What is indicative of a higher DS?
faster moving blood
How to calculate the doppler shift (simplified doppler equation)
Change in freq = 2 X Ft X velocity / C
What angle do we want to be at when using Doppler?
Want to be perfectly parallel (0 deg) but often impossible - best to be less than 60 deg or else large error
Is CD a qualitative or quantitative assessment?
qualitative
Does CD show velocities of flow?
Yes but theyre only estimates, SD shows absolutes
What is the packet size? What does a higher packet size indicate? What is the packet size of CD ?
the amount of pulses per SL (CD has about 3-12)
higher packet size = more accurate estimate of DS freq
What is flow seperation?
Can look like aliasing but has a black line surrounding the change in colour - it is the reversal of blood flow (aliasing is not tis just an artifact)
What is the highest detectable mean velocities in CD
63.6 cm/s away or towards
What must the PRF scale equal in CD?
must be 2x higher than the highest DS freq
How to determine the Nyquist Limit
Max DS = PRF/2 or PRF = 2x the max DSF
What does power doppler display
The density of moving RBC (amplitude of rayleigh scatter)
doesnt display DSF
What does SD display?
a visual spectrum of DS frequencies over time
direction, velocity (absolute), amplitude, quality of flow
When is Fast Fourier Transformation used?
FFT only used with SD - like autocorrelation for CD, displays wide variety of DS into their individual frequency components to plot on graph
How does FFT work?
Sorts the many DSF into groups called bins of similar DSF
each bin corresponds to a spot on the Y axis
more DS in a bin = brighter
how does the SVB size affect the SPL?
increase SVB increases the SPL whihc decreases Axial Res
Relationship between PD and BW
longer ringing period (PD) results in less frequencies/bandwidth but greater sensitivity
What should the spectral trace height be?
about 2/3 of the y axis
What is the angle for the most accurate measurement in SD
0 deg (cosine for 0 is 1)
Other names for AC?
angle of insonation and angle of incidence
What is the returnign signal from blood like?
low amplitude but high DSF
What is the returning signa from tissue?
high amplitude but low DSF
