Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
74 Cards in this Set
- Front
- Back
|
why does collateral circulation develop?
|
because of a change in the PG btw vessels, causes by obstruction or stenosis
-distal to a significant stenosis, there is pressure drop -if the pressure drops enough to attract flow, blood vessels may abandom their normal flow routes to take advantage of the new, lower presssure route ie. subclavian steel |
|
|
name and explain the 3 categories for intracranial collateral circulation
|
1. larg inter-arterial connections: other side of the circle of willis
2. intracranial-extracranail anastamoses(preswillisian anastamosis) 3. small inter-arterial communications(rete mirabelle) |
|
|
if there is a totally occluded Lt ICA,what are some possible collateral flow routes
|
-collateral flow through other side of circle of willis
-colateral route through poterior cerebral circulataion |
|
|
external to internal carotid collaterals
|
-second most NB anastamoses
-aka preswillisian anastamosis -the best known one is btw the ECA and ICA through the orbital and opthalmic arteries |
|
|
collateral possibilities in the brain?
|
-Rete mirabelle(wonderful net)
-occipital branch of the ECA communicating with atlantic branch of the vertebral artery -deep cervical branch of subclavian artery communicating with the proximal branch of the vertebral artery -descending and ascending crvical branches of the subclavian artery connecting w/ branches of the lower vertebral arteries, the atlantic branch of the upper vertebral artery, and the occipital branch of the ICA -the ECA communicating across the midline |
|
|
explain rete mirabelle
|
wonderful network
-network of transdural arteries -may anastamose across the subdural space -tiny arteries covering the surface of the brain |
|
|
when do collaterals form?
|
-depends on the age of the individual and the time of occlusion
OLDER PATIENTS: -collateral pathways are more likely to be hypoplastic -involved with atherosclerotic process ---collateral flow has a better chance of developing in persons with slowly evolving atheroscerotic processes. |
|
|
d-dimer
|
-blood test used for it's negative predictive value(if it isn't present in blood, DVT is excluded)
-D-dimer refers to a family of fibrin fragments that form and circiulate in the blood stream for several days after a thrombotic event. -protien that is released into the circulation during the process of fibrin clot breakdown -d-dimer is elevated if there is a cut, so the presence of d-dimer does not necessarily indicate DVT |
|
|
what are some diagnostic tests for PE and DVT?
|
-lung perfusion-VQ scan(nuc med)
-spiral CT angio -lung/leg MRI -pulmonary angio(gold standard for PE) -isotope venography -contrast venography(gold standard for DVT) |
|
|
Lung perfusion (VQ scan)
|
VQ=ventelation quotient
-commonly used test for suspicion of PE -emboli in the small vessels of the lungs can cause perfusion defects -radioactive xenon gas is inhaled and a series of X-rays are taken to examine the distribution |
|
|
w/ a VQ scan, what does a normal scan, low and intermediate scans, and indeterminate scans show?
|
normal scans-exclude possibility of PE
-low and intermediate scans-do not exclude the diagnosis and adjunctive tests are required -high probability strongly suggests PE -Indeterminate-conclusion could not be reached(test is ineffective) |
|
|
Pulmonary angiography
|
-gold standard in diagnosis of PE
-invasive -carries higher risk(esp. with hypertension, or hypoxemia) -recommended for non-diagnosistic VQ scans |
|
|
Spiral CT angiography
|
-still investigationsl
-useful when evaluating central vessel involvement but not involvement of sugsegmental arteries -lung/leg MRI |
|
|
lung/leg MRI
|
-excellent sensitivity and specifity for the diagnosis of DVT or PE
-may allow for simultaneous detection of them -very expensive and not widely available |
|
|
isotope venography
|
-involves the injection of I-125 labled fibrinogen
-absorbed into thrombus -a scanner then records the amount of labled fibrinogen ar various levels -highly sensitive to actively forming thrombus |
|
|
contrast venography(phlebography)
|
-gold standard study
-catheter inserted into a peripheral vein -contrast injected -radiologies observes movement of solution though veins w/ a floroscope -x-rays taken simultaneously -any filling defect indicates displacement of contrast material vy thrombus |
|
|
What are the advantages and disadvantages of contrast venography?
