a new method of estimating intracranial elastance

Objective: Current methods of calculating Intracranial Elastance Index (IEI) depend from CSF pulse-wave, whose shape may deeply change during ICP rising. The main aim of this study was to evaluate the reliability and specificity of a novel method to calculate IEI (method C), based on the integral of the CSF pulse-wave area. Method: Twenty ventricular infusion-tests of patients with idiopathic NPH were re-evaluated. We have compared method C with the most widely used methods to calculate IEI: a modified Szewczykowski method (diastolic ICP against CSF pulse-wave amplitude-method A) and a modified Czosnyka method (diastolic ICP against the fundamental harmonic-method B). R-squared (R2) was calculated for each test. Means were compared through ANOVA and t-test. Results: Mean R2 values for methods A, B and C were 0.91 ± 0.06, 0.9 ± 0.06 and 0.96 ± 0.03, respectively. Mean R2 values obtained through method A vs C and through method B vs C were significantly different (p = .006 and p = .001, respectively), while values obtained through method A vs B were not (p = 1). Analysis of ICP tracks demonstrated that 9 patients showed no different shape of the ICP wave during the infusion test, while the remaining 11 did. The mean R2 values obtained through method A vs C and through method B vs C were significantly different (p < .001 for both) for patients showing a different shape of the ICP wave during the infusion test. Conclusions: Method C seems to be the most reliable method to calculate IEI, as it is independent from CSF pulse wave modifications.