A new impedance cardiograph device for the non-invasive evaluation of cardiac output at rest and during exercise: comparison with the “direct” Fick method

Abstract

The objectives of this study were to evaluate the reliability and accuracy of a new impedance cardiograph device, the Physio Flow, at rest and during a steady-state dynamic leg exercise (work intensity ranging from 10 to 50 W) performed in the supine position. We compared cardiac output determined simultaneously by two methods, the Physio Flow (Q˙ _cPF) and the direct Fick (Q˙ _cFick) methods. Forty patients referred for right cardiac catheterisation, 14 with sleep apnoea syndrome and 26 with chronic obstructive pulmonary disease, took part in this study. The subjects' oxygen consumption values ranged from 0.14 to 1.19 l · min⁻¹. The mean difference between the two methods (Q˙ _cFick−Q˙ _cPF) was 0.04 l · min⁻¹ at rest and 0.29 l · min⁻¹ during exercise. The limits of agreement, defined as mean difference ± 2SD, were −1.34, +1.41 l · min⁻¹ at rest and −2.34, +2.92 l · min⁻¹ during exercise. The difference between the two methods exceeded 20% in only 2.5% of the cases at rest, and 9.3% of the cases during exercise. Thoracic hyperinflation did not alter Q˙ _cPF. We conclude that the Physio Flow provides a clinically acceptable and non-invasive evaluation of cardiac output under these conditions. This new impedance cardiograph device deserves further study using other populations and situations.