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. Wear testing was performed using a specially designed durability tester that controlled the pressure difference across the closed heart valve prosthesis in a water-glycerol mixture with blood analog viscosity. Conditions were set according to FDA and ISO standards for heart valve testing. Qualitative assessment of wear behavior was performed using light microscopy and scanning electron microscopy at intervals of 10, 40, and each subsequent 50 million cycles. RESULTS: None of the investigated heart valve prostheses failed during the durability tests. Compared to the reference valve made from polymeric materials, wear especially in the hinges could be reduced to an acceptable level by integrating wear-resistant tribomaterials into the leaflets. CONCLUSION: A leaflet design which enables the integration of tribomaterials into the highly loaded hinges of leaflets leads to an optimization of wear behavior of a mechanical heart valve prosthesis made from polymeric materials. Abrasive wear in the hinges may be reduced to an acceptable level for the functionality of the heart valve prosthesis. Durability tests will be continued in order to confirm the promising wear behavior of this novel heart valve prosthesis.

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. Wear testing was performed using a specially designed durability tester that controlled the pressure difference across the closed heart valve prosthesis in a water-glycerol mixture with blood analog viscosity. Conditions were set according to FDA and ISO standards for heart valve testing. Qualitative assessment of wear behavior was performed using light microscopy and scanning electron microscopy at intervals of 10, 40, and each subsequent 50 million cycles. RESULTS: None of the investigated heart valve prostheses failed during the durability tests. Compared to the reference valve made from polymeric materials, wear especially in the hinges could be reduced to an acceptable level by integrating wear-resistant tribomaterials into the leaflets. CONCLUSION: A leaflet design which enables the integration of tribomaterials into the highly loaded hinges of leaflets leads to an optimization of wear behavior of a mechanical heart valve prosthesis made from polymeric materials. Abrasive wear in the hinges may be reduced to an acceptable level for the functionality of the heart valve prosthesis. Durability tests will be continued in order to confirm the promising wear behavior of this novel heart valve prosthesis.

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. METHODS: Aortic roots with aortoventricular diameter 21 mm were obtained from pigs. Root remodeling was performed using a 22-mm graft (group I, n = 6), or valve reimplantation with a 24-mm graft (group II, n = 7). Control roots were treated by supracommissural aortic replacement (22-mm graft; group III, n = 7). Using an electrohydraulic, computer-controlled pulse duplicator, the valves were tested at flows of 2, 4, 5, 7, and 9 I/min at a heart rate of 70 /min and a mean arterial pressure of 100 mmHg. Parameters assessed included: mean pressure gradient, effective orifice area, valve closure and regurgitant volume, and energy loss due to ejection, valve closure and regurgitation. Data were compared using ANOVA. RESULTS: There were no differences between the three groups in terms of regurgitant volume, energy loss due to valve regurgitation, or valve closure. The aortic valve orifice area was largest and systolic gradient lowest in group I at all flow rates (p < 0.001). Ejection energy loss was lowest in group I at all flow rates (9 l/min: group I, 128 +/- 21 mJ; group II, 399 +/- 46 mJ; group III, 312 +/- 27 mJ; p < 0.001). Valve closure volumes were similar in groups I and III, but significantly lower in group II at all flow rates (p = 0.047). CONCLUSION: In this standardized experimental setting, root remodeling--but not valve reimplantation--resulted in physiologic hemodynamic performance of the aortic valve with regard to orifice area, pressure gradient, and systolic energy loss.

