This thesis deals with the mechanics of the Intra-Aortic Balloon Pump (IABP), the most widely used temporary cardiac assist device, whose beneficial action is based on the principle of counterpulsation. The investigation is carried out in vitro in increasingly more realistic setups, including a mock circulatory system with physiological distribution of peripheral resistance and compliance in which IABP counterpulsation was simulated. Pressure and flow measurements show the effect of variables such as intra-luminal pressure, angle and aortic compliance on balloon hemodynamics. These data are complemented by results on the duration of balloon inflation and deflation obtained by means of high-speed camera visualisation. Furthermore, wave intensity analysis is carried out and it is identified as a possible alternative method for the assessment of IABP performance. This work includes two prototypes of intra-aortic balloons of novel shape with the balloon chamber tapering both from and toward the balloon tip. In clinical terms, with reference to the semi-recumbent position in which patients assisted with the IABP are nursed in the intensive care unit, the results presented in this thesis indicate that operating the balloon at an angle compromises the benefit of counterpulsation when assessed in vitro.

Le choc cardiogénique est une pathologie grave pouvant mettre rapidement le pronostic vital du patient en jeu. Malgré de nombreux progrès réalisés dans sa prise en charge, la mortalité liée à cette affection reste très élevée. Une des avancées importantes dans le traitement du choc cardiogénique développée ces dernières années est l’ECMO. Mais force est de constater, que malgré la restauration d’un flux circulatoire adéquat, nous restons confrontés à une mortalité élevée chez ces malades. La première partie de cette thèse est un rappel des principaux concepts du choc cardiogénique de l’ECMO ainsi qu’un rappel des effets de l’hypothermie. Nous rapportons dans la deuxième partie notre recherche expérimentale chez le cochon qui a permis de mettre en évidence un effet bénéfique de l’hypothermie sur la fonction cardiaque et sur la réactivité vasculaire chez les animaux en choc cardiogénique traités par une ECMO. Dans la troisième partie, nous discutons et analysons nos résultats en essayant d’apporter des explications physiologiques / Cardiogenic shock is still considered as a severe medical condition. Despite much progress in the treatment of the cardiogenic shock, this disease is still associated with a high mortality. An important advance in the treatment of the cardiogenic shock is the use of ECMO. However, despite the restoration of a proper circulatory flow, we are still facing significant mortality in these patients. The first part of this manuscript is a reminder of the main concepts of the cardiogenic shock and ECMO and the concept of hypothermia. In the second part, we report the results of our experimental research who highlighted a beneficial effect of hypothermia in cardiac function and vascular reactivity in animals in cardiogenic shock treated by ECMO. In the third part we discuss our results and we try to rapport physiological explications of our results

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Each year all over the world, Millions of patients from infants to adults are diagnosed with heart failure. A limited number of donor hearts available for these patients results in a tremendous demand of mechanical circulatory support (MCS) system, either in the form of total artificial heart (TAH) or a ventricular assist device (VAD). Physiologically MCS are expected to provide heart; a time to rest and potential recovery by unloading the ventricle, while maintaining the adequate peripheral as well as coronary circulation. Existing ventricular assist devices (VAD) have employed either displacement type pulsatile flow pumping systems or continuous flow type centrifugal/rotodynamic pumps systems. Displacement type devices produce a pulsatile outflow, which has significant benefits on vital organ function and end organ recovery. Continuous flow devices are small and can be placed within body using minimal invasive procedures, in addition they reduces infection as well as mechanical failure related complications. Despite availability of success stories for both types of pumping systems, the selection of the either of them is an ongoing debate. This thesis aims to merge the advantages of displacement pumps (pulsatile flow) and axial-flow pumps (continuous flow) into a novel left vertical assist device (LVAD), by designing a novel minimal invasive, miniature axial-flow pump producing pulsating outflow for the patients having early heart failure and myocardial infarction as a Bridge-To-Recovery (BTR) or Bridge-To-Decision (BTD) device. The design of VAD, the experimental setup and dedicated control system were developed for the in vitro evaluation of pulsatile flow. Computational fluid dynamics (CFD) had been employed for the detail investigation of pulsatile flow. In addition, CFD was also applied to optimize the pulse generation for low haemolysis levels. Outcome of the study produces comprehensive understanding for the generation of pulsatile flow using an axial flow pump. Further, it provides the means of generating a controlled pulse that can regulate flow rate for varying heart rate within low haemolysis levels.