Two-Component Laser Velocimeter Measurements Downstream of Heart Valve Prostheses in Pulsatile Flow

1986 ◽  
Vol 108 (1) ◽  
pp. 59-64 ◽  
Author(s):  
W. G. Tiederman ◽  
M. J. Steinle ◽  
W. M. Phillips
Keyword(s):  
Shear Stress ◽  
Pulsatile Flow ◽  
Turbulent Shear ◽  
Prosthetic Heart Valves ◽  
Shear Stresses ◽  
Axial Distance ◽  
Prosthetic Valves ◽  
Disk Valve ◽  
Two Component ◽  
Stress Levels

Elevated turbulent shear stresses resulting from disturbed blood flow through prosthetic heart valves can cause damage to red blood cells and platelets. The purpose of this study was to measure the turbulent shear stresses occurring downstream of aortic prosthetic valves during in-vitro pulsatile flow. By matching the indices of refraction of the blood analog fluid and model aorta, correlated, simultaneous two-component laser velocimeter measurements of the axial and radial velocity components were made immediately downstream of two aortic prosthetic valves. Velocity data were ensemble averaged over 200 or more cycles for a 15-ms window opened at peak systolic flow. The systolic duration for cardiac flows of 8.4 L/min was 200 ms. Ensemble-averaged total shear stress levels of 2820 dynes/cm2 and 2070 dynes/cm2 were found downstream of a trileaflet valve and a tilting disk valve, respectively. These shear stress levels decreased with axial distance downstream much faster for the tilting disk valve than for the trileaflet valve.

Influence of Cardiac Flow Rate on Turbulent Shear Stress from a Prosthetic Heart Valve

1988 ◽  
Vol 110 (2) ◽  
pp. 123-128 ◽  
Author(s):  
A. C. Schwarz ◽  
W. G. Tiederman ◽  
W. M. Phillips
Keyword(s):  
Shear Stress ◽  
Flow Rate ◽  
Time Window ◽  
Prosthetic Heart Valve ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Straight Tube ◽  
Blood Constituents ◽  
Turbulent Shear Stress ◽  
Disk Valve

Elevated turbulent shear stresses associated with sufficient exposure times are potentially damaging to blood constituents. Since these conditions can be induced by mechanical heart valves, the objectives of this study were to locate the maximum turbulent shear stress in both space and time and to determine how the maximum turbulent shear stress depends on the cardiac flow rate in a pulsatile flow downstream of a tilting disk valve. Two-component, simultaneous, correlated laser velocimeter measurements were recorded at four different axial locations and three different flow rates in a straight tube model of the aorta. All velocity data were ensemble averaged within a 15 ms time window located at approximately peak systolic flow over more than 300 cycles. Shear stresses as high as 992 dynes/cm2 were found 0.92 tube diameters downstream of the monostrut, disk valve. The maximum turbulent shear stress was found to scale with flow rate to the 0.72 power. A repeatable starting vortex was shed from the disk at the beginning of each cycle.

Effect of Tilting Disk, Heart Valve Orientation on Flow Through a Curved Aortic Model

1989 ◽  
Vol 111 (3) ◽  
pp. 228-232 ◽  
Author(s):  
J. D. Walker ◽  
W. G. Tiederman ◽  
W. M. Phillips
Keyword(s):  
Shear Stress ◽  
Laser Doppler Velocimeter ◽  
Turbulent Shear ◽  
Human Aorta ◽  
Radius Of Curvature ◽  
Turbulent Shear Stress ◽  
Disk Valve ◽  
Stress Levels ◽  
Flow Through ◽  
Peak Value

The influence of tilting disk valve orientation on pulsatile flow through a curved tube model of the human aorta was studied. Simultaneous, two-component laser Doppler velocimeter measurements were made in a tube having a 22 mm diameter and 41 mm radius of curvature which simulated the average dimensions of the adult aorta. The blood analog fluid had a viscosity of 3.0 cp and matched the refractive index of the glass model aorta. Results at mid-arch showed low turbulence levels in early systole and no influence of valve orientation. During mid-systole, fluid from the ventricle reached mid-arch exhibiting strong influence of valve orientation and increased turbulence levels. With the major orifice of the valve adjacent to the inner curved wall, the peak turbulent shear stress was 307 dynes/cm2 at mid-arch during mid-systole. When the major orifice was rotated 180 degrees, the peak value was reduced to 91 dynes/cm2 at the same location and time. At the exit of the curved section, the flow was independent of the valve orientation and the turbulent shear stress levels were an order of magnitude lower than the peak value at the inlet. This study demonstrated that orienting the major orifice of a tilting disk valve adjacent to the outer curved wall minimized turbulent shear stress levels.

