Extracranial Cerebrovascular Flashcards
What does spectrum analysis sort out?
the doppler frequencies FFT - giving us a velocity
What is extracranial?
outside the brain
carotid studies
What are we evaluating in spectrum analysis blood flow?
pulsatile
flow is slower at the periphery
vessels are not straight
vessels are not uniform
distorted by pathology
What is the proper doppler angle?
60 degrees or less to acquire accurate frequency and velocity information
What is a doppler spectrum
graph of doppler frequencies generated by moving blood
When do you have broad systolic peak and forward flow throughout diastole?
CCA, ICA, vertebral, renal and celiac
low peripheral resistance
entire waveform above or below baseline
When do you get tall, narrow sharp systolic peaks reversed or absent flow through diastole?
extremity artieries, ECA, SMA (fasting)
high peripheral resistance
Arterial flow
What varies depending on location, physiology and pathology alteration, status of cardiac function?
Pulsatility
When does flow velocity accelerate rapidly?
in systole
What might cause acceleration to be slowed?
severe arterial obstruction flow
What causes disturbed flow?
widening of the wave form
vascular disease
normal tortuous vessels
prominent area -bulb
What happens with arterial obstruction?
increase velocity
disturbed flow post stenotic
proximal pulsatility changes
distal pulsatility changes
indirect effects - collateralization
What is Poiseuille’s Law?
a statement of physics
the VELOCITY of the steady flow of a fluid through a narrow TUBE varies DIRECTLY as the PRESSURE and the 4th power of the RADIUS of the tube and INVERSELY as the LENGTH of the tube and the coefficient of VISCOSITY.
what law states: because volume flow is porportional to the 4th power of the radius, even small changes in radius can result in large changes in flow?
Poiseuille’s Law
calculates VOLUME FLOW
Radius is most important because its to the 4th power
According to Poiseuille’s Law what happens to flow rate when pressure, diameter, length and viscoisty is INCREASED?
increase pressure, increase flow rate
increase diameter, increase flow rate
increase length, decrease flow rate
increase viscosity, decrease flow rate
How does Bernoulli’s principle relate velocity and pressure?
they are inversely related
high velocity, low pressure
low velocity, high pressure
With Bernoulli’s principle if you have a stenosis, what happens to the pressure and velocity AT the stenotic segment, prox to stenosis and distal to stenosis?
Stenotic segment - pressure decreases, velocity increases
prox - pressure increase
distal - pressure increase
Flow moves along the path of _________resistance
least
What is a hallmark of high resistance vascular beds?
diastolic flow reversal
it doesn’t need a constant flow, it can hesitate….flow reversal
What is an ischemic stroke?
interruptions of blood flow to the brain
80% - ruptured intracraninal blood vessel
20% intracranial hemorrhage
What are two ways the blood flow gets interrupted to the brain causing a stroke?
Thrombus lodges in a cerebral artery
thrombus in the carotid artery breaks off and travels to a cerebral artery in the brain
What is responsible for more than 50% of all strokes?
extracranial carotid artery disease
What is the third leading cause of death in the USA?
Stroke (cerebrovascular diseases) 137,119
What can detect potential causes of stroke?
carotid imaging
What is the definition of stroke or CVA?
permanent ischemic deficit (permanent damage)
What is the definition of TIA (transient ischemic accident)
temporary - reversible ischemic neurologic deficit
resolves in <24 hr (usually less than one hour)(lasts 1-30 min until full recovery)
What is the definition of RIND?
reversible ischemic neurologic deficit
resolves in >24 hrs (up to three weeks for complete restoration of function)
What is the leading cause of permanent disability?
strokes
What is the best treatment for stroke?
prevention
What is a thrombotic stroke?
clot in the artery in the brain
what is an embolic stroke?
piece of a clot is carried to the brain ( or anywhere)
What is a hemorrhagic stroke?
blood vessel in the brain breaks
What are the non-modifiable risk factors for stroke?
age - risk increases with age
sex - males
race - higher in african american
previous stroke
What are the modifiable or controllable risk factors for stroke?
hypertension
atrial fibrillation
cardiac disease
diabetes mellitus
elevated cholestrol
smoking
sedentary lifestyle
obesity
What are the warning signs for stroke?
sudden numbness or weakness
sudden confusion, trouble speaking
sudden vision issues
sudden trouble walking, dizziness or loss of balance
sudden headache
What does weakness/numbness of one side indicate?
disease on the contralateral carotid
if you have ocular symptoms where is disease indicated?
the same side - ipsilateral
What are some things you can ask people to do if you suspect a stroke?
smile
talk
raise both arms
stick out tongue
What is FAST?
