Abstract: A system for keeping the surface temperature of an electric resistance-type heater element in a thermodilution catheter within safe physiological limits includes, in the preferred embodiment, a heater element core temperature monitor, a monitor for monitoring the power that is supplied to the heater element, and a surface temperature calculator for calculating the surface temperature of the heater element based on the core temperature, supplied power, and information representing the characteristics of the particular catheter under anticipated clinical conditions. A second aspect of the invention involves a system for determining the supply of power to the heater element based on the core temperature of the heater element. A third aspect of the invention involves a system readiness test for determining, in vivo, that the thermodilution catheter system is properly calibrated before the system is operational. Methods of operation for each of the above-referenced aspects of the invention are also disclosed.

Abstract: Methods and apparatus for eliminating the effects of electrosurgical interference on continuous, heat-based cardiac output measurements employing several procedures, including the steps of (1) supplying power via an isolation transformer and carrier frequency to a catheter-mounted heating element; (2) measuring the voltage and current on the primary side of the isolation transformer; (3) determining the voltage and current on the secondary side of the transformer on the basis of the measured primary side voltage and current; and (4) calculating the power delivered to and resistance of the catheter-mounted heater on the basis of the secondary voltage and current. A heater power waveform generated with this process will be substantially free of electrical interference due to electrosurgical devices. Then, a system transfer function may be produced via signal processing techniques which involve cross-correlating the heater power waveform with the blood temperature waveform.

Abstract: Method and apparatus for adapting the volumetric flow rate measurement system taught by Yelderman in U.S. Pat. No. 4,507,974 to clinical environments by reducing the effects of physiological noise. Signal processing techniques are used to characterize the background noise power spectrum of the system under test so that the effect of noise aberrations on the measured data may be eliminated and so that the predominant periodicities of the background noise spectra may be avoided. The invention further cross-correlates the input data of the system with the corresponding ouput data of the system to determine weighting values for each input frequency so that data collected at noisy frequencies is discounted. Low frequency noise or drift is also removed from the output signal by fitting the average of the output data to a quadratic function which is then subtracted from the original output signal, point by point.