Pathophysiology of Ischaemia and Infarction Flashcards
What is hypoxic hypoxia?
Either :
A) Low inspired oxygen levels or,
B) Normal inspired oxygen but low PaO2
What is anaemic hypoxia?
Hypoxia where the inspired oxygen levels are normal but the blood itself is abnormal
What is stagnant hypoxia?
Hypoxia where there is normal inspired oxygen levels but abnormal delivery which is either local e.g. occlusion of a vessel or systemic e.g. shock
What is cytotoxic hypoxia?
When the inspired oxygen levels are normal but oxygen levels are abnormal at the tissue level
What factors affect oxygen supply?
Inspired oxygen levels, pulmonary function, blood constituents, blood flow, integrity of vasculature and tissue mechanisms
What factors affect oxygen demand?
The requirement of the tissue itself and activity of the tissue above the baseline value
What are the functional effects of ischaemia?
Blood/oxygen supply fails to meet the demand due to a decrease in supply; an increase in demand or both
What are the clinical effects of ischaemia?
Dysfunction, pain and physical damage (specialised cells)
What are the possible outcomes of ischaemia?
No clinical effect, resolution, therapeutic intervention or infarction
What is infarction?
Ischaemic necrosis within a tissue/organ in a living body produced by occlusion of either the arterial supply or venous drainage
What are the causes of infarction?
Thrombosis, embolism, strangulation e.g. gut and trauma - cut/ruptured vessel
What factors determine how much damage the ischaemia/infarction will cause?
The time period, tissue/organ affected, pattern of blood supply and previous disease
What are the two types of necrosis?
Coagulative necrosis e.g. heart or lungs and colliquitive necrosis e.g. brain
How does a myocardial infarction progress?
Coronary artery obstruction leads to a decrease in blood flow to a region of the myocardium. This causes ischaemia, rapid myocardial dysfunction and then myocyte death
What will the appearance of an infarct be within 24hrs?
No changes will be visible on a visual inspection. After a few hours swollen mitochondria may be seen on an electron microscopy
How will an infarct appear between 24-48hrs after the event?
In solid tissues e.g. myocardium, spleen and kidneys the infarct will be pale.
In loose/previously congested tissues/second or continuing blood dupply/venous occlusion e.g. lungs and liver the infarct will appear red
Microscopically: Acute inflammation initially at the edge of the infarct and loss of specialised cell features
How will an infarct appear from 72hrs onwards?
Pale infarct - yellow/white with red periphery
Red infarct - little change
Microscopically: Chronic inflammation, macrophages remove debris, granulation tissue and fibrosis
What will be the end result of the appearance of an infarct?
A scar will replace the area of tissue damage
What is a transmural infarction?
Where the ischaemic necrosis affects the full thickness of the myocardium
What is a subendocardial infarction?
The ischaemic necrosis is mostly limited to a zone of myocardium under the endocardial lining of the heart
What are the complications of an MI?
Sudden death, arrhythmias, angina, cardiac failure, cardiac rupture - ventricular wall, septum, papillary muscle, reinfarction, pericarditis, pulmonary embolism secondary to DVT, papillary muscle dysfunction - necrosis/rupture, mitral incompetence, mural thrombosis, ventricular aneurysm and Dressler’s syndrome
