Spatio-temporal Flow Analysis in Bileaflet Heart Valve Hinge Regions: Potential Analysis for Blood Element Damage |
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Authors: | Hélène A Simon Lakshmi P Dasi Hwa-Liang Leo Ajit P Yoganathan |
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Institution: | (1) School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA;(2) Wallace H. Coulter School of Biomedical Engineering, Georgia Institute of Technology & Emory University, Atlanta, GA 30332-0535, USA;(3) Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA |
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Abstract: | Point-wise velocity measurements have been traditionally acquired to estimate blood damage potential induced by prosthetic
heart valves with emphasis on peak values of velocity magnitude and Reynolds stresses. However, the inherently Lagrangian
nature of platelet activation and hemolysis makes such measurements of limited predictive value. This study provides a refined
fluid mechanical analysis, including blood element paths and stress exposure times, of the hinge flows of a CarboMedics bileaflet
mechanical heart valve placed under both mitral and aortic conditions and a St Jude Medical bileaflet valve placed under aortic
conditions. The hinge area was partitioned into characteristic regions based on dominant flow structures and spatio-temporal
averaging was performed on the measured velocities and Reynolds shear stresses to estimate the average bulk stresses acting
on blood elements transiting through the hinge. A first-order estimate of viscous stress levels and exposure times were computed.
Both forward and leakage flow phases were characterized in each partition by dynamic flows dependent on subtle leaflet movements
and transvalvular pressure fluctuations. Blood elements trapped in recirculation regions may experience exposure times as
long as the entire forward flow phase duration. Most calculated stresses were below the accepted blood damage threshold. Estimates
of the stress levels indicate that the flow conditions within the boundary layers near the hinge and leaflet walls may be
more detrimental to blood cells than bulk flow conditions, while recirculation regions may promote thrombus buildup. |
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Keywords: | Pivot Mitral Aortic Platelet activation Hemolysis Viscous stress Reynolds shear stress Laser Doppler Velocimetry |
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