Uni lectures Flashcards
What is another name for perfusion of blood?
Volume flow
What is the equation to calculate perfusion?
Q = v * A
Do doppler waveforms show velocity or flow?
Velocity
How do arteries modify waveforms?
Arteries have elastic walls which aid pulse propagation and flow
What happens to blood pressure following a stenosis?
There is turbulence and a loss of energy after stenosis which causes a pressure drop
What percentage diameter drop causes a significant drop in pressure?
50%
What are the first 3 branches to come off the aorta? (excluding coronary)
Brachiocephalic, Left CCA, left subclavian
How do veins relate to oedema?
Reduced venous return can cause dilation of veins or transfer of fluid to the surrounding tissue (interstitial space)
Which arteries above the thorax have continuous diastolic flow?
Vertebral arteries and ICAs
What waveform feature determines the end of systole and the start of diastole in carotid arteries?
The dicrotic notch
What causes the multiphasic waveform?
Reflections from distal branches
and elasticity of vessel walls
What is the diastolic component of the waveform very sensitive to?
Posture, gravity, temperature, disease, peripheral resistance
What is hyperechoic plaque?
Echogenic, bright plaque (often calcified)
What is hypoechoic plaque?
Dark, echolucent plaque
Which veins surround the SSV?
Gastrocnemius veins
What percentage of strokes are haemorrhagic?
15%
What percentage of strokes are embolic?
85%
What percentage of strokes are due to carotid disease?
15 - 20%
What is the name of the artery formed by the two vertebral arteries?
Basilar artery
What symptoms are associated with vertebro-basilar disease
Dizziness and loss of balance (supplies the hind brain
What do the systolic and diastolic aspects of waveforms show in terms of disease?
Systolic = proximal disease
Diastolic = distal disease
What would a vein with no phasic flow with respiration suggest?
A proximal obstruction
What percentage of diabetics are type 1?
10%
What is type 3 diabetes?
Pancreatectomy / cystic fibrosis
What are the pancreas’ exocrine functions?
Secretes trypsin (protein), lipase (fat) and amylase (starch)
What are the pancreas’ endocrine functions?
Secretes glucagon and insulin
What does insulin increase?
Glucose transport into cells
Liver glyconeogenesis
Utilization of glucose
How many diabetics are there?
3.7 million
How many diabetics are not diagnosed?
1/2 a million
What percentage of the NHS budget is spent on diabetes care?
10%
How does life expectancy decrease with type 1 and 2 diabetes?
Type 1 - reduced by 20 years
Type 2 - reduced by 10 years
How is diabetes diagnosed?
Fasting glucose >7
OGTT >11
HbA1c >48
What are diabetes risk factors?
- Obesity
- Race
- Hypertension
- Age
- Family History
- Inactivity
*Pregnancy
What is Buerger’s Syndrome?
A condition affecting blood vessels (usually in the limbs)
- causes vessels to swell, reducing blood flow
- this can make blood clotting more likely
What is aspirin?
An anti-thrombotic, anti-platelet drug
- also has anti-inflammatory properties
What is clopidogrel?
Anti-platelet drug
What is heparin?
Anticoagulant
What is warfarin?
Anticoagulant
Is CT or MRI more sensitive for detecting brain ischemia in TIA patients?
MRI
What is sensitivity? And when is it very important
Sensitivity = TP / (TP +FN)
Tests with high sensitivities are essential for serious diseases (or where treatment is very expensive)
What is specificity? And when is it important
Specificity = TN / (TN + FP)
It is important when individuals identified as having the disease may be subject to many additional tests or invasive procedures
How many diagnostic tests that use ultrasound take place each year?
~ 9.5 million
What is the range of frequencies used in ultrasound?
Around 1 - 20 MHz
What part of the probe produces soundwaves?
The transducer
What is a bistable image?
Image only containing black and white
What is the range of costs of ultrasound machines?
£30 - 100K
What are the two main ultrasound scans during pregnancy?
- 11 - 14 weeks dating scan
- 18 - 20 week foetal anomaly scan
How can age of foetus be estimated using ultrasound?
Crown rump length
Biparietal diameter
When can you see foetal hearts beat?
6 / 7 weeks
What appearance may cancerous deposits have on ultrasound?
