The Pressure-Volume Index (PVI) with Epidural Mass Expansion
The pressure-volume index (PVI) is intended to provide a measure of the intracranial buffering capacity to be used in predicting the change in ICP course when the craniospinal system is subject to further volume increments. When an intraventricular bolus injection of volume AV is added, rapidly, to the intracranial system, it results in an increase in pressure from a baseline value, Po, to a pressure Pp > Po. It has been shown that the pressure-volume response of the system is nonlinear and can be characterized by a mono-exponential function . In particular, P = Po exp(kΔV), where k = In10/PVI. It follows then that, for a single bolus injection, the value of the PVI is determined as PVI = ΔV/log(Pp/Po).
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