Ischaemia, infarction and shock Flashcards
What is hypoxia?
–Any state of reduced tissue oxygen availability
- Generalised - whole body e.g. altitude, anaemia
- Regional - specific tissues affected
What is ischaemia and why is it worse than hypoxia alone?
–Pathological reduction in blood flow to tissues
–Usually as a result of obstruction to arterial flow
commonly as a result of thrombosis / embolism
–Ischaemia results in tissue hypoxia
Worse as there’s no removal of waste products in addition to hypoxia.
What is PCI for MI?
Percutaneous intervention for myocardial infarction. Only suitable for reversible ischaemia.
What is reperfusion injury?
Generation of ROS by inflammatory cells causes further cell damage.
What is infarction?
–Ischaemic necrosis caused by occlusion of the arterial supply or venous drainage
What causes the majority of infarctions?
Thrombosis and emobolisms. Most common within arteries.
What are the other causes of infarction?
Vasospasm, atheroma, extrinsic compression (eg tumour), twisiting of vessel roots, rupture of vascular supply (eg AAA)
Why do lung infarctions look red?
Dual blood supply. One supply blocked, the vessels for the other are damaged and leak blood into the infarcted area.
What is the difference between coagulative necrosis and liquefactive necrosis?
In coagulative necrosis the tissue retains it’s basic arcitecture, Tissue arcitecture lost in liquefactive as there is no collagen (brain).
What factors influence the severity of the ischaemic damage?
- Nature of the blood supply
- Rate of occlusion
- Tissue vulnerability to hypoxia
- Blood oxygen content
How does the nature of the blood supply influence the severity of the ischaemic damage?
•An alternative blood supply will mean less damage hence severe ischaemia required for infarction
–Lungs (pulmonary and bronchial arteries)
–Liver (hepatic artery and portal vein)
–Hand (radial and ulnar artery)
•Kidneys, spleen, testis etc. have single supplies hence are vulnerable to infarction
How does the rate of occlusion effect the severity of ischaemic damage?
- Slow developing occlusions are less likely to infarct tissues
- Allows time for the development of alternative (collateral) perfusion pathways
- Coronary arteries
–Small anastomoses connect major branches and have minimal flow
–If a coronary arterial branch is slowly occluded flow can be directed through these channels
–Infarction can be avoided even if the main arterial branch is totally occluded
How does the tissue vulnerabilty to hypoxia influence the severity of ischaemic damage?
•The brain
–If a neurone is deprived of oxygen irreversible cell damage occurs in 3 to 4 minutes
–Brain is 1 to 2% of total body weight but requires 15% of cardiac output and 20% of body oxygen consumption
–Therefore very vulnerable to injury
•The heart
–Slightly more resistant with cardiac myocyte death taking 20 to 30 minutes
How does the blood oxygen content influence the severity of ischaemia?
- Reduced oxygen in the blood (anaemia etc.) increases the chances of infarction
- Congestive cardiac failure
–Poor cardiac output and impaired pulmonary ventilation
–May develop an infarct with a normally inconsequential narrowing of the vessels!
•Watershed regions occur at the point of anastomosis between two vascular supplies
–E.g. Splenic flexure and brain
What are the most common causes of an ischaemic stroke?
–Thrombosis secondary to atherosclerosis
–Embolism (e.g. mural thrombus)