|
ADVANTAGES:
-accurate diagnosis of DVT -useful when other modalities fail -identified location, extend and degree of attachment of blood clots DISADVANTAGES: -expensive -invasive(risk infection) -painful -risk of allergic reaction -may cause phlebitis or DVT -may not detect thrombus in duplicated systems |
|
|
what are the controlling risk factors for theraputic interventions?
|
-controlling risk factors:
-promoting venous drainage -preventing endothelial damage -controlling hypercoagulability |
|
|
Phrophylaxis anticoagulation therapy(low molecular weight heparin)
|
-heparin slows the conversion of prothrombin to thrombin, increasing the effect of anithrombin 3 and decreasing platelet adhesions
|
|
|
Name and explain the theraputic surgical interventions?
|
1)Venal caval interuptio:
-greenfiled or bird's nest filter -may be placed in the IVC, FV, or JV -Prevents emboli from moving to the lungs 2)Iliofemoral venous thrombectomy 3)ligation of superficial veins 3)varicose vein stripping or sclerotherapy |
|
|
varicose vein treatment
|
-sclerotherapy
-laser treatmetns -stripping or ligation |
|
|
What are the advantages of duplex ultrasound as a non-invasive way to test veins?
|
ADVANTAGES:
-low cost -not painful -accurate -portable -repeatable -can detect other anomolies DISADVANTAGES: -subjectiveness -porr determination of acute vs. chronic thrombus -cannot detect calf vein thrombus easily |
|
|
duplex reflux testing
|
-similar test to DVT screening
-scan veins and obtain doppler spectral waveform(augment proximal to sampling location) -reversed flow <0.5sec is a sign of competent valves. |
|
|
venous outflow plethsmography
|
-combines 2 tests into 1 procedure; maximum venous outflow(MVO), and venous volume(capacitance)measurements
-allows determination of whether deep vein thrombosis is present at or aboove the knee |
|
|
What is the formula and the meaning of the formula for venous outflow plesthmography?
|
Q=Pcv-Pivc/R
Q=rate of venous outflow Pcv=pressure gradient in calf veins Pivc=PG in IVC R=resistance of the veins btw the calf and IVC |
|
|
how does thrombus in the deep veins of the thigh affect calf outflow?
|
-thrombus in the deep veins of teh thigh increases resistance to calf outflow
-results in measurable decrease in max. venous outflow -decrease in amount of calf volume expansion |
|
|
what are the types of venous outflow plethsmography?
|
-impedance plesmographY(IPG)
-strain guage plesthmographY(SPG) -air plethsmography |
|
|
where are electrodes placed for IPG?
|
electrodes are placed on the widest part of the calf
|
|
|
what does the SPG use on the calf?
|
-silicon filled rubber tube
|
|
|
collecting cuff
|
pneumatic cuff placed around patients thigh
|
|
|
what should IPG/SPG set to?
|
-connected to a strip chart recorder, and set to DC mode
|
|
|
DC coupling?
|
aka direct current
-electrical voltage that is either positive or negative -current flow in only on direction -useful in evaluating very slow flow states |
|
|
AC couplin
|
aka alternating current
-elctrical vontage that reverses its polarity 60 times/sec. -used in arterial studies -requires a more intense change to produce a measurable signal |
|
|
explain the technique for SPG/IPG venous test?
|
-pneumatic cuff inflated to 50mmHg
-results in increase in calf volume -allow rise to continue for 2minutes -Rapidly deflate cuff -resulting decrease in calf volume recorded until volume returns to pretesting levels |
|
|
what do IPG and SPG measure, how are they interpretted?
|
IPG-measures venous outflow and capasitance
-SPG-measures changes in strain on the mercury filled to to determine electrical resistance -interpretation for both involves plotting values read out from a strip chart onto a grid for normal/abnormal comparasins |
|
|
explain venous strain guage plesthmographY?
|
-may detect venous obstruction in lg veins above the knee
-extremely sensitive test -quantifies altered calf volume |
|
|
explain the technique for SGP
|
-silicon tube filled w/ mercury is wrapped around the calf w/ copper electrodes at both ends of the guage
-voltage applied across guage -calibration done at this point -cuff applied around the thigh, and inflated to 50mmHg -when the leg becomes distendeed w/ blood and the corrisponding circuference of the leg changes, voltage also changes |
|
|
HOw is SGP interpreted?
