Mechanical stress activates platelets at a subhemolysis level: an in vitro study.

A feasibility study is performed to quantify sheep platelets (PLTs) and to identify the relationship between PLT count and hemolysis as a consequence of mechanical stress. Six adult, healthy Dorset sheep have been used for in vitro blood sampling test procedures in a hemoresistometer device (HRM). In each experiment, blood of the same animal was exposed to six different shear rates.

Early wear development in a novel mechanical heart valve prosthesis made from polymeric materials.

Background And Aim Of The Study: Currently, 95% of all implanted mechanical heart valve prostheses are constructed completely, or at least partially, from pyrolytic carbon. In order to develop a mechanical heart valve prosthesis made from alternative materials, a special hinge design was tested which enabled the integration of wear-resistant tribomaterials into the highly loaded hinges of leaflets.

Methods: The wear behavior of different material couples was investigated in vitro.

Early wear development in a novel mechanical heart valve prosthesis made from polymeric materials.

Background And Aim Of The Study: Currently, 95% of all implanted mechanical heart valve prostheses are constructed completely, or at least partially, from pyrolytic carbon. In order to develop a mechanical heart valve prosthesis made from alternative materials, a special hinge design was tested which enabled the integration of wear-resistant tribomaterials into the highly loaded hinges of leaflets.

Methods: The wear behavior of different material couples was investigated in vitro.

In vitro comparison of aortic valve movement after valve-preserving aortic replacement.

Objective: In aortic valve regurgitation and aortic dilatation, preservation of the aortic valve is possible by means of root remodeling (Yacoub procedure) or valve reimplantation (David procedure). In vivo studies suggest that reimplantation might substantially influence aortic valve-motion characteristics. Evaluation of aortic valve movement in vivo, however, is technically limited and is difficult to standardize.

In-vitro comparison of aortic valve hemodynamics between aortic root remodeling and aortic valve reimplantation.

Background And Aim Of The Study: Valve-preserving aortic replacement has become an accepted option for patients with aortic valve regurgitation and aortic dilatation. The relative role of root remodeling versus valve reimplantation inside a vascular graft has been discussed, albeit controversially. In the present study, an in-vitro model was used to investigate the aortic valve hemodynamics of root remodeling and valve reimplantation; roots with supracommissural aortic replacement served as controls.

Intravascular blood oxygenation using hollow fibers in a disk-shaped configuration: experimental evaluation of the relationship between porosity and performance.

Implantation of hollow fibers for blood oxygenation within a human vessel has been investigated for the last 15 years. Unfortunately, the combination of limited space inside the venous system and disadvantageous blood flow conditions has resulted until now in limited gas exchange performance of the investigated oxygenators. We are developing a highly integrated intravascular membrane oxygenator (HIMOX) characterized by a homogeneous disk-shaped fiber configuration.

In vivo experimental testing of a microaxial blood pump for right ventricular support.

The incidence of isolated right ventricular (RV) failure is rare in postcardiotomy patients, but high in patients undergoing implantation of a left ventricular assist device or cardiac transplantation. Therefore, we have developed a new microaxial flow device and report on our first in vivo animal trials. Six healthy adult female sheep weighing 80-90 kg underwent implantation of the microaxial blood pump for partial unloading of the right ventricle.

Temporary or permanent support and replacement of cardiac function.

Cardiac assist devices are classified into the traditional engineering categories of displacement and rotary pumps. Clinical use and indications of the various pump categories are outlined and a detailed description of the currently available systems is given. The first section deals with extracorporeal as well as implantable ventricular assist devices of the displacement type and is followed by a section on current developments in the field of total artificial hearts.

In vitro evaluation of aortic valve prosthesis in a novel valved conduit with pseudosinuses of Valsalva.

Objective: This study was undertaken to determine whether the presence of vortices immediately above a prosthetic aortic valve could negatively influence the in vitro hydrodynamic performances of a biologic or mechanical valve implanted in a new Dacron polyester fabric conduit that incorporates sculpted sinuses of Valsalva.

Methods: With a computer-controlled pulse duplicator, the in vitro performance (pressure differences, closure and leakage volumes, and energy losses) of a 25-mm mechanical or biologic prosthesis implanted in a standard Dacron straight conduit or in the new Dacron graft with a sculpted sinus were analyzed and compared.

Results: The mechanical and biologic prostheses at 7 L/min cardiac output showed pressure drops across the valve of 8.

A validated computational fluid dynamics model to estimate hemolysis in a rotary blood pump.

A major part of developing rotary blood pumps requires the optimization of hemolytic properties of the entire pump. Application of a suited computational fluid dynamics (CFD)-based hemolysis model allows approximation of blood damage in an early phase of the design process. Thus, a drastic reduction of time- and cost- intensive hemolysis experiments can be achieved.

