Estimation of cardiac output by a single breath method

Many attempts have been made to quantify cardiac output using both invasive and non-invasive techniques. The results have generally been poorly reproducible and comparisons of techniques have yielded highly variable values. A single breath inert gas method was used in the study, since it offers several advantages over previous methods, chiefly its speed of measurement, and the controlled manner in which it is performed. The method observes the uptake of a semi-soluble inert gas (Freon-22) with respect to an insoluble marker, and calculates cardiac output (pulmonary flow) from the slope of the semi-soluble gas. [Continues.]