A cardiac output monitoring system (10) includes a respiratory flowmeter (14) and a gas analyzer (20, 22) capable of determining cardiac output on a breath-by-breath basis by non-invasively measuring properties of respiratory gasses and applying the Fick principle. The gas analyzer has the capability to simultaneously quantify multiple gas concentrations, including inhaled and end-tidal concentrations of any constituent of respiratory gas mixtures of a known number of possible constituents, in real time on a breath-by-breath basis, by measuring independent properties of the mixture. The respiratory flowmeter determines the volumetric and mass flow rates of any gas/gasses as calculated from the product of measured total respiratory flow and the measured volumetric concentration in real time on a breath-by-breath basis. From these measurements, cardiac output can be determined on a breath-by-breath basis by applying appropriate numerical algorithms based on the Fick principal, including corrections for physiological conditions such as shunts and deadspace.
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