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. The main advantages are a larger fiber surface as well as favorable cross flow through the fibers compared with earlier designs. Fiber porosity represents an important constructive parameter and leads to a trade-off when dimensioning the bundles with the aim of maximum gas exchange at small anatomical size. Low porosity results in higher fiber surface as well as blood velocity. Both effects potentially enhance the gas exchange, but the associated increase of the pressure drop leads to a deformation of the fiber bundle and to a blood shunt. This fluid-structure interaction influences the gas exchange in a complex way. We investigated the influence of porosity on the gas exchange in the proposed fiber configuration in vitro. Bundle deformation was proven by comparing experimental data with a theoretical model. Highest oxygen exchange supplied by a single bundle was achieved at an intermediate porosity of 0.575. Moreover, specific oxygen exchange per fiber surface, which is an indicator of favorable flow conditions, increased with increasing fiber porosity. We achieved up to 450 ml O2 min m, which is a promising result for intravascular membrane oxygenation.

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. Group I calves received either a T1 valve (n = 12) or a control bileaflet valve (n = 5); Group II, either a T2 valve (n = 7) or a control bileaflet valve (n = 5). Valve function, perivalvular leakage, and transvalvular pressure gradients were evaluated. Also, long-term prototype leaflet wear was evaluated in vivo in one Group I calf (502 days) and two Group II calves (385 and 366 days). Calves were euthanized and necropsied at study termination, and major organs weighed and examined. RESULTS: Valve function was excellent and hematologic parameters remained normal in all calves that survived to study termination. Mean peak transvalvular pressure gradients were 10 +/- 7 mm Hg for T1 valves, 6 +/- 3 mm Hg for T2 valves, and 12 +/- 4 mm Hg for bileaflet control valves. Clinically insignificant valvular regurgitation was observed in both prototypes. Explanted valves showed no thrombus-impaired leaflet motion, except in two T1-fitted calves and one T2-fitted calf. Major organs showed no evidence of clinically significant thromboembolic events. There were no other significant differences between the results of experimental and control groups. CONCLUSIONS: Prototype trileaflet valves performed safely and effectively in the mitral position in calves, even without long-term anticoagulation. This warrants their evaluation as an equivalent alternative to bileaflet valves.

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 control values were determined based on simulated physiological pulsatile flow impact loads. A morphological assessment of the early wear was performed using light microscopy and scanning electron microscopy at intervals of 0.1, 1, 10 and 40 million cycles, and at every 40 million cycles thereafter up to 200 million cycles (five equivalent years). A quantitative assessment of the rate of Carbofilm removal was determined using planimetric methods as a function of cycles. RESULTS: The morphology of the Carbofilm wear showed first a gradual thinning of the layer in locations in contact with the leaflets, followed by small areas of film removal, culminating in slowly increasing areas of exposed titanium alloy substrate. Initial substrate exposure began typically between 0.1 million and 10 million cycles. The wear rate stabilized at a relatively low value, typically by 40 million cycles. CONCLUSION: The nature of the early wear development of the Edwards MIRA/Sorin Bicarbon valve has been determined as a process of gradual thinning of the Carbofilm layer, followed by a decelerating area increase of exposed titanium alloy substrate. The process is not one of 'flaking' or spalling of relatively large particles. The exposed titanium alloy surface is typically smooth and burnished. The wear rate is well behaved and stabilized by approximately 40 million cycles. Wear area expansion continues at a decreasing rate up to 200 million cycles.

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. As anticipated, the resulting pulsatile pump flow was a function of the momentary pressure difference across the pump. This varying pump flow showed a significant flow loop hysteresis, indicating that the pressure difference across the pump is not the only parameter governing momentary pump flow of a rotary pump operating at constant speed in a pulsatile environment. Furthermore, flow in the Hp31 was significantly influenced by the inflow situation, blood supply, size of the ventricular cavity, and shape and position of the inflow cannula within the ventricle. Pulsatile flow conditions with good as well as impaired inflow into the pump were accordingly simulated in vitro to verify the in vivo measurements, to characterize the various inflow conditions, and to discuss methods of improved pump management. As a result of the in vivo and in vitro experiments, one can rely on the measurement of nonpulsatile in vitro flow and pressure differences across the pump to characterize the momentary pump flow for good inflow conditions into the pump. For these situations, the flow hysteresis produced, caused by fluid inertia within the pump and cannula, can be neglected. In contrast, for an impaired inflow situation, the calculated pump flow based on pressure difference measurements can be misleading. Consequently, an improved pump management system is required to adjust the pump speed, the pump performance, to any kind of impaired inflow.

