Computational flow study of the continuous flow ventricular assist device, prototype number 3 blood pump

A computational fluid dynamics study of blood flow in the continuous flow ventricular assist device, Prototype No. 3 (CFVAD3), which consists of a 4 blade shrouded impeller fully supported in magnetic bearings, was performed. This study focused on the regions within the pump where return flow occurs to the pump inlet, and where potentially damaging shear stresses and flow stagnation might occur: the impeller blade passages and the narrow gap clearance regions between the impeller-rotor and pump housing. Two separate geometry models define the spacing between the pump housing and the impeller's hub and shroud, and a third geometry model defines the pump's impeller and curved blades. The flow fields in these regions were calculated for various operating conditions of the pump. Pump performance curves were calculated, which compare well with experimentally obtained data. For all pump operating conditions, the flow rates within the gap regions were predicted to be toward the inlet of the pump, thus recirculating a portion of the impeller flow. Two smaller gap clearance regions were numerically examined to reduce the recirculation and to improve pump efficiency. The computational and geometry models will be used in future studies of a smaller pump to determine increased pump efficiency and the risk of hemolysis due to shear stress, and to insure the washing of blood through the clearance regions to prevent thrombosis.     

Hemolytic performance of a MagLev disposable rotary blood pump (MedTech Dispo): effects of MagLev gap clearance and surface roughness

Mechanical shaft seal bearing incorporated in the centrifugal blood pumps contributes to hemolysis and thrombus formation. In addition, the problem of durability and corrosion of mechanical shaft seal bearing has been recently reported from the safety point of view. To amend the shortcomings of the blood-immersed mechanical bearings, a magnetic levitated centrifugal rotary blood pump (MedTech Dispo Model 1; Tokyo Medical and Dental University, Tokyo, Japan) has been developed for extracorporeal disposable application. In this study, the hemolytic performance of the MedTech Dispo Model 1 centrifugal blood pump system was evaluated, with special focus on the narrow blood path clearance at the magnetic bearing between rotor and stator, and on the pump housing surface roughness. A pump flow of 5 L/min against the head pressure of 100 mm Hg for 4 h was included in the hemolytic test conditions. Anticoagulated fresh porcine blood was used as a working fluid. The clearance of blood path at the magnetic bearing was in the range of 100-250 micro m. Pump housing surface roughness was controlled to be around Ra = 0.1-1.5 micro m. The lowest hemolytic results were obtained at the clearance of 250 micro m and with the polished surface (Ra = 0.1 micro m) yielding the normalized index of hemolysis (NIH) of less than 0.001 g/100 L, which was 1/5 of the Biopump BP-80 (Medtronic Inc., Minneapolis, MN, USA, and 1/4 of the BPX-80. In spite of rough surface and narrow blood path, NIH levels were less than clinically acceptable level of 0.005 g/100 L. The noncontact, levitated impeller system is useful to improve pump performance in blood environment.     

Testing of extracorporeal membrane oxygenation circuit related hemolysis using long-term stored packed red cells and fresh frozen plasma

BACKGROUND: The resistance of blood used in these studies to hemolysis differs markedly from that used in neonatal extracorporeal circulation under clinical circumstances. In this study, the possibility of using expired packed red cells to determine hemolysis caused by mechanical and/or environmental factors was investigated. METHODS: Packed red blood cells stored for 42 days were mixed with fresh frozen plasma and the resultant mixture was divided into three groups, two study groups and a control. For the study groups, two different centrifugal pump heads (Medtronic BP 50 and Jostra RF 32) were used in an extracorporeal membrane oxygenation (ECMO) circuit. Free hemoglobin, lactate dehydrogenase, lactic acid, pH, potassium, and glucose were investigated at various time intervals. RESULTS: Hemolysis did not differ between the groups. Free hemoglobin increased in all groups after 12 h. Lactic acid increased linearly in all groups up to 12 h. Glucose and pH decreased steadily in all groups. Hemolysis created during mock ECMO did not differ between the circuits using the two different pump heads noted. CONCLUSION: Human donor blood stored up to its expiration date is a feasible medium for mock circulation tests of up to 12 h duration under the circumstances described.     

