Pressure recordings from 16 patients with normal pressure by hydrocephalus were analysed during controlled intracranial hypertension. Single pulse pressure wave (PPW) analyses were performed on a computer system with programs for automatic computation of mean intracranial pressure (MICP), pulse amplitude (PA), rise time coefficients (RT) and fast Fourier transformation (FFT). We found good correlation between the first harmony, MICP and PA, and between the fifth harmony and RT. The PPW is mainly composed of low-frequency components, but with increasing RT more high-frequency components are present. RT changes as compliance of the brain changes. Therefore the high-frequency components of the FFT may predict changes in the cerebral compliance, although there was no correlation between any of the harmonies and the pressure volume index (PVI). In this investigation PVI was found difficult to perform and evaluate.
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