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

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Luke H. Herbertson ◽  
Steven Deutsch ◽  
Keefe B. Manning
Keyword(s):  
Heart Valves ◽  
Liquid Core ◽  
Mechanical Heart Valve ◽  
Blood Damage ◽  
Mechanical Valves ◽  
Mitral Position ◽  
Disk Valve ◽  
Cavitation Intensity ◽  
The Moment ◽  
The One

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 2500 mm Hg/s and 4500 mm Hg/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.

A Detailed Fluid Mechanics Study of Tilting Disk Mechanical Heart Valve Closure and the Implications to Blood Damage

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Keefe B. Manning ◽  
Luke H. Herbertson ◽  
Arnold A. Fontaine ◽  
Steven Deutsch
Keyword(s):  
Heart Valve ◽  
Heart Valves ◽  
Mechanical Heart Valve ◽  
In Vitro Study ◽  
Mechanical Heart Valves ◽  
Single Shot ◽  
Flow Measurements ◽  
Blood Damage ◽  
Disk Valve

Hemolysis and thrombosis are among the most detrimental effects associated with mechanical heart valves. The strength and structure of the flows generated by the closure of mechanical heart valves can be correlated with the extent of blood damage. In this in vitro study, a tilting disk mechanical heart valve has been modified to measure the flow created within the valve housing during the closing phase. This is the first study to focus on the region just upstream of the mitral valve occluder during this part of the cardiac cycle, where cavitation is known to occur and blood damage is most severe. Closure of the tilting disk valve was studied in a “single shot” chamber driven by a pneumatic pump. Laser Doppler velocimetry was used to measure all three velocity components over a 30ms period encompassing the initial valve impact and rebound. An acrylic window placed in the housing enabled us to make flow measurements as close as 200μm away from the closed occluder. Velocity profiles reveal the development of an atrial vortex on the major orifice side of the valve shed off the tip of the leaflet. The vortex strength makes this region susceptible to cavitation. Mean and maximum axial velocities as high as 7m∕s and 20m∕s were recorded, respectively. At closure, peak wall shear rates of 80,000s−1 were calculated close to the valve tip. The region of the flow examined here has been identified as a likely location of hemolysis and thrombosis in tilting disk valves. The results of this first comprehensive study measuring the flow within the housing of a tilting disk valve may be helpful in minimizing the extent of blood damage through the combined efforts of experimental and computational fluid dynamics to improve mechanical heart valve designs.

scholarly journals Blood Damage Through a Bileaflet Mechanical Heart Valve: A Quantitative Computational Study Using a Multiscale Suspension Flow Solver

2014 ◽  
Vol 136 (10) ◽  
Author(s):  
B. Min Yun ◽  
Cyrus K. Aidun ◽  
Ajit P. Yoganathan
Keyword(s):  
Numerical Method ◽  
Heart Valves ◽  
Computational Study ◽  
Mechanical Heart Valve ◽  
Complex Flow ◽  
Damage Potential ◽  
Spatiotemporal Resolution ◽  
Jude Medical ◽  
Blood Damage ◽  
Flow Through

Bileaflet mechanical heart valves (BMHVs) are among the most popular prostheses to replace defective native valves. However, complex flow phenomena caused by the prosthesis are thought to induce serious thromboembolic complications. This study aims at employing a novel multiscale numerical method that models realistic sized suspended platelets for assessing blood damage potential in flow through BMHVs. A previously validated lattice-Boltzmann method (LBM) is used to simulate pulsatile flow through a 23 mm St. Jude Medical (SJM) Regent™ valve in the aortic position at very high spatiotemporal resolution with the presence of thousands of suspended platelets. Platelet damage is modeled for both the systolic and diastolic phases of the cardiac cycle. No platelets exceed activation thresholds for any of the simulations. Platelet damage is determined to be particularly high for suspended elements trapped in recirculation zones, which suggests a shift of focus in blood damage studies away from instantaneous flow fields and toward high flow mixing regions. In the diastolic phase, leakage flow through the b-datum gap is shown to cause highest damage to platelets. This multiscale numerical method may be used as a generic solver for evaluating blood damage in other cardiovascular flows and devices.

scholarly journals Near Valve Flows and Potential Blood Damage During Closure of a Bileaflet Mechanical Heart Valve

