Session 11 Cerebral Blood Flow pptx
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Transcript of Session 11 Cerebral Blood Flow pptx
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Schedule for the day
1. Importance of studying cerebral blood flow
2. Anatomy of cerebral vasculature
3. Autoregulation of cerebral blood-flow:a. Munroe-Kelly Principle
b. Role of Medullary Vasomotor Centresc. Cerebral Microvasculature
d. Windkessel design
e. Neurovascular Network and astrocytes
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fMRI EEG
spectrum
CerebralBloodFlow
ElectricalA
ctivity
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Interesting facts
THE BRAIN
1. ENTIRELY depends on OXYGEN for itsmetabolism
BUT, the reserve is LIMITED&
2. ENTIRELY depends on GLUCOSE for itsmetabolism
BUT, the reserve is LIMITED
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YET.
There is LIMITED/ FIXED/ RATIONED
BLOOD SUPPLY of 700 ml/minute
because ofRestricted skull volume and distribution of
volume between brain, CSF and blood
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The outcome therefore.!!
A) 1 SECOND INTERRUPTION of blood
all dissolved oxygen in brain is used up!
B) 6 SECOND INTERRUPTION of bloodUNCONSCIOUSNESS!!
C) 6 MINUTE INTERRUPTION of blood
IRREVERSIBLE BRAIN DAMAGE!!!
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Stable blood flow to the brain despite wide
range of peripheral mean arterial pressure
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Hippocampus vs. Ear-lobe blood flow (mouse)
Different vascular regions
in hippocampus identified
Blood flow at single
capillary resolution indifferent regions of
hippocampus and
ear-lobe studied
Blood flow in most
hippocampus remainedconstant across wide
mean arterial pressures
(Kuga et al J. Physiol 2008)
Hippocampus
Ear-lobe
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In spite of constant blood flow
Blood supplyPROMPTLY & DELICATELY
alters to match the levels of
REGIONAL NEURONAL ACTIVITYHow?
Autoregulation of Cerebral Blood Flow
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2a. Anatomy of Cerebral Vasculature: The Circle of Willis
Basilar artery
Internal Carotid
artery
Basilar artery
Internal Carotid
artery
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2a. Anatomy of Cerebral Vasculature: The Circle of Willis
Circle of Willis: The most important communicating
system between the major arteries to the brain
Prog Cardiovasc Dis (2007)
Anatomical Details of Circle of Willis will not be tested
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2b. Anatomy of Cerebral Vasculature:
Distribution of the major arteries
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3. Autoregulation:
a. Munroe-Kelly Principle
Volume ofBrain tissue
Volume ofCerebral
Blood flow
Volume of Cerebrospinal fluid
Brain, Blood and CSF share the fixed limited volume of
the rigid skull. This keeps the blood flow constant.
Fixed
skull
volume
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3. Autoregulation:
b. Role of Medullary Vasomotor Centres
Autonomic Nervous System
Cerebral Cortex
Bloodflow
Medulla
Oblongata
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Medullary vasomotor
centres detect
changes in blood
pressure in incomingblood vessels
They reflexly regulate
the blood flow to thebrainvia AutonomicNervous System
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But, this is far from the fine-tuningof blood-flow to specific corticalareas!
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3. Autoregulation:
c. Cerebral Microvasculature
Note the
branching
pattern ofblood vessels
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3. Autoregulation:
d. Windkessel design
Smooth muscle valves
work like throttles/
Windkessel
Regulate the rate ofblood flow
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The problem of fine-tuningfor demand-supplyremains!.......
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Area of
increaseddemand
Adjacentareas
Remoteareas
Blood vessels
3. Autoregulation:
e. Neurovascular network
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Area of
increaseddemand
Adjacentareas
Remoteareas
Strategy-1: Steal blood from the neighbouring areaBlood vessels
Steal
from theneighbor
3. Autoregulation:
e. Neurovascular network
NOT A GOOD
STRATEGY!22
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Area of
increaseddemand
Adjacentareas
Remoteareas
Blood vessels
Distributed Stealing
GOOD, BUT HOW?
Strategy-2: Steal blood in a distributed fashion
3. Autoregulation:
e. Neurovascular network (contd)
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Area of
increaseddemand
Adjacentareas
Remoteareas
Blood vessels
Distributed Stealing with the help of
neurovascular network
EFFECTIVE AND FAST!
Neurovascular
network
Steal blood in a distributed manner with quicker
response due to Neurovascular Network
3. Autoregulation:
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Neurovascular network regulates regional
cerebral blood flow
1. Network of nerve fibresconnect blood vessels withone another
2. The network is in turn
orchestrated by major areassuch as basal forebrain
3. O2VasoconstrictionCO2 VasodilatationGlutamate VasodilatationGABA Vasoconstriction
4. Astrocytes are majorcomponents of the nerve net!
Progress in Cardiovascular Diseases (2007)
(Details in the diagram
will not be tested)
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CEREBRAL BLOOD FLOW
Summary
1. Oxygen and Glucose are the sole raw materials forbrain functions. Yet they are in limited supply.
2. Circle of Willis forms an important communicationbetween major arteries to the cortex thus providing
alternative source of blood in the event of an
obstruction. But, blockade ofterminal blood vesselscannot be compensated. This leads to stroke.
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CEREBRAL BLOOD FLOW
Summary
3. Munroe Kelly principle and medullary vasomotormechanisms provide a constant blood flow to braindespite wide fluctuations in the peripheral meanarterial pressures.
4. Branched pattern and Windkessel design of bloodvessels along with theirneurovascular network makeinstant, micro-adjustments of blood flow depending onlocal demands.
5. Astrocytes are implicated in swift vascular changesmatching neuronal demands.
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