Jeffrey T. Ellis

A comparison of the hinge and near-hinge flow fields of the St Jude medical hemodynamic plus and regent bileaflet mechanical heart valves

OBJECTIVE The most widely implanted prosthetic valves are the mechanical bileaflets, most of which have good forward flow hemodynamics. However, recent clinical experiences illustrate the importance of understanding the flow structures generated within the hinge. The purpose of this study was to evaluate the hinge-flow dynamics of two new variations of a 17-mm St Jude Medical bileaflet valve: the Hemodynamic Plus and the Regent (St Jude Medical, Inc, St Paul, Minn). METHODS Clinical quality reproductions of the valves were manufactured with clear housings. Laser Doppler velocimetry velocity and turbulent shear stress measurements were conducted within the hinge and thumbnail regions of the valves. RESULTS In the 17-mm Hemodynamic Plus hinge, a rotating flow structure developed in the inflow pocket during forward flow. During systole, velocities through the hinge pocket reached 0.70 m/s, and the turbulent shear stress reached 1000 dynes/cm(2). In the thumbnail, forward flow velocities ranged from 1.4 m/s to 1.7 m/s. In the 17-mm Regent hinge, a rotating flow structure partially developed in the inflow pocket during forward flow. During systole, velocities through the hinge pocket reached 0.75 m/s, and the turbulent shear stress reached 1300 dynes/cm(2). In the thumbnail, forward flow velocities ranged from 1.0 m/s to 1.3 m/s. CONCLUSIONS The active leaflet motion through the St Jude Medical hinge creates a washout pattern that restricts the persistence of stagnation zones and thus may be a contributing factor to its successful clinical performance. The hinge and thumbnail flow dynamics of the 17-mm Regent valve are at least equivalent to, and possibly superior to, those of the 17-mm Hemodynamic Plus valve.

An In Vitro Study of the Hinge and Near-Field Forward Flow Dynamics of the St. Jude Medical® Regent™ Bileaflet Mechanical Heart Valve

AbstractThe most widely implanted prosthetic valve is the mechanical bileaflet. Recent clinical experiences suggest that some designs are more prone to thromboembolic episodes than others. This study evaluated the hinge flow and near-field forward flow of the new St. Jude Medical® Regent™ bileaflet mechanical heart valve. Laser Doppler velocimetry measurements were conducted within the hinge and near-field forward flow regions of the Regent™ valve. These pulsatile flow velocity measurements were animated in time to visualize the flow fields throughout the cardiac cycle. During forward flow, a recirculation region developed in the inflow pocket of the Regent™ hinge but was subsequently abolished by strong backflow during valve closure. Leakage velocities in the hinge region reached 0.72 m/s and Reynolds shear stresses reached 2,600 dyn/cm2. Velocities in the near-field region were highest in the lateral orifice jet, reaching 2.1 m/s. Small regions of separated flow were observed adjacent to the hinge region. Leaflet motion through the Regent™ hinge creates a washout pattern which restricts the persistence of stagnation zones in its hinge. Based upon the results of these studies, the hematological performance of the Regent™ series should be at least equivalent to the performance of the Standard series.

identification of Peak Stresses in Cardiac Prostheses : a Comparison of Two-dimensional versus three-dimensional Principal Stress Analyses

