Stroke Flashcards
Stroke is a clinical diagosis based on what 4 criteria?
1) Sudden onset
2) Focal neurological deficit
3) Of presumed vascular origin
4) Symptoms lasting more than 24 hours or leading to death
What distigusihes a stroke from a TIA?
Symptoms lasting less that 24 hours classified as a TIA
Stroke excludes lesions associated with what 5 things?
1) Trauma
2) Infection
3) Tumour
4) Retinal infarction
5) Most cases of SAH
What are the 2 pathological classifications of stroke, what percentage of strokes does each make up?
1) Cerebral Infarction - 85%
2) Cerebral Haemorrhage - 15%
What are the 3 steps in the pathophysiology of acute ischaemic stroke?
1) Initial reduction in cerebral blood flow
2) Alterations in cellular chemistry caused by ischaemia
3) Cellular necrosis
What percentage of cardiac output makes up cerebral blood flow?
15%
What is the average cerebral blood flow per 100g, how many grams does the average brain weigh?
50-55ml/100g
1400g
The brain uses what percentage of the total body O2 consumption at rest?
20%
What is the whole brain O2 consumption (CMRO2) per mintute?
45ml O2/min
What equation links flow, pressure and resistance?
flow = pressure/resistance
What is the normal OEF (oxygen extraction fraction) of the brain, how does this change with increased ppCO2 (ie. reduced cerebral blood flow)?
30%
Increases with increasing ppCO2
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?
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)
What is the sole substrate for energy metabolism in the brain?
Glucose
Why do neurones require a constant supply of ATP?
Cannot be stored, required to maintain integrity - K+ inside and Na+ outside, Ca2+ also kept outside of cell, constant active transport
Glycolysis produces how many molecules of ATP and what other substance?
Pyruvate
2ATP
What is the difference in ATP production between aerobic and anaerobic break down of pyruvate??
Aerobic - 36ATP
Anaerobic - 2ATP
What is the normal value of cerebral blood flow in mls/100g/min?
45-50ml/100g/min
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?
Below 20mls/100g/minute - electrical function impaired
Below 12mls/100g/minute - K released and movement of water intracellularly
Below 8mls/100g/minute - cell death
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?
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
What is the difference between capacitance and resistance vessels?
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)
How is cerebral blood flow initially maintained in response to reduced cerebral perfusion pressure in an area distal to a blocage?
Resistance vessels dilate ie. cerebral blood volume increases
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?
Oxygen extraction fraction (OEF) increases
Once cerebral blood volume (dilation) and oxygen extraction fraction have increased to their maximum what happens to the brain?
Ischaemia as both blood flow and cerebral metabolic rate of oxygen cannot be maintained - this is when symptoms begin
What 2 things can cause an ischaemic stroke?
1) Thrombosis
2) Embolism
What is a cardiogenic embolism?
Embolism causing ischaemic stroke originating from the heart
What is an artery to artery embolism?
Embolism causing ischaemic stroke originating from proximal arteries
What are the 3 most common mechanism of ichaemic stroke?
1) Large vessel atherosclerosis
2) Cardioembolism
3) Intracranial small vessel disease
What condition commonly leads to the formation of cardioembolism and is thus a significant cause of CVAs?
Atrial fibrilation
What is meant by secondary preventions for CVA?
Prevention of further CVAs following a CVA or TIA
Give 3 secondary preventions for CVA?
1) Aspirin
2) Warfarin(/anticoagulants) - partifcularly in AF
3) Carotid surgery (enarterectomy) - in carotid stenosis
How can stroke be treated to reduce severity of dependecny or death?
1) thrombolysis - effectiveness is time dependent
2) recanalisation - ie stenting
Occulsion of which vessel/s is associated with the highest risk of deaths or severe disability?
Proximal anterior circulation - ie. ICA
Accounts for 18-25% of strokes but 60-70% of deaths or severe disability
