Stroke

Question 1

Stroke is a clinical diagosis based on what 4 criteria?

Answer 1

1) Sudden onset
2) Focal neurological deficit
3) Of presumed vascular origin
4) Symptoms lasting more than 24 hours or leading to death

Question 2

What distigusihes a stroke from a TIA?

Answer 2

Symptoms lasting less that 24 hours classified as a TIA

Question 3

Stroke excludes lesions associated with what 5 things?

Answer 3

1) Trauma
2) Infection
3) Tumour
4) Retinal infarction
5) Most cases of SAH

Question 4

What are the 2 pathological classifications of stroke, what percentage of strokes does each make up?

Answer 4

1) Cerebral Infarction - 85%

2) Cerebral Haemorrhage - 15%

Question 5

What are the 3 steps in the pathophysiology of acute ischaemic stroke?

Answer 5

1) Initial reduction in cerebral blood flow
2) Alterations in cellular chemistry caused by ischaemia
3) Cellular necrosis

Question 6

What percentage of cardiac output makes up cerebral blood flow?

Answer 6

15%

Question 7

What is the average cerebral blood flow per 100g, how many grams does the average brain weigh?

Answer 7

50-55ml/100g

1400g

Question 8

The brain uses what percentage of the total body O2 consumption at rest?

Answer 8

20%

Question 9

What is the whole brain O2 consumption (CMRO2) per mintute?

Answer 9

45ml O2/min

Question 10

What equation links flow, pressure and resistance?

Answer 10

flow = pressure/resistance

Question 11

What is the normal OEF (oxygen extraction fraction) of the brain, how does this change with increased ppCO2 (ie. reduced cerebral blood flow)?

Answer 11

30%

Increases with increasing ppCO2

Question 12

Which 2 mechanisms come into play to increase O2 delivery to the brain when blood vessels become occluded, and they are regulated via rises in what substance?

Answer 12

Regulated by rises in ppCO2

1) Oxygen extraction fraction increases
2) Dilation of cerebral blood vessekls (1mmHg rise in CO2 leads to 3-5% increase in cerebral blood flow)

Question 13

What is the sole substrate for energy metabolism in the brain?

Answer 13

Glucose

Question 14

Why do neurones require a constant supply of ATP?

Answer 14

Cannot be stored, required to maintain integrity - K+ inside and Na+ outside, Ca2+ also kept outside of cell, constant active transport

Question 15

Glycolysis produces how many molecules of ATP and what other substance?

Answer 15

Pyruvate

2ATP

Question 16

What is the difference in ATP production between aerobic and anaerobic break down of pyruvate??

Answer 16

Aerobic - 36ATP

Anaerobic - 2ATP

Question 17

What is the normal value of cerebral blood flow in mls/100g/min?

Answer 17

45-50ml/100g/min

Question 18

Below what levels of cerebral blood flow in mls/100g/minute, is electrical function impaired, then potassium released and what moved intracellularly then cell death?

Answer 18

Below 20mls/100g/minute - electrical function impaired
Below 12mls/100g/minute - K released and movement of water intracellularly
Below 8mls/100g/minute - cell death

Question 19

When a vessel is blocked the vascular territory can be split into what 3 areas moving distally from the blockage, how is each defined, how does each change with time?

Answer 19

1) Core - unsalvageable
2) Penumbra - electrical function impaired but tissue can be salvaged if blood flow can be restored
3) Oligemia - subnormal flow but no comrpomise to function
Over time, oligemia stays the same, core increases and penumbra thus decreases in area

Question 20

What is the difference between capacitance and resistance vessels?

Answer 20

Capacitance vessels - large pipes allowing blood flow to brain
Resistance vessels - have a muscular component which can dilate in response to metabollic demand (ie. ppCO2)

Question 21

How is cerebral blood flow initially maintained in response to reduced cerebral perfusion pressure in an area distal to a blocage?

Answer 21

Resistance vessels dilate ie. cerebral blood volume increases

Question 22

Once resistance vessels have undergone maximum dilation in response to reduced cerebral perfusion pressure distal to a blockage how is cerebral metabolic rate of oxygen (oxygen delivery to the brain) maintained?

Answer 22

Oxygen extraction fraction (OEF) increases

Question 23

Once cerebral blood volume (dilation) and oxygen extraction fraction have increased to their maximum what happens to the brain?

Answer 23

Ischaemia as both blood flow and cerebral metabolic rate of oxygen cannot be maintained - this is when symptoms begin

Question 24

What 2 things can cause an ischaemic stroke?

Answer 24

1) Thrombosis

2) Embolism

Question 25

What is a cardiogenic embolism?

Answer 25

Embolism causing ischaemic stroke originating from the heart

Question 26

What is an artery to artery embolism?

Answer 26

Embolism causing ischaemic stroke originating from proximal arteries

Question 27

What are the 3 most common mechanism of ichaemic stroke?

Answer 27

1) Large vessel atherosclerosis
2) Cardioembolism
3) Intracranial small vessel disease

Question 28

What condition commonly leads to the formation of cardioembolism and is thus a significant cause of CVAs?

Answer 28

Atrial fibrilation

Question 29

What is meant by secondary preventions for CVA?

Answer 29

Prevention of further CVAs following a CVA or TIA

Question 30

Give 3 secondary preventions for CVA?

Answer 30

1) Aspirin
2) Warfarin(/anticoagulants) - partifcularly in AF
3) Carotid surgery (enarterectomy) - in carotid stenosis

Question 31

How can stroke be treated to reduce severity of dependecny or death?

Answer 31

1) thrombolysis - effectiveness is time dependent

2) recanalisation - ie stenting

Question 32

Occulsion of which vessel/s is associated with the highest risk of deaths or severe disability?

Answer 32

Proximal anterior circulation - ie. ICA

Accounts for 18-25% of strokes but 60-70% of deaths or severe disability