Non-invasive cardiac output assessment during moderate exercise: pulse contour compared with CO2 rebreathing.

The arterial pulse contour method called Modelflow 2.1 calculates stroke volume continuously, beat to beat, from the non-invasive blood pressure signal measured by Finapres or Portapres. Portapres is the portable version of Finapres. The purpose of this study was to compare cardiac output (CO) calculated using Modelflow 2.1 (COmf) with CO obtained by the CO2 rebreathing method (COre) during steady state at moderate exercise levels. Twelve subjects visited the laboratory twice and performed submaximal exercise on a bicycle ergometer at 20%, 40% and 60% of their individual peak power output (POpeak). The averaged correlation between COmf and COre gives an r-value of 0.69, whereas the slope and intercept of the regression line were 1.06 and 1.65 respectively. The averaged difference between COmf and COre was 2.27 +/- 3.91 min-1 (mean +/- standard deviation). However, the test-retest difference between COmf and COre was 2.5 +/- 3.1 and 0.5 +/- 1.31 min-1 respectively. These results suggest that Modelflow 2.1 is not an accurate method for estimating CO from non-invasive blood pressure data collected by Portapres during exercise at up to 60% of the individual POpeak corresponding with daily life activity.