Non-invasive assessment of cardiac output and stroke volume in patients during exercise

Summary

A one-step CO₂ rebreathing method for the determination of cardiac output and stroke volume (SV) has been evaluated by comparison with the direct Fick technique during recumbent exercise (10–90 W) in 13 patients. In an initial analysis, the influence of different rebreathing times and of correction for haemoglobin concentration was studied. The best correlation with the direct Fick technique was obtained with the longest analysis time, i. e. 21 s, and correction for variations in haemoglobin concentration further improved the correlation. Consequently, an analysis time of 21 s and correction for haemoglobin have been used. At low cardiac outputs, the CO₂-rebreathing method overestimated the flow compared to the Fick technique. The correlation between the methods, however, was so good that a valid estimate of cardiac output could be obtained from the CO₂ rebreathing method with appropriate corrections (Cardiac output, CO₂ method=2.7+0.77. Cardiac output, Fick; r=0.91; Residual Standard deviation (SD res) =0.77 l · min⁻¹). Stroke volumes measured with the CO₂ rebreathing method did not differ significantly from those obtained with the direct Fick technique, although there was a tendency to overestimate stroke volume with the CO₂ rebreathing method (SV, CO₂ method=12+0.89 · SV, Fick; r=0.82; SD res=11 ml).