Agreement of concomitant cardiac output measurement by thoracic bio‐impedance and inert gas rebreathing in healthy subjects

PURPOSE: Inasmuch as they are deemed valid, noninvasive measurement of cardiac output techniques present advantages of ease and safety for use in humans. Few studies have compared the use of thoracic bioimpedance and inert gas rebreathing techniques for cardiac output (CO) assessment at rest and exercise. This manuscript reports on differences between Physioflow® and Innocor® CO measurements at rest and during cycling in a population of healthy subjects. METHODS: Fifty healthy subjects (52 ± 16 years) underwent an incremental cycle exercise testing (IET) during which standardized Physioflow® and Innocor® CO assessments were achieved. Measurements were completed in a subgroup of twelve subjects during two constant-load 10-min cycling bouts at moderate and high intensities. RESULTS: Mean difference between Physioflow® and Innocor® was of 0.002 ± 0.98 l/min at rest and 0.38 ± 1.31 l/min during IET without statistical difference. Correlation coefficient values were higher for exercise (r = 0.83) than resting (r = 0.40) measurements. Good reproducibility of the two devices was observed on different graded exercises with intraindividual variability lower than 6%, except for rest Innocor® CO measurements (CV = 18%). CONCLUSION: Physioflow® and Innocor® can be easily used concomitantly for noninvasive measurement of CO. Despite finding a strong agreement between techniques for exercise CO, results should not be interpreted as being interchangeable as values are derived from different flow measurements: systemic blood flow for Physioflow® and pulmonary blood flow for Innocor®. However, the concomitant use of both techniques could be of value in clinical setting for noninvasive intrathoracic shunt quantification.