Exam 5 Flashcards
What is hemodynamics?
The Study of Blood Moving Through the body
Flow vs Verlocity
Flow = How much (Volume/time)
Velocity = How fast (distance/time)
What is Phasic flow?
Blood moves with variable velocity.
Accelerates & decelerates as a result of respiration.
Venous circulation
What is pulsatile flow?
Blood moves with a variable velocity. Accelerates and decelerates with cardiac contractions.
Commonly appears in arterial circulation
What effect will the following have on flow and resistance?
Blood vessel radius:
>diameter (bigger)/ < diameter (smaller)
viscosity:
> viscosity(thicker) / < viscosity (thinner)
Length:
>length (long) /
Blood vessel radius
• < diameter = > resistance & < Flow
• > diameter = < resistance & > Flow
Viscosity of blood • > viscosity = > resistance & < Flow • < Viscosity = < resistance & > flow Blood vessel length • > length = > resistance & < Flow • < length = < resistance & > flow
Laminar Flow
Plug Flow
Parabolic Flow
Turbulent flow
Laminar Flow: Normal Blood flow, layers of blood that travel at individual speeds.
Plug: All layers and blood cells travel at the same velocity. - Big vessels such as aorta
Parabolic: Layers travel at individual speeds. Speed is highest at center. - Most common in arteries.
Turbulent flow : flow is chaotic, moving in many different directions- Cardiovascular pathology
Reynolds number predicts what?
Reynolds number is a unit-less number indicating laminar of turbulent flow.
Laminar flow = Reynolds number < 2,000
Turbulent flow= Reynolds number >2,000
ENERGY GRADIENT
BLOOD MOVES FROM REGIONS OF HIGHER ENERGY TO LOWER ENERGY
What is stenosis?
Narrowing of a vessel
In regards to Stenosis, where will you see highest blood velocity & where would turbulent flow be seen?
Where will you see highest velocity? At/in stenosis
When will you see turbulent flow? Post-Stenosis
What effect will stenosis have on blood velocity an pressure?
In stenosis; Velocity highest, pressure down
After stenosis; Turbulent, velocity down, pressure up
What physics principle describes the relationship between blood flow and pressure?
Bernoulli’s principle
Pressure Gradient & Blood flow
The amount of flow is proportional to the pressure gradient. The bigger the pressure gradient, the more blood flow.
Hydrostatic pressure
Energy created as a result of gravity, heaviest pressure at bottom.
Measured in units of mmHg (mm per mercury)
What is the hydrostatic pressure at the level of the heart?
0 mmHg
Measured pressure equation
Measured pressure=circulating pressure + hydrostatic pressure
Example: The BP generated by the heart in a patient who is standing is 140mmHg (Circulatory pressure), what is the arterial measured pressure at the patients waist? 140mmHg+50mmHg= 190mmHg
What is the hydrostatic pressure in the following locations in a STANDING individual?
HEART
HEAD
WAIST
ANKLE
HEART; 0 mmHg
Head; -30 mmHg
Waist; 50 mmHg
Ankles; 100 mmHg
What is the hydrostatic pressure in the followin locations in a SUPINE individual? Heart Head Waist Ankle
0 mmHg
What happens during inspiration?
Diaphragm moves down - Less pressure
ABD - More pressure
Venous blood flow to legs- Decreased
What happens during experation?
Diaphragm moves up- More pressure
ABD pressure - Less Pressure
Venous blood flow to legs increased
If RBC are moving toward the transducer, the reflected frequency Doppler shift will be _____________ than the transmitted frequency. This is ________ Doppler shift
If RBC are moving toward the transducer, the reflected frequency Doppler shift will be HIGHER than the transmitted frequency. POSITIVE Doppler shift.
If the RBC are moving away from the transducer, the reflected frequency Doppler shift will be _____________ than the transmitted frequency. ________ Doppler shift
If the RBC are moving away from the transducer, the reflected frequency Doppler shift will be LOWER than the transmitted frequency. NEGATIVE Doppler shift
Th doppler equation
Doppler shift=(2 x Velocity x transducer frequency x cos)/(Propagation speed)
Which parts of the Doppler Equation are constants?
What effect does the velocity of blood have on the Doppler shifts?
What effect does transducer frequency have on the Doppler shifts?
What effect does the cosꙨ have on the Doppler shifts?
Which parts of the Doppler Equation are constants?
2 & propagation speed
What effect does the velocity of blood have on the Doppler shifts?
