The role of computerized rheoencephalography in the assessment of normal pressure hydrocephalus

The aim of this study was to determine the relationship between arterial compliance derived from rheoencephalography (REG), and the slope of the regression line between pulse amplitude and mean ICP (AMP/P) recorded during a lumbar infusion study. A hypothetical link between these two variables has been suggested in the past. Resistance to the outflow of cerebrospinal fluid (R(out)) and the slope of the amplitude pressure regression line (AMP/P) were calculated in 62 patients diagnosed with posttraumatic normal pressure hydrocephalus (NPH). In all patients, the changes in cerebral electrical impedance related to the pulsatile component of blood flow were studied noninvasively using computerized rheoencephalography. We classified the REG pulse-related waveform (REGpw) according to the number of the inflection points in the ascending branch, which are a manifestation of the elastic properties of the small arteries. In normal subjects, REGpw corresponded with only one inflection point in the ascending branch (category I). For the purpose of this study, we assumed that the presence of three or greater number of inflection points was characteristic of the regressive changes of the arterial wall (category II). The slope of the AMP/P in patients with the category I REGpw was significantly lower than that in patients with category II (p < 0.05). The association between REGpw category II and the increased slope of the aAMP/P regression line may be related to the transmission of the pulse pressure waveform arterial wall to the CSF compartment, which in turn depends on the elastic properties of the cerebral arteries. The outcome of shunting in patients with REGpw category I was significantly better than that in patients with category II, suggesting that small artery disease may be linked to worse clinical outcomes. Our study indicates that REG examination has potential clinical value in diagnosis and prognosis of NPH.