“design and Construction of a New Pulse Duplicator System for in Vitro Evaluation of Prosthetic Heart Valves – Conception of an Experimental Setup on Mitral Position”

Since most complications related to operation of prosthetic heart valves are due to disturbances of flow, its hydrodynamic characterization is a useful aid in the design of new prostheses. Besides durability and biological response to implant, these prostheses should provide a favorable hemodynamic profile, considering that there is a great clinical interest focused on the haemolysis of blood. Haemolysis in heart valves can be induced primarily by cavitation in the closure of the prosthesis and by shear stress in the flow. Velocity and shear stress profiles as well as fluid stagnation and separation regions are different for each type of valve. In addition, damage of the blood cells could be expected in some flow conditions. Simulations of pulsatile flow in cardiac prosthesis began nearly 40 years ago, through the development of diferent mock human circulatory systems (simulating of the left ventricule), improving the interpretation of the clinical results. Brazil is one of the worldwide leaders of heart valves production, where about 8-10 thousand patients per year receive both biological and mechanical cardiac valve prostheses. A new design of a pulse duplicator system was developed at the Polytechnic School of the University of S€o Paulo (EPUSP), in the Mechanical Engineering Department (PME), to study prosthetic heart valves, based on the experience get with the mock circulatory system used in the Department of Bioengineering, Institute Dante Pazzanese of Cardiology (IDPC). This article describes the design and the partial construction of a new pulse duplicator system for heart valves simulations based on state-of-art studies. In this proposed design of a pulse duplicator system, an electric servo-motor controlled by computer emits, through a hydraulic piston, a pulse to the left ventricular chamber model, which is connected to two interchangeable heart valves accommodation, where aortic and mitral valves could be installed. The computer is also used for data acquisition and processing of the physical parameters like pressure, volumetric flow and temperature. Some results of flow, cardiac frequencies and pressures are evaluated according to physiologic ventricular states. To characterize, in the future, the hydrodynamic operation of mitral prosthetic valves (focus of this study), an experimental setup was mounted to provide measurements of volumetric flow, pressure and velociy fields on this valves. Therefore, a suitable working fluid, an eletromagnetic flow meter, pressure transducers, a temperature control system and a Laser Doppler Anemometer (LDA) are predicted on the pulse duplicator system designed. Optical access are conveniently provided on the design, making possible the use, in the future, of a LDA system. In order to improve the analysis of hydrodynamic shear stress and prediction of haemolysis, the experimental results may be used to calibrate a numerical model using ‘Computational Fluid Dynamics’ (CFD).