三种叶片式血泵的体外溶血试验研究

血泵对血液的破坏程度是衡量血泵性能的一个重要指标。本文针对三种叶片式血泵即离心泵、轴流泵、混流泵的溶血试验做一比较分析。在试验中 ,选用了我们研制的Ⅰ型离心血泵、磁耦合型轴流血泵、螺旋混流泵。在一封闭管道中 ,注入新鲜抗凝羊血 5 0 0ml,水浴温度 37℃ ,血泵辅助流量为 5L min ,平均压力10 0mmHg,分别在泵转后 0、 0 5、 1 0、 1 5、… 4 0h测量血浆中游离血红蛋白 (FHB)和纤维蛋白原 (FIB)含量 ,最后计算出三个血泵整个过程中的标准溶血指数NIH。结果表明三种血泵对血液都有一定的破坏 ,它们的NIH值分别为 0 112 5± 0 0 15 7g 10 0L、 0 0 931± 0 0 137g 10 0L和 0 0 5 6 1± 0 0 0 5 8g 10 0L ,由此可得出混流泵对血液的破坏最小。     

应用CFD研究叶轮设计对人工心脏泵内流场的影响

溶血是叶轮血泵常见的一种血液破坏现象，而造成这种现象的内在原因是血液的动力学行为。本研究针对基于流线型设计的叶轮血泵和一种直叶片血泵，应用CFD对其内部流场进行了数值模拟，并通过溶血实验对结果进行了验证。研究结果表明，流线型叶轮血泵内的流动模式符合流线型设计理论，与直叶片叶轮血泵相比，它的溶血较小，更符合血液动力学要求。可以认为，在相同的边界条件下，流线型叶轮血泵具有更好的血液相容性，不容易造成血液破坏。     

磁驱动血泵溶血分析

测试磁驱动轴流心室辅助装置主体血泵溶血性能。利用计算流体力学(CFD)软件ANSYS,基于红细胞受到切应力和相应曝光时间的计算溶血方法预测血泵溶血性能,计算红细胞粒子随着时间推移在血泵内运动轨迹上受到破坏程度。通过体外模拟循环实验实际测试血泵体外溶血性能,计算得到血泵实际标准溶血指数。CFD计算结果转化的标准溶血指数与实际体外实验结果比较相差较大,与CFD计算简化和实际计算循环周期有很大关系。磁驱动轴流心室辅助装置主体血泵有较好的实际溶血性能,血泵实验期间无不良状况发生,可以进行进一步实验。     

混流式血泵的数值模拟及性能分析

轴流式血泵转速过高、离心式血泵容易产生流动死区是造成血液损伤的重要原因,而混流式血泵能有效缓解轴流式血泵的转速过高以及离心式血泵的流动死区问题。基于此,本研究旨在探究闭式叶轮混流式血泵的性能效果。通过数值模拟的方法对闭式叶轮混流式血泵进行数值模拟,分析该类型血泵的流场特性及压力分布情况,探讨其水力性能以及可能对红细胞造成的损伤程度,并与半开式叶轮结构混流式血泵的数值模拟结果进行性能对比。结果表明:本研究中的闭式叶轮混流式血泵具有良好的性能,能够安全高效运行。该泵在5 L/min下能够达到100 mm Hg的扬程,血泵内流动均匀,没有明显的涡流、回流以及流动停滞现象,压力分布均匀合理,可有效地避免血栓;溶血指数平均值(HI)为4.99×10^-4,具有良好的血液相容性;与半开式叶轮混流式血泵相比,闭式叶轮混流式血泵扬程和效率更高、溶血指数平均值更小,且具有更好的水力性能及避免血液损伤的能力。通过本文研究结果,或能为闭式叶轮混流式血泵的性能评价提供依据。     