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. These data are compared to the pump performance in vivo. On the basis of these results, 5 sheep were instrumented for continuous Hemopump flow measurement as well as left ventricular and aortic pressure measurements. The Hemopump flow was relayed instantaneously to the pressure head. Low filling and ventricular failing (through intravenous administration of a beta-blocker) conditions were applied. The in vivo measured flows also are pressure head dependent, but the flow curve shows hysteresis resulting in a loop during each cardiac cycle. The in vivo peak flows (AP = 0) are similar to the in vitro data. The in vivo means flows (A 50 mm Hg) are similar to the in vitro data for the lower pump speeds but are less than that at the higher pump speeds (3.74 ± 0.55 L/min in vivo at Speed 7 versus 4.6 L/min in vitro). Low filling interrupts the AP-flow loop and reduces flow. In the failing ventricle, AP increases and flow is reduced. The cannula leaks and results in aortic insufficiency (0.36 ± 0.05 L/min) when the pump is turned off. Several conclusions have been drawn from these tests: Cardiac activity is beneficial for the pump performance as well as when the aortic pressure curve is nonpulsatile; the longer the systolic phase, the higher the pump flow; the pump should never be turned off in clinical use; and filling is important for the pump's performance.

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. The inflow and outflow conduits were anastomosed to the left atrium and the descending aorta. Pump flow was adjusted to 2-3 L/minute. Hemodynamic and echocardiographic data, as well as blood samples, were measured over the entire test period of 7 days. All internal organs and the pump were explanted for thorough examination at the end of the trial. Mean arterial (range 88.5 +/- 13.1-103.7 +/- 10.7 mm Hg) and mean pulmonary arterial (18.3 +/- 2.7-21.6 +/- 20.5 mm Hg) pressures, as well as the pulmonary capillary wedge pressure (14.2 +/- 3.0 - 16.6 +/- 4.0 mm Hg), remained stable during the whole test period. Cardiac output (4.9 +/- 0.7 --> 3.2 +/- 0.5 L/minute) decreased postoperatively caused by partial unloading of the heart. Left ventricular end diastolic (4.1 +/- 0.5 --> 3.6 +/- 0.3 cm) and end systolic (3.2 +/- 0.4 --> 2.8 +/- 0.5 cm) diameters, as well as the ejection fraction (57 +/- 9 --> 42 +/- 5%), decreased after MDP implantation and did not change during the test period. Mean number of platelets (428 +/- 54 --> 286 +/- 66 x 10(3)/microL) and hemoglobin (9.8 +/- 1.3 --> 6.3 +/- 0.8 g/dL) decreased perioperatively because of surgical reasons and increased continuously in the postoperative course (platelet count and hemoglobin on day 7:441 +/- 74 x 10(3)/microL and 7.2 +/- 1.1 g/dL, respectively). Free hemoglobin was not enhanced in the postoperative course (mean value during the test period: 18.8 mmoL/L). Histologic examination of the organs did not demonstrate any infarctions of internal organs other than typical operative sequelae such as chronic pericarditis and some degree of atelectasis of the left lungs. These results demonstrate that the microdiagonal pump may be a promising alternative to the currently used ventricular assist devices, if long-term trials support these results.

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. The latter part of the article covers the rotary pump category from cardiopulmonary bypass applications to implantable systems, including specific design aspects of radial, diagonal and axial pumps.

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. The version of the appliance providing the best technical advantages was developed to the stage of practical application in patients.