2011 ◽  
Vol 133 (9) ◽  
Author(s):  
L. H. Herbertson ◽  
S. Deutsch ◽  
K. B. Manning
Keyword(s):  
Heart Valve ◽  
Heart Valves ◽  
Mechanical Heart Valve ◽  
In Vitro Study ◽  
Blood Damage ◽  
Bileaflet Mechanical Heart Valve ◽  
Fluid Velocities ◽  
Design Characteristics ◽  
Valve Housing

Blood damage and thrombosis are major complications that are commonly seen in patients with implanted mechanical heart valves. For this in vitro study, we isolated the closing phase of a bileaflet mechanical heart valve to study near valve fluid velocities and stresses. By manipulating the valve housing, we gained optical access to a previously inaccessible region of the flow. Laser Doppler velocimetry and particle image velocimetry were used to characterize the flow regime and help to identify the key design characteristics responsible for high shear and rotational flow. Impact of the closing mechanical leaflet with its rigid housing produced the highest fluid stresses observed during the cardiac cycle. Mean velocities as high as 2.4 m/s were observed at the initial valve impact. The velocities measured at the leaflet tip resulted in sustained shear rates in the range of 1500–3500 s−1, with peak values on the order of 11,000–23,000 s−1. Using velocity maps, we identified regurgitation zones near the valve tip and through the central orifice of the valve. Entrained flow from the transvalvular jets and flow shed off the leaflet tip during closure combined to generate a dominant vortex posterior to both leaflets after each valve closing cycle. The strength of the peripheral vortex peaked within 2 ms of the initial impact of the leaflet with the housing and rapidly dissipated thereafter, whereas the vortex near the central orifice continued to grow during the rebound phase of the valve. Rebound of the leaflets played a secondary role in sustaining closure-induced vortices.

Alternative mechanical heart valves for the developing world

2019 ◽  
Vol 28 (7) ◽  
pp. 431-443
Author(s):  
Elsmari Wium ◽  
Christiaan Johannes Jordaan ◽  
Lezelle Botes ◽  
Francis Edwin Smit
Keyword(s):  
Heart Valve ◽  
Computer Aided Design ◽  
Heart Valves ◽  
Developing World ◽  
Mechanical Heart Valve ◽  
Mechanical Heart Valves ◽  
Design Approach ◽  
Element Analysis ◽  
Mechanical Valves

Due to the prevalence of rheumatic heart disease in the developing world, mechanical heart valves in the younger patient population remain the prostheses of choice if repair is not feasible. Despite their durability, mechanical valves are burdened by coagulation and thromboembolism. Modern design tools can be utilized during the design process of mechanical valves, which allow a more systematic design approach and more detailed analysis of the blood flow through and around valves. These tools include computer-aided design, manufacturing, and engineering, such as computational fluid dynamics and finite element analysis, modern manufacturing techniques such as additive manufacturing, and sophisticated in-vitro and in-vivo tests. Following this systematic approach, a poppet valve was redesigned and the results demonstrate the benefits of the method. More organized flow patterns and fewer complex fluid structures were observed. The alternative trileaflet valve design has also been identified as a potential solution and, if a similar design approach is adopted, it could lead to the development of an improved mechanical heart valve in the future. It is imperative that researchers in developing countries continue their search for a mechanical heart valve with a reduced thromboembolic risk, requiring less or no anticoagulation.

Computational hemodynamic investigation of a new bileaflet mechanical heart valve

SIMULATION ◽  
2019 ◽  
Vol 96 (5) ◽  
pp. 459-469
Author(s):  
Belkhiri Khellaf ◽  
Boumeddane Boussad
Keyword(s):  
Heart Valve ◽  
Heart Valves ◽  
Stokes Equations ◽  
Thrombus Formation ◽  
Mechanical Heart Valve ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Navier Stokes Equations ◽  
Blood Damage ◽  
Flow Through

In this paper, we perform a numerical analysis for simulating steady, two-dimensional, laminar blood flow through our proposed design, known as the Butterfly mechanical heart valve, where the leaflets are fully opened. Blood has been assumed to be Newtonian and non-Newtonian fluid using the Casson model for shear-thinning behavior. A non-uniform Cartesian grid generation technique is presented to generate a two-dimensional grid for the irregular geometry of the Butterfly valve. The governing Navier–Stokes equations of flow, written in a stream function–vorticity formulation, are solved by the finite difference method with hybrid differencing of the convective terms. The computed results show that the blood’s non-Newtonian nature significantly affects the flow field with the existence of recirculation and consequently stagnation causing thrombus formation, as well as an increase of the shear stress along the wall, which contributes to hemolytic blood damage. The results demonstrate that the model is capable of predicting the hemodynamic features most interesting to physiologists. It can be used to assess thromboembolic problems occurring with heart valves and in the design of cardiac prostheses.