|
-max rise in tracing refects max. capacitance of the calf veins
-teh rate of venous outflow is reflected by the decline of teh tracing max-venous outflow -tracing should fall to the baseline within 3 seconds to be normal -if there is an upstream occlusion, calfs will not be able to emptly as quickly, so rate of outflow will be longer -results plotted agains a chart -increased resistance reduces voltage which is shown on a strip chart -as blood volume increases(due to venous outflow blockage), strip chart shows max rise in the tracing compared to the baseline. |
|
|
what are the capabilities of impedence plethsmography/
|
-detect thrombi in iliac, femoral, and popiteal veins
-highly sensitive and easily affected by other factors -measures volume changes -not sensitive to calf vein thrombus |
|
|
what are some false positives w/ IPG?
|
-post thrombotic syndrome w/ large collaterals
|
|
|
explain the IPG test?
|
-current conducted through the electrodes appled to the calf
-measures volume changes caused by changes in blood volume -changes in resistance are major causes for changes in impedance |
|
|
explain how IPG is interpreted?
|
-if venous outflow is empeded, electrons do not move as freely(blood is the conductor, and flow is impared)
-as blood vlolume increases, resistance increases -results in changes in electrical impedance -a strip chart can measure a max venous capacitance as a peak in tracing -outflow is venous emptying after deflation -3 sec is normal outflow time; longer time indicates obstruction upstream |
|
|
impedence
|
hindrince to the passage of an alternating electricl current
|
|
|
ohm's law
|
the expression of the releationship btw voltage, current and resistance in a circit
I=V/R |
|
|
what are the 2 ways to meaure resistance with IPG?
|
-two wire method cannot be calibrated and is rarely used
-4 wire method measures the decrease in the voltage btw 2 points across a wire(more reliable and accurate) |
|
|
what happens to resistance to flow as blood volume increases and decreasees?
|
Blood is a good conductor of electricity, so as blood volume increases, ressistance to flow of electrons decreases, and visa versa
|
|
|
SPG vs. IPG
|
IPG=relection of limb changes in blood volume in the limb
SPG=uses changes on a strain on a mercury filled tube to determine electrical resistance(changes in limb circumference) |
|
|
venous reflux testing: PPG
|
-evaluates venous valve competency in presence of symptomatic venous insufficiency
-PPG transducer emits infared light -relected back from RBC in teh cutaneous capillaries -receiving photo-detector channels signal to DC amplifier ] -displays on a strip chart recorder |
|
|
what are the advantages and limitations of venous reflux PPG?
|
ADVANTAGES:
-requres less time -easier to perform LIMITATIONS: -numerous shortcomings -results often indeterminate |
|
|
how does the line on PPG change with change in blood content?
|
-in DC mode, steady state of blood content=straight line
-decrease in blood content=line descends -increase in blood content=elevated line |
|
|
explain PPG during calf muscle contraction and relaxation?
|
-blood is normally pumped toward the heart
-venous blood volume in calf is reduced -decrease in blood content relects reduced calf venous PPG baseline tracing will course downward w/ each contraction -exercise stopped, blood volume slowly retturns via arterial capillary network -PPG tracing slowly ascends on the strip chart |
|
|
Explain PPG w/ incopetant venous valves( 2 ways)
|
1. Calf volume is not reduced to to incompetant calf-veno motor pump
-PPG tracing oscillates up and down, but there is now lowering of the baseline 2. PPG trace lowers on a strip chart indicateing a decrease in volume, but tracing rapidly retruns to pre-exercise level. -indicates a return of valve volume via incopetent venous channels |
|
|
explain the meaning of incmetant venous valves, exercise testing and PPG
|
-w/ excercise, blood should be pushed out of the calf by the calf muscle pump causing a decreased volume of the limb
-if the valves are working as they should, the refill time should be slow(>20sec) -a shorter refill time indicates valvular incopetence/ |
|
|
if you think reflux may be due to varicose veins, what should you do?
|
-tie a tourniquet around the leg and only tighten enough to occlude the superficial veins, and repeat the exam.