Concept for a new hydrodynamic blood bearing for miniature blood pumps.

The most crucial element of a long-term implantable rotary blood pump is the rotor bearing. Because of heat generation and power loss resulting from friction, seals within the devices have to be avoided. Actively controlled magnetic bearings, although maintenance-free, increase the degree of complexity.

Design, development, and first in vivo results of an implantable ventricular assist device, MicroVad.

The design concept and first in vitro and in vivo results of a long-term implantable ventricular assist device system based on a microaxial blood pump are presented. The blood-immersed parts of the pump consist of a single-stage impeller and a proximally integrated microelectric motor. Both parts are surrounded by a pump housing currently made of polycarbonate to allow visible access to the blood-exposed parts.

Comparison of hydraulic and hemolytic properties of different impeller designs of an implantable rotary blood pump by computational fluid dynamics.

A mixed-flow blood pump for long-term applications has been developed at the Helmholtz-Institute in Aachen, Germany. Central features of this implantable pump are a centrally integrated motor, a blood-immersed mechanical bearing, magnetic coupling of the impeller, and a shrouded impeller, which allows a relatively wide clearance. The aim of the study was a numerical analysis of hydraulic and hemolytic properties of different impeller design configurations.

Compact intra- and extracorporeal oxygenator developments.

For patients with acute lung failure, mechanical ventilation entails the risk of lung tissue damage due to high oxygen pressure and concentration. Membrane oxygenation for one to two weeks can rest the lungs due to decreased ventilation parameters, representing a potential bridge to recovery, but implies the substantial risks of blood damage, plasma leakage and infection, which often have fatal results for patients. At the Helmholtz Institute in Aachen, two types of membrane oxygenators, which aim to overcome previous limits, are under development.

Experimental testing of a new left ventricular assist device--the microdiagonal blood pump.

All existing ventricular assist devices are associated with a considerable number of serious complications. This article reports on the first animal tests with a newly developed microdiagonal blood pump (MDP). Six adult female sheep weighing 80 to 90 kg underwent implantation of the microdiagonal blood pump.

Preclinical assessment of a trileaflet mechanical valve in the mitral position in a calf model.

Background: The bileaflet valve is currently the mechanical replacement valve of choice. Though durable, it does not closely mimic native valve hemodynamics and remains potentially thrombogenic.

Methods: Prototype trileaflet valves (T1 and T2) were implanted in the mitral position in calves.

Shear stress related blood damage in laminar couette flow.

Artificial organs within the blood stream are generally associated with flow-induced blood damage, particularly hemolysis of red blood cells. These damaging effects are known to be dependent on shear forces and exposure times. The determination of a correlation between these flow-dependent properties and actual hemolysis is the subject of this study.

Development of a new fixed functional appliance for treatment of skeletal class II malocclusion first report.

Developed under interdisciplinary cooperation, the Functional Mandibular Advancer (FMA) is a new, rigid and fixed appliance for sagittal correction of the intermaxillary jaw relationship in adolescents and young adults. The appliance is non-dependent on patient compliance and is aimed at providing an alternative to the Herbst and MARA appliances. A number of designs, all based on the mechanical principle of the inclined plane combined with guide pins and allowing reactivation, were developed.

In-vitro assessment of the wear development mechanism and stabilization of wear in the Edwards MIRA/Sorin Bicarbon mechanical heart valve orifice ring.

Background And Aim Of The Study: Currently, there appears to be no detailed published information specifically describing the early 'wear-in' and stabilization periods of wear in a bileaflet mechanical heart valve. This study presents a detailed morphological description of the early to middle (0 to 200 million cycles) stages of wear in the Carbofilm carbon coating on the Edwards MIRA/Sorin Bicarbon valve housing (orifice ring) pivot slots.

Methods: Wear testing was performed using a specially designed durability tester that controls the impact load of the occluder against the housing.

The Heart-Hemopump Interaction: A Study of Hemopump Flow as a Function of Cardiac Activity.

The Hemopump is a useful left ventricular assist device. Because it is a rotary blood pump, the pump performance is not constant and is dependent on the cardiac cycle. We measured the static flow delivered by the pump at varying pressure heads (ΔP) in a mock circulation.

Hemodynamic System Analysis of Intraarterial Microaxial Pumps In Vitro and In Vivo.

Because of the lack of a sophisticated pump management system, the performance of the Hemopump in patients cannot be assessed successfully. To clarify the interrelationship between an intravascular nonpulsatile pump and a pulsating ventricle, an in vitro study was set up under controlled conditions. Before these in vitro experiments, a series of in vivo experiments were performed in sheep using Hp31 cannulae.