Elastomers for Use in Heart Valves

Abstract Approximately 0.1 per cent of silicone rubber balls from the estimated 18,000 implanted Starr-Edwards heart valve prostheses have been found to be variant. This material variation has initiated investigations of present material and accelerated the search for new and improved elastomers. Descriptions of various types of artificial heart valve prostheses, environmental conditions, design requirements and test apparatus are presented. Variant balls exhibit external physical damage by surface grooves and splits. Internal changes and discolorations from absorbed lipid materials have also been observed. Variant silicone rubber balls have poor physical properties compared with nonvariant or non-implanted balls. This reduction lowers the resistance to damage. The engineering laboratory evaluation program of elastomeric materials includes the compilation of test data on balls molded from silicone, butyl, ethylene propylene, polybutadiene and chlorohydrin rubbers. Butyl and polybutadiene rubbers were selected to demonstrate the extremes of the resilience spectrum with respect to the hydraulic performance of the ball type prosthesis. Compounds with low resilience for less ball rebound appear to be advantageous in this application To date, butyl rubber has exhibited excellent wear resistance in laboratory durability testers.

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In Vitro Hemolysis by Mechanical Heart Valve Prostheses with Tilting Disc

The International Journal of Artificial Organs ◽

10.1177/039139889201501112 ◽

1992 ◽

Vol 15 (11) ◽

pp. 681-685 ◽

Cited By ~ 1

Author(s):

M.O. Wendt ◽

M. Pohl ◽

S. Pratsch ◽

D. Lerche

Keyword(s):

Heart Valve ◽

Test Chamber ◽

Mechanical Heart Valve ◽

Hemoglobin Concentration ◽

Clinical Results ◽

Artificial Heart Valve ◽

Valve Prosthesis ◽

Heart Valve Prostheses ◽

Valve Prostheses

Hemolytic and subhemolytic blood damage by mechanical heart valve prostheses have been observed in both clinical and in vitro investigations. A direct comparison between these studies is not possible. Nevertheless the transfer of some in vitro results to the behaviour of the valve in situ may be performed considering the similarity principle. This requires the use of dimensionless similarity numbers such as the plasma's hemoglobin concentration (PHb) or others, instead of dimensioned parameters. To evaluate the in vitro hemolysis of valve prosthesis a test chamber filled with human banked blood was used. An artificial ventricle ensuring an oscillatory flow through the valve was also used. The rise of PHb was evaluated in terms of a similarity number, called the lysis number. This number describes the probability of destroying a single red blood cell participating once in the hemolytic process under consideration. The lysis number, a Björk-Shiley valve (TAD 29), was found to be in the order of 2 × 10−4. From this, the survival time of erythrocytes in patients with an artificial heart valve was estimated. It was found to be in the order of 20 d of T50 Cr in agreement with clinical results

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Prophylaxis of thrombotic complications in a pregnant patients with prosthetic heart valves

Journal of obstetrics and women s diseases ◽

10.17816/jowd61510-24 ◽

2012 ◽

Vol 61 (5) ◽

pp. 10-24

Author(s):

Aleksandr Davidovich Makatsariya ◽

Viktoriya Omarovna Bitsadze ◽

Dzhamilya Khizriyevna Khizroyeva ◽

Vyacheslav Borisovich Nemirovskiy ◽

Svetlana Vladimirovna Akinshina

Keyword(s):

Heart Valve ◽

Heart Valves ◽

Anticoagulation Therapy ◽

Mechanical Heart Valve ◽

Prosthetic Heart Valves ◽

Dose Selection ◽

Heart Valve Prostheses ◽

Adequate Dose ◽

Thrombotic Complications ◽

Valve Prostheses

In patients with prosthetic heart valves pregnancy and labor are associated with high risk. There are no established anticoagulation guidelines in pregnant women with mechanical heart valve prostheses. More often physiological hypercoagulable state during pregnancy can reveal acquired and/or inherited hemostasis abnormalities which were asymptotic before pregnancy. The presence in the history of patients the foetal loss syndrome, severe obstetric complications (severe preeclampsia, abruptio placenta, antenatal fetal death, feto-placental insufficiency), thrombosis events is an indication for the screening for genetic thrombophilia and antiphospholipid syndrome. The diagnosis of thrombophilia in patients with mechanical heart valve prostheses can explain the inefficiency of anticoagulation therapy, warfarin resistance, «floating» hemostasis markers and difficulties in adequate dose selection

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Pressure sensor emulator to improve longterm stability of heart valve testing systems

Current Directions in Biomedical Engineering ◽

10.1515/cdbme-2019-0124 ◽

2019 ◽

Vol 5 (1) ◽

pp. 493-495

Author(s):

Wolfram Schmidt ◽

Carsten Tautorat ◽

Niels Grabow ◽

Sebastian Kaule ◽

Jörg Kaminsky ◽

...

