Noninvasive monitoring of cardiac output during exercise by inductance cardiography

Introduction/Purpose: Inductance cardiography is a noninvasive technique that monitors changes in cardiac output from an inductance plethysmographic transducer encircling the chest at the level of the heart. The method has been previously validated in supine patients at rest by comparisons to thermodilution. Our purpose was to investigate whether the technique can be employed during bicycle exercise. Methods: We simultaneously measured cardiac output by inductance cardiography and by two gas exchange methods based on the Fick principle during upright cycle ergometry in healthy volunteers. Results: In I I subjects, comparisons of changes in cardiac output by inductance cardiography agreed well with values measured by carbon dioxide rebreathing during a steady-state exercise protocol. In 12 subjects, cardiac output changes measured by inductance cardiography and an oxygen uptake method agreed closely during a progressive ramp exercise protocol to exhaustion. The bias (mean difference to reference methods) and limits of agreement (+/-2 SD of bias) for estimation of relative changes in cardiac output by inductance cardiography were 1% +/- 21% in 67 comparisons to the carbon dioxide rebreathing technique, and 0% +/- 22% in 98 comparisons to the oxygen uptake method. Conclusion: In healthy subjects, inductance cardiography accurately and unobtrusively estimates changes in cardiac output during bicycle exercise in comparison to gas exchange methods.