Chp 4 - Hemodynamics and Doppler Flashcards
What does Bernouillis Principle describe?
the inverse relationship between velocity and pressure
What is the continuity equation
Q = VA - change in velocity must occur in a change of area to maintain the volume of blood flow
What is directional PD
uses CD and PD - sensitivity of PD but direction of flow from CD
What is duplex imaging
real time 2D imaging with SD
What is the ensemble length?
the number of pulses per SL in CD (aka packet size)
What is FFT?
Fast Fourier transform - process for processing doppler signal to produce SD
What is the flow equation?
Q = volume of blood/time
What is the frequency shift?
the difference between the transmitted and received frequencies
What is Ohm’s law?
A law used in electronics where flow = pressure differential / resistence
V=IR
What does the phase quadrature do?
determines positive and negative frequency shifts in doppler therefore direction of flow
What is the vasa vasorum?
a network of small BV that supply blood to the walls of arteries and veins
When do we have energy loss related to inertia?
every time blood changes direction
Where is plug flow found?
in large BV and at the entrance of vessels
it is a result of systole
What Reynolds number represents true turbulence
greater than 2000
Reynolds number equation
Re = v X 2r X p / viscosity
v = velocity of blood
What AR and DR = hemodynamically significant
75% decrease in area and 50% decrease in diameter
Where is the highest hydrostatic pressures typically located
at more distal parts of the body like feet and ankles
What is transmural pressure
the difference between the pressure inside the vein and surrounding tissue
What happens with an increased transmural pressure?
flow inside the vein is higher than the surrounding tissue - the vein get sthe circular shape (it will collapse when lower)
What does it mean if there is pulsatility in the peripheral veins?
may indicate problems with the right side of the heart
When is tardus parvus seen?
when there is a proximal obstruction
What is the doppler effect?
When frequencies of sound hit a moving object the frequencies come back higher
What is the relationship between frequency and scatter?
as frequency increases, scatter increases to the fourth power
What is the RI formula?
RI = PSV - EDV / PSV
PI formula?
PI = PSV-EDV / mean velocities
Nyquist limit formual:
1/2 of the PRF
In CD what does increasing the persistence setting do?
it reduces the effect of noise and makes it easier to follow small vessels
but decreases FR
What is tissue doppler used for?
cardiac imaging
high amplitude, low velocity
What provides the potential energy in the cardiovascular system?
The beating heart
When is the Doppler shift highest?
When the beam is parallel to the direction of flow
When a reflector moves toward the transducer, what will happen to the
reflected frequency?
It will be increased
In the exercising patient, what is the response to peripheral resistance with arteriolar dilatation?
the peripheral resistence decreases
What will happen with under sampling of the blood flow?
aliasing
What is the spectral amplitude/brightness that make up SD represent?
the amount of RBC
The doppler shift is lowest at what angle?
90 deg
What is the fewest number of crystals a PW Doppler device may have?
one
Which type of Doppler does not rely on the frequency shift but instead
relies on the strength of the shift?
Power Doppler
What is the duty factor of CW Doppler?
1
What is seen proximal to a low resistence bed?
monophasic flow
