Decreased cerebral blood flow

Decreased cerebral blood flow

Too little blood flow (ischemia) results if blood flow to the brain is below 18 to 20 ml per 100 g per minute, and tissue death occurs if flow dips below 8 to 10 ml per 100 g per minute.

Decreased cerebral blood flow is seen with high oxygen tension. But it is a protective effect caused by cerebral vasoconstriction.

Oxygen toxicity can be both acute and chronic.

Acute toxicity develops following exposure to high oxygen tension even for a short duration. It mostly affects the CNS – Bert effect. It is characterised by muscle twitching, convulsions and coma.

Chronic toxicity develops following long term exposure to relatively lower concentration of oxygen. Pulmonary effects are more common – Smith effect. Manifestations are pulmonary edema, atelectasis and congestion of lung passages.

Retrolental fibroplasia (retinopathy of prematurity) is seen following administration of high concentration of oxygen to neonates. It can lead to blindness. It is caused by angiogenesis.