Estimation of turbulent shear stresses in pulsatile flow immediately downstream of two artificial aortic valves in vitro

1990 ◽  
Vol 23 (12) ◽  
pp. 1231-1238 ◽  
Author(s):  
H Nygaard ◽  
M Giersiepen ◽  
J.M Hasenkam ◽  
D Westphal ◽  
P.K Paulsen ◽  
...  
Keyword(s):  
Pulsatile Flow ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Aortic Valves

Influence of turbulent shear stresses on the numerical blood damage prediction in a ventricular assist device

2019 ◽  
Vol 42 (12) ◽  
pp. 735-747 ◽  
Author(s):  
Benjamin Torner ◽  
Lucas Konnigk ◽  
Frank-Hendrik Wurm
Keyword(s):  
Shear Stress ◽  
Equivalent Stress ◽  
Volumetric Analysis ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Ventricular Assist ◽  
Damage Prediction ◽  
Blood Damage ◽  
Damage Models ◽  
Order Of Magnitude

The blood damage prediction in rotary blood pumps is an important procedure to evaluate the hemocompatibility of such systems. Blood damage is caused by shear stresses to the blood cells and their exposure times. The total impact of an equivalent shear stress can only be taken into account when turbulent stresses are included in the blood damage prediction. The aim of this article was to analyze the influence of the turbulent stresses on the damage prediction in a rotary blood pump’s flow. Therefore, the flow in a research blood pump was computed using large eddy simulations. A highly turbulence-resolving setup was used in order to directly resolve most of the computed stresses. The simulations were performed at the design point and an operation point with lower flow rate. Blood damage was predicted using three damage models (volumetric analysis of exceeded stress thresholds, hemolysis transport equation, and hemolysis approximation via volume integral) and two shear stress definitions (with and without turbulent stresses). For both simulations, turbulent stresses are the dominant stresses away from the walls. Here, they act in a range between 9 and 50 Pa. Nonetheless, the mean stresses in the proximity of the walls reach levels, which are one order of magnitude higher. Due to this, the turbulent stresses have a small impact on the results of the hemolysis prediction. Yet, turbulent stresses should be included in the damage prediction, since they belong to the total equivalent stress definition and could impact the damage on proteins or platelets.

An Analysis of Turbulent Shear Stresses in Leakage Flow Through a Bileaflet Mechanical Prostheses

2002 ◽  
Vol 124 (2) ◽  
pp. 155-165 ◽  
Author(s):  
Brandon R. Travis ◽  
Hwa L. Leo ◽  
Parina A. Shah ◽  
David H. Frakes ◽  
Ajit P. Yoganathan
Keyword(s):  
Pulsatile Flow ◽  
Laser Doppler Velocimetry ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Leakage Flow ◽  
Cyclic Variation ◽  
Doppler Velocimetry ◽  
Reynolds Stresses ◽  
Mechanical Prostheses ◽  
Flow Through

In this work, estimates of turbulence were made from pulsatile flow laser Doppler velocimetry measurements using traditional phase averaging and averaging after the removal of cyclic variation. These estimates were compared with estimates obtained from steady leakage flow LDV measurements and an analytical method. The results of these studies indicate that leakage jets which are free and planar in shape may be more unstable than other leakage jets, and that cyclic variation does not cause a gross overestimation of the Reynolds stresses at large distances from the leakage jet orifice.

Laser Anemometry Measurements of Steady Flow Past Aortic Valve Prostheses

1993 ◽  
Vol 115 (3) ◽  
pp. 290-298 ◽  
Author(s):  
Y. T. Chew ◽  
H. T. Low ◽  
C. N. Lee ◽  
S. S. Kwa
Keyword(s):  
Steady Flow ◽  
Heart Valves ◽  
Flow Region ◽  
Ball Valve ◽  
Prosthetic Heart Valves ◽  
Shear Stresses ◽  
Normal Stresses ◽  
Reversed Flow ◽  
Disk Valve ◽  
Wall Shear

