In-vivo blood characterization system

A blood-impedance measurement system is presented. It is intended for in-vivo analysis of hematocrit and blood viscosity. Using a specially designed central-venous catheter, blood impedance and blood temperature is on line examined The measurements are performed inside the right atrium, where a strong intracavitary ECG signal is recorded as well. The impedance is measured with sinusoidal signals at five discrete frequencies in the range from 20 kHz to 1.2 MHz. The temperature is measured with a tiny thermistor incorporated in the catheter's tip. From the various blood-impedance components, the measurement system derives plasma resistance, cell membrane capacitance and cell interior resistance. Proper catheter positioning and processing of the measured impedance components are guided by the ECG signal, sensed with the same impedance sensor. A wide variety of biocompatibility issues has thoroughly been identified and related problems have been solved.