A procedure has been developed for calculating the work performed by the left ventricle during the heartbeat. This procedure involves the continuous direct measurement of fluid mixture temperature in the left ventricle during and after the controlled injection, through a catheter, of a known volume of cold saline into the left ventricle. The measured mixture temperatures are used to calculate instantaneous ventricular volumes during the entire heartbeat. The equations employed in the calculations were derived from an analysis of the flow processes through the ventricle and the application of the conservation of mass and energy principles. The procedure employs a “Thermocatheter” which is a unique device which allows for the continuous injection of cold saline into the left ventricle and the measurement of left ventricular fluid temperature. The thermocatheter consists of a specially designed fast response thermocouple and catheter assembly. The thermocouple signal is amplified by a high gain, low noise direct current amplifier The volume versus time plot calculated from the measured ventricular fluid temperatures is combined with the measured ventricular pressure trace for the heartbeat. This results in a pressure versus volume plot or work diagram for the left ventricle. Thermodilution studies performed in man, at the Saint Michael Medical Center, indicated that this approach to the evaluation of cardiac work is important in the assessment of cardiac state.

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