Cardio-respiratory mechanical simulator for in vitro testing of impedance minute ventilation sensors in cardiac pacemakers

We developed a Cardio-Respiratory Mechanical Simulator (CRMS), a system able to reproduce both the cardiac and respiratory movements, intended to be used for in vitro testing of impedance Minute Ventilation (iMV) sensors in cardiac pacemakers. The simulator consists of two actuators anchored to a human thorax model and a software interface to control the actuators and to acquire/process impedance signals. The actuators can be driven separately or simultaneously to reproduce the cardiac longitudinal shortening (LS) at a programmable heart rate (HR) and the diaphragm displacement (DD) at a programmable respiratory rate (RR). A standard bipolar pacing lead moving with the actuators and a pacemaker case fixed to the thorax model have been used to measure impedance (Z) variations during the simulated cardio-respiratory movements. The software is able to discriminate the low-frequency component due to respiration (ZR) from the high-frequency ripple due to cardiac effect (ZC). iMV is continuously calculated from ZR and RR. From preliminary tests the CRMS proved to be a reliable simulator for in vitro evaluation of iMV sensors. ZR recordings collected during cardio-respiratory movements reproduced by the CRMS were comparable in morphology and amplitude with in vivo assessments of transthoracic impedance variations.