磁力驱动轴流血泵溶血实验和动物实验

目的对研制开发的一种新型的磁力外驱动轴流式心室辅助血泵的血液相容性能进行测试。方法利用特制血袋作为模拟循环管道,羊血作为循环介质,采用标准溶血指数衡量体外溶血实验性能。通过3只山羊12h在体实验衡量其在体适应性。结果实验测得轴流血泵体外实验标准溶血指数(NIH)为(0.158±0.043)mg/L。3例实验动物12h在体辅助无机械故障,血泵辅助后实验动物血液中游离血红蛋白(FHb)开始上升,最高达到164.8mg/L。结论磁力外驱动轴流血泵实验结果比较理想,值得进一步改进。     

介入式微型轴流血泵溶血机理及影响因素分析

溶血性能是判别血泵是否可靠的重要评价因素之一,也是血泵研发过程中的一大难题。本文基于介入式微型轴流血泵的结构特点对其溶血发生机理和关键影响因素进行探究和综述。首先,介绍介入式微型轴流血泵的结构特点:体积小、转速高、叶轮轮缘与泵壳间隙小。然后从剪力溶血和空化溶血两个方面对溶血发生机理进行阐述。最后重点分析导致介入式微型轴流血泵机械溶血的主要力学因素,即剪力和负压。泵内剪力过大或作用时间过长会导致红细胞受损而发生溶血,而负压可能引起血泵空化从而对血液造成损伤。总之,血泵结构设计不当会导致血液在机械运动和湍流运动过程中受到高剪切应力和局部负压的作用产生溶血,所以在设计阶段应全面考虑各因素对血泵溶血的影响。     

磁液悬浮离心血泵体外溶血的实验及耐久性实验

通过建立模拟循环管路系统来研究磁液悬浮离心血泵的溶血性能及机械稳定性。建立体外模拟循环管路系统,体外溶血实验中以新鲜羊血为循环介质,调节前负荷和后负荷分别为15、100 mmHg,血泵转速设定为2 900 rpm,测定血浆游离血红蛋白含量（FHb）和红细胞压积（Hct）,计算血泵标准溶血指数（NIH）;耐久性试验其他各项设定同体外溶血实验,循环介质改为甘油水溶液。在体外溶血实验中,测得磁液悬浮离心血泵NIH值为（0.0038±0.0008）g/100L;耐久性实验中血泵连续正常运转90 d,期间无卡壳、停泵等现象,电压、电流、转速稳定。该血泵溶血性能处于较高水平,机械性能稳定可靠,满足进一步进行动物实验的要求。     

基于热流耦合的轴流式血泵温升影响因素研究

人工心脏已进入临床发展阶段，溶血现象是制约人工心脏长久使用的一大难题。不正常的温度条件会使红细胞的正常生理机能和形态发生改变，从而影响其携氧能力。为研究人工心脏正常运转时的温升情况，先利用Solidworks软件建立轴流式血泵的三维仿真模型，然后基于ANSYS Workbench软件对血泵整体进行热流耦合温度场仿真，探究了定子绕组相阻值、血泵转速、定子外壳和泵外壳之间的气隙导热系数以及血液导热系数对血泵及血液整体温升的影响。结果表明，在满足血泵供血要求的前提下，适当减小定子绕组相阻值、降低转速可有效降低血泵整体温升，而气隙物质和血液导热系数的变化对血泵整体温度的影响不是很明显。     

轴流式血泵溶血数学模型的探究

溶血的定量评价对于血泵的设计和研究十分重要,而建立血泵溶血的数学模型,对于血泵溶血的预测,提高其血液相容性具有十分重要作用.本文在分析与血泵溶血相关因素的基础上,首先从能量守恒定律确定轴流式血泵叶轮驱动力的输出功可分两部分提供给血液：用于提高血液压力的能量以及用作血液溶血的能量.然后采用动力系统转矩方程和能量方程,建立血泵辅助循环溶血模型.最终建立了能够定量评价血泵在不同工作状态下（正常状态和抽吸状态）溶血程度的数学公式.本文对轴流式血泵的溶血问题提供了新的研究思路,将对血泵及其控制系统的改进提供重要的依据.     

