Metrological properties evaluation of a chest wall simulator during simulated quiet breathing

Opto-electronic Plethysmography (OEP) is a motion analysis system used to measure chest wall kinematics and to indirectly evaluate respiratory volumes during breathing. Its working principle is based on the time-per-time computation of marker displacements placed on the thorax. This work aims at evaluating the metrological properties of a custom made chest wall simulator (CWS) developed to reproduce human chest wall kinematic. The CWS metrological properties were estimated by the comparison of two different motion control strategies of the CWS: the first one is based on the script writing into each motion controller, the second one on macro command sent to the CWS. Three sets of experiments were carried out with the aim to: (i) evaluate precision and accuracy in performing target displacements (i.e., ranging from 2 mm to 8 mm), (ii) evaluate the differences between set and simulated breathing period (i.e., from 10 to 30 breathing per minute), and (iii) assess the movement reproducibility. The precision error, expressed as the ratio between measurement uncertainty and the measured displacement, is always lower than 0.32% (27 μm) with script-based motion control and 0.25% (6 μm) with the macro one, for all the target displacements. The difference between the simulated breathing period and the set one is always lower than 0.30 s in both strategies of motion control (percentage error always lower than 15%). Standard deviation between measure, assumed as reproducibility index, showed values always lower than 37 μm. These performances allows considering both the strategies of control adoptable to be employed for CWS motion control during the OEP performance in further works.