Bright white areas
What appearance may metastases have on ultrasound?
Darker larger structures
What is a pseudoaneurysm?
A hole in an artery often caused by catheter or needle insertion
What is FAST scanning?
Scans performed in A&E following trauma.
Focused assessment using sonography for trauma. Assesses: heart, spleen, liver, pelvis, aorta
What is sheer wave elasticity?
Ultrasound scan that measures small changes in displacement
- disease alters elasticity of structures
When was ultrasound first used in medicine?
1941 - second world war
What are two reasons why ultrasound is used in obstetrics?
Estimating foetal age and looking for foetal anomalies
What is the pressure in the pulmonary circulation?
25 / 15 mmHg = upper limit
15 / 10mmHg = lower limit
What are the 3 main layers of arteries?
Intima, media, adventitia
(also has elastic lamina between layers)
What are the 3 main layers of veins?
Intima, media, adventitia
(NO elastic lamina between layers)
Which layers of veins form the valves?
Intima and media
What is artery intima composed of?
Vascular endothelium
What is artery media composed of?
Elastin + collagen + smooth muscle
What is artery adventitia composed of?
Strong thick collagen layer with some elastin
Which veins have smooth muscle control?
Only the portal system
Which veins have valves?
Distal veins
How big are arterioles?
< 1 mm in diameter
What is the function of arterioles?
Control perfusion of capillary bed
What are pre-capillary sphincters?
Smooth muscle segments that direct blood flow into capillaries
What muscle in the neck is seen on carotid scans?
Sternomastoid
What bone is scanned over when viewing subclavian?
Clavicle
Are the branches of the aorta anterior or posterior to the superior vena cava?
Posterior
Which arteries usually come off the aorta anteriorly?
Cephalic trunk, IMA and SMA
Where do the gonadal arteries come off the aorta?
Between the renals and IMA (usually)
What artery comes off the abdominal aorta inferiorly, between the iliacs?
The median sacral artery
What are perforator veins?
Veins that connect the superficial and deep venous systems - from superficial to deep
Roughly how many perforating veins are there in each leg?
150
How is the basilic vein related to the cephalic vein anatomically?
Basilic vein is more medial
How is the IVC related to the aorta?
Is posteriorly and to the right
How is blood flow homeostatically controlled?
- Arterial sensors - carotid and aortic arch
- Venous sensors - atrial stretch
- Cerebrovascular control centre
- Renal perfusion
- Local factors
What forces determine fluid exchange in capillaries?
Starling’s Forces:
- Hydrostatic pressure
- Osmotic pressure
In addition to measuring > 5.5cm in diameter, what other classification can be used for AAAs?
> 1.5 times the suprarenal diameter
Is diabetes a risk factor for AAAs?
No, the risk of developing a AAA is halved with diabetes
What imaging modality is used to assess AAA rupture?
Usually CTA
How does ethnicity impact risk of AAA?
Whites are more likely to develop an AAA that Asians or African Americans
What management can help slow AAA growth?
Only stopping smoking. Not exercise, drugs etc.
What events are AAAs associated with?
Cardiovascular events
What percentage of aneurysm ruptures are fatal?
Over 80%
What is a juxtarenal AAA?
An AAA extending up to but not involving the renal arteries
(no neck)
What is a suprarenal AAA?
An AAA extending up to the SMA, involving one or both of the renal arteries (i.e. no neck)
What size is considered an aneurysmal common iliac?
> 18 mm in men and >15 mm in women
- >1.5 times the normal diameter
What size is considered an aneurysmal internal iliac?
> 8 mm
How many different classifications of iliac aneurysms are there?
4
What are mycotic AAAs?
Infected AAAs
What is an artery dissection?
A tear in the intima layer
What is a pseudoaneurysm?
Caused by injury, they are a tear in the vessel wall where blood leaks out
- the wall of a pseudoaneurysm contains clotting factors
When does the thoracic aorta become the abdominal aorta?
When it crosses the diaphragm
What mechanisms can cause wall weakening and aneurysms?
(4 reasons)
Inflammation, oxidative stress, mechanical stress and proteolysis
- decreases levels of structural proteins including elastin and collagen
How many deaths per year do ruptured AAAs in England and Wales cause?
4000
What are symptoms of a AAA rupture?
