The Influence of Open Leaflet Geometry on the Haemodynamic Flow Characteristics of Polyurethane Trileaflet Artificial Heart Valves

1996 ◽  
Vol 210 (4) ◽  
pp. 273-287 ◽  
Author(s):  
J Corden ◽  
T David ◽  
J Fisher
Keyword(s):  
Axial Velocity ◽  
Heart Valves ◽  
Flow Characteristics ◽  
Manufacturing Method ◽  
Blood Damage ◽  
Flow Recirculation ◽  
Maximum Value ◽  
Artificial Heart Valves

In vitro velocity data were obtained downstream of two versions of the Leeds polyurethane trileaflet heart valve in a simulated pulsatile flow regime using laser Doppler velocimetry. The main difference between the two valves studied was the manufacturing method used to create the valves. The film-fabricated valve was constructed from solvent-cast sheets of polyurethane, thermally formed into the correct leaflet geometry. The dip-cast valve used a stainless steel mould which was dipped into a polyurethane solution to produce the valve leaflets. Significant differences were visible between the fully open leaflet shape of each valve. The distribution of mean axial velocity and Reynolds normal stress (RNS) was shown to be dependent on the shape of the fully open valve orifice. For the film-fabricated valves, flow recirculation and high values of RNS were present downstream of the frame posts. The maximum value of RNS obtained downstream of the film-fabricated valve at peak systole was 147 N/m2. Results for the dip-cast valve showed a more uniform distribution of mean axial velocity and RNS resulting from the more circular central orifice produced by the dip-cast leaflets. The maximum value of RNS obtained downstream of the dip-cast valve at peak systole was 109 N/m2. These results demonstrate the effect of the open valve geometry on the flow characteristics downstream of trileaflet valves and that minor changes to the open leaflet geometry can significantly affect the flow characteristics and the possibility of flow-related blood damage occurring in vivo.

Calcification Modelling in Artificial Heart Valves

1992 ◽  
Vol 15 (5) ◽  
pp. 284-288 ◽  
Author(s):  
A.C. Fisher ◽  
G.M. Bernacca ◽  
T.G. Mackay ◽  
W.R. Dimitri ◽  
R. Wilkinson ◽  
...  
Keyword(s):  
Artificial Heart ◽  
Heart Valves ◽  
Test Protocol ◽  
Tissue Sections ◽  
Artificial Heart Valves ◽  
In Vivo Tests ◽  
Tissue Contents ◽  
Histological Staining

This study has examined a range of methods of studying the calcification process in bovine pericardial and polyurethane biomaterials. The calcification methods include static and dynamic, in vitro and in vivo tests. The analytical methods include measurement of depletion rates of calcium and phosphate from in vitro calcifying solutions, analysis of tissue contents of calcium, histological staining of tissue sections for calcium, X-ray elemental analysis, by scanning electron microscopy, of calcium and phosphorus distributions over valve leaflets calcified in vitro under dynamic conditions. Bovine pericardium, in all test settings, calcified to a much greater degree than polyurethane biomaterials. Polyurethane extracts calcified to a greater degree than bulk polyurethanes. The test protocol used allows progress through increasily demanding calcification tests, with the possibility of eliminating unsuitable materials with tests of limited complexity and expense.

A Method to Measure the Station of Artificial Mechanical Heart Valves

2013 ◽  
Vol 683 ◽  
pp. 712-715
Author(s):  
Feng Zhou ◽  
Liang Liang Wu ◽  
Yuan Yuan Cui ◽  
Ying Chen ◽  
Jie Yang ◽  
...  
Keyword(s):  
High Speed ◽  
Heart Valves ◽  
Ultrasonic Method ◽  
High Speed Photography ◽  
In Vitro Experiments ◽  
In Vivo Experiments ◽  
Artificial Heart Valves ◽  
Economic Injury

The experiments of artificial heart valves were divided into in vivo and in vitro experiments; in vivo experiments provide accurate experimental parameters serving in vitro research. Simulation experiment used in vitro usually goes like this, firstly design a similar model or prototype phenomenon, then analysis the model working out the regular parameters related to the process, ruled out the possibility of impact on the study of individual exist in vivo experiment. In vitro experiments are likely designed; performance can be simplified and prominently concerned about contents, even designed some extreme conditions to test. A number of means related to fluid experimental measurement are included, such as the Particle Image Velocimetry（PIV）[1], Dual Catheter Method [2]，and ultrasonic method[3] and so on. However, these methods have different kinds of limitations, for example the Dual Catheter Method cannot be used as a routine determination for clinic due to its destructiveness, and PIV test requires expensive equipment. This study was designed by the image processing technology of high-speed photography aiming at the production of a reliable, simple, economic, injury-free and non-contact measurement method.

