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CSF FLOW.ppt
1.
2. Clinical importance
Abnormalities of
Blood flow
Metabolism
Fluids
Composition
Pressure
Affect brain function profoundly
Decrease blood flow for 5-19sec
loss of consciousness
Increase in H+ ions
depresses neuronal activity
decreases brain activity
3. Outline
Vascular anatomy of brain
Control of cerebral blood flow
Determinants of cerebral perfusion pressure
Local regulation of cerebral blood flow
Regulation of CBF by arterial pO2 and pCO2
Neurohumoral regulation
Cushing reflex
Control by neuropeptides
Conditions related to altered cerebral blood flow
5. Cerebral blood flow
Normal blood flow 50-65mls/100gr/min
Entire brain=750-900 mls/min
15 % of resting cardiac ou put
6. Regulation of cerebral circulation
Constant total cerebral blood flow is maintained
under varying conditions.
1. ABP at brain level.
2. Venous pressure at brain level.
3. Intracranial pressure.
4. Blood viscosity.
5. Degree of active constriction or dilation of cerebral
vessels.
7. Regulation of blood flow
Highly related to tissue metabolism
1. Concentration of carbondioxide
2. Hydrogen ions concentration
3. Oxygen concentration
Excess CO2 or H+
Increase cerebral blood flow
Vasodilator effect
Indirect effect of CO2
CO2 + H2O= H+ + HCO3-
Others
Metabolic acids
Lactic acid & Pyruvic acid
8. Importance of cerebral blood flow
Increased H+ conc greatly depresses neuronal activity
Increased H+ leads to increased blood flow
In turn carries H+ , CO2 and other acids forming
substances from the brain tissue
Decreased H+ conc
Achieves normal neuronal activity
Oxygen deficiency
Normal oxygen utilization 3.5+/- 0.2 mls O/100gr/min
Decreased oxygen supply below normal
Vasodilatation
increased blood flow and O2 transport to the tissue
9. Normal PO2 in cerebral blood is 35-40mmHg
Decreased in cerebral tissue PO2 below 30mmHg
increase blood flow
Below 20mmHg comma ensues
10. Measurement of blood flow
Inject radio active substance in carotid artery
Record radioactivity of each cerebral segment
Press detectors against the surface of the cortex
Detect rapidity of rise and decay of radioactivity in
each tissue segment
Record increased blood flow where there is activity
11. 2. Autoregulation of cerebral blood flow
Autoregulation:
Ability of tissue to regulate their blood flow according
to their activity.
When the arterial pressure changes
CBF is auto regulated extremely well
Between arterial pressure limits
60-140mmHg
there is no significant changes in cerebral blood flow
14. Cerebral Autoregulation
(Possible Mechanisms)
Metabolic
Decreased perfusion pressure leads to:
pO2 (decreased O2 delivery)
pCO2 (decreased CO2 washout)
H+ (decreased H+ washout plus lactic acid)
adenosine (hypoxia resulting in net loss of ATP)
Each of the above changes produces vasodilation
Myogenic
Decreased perfusion pressure decreases stretching of
arteriolar smooth muscle which causes relaxation
15. 3. Autonomic Control
Sympathetic
Innervation from superior cervical ganglion primarily
to larger cerebral arteries on brain surface
Very weak sympathetic vascular tone
Sympathetic blockade has little effect on flow
Maximal sympathetic stimulation increases resistance
by 20-30% (cp >500% in muscle)
Shifts autoregulatory curve to right
Parasympathetic
Innervation from facial nerve (VII)
Weak dilator effect on pial vessels
Baroreceptor reflexes
Very weak
17. Role of sympathetic NS in controlling CBF
There is strong sympathetic innervations in the brain
Inhibition or mild to moderate sympathetic
stimulation has mild or no effect in CBF changes
Auto regulation overrides the nervous effect
Important in preventing stroke
Cerebral vascular accidents
Incase of acute increase of Arterial pressure
Strenuous exercise
Excessive circulatory activity
Constrict large and intermediate sized brain arteries
High pressure is prevented reaching smaller brain vessels
Prevent vascular hemorrhages
18. 4. Effects of Intracranial Pressure
(CNS Ischemic Reflex)
Increased intracranial pressure leads to
mechanical compression of cerebral vasculature
and decreased flow
Increased intracranial pressure elicits arterial
hypertension (“Cushing reflex”)
May be caused by bulbar ischemia, which in turn
stimulates medullary cardiovascular centers and
increases sympathetic outflow to systemic
vasculature
Bradycardia often accompanies the hypertension
because of baroreceptor activation of vagal efferents
to the heart
19. 5. Humoral Control
Catecholamines
Weak alpha-adrenergic vasoconstriction is masked by
autoregulation although very high doses of
epinephrine can decrease flow
Beta-adrenoceptors cause vasodilation; however, this
is masked by autoregulation
Angiotensin II
Very little or no effect
20. Neuropeptides and Other Vascular
Control Mechanisms
Vasodilation
Calcitonin gene-related peptide (CGRP)
Substance-P
Vasoactive intestinal peptide (VIP)
Vasoconstriction
Neuropeptide-Y (NPY)
Endothelin (vascular and neuronal ET-1 and neuronal ET-3
acting primarily on ETA receptors)
22. Cerebrospinal Fluid system
Capacity of entire cerebral
cavity enclosing the brain
and spinal cord
1600-1700 mls
150mls is CSF
1450-1550 mls Brain & spinal
cord
Areas CSF formed
Chambers in the brain
Ventricles
Cisterns around the outside
of the brain
Subarachnoid space around
both & spinal cord
Chambers are
interconnected
Pressure of the fluid is
maintained at a constant
level
23. Function of Cerebrospinal Fluid
The purpose of this fluid is
to protect the brain and
spinal cord
acting as a shock absorber.