Sudden intense back or abdominal pain, hypotension, high heart rate
What measurements are taken in NAAASP?
2 AP measurements
- 1 in transverse and 1 in longitudinAL
In which state of the cardiac cycle should we measure AAA size?
Peak systole - aorta is widest
What is the interoperator variability of scanning 4 - 5.5 cm AAAs?
0.2 cm
Other than DUS, which imaging modalities can be used for AAAs?
CT and MRI
What is a type 1 endoleak?
Proximal or distal leakage of blood into sac from EVAR attachment site
What is a type 2 endoleak?
Leak into the sac from aortic side branches
What is a type 3 endoleak?
Defect in the stent or tear in fabric
What is a type 4 endoleak?
Graft porosity
What is a type 5 endoleak?
An endoleak with no known cause
What are the sensitivities and specificities of using ultrasound for AAA screening?
Specificity = 98 - 100%
Sensitivity = 94 - 100%
In the MASS trial, what was the percentage of elective AAA repair deaths compared with emergency repairs?
Elective mortality = 6%
Emergency mortality = 37%
What is CRP indicative of?
CRP is produced by the liver in response to inflammation
What are the two types of antithrombotic drugs?
- Anticoagulants
- Antiplatelets
What are common anticoagulants?
Heparin, warfarin and DOACs (riveroxiban and other bans)
How do anticoagulants work?
Slow down clots and prevent them from forming by reducing fibrin formation - used to help prevent DVTs unlike antiplatelets
What are some of the main differences between antiplatelets and anticoagulants?
Anticoagulants are used to prevent DVTs and in AF
Antiplatelets are used to prevent heart attacks
Which drugs cause the breakdown of clots?
Thrombolytics
What are examples of thrombolytics?
Streptokinase, reteplase, alteplase (other -ase or -kinase drugs)
How is the basilic vein related to the cephalic?
The basilic vein is more medial
- Note: both veins extend down the length of the arm, including the forearm
What are the deep veins of the arm?
Axillary -> Brachial -> radial and ulnar
Where do most of the gastrocnemius veins drain into?
The popliteal vein
How do ultrasound probes create soundwaves?
Displacement of particles in longitudinal plane
What is the equation for the speed of sound?
c = lambda * f
What is the speed of sound in bone?
3500 m/s
What is the speed of sound in air?
330 m/s
What is the assumed speed of sound in tissue?
1540 m/s
What is the named frequency on an ultrasound probe?
Its resonant frequency - the frequency when the thickness of the element is half the wavelength of sound created within it
What is the equation for calculating distance of an ultrasound image?
c = 2 * d / t
d = tc / 2
How many cycles of a soundwave are typically transmitted in a pulse?
1 - 3
What happens to the range of frequencies within the pulse when pulse length is reduced?
The number of frequencies increases
What determines the proportion of sound reflected and transmitted at an interface?
The acoustic impedance of the interface
What does increased acoustic impedance cause?
Increased reflection at the boundary
What is the ratio of sound reflected at muscle/blood interface?
0.03
What is the ratio of sound reflected at muscle/bone interface?
0.63
What is the ratio of sound reflected at soft tissue / air interface?
0.9995
Why is microvasculature assessment difficult?
- Vessel structure is spatially inhomogeneous
- Perfusion varies greatly over time
What are the 4 established methods for microvascular assessment?
- Laser doppler perfusion imaging
- Laser speckle contrast imaging
- Thermal imaging
- Nailfold capillaroscopy
Why is microvascular assessment important in burns patients?
It can be used to assess depth of burn
What is Raynaud’s?
Exaggerated response to cold or emotional stress with vasospasm and ischemia of the extremities
How does infrared thermography assess perfusion?
Secondary to skin temperature
What two qualities are ideal for tests measuring microvascular function?
- Assess wide surface area
- Rapid frame rate
What is pre-arterial sympathectomy?
A surgical procedure where specific nerves are chemically inactivated, reducing sympathetic vasomotor tone
- causes targeted vasodilation
What is a limitation of laser doppler perfusion imaging?
Slow data capture
How does the body control the microvascular system?
