An analysis of the dominating influences in cerebral physiology

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An analysis of the dominating influences in cerebral physiology

Advanced Search Key points The brain is enclosed in a rigid box with a fixed volume and an increase in the volume of any of its constituents will lead to an increase in intracranial pressure ICP.

The volume of venous blood in the cerebral vasculature is small but very important as it can provide immediate compensation for increases in ICP. The cerebrospinal fluid provides the largest compensation for raised ICP but changes occur slowly. Volatile anaesthetic agents increase the ratio of cerebral blood flow and cerebral metabolism.

Maintaining sufficient cerebral blood flow to meet metabolic demands after a neurological insult is important to prevent secondary ischaemic brain injury. The brain is a very complex organ which needs a continuous delivery of oxygen and nutrients. To sustain consciousness, satisfactory perfusion and adequate oxygen delivery is vital but it is equally essential to maintain a constant supply of glucose as the brain has virtually no stores of glucose.

Loss of consciousness ensues within seconds of ischaemia secondary to a reduction in cerebral blood flow CBFwith permanent brain damage occurring with 3—8 min of insufficient blood supply. Cerebral blood volume The brain receives its blood supply from the internal carotid and vertebral arteries Fig.

The volume of blood in the whole brain is small and contained mainly in the venous sinuses and pial veins. The grey matter is composed of the cell bodies of the neurons which are involved with the complex functions of the human body and hence requires a larger proportion of the arterial blood supply.

On the other hand, the white matter is essentially composed of axons which transmit impulses in between the neurons. As it is involved with less complicated functions than the grey matter, it needs a smaller fraction of the blood supply.

Anterior inferior cerebellar artery.

An analysis of the dominating influences in cerebral physiology

Posterior inferior cerebellar artery. The CBF is best described by the Hagen—Poiseuille equation for laminar flow, which demonstrates a direct relationship between flow, cerebral perfusion pressure CPPand calibre of cerebral vessels: Cerebral perfusion pressure Perfusion pressure is the difference in the pressures between the arterial and venous circulation which dictates the blood flow to the organ.

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In the brain, the perfusion pressure or the CPP is affected by another pressure within the skull [i. In pathological conditions, if the ICP is increased, the flow through the cerebral blood vessels can be restricted.

When the CPP decreases below 50 mm Hg, there is an increased risk of brain ischaemia affecting the electrical activity in the brain. The cerebrovascular resistance CVR is essentially the hindrance to the CBF determined predominantly by the calibre of the vessels.

When cerebral vasodilatation occurs, the increase in the radius of the vessels not only decreases the CVR but also augments CBF. Cerebral metabolic rate The cerebral metabolic rate CMR is the rate at which the brain utilizes metabolic substrates [e.

The brain has the highest metabolic requirements of any organ in the body which is reflected by its high blood flow. Because CBF is adjusted to meet the metabolic demand, oxygen by the grey matter is approximately five times more than by the white matter.

Under aerobic conditions, oxidative phosphorylation produces 38 molecules of ATP for every molecule of glucose. Sixty per cent of the energy produced is utilized for the functioning of the neurons i.

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Cerebral palsy of spastic quadriplegic or dyskinetic type. 4. Exclusion of other identifiable causes of cerebral palsy, eg, coagulation or genetic disorders, infectious conditions, intrapartum pyrexia, antepartum hemorrhage, prematurity, intrauterine growth restriction, tight nuchal cord, complications of multiple pregnancy.

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Cerebral physiology | BJA Education | Oxford Academic