In-virtro test of a stentless pericondial attached commissures (SPAC) valve

• Main Author: Ko, Zi Kai.
• Other Authors: Yeo Joon Hock
• Format: Final Year Project
• Language: English
• Published: 2010
• Subjects: DRNTU::Engineering::Mechanical engineering::Bio-mechatronics; DRNTU::Engineering::Mechanical engineering::Surgical assistive technology
• Online Access: http://hdl.handle.net/10356/40481
• Institution: Nanyang Technological University

Occurrences of aortic valve disease is increasing worldwide, concomitant with the ageing of the general population and the habitual consumption of diets high in calories and cholesterol. Aortic valve replacement surgery is the most efficient solution to aortic valve diseases. The clinical results show that stentless biological prostheses provide a better haemodynamic performance and fewer complications compared with their mechanical counterparts. Advancements in aortic valve replacements saw the materialization of the truly-stentless aortic bioprosthetic valves with full pericardial constructs and the Single Point Attached Commissure implantation (SPAC) technique. The SPAC technique involves suturing the base of the valve to the aortic annulus in a circular line and the commissures attached to the aortic wall at the level of sinotubular junction at three single points, which greatly simplifies the implantation procedure. The geometric profile of the valve leaflets is crucial in the performance of bioprosthetic valves. For the pericardial SPAC valves, two leaflet geometric designs are currently available: one with a simple flat tubular geometry and the other with a complex three-dimensional molded profile resembling the natural valve. Our overall objective is to compare the hemodynamic performance of the two leaflet designs, the tubular versus the molded, in both symmetric and asymmetric implantation conditions. The scope of this in-vitro experimental study is mainly to investigate the flow dynamics of the molded pericardial SPAC valve using Particle Image Velocimetry (PIV). This study is the first attempt to use PIV to measure detailed flow patterns of bioprosthetic (tissue) aortic valves in unsteady conditions An experimental rig was established for the purpose of simulating the function of the left heart and the circulatory system. The physical model included a molded tissue aortic valve made from porcine pericardium which was sutured to a silicone aortic root using the SPAC technique. Pressure transducers were placed proximal and distal to the aortic valve to monitor and record the left ventricular and the aortic pressure waveforms. The mean flow rate was measured by an electromagnetic flow meter and was kept at 4.5 L/min. The PIV system was focused on the test section to visualize and capture the detailed flow patterns immediately downstream of the aortic valve. We have successfully established an in-vitro mock circulatory system that simulates the left heart and that can produce physiological pressure waveforms and flow rates across the aortic valve. The novel design of the test section allows PIV measurement with good optical access and image resolution. The flow patterns around the SPAC valve at different time points of the cardiac cycle, such as the streamlined forward central flow in the aorta during systole, the characteristic vertical flow in the aortic sinuses, and the reversed aortic flow during diastole, are well-captured by the PIV. This experiment has demonstrated that PIV flow measurement of bioprosthetic aortic valves in unsteady conditions is feasible and the results obtained are meaningful.