Physioflow

During exercise, heart rate (HR), stroke volume (SV) and cardiac output (Q̇) were measured continuously using impedance cardiology (PhysioFlow^®, Manatec Biomedical, France) (Charloux et al., 2000 (link); Richard et al., 2001 (link)). The theoretical basis for determining cardiac output from this method and its validity during rest and exercise has been described previously (Charloux et al., 2000 (link); Lepretre et al., 2004 (link)), and has been validated against the direct Fick method (Richard et al., 2001 (link)). Two sets of electrodes (Skintact FS-50, Leonhard Lang Gmbh, Austria) – one transmitting, one sensing – were applied above the supra-clavicular fossa at the left base of the neck, and along the xiphoid process. Another two electrodes were used to monitor a single electrocardiographic signal (ECG; CM5 position). Blood pressure was assessed (Digital blood pressure monitor, UA-767, A&D Instruments Ltd., United Kingdom) as part of standard calibration process for the PhysioFlow^® prior to the exercise test. During the experimental trials (Figure 1), HR, SV, and Q̇ data were sampled at 5-s intervals, with the average for each interval determined during moderate and high loads. The coefficient of variation of cardiac output measures during peak exercise using this method has been reported as 3.4–3.6% (Hsu et al., 2006 (link)).