An experimental investigation was conducted in steady flow to examine the fluid dynamics performance of three prosthetic heart valves of 27 mm diameter: Starr-Edwards caged ball valve, Bjork-Shiley convexo-concave tilting disk valve, and St. Vincent tilting disk valve. It was found that the pressure loss across the St. Vincent valve is the least and is, in general, about 70 percent of that of the Starr-Edwards valve. The pressure recovery is completed about 4 diameters downstream. The velocity profiles for the ball valve reveal a large single reversed flow region behind the occluder while those for the tilting disks valves reveal two reversed flow regions immediately behind the occluders. Small regions of stasis are also found near the wall in the minor opening of Bjork-Shiley valve and in the major opening of St. Vincent valve. The maximum wall shear stresses of the three valves at a flow rate of 30 l/min are in the range 30–50 dyn/cm2 which can cause hemolysis of attached red blood cells. The corresponding maximum Reynolds normal stresses are in the range of 1600–3100 dyn/cm2. The Reynolds normal stresses decay quickly and return approximately to the upstream undisturbed level at about 4 diameters downstream while the wall shear stresses decay at a slower rate. The maximum Reynolds normal stresses occur at about 1 diameter downstream while the maximum wall shear stress is at about 2 diameters downstream. In general, the St. Vincent valve has better performance. A method to compensate for refractive index variations and curvature effect of the sinus region of the aorta root using laser doppler anemometer measurements is also proposed.

Investigation of the Effects of Dynamic Change in Curvature and Torsion on Pulsatile Flow in a Helical Tube

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
N. K. C. Selvarasu ◽  
Danesh K. Tafti
Keyword(s):  
Shear Stress ◽  
Coronary Artery ◽  
Wall Shear Stress ◽  
Secondary Flow ◽  
Pulsatile Flow ◽  
Flow Patterns ◽  
Shear Stresses ◽  
Wall Shear ◽  
Vorticity Flux ◽  
Curvature And Torsion

Cardiovascular diseases are the number one cause of death in the world, making the understanding of hemodynamics and the development of treatment options imperative. The effect of motion of the coronary artery due to the motion of the myocardium is not extensively studied. In this work, we focus our investigation on the localized hemodynamic effects of dynamic changes in curvature and torsion. It is our objective to understand and reveal the mechanism by which changes in curvature and torsion contribute towards the observed wall shear stress distribution. Such adverse hemodynamic conditions could have an effect on circumferential intimal thickening. Three-dimensional spatiotemporally resolved computational fluid dynamics (CFD) simulations of pulsatile flow with moving wall boundaries were carried out for a simplified coronary artery with physiologically relevant flow parameters. A model with stationary walls is used as the baseline control case. In order to study the effect of curvature and torsion variation on local hemodynamics, this baseline model is compared to models where the curvature, torsion, and both curvature and torsion change. The simulations provided detailed information regarding the secondary flow dynamics. The results suggest that changes in curvature and torsion cause critical changes in local hemodynamics, namely, altering the local pressure and velocity gradients and secondary flow patterns. The wall shear stress (WSS) varies by a maximum of 22% when the curvature changes, by 3% when the torsion changes, and by 26% when both the curvature and torsion change. The oscillatory shear stress (OSI) varies by a maximum of 24% when the curvature changes, by 4% when the torsion changes, and by 28% when both the curvature and torsion change. We demonstrate that these changes are attributed to the physical mechanism associating the secondary flow patterns to the production of vorticity (vorticity flux) due to the wall movement. The secondary flow patterns and augmented vorticity flux affect the wall shear stresses. As a result, this work reveals how changes in curvature and torsion act to modify the near wall hemodynamics of arteries.

Effects of Pulsatile Flow on Cultured Vascular Endothelial Cell Morphology

1991 ◽  
Vol 113 (2) ◽  
pp. 123-131 ◽  
Author(s):  
G. Helmlinger ◽  
R. V. Geiger ◽  
S. Schreck ◽  
R. M. Nerem
Keyword(s):  
Shear Stress ◽  
Endothelial Cell ◽  
Pulsatile Flow ◽  
Cell Shape ◽  
Vascular Endothelial Cell ◽  
Shear Stresses ◽  
Type I ◽  
Vascular Endothelial ◽  
Type Ii

