Intracranial compliance (ICC) represents the change in volume (ΔV) per unit change in pressure (ΔP), and is exactly the inverse of elastance. In other words, ICC determines the ability of the intracranial compartment to accommodate an increase in volume without a large increase in intracranial pressure (ICP).
Compliance= ΔV/ΔP = 1/elastance
In normal conditions there are both normal intracranial volumes and ICP values and a high intracranial compliance. The ICC will explain why, despite having a small increase in intracranial volume (e.g. cerebral haematoma or cerebral oedema), there are minimal changes in ICP values (the highly compliant nature of the intracranial contents can be explained by mechanisms such as: CSF displacement through the foramen magnum into the paraspinal space and blood displacement from compressed brain tissue). When these mechanisms are exhausted further increases in volume are directly reflected as increases in pressure.
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