- Monitors - temperature, blood pressure and tissue oxygenation
- Response - using hormones and parasympathetic NS
- Action - smooth muscle cells via [Ca2+] or myosin dephosphorylation
- Vasodilation and constriction can be localised or systemic
What are the 4 main ways microcirculation can go wrong?
- Sudden drop in BP - vasovagal syncope
- Over-reaction to cold exposure - reactive hyperaemia
- Chronic hypertension
- Chronic inflammation - cell damage, impaired healing
Which diseases can affect the microvascular system?
- Connective tissue disorders
- Vasculitis
- Diabetes mellitus
- Chronic kidney disease
- Arterial hypertension
- Raynaud’s phenomenom
What are the tri-phasic colour changes of Raynaud’s?
White - vasoconstriction
Blue - tissue hypoxia
Red - hyperaemia
How is Raynaud’s phenomenon detected?
- 10 min baseline scan of hands
- Cold challenge - 1 min with gloved hands in 20 degree water
- Rewarming images (10 mins)
What is capillaroscopy?
Illumination of the nailfold by green wavelength light which is selectively absorbed by red blood cells
What are 4 aspects of pathology that can be identified within the microvascular circulation?
- Dilation - normal diameter < 20um, slightly enlarged (non-pathological) 20-50um, Pathological = Giant loops - diameter >50um
- Density - can grade mild, moderate or extensive loss
- Bushing - tortuosity, branching, angiogenesis
- Extravasation - haemorrhaging capillaries
What are treatments for Raynaud’s?
- Conservative management - gloves
- Vasodilators - Ca channel blockers, ACE inhibitors, PDE5 inhibitors (Viagra)
What are treatments for more seriously threatened microvascular ischemia? e.g. digital ulcers secondary to scleroderma
IV prostacyclins e.g. iloprost
What is fluorescence?
Light at one wavelength re-emitted at a longer wavelength
What are the 3 light techniques used to measure microvascular function and some examples?
- Visualising microvascular structure - near infrared imaging, microscopy (capillaroscopy) optical coherence tomography
- Determining tissue composition - pulse oximetry, photoplethysmography, hyperspectral imaging, tissue oxygen saturation
- Measuring/imaging microvascular function - Thermal imaging, laser doppler flowmetry, laser doppler imaging, laser speckle contrast imaging
What is Klippel-Trenaunay syndrome? And how can it present?
A rare congenital condition whereby blood vessels or lymph vessels fail to form properly
- presents as port wine stains, varicose veins and hypertrophy of bony and soft-tissues
What is giant cell arteritis?
Inflammatory disease of the large blood vessels of the scalp, neck and arms.
- inflammation causes narrowing or blockages in the blood vessels
When is ultrasound ineffective for giant cell arteritis patients?
When they have already started steroids - reduces inflammation
Why are RBCs not visualised well on ultrasound?
They are smaller than
What are the risk factors for giant cell arteritis?
> 50 years old
Female - 3F : 1M
What are some symptoms of giant cell arteritis?
Temple tenderness, tongue or jaw claudication, constitutional (e.g. weight loss, fatigue), arm claudication
What is the treatment for giant cell arteritis?
Steroids e.g. prednisone
What is Buerger’s syndrome?
Swelling and inflammation of the arteries
- prevents blood flow and encourages clot
Who are typical Buerger’s syndrome patients?
Young male smokers
What are some symptoms of Buerger’s syndrome?
Pain, tissue loss, gangrene, amputation
What can be compressed in TOS?
Subclavian artery, subclavian vein and brachial plexus
What are the two common causes of compression in TOS?
Cervical rib or muscular
How can you determine which TOS it is?
Neural - arm weakness, finger pain, most common form
Females > Males
Arterial - persistent pain + numbness, impaired temperature sensation, cold limb, least common
Males = Females
Venous - oedema, cyanosis, deep pain
Males > Females
What compresses in Adsons TOS and what position?
Cervical rib or scalene
- and with arm out
What percentage of the population experience popliteal entrapment?
10 - 15%
What are the symptoms of Pop entrapment?
Sudden onset calf pain
What percentage of strokes in patients aged < 45 are caused by carotid dissection?
25%
What is Klippel-Trenaunay syndrome?
Triad of:
1. Capillary malformations (port-wine
stains) (98%)
2. Large venous malformations or
varicosities (72%)
3. Bone and soft tissue hypertrophy (67%)
How does renal stenosis often present?
