Week 3 - Lesson 1 (Part 8) Flashcards
What does biphasic flow indicate if seen in a vessel supplying a high resistance bed?
Indicates mild disease
How does a biphasic flow wave appear sonographically? (3)
- High pulsatility
- not as much as triphasic - High resistance
- 2 points
- one above and one below the baseline
What happens to the walls during biphasic?
They start to become stiff and rigid
- start to see some changes
How does a monophasic flow wave appear sonographically? (3)
- Flow is all above the baseline
- Low pulsatility
- Low resistance
What are examples of low resistance? (6)
- Vertebral arteries
- Brain
- Distal ICA
- Ovaries
- Testicles
- Kidneys
What is working hard during digestion?
SMA
What kind of flow is monophasic? (2)
- Continuous flow
2. Low resistance
When is monophasic seen abnormal?
If seen in a vessel supplying a high resistant bed
Critical stenosis
Encroachment on the lumen of an artery by an arteriosclerotic plaque can result in diminished pressure and flow distal to the lesion
Why does encroachment on the lumen have to be relatively extensive before hemodynamic changes are manifested?
Because large arteries offer little resistance to flow compared to smaller distal arteries
What are factors that determine the stenosis effect? (7)
- Length and diameter of the narrowed segment
- Roughness of the epithelial surface
- Degree of irregularity of the narrowing and its shape
- Ratio of the cross-sectional area of the stenotic zone to that of the normal vessel
- The rate of flow
- The arteriovenous pressure gradient
- Peripheral resistance beyond the stenosis
What is the most important factor determining the stenosis effect?
Diameter
Tandem lesion
One stenotic lesion after another, after another
What is important to recognize about tandem lesions?
That two or more stenotic lesions that occur in series have a more pronounced effect on distal pressure and blood flow than does a single lesion of equal total length
What is the result of tandem lesions?
Is large losses of energy at the entrance and particularly at the exit of the lesion
What kind of flow patterns do tandem lesions have?
Disturbed
- jets, turbulence and eddy formation
What happens to the total blood flow to an extremity during a severe stenosis?
It can remain normal
Why can total blood flow to an extremity during a severe stenosis remain normal?
Because of the development of collateral circulation as well as a compensatory decrease in the peripheral resistance
What is a better method of assessing the presence and severity of the occlusive disease?
Measurement of systolic pressure
- listening to blood flow is very important
Where does blood flow appear to have a higher resistance pattern?
Proximal to a critical stenosis or occlusion
- due to the pressure drop across the stenosis
When does flow reversal disappear?
Distal to a stenosis
What kind of waveform does doppler have?
Single component
- monophasic
When does the monophasic signal only occur?
During systole
What are the factors that contribute to the disappearance of reversed flow distal to the stenosis? (4)
- The maintenance of a relatively high level of forward flow throughout the cardiac cycle
- Resistance to reverse flow created by the stenotic lesion
- A decrease in peripheral resistance as a result of ischemia
- Damping of the pressure wave by the lesion,resulting in attenuated pressure pulses
What is the normal blood flow of arteries? (2)
- Blood flow velocity increases rapidly to a peak during early systole
- Decreases during early diastole when flow reversal can occur
What does the shape of the resulting pulse velocity wave reflect on?
The pressure gradient
How many sounds are heard over normal peripheral arteries?
Double or triple sounds
What is the second sound that is heard over normal peripheral arteries?
Diastolic flow reversal
- biphasic
What is the third sound that is heard over normal peripheral arteries?
Second forward component
- triphasic
What is doppler spectrum critically related to?
The detailed variation of velocity within the vessel of interest
What does the velocity of blood depend on?
Its position within the vessel
- this is the velocity profile
What does steady laminar flow demonstrate?
A parabolic velocity profile as seen in a long straight tube
- eg. CCA
Where is max velocity of a blood vessel?
In the centre
Where is min velocity of a blood vessel?
By the periphery
- walls
