Reliability of peak $\dot V{\text{O}}_2$ and maximal cardiac output assessed using thoracic bioimpedance in children

Abstract

The purpose of this study was to evaluate the reliability of a thoracic electrical bioimpedance based device (PhysioFlow) for the determination of cardiac output and stroke volume during exercise at peak oxygen uptake (peak $\dot V{\text{O}}_2$ in children. The reliability of peak $\dot V{\text{O}}_2$ is also reported. Eleven boys and nine girls aged 10–11 years completed a cycle ergometer test to voluntary exhaustion on three occasions each 1 week apart. Peak $\dot V{\text{O}}_2$ was determined and cardiac output and stroke volume at peak $\dot V{\text{O}}_2$ were measured using a thoracic bioelectrical impedance device (PhysioFlow). The reliability of peak $\dot V{\text{O}}_2 ,$ cardiac output and stroke volume were determined initially from pairwise comparisons and subsequently across all three trials analysed together through calculation of typical error and intraclass correlation. The pairwise comparisons revealed no consistent bias across tests for all three measures and there was no evidence of non-uniform errors (heteroscedasticity). When three trials were analysed together typical error expressed as a coefficient of variation was 4.1% for peak $\dot V{\text{O}}_2 ,$ 9.3% for cardiac output and 9.3% for stroke volume. Results analysed by sex revealed no consistent differences. The PhysioFlow method allows non-invasive, beat-to-beat determination of cardiac output and stroke volume which is feasible for measurements during maximal exercise in children. The reliability of the PhysioFlow falls between that demonstrated for Doppler echocardiography (5%) and CO₂ rebreathing (12%) at maximal exercise but combines the significant advantages of portability, lower expense and requires less technical expertise to obtain reliable results.