Chapter 17: Blood Supply

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Chapter 17 Blood Supply

• Chris Rorden
• University of South Carolina
• Norman J. Arnold School of Public Health
• Department of Communication Sciences and
  Disorders
• University of South Carolina

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Role of Blood Supply

• Nutrition to parenchyma (brain cells).
• Brain is completely dependent on oxygen supply -
  No O2 reserves.
• Irreversible damage in 4-6 minutes if no oxygen
• Brain requires 20 of O2 for 2 of body weight.
• Brain requires glucose for energy
• No ability to use fat
• Remove carbon dioxide and waste-products from
  cells
• Cerebral perfusion
• gt 60 ml/100gr min-1 in Gray matter
• 40 lt X lt 60 in White matter
• 750mL blood pumped per minute and circulated
  blood returned for reoxygenation

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Vascular Network

• Network of arteries and veins
• Arteries carry blood away from the heart
• Arteries divide into smaller vessels called
  arterioles
• Arterioles divide further into capillaries
• Vascular Network
• Veins carry blood toward the heart
• Smallest level are venules that are connected to
  capillaries
• Venules Carry blood to sinuses on cortical
  surface

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Local blood flow

• Arteries
• Arterioles
• Capillaries
• Venules
• Sinuses

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Cerebrovascular Supply

• Two Systems
• Carotid System
• Vertebral Basilar System
• Meet in Circle of Willis

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Vertebral / Basilar Arteries

• Brain stem
• Basilar Artery
• Vertebral Arteries

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Vertebral Basilar System

• Two Vertebral Arteries enter skull through
  Foramen Magnum
• Join to form the Basilar Artery and then Circle
  of Willis
• Numerous small branches
• Supplies the brainstem and cerebellum
• Posterior Inferior Cerebellar Artery (PICA) is
  one that serves cerebellum.

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Carotid Arteries
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Carotid System

• Common Carotid Artery
• Divides into two branches
• External Branch
• Supply blood to facial muscles, forehead and
  oral, nasal and orbital cavities
• Internal Branch (enters the skull through the
  carotid foramen)
• Anterior choroidal artery (supplies optic tract,
  posterior limb of internal capsule, branches to
  midbrain,and lateral geniculate nucleus).
• Ophthalmic artery (Supplies blood to the eyeball
  and ocular muscles)
• Major source of blood to the brain
• After joining Circle of Willis becomes anterior
  cerebral and middle cerebral arteries

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Circle of Willis
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Circle of Willis

• Wreath-shaped circle of Willis located at ventral
  surface of brain
• Connects Carotid and Vertebral Basilar Systems
• Middle and Anterior Cerebral Arteries
• Anterior Communicating Artery
• Posterior Cerebral Artery
• Posterior Communicating Artery

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Cortical Blood Supply

• ACA Medial Frontal Perfusion
• MCA Lateral Perfusion
• PCA Posterior medial Perfusion, cerebellum
• Watershed Areas overlap between major arteries

Major Arteries ? Carotid ? Anterior Cerebral ?
Middle Cerebral ?Posterior Cerebral
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Two Types of Arteries

• Cortical (Circumferential) Branches
• Supply External Brain Structures
• Central (Penetrating) Branches
• Small
• Penetrate ventral surface to supply internal
  brain structures

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Anterior Cerebral Artery

• Supplies Orbital and Medial Surfaces of Frontal
  and Parietal Lobes
• Interruption causes
• Cortical Arteries
• Paralysis of legs and feet
• Difficulty in prefrontal lobe functions of
  cognitive thinking, judgment, motor initiation
  and self monitoring

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Middle Cerebral Artery

• Direct continuation of carotid artery
• Cortical Branches
• Temporal
• Parietal
• Frontal

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MCA Cortical Branches

• Supplies blood to entire lateral surface of brain
• Somatosensory Cortex
• Motor Cortex
• Broca's Area
• Heschls Gyrus
• Wernickes Area
• Therefore, symptoms include
• Aphasia
• Motor deficits
• Neglect (right hemisphere)

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MCA Penetrating Arteries

• Supplies basal ganglia and diencephalon
• Interruption causes
• Contralateral hemiplegia
• Impaired sensory systems
• Touch
• Pain and temperature

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Central Penetrating Arteries

• Arise from cortical arteries or from Circle of
  Willis
• Penetrate inferior surface of brain
• Can form channels to facilitate blood supply
• Central (Penetrating) Arteries
• Supply
• Thalamus
• Hypothalamus
• Basal Ganglia
• Internal capsule
• Choroid Plexus

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Posterior Cerebral Artery

• Supplies blood to anterior and inferior temporal
  lobes, uncus, inferior temporal gyri, inferior
  and medial occipital lobe
• Watersheds with middle cerebral artery
• Interruption causes
• Homonymous hemianopsia
• Possible total blindness
• Cerebellar symptoms

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Collateral Circulation

• Redundant arteries provide alternative supply
  when primary supply is lost
• Small, normally closed arteries open up after
  occlusion, connecting two larger arteries or
  different parts of the same artery.
• Dependent on location and severity of blockage
• Better collateral circulation if blockage is near
  main trunk
• Better if blockage occurs gradually

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Vascular Pathologies

• Occlusive (Something is blocked causing
  ischemia). 80 of strokes are ischemic
• Embolism object from another part of the body
  which travels through artery until it gets stuck.
• Thrombosis object originating within a blood
  vessel local buildup of fatty substances usually
  at a bifurcation of artery, these can rupture
  leading to catastrophic blockage
• Hemorrhagic (Bleed). 20 of strokes are due to
  arteries rupturing.

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Risk factor for ischemic stroke

• Atherosclerosis from reduced lumen due to lipids,
  calcium fatty particles etc. (Athera porridge
  in Greek)
• A form of Arteriosclerosis a general term
  describing any hardening (and loss of elasticity)
  of arteries.
• Leads to stenosis (narrowing) of the artery,
  gradually leading to insufficient blood supply
• Plaques can rupture, creating a thrombus in blood
  supply

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Vascular Pathologies - Bleeds

• Hemorrhagic
• Bleeding from ruptured vessels
• Types
• Intracerebral More common in thalamus and basal
  ganglia
• Subdural
• Aneurysm

Aneurysm
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Haemorrhages

• 20 of strokes are bleeds
• Typically, due to ruptured aneurysm
• An aneurysm is a sac-like protrusion of an artery
  caused by a weakened area within the vessel wall.
  
• Introspectively, the worst headache of your life.
• http//www.microvent.com/
• Surgery to clip aneurysm can save patients life.

CT of recent haemorrhage
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Arteriovenous Malformations

• AVMs can cause hemorrhagic strokes
• Tangled web of arteries and veins present since
  birth

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Venous Sinus System

• Blood returns to lungs for oxygen
• Drain into Sinus System
• Dural Sinuses
• Superior Sagittal Sinus
• Inferior Sagittal Sinus
• Straight Sinus
• Transverse Sinus
• Cavernous Sinus
• Petrosal Sinuses

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Notes

• Regulation of Cerebral Blood Flow
• Closed system under constant pressure
• Controlled by elasticity of blood vessels, and
  metabolic needs
• Aging can cause less elasticity responsiveness
  and eveness of flow
• Blood-Brain Barrier
• Tight system does not allow direct contact of all
  brain tissues with blood
• Specialized system to extract needed molecules
• May impede medicine entering the brain