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 (normal intracranial volumes and ICP), there is high intracranial compliance. This explains why, despite having a small increase in intracranial volume (e.g. cerebral hematoma or cerebral edema), there are minimal changes in ICP values.
The highly compliant nature of the intracranial system can be explained by mechanisms such as:
- CSF displacement through foramen magnum into the paraspinal space
- blood displacement from compressed brain tissue
When these mechanisms are exhausted, further increases in volume are directly reflected as increases in ICP.
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