Physiology (Neuronal)

Question 1

What is the Monro-Kelly doctrine?

Answer 1

An increase in volume of one of it’s contents must be compensated by the the reduction in the volume of the other in order to avoid a rise of ICP

Question 2

What are the compartments of the skull?

Answer 2

• Brain = 85%
• CSF = 10%
• Blood = 5%

Question 3

Mechanism of autoregulation of ICP?

Answer 3

• Decrease in venous blood volume
• Decrease in CSF volume
• Decrease in arterial blood volume
• Maintains pressure < 20mmHg

Question 4

Classification of ICP based on ischaemic effect?

Answer 4

• <20 mmHg - Compensated
• 20-45 mmHg - Focal ischaemia
• > 45mmHg - Global ischaemia

Question 5

What is the normal blood flow to the brain?

Answer 5

50ml/100g/min of tissue

Question 6

What is the formula for calculating CPP?

Answer 6

CPP = MAP - (CVP+ICP)

Question 7

Degree of CP impairment & consequences?

Answer 7

• CBF ˂ 40 ml.100g-1 .min-1 Protein synthesis impaired
• CBF ˂ 30 ml.100g-1 .min-1 Cerebral edema occur
• CBF ˂ 20 ml.100g-1 .min-1 Electrical dysfunction occur
• CBF ˂ 10 ml.100g-1 .min-1 Cell death

Question 8

Normal range of CPP?

Answer 8

It is constant in the MAP range of 50-150mmHg. Flow becomes pressure dependent out of these ranges

The curve is shifted to the right in terms of chronic HTN

Question 9

Extrinsic mechanisms of regulating ICP?

Answer 9

• Respiratory gas tension
• Temperature
• Autonomic influence
• Viscosity
• Pharmacological

Question 10

What are the effects of CO2 on CBF?

Answer 10

• CBF will increase with CO2
• Curve shifts to the right in chronic hypercapnia - Reset of autoregulatory point

Question 11

What are the effects of PO2 on CBF?

Answer 11

• PO2 > 8kpa - Constant blood flow
• < 8kpa - Vasodilation + Rise in ICP

Question 12

What the effects of volatile agents on CBF?

Answer 12

• CBF increases with increasing MAC
• Decreased metabolic rate

Question 13

CSF formation?

Answer 13

CSF is formed in the choroid plexus located in the ventricles of the brain

500mls /day or 1.35ml/min

Total volume is 150mls

Question 14

Describe the circulation of CSF?

Answer 14

• Produced - Choroid plexus of lateral Ventricle
• Pass through Foramen of Monro
• 3rd ventricle
• Passes through Sylvian Aqueduct
• 4th Ventricle
• Passes through foramen of Magendie-Medial
• Passes through foramen of Lushka-Lateral
• Enters the spinal canal
• Absorbed by arachnoid villi in venous sinus