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NEUROLOGICAL SYSTEM PART IV. DENNIS STEVENS CRNA, MSN, ARNP SEPTEMBER 2007 FLORIDA INTERNATIONAL UNIVERSITY ADVANCED BIOSCIENCE IN ANESTHESIOLOGY II NGR 6145. CEREBRAL BLOOD FLOW AND BLOOD-BRAIN BARRIER. OBJECTIVES Discuss significant aspects of cerebral vascularization.

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neurological system part iv
NEUROLOGICAL SYSTEMPART IV

DENNIS STEVENS CRNA, MSN, ARNP

SEPTEMBER 2007

FLORIDA INTERNATIONAL UNIVERSITY

ADVANCED BIOSCIENCE IN ANESTHESIOLOGY II

NGR 6145

cerebral blood flow and blood brain barrier
CEREBRAL BLOOD FLOWANDBLOOD-BRAIN BARRIER

OBJECTIVES

  • Discuss significant aspects of cerebral vascularization.
  • Explain arterial circulation of the brain including the circle of Willis.
  • Describe venous drainage of the brain and corresponding structures.
  • Discuss cerebral perfusion pressure and autoregulation associated with cerebral blood flow.
  • Explain significant aspects of the blood-brain barrier including those factors that may disrupt it
cerebral blood flow and blood brain barrier3
CEREBRAL BLOOD FLOWANDBLOOD-BRAIN BARRIER

CEREBRAL VASCULARIZATION

  • Introduction:
    • Approximately 18% of total blood volume circulates in the brain
    • Brain is responsible for 20% of total body oxygen consumption
    • Constant flow of oxygen must be maintained:
      • Loss of consciousness
      • Irreparable damage
    • Cerebrovascular disease occurs secondary to vascular compromise or hemorrhage in the CNS
cerebral blood flow and blood brain barrier4
CEREBRAL BLOOD FLOWANDBLOOD-BRAIN BARRIER

ARTERIAL SUPPLY OF THE BRAIN

  • Extra cerebral vessels; R carotid artery arises from R subclavian, L carotid artery arises from aortic arch
  • Intracranial cerebral vessels; internal carotid artery divides into anterior cerebral and middle cerebral arteries
  • Two vertebral arteries (arising from the subclavian arteries) join to form the basilar artery which gives rise to the posterior cerebral artery; supplying occipital lobes and brain stem
cerebral blood flow and blood brain barrier5
CEREBRAL BLOOD FLOWANDBLOOD-BRAIN BARRIER

CIRCLE OF WILLIS

  • Circle of Willis is a confluence of vessels that gives rise to all major cerebral arteries
  • It is fed by the paired internal carotid arteries and the basilar artery
  • When the circle is complete, it contains a posterior communicating artery on each side and an anterior communicating artery
  • Each major artery supplies a certain territory
  • Sudden occlusion affects its territory immediately, sometimes irreversibly
cerebral blood flow and blood brain barrier6
CEREBRAL BLOOD FLOWAND BLOOD-BRAIN BARRIER

VENOUS DRAINAGE

  • Venous drainage of the brain and coverings includes veins of the brain itself, dural venous sinuses, dura’s meningeal veins, and diploic veins
  • Eventual cerebral venous drainage is the internal jugular vein
  • Cerebral veins contain no valves
cerebral blood flow and blood brain barrier7
CEREBRAL BLOOD FLOWANDBLOOD-BRAIN BARRIER

REGULATION OF CEREBRAL BLOOD FLOW

  • Cerebral perfusion pressure (CPP) is the difference between mean arterial pressure (MAP) and intracranial pressure (ICP)
    • CPP = MAP – ICP
  • CPP is normally 80 – 100 mmHg
  • Moderate to severe increases in ICP can significantly compromise CPP and CBF
  • Decreased CPP associated with changing EEG patterns
  • Sustained CPP less than 25 mmHg results in irreversible damage
cerebral blood flow and blood brain barrier8
CEREBRAL BLOOD FLOWANDBLOOD-BRAIN BARRIER

CEREBRAL AUTOREGULATION

  • Cerebral blood flow remains nearly constant between MAP of 60 – 160 mmHg
  • Beyond these limits blood flow becomes pressure dependent
  • Cerebral autoregulation curve is shifted to the right in patients with chronic arterial hypertension
  • Long-term antihypertensive therapy…!
  • Pressures greater than 150 – 160 mmHg can disrupt the blood-brain barrier:
    • Cerebral edema
    • Hemorrhage
cerebral blood flow and blood brain barrier9
CEREBRAL BLOOD FLOWANDBLOOD-BRAIN BARRIER

CEREBRAL AUTOREGULATION

  • Extrinsic factors affecting autoregulation:
    • Respiratory gas tensions:
      • CBF directly proportionate to PaCO2
    • Temperature:
      • CBF changes 5 – 7% per 1° C
    • Viscosity
    • Autonomic influences
cerebral blood flow and blood brain barrier10
CEREBRAL BLOOD FLOWANDBLOOD-BRAIN BARRIER

BLOOD-BRAIN BARRIER

  • Cerebral blood vessels are unique in that the junctions between vascular endothelial cells are nearly fused. Paucity of pores responsible for the blood-brain barrier
  • Effectively isolates the brain and spinal cord extracellular compartment from the intravascular compartment
  • A number of midline brain structures receive neurosecretory products from the blood and therefore lack a blood-brain barrier
cerebral blood flow and blood brain barrier11
CEREBRAL BLOOD FLOWANDBLOOD-BRAIN BARRIER

BLOOD-BRAIN BARRIER

  • Allows passage of lipid-soluble substances but restricts movement of those that are ionized or have large molecular weights
  • Movement of a given substance across the blood-brain barrier is governed simultaneously by…
  • Carbon dioxide, oxygen, and lipid-soluble substances freely enter the brain, whereas most ions, proteins, and large substances penetrate poorly
  • CNS endothelial cells lack transport mechanisms
cerebral blood flow and blood brain barrier12
CEREBRAL BLOOD FLOWANDBLOOD-BRAIN BARRIER

BLOOD-BRAIN BARRIER

  • Rapid changes in plasma electrolyte-concentration produce a transient osmotic gradient between plasma and the brain
  • Acute hypertonicity of plasma results in net movement of water out of the brain, while acute hypotonicity of plasma results in a net movement of water into the brain
  • Marked abnormalities in serum sodium or glucose concentrations should generally be corrected slowly
cerebral blood flow and blood brain barrier13
CEREBRAL BLOOD FLOWANDBLOOD-BRAIN BARRIER

BLOOD-BRAIN BARRIER

  • Blood-brain barrier may be disrupted by:
    • Severe HTN
    • Tumors
    • Trauma
    • Strokes
    • Infections
    • Marked hypercapnia
    • Hypoxia
    • Sustained seizure activity
  • Hypothermia stabilizes the blood-brain barrier
cerebral blood flow and blood brain barrier14
CEREBRAL BLOOD FLOWAND BLOOD-BRAIN BARRIER

REFERENCES

Morgan, G.E., Mikhail, M.S., and Murray, M.J. (2006).

Clinical Anesthesiology. (4th Ed.) New York, NY:

McGraw-Hill.

Nagelhout, J.J. and Zaglaniczny, K.L. (2005). Nurse

Anesthesia. (3rd Ed.) St. Louis, MO: Elsevier-

Saunders.

Waxman, S.G. (2000). Correlative Neuroanatomy (24th ed.). New York, NY:McGraw-Hill.