Doppler Review Flashcards
What is the formula for velocity of blood flow?
V = [f (Freq change) x C (spd of sound)] / 2 x fo (operating freq) x Cos theta
What is the main advantage of PW doppler?
Range specificity - Able to map velocities at any point in the heart
What are the two main things PW Doppler is limited by?
- Nyquist limit/PRF (aliasing)
2. Speed of sound in soft tissue
What is the Nyquist limit and when is it exceeded?
1/2 PRF
When the scale is exceeded (1/2 PRF) aliasing will occur
What is the main advantage of CW?
Can measure high velocities
What is the main disadvantage of CW doppler?
No range resolution (only the max velocity is measureable)
Why is TDI more intense?
Tissue is more dense
What relationship does the Bernoulli Equation outline?
The inverse relationship between velocity and pressure.
What is the simplified Bernoulli?
Change in P = 4V^2
How is the maximum pressure gradient calculated?
Using the Simplified Bernoulli formula but using the max velocity
How can pressure gradients be underestimated?
By not sampling completely parallel to flow
How would a 20 degree offset from flow direction affect the calculation of the blood flow velocity?
A 20 degree offset from flow direction = 6% underestimation of blood flow velocity
What must be done when calculating the velocity or pressure gradients in the presence of arrhythmias?
Measuring 3-5 beats and the averaging to find the answer.
3 factors that would lead to an underestimation of pressure gradients?
- Flow acceleration (prosthetic valves)
- Viscous forces (long stenosis over 10 mm, eccentric wall jets)
- Increased proximal velocities
When must the expanded Bernoulli equation be used?
When measuring velocities greater than or equal to 1.2 m/s
What is the “Peak to Peak” gradient?
When a catheter is used to derive the pressure gradient it measures the difference between the peak LV pressure and the peak aortic pressure
In the presence of aortic stenosis, how is the doppler derived pressure gradient affected?
It will be higher than a normal AV and it will be higher than the catheter derived gradient as well.
What is another name for stroke volume?
The volumetric flow rate
What is the formula for SV?
SV = CSA x VTI
What is the formula for CSA?
CSA = 0.785 x D^2
How is VTI measured?
From a trace of the area under the spectral trace when doing CW or PW on the AV
What is the formula for CO?
CO = (CSA x VTI x HR) / 1000
How does the SV differ between the valves in a normal heart?
It doesnt, the SV should be the same in every valve.
What is the formula for SV of a regurg valve?
SV regurg valve = SV competent valve + Regurgitant Volume
What is necessary to calculate the Regurg Volume and what is the formula?
An estimation of the SV through the regurg valve
Regurg volume = SV regurg valve - SV competent valve
What is the regurgitant fraction?
RF = Regurg volume / SV regurg valve
What does Peak Velocity measure? (2)
- Peak velocity
- Max Instantaneous Pressure Gradient
If the area of a valve is reduced by half, how is the velocity affected?
It doubles
What does Velocity Time Integral measure (VTI)? (4)
- Peak velocity
- Mean velocity
- VTI (cm)
- Max PG
- Mean PG
How does the VTI shape differ in the presence of stenosis?
Parabolic
What does acceleration time measure?
The time is takes for any flow to reach its peak velocity
What does deceleration time measure? (3)
- Peak velocity
- Deceleration time
- Deceleration slope
What is pressure half time?
The time it takes for the pressure to decay to half it’s original value
What does the Pressure Half time measure?
- Peak velocity
- Slope
- Pressure half time
What is important to note about sweep speed?
It affects accuracy
What does Delta P/Delta T measure?
The rise (or fall) of the pressure divided by the change in time when MR is present
What must be increased in order to measure change in pressure / change in time?
Sweep speed to max setting
