[Analog integration of the area under a thermodilution curve]

The problem of computing the area under the thermodilution curve to determine the cardiac output by the thermodilution method is discussed. The circuit of an analog integrator is developed that outputs continuously a current area value. Recommendations for the choice of main integrator elements and methods of computing the cardiac output with the analog integrator are given. Two thermosensitive probes with different thermal lag have been tested by using a physical model of the circulation system, and some experimental results are presented. When defining the integration threshold for the area under the thermodilution curve the thermal lag of the probe should be taken into consideration.