What is not a feature of raised ICT-
Correct Answer: Tachycardia
Description: Ans. is 'b' i.e., Tachycardia o The cranial vault is a rigid structure with a fixed total volume consisting of brain (80%) blood (12%) and C.S.F. (8%).o Any increase in one component must be off set by an equivalent decrease in another to prevent a rise in I.C.P.o Intracranial pressure by convention means supratentorial C.S.F. pressure measured in the lateral ventricles and is normally l Onm Hg or less.o If the intracranial pressure increases, it decreases the cerebral perfusion.o Cerebral persusion pressure is the difference between mean arterial pressure (MAP.) and intracranial pressure CPP (cerebral perfusion pressure) = Mean Arterial pressure - Intracranial pressure.Thus any increase in intracranial pressure decreases cerebral perfusion and produces following clinical features.o Headacheo Nausea, vomitingo Drowsinesso Papilloedemao Sixth nerve palsyQo BradycardiaQo Increased B.PQHeadacheso As the brain has no sensation, headache is caused by traction and distortion of the pain sensitive blood vessels and dura.o Headaches are typically progesssiveQ but relieved by an upright positionQ and are frequently associated with nausea and vomiting.o The headaches are usually worse in the morning owing to vasodilatation caused by hypoventilation and consequent CO, retention during sleep.Papilledemao As the eyes are extension of the forebrain, the optic nerves carry with them the meningeal coverings.o The raised I. C.P. is thus transmitted directly to the optic nerve head via the C.S.F.o This results in obstruction to axoplasmic flow in the retinal neurones that cause the swelling of the optic disc,o This is seen in fundoscopy as papilledemaDrowsinesso Compression of the reticular activating system in the brainstem results in drowsiness.Bradycardia and Increased B.P.o When intracranial pressure; increase the blood supply to the vasomotor area is compromised.o This stimulates the vasomotor centre.o The increase in discharge from the vasomotor centre increases the arterial blood pressure. The increased blood pressure restores the blood supply to the brain but the rise in arterial blood pressure causes a reflex decrease in heart rate via the arterial baroreceptors and this is why bradycardia rather than tachycardia is characteristically seen in patients with increased I.C.P.o The reflex increase in arterial pressure when the I.C.P. increases is called cushing's reflex.
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