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.     

计算流体动力学在叶轮式心脏泵中的应用研究

造成溶血、血栓等血液破坏现象的内在原因之一是血液的动力学行为。研究表明，不规则的流动模式尤其是切变流中产生的机械切应力直接导致血液的破坏。计算机技术的迅速发展使得微观动力学的数值模拟成为可能。本文针对基于流线型设计的叶轮心脏泵和直叶片叶轮心脏泵，应用计算流体动力学对其内部的流动行为进行了数值模拟。分析两种心脏泵的内流场和切应力分布，认为在相同的边界条件下，流线型设计的叶轮心脏泵要比直叶片心脏泵更符合血液动力学的要求，对血液的破坏较小。     

Durability improvement of polymer chamber of pulsatile extracorporeal life support system in terms of mechanical change

Twin Pulse Life Support, T-PLS™ has received the CE mark (2003) and Korea Food and Drug Administration (KFDA) approval (2004) for short-term application as an Extracorporeal Life Support system (ECLS). T-PLS’s original intention was to apply for not only short-term but also long-term application such as Extracorporeal ventricular assist device (VAD). Hence, a long-term durability test was conducted. The 1-year reliability of the systems tested in this study did not meet the STS/ASAIO standard of 80% reliability with 60% confidence for a 1-year mission life. However, without the disposable units, which are only designed to operate for 6 h, the 1-year reliability exceeded the STS/ASAIO standard of 80% reliability with 60% confidence. In this study, by using the existing analysis methods and analyzing the root cause of the failure used by a numerical analysis. As eliminating or mitigating of the root cause of the failure, we improved the durability of blood chamber and evaluated the performance of the modified system via the hemolysis test.     

新型MAO钛基生物材料的血液相容性研究

目的初步评价新型钛基材料的血液相容性。方法采用新西兰大白兔新鲜全血,抗凝后分别与实验组和阳性对照、阴性对照组接触,用紫外-可见光分光光度计比色,评价各组的溶血率。实验符合国际化标准组织规定要求。结果新型微弧氧化钛基材料直接接触溶血率为0.79％,符合医用材料的溶血率不大于5％的要求。结论新型钛基材料具有良好的血液相容性。     

珊瑚涂层人工骨的制备及溶血实验研究

目的根据生物工程及化工等原理,制备珊瑚人工骨,并检测此珊瑚(Coral)复合人工骨的血液相容性。方法将制备的珊瑚复合人工骨、按照国际标准化组织和我国国家标准规定要求,采用将珊瑚复合人工骨及其浸提液与抗凝稀释兔血直接接触,测定红细胞释放的血红蛋白量(OD值),将测得的OD值换算为溶血率。结果珊瑚复合人工骨材料浸提液组的溶血率为1．81％,材料与血液直接接触组溶血率为1．41％,阴性对照组和阳性对照组溶血率分别为0％、100％。结论珊瑚复合人工骨材料无溶血作用,血液相容性良好。     

Scaling of Hemolysis in Needles and Catheters

Hemolysis in clinical blood samples leads to inaccurate assay results and often to the need for repeated blood draws. In vitro experiments were conducted to determine the influence on hemolysis in phlebotomy needles and catheters of pressure difference, cannula diameter, and cannula material. Fresh blood from five human volunteers was forced from a syringe inside a pressurized chamber through 14, 18, and 22 gauge 304 stainless steel needles and polyurethane and Teflon^® catheters, all 40 mm long. Hemolysis was measured in the samples by a spectrophotometer. It was found that hemolysis increased with increases in pressure difference and cannula diameter and no consistent trend could be identified with regard to cannula material. The pressure differences required for significant hemolysis were above those typical of clinical venipuncture blood draws. While there was substantial variability among individuals, the hemolysis values scaled with exponent S=(t/t₀)[( / ₀)–1]², where t is the characteristic duration of shear, t₀ is a time constant, is the wall shear stress, and ₀ is the wall shear stress threshold below which no hemolysis occurs. A hemolysis threshold including both time and shear stress was also defined for S=constant. The threshold implies that a threshold shear stress exists below which erythrocytes are not damaged for any length of exposure time, but that red cells may be damaged by an arbitrarily short period of exposure to sufficiently large shear stress. © 1998 Biomedical Engineering Society. PAC98: 8745Hw, 8722-q     