In Vitro Blood Damage by High Shear Flow: Human versus Porcine Blood

2002 ◽  
Vol 25 (4) ◽  
pp. 306-312 ◽  
Author(s):  
S. Klaus ◽  
S. Körfer ◽  
K. Mottaghy ◽  
H. Reul ◽  
B. Glasmacher
Keyword(s):  
Human Blood ◽  
Heart Valves ◽  
High Shear ◽  
Blood Damage ◽  
Shear Rates ◽  
Porcine Blood ◽  
High Shear Rates ◽  
Blood Pumps ◽  
Artificial Heart Valves

Devices for modern heart support are minimized to reduce priming blood volume and contact area with foreign surfaces. Their flow fields are partly governed by very high velocity gradients. In order to investigate blood damage, porcine and human blood was passed through a narrow Couette type shear gap applying defined high shear rates within the typical range for devices such as blood pumps or artificial heart valves (γ = 1800/s to 110,000/s for 400 ms). Traumatization profiles of both blood species were recorded in terms of hemolysis and platelet count. Sublethal damage in terms of platelet (PF4) and complement activation (C5a) was additionally measured for human blood. Results for porcine and human blood were very similar. Hemolysis was not started until critical shear rates of about 80,000/s. Impact on platelets was severe with drops in cell count of up to 65% (at γ = 55,000/s to 110,000/s) likely to set stronger limits to the design layout of devices than hemolysis. Concentrations of PF4 and C5a clearly increased with shear rate exhibiting stronger gradients where hemolysis started. Due to the similar results of porcine and human blood for hemolysis and platelet drop, porcine blood seems to be suitable for device testing. Selection of blood species would thus depend on handling, availability and analysis demands.

Past and future of blood damage modelling in a view of translational research

2018 ◽  
Vol 42 (3) ◽  
pp. 125-132 ◽  
Author(s):  
Leonid Goubergrits ◽  
Ulrich Kertzscher ◽  
Michael Lommel
Keyword(s):  
Residence Time ◽  
High Velocity ◽  
Heart Valves ◽  
Pressure Fluctuations ◽  
Artificial Organs ◽  
Blood Damage ◽  
Damage Models ◽  
Heart Assist Devices

Anatomic pathologies such as stenosed or regurgitating heart valves and artificial organs such as heart assist devices or heart valve prostheses are associated with non-physiological flow. This regime is associated with regions of spatially high-velocity gradients, high-velocity and/or pressure fluctuations as well as neighbouring regions with stagnant flow associated with high residence time. These hemodynamic conditions cause destruction and/or activation of blood components and their accumulation in regions with high residence time. The development of next-generation artificial organs, which allow long-term patient care by reducing adverse events and improve quality of life, requires the development of blood damage models serving as a cost function for device optimization. We summarized the studies underlining the key findings with subsequent elaboration of the requirements for blood damage models as well as a decision tree based on the classification of existing blood damage models. The four major classes are Lagrangian or Eulerian approaches with stress- or strain-based blood damage. Key challenges were identified and future steps towards the translation of blood damage models into the device development pipeline were formulated. The integration of blood damage caused by turbulence into models as well as in vitro and in vivo validation of models remain the major challenges for future developments. Both require the development of novel experimental setups to provide reliable and well-documented experimental data.

