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 vo lume continuously, beat to beat, from the non-invasive blood pressure signa l measured by Finapres or Portapres. Portapres is the portable version of F inapres. The purpose of this study was to compare cardiac output (CO) calcu lated using Modelflow 2.1 (COmf) with CO obtained by the CO2 rebreathing me thod (COre) during steady state at moderate exercise levels. Twelve subject s visited the laboratory twice and performed submaximal exercise on a bicyc le ergometer at 20%, 40% and 60% of their individual peak power output (POp eak) The averaged correlation between COmf and COre gives an r-value of 0.6 9, whereas the slope and intercept of the regression line were 1.06 and 1.6 5 respectively. The averaged difference between COmf and COre was 2.27 +/- 3.91 min(-1) (mean +/- standard deviation). However, the test-retest differ ence between COmf and COre was 2.5 +/- 3.1 and 0.5 +/- 1.3 l min(-1) respec tively. These results suggest that Modelflow 2.1 is not an accurate method for estimating CO from non-invasive blood pressure data collected by Portap res during exercise at up to 60% of the individual POpeak corresponding wit h daily life activity.