探讨血小板计数在血泵离体实验中的意义

为了探讨血小板计数在血泵离体实验中的意义。我们用两种滚压泵分成两组，作5对16小时离体长时间转流实验，血样本为转前作对照组、转流4h后每隔2h抽1次。测定项目：血小板计数、游离血红蛋白。结果：两组血小板计数值均随转流时间延长而呈线性逐渐增加，各时点值与前时点比（P＜0．05），有显著差异，两组游离血红蛋白量也随转流时间延长而呈线性增加。血小板计数与游离血红蛋白呈直线回归相关关系。结论；在血泵离体转流实验中，血小板计数可反映血细胞碎片的数量，因此可作为一项评价血泵离体溶血性能的客观指标。     

Mechanical White Blood Cell Damage in Rotary Blood Pumps

Abstract: Mechanical trauma of white blood cells (WBC) due to the operation of a rotary blood pump was examined, using a simple method of trypan blue dye exclusion test for a cell viability measurement. The degree of WBC trauma was investigated using a roller pump (RP) and 3 commercially available centrifugal pumps (Bio-Medicus [BP], Capiox [CP], Nikkiso [NK]), and compared with the red blood cell (RBC) trauma. Each pump was operated 3 times at a flow rate of 5 L/min against the total pressure head of 350 mm Hg for 6 h in a mock circuit with 400 ml of fresh bovine blood. Blood was sampled at 2 h intervals measuring plasma free hemoglobin concentration and the percentage of damaged WBC in the trypan blue dye exclusion test. Each pump demonstrated a linear increase in the degree of WBC trauma, and there were differences among the tested pumps (RP > BP > CP > NK). These findings were similar to those of the free hemoglobin measurements. To compare the degree of RBC and WBC trauma, the probability (γ,ω) of RBC and WBC to be damaged was calculated, respectively.
γ=δ D_RBC δAN , ω =δ D_WBC δAN
where D_RBC and D _WBC are the ratios of the damaged RBC and WBC, respectively, and N is the passing number defined as Qt/V (Q , flow rate; t , time; V , circulating volume). The data of this study demonstrated that the ω value was approximately 20 times or more greater than the γ equally in all the tested pumps. This suggests that a WBC is more vulnerable to mechanical damage by a rotary blood pump than a RBC.     

Effects of Self Washout Structure on the Antithrombogenicity and the Hemolytic Properties of a Centrifugal Pump

Abstract: Antithrombogenicity in an initial type (Nl) of a centrifugal pump (CP) developed in our institute is provided by the central balancing hole of an impeller. A new CP (N2) was modified to obtain better antithrombogenicity, in which the balancing hole was widened to improve self washout flow velocity (Vsf), and an edge of the thrust bearing was rounded off to minimize flow separation. Effects of the modifications were assessed in vitro and in vivo studies. The Vsf of the Nl and the N2 evaluated by a Doppler velocimeter were 12.8 and 22.1 cm/s, respectively. Flow around the thrust bearing, which was visualized by a light cutting method, confirmed less flow stagnation in the N2. The hemolytic indices of the Nl and the N2 were 0.023 and 0.008 mg/dl, respectively. In vivo antithrombogenicity and the hemolytic properties of the N2 and the Nl were investigated without anticoagulation therapy in 3 goats. In each goat the N2 was driven for 1 week and exchanged for the Nl, which was driven for the same period. Red thrombi at the thrust bearing were found in 2 Nls, and 2 small thrombi were on the impeller of another Nl, whereas a thrombus of less than 1 mm³ at the TB was noted in 1 N2. Plasma free hemoglobin was not increased in either CP. These results indicate that the N2 has better antithrombogenicity and hemolytic properties than the Nl.     

Toxicological properties of surfactants

Surfactants are of considerable importance in the field of detergents and in cosmetics. Of the anionic, nonionic, and cationic surfactants the most important products — as far as sales volume is concerned — belong to the anionic type. Anionic and nonionic surfactants taken orally are of low toxicity according to acute toxicity tests as well as long term studies, while certain cationics are moderately toxic. In local application, compatibility with skin and mucous membranes is strongly dependent on concentration. Surfactant action on biological systems can largely be explained on the basis of physico-chemical properties of the surfactants. Some surfactants show pharmacological activity.