The Consistency of Carbon Dioxide Rebreathing as a Non-invasive Method to Determine Exercise Cardiac Output

The present study utilized the extrapolation method of Defares and the Bohr equation to determine Pv¯CO2 and PaCO2, respectively from carbon dioxide rebreathing. Subjects rode a bicycle ergometer at average workloads of 600 and 900 kilopond metres per minute resulting in oxygen consumptions of 1600 ml/min and 2300 ml/min respectively. Significant repeatability was shown for both workloads and compared favourably with data using invasive techniques. The cardiac outputs appeared clustered at low normal values with respective oxygen consumptions and this was theorized as a cardiac conserving adjustment resulting from the trained characteristics of the subjects.