High-resolution measurements of leakage flow through bileaflet mechanical heart valve hinges
Klusak, Ewa, Monika
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To restore proper function of the heart, diseased valves require repair or replacement. Mechanical heart valves are one of the treatments available. Despite their superior durability in comparison with biological prostheses, mechanical heart valves are associated with life-threatening complications, known to be induced by non-physiological fluid dynamics, generated by valve geometrical features. The aim of this study is to resolve the turbulent nature of the leakage flow through bileaflet mechanical heart valves, and resolve flow structures that may induce blood damage, to improve future valve designs. Therefore, the objective of this research is to obtain comprehensive knowledge of the fluid dynamics near and inside the hinge cavity of bileaflet mechanical heart to enhance understanding of its role in blood damage, for future design improvements. To study complexity of the flow dynamics at high-resolution, scaling of the key geometrical features of the valve was performed. Scaled-up hinge models were developed and tested in a large-scale heart valve flow simulator. The flow dynamics was investigated utilizing Particle Image Velocimetry technique, a laser-based, non-intrusive measurement method. It has been demonstrated that the leakage flow inside the hinge and downstream of the hinge of a bileaflet mechanical heart valves is highly unsteady. Inside the hinge, flow features indicating that flow perhaps separates from the surface of the hinge cavity has been identified. High velocity fluctuation inside and downstream of the hinge were observed. This features suggest that leakage flow is highly-three dimensional and turbulent, which align with findings from previous studies. This study quantified viscous shear stresses of the leakage flow inside and down- stream of bileaflet mechanical heart valve hinges. It has been demonstrated that shear stress inside and downstream of the hinge exceeds the threshold of platelet activation but it remains below that of haemolysis. Flow features such as stagnation, recirculation zones and perhaps flow separation inside the hinge, were observed. These findings indicate that leakage flow may induce damage to blood elements and be favorable for the formation of the thrombus inside and near hinge of bileaflet mechanical heart valves. In this work it was shown that measurement spatial and temporal resolution has a high impact on ability to resolve flow structures in leakage flow inside and downstream of the hinge cavity of a BMHV. Experiments at higher spatial in-plane and out-of-plane resolution revealed flow structures that have not been measured in experiment with clinical scale MHVs models. This work demonstrated that whole-field, high-spatial resolution measurement offered by PIV along with a novel scaled-up models allow gain better understanding of complex flows.
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