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. Free hemoglobin levels and PLT count for each shear rate were detected. In all animals (A-F), hemolysis increased significantly between the shear rates of 2325 and 3100/s (P < 0.05) and the mean PLT count dropped immediately (contact, low shear) 40% in the beginning, between the shear rates of 0 and 775/s (P < 0.05). PLT count increased slightly as soon as hemolysis started. At higher shear rates, hemolysis increased and PLTs reduced further. Precise counting of PLTs indicates that PLTs are consumed dramatically at very low shear (by contact) and further by applied mechanical stress when hemolysis is obvious. A repetition of these tests with human blood could indicate species differences.

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. This pump is a miniaturized rotary blood pump with a diameter of only 6.4 mm and a weight of 11 g. The inner volume of the pump is limited to 12 mL, and the inner artificial blood contacting surface is 65 cm(2). The pump consists of a rotor driven by an incorporated brushless direct current motor, the housing of the rotor, the inflow cage, the outflow cannula, and the driveline. At the maximum speed of 32,500 rotations/min, a flow of 6 L/min can be delivered. The inflow and outflow conduit were anastomosed to the right atrium and the main pulmonary artery, respectively. Hemodynamic and echocardiographic data as well as blood samples were measured over the whole test period of 7 days. The hearts and lungs as well as the pump were explanted for a thorough examination at the end of the trial. Systemic arterial blood pressures remained unchanged during the entire test period. RV cardiac output was diminished significantly as demonstrated by the echocardiographic studies. The number of platelets decreased perioperatively, but recovered within the test period. The free hemoglobin was not enhanced postoperatively indicating no significant hemolysis. Liver function was only slightly impaired due to operative reasons (increase in bilirubin on the first postoperative day but normalization within the test period). The pathologic examination revealed some clots at the inflow cage and fibrin depositions on the impeller as well as on the inner surface of the outflow graft without an impairment of pump function. Our results demonstrate that this newly developed microaxial blood pump is a promising device for RV support, but it cannot be driven without any anticoagulation.

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. We evaluated the aortic valve-motion pattern echocardiographically in vitro after reimplantation and remodeling. METHODS: By using aortic roots of house pigs (aortoventricular diameter, 22 mm) a Yacoub procedure (22-mm graft; group Y, n = 5) or a David I procedure (24-mm graft; group D, n = 5) was performed. Roots after supracommissural replacement (22-mm graft; group C, n = 5) served as control valves. In an electrohydraulic, computer-controlled pulse duplicator the valves were tested at flows of 2, 4, 7, and 9 L/min. Echocardiographically assessed parameters were rapid valve-opening velocity, slow valve-closing velocity, rapid valve-closing velocity, rapid valve-opening time, rapid valve-closing time, ejection time, maximum valve opening, slow valve-closing displacement, and maximum flow velocity. RESULTS: Mean rapid valve-opening velocity and mean rapid valve-closing velocity at a cardiac output of 2 to 9 L/min were fastest in group D (rapid valve-opening velocity: 69 +/- 10 cm/s [group D] vs 39 +/- 4 cm/s [group Y] vs 42 +/- 4 cm/s [group C], P = .0041; rapid valve-closing velocity: 22 +/- 2 cm/s [group D] vs 16 +/- 2 cm/s [group Y] vs 17 +/- 1 cm/s [group C], P = .0272), and slow valve-closing velocity was slowest in group D (0.2 +/- 0.1 cm/s [group D] vs 1.0 +/- 0.3 cm/s [group Y] vs 0.6 +/- 0.1 cm/s [group C], P = .0063). With increasing cardiac output, the difference in rapid valve-opening velocity between the groups increased, the difference in slow valve-closing velocity remained unchanged, and the difference in rapid valve-closing velocity decreased. CONCLUSIONS: In this standardized experimental setting remodeling of the aortic valve provides significantly smoother valve movements. This might contribute to preservation of a better valve performance during long-term follow-up.

