Pathophysiology of Ischaemia and Infarction Flashcards Preview

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Flashcards in Pathophysiology of Ischaemia and Infarction Deck (50)
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1

What is hypoxia?

Relative lack of blood supply to the tissue/organ, leading to inadequate oxygen supply to meet the needs of that tissue/organ

2

What are the main types of hypoxia?

Hypoxic
Anaemic
Stagnant
Cytotoxic

3

What is seen in hypoxic hypoxia?

Low inspired O2 level
or
Normal inspired O2 but low PaO2

4

What is seen in anaemic hypoxia?

Normal inspired O2 but abnormal blood

5

What is seen in stagnant hypoxia?

Normal inspired O2 but abnormal delivery, either local e.g. occlusion of a vessel or systemic e.g. shock

6

What is seen in cytotoxic hypoxia?

Normal inspired O2 but abnormal at tissue level

7

What factors affect oxygen supply?

Inspired O2
Pulmonary function
Blood constituents
Blood flow
Integrity of vasculature
Tissue mechanisms

8

What factors affect oxygen demand?

The tissue itself - different tissues have different requirements
Activity of the tissue above baseline value e.g. in exercise

9

What is ischaemia?

Inadequate blood supply to an organ or tissue

10

What is infarction?

Obstruction of the blood supply to an organ or tissue resulting in local cell death
Ischaemic necrosis within a tissue or organ in the living body

11

What is atheroma?

A localised accumulation of lipid and fibrous tissue in the intima of arteries

12

What does established atheroma in coronary arteries result in?

Stable angina

13

What does complicated atheroma in coronary arteries result in?

Unstable angina

14

What do ulcerated or fissured atheromatous plaques result in?

Thrombosis, causing ischaemia or infarction

15

What can atheroma in the aorta result in?

Aortic aneurysm

16

What are the clinical consequences of atheroma?

MI
TIA
Cerebral infarction
Abdominal aortic aneurysm
Peripheral vascular disease
Cardiac failure

17

What is the effect of atheroma on blood flow, according to Poiseuille's formula?

Atheroma leads to narrowing of the vessel lumen due to occlusion or thrombus
A reduction in vessel radius in an atheromatous vessel results in a 16 fold reduction in blood flow
This reduced blood and therefore oxygen flow leads to ischaemia or infarction

18

What are the functional consequences of ischaemia?

Blood/O2 supply fails to meet demand due to low supply, high demand or both

19

What are the general consequences of ischaemia?

Acute - obvious signs and symptoms
Chronic - may go unnoticed over a long period of time, insidious onset
Acute on chronic - acute signs/symptoms on already compromised tissues

20

What are the biochemical consequences of ischaemia?

Normal aerobic metabolism affected
Anaerobic metabolism occurs, causing cell death

21

What are the cellular consequences of ischaemia?

Different tissues have variable O2 requirements so are variably susceptible to ischaemia
Cells with high metabolic rate e.g. cardiac cells and neurons are greatly and quickly affected by ischaemia
Cells with low metabolic rate e.g. fat cells are much less affected by ischaemia

22

What are the clinical consequences of ischaemia?

Dysfunction
Pain
Physical damage of specialised cells

23

What are the potential outcomes of ischaemia?

No clinical effect
Resolution
Therapeutic intervention
Infarction

24

What might result in supply issues in IHD?

Coronary artery atheroma
Cardiac failure
Pulmonary function due to another disease causing pulmonary oedema e.g. left ventricular failure
Anaemia
Previous MI

25

What results in demand issues?

Increased exertion and stress

26

What causes infarction?

Occlusion of the arterial supply or the venous drainage

27

What might cause the cessation of blood flow?

Thrombosis
Embolism
Strangulation
Trauma

28

What does the scale of damage resulting from ischaemia or infarction depend on?

Time period
Tissue/organ affected
Pattern of blood supply
Previous disease

29

What is the basic process of infarction?

Anaerobic metabolism
Cell death
Liberation of enzymes
Breakdown of tissue
Coagulative necrosis e.g. heart, lung
Colliquitive necrosis e.g. brain

30

What occurs in myocardial ischaemia?

Anaerobic metabolism - within seconds
Loss of myocardial contractility - in under 2 minutes
Ultrastructural changes - within a few minutes
Severe ischaemia - within 20-30 minutes
Myocyte necrosis - within 20-40 minutes
Injury to microvasculature - over 1 hour