Persistent, treatment resistant hypertension
How does renal stenosis cause symptoms?
Activation of RAAS pathway -> AT2 production -> sodium excretion, sympathetic nerve activity, prostaglandins, NO -> Renovascular hypertension
How do you calculate volume-flow (perfusion)?
velocity * area
What is an ectatic aorta?
A diffuse/global widening of the aorta diameter, however not of aneurysmal size
What are the arteries of the Circle of Willis?
Basilar, vertebral, median communicating, anterior communicating, posterior communicating arteries
What is the biggest risk factor for developing an AAA?
Smoking
Are the popliteal veins usually paired?
No
Is there a brachiocephalic vein?
Yes - there are two
What are the continuations of the subclavian artery?
Vertebral and axillary arteries
Is CLI pain relieved by sitting?
No
Which imaging modalities are useful for investigating PAD?
ABPI, Doppler, CTA and MRA
What medications are PAD patients prescribed?
Clopidogrel, statins, ACE inhibitors, BP control
- note: not anticoagulants
What is the difference in use of anti-platelets and anti-coagulants?
Anticoagulants (e.g. warfarin, heparin, DOACs) are used in DVT patients & in HF patients
Anti-platelets are used in PAD patients
True or False: Iliac arteries respond poorly to stenting - bypass is preferred
False
If sensitivity is a priority when imaging a deep artery at 7cm, which probe should be used?
The lowest frequency one (e.g. 3MHz)
What percentage of ultrasound is reflected and absorbed by bone?
Around 50% (actually 64%) is reflected but it also absorbs ultrasound
What percentage of US is reflected at soft tissue / air boundary?
99%
What percentage of US is reflected at bone/muscle boundary?
64%
What percentage of US is reflected at fat/muscle boundary?
10%
What percentage of US is reflected at muscle/blood boundary?
3%
What is attenuation?
Loss of energy from the ultrasound beam as it passes through the tissue
- the more energy that is attenuated by the tissue, the less that returns to the probe
What are some of the several processes that cause attenuation?
Absorption (causes conversion to heat)
Scattering
Reflection
Divergence
What is the average attenuation coefficient at 1MHz in soft tissue?
70
What happens to attenuation coefficients as tissue density increases?
They increase
Are higher or lower US frequencies attenuated more quickly?
Higher
How many piezoelectric elements are typically in an ultrasound transducer?
128
What are the two methods for increasing amplitude of returning US signal?
Increasing power output (i.e. amplitude) and increasing receiver gain
- increasing power causes the patient to be exposed to more US energy
True/False: Handheld dopplers use the doppler effect to calculate flow velocity
False
- they calculate frequency shift for waveform
What is the y axis on spectral waveforms?
Frequency shift
What is the greyscale on spectral waveforms?
The number of reflectors
How can you calculate Doppler shift from observed and transmitted frequencies?
fd = fr - ft
frequency difference = frequency received - frequency transmitted
What is the Doppler equation?
fd = (2 * v * ft * Cos(theta)) / c
ft = frequency transmitted
v = velocity
c = speed of sound
What is the output of continuous wave handheld dopplers?
Frequency shift
What is aliasing caused by?
Insufficient sampling of the signal
What is frequency shift proportional to?
Relative velocities of the source
What is A-mode ultrasound?
The simplest form - transmits a single pulse through the body
What makes up most of the received ultrasound signal?
Backscatter
When does scattering of an ultrasound beam occur?
At rough surfaces or at small particles
Does 1 large stenosis or 2 shorter adjacent ones cause a greater drop in blood pressure?
2 shorter ones
- the entrance and exit of a stenosis accounts for most of the pressure drop
Are ultrasound waves transverse or longitudinal?
Longitudinal
How many dimensions do ultrasound waves have?
3D
What does speed of sound depend on?
Density and stiffness
What can cause ultrasound waves to have increased brightness on the greyscale?
Increased amplitude (power output)
What is the ceramic in ultrasound probes usually made from?
PZT
Lead Zirconate Titanate
What are the basic components of a PZT transducer?
Front and rear electrodes, lens, electrical leads, backing layer, matching layer
What is the role of the backing layer in the transducer?
It absorbs unwanted waves
What is the role of the matching layer in the transducer?
