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An embolus is adetached intravascular
solid, liquid, or gaseousmass that is carried bythe blood to a sitedistant from its pointof
origin
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In more than 95% of cases, PEs originate from legdeep vein thromboses (DVTs)
Most pulmonary emboli (60% to 80%) areclinically silent because they are small
Sudden death, right heart failure (cor pulmonale),
or cardiovascular collapse occurs when emboliobstruct 60% or more of the pulmonarycirculation
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Embolic obstruction of medium-sized arterieswith subsequent vascular rupture can result inpulmonary hemorrhage but usually does notcause pulmonary infarction
Embolic obstruction of small end-arteriolarpulmonary branches usually does result in
hemorrhage or infarction
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Emboli in the arterial circulation.
Most (80%) arise from intracardiac mural thrombi
2/3 of which are associated with left ventricular
wall infarcts 1/4 with left atrial dilation and fibrillation
The remainder originate from aortic aneurysms,thrombi on ulcerated atherosclerotic plaques, or
fragmentation of a valvular vegetation
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Arterial emboli can travel to a wide variety of sites
Major sites : lower extremities (75%)
brain (10%) intestines, kidneys, spleen, and upper extremities
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The consequences of embolization in a tissuedepend on: its vulnerability to ischemia,
the caliber of the occluded vessel,
collateral blood supply
In general, arterial emboli cause infarction of the
affected tissues
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after fractures of longbones (which havefatty marrow)
rarely in the setting of
soft tissue trauma andburns
characterized bypulmonary
insufficiency,neurologic symptoms,anemia, andthrombocytopenia
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Gas bubbles within the circulation can coalesce toform frothy masses that obstruct vascular flow(and cause distal ischemic injury).
Decompression sickness, occurs when individualsexperience sudden decreases in atmosphericpressure
Chronic form of decompression sickness is calledcaisson disease
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An infarct is anarea of ischemic
necrosis caused byocclusion of eitherthe arterial supplyor the venousdrainage
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Myocardial infarction
Cerebral infarction
Pulmonary infarction
Diabetic (gangrenous infarction)
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Thrombotic or embolic arterial occlusion
Other mechanism:
Local vasospasm
Extrinsic vessel compression (eg.tumor) Torsion of vessel (infark testis)
Vascular trauma
Edema (compartment syndrome)
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Red infarcts (1) with venous occlusions (e.g., ovary),
(2) in loose tissues (e.g., lung)
(3) in tissues with dual circulations
(4) in tissues previously congested by sluggishvenous outflow,
(5) when flow is re-established to a site of previousarterial occlusion and necrosis (e.g., following
angioplasty of an arterial obstruction).
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White infarcts arterial occlusions in solid organs with end-arterial
circulation (e.g., heart, spleen, and kidney)
where tissue density limits the seepage of blood
from adjoining capillary beds into the necroticarea.
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1) the nature of the vascular supply,
2) the rate at which an occlusiondevelops,
3) vulnerability to hypoxia
4) the oxygen content of the blood.
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