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Technical Briefs

Modifying a Tilting Disk Mechanical Heart Valve Design to Improve Closing Dynamics

[+] Author and Article Information
Luke H. Herbertson

Department of Bioengineering, The Pennsylvania State University, University Park, PA 16802lhh113@psu.edu

Steven Deutsch

Department of Bioengineering, The Pennsylvania State University, University Park, PA 16802sxd2@only.arl.psu.edu

Keefe B. Manning

Department of Bioengineering, The Pennsylvania State University, University Park, PA 16802kbm10@psu.edu

J Biomech Eng 130(5), 054503 (Sep 17, 2008) (4 pages) doi:10.1115/1.2978987 History: Received April 24, 2007; Revised May 21, 2008; Published September 17, 2008

The closing behavior of mechanical heart valves is dependent on the design of the valve and its housing, the valve composition, and the environment in which the valve is placed. One innovative approach for improving the closure dynamics of tilting disk valves is introduced here. We transformed a normal Delrin occluder into one containing a ”dynamic liquid core” to resist acceleration and reduce the moment of inertia, closing velocity, and impact forces of the valve during closure. The modified occluder was studied in the mitral position of a simulation chamber under the physiologic and elevated closing conditions of 2500mmHg/s and 4500mmHg/s, respectively. Cavitation energy, detected as high-frequency pressure transients with a hydrophone, was the measure used to compare the modified valve with its unaltered counterpart. The cavitation potential of tilting disk valves is indicative of the extent of blood damage occurring during valve closure. Initial findings suggest that changes to the structure or physical properties of well established mechanical valves, such as the one described here, can reduce closure induced hemolysis by minimizing cavitation. Compared with a normal valve, the cavitation intensity associated with our modified valve was reduced by more than 66% at the higher load. Furthermore, the modified valve took longer to completely close than did the standard tilting disk valve, indicating a dampened impact and rebound of the occluder with its housing.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 4

The normalized frequency spectrum for (a) the normal valve indicates a substantial amount of energy in the spectral range where cavitation is known to occur (>35 kHz) compared with (b) the modified valve

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Figure 3

The filtered acoustic energy (including cavitation and mechanical closure) is significantly greater for (a) a normal tilting disk DR MHV than for (b) the modified valve closure at a dP/dt of 4500 mm Hg/s. Valve impact is detected roughly 4 ms into the frame.

Grahic Jump Location
Figure 2

To create a disk with a partial liquid core, the DR leaflet was cut lengthwise into two pieces and a channel was milled into the distal side. Glycerin was added to the channel before the two sides were rejoined and polished. Photographs of a (a) normal and (b) modified tilting disk valve are displayed. The fluid core is highlighted.

Grahic Jump Location
Figure 1

The in vitro chamber has windows that allow for visualization of the mechanical heart valve positioned in the mitral position

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