Non-invasive cardiac output evaluation during a maximal progressive exercise test, using a new impedance cardiograph device

Abstract.

One of the greatest challenges in exercise physiology is to develop a valid, reliable, non-invasive and affordable measurement of cardiac output (CO). The purpose of this study was to evaluate the reproducibility and accuracy of a new impedance cardiograph device, the Physio Flow, during a 1-min step incremental exercise test from rest to maximal peak effort. A group of 12 subjects was evaluated to determine the reproducibility of the method as follows: (1) each subject performed two comparable tests while their CO was measured by impedance cardiography using the new device (CO_Imp1, CO_Imp2), and (2) in a subgroup of 7 subjects CO was also determined by the direct Fick method (CO_Fick) during the second test. The mean difference between the values obtained by impedance (i.e. CO_Imp1–CO_Imp2) was –0.009 l·min^–1 (95% confidence interval: –4.2 l·min^–1, 4.2 l·min^–1), and CO ranged from 3.55 l·min^–1 to 26.75 l·min^–1 (n=146). When expressed as a percentage, the difference (CO_Imp1–CO_Imp2) did not vary with increasing CO. The correlation coefficient between the values of CO_Imp and CO_Fick obtained during the second exercise test was r=0.94 (P<0.01, n=50). The mean difference expressed as percentage was –2.78% (95% confidence interval: –27.44%, 21.78%). We conclude that CO_Imp provides a clinically acceptable evaluation of CO in healthy subjects during an incremental exercise.