Hemodynamics from new textbook Flashcards
How much blood is pumped out of the heart per minute?
5-6L
Equation for cardiac output?
CO=SVxHR
Bernoulli’s principle:
Pressure and velocity have an inverse relationship
Poiseuille’s Law
The higher the pressure gradient, the more flow. The more viscous the fluid, the less flow there is. The longer the tube, the more resistance and less flow
What’s the component that’s most likely to change in Poiseuille’s Law?
Radius
The more vessels there are in a parallel, the ____ the resistance
lower
What is the 0 velocity at the vessel wall called?
Boundary layer
What’s the most common flow found in the body?
Laminar
Reynold’s #
Signifies turbulance. >2000
When do you see a tardus parvus?
With a proximinal obstruction
Critical stenosis is defined as:
Area reduction >75%
Diameter reduction >50%
3 Ways for venous blood to return to the heart:
Calf muscles
Valves
Intrathoracic pressure changes
Doppler shift:
change in frequency of sound caused by a moving reflector when observed by a stationary source
What causes the Doppler shift in US?
RBC’s
Strongest/most accurate DS:
0
Lowest DS:
90
Should you increase or decrease the Doppler angle to reduce aliasing?
Increase
RI is:
Peripheral resistance to flow
PI is:
how dampened a waveform is
RI formula:
PSV-EDV/PSV
PI formula:
PSV-EDV/mean velocity
What is the most common gray scale artifact? How can it be fixed?
Reverb
THI
What vessel are we likely to see color Doppler mirroring?
SCA
You see a color bruit (color pixels present in soft tissue). What could be causing it?
Commonly occurs as a result of a stenosis in a nearby vessel, causing a thrill in the adjacent tissue
Monophasic flow in a resting lower extremity artery …
Indicates dilatation in the distal arterioles, which can be indicative of moderate to severe disease
In the venous circulation, which of the following is the only variable of hydrostatic pressure?
Height, gravity, density or viscosity
Height (only variable in the equation)
????What about gravity
Ohm’s law is analogous to Poiseuille’s law, where current is represented by:
Ohm’s law (I = V/R) is analogous to Poiseuille’s law (Q = ΔP/R). Pressure is represented by voltage, flow is current, and resistance is the same for both
What is the Ohm’s law equation:
I=V/R
Which of the following is representative of normal lower extremity peripheral venous flow?
(A) Pulsatile flow
(B) Respiratory phasicity
(C) High transmural pressure
(D) Nonspontaneous flow
Lower extremity peripheral venous flow should be spontaneous, have respiratory phasicity, be noncontinuous, and be nonpulsatile. Veins typically have low transmural pressure, and will appear elliptical when supine due to the increased pressure outside the vessel compared to the pressure inside the vessel.
Rayleigh scatters:
Scatter to the fourth power of the frequency
A sonographer switches to a higher frequency transducer. What effect will that have on aliasing?
Increased risk of aliasing. Freq shift is directly related to operating frequency. The higher the frequency shift, the greater the risk for aliasing.
FFT
Spectral Doppler
Autocorrelation
Color Doppler
The higher the ensemble length (packet size)…
the better the ability to document slow flow and the more accurate the measured mean velocities. Tradeoff is a worse frame rate
Aliasing occurs for which of the following reasons?
(A) The velocities are too low
(B) The PRF is too high
(C) The sampling rate is too slow
(D) The sampling rate is too high
C
Increasing the pulse repetition frequency
(A) Decreases the number of cycles in a pulse
(B) Decreases the number of pulses per second
(C) Increases the imaging depth
(D) Increases the measurable frequency shift
D
more accurately measure acceleration time. Which control needs to be adjusted so the waveform can be stretched out to permit a more accurate measurement?
(A) Doppler gate
(B) Scale
(C) Wall filter
(D) Sweep speed
D
What angle to flow is the most accurate?
(A) 0 degrees
(B) 90 degrees
(C) 60 degrees
(D) 15 degrees
0
What is the most optimal angle for 2D, gray scale imaging?
(A) 0 degrees
(B) 90 degrees
(C) 60 degrees
(D) 15 degrees
B
How many samples per cycle to avoid aliasing?
2-3
When must angle correction be used in spectral Doppler?
(A) At all times
(B) Any time continuous-wave Doppler is used
(C) Whenever arterial flow is measured
(D) When velocity information is needed
D. Angle correction is possible with PW spectral Doppler. Angle correction permits peak systolic and end diastolic flow velocities to be measured. Angle correction is not limited to arterial flow, as there are some studies where venous velocities need to be measured. Angle correction is not possible with CW Doppler.
Which of the following is directly related to the amplitude of the Doppler shift?
(A) The Doppler angle
(B) The operating frequency
(C) The velocity of flow
(D) The number of red blood cells present
D
Which setting can be adjusted to permit color Doppler twinkling artifact as an aide in identifying small calcifications?
(A) Scale
(B) Frequency
(C) Priority
(D) Persistence
C – allows color pixels to replace grayscale pixels (or vice versa) as selected by the operator
Which of the following is a constant and does not change in a nonhemodynamically significant stenosis?
(A) Area
(B) Velocity
(C) Flow
(D) Pressure
(C) Flow is a constant and does not change in a nonhemodynamically significant stenosis.