scholarly journals P806 Cavitation phenomenon in mechanical valves: not only microbubbles

2020 ◽  
Vol 21 (Supplement_1) ◽  
Author(s):  
O Vriz ◽  
F Archi ◽  
M Aldmawi ◽  
M Ahmed ◽  
M Alhumaid ◽  
...  
Keyword(s):  
Valve Replacement ◽  
Mechanical Valve ◽  
Control Group ◽  
Cavitation Phenomenon ◽  
Cavitation Bubbles ◽  
Mechanical Valves ◽  
Mitral Position ◽  
Disk Valve ◽  
High Gradients ◽  
In Trans

Abstract Introduction It is well described the presence of microbubbles (MBs) which are high-velocity, small, bright echoes presences that occur with the closing/opening of the mechanical double disk valve, more frequently in mitral position but less frequent growth of the cavitation bubbles are described. We considered the echo studies of patients with growth of cavitation bubbles and we evaluate the possible impact of the hemodynamic parameters of their formation and then misdiagnosis with endocarditis. Methods We analyzed retrospectively the echocardiographic studies of 49 patients with growth of cavitation bubbles and we went back to all studies until the date of surgery if available, to see in how many of those echos, this phenomenon was present. Patient"s blood pressure (BP) and heart rate (HR) measurement were available for each echo study. For the present analysis the last echo study with or without growth of cavitation bubbles were considered. The last echo study without growth of cavitation bubbles was considered as control group. Results Fourty nine patients (M26/F23) with mean age of 46.5 ± 13.6 years were identify as having growth of the cavitation bubbles and a total of 325 echo studies were reviewed. All patients had mitral valve replacement but 4, that had only aortic mechanical valve. 43% had mitral-aortic valve replacement and 5 had 3 or 4 valves replaced. The follow-up period was of 3697 ± 2481 days, 52%±31% of the echo studies reviewed had growth of the cavitation bubbles. At the time of the study systolic BP was 124 ± 12.5 vs 121.1 ± 16.4 mmHg, p = 0.1 (echo study with versus without growth cavitation respectively), diastolic 72.7 ± 10.1 vs 69.4 ± 14.9 mmHg, p= 0.2; HR 81.3 ± 19.4 vs 73.7 ± 14.1 bpm, p = 0.05. No statistical differences in trans mitral gradients were found between the two groups (peak 11.8 ± 3.9 vs 11.7 ± 4.3 mmHg, p = 0.7; mean 4.6 ± 1.9 vs 4.2 ± 1 mmHg.6p = 0.1). 33 TEE were performed and in 50% of cases because of suspecion of endocarditis. Only 2 TEE were positive for endocarditis and one positive for pannus and high gradients across the valve in addition to cavitation. Conclusion Cavitation phenomenon in mechanical valves, in particular mitral bi-leaflet valve is well known but growth of cavitation bubbles is seldom described. We found that this fenomenon is frequently present although not constant, is related with increased HR and can be responsible of misdiagnosis with endocarditis. Abstract P806 Figure.

Observation and Quantification of Gas Bubble Formation on a Mechanical Heart Valve

2000 ◽  
Vol 122 (4) ◽  
pp. 304-309 ◽  
Author(s):  
Hsin-Yi Lin ◽  
Brian A. Bianccucci ◽  
Steven Deutsch ◽  
Arnold A. Fontaine ◽  
J. M. Tarbell
Keyword(s):  
High Speed ◽  
Heart Valves ◽  
Bubble Formation ◽  
Mechanical Heart Valve ◽  
Gas Bubbles ◽  
Co2 Concentration ◽  
Video Camera ◽  
Gas Content ◽  
Gas Bubble ◽  
Cavitation Intensity

