Physical Characteristics of Various Methods for Measuring ICP

Abstract

Many data have been published on different methods for measuring “ICP” via ventricular, epidural, subdural or parenchymal record. Also during this meeting, several new devices are presented. However, most investigations only consider the static criteria of the methods, like linearity, zero point stability and hysteresis (Gaab and Heissler 1984, 1988). Little attention has been paid to the dynamic properties of the devices. Such data on frequency resolution (band width) and phase, however, are especially important for computerized evaluation of ICP dynamics including waveform analysis (Chopp and Portnoy 1980; Gaab et al. 1983; Gaab and Heissler 1984, 1988; Portnoy et al. 1983; Varju 1977). ICP pulse waves and the transfer characteristics from arterial blood pressure (SAP) to ICP contain continuous information on intracranial elastance, vasoregulation and CSF dynamics (Branch et al. 1988; Chopp and Portnoy 1980; Portnoy et al. 1983). Dynamic analysis could therefore replace invasive methods like bolus and infusion tests (Anile et al. 1988; Branch et al. 1988; Chopp and Portnoy 1980; Portnoy et al. 1983). However, the waveform investigation e.g., with Fourier transformation up to the 5th harmonic of the ICP pulsation (Piper et al. 1988) requires a bandwidth for recording of > 40 Hz (Gaab and Heissler 1984, 1988). We therefore investigated the frequency resolution and the phase lag of current methods used for measuring ICP and blood pressures.