[Non-invasive measurement of cardiac output by the CO2 rebreathing method and its reliability in clinical practice]

A Commercially available, non-invasive system for estimation of cardiac output by the CO2-rebreathing method (Sensormedicus MMC4400) was evaluated to determine its reliability in clinical practice. Values of cardiac output were obtained at rest and during mild to moderate bicycle ergometer work in patients with ischemic heart disease or hypertension. Cardiac output measured by the CO2-rebreathing method was significantly correlated with that measured simultaneously by dye dilution or thermodilution methods. Cardiac output values determined by the CO2-rebreathing method were the same as those obtained by the two invasive methods in reproducibility. When cardiac output and Vo2 were normalized for body weight, they were significantly correlated with each other. This result was obtained both by the CO2-rebreathing method, and by the two invasive methods. These results indicate that MMC4400 will provide a value for cardiac output substantially the same as that obtained by using more laborious invasive methods. Clinical use of the CO2-rebreathing method has been limited by technical difficulties. However, the recently developed non-invasive cardiac output measurement system (MMC4400) uses a microcomputer to analyze the results, and the operator can determine the values for cardiac output easily. Furthermore, it simultaneously measures VO2, VCO2 and VE, so the operator can estimate the measured values for cardiac output with background information on ventilatory gas analysis. Determination of cardiac output through the use of the CO2-rebreathing method is suitable particularly for exercise studies, and it is expected to be a useful device, in the near future, for evaluating cardiac function of patients with primary cardiac diseases.