Velocity and Shear Stress Distribution Downstream of Mechanical Heart Valves in Pulsatile Flow

1989 ◽  
Vol 12 (4) ◽  
pp. 261-269 ◽  
Author(s):  
M. Giersiepen ◽  
U. Krause ◽  
E. Knott ◽  
H. Reul ◽  
G. Rau
Keyword(s):  
Shear Stress ◽  
Heart Valves ◽  
Laser Doppler Anemometry ◽  
Fluid Dynamic ◽  
In Vitro Study ◽  
Turbulent Shear ◽  
Momentum Exchange ◽  
Jude Medical ◽  
Turbulent Shear Stress

Ten mechanical valves (TAD 27 mm): Starr-Edwards Silastic Ball, Björk-Shiley Standard, Björk-Shiley Concave-Convex, Björk-Shiley Monostrut, Hall-Kaster (Medtronic-Hall), OmniCarbon, Bicer Val, Sorin, Saint-Jude Medical and Hemex (Duromedics) are investigated in a comparative in vitro study. The velocity and turbulent shear stress profiles of the valves were determined by Laser Doppler anemometry in two different downstream axes within a model aortic root. Depending on the individual valve design, velocity peaks up to 1.5 m/s and turbulent shear stress peaks up to 150 N/m2 were measured during the systolic phase. These shear stress peaks mainly occurred in areas of flow separation and intense momentum exchange. Directly downstream of the valves (measuring axis 0.55.dAorta) turbulent shear stress peaks occurred at peak systole and during the deceleration phase, while in the second measuring axis (1.5.dAorta) turbulence levels were lower. Shear stress levels were high at the borders of the fluid jets. The results are discussed from a fluid-dynamic point of view.

Platelet Damage Accumulation and Recovery due to Hemodynamic Shear Stresses: An In Vitro Study

2008 ◽  
Author(s):  
Jawaad Sheriff ◽  
Jolyon Jesty ◽  
Danny Bluestein
Keyword(s):  
Shear Stress ◽  
Damage Accumulation ◽  
Heart Valves ◽  
In Vitro Study ◽  
Shear Stresses ◽  
Special Importance ◽  
Prosthetic Devices ◽  
Recovery Potential ◽  
Low Shear

It is well established that shear stress exposure activates platelets, and it has been shown that this flow-induced activation contributes significantly to thromboembolic complications in mechanical heart valves (MHVs) [1]. In addition, the platelet activation state (PAS) assay has been demonstrated to be an efficient technique to measure procoagulant activity [2]. However, there is a lack of reliable models to predict platelet damage accumulation. Such a tool allows thrombogenicity optimization of implanted prosthetic devices. Prior to developing this tool, certain aspects of platelet behavior in response to shear stress must be elucidated. Of special importance for developing accountable damage accumulation models is the recovery potential of platelets during repeated passages through devices, when not exposed to the elevated stresses characterizing blood flow in these devices. To accomplish this, PAS measurements were conducted in a Hemodynamic Shearing Device (HSD), where platelets were exposed to prescribed waveforms with alternating periods of high and low shear stresses.

An In Vitro Comparative Study of St. Jude Medical and Edwards-Duromedics Bileaflet Valves Using Laser Anemometry

1989 ◽  
Vol 111 (4) ◽  
pp. 298-302 ◽  
Author(s):  
R. Fatemi ◽  
K. B. Chandran
Keyword(s):  
Comparative Study ◽  
Laser Doppler Anemometry ◽  
Fluid Dynamic ◽  
Velocity Profiles ◽  
Flow Conditions ◽  
Tilt Axis ◽  
Jude Medical ◽  
Laser Anemometry ◽  
Bileaflet Valves

An in vitro comparative study of St. Jude (SJ) and Edwards-Duromedics (DM) Bileaflet valves was performed under steady and physiological pulsatile flow conditions in an axisymmetric chamber using Laser Doppler Anemometry (LDA). LDA measurements were conducted in two different orientations; in the first orientation, the LDA traverse was perpendicular and, in the second orientation, parallel to the tilt axis of the leaflets. The axial velocities were measured in both orientations at two different locations distal to the valves. The velocity profiles at peak systole show the presence of stronger vortex in the sinus region for flow past SJ valve in the first orientation compared to the DM valve. Velocity profile distal to the SJ valve in second orientation was relatively flat where as for the DM valve, a jet-like flow was present. The differences found in the velocity profiles between the two valves can be attributed to the differences in geometry with thicker leaflets, smaller angle of leaflets opening and the presence of the leaflet curvature for the DM valve. The results obtained in this study do not show any fluid dynamic advantages due to the curved leaflet geometry of the DM valve.