微型轴流血泵溶血的数值模拟

基于N-S方程和标准K-ε湍流模型,采用非结构网格技术,对微型轴流血泵内部三维流场进行了数值模拟,得到了速度场、压力场等流场细节;同时采用Lagrange粒子追踪法获得了沿不同流线的剪应力以及红细胞暴露接触时间的分布,并引入溶血计算的经验公式,计算对比了不同转速条件下血泵的溶血指标,重点分析了血泵在5L/min、8000r/min工况下的溶血性能,对于血泵溶血的估算,本方法是可行的.     

Computer assisted design for the implantable left ventricular assist device (LVAD) blood pump using computational fluid dynamics (CFD) and computer-aided design and manufacturing (CAD/CAM)

Thrombus formation and hemolysis are critical issues in the design of a long-term implantable LVAS (left ventricular assist system). The fluid dynamic characteristics of the blood flow are one of the main factors that cause thrombus formation and hemolysis. In this study, we optimized blood chamber geometry, port design, and fluid dynamics in our implantable LVAS to ensure minimization of shear-stress-related blood damage. A blood pump chamber (stroke volume, 65 ml) and an inflow and outflow port were designed with three-dimensional CAD (computer-aided-design) software (Pro-Engineering version 20) and estimated by FEM (fine-element method) computational fluid dynamic (CFD) analysis (Ansys version 5.5). We adopted three-dimensional distribution of CFD results for qualitative evaluation, and we also tried to estimate the normalized index of hemolysis (NIH) and time-series change of hematocrit from the results of CFD analysis as quantitative index of optimization for geometry of the blood pump chamber. With the use of this design, the blood pump geometry was optimized as the decrease of NIH from 2.72 g/1001 in the first model to 0.098 g/1001 in the second model, corresponding to the decrease in shear stress. The hematocrit also improved from 0.7% in the first model to 11.5% in the second model 2 years after implantation of the pump. Areas where flow stagnation was observed in the first model were free of stagnation in the second model. The results show that computer-aided design of the blood pump contributes to optimizing a blood pump chamber for reducing thrombus formation and hemolysis, and also contributes to reducing cost and time in developing the implantable LVAS.     

Flow visualization for different port angles of a pulsatile ventricular assist device

The "washout effect" inside a blood pump may depend in part on the configuration of the blood pump, including its "port angle." The port angle, which is primarily decided based on anatomical considerations, may also be important from the rheological viewpoint. In our department, a next-generation diaphragm-type blood pump is being developed. In this study, we examined the influence of the port angle on flow conditions inside our new blood pump. Acrylic resin mock pumps with three different port angles (0°, 30°, and 45°) were prepared for flow visualization. Mechanical monoleaflet valves were mounted on the inlet and outlet ports of the mock pumps. Flow conditions within the mock pumps were visualized by means of particle image velocimetry during a half stroke. As a result, a high flow velocity region was seen along the main circular flow from the inlet to the outlet port. This circular flow was almost uniform and parallel to the plane of the diaphragm-housing junction (DhJ) when viewed from the inlet and outlet sides. Moreover, the proportion of high flow velocity vectors in the plane in the vicinity of the DhJ decreased as the degree of the port angle increased. In conclusion, we found that the flow behavior in the plane in the vicinity of the DhJ changed with the port angle, and that a port angle of 0° may be suitable for our diaphragm-type blood pump in view of the washout effect.     

The effect on hemolysis of the raceway profile of roller pumps used in cardiopulmonary bypass

This study aims at the influence on hemolysis of the differences between the maximum and minimum amplitudes of pressure in the outlet of three roller pump models adjusted by dynamic calibration method. Tests were performed with silicone tubes (? × (3)/(16) inches) in fluid analogous to blood and fresh bovine blood from slaughterhouse. Tests with analogous solution to blood were performed varying the dynamic calibration pressure between 78 and 500 mm Hg. Tests with fresh bovine blood were performed with the three pumps simultaneously, and pressure differences and free hemoglobin in the plasma were measured during 360 minutes. Tests with both analogous solution to blood and fresh bovine blood showed differences of mean pressures of pump 2 related to pumps 1 and 3 (p < 0.01). The different models of roller pumps analyzed presented differences in pressure amplitudes (p < 0.01) and hemolysis (p < 0.01) adjusted for the same dynamic calibration pressure. Raceway profile of pump 2 resulted in smaller pressure amplitude, implying lower hemolysis rate compared with pumps 1 and 3.     

