Brain blood supply

1. Circulatory System
• Heart
• Vessels

2. Brain Capillaries
SkinArterioles
Heart Regulation
FetusVeins

4. Cerebral circulation-
Measurement and regulation

5. Anatomy

10. Virchow–Robin space
Virchow–Robin spaces (VRS), also
known as perivascular spaces, are
the immunological spaces between
the arteries and veins (not
capillaries) and pia mater that can
be expanded by leukocytes.

11. © TheMcGraw-HillCompanies,Inc,2011
Chapter 33 Circulation through Special Regions
BLOOD
BRAIN
BARRIER

12. Circumventricular organs

13. Normal
Blood Flow
Continuous
Blood Flow
Stop 5-10 s
Unconscious
Stop 3-4 min
Brain Damage
15% of Tot
Blood flow
18mL/100g
tissue Critical
flow level

14. Normal O2 consumption
• Total 50mL/min
– 3.3mL/100 g/min
• Gray matter has more O2 consumption

15. Measurement of Cerebral Blood Flow
1. Kety method
2. SPECT
1. Single Photon Emission Computed Tomography
3. PET
1. Positron Emission tomography
4. MRI
1. Magnetic Resonance Imaging

16. Kety method
• Fick’s principle using 15 % N2O for 10 min
• Cerebral blood flow (CBF) =
– N2O taken by brain tissue per min
/ A-V diff of [N2O ]

17. • Single-Photon
Emission Computed
Tomography
(SPECT)
• PET
• MRI

18. Using Xenon Scintigraphy

19. CEREBRAL
BLOOD FLOW
& ITS
REGULATION
Arterial
Blood
pressure
Intracranial
Pressure
Resistance
(Viscosity)
Diameter

20. CEREBRAL PERFUSION PRESSURE
• CPP can be defined as the pressure gradient
causing cerebral blood flow (CBF) such that
• CBF = CPP/CVR
• CVR is cerebrovascular resistance
• An alternative definition of CPP is
• CPP=MAP-ICP where:
– MAP is mean arterial pressure
– ICP is intracranial pressure

21. REGULATION OF CEREBRAL BLOOD FLOW
• Metabolic regulation
• Auto-regulation of CBF
• ICP in regulation of CBF
– Monro Kellie Doctrine
– Cushing reflex
• Nervous regulation of CBF

22. Representation of the effects of arterial Po2 and Pco2 on cerebral blood flow.
Michael G. Levitzky Advan in Physiol Edu 2008;32:196-202
©2008 by American Physiological Society

23. Substances released
from Astrocytes in
response to neuronal
activity

24. Autoregulation
Inspite of systemic
pressure changes
within 60-140
mmHg range BP
CBF in brain is
unchanged.

25. Monro-Kellie doctrine
Brain tissue and spinal
fluid are essentially
incompressible, the
volume of blood, spinal
fluid, and brain in the
cranium at any time must
be relatively constant.

26. Cushing Reflex
• Cushing's triad of
– increased blood pressure,
– irregular breathing,
– reduction of the heart rate

27. Cushing
reaction

28. REGULATION OF CEREBRAL BLOOD FLOW
• Metabolic regulation
• Auto-regulation of CBF
• ICP in regulation of CBF
– Monroe Kellie Doctrine
– Cushing reflex
• Nervous regulation of CBF

29. Stroke
Stroke, also known as
cerebrovascular accident
(CVA), cerebrovascular
insult (CVI), or brain attack,
is when poor blood flow to
the brain results in cell
death.