Face
Arm
Speech
Time
Can a stroke be asymptomatic?
yes
check for bruit if you have a risk factor but no symptoms
What is Amaurosis fugax?
transient vision loss
what is hemiparesis?
paralysis
what is dysarthria?
speech difficulty
what is aphasia?
inability to communicate (not making any sense)
What is dysphagia?
difficulty swallowing
what is ataxia?
what is gait disturbances
what is diplopia?
double vision
what is vertigo?
sensation of moving objects
What is another name for the brachocephalic?
innominate artery
What vessels come off of the aortic arch?
brachiocephalic
Left common carotid
left subclavian
where does the aorta branch out of?
left ventricle
the innominate or brachiocephalic artery divides into the _______
Rt CCA
Rt Subclavian - gives rise to the Rt. vertebral
Which CCA is longer, left or right/
left is longer
the left subclavian gives rise to what?
the lt vertebral
see slide 48
What are variants of the aortic arch?
L CCA forms a common origin with the innominate artery
L vertebral artery arising from the arch
R subclavian artery arises from the arch distal to the Lt
Lt innominate may exist
left innominant may exist
What vessels are enclosed in connective tissue called the carotid sheath?
carotid artery
jugular vein
vagus nerve
where is the common carotid artery found?
anterolaterally in the neck
medial to the jugular vein
lateral to the trachea
lateral to the thyroid gland
where does the vagus nerve lie in relation to the artery and vein?
between
does the common carotid artery branch?
no it terminates at the bifurcation of the ICA and the ECA
Where is the external carotid artery found?
originates at the mid cervical level
What kind of waveform does the ECA have?
high resistance, low diastolic with a notch
usually the smaller vessel
What are the identifying characteristics of the ECA?
smaller than ICA in diameter
usually the anteriomedial vessel
the ICA frequently has a mild dilatation at its origin termed the carotid bulb, the ECA has no bulb
cervical portion has branches, the ICA rarely has cervical branches
doppler signals normally more resistive in the ECA
response to temporal percussions (tapping in front of the ear makes the waveform vibrate)
what is the first and most important branch off of the ECA?
superior thyroid
What may form when significant disease is present in the ICA?
collateral pathways
What does the ECA supply?
face
scalp
tongue
neck
runs medially and anteriorly to ICA
Where does the ICA arise from?
the CCA birfucation
where does the ICA enter the skull?
enters base of skull through petrous bone
which is the larger of the CCA terminal branches?
ICA
What is an unseen branch of the ICA?
opthalmic artery
what does the ICA supply?
brain
eye
forehead
part of the nose
What is the bulb?
where the ICA and ECA branch
includes distal CCA, proximal ECA and ICA
may be curved or tortuous
Where does the ICA terminate?
at the circle of Willis
distributes to the low resistance vascular bed
see slide 78
What are the differences between ICA and ECA
ICA: ECA:
lat/posterior med/anterior
no branches in neck branches early in neck
low resistance waveform high resistance waveform
no response/temp tap alterations waveform w/t tap
What is the standard patient position for carotid scanning?
supine, head turned slightly (patient on your rt side)
vascular lab approach: patient upside down
no matter patient position, picture should be the same
What are you looking for when scanning a carotid?
location of stenosis
extent of plaque and patency of the distal ICA
presence tortuosity or kinking vessels
plaque characteristics (smooth, irregular etc)
What transducer do you use for carotid?
high frequency linear array 7-10MHZ
color with red being artery
angle correct
color display small
doppler parallel to vessel walls
What needs to be adjusted throughout the carotid exam?
PRF or scale
wall filter
color box/gain
What is the spectral waveform of the CCA?
demonstrates high and low resistance flow from ICA and ECA
CCA doppler signal will display + doppler shift throughout cardiac cycle
color flow pattern will have continuous color throughout cardiac cycle
What is the boundary layer separation?
normal flow disturbance
detected as a transient reversal of blood flow along posterior wall of the bulb
sample volumes for ICA should start just distal to this area
What is the vertebral artery?
branch of the subclavian
feeds cerebral part of the brain
what are the segments of the vertebral artery?
extravertebral - evaluated during carotid exam
intervertebral
horizontal
intracranial
the subclavian artery blockage will cause reverse flow in ______
vertebral artery
What creates a 20mm hg difference in blood pressure between the two arms?
a subclavian artery blockage which causes the vertebral artery flow to go the wrong way
What is a subclavian steal?
reversal of vertebral artery blood flow direction secondary to a sig obstruction prox to the orgin of the vertebral artery in the ipsilateral subclavian or innominate artery
a phenomenon
What is the normal carotid doppler of the CCA?
sharp upstroke
clear doppler window
diastolic flow
Why will the color pattern of the ICA have continuous color throughout the cardiac cycle?
due to low peripheral resistance of the brain
Why does the ECA demonstrate a more pulsatile doppler signal?
because it supplies blood to skin, and muscular bed of scalp of face
has faster slope to peak systole and near zero in diastole
normal color flow pattern will reflect higher resistance of scalp/face
