Impedance cardiography applied to maximal arm cranking exercise: a matter of sampling and processing strategy

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 first time derivative of impedance changes (dZ/dt) over several cardiac cycles differs from previously reported techniques with respect to cycle selection strategy, according to fixed criteria, and processing methods.

First, the primary elements of the Kubicek stroke volume (SV) formula, as determined by EA, were compared with the values determined by the standard hand-processing (HP) method over a large range of cardiac outputs.

Results showed a very high reliability for 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 cranking test to volitional fatigue. The present technique allowed for an effective filtering of movement and breathing artifacts of the original signal. Thus, interpretation of the dZ/dt wave form was convenient, even at maximal arm cranking power outputs up to 120 W. Stroke volume ranged from 63.83 to 127.18 mL.beat-1, showing no significant variations with oxygen consumption. Cardiac output increased linearly with oxygen uptake, reaching a mean maximal value of 16 L.min-1.

The present procedure opens a new field of application to impedance cardiography, permitting to measure cardiac output during maximal arm cranking exercise.