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. For the MicroDiagonal Pump (MDP), still under development at Helmholtz-Institute in Aachen, Germany, different pump configurations have been analyzed, both numerically and experimentally. The CFD model of the pump has been successfully validated based on the comparison of the pressure head curves (H-Q curves), as discussed in a prior publication. In the present study, the authors focus on the development of a semiempiric blood damage model using the CFD and in vitro hemolysis data. On the one hand, mean key characteristics (shear stress and exposure time) and other characteristics affecting blood damage have been calculated based on numerical data. On the other hand, in vitro hemolysis tests have been accomplished in order to determine the hemolytic curves of two different pump configurations (with the same impeller but different tip clearances). Finally, a new function based on a general power law has been defined by means of the mean key characteristics. The unknown constants of the function have been determined by multidimensional regression analysis using the hemolytic curves. For the final validation of this new blood damage model, the calculated and the in vitro obtained hemolysis indices at the specific VAD operating point have been compared for all pump configurations. The comparison showed an excellent agreement, both qualitatively and quantitatively.

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 8.72 mm Hg and 13.45 mm Hg, respectively, when inserted in the new Valsalva-style graft and of 7.97 mm Hg and 12.94 mm Hg, respectively, when inserted in the standard graft. The closure and leakage volumes for mechanical valves were higher than those for biologic valves; however, the presence or absence of sinuses did not result in significant differences in closure and leakage volumes. The maximal total energy losses were 5.89% and 9.49% for mechanical and biologic valves, respectively. No differences were evident between the two different Dacron grafts for each prosthetic heart valve. CONCLUSION: The normal opening and closing behavior of a prosthetic aortic valve was not altered or modified by a different root shape above the heart valve. The presence of vortices inside the pseudosinuses of Valsalva did not influence the hydrodynamic properties of the biologic and mechanical valves tested.

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. Hydrodynamic bearings for magnetically coupled rotors may offer an alternative solution to this problem. Additionally, for miniature pumps, the load capacity of hydrodynamic bearings scales slower than that of, for example, magnetic bearings because of the cube-square-law. A special kind of hydrodynamic bearing is a spiral groove bearing (SGB), which features an excellent load capacity. Mock-loop tests showed that SGBs do not influence the hydraulic performance of the tested pumps. Although, as of now, the power consumption of the SBG is higher than for a mechanical pivot bearing, it is absolutely contact-free and has an unlimited lifetime. The liftoff of the rotor occurs already at 10% of design speed. Further tests and flow visualization studies on scaled-up models must demonstrate its overall blood compatibility.

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. Both present compact designs, reduced surface and priming volumes and easier handling. HEXMO is a miniaturized extracorporeal membrane oxygenator. The integration of a small rotary blood pump into the centre of the oxygenator reduces the amount of tubing and connectors in the system. Blood is convectively warmed by the pump motor housing, thus, the use of a heat-exchanger can be avoided. This compact design reduces surface and priming volume and allows better handling, especially in critical situations. A second development is the intravascular oxygenator HIMOX, which is inserted directly into the vena cava. Priming volume and blood contact surface are reduced, as well as infection risk and control needs for the patient. A new cross-flow fibre configuration is used for improving gas transfer within the limited space inside the vena cava. A microaxial blood pump is integrated into the device for compensating the pressure drop across the fibres and allowing venous return and physiological pressure in the organs proximal to the oxygenator.

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. In vitro testing and numerical simulation techniques (computational fluid dynamics [CFD]) were applied to achieve a comprehensive overview. Pressure-flow charts were experimentally measured in a mock loop in order to validate the CFD data. In vitro hemolysis tests were performed at the main operating point of each impeller design. General flow patterns, pressure-flow charts, secondary flow rates, torque, and axial forces on the impeller were calculated by means of CFD. Furthermore, based on streak line techniques, shear stress (stress loading), exposure times, and volume percentage with critical stress loading have been determined. Comparison of CFD data with pressure head measurements showed excel-lent agreement. Also, impressive trend conformity was observed between in-vitro hemolysis results and numerical data. Comparison of design variations yielded clear trends and results. Design C revealed the best hydraulic and hemolytic properties and was chosen as the final design for the mixed-flow rotary blood pump.