Figure 4. Comparison of the accuracy of the acetylene (C₂H₂) rebreathing technique and thermodilution method vs the direct Fick method for assessment of Qc during upright exercise in healthy patients and those with clinical disease.

A, Accuracy of C₂H₂ rebreathing for estimation of Qc during exercise in healthy patients; (B) Accuracy of thermodilution for estimation of Qc during exercise in healthy patients; and (C) Accuracy of C₂H₂ rebreathing for estimation of Qc during exercise in clinical populations. Qc indicates cardiac output.