Clinical studies using transcranial Doppler ultrasonography in patients with mechanical heart valves (MHV) have detected gaseous emboli. The relationship of gaseous emboli release and cavitation on MHV has been a subject of debate in the literature. To study the influence of cavitation and gas content on the formation and growth of stable gas bubbles, a mock circulatory loop, which employed a Medtronic-Hall pyrolytic carbon disk valve in the mitral position, was used. A high-speed video camera allowed observation of cavitation and gas bubble release on the inflow valve surfaces as a function of cavitation intensity and carbon dioxide CO2 concentration, while an ultrasonic monitoring system scanned the aortic outflow tract to quantify gas bubble production by calculating the gray scale levels of the images. In the absence of cavitation, no stable gas bubbles were formed. When gas bubbles were formed, they were first seen a few milliseconds after and in the vicinity of cavitation collapse. The volume of the gas bubbles detected in the aortic track increased with both increased CO2 and increased cavitation intensity. No correlation was observed between O2 concentration and bubble volume. We conclude that cavitation is an essential precursor to stable gas bubble formation, and CO2, the most soluble blood gas, is the major component of stable gas bubbles. [S0148-0731(00)00204-1]

Simulations of Flow Through Bileaflet Mechanical Heart Valves With Asymmetric Leaflet Motion

2012 ◽  
Author(s):  
B. Min Yun ◽  
Lakshmi P. Dasi ◽  
Cyrus K. Aidun ◽  
Ajit P. Yoganathan
Keyword(s):  
Heart Valve ◽  
Heart Valves ◽  
Mechanical Heart Valve ◽  
Prosthetic Heart Valve ◽  
Prosthetic Heart Valves ◽  
Thromboembolic Events ◽  
Complex Flow ◽  
Blood Damage ◽  
Flow Through ◽  
Leaflet Motion

Prosthetic heart valves have been used for over 50 years to replace diseased native valves but still lead to severe complications such as platelet aggregation and thromboembolic events. The most widely implanted design is the bileaflet mechanical heart valve (BMHV). Most modern BMHV designs have better flow hemodynamics and blood damage performance than earlier-generation counterparts. However, blood element trauma and thromboembolic events still remain as major complications of current BMHV designs. These problems have been linked to blood damage caused by non-physiological stresses. These stresses are caused by the complex flow fields that arise due to prosthetic heart valve design. In order to reduce the severity of these complications, the blood damage that occurs in flows through prosthetic heart valves must be well understood.

Simulations of Flow Through Bileaflet Mechanical Heart Valves to Assess Platelet Damage

2011 ◽  
Author(s):  
B. Min Yun ◽  
Jingshu Wu ◽  
Cyrus K. Aidun ◽  
Ajit P. Yoganathan
Keyword(s):  
Heart Valve ◽  
Heart Valves ◽  
Mechanical Heart Valve ◽  
Prosthetic Heart Valve ◽  
Prosthetic Heart Valves ◽  
Thromboembolic Events ◽  
Complex Flow ◽  
Valve Design ◽  
Blood Damage ◽  
Flow Through

Prosthetic heart valves have been used for over 50 years to replace diseased native valves but still lead to severe complications such as hemolysis, platelet aggregation, and thromboembolic events. The most widely implanted design is the bileaflet mechanical heart valve (BMHV). Most modern BMHV designs have better flow hemodynamics and blood damage performance than their earlier-generation counterparts. However, blood element trauma and thromboembolic events still remain as major complications of current BMHV designs. These problems have been linked to blood element damage caused by non-physiological stresses. These stresses are caused by the complex flow fields that arise due to prosthetic heart valve design, particularly in the leaflet hinge region. In order to reduce the severity of these complications, the blood damage that occurs in flows through prosthetic heart valves must be well understood.

The Munich conference of Minister-Presidents of German lands in 1947

2020 ◽  
Vol 2020 (10-2) ◽  
pp. 86-98
Author(s):  
Ivan Popov
Keyword(s):  
The State ◽  
State Governments ◽  
The West ◽  
Constitutional Development ◽  
The Moment ◽  
The One

The paper deals with the organization and decisions of the conference of the Minister-Presidents of German lands in Munich on June 6-7, 1947, which became the one and only meeting of the heads of the state governments of the western and eastern occupation zones before the division of Germany. The conference was the first experience of national positioning of the regional elite and clearly demonstrated that by the middle of 1947, not only between the allies, but also among German politicians, the incompatibility of perspectives of further constitutional development was existent and all the basic conditions for the division of Germany became ripe. Munich was the last significant demonstration of this disunity and the moment of the final turn towards the three-zone orientation of the West German elite.

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