applied sciences  
In Vitro Analysis of Hemodynamics in the Ascending Thoracic Aorta: Sensitivity to the Experimental Setup  
[PERSON],*(), [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON]  
1 Dipartimento di Ingegneria Civile ed Industriale, University of Pisa, Largo [PERSON] 2, 56122 Pisa, Italy 12 BioCardioLab --Heart Hospital, Fondazione Toscana G. Monasterio, Via Aurelia Sud, 54100 Massa, Italy 2  
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e.g., [9; 10; 11; 12; 13]). Available tools for hemodynamic investigations at a patient-specific level include in silico analyses through computational fluid dynamics (CFD) simulations and in vitro experiments. In recent years, both approaches have been increasingly used for cardiovascular studies, thanks to procedures that integrate in vivo data (from magnetic resonance imaging (MRI), computer tomography (CT), and color Doppler ultrasound (CD-US)) in simulations and experiments (see, e.g., [14; 15; 16; 17; 18; 19]). CFD simulations, usually carried out by using finite-element and/or finite-volume approaches, allow the computation of the spatial and temporal distributions of the hemodynamic parameters with a level of accuracy not obtainable by any in vivo measurement. To obtain patient-specific predictions, the results of clinical exams are usually used as boundary conditions for the simulations (as in [16; 17; 20; 21; 22]). However, in silico analyses suffer from the presence of multiple sources of uncertainty that may reduce the accuracy of the results. Particular attention should be devoted to the segmentation of in vivo-acquired geometries and to the definition of inflow/outflow boundary conditions (see, e.g., [23; 24; 25; 26; 27; 28; 29; 30; 31]). in vitro approaches may be synergistically used with in silico ones to contribute to the validation of numerical simulations, since they avoid some of the sources of uncertainties that may lead to discrepancies between the in silico and in vivo results (see, e.g., [32; 33]). Recent patient-specific experiments have been carried out using phantoms that are 3D-printed or produced using a lost casting technique from in vivo acquisitions (see, e.g., [34; 35; 36]). Among the different experimental apparatus, the sensorized mock circulatory loop (MCL) developed in [37; 38] ensures perfect control and knowledge of the flow rate and pressure conditions and of the vessel geometry and wall properties. The proposed MCL has a versatile setup composed of a custom pulsatile left ventricular pump system, patient-specific 3D-printed phantoms, and chambers and pinch valves to emulate the effects of the downstream organs and vessels. It was demonstrated in [37] that the system was able to cover a wide range of aortic and mitral flows and to reproduce patient-specific cases both in terms of flow and pressure waveforms. Flow and pressure waveforms have been successfully validated with in vivo data from magnetic resonance analysis of patients in the preliminary results reported in [39; 40]). In the experimental framework, the assessment of a reliable and accurate setup for device testing represents a pivotal step in the reproduction of realistic hemodynamic conditions in a controlled environment (see, e.g., [41]). Thus, in this paper, we carried out a systematic analysis of the sensitivity of the experimental setup conditions to evaluate their impact on in vitro-measured quantities. We consider different healthy and disease geometries of the aorta, and we focus on the inflow conditions that have shown to be a crucial issue in both experiments and simulations (see, e.g., [21; 22; 30; 31; 42]). In particular, we consider two parameters characterizing the inlet flow-rate waveform, which are the cardiac-cycle period and the volume of blood introduced in the ascending aorta at each cycle.