It also carries away
disposed materials.
24. Functions of CSF, continued,…
2. Facilitation of pulsatile cerebral blood flow,
3. Distribution of peptides, hormones, neuroendocrine
factors and other nutrients and essential substances to
cells of the body,
4. Wash away waste products.
25. Formation, flow and absorption
Rate per day
500mls/day
3-4 times its volume
2/3rds secreted by choroid
plexus in ventricles
Mainly 2 lateral ventricles
Ependymal surface of all
ventricles
Arachnoid membranes
Brain itself
26. Composition of the CSF
The composition of CSF is essentially the same as
brain ECF
Substance CSF Plasma
Na+ 147 150
K+ 2.9 4.6
HCO3- 25 24.8
PCO2 50 39.5
pH 7.33 7.4
Osmolality
Glucose
289
64
289
100
27. flow
1. From lateral ventricles
2. to 3rd ventricles
3. to Aqueduct of sylvius
4. to 4th ventricle
5. then passes through the three small openings
1. Two lateral foramina of lushka
2. Foramen magandie on the middle
3. And then enters cisterna magna
6. Then upwards through the subarachnoid space
surrounding the cerebrum
7. Finally to large sagital venous sinuses
28.
29. Choroid plexus
Is a cauliflower like growth of blood vessels covered by
a thin layer of epithelial cells
Mechanism of CSF formation
Na+ actively pumped outside the epithelial cells
Pulls along with it Cl- ions
Creates osmotically active environment
Water flows by osmosis
30. Absorption of CSF
Through arachnoidal villi
Are microscopic fingerlike inward projections of
arachnoidal membrane
Have vesicular passages in them that allows the
passage of
CSF
Dissolved protein molecules
Particles as large as RBC & WBC
into the venous blood
31. Perivascular space
Space existing between pia matter and blood vessels in the
brain
Act as a specialized lymphatic system for the brain
Excess protein in the brain tissue leaves the tissue
flowing with fluid through perivascular spaces into
subarachnoid space
Also transport extraneous particulate matter of the brain
such as dead WBC and other debris after brain
infection
32. Cerebrospinal fluid pressure
Normal average 10 mm Hg
Regulated by arachnoidal villi
Mechanism
Arachnoidal villi function as a valve system
Allows CFS and its contents to flow readily in the blood
of the venous sinuses
while not allowing blood to flow backwards in the opposite
direction
Operate when CSF pressure is about 1.5 mmHg greater
than the pressure in the venous sinuses
33. Disorders of CSF circulation
Disease states
Blocks the system
Increase CSF pressure
1. Large brain tumors-
decrease reabsorbption of CSF into the blood
Increase 4x above normal
2. Haemorhage
3. Infection
In cranial vault
Release Large number of RBC+/- WBC in CSF
block the system
34. Disorders of CSF circulation
4. Abnormal villi system
Few arachnoid villi
Or abnormal absorptive properties
Hydrocephallus
Excess water in the cranial vault
Cause
Obstruction of CSF flow
Types
Communicating
Non communicating
35. Disorders of CSF circulation
Communicating
Fluid flow normal from ventricular system to arachnoid
spaces
Non communicating
There is blockage in fluid flow from one or two
ventricles
Blockage of aqueduct of sylvius secondary top atresia
(closure) before birth
Brain tumor at any age
Communicating
Blockage of arachnoid villi or subarachnoid spaces
Fluids collects outside the brain
36. Brain barriers
1. Blood cerebral spinal fluid barrier
Barrier formed between blood and cerebral spinal fluid
2. Blood brain barrier
Barrier formed between blood and brain fluid
Permeability Characteristics
Highly permeable to H2O,CO2,O2, and most lipid
soluble substances e.g alcoholic & anaesthetics
Slightly permeable to electrolytes Na+, Cl- and K+
Glucose : its passive penetration is slow, but is
transported across brain capillaries by GLUT1
totally impermeable to placenta proteins and non lipid
soluble large organic molecules
37. Cause of barrier
Manner in which the endothelial cells of the brain
tissue capillaries are joined to one another
Joined by tightly junctions
Membranes of adjacent endothelial cells are tightly
fused rather than having large slit spores between
them
Unlike other capillaries which have large pores
38. Functions of BBB
Maintanins the constancy of the environment of the
neurons in the CNS.
Protection of the brain from endogenous and
exogenous toxins.
Prevent escape of the neurotransmitters into the
general circulation.
39. Development of BBB
Premature infants with hyperbilirubinemia, free
bilirubin pass BBB, and may stain basal ganglia
causing damage (Kernicterus).
40. Clinical implications
Some drugs penetrate BBB with difficulty e.g.
antibiotics and dopamine.
BBB breaks down in areas of infection, injury, tumors,
sudden increase in blood pressure, and I.V injection of
hypertonic fluids.
Injection of radiolabeled materials help diagnose
tumors as BBB is broken down at tumor site because of
increased vascularity by abnormal vessels.
41. Circumventricular organs
• Posterior pituitary.
• Area postrema.
• Organum vasculosum of the lamina terminalis (OVLT).
• Subfornical organ (SFO).
These areas are outside the blood brain barrier. They have
fenestrated capillaries .
Functions:
- Chemoreceptor trigger zone. As area postrema that trigger
vomiting & cardiovascular control.
- Ang II acts on SFO and OVLT to increase H2O intake.
- IL2 induce fever by (+) circumventricular organs.