cerebral circulation
Post on 15-Jul-2015
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Most vital organ
Containing center for circulation ,
respiration and most other bodily
functions
Needs continues blood supply
Highly sensitive to hypoxia
Uses glucose as main fuel
Metabolic requirements are fairly
constant irrespective of needs
Cerebral arteries are end arteries
Volume of blood , ecf , csf remains fairly
constant
Capillaries in brain are mostly non-
fenestrated
Capillaries are surrounded by foot
process of astrocytes
Forming blood brain barrier
BBB allows selective permeability of
substances
Not well developed in infants
Narrow tight junctions
Thick basement membrane
Receives blood from two major sources
1. Vertebro-basilar system
2. Internal carotid arteries
Both systems unite to form circle of willis
Which give rise to three pairs of major
vessels
Anterior cerebral arteries
Middle cerebral arteries
Posterior cerebral arteries
Deep veins
Dural venous sinuses
Draining into internal jugular vein
750ml per min
Wt of brain is 1400g
54ml/100g tissue /min
3.3ml of O2/100g/min
Kety method
By using radioactive subs
› Single photon emission tomography (SPECT)
› Positron emission tomography (PET)
Mri
Uses ficks principle
Subject is made to brath 15% mix of N2O
and air for 10 min
Blood samples are taken every min from
IJV and peripheral artery
CBF = N2o taken by brain tissue /min
AV diff of N2o concentration
Disadvantages › Average value and no information about
regional circulation
› Cannot be used in changing BP
Perfusion pressure determines CBF
MAP at the level of head – JVP
Metabolic
Autoregulation
Role of intracranial pressure
Nervous regulation
Carbon dioxide – most potent
vasodialator
I mm raise in Pco2 raises CBF by 3ml/100g
tissue
1 mm decrease will reduce CBF by 1.5 ml
Effect of pco2 is mediated by H+ ions in
csf
Hypoxia – vasodialtion
Hyperbaric oxygen
K+ ions causes vaodilatation
BP of 60 – 140 mm/hg
Monro-kellie doctrine – brain tissue , csf ,
blood in vessels are in equilibrium inside
rigid cranial cavity
Positive G , Negative G
Raised ICP
Vasocontriction
Bradycardia
Inceased BP
Fainting or transient LOC due to
temporary loss of blood supply to brain
Cardiogenic
Non- cardiogenic
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