Impact of fluid turbulent shear stress on failure surface of reservoir bank landslide

2018 ◽  
Vol 11 (22) ◽  
Author(s):  
Xuan Zhang ◽  
Liang Chen ◽  
Faming Zhang ◽  
Chengteng Lv ◽  
Yi feng Zhou
Keyword(s):  
Shear Stress ◽  
Failure Surface ◽  
Turbulent Shear ◽  
Turbulent Shear Stress

Physiological fluid shear stress causes downregulation of endothelin-1 mRNA in bovine aortic endothelium

1992 ◽  
Vol 263 (2) ◽  
pp. C389-C396 ◽  
Author(s):  
A. Malek ◽  
S. Izumo
Keyword(s):  
Shear Stress ◽  
Fluid Shear Stress ◽  
Fluid Velocity ◽  
Low Frequency ◽  
Turbulent Shear ◽  
Specific Response ◽  
Dependent Manner ◽  
Fluid Shear ◽  
Endothelin 1

We report here that the level of endothelin-1 (ET-1) mRNA from bovine aortic endothelial cells grown in vitro is rapidly (within 1 h of exposure) and significantly (fivefold) decreased in response to fluid shear stress of physiological magnitude. The downregulation of ET-1 mRNA occurs in a dose-dependent manner that exhibits saturation above 15 dyn/cm2. The decrease is complete prior to detectable changes in endothelial cell shape and is maintained throughout and following alignment in the direction of blood flow. Peptide levels of ET-1 secreted into the media are also reduced in response to fluid shear stress. Cyclical stretch experiments demonstrated no changes in ET-1 mRNA, while increasing media viscosity with dextran showed that the downregulation is a specific response to shear stress and not to fluid velocity. Although both pulsatile and turbulent shear stress of equal time-average magnitude elicited the same decrease in ET-1 mRNA as steady laminar shear (15 dyn/cm2), low-frequency reversing shear stress did not result in any change. These results show that the magnitude as well as the dynamic character of fluid shear stress can modulate expression of ET-1 in vascular endothelium.

Contribution towards a Reynolds-stress closure for low-Reynolds-number turbulence

1976 ◽  
Vol 74 (4) ◽  
pp. 593-610 ◽  
Author(s):  
K. Hanjalić ◽  
B. E. Launder
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Reynolds Stress ◽  
Dissipation Rate ◽  
Numerical Solutions ◽  
Low Reynolds Number ◽  
Transport Processes ◽  
Turbulent Shear ◽  
Turbulent Shear Stress ◽  
Low Reynolds

The problem of closing the Reynolds-stress and dissipation-rate equations at low Reynolds numbers is considered, specific forms being suggested for the direct effects of viscosity on the various transport processes. By noting that the correlation coefficient$\overline{uv^2}/\overline{u^2}\overline{v^2} $is nearly constant over a considerable portion of the low-Reynolds-number region adjacent to a wall the closure is simplified to one requiring the solution of approximated transport equations for only the turbulent shear stress, the turbulent kinetic energy and the energy dissipation rate. Numerical solutions are presented for turbulent channel flow and sink flows at low Reynolds number as well as a case of a severely accelerated boundary layer in which the turbulent shear stress becomes negligible compared with the viscous stresses. Agreement with experiment is generally encouraging.

Conditional Sampling in a Transitional Boundary Layer Under High Freestream Turbulence Conditions

2003 ◽  
Vol 125 (1) ◽  
pp. 28-37 ◽  
Author(s):  
Ralph J. Volino ◽  
Michael P. Schultz ◽  
Christopher M. Pratt
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Streamwise Velocity ◽  
Turbulent Shear ◽  
Conditional Sampling ◽  
Freestream Turbulence ◽  
Mean Velocity ◽  
Transitional Boundary Layer ◽  
Turbulent Shear Stress ◽  
Order Of Magnitude

Conditional sampling has been performed on data from a transitional boundary layer subject to high (initially 9%) freestream turbulence and strong (K=ν/U∞2dU∞/dx as high as 9×10−6) acceleration. Methods for separating the turbulent and nonturbulent zone data based on the instantaneous streamwise velocity and the turbulent shear stress were tested and found to agree. Mean velocity profiles were clearly different in the turbulent and nonturbulent zones, and skin friction coefficients were as much as 70% higher in the turbulent zone. The streamwise fluctuating velocity, in contrast, was only about 10% higher in the turbulent zone. Turbulent shear stress differed by an order of magnitude, and eddy viscosity was three to four times higher in the turbulent zone. Eddy transport in the nonturbulent zone was still significant, however, and the nonturbulent zone did not behave like a laminar boundary layer. Within each of the two zones there was considerable self-similarity from the beginning to the end of transition. This may prove useful for future modeling efforts.

Coronary stents cause high velocity fluctuation with a flow acceleration and flow reduction in jailed branches: An in vitro study using laser-Doppler anemometry

Biorheology ◽  
2012 ◽  
Vol 49 (5-6) ◽  
pp. 329-340 ◽  
Author(s):  
Jakob Dörler ◽  
Matthias Frick ◽  
Monika Hilber ◽  
Harald Breitfuss ◽  
Mohammed N. Abdel-Hadi ◽  
...  
Keyword(s):  
High Velocity ◽  
Velocity Fluctuation ◽  
Laser Doppler Anemometry ◽  
In Vitro Study ◽  
Coronary Stents ◽  
Laser Doppler ◽  
Vitro Study ◽  
Flow Acceleration ◽  
Flow Reduction
Sign in / Sign up

Export Citation Format

Share Document