Importance

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Abstract

A method and apparatus for correcting thermal drift in cardiac output measurements based upon a temperature signal indicative of the change in temperature of blood leaving the heart is disclosed. In a first preferred embodiment of a cardiac output monitoring system (10), the catheter (14) is provided with an electrical resistance heater (22). An electrical current having a sinusoidal waveform with a period of from 30 to 60 seconds is applied to the heater, causing power to be dissipated into the blood within a patient's heart (12). A temperature sensor (24) disposed near a distal end of the catheter produces a signal indicative of the temperature of blood leaving the heart. The temperature signal and the signal corresponding to the electrical power dissipated in the heater (an input signal) are filtered at a frequency .omega.n corresponding to the frequency of the applied electrical current, i.e., the frequency of the input signal. An output signal indicative of the temperature of the blood leaving the heart corrected for the effects of thermal drift is then calculated. The blood temperature output signal is first split into two equal overlapping time periods. The two signals are then filtered separately to produce two partially independent output signals in the frequency domain. These two frequency domain output signals are then combined into a single corrected frequency domain output signal with the effects of thermal drift removed. The amplitude of the input power, the amplitude of the temperature signal corrected for thermal drift, and their phase difference are then used in calculating cardiac output.

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First Claim