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Physiology

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Cardiovascular System

Question
6 out of 19
 

Cerebral blood flow is does not depend on? (AIIMS MAY 2008)



A Cerebral Metabolic rate

B CO2

C Blood pressure

D K+

Ans. D K+

a.For adequate function of brain, a continuous blood flow is required.

b.Normal cerebral blood flow is 15% of resting cardiac output (750ml /min) or about 50- 55 ml blood /100gm tissue / min.

c.50 - 70 % of CSF is formed in the choroid plexuses and the remainder is formed along the ventricular walls and the blood vessels.

d.VOLUME - 150 ml

e.Rate of CSF production is 550ml / day.

f.The composition of brain CSF is the same as that of brain E.C.F

g.Interruption of CSF for 5-10 seconds causes loss of consciousness and circulatory arrest for only 3-4 min results in irreversible brain damage.

h.Cerebral perfusion pressure is defined as mean systemic arterial pressure minus intra cranial pressure.

i.Option (3) cerebral autoregulation & effect of B.P

j.If systemic B.P drops cerebral perfusion is preserved through - vasodilatation of arterioles of brain; likewise arteriolar vasoconstriction occurs at high systemic pressure to prevent hyper perfusion. But cerebral autoregulation is effective over a range of 80 -180 mm Hg only.

k.Option (2) CBF & effect of pH & CO2

l.CBF increases with hypercapnia & acidosis and decreases with hypocapnia & alkalosis. This forms the basis of use of hyperventilation to lower intra cranial pressure.

Note: Metabolic acid base imbalances produce opposite changes in CSF.

i.Respiratory acid base imbalances (change in arterial CO2 tension) produce parallel changes in CSF

Option (1) CBF & cerebral metabolic rate

ii.Cerebral autoregulation may be disordered focally &unpredictably in disease states such as traumatic brain injury and severe focal cerebral ischemia.

iii.Since about option (3), (2) & (1) it is clearly mentioned in HARRISON'S; the best answer of exclusion should be option (4).

Cardiovascular System Flashcard List

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