Diagnostic in normal pressure hydrocephalus: A mathematical model for determination of the ICP-dependent resistance and compliance.

The internationally accepted calculation methods concerning cerebrospinal fluid dynamics proceed from a pressure independent resistance to cerebrospinal fluid outflow. In a new model we focus our attention on the pressure dependency of resistance. In our calculation model we are monitoring the complete pressure course p(t) over the time during and after the infusion. The comparison of the pressure rise On(p) during the infusion and the descent Off(p) after the infusion at the same pressure level allows one to construct all formulas for the compliance C(p) and resistance R(p). The computerized analysis of the results of the intrathecal infusion test using our mathematical computation leads to a simplification of this investigation. The simultaneous measurement of the resistance and compliance during a single investigation allows one to minimize the patient's discomfort. In contrast to the classical methods it is not necessary that the ICP reaches a plateau. Our mathematical method diverges with the description of a pressure dependent slope of the function for the resistance from the static examination models. For that we are able to take the non-linearity of the cerebrospinal fluid resorption into consideration.