Erythrocyte Fragment Count Predicts Hemolysis in Roller Pumps

Objective： Hemolysis in blood pumps has been measured by various in vitro test methods, in which normalized index of hemolysis （NIH） was established. As NIH is complicated and difficult to calculate, erythrocyte fragment count is proposed in the present study to predict hemolysis in roller pumps. Methods： Five paired in vitro tests were conducted using the POLYSTAN pediatric pump（group A） and COBE pump（ group B）. Ten whole blood samples （400 ml ） were circled in the roller pump for 16 h. Erythrocyte fragments count and plasma-free hemoglobin （FHb） were measured before pumping and every two hours through circulation after four-hour-pumping. The morphological changes of erythrocyte were observed by scanning electron microscope. Results： The two groups＇ EFC and FHb levels were increased linearly during a long duration of pumping and linear regression of erythrocyte fragments count and plasma-free hemoglobin were correlated. Conclusion： Erythrocyte fragments count could be used as an index in evaluating the in vitro hemolytic properties of blood pumps.     

Performance of a newly developed implantable centrifugal blood pump

The performance of the newly developed implantable centrifugal blood pump was investigated in vitro. The pump was developed with the end goal of building a versatile system that includes a left ventricular assist system with an internal secondary battery or an implantable biventricular assist system with two implantable blood pumps. The hydrodynamic characteristics and efficiency of the blood pump were evaluated, and the mechanical damage to the blood caused by the blood pump was assessed through a hemolysis test using fresh goat blood. The pump could generate 120 mm Hg at a flow rate of 5 L/min and a motor speed of 2,500 rpm. The electric input power to the pump was approximately 5 watts under these working conditions. The hemolysis caused by the pump was a bit higher than that by the former model, but stayed within an acceptable range. Performance of the pump in vitro was considered sufficient for a left ventricular assist device, although further design improvement is necessary in terms of hemolysis and system efficiency to improve biocompatibility of the pump.     

血细胞碎片计数评价滚压泵溶血的意义

探讨血细胞碎片计数在血泵离体实验中的意义.分别采用POLYSTAN和COBE滚压泵,对血样本各作5次16 h离体长时间转流实验.转流前血样本作对照组、转流后4 h第1次抽取血标本,以后每隔2 h抽取1次血标本.检测指标:血细胞碎片计数、游离血红蛋白和红细胞形态学电镜观察.结果发现:分别用两种滚压泵转流后,血细胞碎片计数值均随转流时间延长而呈线性逐渐增加,各时点值与前一时点相比,有显著差异(P＜0.05).两组游离血红蛋白量也随转流时间延长而呈线性增加.血细胞碎片计数与游离血红蛋白呈直线回归相关关系.红细胞形态学电镜观察亦表明,转流时间越长,红细胞损伤越严重.实验结果提示,在滚压式血泵离体转流实验中,血细胞碎片计数可以作为一项评价血泵离体溶血性能的方便、客观指标.     