&NA; This study assessed the accuracy of using a two‐dimensional principal stress analysis compared to a three‐dimensional analysis in estimating peak turbulent stresses in complex three‐dimensional flows associated with cardiac prostheses. Three‐component, coincident laser Doppler anemometer measurements were obtained in steady flow downstream of three prosthetic valves: a St. Jude bileaflet, Bjork‐Shiley monostrut tilting disc, and Starr‐Edwards ball and cage. Two‐dimensional and three‐dimensional principal stress analyses were performed to identify local peak stresses. Valves with locally two‐dimensional flows exhibited a 10‐15% underestimation of the largest measured normal stresses compared to the three‐dimensional principal stresses. In nearly all flows, measured shear stresses underestimated peak principal shear stresses by 10‐100%. Differences between the two‐dimensional and three‐dimensional principal stress analysis were less than 10% in locally two‐dimensional flows. In three‐dimensional flows, the two‐dimensional principal stresses typically underestimated three‐dimensional values by nearly 20%. However, the agreement of the two‐dimensional principal stress with the three‐dimensional principal stresses was dependent upon the two velocity‐components used in the two‐dimensional analysis, and was observed to vary across the valve flow field because of flow structure variation. The use of a two‐dimensional principal stress analysis with two‐component velocity data obtained from measurements misaligned with the plane of maximum mean flow shear can underpredict maximum shear stresses by as much as 100%. ASAIO Journal 1996;42:154‐163.

An in vitro assessment by means of laser Doppler velocimetry of the medtronic advantage bileaflet mechanical heart valve hinge flow

OBJECTIVE The aim of this study was to evaluate the hinge flow field characteristics of the Medtronic Advantage bileaflet valve and compare them with the flow fields of the St Jude Medical standard valve. The present study provides laser Doppler velocimetry results for the Advantage and St Jude Medical valves to make a direct comparison of the flow fields of the 2 valve designs. This study aids in determining the preclinical efficacy of Medtronics new bileaflet valve hinge design. METHODS Two-dimensional laser Doppler velocimetry was used to measure the velocities in the hinge regions of size 29 Medtronic Advantage and St Jude Medical standard bileaflet valve designs. Exact dimensional models of the bileaflet valves, including the hinge regions, were cast from transparent plastic materials to conduct these measurements under simulated physiologic conditions. Laser Doppler velocimetry measurements were conducted under physiologic conditions, with the valves placed in the mitral position of a pulsatile flow loop. Measurements were taken at several elevation levels in the hinge region. Multiple measurement locations obtained in each plane provided a grid work by which the flow fields could be detailed. RESULTS Velocity measurements obtained for each valve design in the hinge recess were used to reconstruct the flow fields. For the Advantage valve, the peak velocities during leakage flow in the hinge at zero depth, one-third depth, and two-thirds depth levels into the hinge recess were 0.9, 1.6, and 1.8 m/s, respectively. Corresponding values for the St Jude Medical valve were 1.3, 1.6, and 2.1 m/s, respectively. From the reconstructed flow fields, the flow patterns seen within the 2 hinge designs exhibited similar features, with more dynamic flow patterns observed in the Advantage hinge during the forward flow phase. CONCLUSIONS The present study demonstrated that the hinge flow dynamics of the Advantage bileaflet design were similar to those of the St Jude Medical hinge design. The velocities within the hinge were slightly higher for the St Jude Medical valve but not significantly different. There appears to be more dynamic flow through the hinge of the Advantage valve during the forward flow phase.

An automated method for analysis and visualization of laser doppler velocimetry data

The analysis and visualization of large data sets collected by use of laser Doppler velocimetry has presented a challenge to researchers using this technique to investigate complex flow fields. This paper describes an automated procedure for analysis and animation of two- and three-dimensional laser Doppler velocimetry data. The procedure consists of a suite of FORTRAN programs for calculating phase window averages of velocity and the Reynolds stress tensor, calculating the principal normal stresses, maximum shear stresses, and preparation of data files for input into Plot-3D compatible data visualization software. An example application of these techniques to data collected from anin vitro investigation of the retrograde flow field associated with a bileaflet mechanical heart valve is also presented.

Leakage flow through mechanical prostheses: an initiator of platelet damage

The clinical histories of two bileaflet valves suggest that leakage flow could be an initiator of thromboembolic complications. To test this hypothesis, measurements of the flow field around bileaflet prostheses were combined with measurements of blood damage initiated by leakage flow through a prosthesis. The results of these studies show that leakage flow through bileaflet prostheses creates high Reynolds shear stresses and is responsible for platelet trauma.