Measurements of Cardiac Output during Constant Exercises: Comparison of Two Non-Invasive Techniques

We compared cardiac output (CO) determined simultaneously by electrical impedance cardiography method (CO_ICG) and by the CO₂ rebreathing technique (CO_2REB) during three different steady-state exercises (target heart rate of 120, 140, and 160 min^-1) in 8 healthy fit young men. The mean difference correlation coefficient obtained between the values of CO_ICG and CO_2REB was 0.85 and the mean difference (CO_ICG-CO_2REB) was 0.06 l/min (0.12%). At 120 min^-1, CO_ICG was lower than CO_2REB but the tendency was reversed at 140 and 160 min^-1 where CO_ICG was higher than CO_2REB. This evolution may be explained by the difficultly of using CO₂ rebreathing technique at the highest steady-state exercises and by the progressive acidemia due to exercise. The present results suggest that electrical impedance cardiography method provides acceptable evaluation of CO and may favourably replace the CO₂ rebreathing technique during mild (or moderate) to high steady-state exercises.