血泵溶血的研究进展

国内外研究人员为克服溶血问题做了大量的工作,对血泵溶血性能作出了评价标准,通过利用实验和仿真手段对可能造成溶血的因素,如血泵结构、叶轮参数、血泵材料、血泵流场分布等做了很多的研究,分析了这些因素与血泵溶血的关联性,从而为在一定程度上解决血泵的溶血问题找到了方法。我们对目前血泵溶血的研究进行了综述。     

Hemodialysis using a valveless pulsatile blood pump

Research on pulsatile blood pumps for extracorporeal life support has been widely performed because of the proven advantageous effects of blood pulsation. However, studies on the use of pulsatile blood pumps for hemodialysis are limited, although available evidence demonstrates that pulsatile blood flow has a positive influence on dialysis outcome. Therefore, the authors designed a new pulsatile pump, which is characterized by minimal-occlusion of blood-containing tubing, no requirement for valves, and no blood flow regurgitation. In-vitro hemolysis tests were conducted using fresh bovine blood, and the normalized index of hemolysis was adopted to compare blood traumas induced by the devised pulsatile pump and a conventional roller pump. In addition, experimental hemodialyses with a canine renal failure model were performed using the devised pump. Normalized index of hemolysis levels obtained was much smaller for the devised pulse pump (45 +/- 21 mg/100 L) than for the roller pump (103 +/- 10 mg/100 L), and no technical problems were encountered during dialysis sessions. Blood and dialysate flow rates were maintained at predetermined values and molecular removal was satisfactory. Postdialysis urea and creatinine reduction ratios were 61.8% +/- 10.6% and 57.4% +/- 9.0%, respectively. Pulsatile flow has usually been generated using pulsatile devices containing valves, but the valves cause concern in terms of the clinical applications of these devices. However, the described pulsatile pump does not require valves, and yet no blood flow regurgitation was observed.     

Terumo implantable left ventricular assist system: results of long-term animal study

The research group of Terumo Corporation, NTN Corporation, and the Setsunan University have been developing an implantable left ventricular assist system (T-ILVAS) featuring a centrifugal blood pump with a magnetically suspended impeller (MSCP). The present study describes results of chronic animal experiments using the MSCP. The MSCP has been tested ex vivo and in vivo in 6 sheep as a left heart bypass between the left ventricular apex and descending aorta. Ex vivo chronic sheep experiments using Model I demonstrated long-term durability, nonthrombogenicity, low hemolysis (<6 mg/dl), and excellent stability of the magnetic bearing with long-term survival for up to 864 days. Average pump flow rate was 4 L/min at a fixed rotational speed of 2000 rpm. Power spectral analyses of heart rate, aortic pressure, and blood temperature maintained normal 1/f fluctuation during the study. The retrieved pump was completely free from thrombus formation and there was no evidence of infarct in major organs. The implantable Model II was evaluated ex vivo in two sheep and intra-thoracically implanted in a sheep. These experiments were terminated at 70, 79, and 17 days due to blood leakage through the connector system within the housing. No thrombus formation was observed in any of the retrieved pumps. A modified Model II with a new connector system was subsequently intra-thoracically implanted in a sheep. The sheep survived for 482 days without any sign of thromboembolic complication or hemolysis at a fixed rotational speed of 1700 rpm and an average pump flow rate of 5 L/min. There was no intra-device thrombus formation or infarct in major organs. The Model III system, consisting of an implantable controller and a new MSCP with a reduced input power of 13 W, has been developed and implanted in a chronic sheep model. The MSCP was implanted in the left pleural space and the controller in the abdominal wall. The experiment is still in progress for more than 30 days without any significant complication to date. These animal studies strongly suggest the feasibility of the MSCP for use as long-term circulatory assist.     

基于CFD的离心式人工心脏泵的溶血预测方法

溶血的定量评价对于人工心脏泵的设计和研究十分重要.本研究应用CFD（computational fluid dynamics）技术,针对两种叶轮设计的离心血泵进行了数值模拟,计算得到了其内部的流线分布.根据溶血、切应力和暴露时间三者之间的幂函数模型,对血泵的溶血进行了预测.最后,用溶血实验结果进行了验证.结果表明,在相同的边界条件下,流线型叶轮泵内的溶血值要小于直叶片叶轮泵,与溶血实验结果一致.可见,应用CFD实现溶血的定量计算是可行的,溶血、切应力和暴露时间之间的幂函数模型能较好地反映血泵的溶血性能.