Cerebral Ischaemia and Stroke Flashcards
What is the circle of Willis?
The blood supply system to the brain, which has different arteries that supply different areas of the brain. The system allows collateral circulation in the case of a major artery occlusion
What is a stroke?
A stroke is a loss of brain function caused by a disruption of blood supply, usually leading to a permanent sensory, motor/cognitive deficit. AKA cerebrovascular accident. Defined as a rapidly developing focal (localised) disturbance of brain function of presumed vascular origin and of >24hr duration.
What are the neurological deficits that result from a stroke?
Hemiplegia (paralysis on one side), balance problems, loss of sensation, visual field, language, motor planning skills, personality change. Manifestation depends on the affected area but severity doesnt equal tissue loss
What is an ischaemic stroke?
A stroke that results due to a restriction of blood supply (>20% of normal flow). Can be focal or global. Responsible for 85% of strokes. Focal eg. occlusion in a cerebral vessel. Global eg. Blood flow to brain is halted or drastically reduced eg. by cardiac arrest.
What is the difference between a thrombosis and an embolism?
A thrombosis is a platelet plug in the vessel itself, and an embolism is a blood clot/other material (fat/air) that originates elsewhere.
What determines the degree of tissue damage in a stroke?
The extent and duration of the occlusion, and the degree of blood supply from other vessels.
Describe the tissue that results from a stroke ie. core and penumbra
The core is tissue that undergoes irreversible damage due to the ischaemia - called an infarct. Cells suffer necrotic death very quickly. The penumbra is the area surrounding the core that has undergone damage but not irreversible because it receives collateral flow from surrounding vessels. Over hours the infarct can spread from the core to the penumbra
Which area of the ischaemic tissue is the target of therapy?
The penumbra because it offers a window of oppurtunity to preserve tissue. The more collateral vessels surround the region means there is more penumbra because more tissues receive O2 and glucose.
What is a transient ischaemic attack?
A rapidly developing focal disturbance of presumed vascular origin that completely resolves within 24hr. Occurs when blood flow is briefly interrupted. The symptoms are similar to a stroke but don’t last as long.
What is the importance of a TIA and what are the risk factors?
Often a warning sign for risk of a more serious and debilitating stroke. Most important factors are high BP, smoking, heart disease, carotid artery disease, diabetes, heavy alcohol use.
What is a haemorrhagic stroke?
A stroke that results from bleeding in the brain
What is an intracerebral haemorrhagic stroke?
An intracerebral haemorrhagic stroke is when the vessel inside the brain bursts and leaks blood into the surrounding tissue. It is often caused by an aneurysm (sac-like malformation of a vessel, protruding from vessel wall and weakening it)
What is a subarachnoid haemorrhagic stroke?
Bleeding between the brain and the tissue covering the brain (subarachnoid space). It causes brain cells to die and affected parts of the brain to stop working properly. Cells in the area suffer from: lack of blood, compression by blood leaking out of the vessel and forming a clot, causing secondary inflammation and toxicity. High BP and ageing blood vessels are the most common causes
Explain the risk factors for a stroke
Hypertension - Main risk factor for haemorrhagic stroke but contributes to atherosclerosis which can lead to ischaemic
Age - Stroke risk increases with age
Cardiac disease - Left atrial dysfunction including fibrillation is associated with a risk of thromboembolism which can cause a stroke
Smoking - Contributes to 15% of annual stroke deaths
Diabetes - Stroke causes 20% of diabetic deaths
High LDL cholesterol - Can promote atherosclerotic build up
Sedentary behaviour, diet, obesity - Affect all the others, so impact is secondary.
What is global ischaemia?
Results from temporary blockage of blood flow to the brain eg. cardiac arrest.
Which neuronal cell types are particularly vulnerable to global ischaemia?
Pyramidal cells of CA1 hippocampus area, pyramidal neurons of neocortex (layers 3, 5, 6), Purkinje cells of cerebellum, striatum neurons. They die after 10-20 mins.
What happens to the neurons in the CA1 hippocampus during global isachemia?
They die quickly and lesions in this area commonly manifest as memory loss. The cell death isn’t immediate, and while the cells appear to recover and resume normal function, global ischaemia has triggered delayed neuronal death
Why does the brain use so much glucose?
Uses 20% of total glucose and up consumption (up to 50% in intense activity) mainly to maintain transmembrane ion gradients and restoring them after each action potential
Why does the brain need a continuous supply of glucose?
Because it cannot store or synthesise glucose and can’t utilise other energy sources. Glucose can be supplemented (but not replaced) by lactate or ketone bodies in extreme circumstances eg. starvation
What are the effects of hypoglycaemia?
Disorientation, slurred speech, impaired motor function. Glucose < 2mM can lead to loss of consciousness, coma, or death
Why does the brain need a continuous supply of O2?
It needs to produce ATP via oxidative phosphorylation. Because the energy demand of the brain is so high, in hypoxic condition, anaerobic respiration is only sufficient for a couple of minutes to keep cells alive. Complete lack of O2 to the brain is called anoxia
How does limited blood flow affect the brain?
If blood flow is < 50%, functions significantly impaired. If total blood flow is interrupted for 4 seconds, there’s loss of consciousness. After a few minutes, irreversible damage occurs to the brain
What are the differences between the different types of cell death that occur during ischaemia?
In the focal core, all cells die rapidly due to a lack of energy to maintain function and integrity. This passive unregulated cell death is necrosis.
The delayed neuronal cell death occuring in global ischaemia is programmed cell death, the most well known being apoptosis.
How can ischaemic strokes be treated with drugs?
Tissue-type plasminogen activator, a thrombolytic agent, helps to dissolve the clot to restore blood flow