|
|
|
explain the method for testing for PPG
|
-warm room
-patient sitting on edge of stretcher -PPG trx applied cephalad to medial malleolus w/ double sided tape -allow system to equalibriate(steady baseline) -strip chart speed=5mm/sec -have patient plantarflex, and dorsiflex 5 times in 5 seconds -observe PPG during exercise and recovery period -stop test when PPG tracing achieves pre-exercise baseline level, reaches stable plateau, or 60 seconds elapses. -measure recovery time |
|
|
when should a PPG test be stopped?
|
-when the pre-exercise baseline has been reached
-reaches a stable plateau -after 60 seconds |
|
|
what should be done if the calf blood volume cannot be reduced?
|
squeeze calf muslces 5 times to simulated exercise
|
|
|
what should be done if there is an abnormal Venous PPG test?
|
-repeat test to verify study
-preceed to touniquet test. |
|
|
What are the normal venous refill times for PPG, SPG, and IPG?
|
PPG->25 seconds
SPG->12 seconds IPG>11sec |
|
|
what is abnormal venous refilling times with PPG?
|
<20 seconds
|
|
|
Touniquet test;why is it useful? what should you use?
|
-Can differentiate superficial from deep vein incompetence.
-Use: preoperative assessment for vein stripping or ligation in the treatment of venous insufficiency. |
|
|
what is the test method for touniquet?
|
-apply blood pressure cuff to lower thigh
-inflate 50mmHg(occludes GSV, but not deep veins) -repeat PPG test |
|
|
explain the interpretation of the touniquet test?
|
-if test resuts normalize, insufficiency in the GSV.
-if test remains positive, repeate exam placing touniquet on upper calf to occlude LSV -If test normal=insufficiency in LSV -If test remains positive, deep veins are incompitent |
|
|
explain the normal results of tourniquet test?
|
-PPG indicates good venous emptying
-recovory time exceeds 20 seconds |
|
|
Explain the abnormal interpretation of tourinquet test?
|
-venous recovery time <20seconds or
-lack of venous emptying |
|
|
explain how the tourniquet test affects varicose veins?
|
Primary varicose veins:
-superficial venous system -therefore usuing a tourniquet will result in a repeat test returing to normal SECONDARY VARICOSE VEINS: -rapid filling times(abnormal) with or without tourniquet |
|
|
Explain testing accuracy(Li and anderson)
|
-If recovory trace returned to baseline, overall accuracy=98%
-Tangent line measurable in 98% of test(84% accuracy) -measurement to stable point produced accuracy of 94%(obtained in 79% of tests) |
|
|
Light reflective rheography
|
-refinement of PPG
-added compartment of a thermistor which measures skin temperature -relies on the same principle where increased temperature=increased blood flow, and increased volume -produces the same type of results as PPG PITFALLS: -not specific -cannot reliably detect obstruction |
|
|
foot volumetry
|
-patient's foot is placed in a water
-water displaced following exercise -blood volume displacedment can be anylized |
|
|
air plethysmography(APG)
|
-used to assess the presence and severity of venous reflux
-a 14 inch long, 5L capacity polyvynil chloroid air chamber surrounds patients leg from knee to ankle -a bag is placed btw patients leg and chamber for calibration -patient lies supine w/ legs elevated 45 degrees -cuff is connected to a pressure transducer, an amplifier and a recorder |
|
|
technique for air plethsmography
|
--inflate chamber to 6mmHg
-ask patient to stand w/ weight on opposite extremity -the change in volume from supine to erect results from venous filling -have patient stand on both legs and do 10 heel raises -EF and residual volume may be measured w/ this method |
|
|
how is ejection fraction for air plethsmography calculated?
|
-by taking the expelled volume after doing 10 heel raises and dividing it by the total venous volume x 100.
|
|
|
explain how APG is interpereted?
|
-venous filling 100-350ml is seen where there is vascualr insufficinecy
-venous filling index obtained -filling index of 2ml/sec or less=normal -filling index of 7ml/sec=severe skin changes, chronic edema and ulceration |
|
|
how may venous filling index be obtained?
|
-by taking 90% of the venous volume and dividing it by the time taken to achieve 90% filling.
|
