AN INVASIVE CATHETER FLOW SENSOR WITH ON-CHIP CMOS READOUT ELECTRONICS FOR THE ONLINE DETERMINATION OF BLOOD-FLOW

A silicon flow sensor with integrated electronics for invasive blood-f low measurement has been developed and investigated. The flow sensor i s based on a silicon-on-insulator SIMOX (separation by implanted oxyge n) substrate with a backside etched silicon membrane containing oxide trenches and uses a differential thermal measurement principle. The ch osen fabrication process is fully CMOS-compatible. An on-chip switched -capacitor circuitry converts the Row signal into a pulse-width-modula ted signal. The device has been tested in a blood-circulation simulato r in the flow range 0-101 min(-1) within a vessel with a diameter of 2 cm. It has been found to be useful for the observation of time-depend ent flow pulses as well as for the determination of the cardiac output . A prototype version of the Bow-sensor system has a membrane temperat ure of less than 2 K above ambient temperature, a total power consumpt ion of 5 mW and shows a pulse-width change from 45 to 25 mu s for the flow range 0-101 min-(1).