Pathophysiology of Ischaemia & Infarction Flashcards
What is ischaemia?
restriction in blood supply to tissues, causing a shortage of oxygen.
What is hypoxia?
a condition in which the body or a region of the body is deprived of adequate oxygen supply at the tissue level.
Describe the four ways that hypoxia can occur?
4
- Hypoxic = low inspired O2, or inspired O2 normal and PaO2 abnormal.
- Anaemic = normal inspired O2, abnormal blood e.g. low Hb
- Stagnation = normal inspired O2, abnormal delivery e.g. ischaemia, shock
- Cytoxic = normal inspired O2, abnormal at tissue level
What is infarction?
tissue death (necrosis) due to inadequate blood supply to the affected area
What are the factors affecting oxygen supply?
6
- inspired O2
- pulmonary function
- blood flow (e.g. atheroma)
- blood constituents (e.g. Hb level)
- integrity of vasculature
- tissue mechanisms
Which factors affect oxygen demand?
2
- tissue itself - different tissues have varying O2 requirements.
- activity of tissue e.g. during exercise
What is cytotoxic hypoxia?
organelles cannot function properly even though they have adequate oxygen e.g. cyanide poisoning
What are the supply issues that can cause ischaemic heart disease?
(5)
- coronary artery atheroma
- cardiac failure (flow)
- pulmonary function: pulmonary oedema (from LVF)
- anaemia
- previous MI
What are demand issues that can cause ischaemic heart disease?
(2)
heart has high intrinsic demand
exertion/stress
How can atherosclerosis cause stable angina?
3
- established atheroma
- sufficient O2 supply at rest
- demand > supply on exertion = angina
How can atherosclerosis cause unstable angina?
4
- complicated atheroma
- insufficient O2 supply at rest
- demand > supply at rest = angina
- worsening pain
What do ulcerated and fissure plaques in the coronary artery lead to?
(2)
- rupture/thrombosis
- ischaemia/infarction
What does atheroma in aorta cause?
How?
aneurysm
dilatation of the aorta due to weakening of the vascular wall from inflammation
What conditions can atheromatous plaques lead to?
6
- Coronary artery disease, MI
- TIA
- Cerebral infarction
- Abdominal aortic aneurysm
- Peripheral vascular disease
- Cardiac failure
Briefly how would you describe the relationship between flow and radius of vessel?
What clinical problem does this result in?
small decrease in radius = large decrease in flow
ischaemia
Give an example of where ischaemia can be chronic?
2
- peripheral vascular disease
- claudication on walking
Give an example of when ischaemia can be acute-on-chronic?
3
- peripheral vascular disease
- claudication on walking
- can become an acute incident e.g. CLI
How does ischaemia affect the biochemistry of cells?
5
- reduced aerobic respiration
- increases anaerobic respiration
- lactate builds up
- acid-base imbalance
- infarction/necrosis
What are the three general clinical effects of ischaemia?
- dysfunction
- pain
- physical damage
What dysfunction can ischaemia cause in the heart?
If it is next to the SA node then there is the chance that it may lead to cardiac arrhythmia.
What are the three potential outcomes of ischaemia?
- no clinical effect
- resolution (normally need therapeutic intervention)
- infarction
What are the 4 possible causes of infarction?
- thrombosis
- embolism
- strangulation
- trauma-cut/ruptured vessel
What are the factors that determine the scale of damage from ischaemia or infarction?
(4)
- Time period
- Tissue/organ
- Pattern of blood supply
- Previous disease e.g. MI
What is coagulative necrosis?
Give an example of where this may occur?
necrosis in which the organ maintains its shape after necrosis
e.g. heart, lung
