Measurement of cardiac output by carbon dioxide rebreathing.

Twenty patients were studied on a bicycle ergometer at rest and at varying workloads to compare methods of measuring cardiac output. In nine patients, a comparison of carbon dioxide rebreathing and dye dilution techniques for measuring cardiac output were made. In eleven patients, comparisons between carbon dioxide rebreathing, dye dilution, and direct oxygen Fick techniques were made. The cardiac output measured by carbon dioxide rebreathing was reproducible and compared well with both the dye dilution and direct oxygen Fick. The correlation coefficient for the relationship between carbon dioxide rebreathing and direct oxygen Fick cardiac outputs was 0.80 and between carbon dioxide rebreathing and dye dilution cardiac outputs was 0.75. The relationship between dye dilution and direct oxygen Fick cardiac output was 0.71. The carbon dioxide rebreathing technique is a safe, non-invasive and reproducible method to measure cardiac output. The results compare well with the cardiac output measured by either the direct oxygen Fick or dye dilution technique.