Thermal drift correction while continuously monitoring cardiac output

Abstract

A method for compensating the determination of cardiac output for a baseline blood temperature drift, or other long-term noise. The method is applicable to the continuous monitoring of cardiac output, which is carried out by modifying the temperature of blood within a heart (12) using a periodically varying electrical current that is applied to a heater (22) disposed on the outer surface of a catheter (14) inserted within the heart. A temperature sensor (24) disposed near a distal end (18) of the catheter monitors the temperature of blood leaving the heart, producing a blood temperature signal that periodically varies in a manner corresponding to the input signal. Alternatively, the temperature of blood within the heart can be modified by heat exchange with a fluid circulated within a heat exchanger (16) on the catheter, so that heat is transferred between the fluid and blood. Changes in the baseline blood temperature caused by a gradual warming of the patient from a chilled condition or due to other long term noise are compensated by either carefully selecting a measurement interval during which the blood temperature signal is filtered (by performing a discrete Fourier transform) so that the blood temperature signal (without the effect or drift) comprises only a real component, or by shifting the starting point of the input power signal to achieve the same result. The baseline temperature drift of the blood or other noise is thus in quadrature with the blood temperature signal (without drift) and has little effect on the determination of cardiac output. Further compensation in the measurement interval and/or starting time of the input signal can be made to compensate for other time delays, such as delays due to mixing volume, transport delay, and delays associated with the time constants of the apparatus used to modify the temperature of the blood and determine its temperature.

Dependencies are inferred from the claim text.