Intracranial pulse pressure dynamics in patients with intracranial hypertension.

The pulsative inflow of blood to the brain causes fluctuations in the cerebral blood volume, and this is considered to be the main cause of the pulsations of the intracranial pressure (ICP). This statement allows discrimination between two different factors that influence the pulse amplitude of the ICP: 1. The pulsatile pattern of the cerebral arterial blood flow. 2. The slope of the intracranial pressure-volume curve. In order to clarify the relative contributions of the two factors we have developed a simulation model of the intracranial pressure-volume curve and the cerebral blood flow. Measurements from clinical practice and data from other authors can be interpreted with reference to this model. The increase in the pulse amplitude due to a moderate increase in the ICP is mainly explained by the decrease of the intracranial compliance. However, it is recognized that, when the ICP approaches the arterial blood pressure, the ICP amplitude increases disproportionally with increasing ICP. In this situation the transmural pressure of the cerebral arteries approaches zero, and the compliance relevant to the arterial flow system is no longer that of the vessel wall but the compliance of the craniospinal compartment.