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What does Poiseuille's Law?
Flow occurs primarily because of energy gradients but observed as pressure gradient or differences in pressures.
What must exist for flow to occur?
an energy gradient
Flow moves from the area of ______ pressure to the area of _________ pressure.
higher pressure to lower pressure
The _______ the pressure gradient, the ________ the flow rate.
greater the pressure gradient, the greater the flow rate.
What does Poiseuille's Law explain?
the relationship among...
Pressure, viscosity and flow
What has the greatest effect on resistance?
What is the relationship between viscosity and resistance?
Both increase together.
What is the relationship between radius and resistance?
When one decrease, the other increases.
What is the relationship between flow and resistance?
When one decreases the other increases.
When there is an obstruction in a blood vessel...
- Radius decreased? YES
- Resistance? YES
- Pressure gradient? YES
- Velocities? YES
What is considered a hemodynamically significant lesion?
Diameter reduction of =
Area reduction of =
Diameter reduction of = 50%
Area reduction of = 75%
When graded carotid artery disease do we use diameter reduction or area reduction?
What should we do if we have calificated plaque that covers up any potential stenosis on the posterior wall?
- That's why Doppler measuring velocities is important. Can get velocity measurements after stenosis. If higher velocities than larger stenosis. If lower velocities smaller stenosis.
- Still there even if can't visual see well.
What is the best mode to see degree of narrowing?
First do what?
B-mode is the most appropriate method to see degree of narrowing
1st- visualize the plaque in the transverse section.
It is possible to overestimate and underestimated eccentric disease when imaging in longitudinal section.
What ratios do we find for the evaluation of ICA stenosis? (2)
What do we use for this? (3)
- ICA/CCA PSV ratio
- ICA/CCA EDV ratio
- ICA PSV- use the highest PROX, MID, DIST
- ICA EDV-
- CCA PSV- use DIST CCA
What happens if the 2D image and the PSV don't match the % of stenosis?
Need to document.
What are 7 reasons why we calculate ICA and CCA ratios?
- 1.) the PSV and EDV don't fall in the same category.
- 2.) Presence of tandem lesions.
- 3.) Contralateral high-grade stenosis
- 4.) Discrepancy between visual assessment of the plaque and ICA PSV.
- 5.) Elevated CCA velocities- from older age.
- 6.) Hyperdynamic cardiac states
- 7.) A person may have poor CO, therefore have a low CCA velocities
Reminder need to practice Diameter Reduction Problems
Reminder need to practice Area Reduction Problems
Reminder need to practice ICA/CCA Ratios
If a doctor orders a unilateral carotid, what should you do?
Always do a bilateral carotid so you have both sides to compare.
Check hospital or clinic protocol.
What are two main trials performed on the efficacy of carotid endarterectomy (CEA)?
What have these two trials changed?
1.) North American Symptomatic Carotid Endarterectomy Trial (NASCET)
2.) Asymptomatic Carotid Atherosclerosis Study (ACAS)
Have changed the way many interpret and report carotid duplex examinations.
What is another more common trial?
European Carotid Surgery Trialists' Collaborative GRoup
Which two trials of reporting the degree of narrowing seen on carotid angiograms?
1.) NASCET- North American Symptomatic Carotid Endarterectomy Trail
2.) ECST- European Carotid Surgery Trailists' Collaborative Group
Review of Subclavian Steal
Where is the stenosis or occlusion usually located?
Where is the abnormal flow seen?
Waveform in the subclavian artery?
Stenosis or occlusion in PROX Lt. Subclavian A. before Vertebral A takeoff.
In the Vertebral A. - May see To-Fro flow or Retrograde flow.- Need to do exercise like reactive hyperemia.
Waveform will be monophasic in subclavian
- Symptoms? Usually asymptomatic.
- If symptoms- Vertebrobasilar
What three arteries can we palpate around the eye?
1.) Supraorbital A.
2.) Frontal A.
3.) Nasal A. - Angular A. - Facial A. - ECA
When dopplering the supraorbital which way would the flow go to be considered?
If the ICA is blocked where might the ECA send blow flow to get into the ICA?
1.) Supraorbital A.
2.) Frontal A.
What is more dominate MCA or ACA?
MCA is more dominate.
If you have an MCA occlusion where will you notice it in?
ICA and CCA
What three things do you see with ulcerated plaque?
3.) swirling color flow
When have a carotid dissection what is the resistance in the false lumen?
High resistance flow
What three main questions should you ask and answer when you find a Carotid dissection?
1.) How long?
2.) How far is the dissection?
3.) How is the flow in both the lumens?
What does Dolichocarotid Arteries mean?
when carotid arteries have an unusual shape.
What are 4 possible odd shapes of carotid arteries?
- 1.) looped or coiled
- 2.) Kinked
- 3.) C-shaped
- 4.) S-shaped
What are 7 possible risk factors for plaque?
- 1.) Atherosclerosis
- 2.) History
- 3.) Increased cholestrol
- 4.) Smoking/tobacco use
- 5.) Age
- 6.) Sedentary lifestyle
- 7.) Unhealthy diet
What are the 5 spectral waveform charasteristics we look at?
- 1.) movement of blood
- 2.) velocity of blood
- 3.) turbulence
- 4.) direction of blood flow
- 5.) amplitude
What is the relationship that Bernoulli's explains?
pressure and velocity have inverse relationship
At a stenosis what happens with...
Distal to a stenosis what happens with...
What can happen to the velocities in a long segment stenosis?
What should you do?
May not have velocity changes.
Need to go off appearance to get percentage of stenosis and not velocities for classification.
When is carotid stenting used for instead of CEA? (2)
- Used instead of CEA when...
- 1.) Patients are a high risk with coronary, pulmonary or renal diseases.
2.) Used when the atheroma extends beyond the accessible surgical field.
What velocity measurements should be token when doing a carotid duplex with a stent? (3)
What happens if you see higher velocities at the distal end of a stent?
Can be normal.
What are the 4 steps of a CEA?
- 1.) Clamping off ICA, ECA, and CCA.
- 2.) Sense cerebral circulation can be compromised a temporary plastic shunt can be used.
- 3.) Use of TCD to measure MCA blood velocity to see if shunt is failure.
- 4.) Vein or prosthetic patch may be used to close the site of the endart.
What can the patch cause... (1)
1.) slightly dilated bifurcat
What appears brighter on the image...
A prosthetic patch or a vein patch?
A prosthetic patch will appear brighter.
What are vein patches susceptible to?
What are prosthetic patches susceptible to?