Continuous Fick cardiac output measurement during exercise by monitoring of mixed venous oxygen saturation and oxygen uptake

Abstract

To determine whether continuous Fick cardiac output measurement is applicable to exercise testing, cardiac output data obtained by the continuous Fick method (Qcf) during exercise were compared with data obtained by the thermodilution method (Qth). Seventeen patients with old myocardial infarction underwent a 1-min or 3-min incremental exercise test (protocols 1 and 2, respectively). During exercise, the oxygen consumption (VO2), arterial oxygen saturation (SaO2), and mixed venous oxygen saturation (SvO2) were monitored continuously. Qcf was calculated at 12-s intervals by the Fick equation. The SaO2 remained almost constant during exercise. The SvO2 showed four characteristic phases during exercise protocol 1. SvO2 values changed rapidly in phases 2 and 4, but only slightly during phase 3. In exercise protocol 2, SvO2 almost reached a steady-state by the end of each stage. The correlation between Qcf and Qth was good in protocol 1 (r = 0.86), except in phases 2 and 4, and was also good in protocol 2 (r = 0.80). We conclude that the continuous Fick method may be applicable for determining the cardiac output during exercise provided that the variation in SvO2 is slight.