Correction of cardiac output obtained by Modelflow® from finger pulse pressure profiles with a respiratory method in humans

The beat-by-beat non-invasive assessment of cardiac output (Q˙ , litre · min−1) based on the arterial pulse pressure analysis called Modelflow® can be a very useful tool for quantifying the cardiovascular adjustments occurring in exercising humans. ˙Q was measured in nine young subjects at rest and during steady-state cycling exercise performed at 50, 100, 150 and 200 Wby using Modelflow® applied to the Portapres® non-invasive pulse wave (˙QModelflow) and by means of the open-circuit acetylene uptake (˙QC2H2 ). ˙Q values were correlated linearly (r=0.784), but Bland–Altman analysis revealed that mean ˙QModelflow − ˙QC2H2 difference (bias) was equal to 1.83 litre · min−1 with an S.D. (precision) of 4.11 litre · min−1, and 95% limits of agreement were relatively large, i.e. from −6.23 to +9.89 litre · min−1. ˙QModelflow values were then multiplied by individual calibrating factors obtained by dividing ˙QC2H2 by ˙QModelflow for each subject measured at 150 Wto obtain corrected˙Q Modelflow (˙Qcorrected) values. ˙Qcorrected values were compared with the corresponding ˙QC2H2 values, with values at 150 Wignored. Data were correlated linearly (r=0.931) and were not significantly different. The bias and precision were found to be 0.24 litre · min−1 and 3.48 litre · min−1 respectively, and 95% limits of agreement ranged from −6.58 to +7.05 litre · min−1. In conclusion, after correction by an independent method, Modelflow® was found to be a reliable and accurate procedure for measuring ˙Q in humans at rest and exercise, and it can be proposed for routine purposes.