Enhanced cardiac thermal dilution measurement of cardiac output, volumes, regurgitation, valve effective diameters, ventricular power and efficiency – Feasibility analysis using digital simulation

Abstract

Cardiac output is measured by the thermal dilution method which uses a quadruple lumen catheter, with a thermistor on the tip, through the right atrium, right ventricle and into the pulmonary artery. Cold saline is injected into the right atrium and the resulting pulmonary artery temperature profile is integrated. The same procedure performed with three thermistors and three pressure sensors located on the catheter to measure temperature and pressure in the atrium, ventricle and artery respectively will produce a set of temperature and pressure curves with shapes determined by injectate temperature, injectate volume, heart rate, systolic time interval, body temperature, cardiac output, volumes, flow rates and valve openings. A digital computer program has been developed to optimize the fit of a lumped parameter model to the thermodilution curves in order to determine heart rate, systolic time as a fraction of cardiac cycle, right atrial systolic and diastolic volumes, ventricular systolic and diastolic volumes, cardiac output, inflow valve forward and reverse flow rates and effective diameters, outflow valve forward and reverse flow rates and effective diameters, ventricular power and efficiency. The program has been tested over a range of operating conditions including noise in the temperature and pressure signals, randomly varying heart rate and cardiac cycle. All of the data for the tests were produced by a digital computer simulation of a pulsatile artificial heart. The results of these tests indicate that the enhanced thermal dilution analysis method is feasible.