Performance evaluation of a portable bioimpedance cardiac output monitor for measuring hemodynamic changes in athletes during a head-up tilt test

Cardiac output (CO) monitoring is useful for sports performance training, but most methods are unsuitable as they are invasive or hinder performance. The performance of PhysioFlow (PF), a portable noninvasive transthoracic bioimpedance CO monitor, was evaluated and compared with a reference Doppler CO monitor, USCOM, using a head-up tilt (HUT) test. With ethics committee approval, 20 healthy well-trained athletes were subjected to HUT in a fixed order of 0°, 70°, 30°, and 0° for 3 min each. Simultaneous hemodynamic measurements using PF and USCOM were made 30 s after a change in HUT and analyzed using tests, ANOVA, and mountain plots. Heart rate (HR) and stroke volume (SV) from both monitors changed according to physiological expectation of tilt, but PF measurements of SV were higher with a positive bias (PF vs. USCOM, 0°: 87.3 vs. 54.0 mL, < 0.001; 70°: 76.5 vs. 39.5 mL, < 0.001; 30°: 81.4 vs. 50.1 mL, < 0.001; 0°: 88.3 vs. 57.1 mL, < 0.001). Relative changes in SV (∆SV) after each tilt measured using PF were lower with a negative bias (PF vs. USCOM, 0° to 70°: -12.3% vs. -26.3%, = 0.002; 70° to 30°: +6.4% vs. +31.2%, < 0.001; 30° to 0°: +9.2% vs. +15.8%, = 0.280). CO measurements using PF at 70° were erroneous. Compared with USCOM, PF overestimated SV measurements but underestimated the ∆SV between HUT. Accuracy of the PF deteriorated at 70°, implying a gravitational influence on its performance. These findings suggested that the suitability of PF for sports use is questionable. The use of impedance cardiography to monitor physiological changes in sports is rarely reported. Using head-up tilt test, we evaluated a portable noninvasive impedance cardiography device (PhysioFlow) by comparing it with a reference Doppler monitor (USCOM). Accuracy in tracking hemodynamic changes deteriorated with higher tilt, implying a gravitational influence on its performance. Stroke volume measurements were overestimated, but the changes were underestimated. Despite its convenient physical features, the suitability of PhysioFlow for sports use is questionable.