Determination of Cardiac Output by Rebreathing Method ; with Special Reference to Its Reliability and Merit in Clinical Use

The PV^^co2, was determined graphically by the rate of rise in CO2 concentration while rebreathing pure oxygen. The reproducibility of consecutively determined PV^^co2 was fairly well and it correlated significantly with the PaCO2= directly measured from arterial blood. To make the procedure determining the cardiac output strictly non-bloody, PaCO2 was also determined indirectly by the end-tidal gas analysis. The CO2 output was measured conventionally. The PV^^co2 and PaCO2 were converted to their con-tent with CO2 dissociation curve for fully oxygenated blood, then the cardiac output was calculated applying these values to the Fick's formula. The range of the cardiac output determined consecutively during an hour was considered small enough to be included within the physiological fluctuation, and the cardiac output thus determined correlated significantly with that by direct Fick method. The cardiac output was significantly different between one another in three groups (healthy, ischemic heart disease and ischemic heart failure). The result agreed with that made by the dye dilution method and apexcardiogram. Having fairly good reproducibility and showing good accordance with the results by the other techniques, it was proved that this indirect Fick method is of great clinical use. Besides, the procedure does not give almost any mental or physical load to subjects.