Endothelial cells (EC) appear to adapt their morphology and function to the in vivo hemodynamic environment in which they reside. In vitro experiments indicate that similar alterations occur for cultured EC exposed to a laminar steady-state flow-induced shear stress. However, in vivo EC are exposed to a pulsatile flow environment; thus, in this investigation, the influence of pulsatile flow on cell shape and orientation and on actin microfilament localization in confluent bovine aortic endothelial cell (BAEC) monolayers was studied using a 1-Hz nonreversing sinusoidal shear stress of 40 ± 20 dynes/cm2 (type I), 1-Hz reversing sinusoidal shear stresses of 20 ± 40 and 10 ± 15 dynes/cm2 (type II), and 1-Hz oscillatory shear stresses of 0 ± 20 and 0 ± 40 dynes/cm2 (type III). The results show that in a type I nonreversing flow, cell shape changed less rapidly, but cells took on a more elongated shape than their steady flow controls long-term. For low-amplitude type II reversing flow, BAECs changed less rapidly in shape and were always less elongated than their steady controls; however, for high amplitude reversal, BAECs did not stay attached for more than 24 hours. For type III oscillatory flows, BAEC cell shape remained polygonal as in static culture and did not exhibit actin stress fibers, such as occurred in all other flows. These results demonstrate that EC can discriminate between different types of pulsatile flow environments. Furthermore, these experiments indicate the importance of engineering the cell culture environment so as to include pulsatile flow in investigations of vascular endothelial cell biology, whether these studies are designed to study vascular biology and the role of the endothelial cell in disease processes, or are ones leading to the development of hybrid, endothelial cell-preseeded vascular grafts.

scholarly journals Analysis of leaflet flutter in biological prosthetic heart valves using PIV measurements

2019 ◽  
Vol 42 ◽  
pp. e41746
Author(s):  
Artur Henrique de Freitas Avelar ◽  
Mairon Assis Guimaris Eller Stófel ◽  
Glenda Dias Vieira ◽  
Jean Andrade Canestri ◽  
Rudolf Huebner
Keyword(s):  
High Speed ◽  
Heart Valves ◽  
Particle Image ◽  
Prosthetic Heart Valves ◽  
Shear Stresses ◽  
Lower Velocity ◽  
Piv Measurements ◽  
Prosthetic Valves ◽  
Image Velocimetry ◽  
Experimental Bench

The use of biological prosthetic valves has increased considerably in recent decades since they have several advantages over mechanical ones, but they still possess the great disadvantage of having a relatively short lifetime. An understudied phenomenon is the flutter effect that causes oscillations in the cusps, which is associated with regurgitation, calcification and fatigue, which can reduce even more the lifetime of bioproteses. In an experimental bench that simulates the cardiac flow, the behavior of a porcine and a bovine pericardium valves was recorded by a high-speed camera to quantify the oscillations of the cusps and an experiment using particle image velocimetry was conducted to study the velocity profiles and shear stresses and their relations with flutter. Results showed that the pericardial valve has lower values of frequencies and amplitudes compared to the porcine valve. Lower velocity values were found in the cusps that did not have flutter, but no relationship was observed between shear stress values and leaflet vibrations. These results may assist in future projects of biological prosthetic valves that have less flutter and longer lifespan.

Design, Modeling, and Experimental Characterization of A Valveless Pulsatile Flow Mechanical Circulatory Support Device

2021 ◽  
Vol 15 (2) ◽  
Author(s):  
Mengtang Li ◽  
Ye Chen ◽  
Marvin J. Slepian ◽  
Joseph Howard ◽  
Seth Thomas ◽  
...  
Keyword(s):  
Shear Stress ◽  
Flow Rate ◽  
Pulsatile Flow ◽  
Mechanical Circulatory Support ◽  
Blood Flow Rate ◽  
Experimental Tests ◽  
Ventricular Assist Devices ◽  
Circulatory Support ◽  
Bleeding Events ◽  
Prosthetic Valves

Abstract Mechanical circulatory support (MCS) devices, i.e., ventricular assist devices (VADs) and total artificial hearts (TAHs), while effective and vital in restoring hemodynamics in patients with circulatory compromise in advanced heart failure, remain limited by significant adverse thrombotic, embolic and bleeding events. Many of these complications relate to chronic exposure, via these devices, to nonpulsatile flow and the high shear stress created by current methods of blood propulsion or use of prosthetic valves. Here we propose a novel noncompressing single sliding vane MCS device to: 1) dramatically reduce pump operating speed thus potentially lowering the shear stress imparted to blood; 2) eliminate utilization of prosthetic valves thus diminishing potential shear stress generations; 3) allow direct flow rate control to generate physically desired blood flow rate include pulsatile flow; and 4) achieve compactness to fit into the majority of patients. The fundamental working principle and governing design equations are introduced first with multiple design and performance objectives presented. A first prototype was fabricated and experimental tests were conducted to validate the model with a 93.10% match between theoretical and experimental flow rate results. After model validation, the proposed MCS was tested to illustrate the ability of pulsatile flow generation. Finally, it was compared with some representative MCS pumps to discuss its potential of improving current MCS design. The presented work offers a novel MCS design and paves the way for next steps in device hemocompatibility testing.

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