Fast three-dimensional numerical hemolysis approximation

The in vivo implantation of a mechanical device contributes to hemodynamic disturbances, which are responsible for damage to the membranes of red blood cells that in turn can lead to their rupture (hemolysis). It is important to ascertain at the design stage of such mechanical devices that they are innocuous to blood. Because there is no in vivo hemolysis index, we concentrated our efforts on the in vitro hemolysis index of the American Society for Testing and Material (ASTM) standard. We present in this work a framework for minimizing medical device-induced hemolysis by the development of a numerical method for predicting hemolysis similar to that used in in vitro experiments. The method is based on a novel interpretation of the Giersiepen-Wurzinger blood damage correlation that replaces the computation of blood damage along the streamline by a volume integration of a damage function over the computational domain. We assess the behavior and accuracy of this methodology with 3D examples.     

Development of Design Methods for a Centrifugal Blood Pump with a Fluid Dynamic Approach: Results in Hemolysis Tests

The purpose of this study was to examine the relationship between local flow conditions and the hemolysis level by integrating hemolysis tests, flow visualization, and computational fluid dynamics to establish practical design criteria for centrifugal blood pumps with lower levels of hemolysis. The Nikkiso centrifugal blood pump was used as a standard model, and pumps with different values of 3 geometrical parameters were tested. The studied parameters were the radial gap between the outer edge of the impeller vane and the casing wall, the position of the outlet port, and the discharge angle of the impeller vane. The effect of a narrow radial gap on hemolysis was consistent with no evidence that the outlet port position or the vane discharge angle affected blood trauma in so far as the Nikkiso centrifugal blood pump was concerned. The radial gap should be considered as a design parameter of a centrifugal blood pump to reduce blood trauma.     

A preliminary study of microcapsule suspension for hemolysis evaluation of artificial organs

A microcapsule suspension, a substitute for animal blood in hemolysis tests, has been developed for evaluation of the absolute hemolytic properties of circulatory artificial organs. The microcapsule suspension was made by dispersing microcapsule slurry into an ethylene glycol sodium chloride solution. The microcapsule slurry was composed of a leuco dye solution and polyurethane membrane made by the reaction between aliphatic poly-isocyanate and polyamine by interfacial polycondensation. The microcapsule was a small particle containing dye inside. The microcapsule suspension was white; the diameter of the microcapsules was from 5 to 100 microns. The specific gravity of the suspension was 1.024, and the membrane was elastic. The fluid showed Newtonian characteristics, different from animal blood, and its viscosity was approximately 5.8 mPa.s. After the microcapsules were destroyed, the leuco dye was extracted with n-hexane from the suspension and was measured by spectroscopy after being colored with acid ethanol. Hemolysis can be regarded as a fatigue fracture of cell membranes rather than a static fracture. The destruction of microcapsules by a Potter type tissue grinder was observed at a low stroke number region and was compared to rat blood. Moreover, hemolysis tests of a commercially available centrifugal blood pump and the prototype of our centrifugal pump for mechanism checks were carried out with bovine blood. The hemolysis level of the prototype pump increased with time while the hemolysis level of the commercial blood pump did not change as much as that of the control when both pumps were tested with the microcapsule suspension. These results are similar to tests utilizing bovine blood. Therefore, hemolysis tests of circulatory artificial organs completed with microcapsule suspension are expected to provide results similar to tests with animal blood.     

Die Beziehungen von Kalium und Hämoglobin im Verlauf der osmotischen Hämolyse

Zusammenfassung Venöses, mit Heparin ungerinnbar gemachtes Blut (Vollblut oder Erythrocyten) von 22 Kindern wurde durch Zusatz ansteigender Mengen Aqua bidest stufenweise hämolysiert. Aus dem Hämolysat wurden Kalium- und Hämoglobinkonzentrationen zueinander in Beziehung gesetzt. Es ergab sich eine typische sigmaförmige Hämolysekurve mit engen Beziehungen zwischen Kalium und Hämoglobin. Die Beziehung des prozentualen Anstiegs von Kalium und Hämoglobin wurde durch Anwendung quadratischer Funktionen untersucht.Zu Beginn der Hämolyse ist der Anstieg der Kaliumkonzentration größer als der der Hämoglobinkonzentration. Diese Differenz nimmt mit zunehmender Hämolyse ab. Diese Ergebnisse stimmen mit der Vorstellung eines prolytischen Kaliumverlusts bei der osmotischen Hämolyse überein. Die Erythrocytenmembran wird für Kationen bereits durchgängig, bevor Hämoglobin austreten kann.Mit Hilfe der quadratischen Funktion y=a+bx+cx ² lassen sich die Beziehungen zwischen Kalium und Hämoglobin in jedem Stadium der Hämolyse beschreiben. Damit ist eine Methode angegeben, mit deren Hilfe eine erhöhte Kaliumkonzentration im hämolytischen Serum korrigiert werden kann. Hierzu ist die Bestimmung von Kalium- und Hämoglobinkonzentration sowohl der Erythrocyten oder des Vollbluts als auch des hämolytischen Serums erforderlich. Ein solcher Aufwand wird sich jedoch nur in wenigen Situationen lohnen. Im allgemeinen wird es einfacher sein, die Serum-Kalium-Bestimmung zu wiederholen.

