Bb W4 Cerebral Blood Flow And Intracranial Pressure

Front 1

Equation for flow

Back 1

Pressure/Resistance

Front 2

Equation for cerebral blood flow

Back 2

CPP/CVR
CPP = cerebral perfusion pressure
CVR = cerebral vascular resistance (experimental)

Front 3

Equation for cerebral perfusion pressure

Back 3

MAP - ICP
MAP = mean arterial pressure
ICP = inctracranial pressure

Front 4

Poiseulle's law

Back 4

States that the major determinants of cerebral blood flow are: vessel radius, pressure gradient, and blood viscosity

Front 5

Factors regulating cerebral blood flow via resistance changes

Back 5

– Pressure [autoregulation]
– Arterial PCO2 and PO2
– Cerebral metabolism
– Neurogenic

Front 6

Describe pressure autoregulation

Back 6

At pressures between 50 –160mmHg MAP, a constant flow of blood to the brain is maintained
– Pre-capillary arterioles dilate or contract
– Myogenic

Front 7

Describe the mechanisms of myogenic pressure autoregulation

Back 7

Stretch sensitive calcium channels respond to changes and systemic blood pressure

Front 8

Describe the influence of PCO2 on cerebral blood flow

Back 8

– Cerebral vessels are very sensitive to changes in PCO2
– Hypercarbia causes vasodilation increases CBF
– Hypocarbia causes vasoconstriction and decreases CBF
– Changes mediated by extracellular [H]

Front 9

Describe the influence of PO2 on cerebral blood flow

Back 9

– CBF does not very with small variations in PaO2
– When PaO2 falls below 50mmHg --> CBF begins to rise exponentially
– hypoxia --> NO and Adenosine production --> vasodilation

Front 10

What recieves more bloodflow:
White or gray matter

Back 10

Gray matter

Front 11

Role of astrocytes and cerebral blood flow

Back 11

Coupling of neuronal activity and CBS
– Send processes to synapses and blood vessels --> Increase neuronal activity --> increased blood flow to area
- communicate with other astrocytes through gap junctions

Front 12

Neurogenic control of blood flow

Back 12

No major role.

Front 13

What is the normal cerebral blood flow (in cc/100g/min) at rest, in gray matter and in white matter?

Back 13

– Normal brain that rest 45 – 65
– Grey matter 75 – 80
– White matter 20 – 30

Front 14

What are some ways that cerebral blood flow can be measured clinically

Back 14

– PT
– SPECT
– Xenon CT
– CT perfusion
– MRI perfusion

Front 15

How does the PET work for measuring CBF

Back 15

– USES A OXYGEN LABELED WATER AS A TRACER
– MEASURES OXYGEN UTILIZATION/EXTRACTION

Front 16

Advantages of using PET for measuring CBF

Back 16

– High spatial resolution (5mm^3)
– Most quantitative method

Front 17

How does a SPECT work and measuring CBF

Back 17

– Uses lipophilic tracers that cross the blood brain barrier and are fully extracted on first pass through cerebral circulation

Front 18

Advantages/ disadvantages of SPECT

Back 18

+ High spatial resolution (9mm^3) but less than PET
– Semi-quantitative

Front 19

How does a Xenon CT work?

Back 19

– Xenon gas is inhaled, dissolves in the blood and readily cross BBB
– High atomic number of xenon allows it to the measured on CT
– Wash out method employed: steady-state is achieved and then the rate of decay relates to superfusion

Front 20

Advantages to using CT perfusion method

Back 20

Allows analysis of:
– Mean transit time
– Cerebral blood volume
– Cerebral blood flow

Front 21

Disadvantages to using CT perfusion method

Back 21

- IV bolus of iodinated contrast
- acquisition is limited to 2 cm slab

Front 22

How does MRI perfusion method for measuring CBF work

Back 22

– IV injection of paramagnetic contracts followed by rapid acquisition of images
– Dephasing of immediately adjacent tissues and the signal loss closely related to cerebral perfusion

Front 23

Normal values for intracranial pressure

Back 23

Adults: <15cm H20
Children: <5cm H20

Front 24

Advantages of the anatomy of the skull

Back 24

Provides excellent protection for the brain

Front 25

Disadvantages to the anatomy of the skull

Back 25

Intolerant to internal volume changes

Front 26

Skull contents

Back 26

80% brain
10% CSF
10% blood

Front 27

Monro-kellie doctrine

Back 27

Vk = Vbrain + Vcsf + Vblood

As long as the volume relationship is maintained, the pressure inside this skull will remain normal
– Any added volume to the skull will displace the normal three constituents and can eventually cause an increase in pressure

Front 28

What pathological processes contribute to ICP

Back 28

– Neoplasm
– Stroke
– Head injury
– Infection

Front 29

What pathological situations can increased volume in brain and increase icp

Back 29

– Tumor
– Cerebral edema
– Hemorrhage
– Abscess

Front 30

How to the cranial contents respond to an added volume

Back 30

– Compensation depends on how fast the volume is added

Rapid addition: two phases
- Phase 1: CSF and blood redistribute, ICP unchanged
– Phase 2: maximal redistribution reached, ICP rises

Front 31

Intracranial hypertension

Back 31

– One compensation is exhausted, pressure is exerted onto the brain
– Cellular effects: mechanical compression on neurons, glia, and cerebral blood vessels
– Neurological effects: general and focal

Front 32

What are some general and focal neurologic or effects of intracranial hypertension

Back 32

General (diffuse increased ICP):
– Headache
– Nausea
– Vomiting
– Papilledema
– Cushing's response [HTN, bradycardia]

Focal (compression):
– Paralysis
– Aphasia
– Cranial
– Nerve palsy
– Drowsiness
– Apnea

Front 33

Consequences of acute and severe increased ICP

Back 33

– Focal areas of the brain shift along pathways of least resistance --> herniate
– Herniation syndromes

Front 34

Types of herniation syndromes

Back 34

– Subfalcine herniation: herniation of frontal lobe under the falx
– Midline shift: movement of one hemisphere towards other
– Tonsillar herniation: herniation of cerebral tonsils through foramen magnum
– Uncal herniation a.k.a. transtentorial herniation: herniation of uncus (medial temporal lobe) through tentorial hiatus and against brainstem

Front 35

Consequences of uncal herniation

Back 35

Pressure on CN III and midbrain peduncle
– Can cause immediate death and is it true medical emergency

Front 36

Monitoring ICP

Back 36

– External ventricular drain
– Fiber-optic pressure transducers

Front 37

What is contraindicated in cases of elevated ICP

Back 37

Lumbar puncture

Front 38

Management of intracranial hypertension

Back 38

– Head elevation
– Diuretics
– Hyperventilation
– Sedation/paralysis
– Barbiturates
– Surgery [CSF drainage, evacuate the mass, craniectomy]