Keyword(s):

Heart Valve ◽

Artificial Heart ◽

Dynamic Properties ◽

Pressure Sensors ◽

Artificial Heart Valve ◽

Test Procedures ◽

Heart Valve Prostheses ◽

System Verification ◽

Valve Prostheses

AbstractFluid mechanical characterization of artificial heart valve prostheses requires reliable measurement of temperature, flow and pressure at normal heart rate. In vitro fatigue test procedures of artificial heart valve prostheses can take several months with up to 400 million cycles to assess valve performance and durability under simulated cardiac conditions at increased pulse frequency. In both cases, a minimum of user interventions for recalibration are required. In these tests, pressure data are collected for hydrodynamic heart valve characterization and for closed-loop control of pressure loading. In our study, the improvement of commercial heart valve testing systems (Vivitro Pulse Duplicator, Vivitro Labs Inc. and VDT-3600i, BDC Laboratories) is considered by substituting the built-in disposable pressure sensors (lifetime: one week) by longterm stable sensors. The selected highly accurate sensors (86A, TE Connectivity Corp.) provide amplified, linearized, calibrated and temperature compensated analog output signals. Their stainless steel construction allows for high media compatibility with corrosive liquids. Due to different sensitivity characteristics, these sensors are not fully compatible to the testing devices. To overcome this limitation, application-specific emulator interfaces were developed to connect the new sensors to the data acquisition part of the validated valve testing systems. To stay consistent with manufacturer’s device and software specification, we utilized fast analog signal conditioning, including scaling, offset calibration, out of range alarm and status indication. Compared to the originally equipped pressure sensors, emulator parameters, such as pressure range, precision, resolution and accuracy remained unchanged or even improved. For system verification the response characteristic, long-term stability and dynamic properties were examined in comparative studies

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Recent Advances in Polymeric Heart Valves Research

International Journal of Biomaterials Research and Engineering ◽

10.4018/ijbre.2011010101 ◽

2011 ◽

Vol 1 (1) ◽

pp. 1-17 ◽

Cited By ~ 14

Author(s):

Yee Han Kuan ◽

Lakshmi Prasad Dasi ◽

Ajit Yoganathan ◽

Hwa Liang Leo

Keyword(s):

Valve Replacement ◽

Heart Valve ◽

Animal Studies ◽

Heart Valves ◽

Heart Valve Replacement ◽

Artificial Heart Valve ◽

Polymer Science ◽

Cardiovascular Devices ◽

Valve Prostheses ◽

Hemodynamic Performance

Heart valve replacement is fast becoming a routine surgery worldwide, and heart valve prostheses are today considered among the most widely used cardiovascular devices. Mechanical and bioprostheses have been the traditional choices to the replacement surgeries. However, such valves continue to expose patients to risks including thrombosis, infection and limited valve durability. In recent years, advances in polymer science give rise to an important new class of artificial heart valve made predominantly of polyurethane-based materials, which show improved biocompatibility and biostability. These polymeric heart valves have demonstrated excellent hemodynamic performance and good durability with excellent fatigue stress resistance. Advancements in the designs and manufacturing methods also suggested improved in the durability of polymeric heart valves. Animal studies with these valves have also shown good biocompatibility with minimal calcification of the valve leaflets. With these promising progresses, polymeric heart valves could be a viable alternative in the heart valve replacement surgeries in the near future.

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Design of Biomorphic Polymeric Heart Valve Prosthes by Means of FEM Modeling

ASME 2010 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2010-19420 ◽

2010 ◽

Author(s):

Adriano Zaffora ◽

Joanna Stasiak ◽

Geoff D. Moggridge ◽

Maria Laura Costantino ◽

Roberto Fumero

Keyword(s):

Heart Valve ◽

Heart Valves ◽

Significant Risk ◽

Artificial Heart Valve ◽

Fem Modeling ◽

Good Reliability ◽

Hard Materials ◽

Tissue Degradation ◽

Valve Prostheses ◽

New Generation

Severe stenotic or insufficient native heart valves (nHV) must be substituted with artificial heart valve prostheses (aHV) to prevent heart failure. Nowadays, surgeons can implant two types of aHVs: mechanical aHV or bioprosthetic aHV. Mechanical aHVs, which are built up from synthetic hard materials, assure good reliability but require daily anticoagulant treatment to avoid blood cells damage. On the contrary, bioprosthetic aHVs, which are made from animal or human tissues, display better hemocompatibility but significant risk of failure due to tissue degradation. Despite current development in manufacturing of valve prostheses, long-term clinical applications claim for new generation of aHVs able to meet reliability and effectiveness requirements [2].

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