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Potassium and hemoglobin interrelation during osmotic hemolysis

Heparinized venous blood (whole blood or erythrocytes) of 22 children is stepwise hemolized by adding increasing amounts of distilled water. potassium and hemoglobin concentrations are determined in the supernatant fluid and their interrelation studied, expressed as percentage of whole blood and erythrocyte concentration. The hemolysis curve is sigma shaped and shows a close correlation between potassium and hemoglobin. A quadratic equation is used to further investigate the interrelation between the increase in potassium and hemoglobin.With minimal hemolysis the increase in potassium concentration is greater than that in hemoglobin concentration. The difference, however, diminishes with increasing hemolysis. These results are in agreement with the concept of a prolytic potassium loss during osmotic hemolysis. The membrane of the erythrocyte is already permeable for cations before hemoglobin can extravasate.The movements of potassium and hemoglobin follow the function y=a+bx+cx ² in every stage of hemolysis. Thus an increased potassium concentration in the serum due to hemolysis can be corrected. This, however, requires a potassium and hemoglobin determination in erythrocytes (or whole blood) and in the hemolytic serum.

     

Hemolytic pattern of erythrocytes in the newborn measured by the coil planet centrifuge system and its relationship to neonatal jaundice

Dynamic osmotic fragility of erythrocytes in cord blood and its changes during the neonatal period were studied by means of a coil planet centrifuge system. The starting-point for hemolysis in the newborn become similar to that of adult blood after approximately a week, while the shift of the end-point to the adult range required one month or more.The percentage of fragile cord blood cells with a hemolysis starting-point above 110 m osmol and the maximum bilirubin level during neonatal period were examined. A high percentage of fragile cells was associated with high bilirubin levels, and when fragile cells comprised more than 7.0% of the total cord blood erythrocytes, the bilirubin level tended to rise above 15 mg/dl.This study was aided by a grant from the Ministry of Health and Wellfare of Japan for research on handicapped children, 1976     

Gap velocity measurements of a blood pump model

This paper presents the velocity measurements in the gap between the impeller and the pump casing of a 5:1 enlarged centrifugal blood pump model at operating condition. Both the radial and tangential velocity at the gap were measured. It was found that there was no cross flow in both the radial and tangential velocity distributions at the seven radial locations. This implies that the 0.2 mm gap in the prototype should be the optimal clearance of the pump. The vector plot of the resultant velocity showed that the double volute design of the pump, especially the splitter plate that started at theta; = 180 degrees, has created a washout mechanism in the clearance gap; that is, a sector of flow ranging from theta; = 100 degrees to theta; = 190 degrees has directed strongly toward the eye while the rest of the flow in the gap is in a tangential direction. It is important that the blood should flow out of the gap through the eye instead of continuing to circulate in the clearance gap. This explains why the pump has minimum hemolysis and thrombus formation and is able to function with nominal efficiency as compared to other centrifugal pumps.     

Chronic evaluation of the Cleveland Clinic CorAide left ventricular assist system in calves

The Cleveland Clinic CorAide left ventricular assist system is based on a third-generation, implantable, centrifugal pump in which a rotating assembly is suspended fully. To evaluate chronic in vivo system performance and biocompatibility, the CorAide blood pump was implanted in 18 calves for either 1 month or 3 months. Hemodynamics were stable in all calves with a mean pump flow of 5.9 +/- 1.2 L/min and a mean systemic arterial pressure of 98 +/- 5 mm Hg. There were no incidences of bleeding, organ dysfunction, or mechanical failure in any of the 18 calves. Hemolysis occurred in only 1 calf due to outflow graft stenosis. Thrombus inside the pump, seen in 4 of the first 6 cases, was totally eliminated by a final redesign in the remaining cases, including the last 6 implants conducted without anticoagulation therapy. The CorAide blood pump demonstrated good biocompatibility and reliable, effective system performance.