Module 1 : Doppler Review Flashcards
6 purposes of doppler in echo
- detect areas of normal flow
- detect areas of abnormal flow
- differentiate between tissue and areas of blood flow
- assess systolic function
- assess diastolic function
- provides functional info (pressure gradients through valves)
4 advantages to PW doppler
- range specificity
- adjustment of sample volume size and position
- able to map any velocities at any point in the heart
- 2D display
2 disadvantages to PW doppler
- inability to measure due to aliasing
- limited by the speed of sound in tissue and PRF
main advantage to CW doppler
- high velocity range (sample high velocities)
main disadvantage to CW doppler
- no range resolution
+ only max velocity is measurable along a scan line
+ can’t be sure that a velocity is coming from a specific location
tissue doppler imaging TDI characteristics
- movement of myocardial tissue not red blood cells
- TISSUE DOPPLER SIGNAL IS GREATER INTENSITY(brighter) = almost all echoes return
4 advantages to TDI
- easily reproducible
- provides other systolic and diastolic info in one waveform
- can be performed on every patient
- less volume dependant than MV inflow
5 disadvantages to TDI
- TDI is angle dependant
- ideally e primes measured at end expiration (larges e wave)
- filter settings can vary between vendors
- gain setting on Phillips to low
- velocity will be lower than myocardium in rest of LV if they have (prosthetic valves, MAC, mitral annular ring)
baseline settings for spectral doppler
- flow toward probe = baseline lowered to 1/4 from bottom
- flow away probe = baseline raised to 1/4 from top
- for pulmonary valve = baseline middle
- wave form should take up 50% of available scale
speed of MR flow
5-7m/s
3 advantages to color doppler
- sensitivity = can detect small amount of flow
- region of interest = anatomic and hemodynamic info on one image
- laminar vs turbulent = determine laminar flow from turbulent
2 disadvantages to color doppler
- aliasing = blood flow exceeds color scale
- directional ambiguity = blood flow perpendicular confuses machine not sure where blood is flowing
Bernoulli equation relationships (velocity and pressure)
- as velocity of a moving fluid increases the pressure within the fluid decreases
- the drop in pressure creates a pressure difference between the region proximal to a narrowing and within the narrowing
simplified Bernoulli equation
P1 - P2 = 4V^2
maximum instantaneous gradient
- calculated from a maximum velocity
- P max = 4V^2 max
mean pressure gradient
- calculated by averaging the instantaneous gradients over the ejection period
7 limitations of pressure gradient estimations
- you must be parallel to blood flow
- values are usually higher than invasively derived values
- 20 degree offset from flow direction = 6% underestimation of velocity
- must measure 3-5 beats when arrhythmias are present
- significant flow acceleration
- viscous forces
- increased proximal velocities
continuity principle
- the volumetric flow rate (stroke volume) through a tube of a constant diameter is equal to the product of the criss sectional area(CSA) of the tube and mean velocity of fluid through the tube (VTI)
stroke volume equation
SV = 0.785D^2 x VTI
if there is no significant regurge or stenosis what will the volume of flow be through each valve
- it will all be equal
with a regurgitant valve what will eb the change in volume across the valves
- the stroke volume through a regurgitant valve will be higher than a competent valve
stroke volume through a regurgitant valve equation
SV rv = SV cv + RV
regurgitant fraction equation
RF = RV / SV rv
5 assumptions made by volumetric flow calculations
- flow is occurring in a rigid circular tube
- there is uniform velocity across the vessel
- the rived CSA is circular
- CSA remains constant throughout the period of flow
- the PW sample volume position remains constant
3 realities of volumetric flow calculation s
- the heart and vessels are flexible and changing shape throughout the cycle
- annular diameters may change throughout the cycle
- MV and TV annuli are more elliptical than circular
5 errors with SV calculations VTI method
- non parallel to the flow leads to underestimation
- failure to trace the modal (bright) velocity
- incorrect placement of sample volume
- filter settings
- failure to average several beats
3 errors with SV calculations diameter
- measurement of the diameter during the wrong phase of the cardia cycle
- inconsistant annulus measurement
- difficulty in measuring in the RVOT
what should the baseline be adjusted to
- according to direction of flow of interest
* ** 3/4 the way from the top or the bottom**
what should the velocity range (scale) be adjusted to
- adjust the scale after the baseline is adjusted
- useful part of the spectral should occupy 1/2 to 3/4 of the total scale
- make signal as big as you can without aliasing
what 5 things does the velocity time integral VTI measure
- peak velocity (m/s)
- mean velocity (m/s)
- VTI (cm)
- Max PG (mmHg)
- Mean PG (mmHg)
can the VTI be used for any valve
- yes
what is the acceleration time
- time it takes for any flow to reach its peak velocity
- measured in milliseconds
deceleration time measures what 2 things
- peak velocity (m/s)
- deceleration time (ms)
what 3 things does pressure half time measure
- peak velocity (cm/s)
- slope (cm/s^2)
- pressure half time (ms)
when is it important to optimize sweep speed
- whenever measuring time
if you have a higher sweep speed do you see more or less spectral trace
- see less waveforms
is a higher or lower sweep speed better for time measurements
- a higher sweep speed
what does the change in pressure / change in time represent
- the rise or fall of pressure divided by the change in time
- measures how quickly the LV can generate pressure
when is Dp/Dt used the most
- used to assess LV global systolic function
