IMPEDANCE CARDIOGRAPHY APPLIED TO MAXIMAL ARM CRANKING EXERCISE - A MATTER OF SAMPLING AND PROCESSING STRATEGY

Purpose: A new ensemble-averaging (EA) approach was developed with the goal of investigating central hemodynamics by transthoracic impedance cardiography during maximal arm cranking. This EA procedure of the fi rst time derivative of impedance changes (dZ/dt) over several cardiac cycles differs from previously reported techniques with respect to cyc le selection strategy, according to fixed criteria, and processing met hods. Methods: First, the primary elements of the Kubicek stroke Volum e (SV) formula, as determined by EA,were compared with the values dete rmined by the standard hand-processing (HP) method over a large range of cardiac outputs. Results: Results showed a very high reliability fo r ventricular ejection time (r = 0.996), (dZ/dt)(min) (r = 0.995), SV (r = 0.977), and heart rate (r = 0.999). Second, the EA procedure was applied to six subjects performing a continuous, multistage arm cranki ng test to volitional fatigue. The present technique allowed for an ef fective filtering of movement and breathing artifacts of the original signal. Thus, interpretation of the dZ/dt wave form was convenient, ev en at maximal arm cranking power outputs up to 120 W. Stroke volume ra nged from 63.83 to 127.18 mL . beat(-1), showing no significant variat ions with oxygen consumption. Cardiac output increased linearly with o xygen uptake, reaching a mean maximal value of 16 L . min(-1) Conclusi on: The present procedure opens a new field of application to impedanc e cardiography, permitting to measure cardiac output during maximal ar m cranking exercise.