PIV Measurements of Flow in a Centrifugal Blood Pump: Steady Flow

2004 ◽  
Vol 127 (2) ◽  
pp. 244-253 ◽  
Author(s):  
Steven W. Day ◽  
James C. McDaniel
Keyword(s):  
Shear Stress ◽  
Artificial Heart ◽  
Heart Valves ◽  
Blood Pump ◽  
Reynolds Stresses ◽  
Centrifugal Blood Pump ◽  
Flow Rates ◽  
Blood Damage ◽  
Artificial Heart Valves ◽  
Stagnant Flow

Magnetically suspended left ventricular assist devices have only one moving part, the impeller. The impeller has absolutely no contact with any of the fixed parts, thus greatly reducing the regions of stagnant or high shear stress that surround a mechanical or fluid bearing. Measurements of the mean flow patterns as well as viscous and turbulent (Reynolds) stresses were made in a shaft-driven prototype of a magnetically suspended centrifugal blood pump at several constant flow rates (3–9L∕min) using particle image velocimetry (PIV). The chosen range of flow rates is representative of the range over which the pump may operate while implanted. Measurements on a three-dimensional measurement grid within several regions of the pump, including the inlet, blade passage, exit volute, and diffuser are reported. The measurements are used to identify regions of potential blood damage due to high shear stress and∕or stagnation of the blood, both of which have been associated with blood damage within artificial heart valves and diaphragm-type pumps. Levels of turbulence intensity and Reynolds stresses that are comparable to those in artificial heart valves are reported. At the design flow rate (6L∕min), the flow is generally well behaved (no recirculation or stagnant flow) and stress levels are below levels that would be expected to contribute to hemolysis or thrombosis. The flow at both high (9L∕min) and low (3L∕min) flow rates introduces anomalies into the flow, such as recirculation, stagnation, and high stress regions. Levels of viscous and Reynolds shear stresses everywhere within the pump are below reported threshold values for damage to red cells over the entire range of flow rates investigated; however, at both high and low flow rate conditions, the flow field may promote activation of the clotting cascade due to regions of elevated shear stress adjacent to separated or stagnant flow.

scholarly journals Adverse Hemodynamic Conditions Associated with Mechanical Heart Valve Leaflet Immobility

2018 ◽  
Vol 5 (3) ◽  
pp. 74 ◽  
Author(s):  
Fardin Khalili ◽  
Peshala Gamage ◽  
Richard Sandler ◽  
Hansen Mansy
Keyword(s):  
Heart Valve ◽  
Heart Valves ◽  
Computational Study ◽  
Cell Damage ◽  
Mechanical Heart Valve ◽  
Flow Characteristics ◽  
Maximal Velocity ◽  
Valve Dysfunction ◽  
Promising Tool ◽  
Artificial Heart Valves

Artificial heart valves may dysfunction, leading to thrombus and/or pannus formations. Computational fluid dynamics is a promising tool for improved understanding of heart valve hemodynamics that quantify detailed flow velocities and turbulent stresses to complement Doppler measurements. This combined information can assist in choosing optimal prosthesis for individual patients, aiding in the development of improved valve designs, and illuminating subtle changes to help guide more timely early intervention of valve dysfunction. In this computational study, flow characteristics around a bileaflet mechanical heart valve were investigated. The study focused on the hemodynamic effects of leaflet immobility, specifically, where one leaflet does not fully open. Results showed that leaflet immobility increased the principal turbulent stresses (up to 400%), and increased forces and moments on both leaflets (up to 600% and 4000%, respectively). These unfavorable conditions elevate the risk of blood cell damage and platelet activation, which are known to cascade to more severe leaflet dysfunction. Leaflet immobility appeared to cause maximal velocity within the lateral orifices. This points to the possible importance of measuring maximal velocity at the lateral orifices by Doppler ultrasound (in addition to the central orifice, which is current practice) to determine accurate pressure gradients as markers of valve dysfunction.

scholarly journals In vitro experiments of cerebral blood flow during aspiration thrombectomy: potential effects on cerebral perfusion pressure and collateral flow

2015 ◽  
Vol 8 (9) ◽  
pp. 969-972 ◽  
Author(s):  
Frank Lally ◽  
Mitra Soorani ◽  
Timothy Woo ◽  
Sanjeev Nayak ◽  
Changez Jadun ◽  
...  
Keyword(s):  
Direct Contact ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Collateral Flow ◽  
In Vitro Experiments ◽  
Aspiration Thrombectomy ◽  
Flow Solver ◽  
Catheter Tip

