Méthodologie de conception d'activateurs pour ventricule d'assistance cardiaque implantable
The electronic miniaturization and the computer evolution (microprocessor, transputer) have contributed to the use of electric drives in a lot of applications. Because of its flexibility, the electric drive becomes an essential element to work out new concepts of artificial prosthesis. The progress of biomaterial technology, which gave birth to several artificial organs like permeable membrane (oxygenator), biodegradable material (vascular surgery), artificial arteries, etc., now permits to envisage the realization of totally implantable cardiac prosthesis. in order to relieve the failing cardiac muscle, the use of prosthesis, such as the artificial ventricle, permits the replacement of the cardiac function as a temporary or permanent basis. During a sustained clinical assistance, the failing heart is able, in some cases, to recover its normal cardiac function. The idea of a permanent ventricular assistance appears, in some cases, as a treatment of cardiomyopathies, which allows to avoid the cardiac transplantation. The research of new totally implantable ventricle concepts must be completed by a systematic study of all possible electromechanic solutions to realize the ventricle actuator, as well as guaranteeing a long term implantation without biocompatible problems. Thus, existing variants study has been made by major research groups in the world. The obtained results show the different advantages and disadvantages of each solution principle. This allows to avoid some concepts, which would not be compatible with the fixed goals. The new solutions research is realized in studying the two motor types, linear or relative, in designing each variant and finally in comparing the different characteristics of each solution. This analysis allows to conclude that the relative brushless DC motor is the only one which permits to attain the specifications. The rotative motor solution is the purpose of the fourth chapter, which presents each step of the different motor parameters choice and the design proper. Moreover, a numerical simulation allows to verify the hypothesis quality and to present the motor characteristics. As the ventricle biocompatibility is a very important point of the specifications, thermal aspects of the prosthesis is studied with care in the last chapter of this work. A study by the finite elements method is used to visualize ventricle isotherms, where the motor is the principal heat source and when the latter is implanted in the human body. Hot points on the housing are displayed and a solution to reduce them is presented. The obtained results correspond to specifications given in the existing ventricle comparison. The designed solution, compared to the other studied variants in chapter 2, presents better characteristics in term of mass, volume, efficiency and maximum housing temperature, which gives the possibilities of a long term ventricle implantation in the human body without harming the organism.