Directly related
What effect does transducer frequency have on the Doppler shifts?
Directly related
What effect does the cosꙨ have on the Doppler shifts?
Directly related
What Doppler angle has a cos of (1)
What Doppler angle has a cos of (.5)
What Doppler angle has a cos of (0)
How are cos and Doppler angle related?
What is the best angle for 2D gray scale imaging, what is the most accurate angle for Doppler?
What Doppler angle has a cos of (1) 0
What Doppler angle has a cos of (.5) 60 - Half of actual doppler shift
What Doppler angle has a cos of (0) 90 no doppler shift can be measure.
How are cos and Doppler angle related? Indirectly
What is the best angle for 2D gray scale imaging, what is the most accurate angle for Doppler? 60 Or less
How is Doppler information displayed?
Spectral doppler display
How is spectral doppler display accomplished?
Fast Fouier Transform (FFT)
How doppler info gets from transducer to graph
How will turbulence appear on the Spectral doppler display?
Spectral broadening - Spectral window filled in
How will laminar flow appear on spectral doppler display?
The presence of a spectral window implies the presence of laminar flow.
Continuous wave doppler
How many crystals?
Advantages
Disadvantages
How many crystals?
2 crystals – one constantly transmits and one constantly receives reflections from the red blood cells.
ADVANTAGE: Accurately measure very HIGH velocities (Aliasing artifact does not occur) , Small probe size, & higher frequencies can be used. No speed limit.
DISADVANTAGE: Exact location of the red blood cells cannot be determined. Signals are arising from all blood cells in the region of beam overlap – RANGE AMBIGUITY
Pulsed Wave Doppler
How many crystals?
Advantages
Disadvantages
How many crystals?
1 Single crystal will transmit and than wait to receive the returning signal
ADVANTAGE:
Able to select the EXACT location, this is called RANGE RESOLUTION or RANGE SPECIFICITY
DISADVANTAGE:
Inaccurate measurement of high velocity signals, the high velocity flow in one direction will be incorrectly displayed as traveling in the opposite direction, this is known as ALIASING.
When will aliasing occur?
Aliasing is the most common error associated with doppler ultrasound. Aliasing occurs when velocity is above the nyquist limit.
How is the Nyquist limit (Nyquist Frequency) determined?
By equation
Nyquist limit (Hz)=(PRF(Hz))/2
This equation states that the highest frequency shift that can be measured is equal to one half the pulse repetition frequency.
What are 5 steps you can take to fix Aliasing?
- Increase PRF scale setting will Raise the Nyquist limit
- Lower baseline
- Depth – move transducer so image is shallow
- Frequency- lower frequency = smaller doppler shifts are less likely. To exceed Nyquist limit
(higher frequency =higher doppler shift thus creating more aliasing) - Continues wave transducer – because this has no aliasing
Color Doppler
What velocities are displayed by color Doppler?
Is color Doppler continuous wave or pulsed wave?
What are the two types of color maps used to display color Doppler information?
What is advantage of a larger color packet/ensemble?
What is a disadvantage?
Color Doppler
What velocities are displayed by color Doppler?
Averae/mean velocity
Is color Doppler continuous wave or pulsed wave?
Pulsed
What are the two types of color maps used to display color Doppler information?
Velocity or Variance Mode
What is advantage of a larger color packet/ensemble?
More accurate velocity measurement
What is a disadvantage?
Increased sensitivity to low flow
Power Doppler (energy mode or angio mode)
Does Power Doppler report velocities or direction?
Advantages:
Disadvantages:
Power Doppler (energy mode or angio mode)
Does Power Doppler report velocities or direction?
Only identifies the presence of the doppler shift, no speed or direction. The strength (amplitude) of the reflected signal is processed not the direction or speed.
Advantages:
- ) Increased sensitivity to LOW flow
- ) Unaffected by Doppler angle (unless exactly 90*
- ) NO aliasing (velocity information ignored)
Disadvantages:
- ) No velocity Measurement
- ) Lower temporal resolution
- ) Susceptible to motion artifact (flash artifact)
Doppler Artifacts
• Crosstalk
why does crosstalk occur?
How to fix cross talk;
Doppler Artifacts
• Crosstalk
o A Spectral doppler form of “mirror image” artifact
o Appears as identical doppler spectrum above and below the baseline.
why does crosstalk occur?
Gain is TOO HIGH -OR- Angle is close to 90*
How to fix cross talk;
Decrease gain
Adjust angle (<90*)