To prevent unwanted internal reflections
How many frames per second for a normal B-mode display?
10 - 30 frames per second
How can cellulitis impact the colour of interstitial fluid on B-mode displays?
It makes interstitial fluid appear dark
What does duplex mean?
Imaging plus doppler
What is the doppler equation?
fd = (2 * v * ft * Cos(theta)) / c
How many transmission pulses does a colour line require?
7 - 10
What is the typical protocol for treadmill exercise ABPIs?
- 5 mins
- 3 km/h
- 10 degrees slope
- 250m
What ABPI values indicate incompressible foot arteries?
> 1.4 = compressible (sometimes stated as > 1.2)
What ABPI value range indicates mild arterial disease?
0.8 - 0.9
What ABPI value range indicates severe arterial disease?
< 0.5
What ABPI value range indicates moderate arterial disease?
0.5 - 0.8
What ABPI value range indicates a normal result?
0.9 - 1.4
How many people die from cardiovascular disease each year?
160,000
How many people die from strokes each year?
41,000
How many people die from arterial, arteriole or capillary disease each year?
10,000
How many people die from ruptured AAAs each year?
6000
What cost per QALY is deemed effective by NICE and what is the maximum cost of treatment for one QALY?
£20,000 per QALY is considered effective and with greater evidence, up to £30,000 could potentially be implemented
What is Virchow’s triad?
The 3 cellular factors contributing to thrombosis:
- Intravascular vessel wall damage
- Stasis of flow
- Presence of hypercoagulable state
What is thrombosis?
Formation of blood clot within a vessel
Following DVT, what percentage of patients develop PTS?
20 - 50%
What are symptoms of PTS?
Similar to venous reflux e.g. pain, swelling, oedema, reflux, skin changes
Are varicose veins more common in men or women? and what are estimated percentages in the population?
More common in women than men
Female = 20 - 25%
Male = 10 - 15%
What separates the deep from the superficial veins?
The muscular fascia
Where is the soleal vein located?
In the middle of the calf, posteriorly
- branches superiorly to TPT
(note the peroneal is lateral posterior)
Which calf veins are paired?
ATA, PTA, Pero A and gastrocnemius
(not Pop A)
Is the profunda artery more medial or lateral when compared with the SFA?
Prof A is more lateral
What artery runs proximally through the adductor canal?
SFA
Which veins usually do not have valves?
IVC, CIV don’t have valves
EIV and CFV don’t in most of population
Usually valves start at the proximal end of the CFV
What causes venous ulceration?
Chronic venous hypertension
What length of reflux is present in normal valve function?
< 0.5 seconds
What length of reflux is present in moderate reflux?
0.5 - 1 second
What length of reflux is present in significant reflux?
1 - 2 seconds
What length of reflux is present in gross reflux?
> 2 seconds
Is the brachial vein paired?
Yes, most people have 2
How do prostacyclins work?
They inhibit platelet activation and cause vasodilation by reducing smooth muscle tone
What is the difference between CLTI and ALI
Acute limb ischemia only lasts < 2 weeks
What are the muscles of the calf?
Gastrocnemius and Solial
In regards to colours of the fingers, what do the colours show:
1. White
2. Blue
3. Red
- Vasoconstriction
- Tissue hypoxia
- Hyperaemia
What does primary Raynaud’s mean?
No underlying cause e.g. connective tissue disorder
What is the difference between supra-renal, para-renal, juxtarenal and infrarenal AAAs?
Supra-renal include renals and SMA
Para-renal extend up to and include renals
Juxtarenal are just below the renals
Infra-renal are below the renals
When does the axillary vein become the subclavian?
After the cephalic has joined it
When does the brachial vein become the axillary vein?
When the basilic vein joins it
What vein joins the cephalic to the basilic vein?
The median cubital vein
Are the brachial veins paired?
Yes
How is ABPI calculated?
The highest from the PT or DP and the highest brachial artery
What are some examples of microvascular deformities seen in capillaroscopy?
Dilation
Reduced density
Bushing
What test is used to identify Reynaud’s phenomenom?
Medical thermography
How do the treatments for type 1 and 2 diabetes vary?
Type 1 = treat with insulin
Type 2 = treat with oral hypoglycaemic agents
