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J Thorac Cardiovasc Surg 2002;124:561-574
© 2002 The American Association for Thoracic Surgery

Surgery for Acquired Cardiovascular Disease (ACD)

Microflow fields in the hinge region of the CarboMedics bileaflet mechanical heart valve design

From the School of Mechanical Engineering^a and the Wallace H. Coulter School of Biomedical Engineering,^b Cardiovascular Fluid Mechanics Laboratory, Georgia Institute of Technology, Atlanta, Ga.

This study was funded by a research grant from St Jude Medical Inc, Minneapolis, Minn.

Received for publication Oct 19, 2001. Revisions requested Jan 4, 2002; revisions received Feb 26, 2002. Accepted for publication March 2, 2002. Address for reprints: Ajit P. Yoganathan, MD, Associate Chair, School of Biomedical Engineering, Georgia Institute of Technology, 315 Ferst Dr, IBB Building, Room 1121, Atlanta, GA 30332-0535 (E-mail: ajit.yoganathan{at}bme.gatech.edu).

Objective: The design of bileaflet mechanical heart valves includes some degree of leakage flow on valve closure for the reverse flow to wash the hinge and pivot region of the valve. It is believed that this reverse flow helps to prevent areas of stasis and inhibit microthrombus formation. However, the magnitude of this retrograde flow may also give rise to unacceptable levels of blood element damage and lead to platelet activation or hemolysis as a result of the increased flow velocities through the hinge region. The purpose of this study was to evaluate the hinge flow dynamics of a 23-mm CarboMedics bileaflet mechanical valve (Sulzer CarboMedics Inc, Austin, Tex) and then to compare the results with those of the St Jude Medical 23-mm Regent (St Jude Medical Inc, Minneapolis, Minn) and Medtronic Parallel (Medtronic, Inc, Minneapolis, Minn) valves studied earlier. This comparison allows new insight into the microflow fields within the hinge region of the CarboMedics bileaflet mechanical valve, which have not been previously assessed during its clinical history.
Methods: Two-dimensional laser Doppler velocimetry was used to measure the velocity and turbulent shear stress fields in the hinge regions. To conduct these measurements, exact dimensional models of the bileaflet hinge regions were cast or machined from transparent plastic materials. The experiment was conducted in a pulsatile flow loop with measurements taken at different levels within the pivot and hinge regions.
Results: In the 23-mm CarboMedics valve hinge, the phase-averaged forward velocity obtained at the flat level and levels of 190 µm and 390 µm above flat and 1 mm below flat were 0.54 m/s, 0.77 m/s, 0.3 m/s, and 1.0 m/s, respectively. Corresponding values of the peak phase-averaged leakage velocities were 3.17 m/s, 2.91 m/s, 2.52 m/s, and 0.5 m/s, respectively. Corresponding turbulent shear stresses were 5510 dyne/cm², 5640 dyne/cm², 4380 dyne/cm², and 4810 dyne/cm², respectively.
Conclusions: The hinge flow dynamics of the CarboMedics bileaflet design lie somewhere in between those of the St Jude Medical and the Medtronic Parallel valve designs. The fluid dynamics of the investigated valve were found to be similar to those of the St Jude Medical valves, although with slightly higher leakage velocities and turbulent shear stresses. This discrepancy may be a result of the sharper corners associated with the hinge design of the CarboMedics valve. It could also be due to the incremental enlargement of the internal orifice area of the St Jude Medical Regent design.

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