CA2188929A1 - Implantable Capacitive Absolute Pressure and Temperature Monitor System - Google Patents

Abstract

A capacitive pressure and temperature sensing system for providing signals representative of the magnitude of body fluid absolute pressure at a selected site and ambient operating conditions, including body temperature, at the site. An implantable lead having a sensor module formed in its distal end is coupled to a monitor that powers a sensor circuit in the sensor module and demodulates and stores absolute pressure and temperature data derived from signals generated by the sensor circuit. The sensor module is formed with a pickoff capacitor that changes capacitance with pressure changes and a reference capacitor that is relatively insensitive to pressure changes. The sensor circuit provides charge current that changes with temperature variation at the implant site, alternately charges and discharges the two capacitors, and provides timing pulses having distinguishable parameters at the end of each charge cycle that are transmitted to the demodulator. The demodulator detects and synchronizes the timing pulses and derives pressure and temperature analog voltage values representative of the intervals between the timing pulses which are digitized and stored in the monitor. The monitor may also be coupled with other sensors for measuring and storing related patient body parameters, e.g. blood gas, EGM, and patient activity.