31 - Stroke Flashcards
What is a stroke
Ischaemia and hypoxia due to cerebrovascular disease
What are causes of a stroke
Infarction
Haemorrhage
Parenchymal stroke
Stroke in brain tissue
Subarachnoid stroke
Into subarachnoid space
Where do most strokes occur and why
Branches of middle cerebral artery as highly tortuous
The branches from MCA form lenticulo-striate arteries which leave the MCA at 90 degree angle
What do the lenticulo-striate arteries supply blood to
Basal ganglia adn internal capsule
Symptoms of a stroke
ALL SUDDEN Numbness, weakness of arm/face on one side of the body Confusion trouble seeing trouble walking severe headache
What does FAST stand for
F - Face
A - Arms
S - Speech
T - Time (quicker help means more brain function can be preserved)
What are the types of stroke
TIA Thrombotic Ischaemic Hemorrhagic Lacunar
Which are the most common strokes
Thrombotic and embolic strokes make up 85% of all strokes
Transient Ischaemic Attack
Lasts less than 24 hours
Result of a small emboli
Mini-stroke
Thrombotic Stroke
Ischaemic stroke
The blood clot in cerebral artery, plaque opens and collagen and TF are exposed that produce a thrombus that blocks blood supply
What percentage of thrombotic strokes develop during sleep and what is the reason
60%
Due to obstructive sleep apnea that increases BP and ruptures the plaque
Embolic Stroke
Ischaemic
Can be blood broken from a thrombus or bacteria
Neurological signs develop rapidly
Usually occur during activity
What is the usual source for an embolic stroke
Left side of the heart - A Fib, MI, defective valves
Hemorrhagic stroke
Sudden neurological symptoms
Severe headache
Causes stupor or coma
Usually hypertensive
Lacunar stroke
Occlusion in one of the arteries that provides blood to the brain’s deep structures
What are example of the brain’s deep structures
Basal ganglia, cerebral white matter, thalamus, pons,cerebellum
What percentage of ischaemic strokes are lacunar strokes
15-25%
Motor hemiparesis with dysarthria
33-55%(most common) infarct in posterior limb of internal capsule
Ataxia & hemiparesis
infarct also in posterior limb of internal capsule
Dysarthria & clumsy hand
infarct in anterior limb of internal capsule
Risk factors
Hypertension Heart disease (AFIB) Hyperlipidaemia (use statins) Diabetes Smoking Obstructive Sleep Apnea Low potassium diet
How do you diagnose a stroke
Physical examination (BP) Blood tests (Cholesterol, C-reactive protein) CT Scan (Show haemorrhage, tumor, stroke) MRI - Detect damaged brain tissue
Why do nerve cells have a high ATP usage
To fuel a sodium pump
What happens when a Na pump stops working bc of hypoxia
Na leaks into cells
Cell swelling
Swelling exerts pressure on the cells and EC space decreased
Cells contact each other - Raise in intercranial pressure
By how much does the EC space decrease in a normal brain to hypoxic brain
20% to 5%
What can a severe raise in ICP cause
Cerebellum extrudes through the foramen magnum
Compression on lower brainstem
What removes the potassium that is released into ECS and what happens in a hypoxic brain
Glial cells
In a hypoxic brain - K+ not removed so excess NT release
What is excitotoxicity
Follows a stroke
Hypoxic brain cells subjected to excessive NTS due to a smaller ECS and reduced reuptake
Lead to cell damage
What is the main excitatory brain transmitter and what does it act on
Glutamate anion
Main excitatory brain transmitter
Acts on NMDA and AMPA receptors
What does excess NMDA receptor stimulation and excess AMPA receptor stimulation cause
Excess NMDA receptor stimulation - Excess influx of Ca ions into nerve cells
Excess AMPA receptor stimulation - Slow excitotoxicity
What happens to ATP-ase uptake sites for glutamate in hypoxia and what is the result of this
The ATP drops
reuptake fails
post synaptic glutamate receptors overstimulated
Leads to an influx of calcium and the excitotoxic loop
What does an influx of calcium lead to
increased metabolic demand on the cell
Uses more oxygen
when no oxygen there is free radical formation which triggers apoptosis
What is the penumbra region
neurons are hypoxic and /or damaged but survival is possible
What happens to cells in the middle and outside in a stroke
Cells in the middle face inevitable death
Cells on the outside will survive
What are the 3 main treatment strategies for a stroke
Restore blood flow
Combat excitotoxicity
Combat free radical damage
How can you restore blood flow
Tissue plasminogen activators – thrombolysis
How can you combat excitotoxicity?
- NMDA antagonists e.g Cerestat – block NMDA receptors and fast excitotoxicity but has serious side effects
- AMP antagonists e.g NBQX – reduce slow excitotoxicity
How can you combat free radical damage?
- Antioxidants e.g Vitamin C and E to boost brain’s antioxidant defences
- Dietary vitamin C and E reduce risk in vulnerable populations
- Free radical scavenging enzymes e.g superoxide dismutase low in in patients
- Cool down the brain – reduces oxygen demand
How do you reduce the primary risk of stroke
Treat hypertension - Diuretics, ACE inhibitors, AR antagonist, change diet
Treat A Fib - Give Aspirin
Statins - reduce LDL cholesterol
