Blood Supply to the Brain Flashcards
What are the main blood vessels in/to the brain?
See diagram in lecture notes
What percentage of your body mass is the brain and what percentage of cardiac output does it receive? What percentage of total body oxygen and glucose?
- ~ 2% of body weight
- Receives 15% of cardiac output and uses 20% of total body O2 and 25% of total body glucose
What is the average value of brain blood flow?
- Average brain blood flow = 46mL/100 grams of brain per minute
How long would anoxia to the brain need to last to lead to unconsciousness? What about permanent unconsciousness?
- 20 secs of anoxia lead to unconsciousness
- > 5 mins permanent unconsciousness
How is brain blood flow regulated?
- Flow regulated by auto-regulation
o Normotensive cerebral blood flow = ~50mL per 100g of brain tissue per min if cerebral perfusion pressure between 60-160mmHg
o ↓O2, ↑CO2 = ↑flow
What are the arteries and veins like in the brain?
- Arteries, thin walled, easily blocked, distorted or ruptured
- Veins, no valves, thin walled, no muscles or elasticity to help return
Below what PO2 will blood flow increase and by how much?
- Blood flow does not change until PO2 falls below ~50mmHg when cerebral blood flow increases if hypoxia decrease PO2 further then cerebral blood flow can increase up to 400% above resting levels.
What effect does CO2 have on blood flow and by how much?
- CO2 has a profound effect – hypercapnia causes marked dilation of cerebral arteries and increased blood flow hypocapnia constriction and decreased blood flow. 5% CO2 inhalation increases cerebral blood flow by 50%, 7% CO2 increases cerebral blood flow by 100%.
What percentage each do the internal carotids and vertebral arteries provide of the cerebral blood flow?
- Internal carotids = 80% of total cerebral blood flow to anterior 2/3rd of cerebral cortex
- Vertebral arteries = 20% of total cerebral blood flow to posterior 1/3rd of cerebral cortex, brainstem and spinal cord
See diagrams in lecture notes
What are the components of the circle of Willis?
See diagrams and angiograms in lecture notes
What would the Circle of Willis look like in a normal angiogram? In what percentage of the population can a classic Circle of Willis be seen?
- Under normal situations anterior communicating and posterior communicating closed
- Classic Circle of Willis seen in only 34.5% of population
When only should the collateral circulation be open? What does this mean?
- Collateral circulation should only open when there is a pressure difference
- Collateral circulation opens in pathologies
What do variants in cerebral arterial circle look like on an angiogram?
See diagrams in lecture notes
What are the main branches of the internal carotid artery (ICA) in the anterior circulation? What do they supply?
- Ophthalmic
o Orbit and retina – connects to external carotid artery - Posterior communicating
o Connects carotid and vertebral artery system - Middle cerebral artery
o Basal ganglia and internal capsule (striate arteries), lateral 2/3rds of cortex - Anterior cerebral
o Internal capsule, medial side of frontal and parietal lobes.
o Anastomose with MCA
See diagram and angiograms in lecture notes
Which artery supplies each part of the cerebral cortex?
See diagrams in lecture notes
What are the main branches of the posterior circulation?
- Vertebral o Spinal cord o Dorsal medulla of brainstem - PICA - Basilar o Pons o cerebellum - Posterior cerebral artery o Inferior and medial aspects of temporal and occipital cortex o Thalamus and posterior internal capsule o Midbrain o Anastomose with MCA
What are the abbreviations for the components of the posterior circulation?
- ASA = anterior spinal artery
- AICA = anterior inferior cerebellar artery
- PICA = posterior inferior cerebellar artery
- VA = vertebral artery
- BA = basilar artery
- VI = abducents
- OMN = oculomotor nerve
- MB = mammillary body
- PCA = posterior cerebral artery
- V3 = floor of 3rd ventricle
- SCA = superior cerebellar artery
See diagrams in lecture notes
Where are the superficial cerebral veins and what allows the CSF to flow into them? How is backflow prevented?
- Superficial cerebral veins cross the subarachnoid space
- Bridging veins pierce dura as they enter intracranial (dural) venous sinuses
- Mainly superior sagittal sinus
- Arachnoid granulations allow CSF to flow into venous blood of sinuses but prevent backflow of blood into sub-arachnoid space
What is the cavernous sinus? When can they be seen?
- Large collection of thin walled veins
- Only place where an artery travels through a venous structure
- ICA make acute bends and can be seen twice
What is the blood supply to the spinal cord?
See diagrams in lecture notes
(Great segmental medullary artery (artery of Adamkiewicz) on left in 65% of population reinforces circulation to 2/3rds of spinal cord)
What may happen during surgery for an aortic aneurysm? What can cause these problems and what may be the effects?
Ischaemia of spinal cord
- Patients undergoing surgery for an aortic aneurysm may lose all sensation and voluntary movement inferior to level of occlusion
- Severe drop in BP for 3-6 mins may be reduce or stop blood flow from the segmental medullary to anterior spinal artery
What are the major causes of stroke?
- Major causes of stroke o Atherosclerosis o Hypertension o Aneurysm o Elderly o Head injury (trauma) o Alcoholics o Arteriovenous malformation
What are the most common non-traumatic causes of intracerebral haemorrhage?
Hypertension (36%)
Aneurysm (36%)
AV Malformation (11%)
Other (17%)
What are the 2 types of brain aneurysm? What is the likelihood of developing one and who is most at risk? When do they become dangerous?
- 2 types o Saccular (berry is a subtype) o Fusiform - 1:15 people develop a brain aneurysm - Women at higher risk 3:2 - Danger comes if it ruptures
Where can an middle cerebral artery (MCA) stroke occur and what does it cause?
- MCA stroke o Dominant hemisphere (Left) Global aphasia Sensorimotor loss on contralateral face, upper limb and trunk o Striate arteries often involved o Non-dominant (R.parietal lobe) Neglect syndrome - Unilateral neglect are able to describe only the parts of a mental scene represented by the undamaged cortex. Both left and right parietal damage will result in hemispatial neglect, but patients with L parietal damage tend to recover quickly
What effects can an ACA stroke cause?
o Contralateral sensorimotor loss below waist
o Urinary incontinence
o Personality defects
o Split-brain syndrome
What effects can a PCA stroke cause?
o Contralateral homonymous hemianopsia
o Reading and writing deficits
o Impaired memory
What are the characteristics and symptoms of lateral medullary syndrome (Wallenberg syndrome) PICA?
o Vertigo, nystagmus, nausea and vomiting, dysarthia, dysphonia, loss of pain and temp in body (contralateral), loss of pain and temp in face (ipsilateral), loss of gag reflex (nucleus ambiguus)
o Horner syndrome (ipsilateral)
What is a transient ischaemic attack (TIA)? What are its symptoms
- “A transient episode of neurologic dysfunction caused by focal brain, spinal cord, or retina ischemia, without acute infarction”
- Diagnosis based on symptoms alone
- Warning sign of heart attack or stroke
o 5% in 1st 48 hours
o 10% within 90 days
o 30-40% in 3-5yrs - TIA symptoms
o Anterior circulation
Motor weakness
Hemi-sensory loss
Dysarthria
Transient monocular blindness
o Posterior circulation
Vertigo
Diplopia
Ataxia
Amnesia
