Theoretical Validation of the Thermal Dilution Method for Cardiac Output Determination

The basic formula of the thermal dilution method for the measurement of cardiac output is proven for pulsatile flow, assuming constant stroke rate, equal stroke volumes, and ideal ventricular mixing. Firstly, for an ideal thermistor of negligible response time which presents the temperature of the blood in the pulmonary artery as a step function; then it is shown that the area under the curve of temperature versus time is independent of the response time of the thermistor; hence, the formula holds for all thermistors.