BackgroundMechanical thrombectomy with stent retriever devices is associated with significantly better outcomes than thrombolysis alone in the treatment of acute ischemic stroke. Thrombus aspiration achieves high patency rates, but clinical outcomes are variable. The aim of this study was to examine the effect of different suction conditions on perfusate flow during aspiration thrombectomy.MethodsA computational fluid dynamics model of an aspiration device within a patent and occluded blood vessel was used to simulate flow characteristics using fluid flow solver software. A physical particulate flow model of a patent vessel and a vessel occluded by thrombus was then used to visualize flow direction and measure flow rates with the aspiration catheter placed 1–10 mm proximal of the thrombus, and recorded on video.ResultsThe mathematical model predicted that, in a patent vessel, perfusate is drawn from upstream of the catheter tip while, in an occluded system, perfusate is drawn from the vessel proximal to the device tip with no traction on the occlusion distal of the tip. The in vitro experiments confirmed the predictions of this model. In the occluded vessel aspiration had no effect on the thrombus unless the tip of the catheter was in direct contact with the thrombus.ConclusionsThese experiments suggest that aspiration is only effective if the catheter tip is in direct contact with the thrombus. If the catheter tip is not in contact with the thrombus, aspirate is drawn from the vessels proximal of the occlusion. This could affect collateral flow in vivo.

Parameters and Methods for Testing Artificial Heart Valves

1989 ◽  
Vol 12 (4) ◽  
pp. 252-260 ◽  
Author(s):  
J.C. Köhler ◽  
J.G. Tech
Keyword(s):  
Heart Valves ◽  
Close Correlation ◽  
Test Methods ◽  
In Vitro Tests ◽  
Geometrical Parameters ◽  
Test Standards ◽  
Artificial Heart Valves ◽  
Minimum Requirements ◽  
Definition Of

The report describes the development of heart valve test standards. The aim is comprehensive quality assurance by in vitro tests. The project includes three test fields: general basis, development and definition of test methods and test devices and comparative in vitro assessment of valves for the definition of minimum requirements. A preliminary list of test parameters and test steps has been defined: geometrical, flow, deformation, force, and conditioning parameters. A system of geometrical parameters has been developed for standardized aortic models. Geometrical parameters of 31 valves of six types and different sizes underline a close correlation between geometrical and hemodynamic parameters. The relative ostium cross-section Ae/AT increases with valve size and lies between 0.3 and 0.5. Two new measurement devices with quasi-steady flow are proposed as quick testers for leakage flow and pressure loss.

scholarly journals In Silico Performance of a Recellularized Tissue-Engineered Transcatheter Aortic Valve

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Christopher Noble ◽  
Joshua Choe ◽  
Susheil Uthamaraj ◽  
Milton Deherrera ◽  
Amir Lerman ◽  
...  
Keyword(s):  
Mechanical Behavior ◽  
Heart Valves ◽  
Mechanical Response ◽  
Mechanical Performance ◽  
Fe Analysis ◽  
Model Parameters ◽  
Biaxial Testing ◽  
Principal Stresses

Commercially available heart valves have many limitations, such as a lack of remodeling, risk of calcification, and thromboembolic problems. Many state-of-the-art tissue-engineered heart valves (TEHV) rely on recellularization to allow remodeling and transition to mechanical behavior of native tissues. Current in vitro testing is insufficient in characterizing a soon-to-be living valve due to this change in mechanical response; thus, it is imperative to understand the performance of an in situ valve. However, due to the complex in vivo environment, this is difficult to accomplish. Finite element (FE) analysis has become a standard tool for modeling mechanical behavior of heart valves; yet, research to date has mostly focused on commercial valves. The purpose of this study has been to evaluate the mechanical behavior of a TEHV material before and after 6 months of implantation in a rat subdermis model. This model allows the recellularization and remodeling potential of the material to be assessed via a simple and inexpensive means prior to more complex ovine orthotropic studies. Biaxial testing was utilized to evaluate the mechanical properties, and subsequently, constitutive model parameters were fit to the data to allow mechanical performance to be evaluated via FE analysis of a full cardiac cycle. Maximum principal stresses and strains from the leaflets and commissures were then analyzed. The results of this study demonstrate that the explanted tissues had reduced mechanical strength compared to the implants but were similar to the native tissues. For the FE models, this trend was continued with similar mechanical behavior in explant and native tissue groups and less compliant behavior in implant tissues. Histology demonstrated recellularization and remodeling although remodeled collagen had no clear directionality. In conclusion, we observed successful recellularization and remodeling of the tissue giving confidence to our TEHV material; however, the mechanical response indicates the additional remodeling would likely occur in the aortic/pulmonary position.

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