Estimation of cardiac output and stroke volume during incremental exercise from the course of oxygen uptake: application of the non-invasive Stringer method in CAD-patients and endurance-trained subjects

Based on data from right heart catheterizations, Stringer et al. proposed in 1997 a method to calculate the cardiac output (CO) from gas exchange measurements. The Fick principle was applied with the assumption of a predictable peripheral arterio-venous oxygen difference. To check if this method leads to plausible results, 35 healthy endurance-trained subjects (ET) and 24 patients suffering from coronary artery disease (CAD) performed a maximal incremental exercise test on a cycle ergometer with simultaneous gas exchange measurements. CO increased linearly in both groups while the stroke volume (SV) showed a plateau after an initial increase. At the 100 W stage, ET reached a significantly higher SV (160 +/- 22 vs. 102 +/- 17 ml; p < 0.0001) and CO (18.4 +/- 1.0 vs. 11.5 +/- 1.1 l*min(-1); p < 0.0001) than CAD. Our results are in agreement with invasive measurements reported in the literature. Thus, the Stringer method leads to plausible results for SV and CO and can, therefore, be regarded as a simple, low-risk and cheap alternative for the determination of relevant central hemodynamic parameters.