A New Blood Pump for Cardiopulmonary Bypass: The HiFlow Centrifugal Pump

Abstract: Centrifugal blood pumps are considered to be generally superior to the traditionally used roller pumps in cardiopulmonary bypass. In our institute a new lightweight centrifugal sealless blood pump with a unique spherical thrust bearing and with a magnetic coupling was developed, the HiFlow. The small design makes the pump suitable for applications in complex devices or close to a patient. Hemolysis tests were carried out in which the BioMedicus pump BP-80 and a roller pump were used as reference. The centrifugal pump HiFlow showed the least blood trauma within the group of investigated pumps. In summary, the HiFlow pump concept with its low priming volume and limited contact surfaces shows great potential for clinical applications in cardiopulmonary bypass. Also, the possibility of using the pump as a short-term assist device with an option of a pulsatile driving mode was demonstrated.     

A Compact Centrifugal Pump for Cardiopulmonary Bypass

A majority of the cardiopulmonary bypass (CPB) systems still utilize bulky roller pumps. A direct-drive small centrifugal pump intended for second-generation CPB pump has been developed. The pump has a 50 mm diameter impeller and provides a 6 L/min flow at 3,000 rpm against 300 mm Hg. A flexible drive shaft allows us to separate the pump head from the console resulting in easier manipulation. An in vitro study showed that the pump generated less hemolysis (index of hemolysis = 0.0011, comparable to the value for Bio-medicus BP-80). To improve blood flow around the shaft-seal region and to reduce thrombus formation around the shaft, six holes were drilled through the impeller. In biventricular bypass experiments using calves, our pump demonstrated excellent antithrombogenicity and durability for 48 h. And the compact and atraumatic centrifugal pump system showed excellent performance and easy manipulation under actual CPB conditions in animal.     

Development of an Atraumatic Small Centrifugal Pump for Second-Generation Cardiopulmonary Bypass

A small and light direct-drive centrifugal pump has been developed for cardiopulmonary bypass. In the development process, blood compatibility studies including a hemolysis study, an in vitro fluid dynamic performance study, and in vivo durability and feasibility studies were performed. The centrifugal pump with a 50 mm diameter impeller resulted in almost the same index of hemolysis value as did a Bio-Medicus centrifugal pump. Heat dissipation from the motor was prevented by using a flexible drive cable. Forty-eight-hour sealing durability around the driving axis was accomplished by using a fluoro-rubber V-ring that connected to the hard chrome-plated stainless steel. In vitro and in vivo performances of the pump were satisfactory. Thrombus formation behind the impeller was prevented by using a holed impeller that generated blood flow from the back to the surface of the impeller. Elimination of air during priming procedures was also easier with this modification. This centrifugal pump has one-quarter of the priming volume, size, and weight of magnetically coupled centrifugal pump systems.     

A Fluid Dynamic Analysis of a Rotary Blood Pump for Design Improvement

Abstract: The proper design of a left ventricular assist device (LVAD) requires an understanding of the pump's fluid dynamic and biocompatible properties. A hydraulically efficient system minimizes the power required for pumping. Biocompatibility refers to the ability to pump blood with minimal hemolysis and thrombus formation. Typically, shear stresses below a threshold level will not damage blood significantly. A fluid dynamic analysis of a prototype centrifugal pump designed for use as an LVAD was performed to establish flow characteristics. A flow visualization technique using Amberlite particles suspended in a glycerin/water blood analogue was used. The system was illuminated with a 1 mm planar beam strobed helium-neon laser, and the results were recorded photographically. An analysis of photographs revealed laminar and turbulent flows with vortices within an illuminated plane in both the inlet and outlet port areas. From these data, velocity and shear stress profiles were generated that showed possible areas of improvement. It was concluded that the outlet port design could be improved by changing its angle and the continuity of its expansion. The inlet port could also be improved by smoothing the transition area between the inlet tube and the pump body to allow for gradual acceleration of the entering fluid.     

Cardiopulmonary Bypass with Nikkiso and BioMedicus Centrifugal Pumps

Abstract: In our department, a new compact and atraumatic centrifugal pump, Nikkiso, was developed as a second-generation cardiopulmonary bypass pump. To assess and confirm the function and controllability of this pump, comparative studies of cardiopulmonary bypass with Nikkiso and BioMedicus centrifugal pumps were performed using calves. Both pumps provided pump flows of 60–70 ml/kg/min without incidence. The hemodynamics of both groups were stable and within the normal range, and no leakage or thrombus formations were observed in either pump. All hematology and biochemistry data showed no significant differences between the two groups. Plasma free hemoglobin values of the Nikkiso pump tended to be lower than those of the BioMedicus pump. The Nikkiso pump was easy to handle because of its smaller size, and air removal was easily performed because of its low priming volume. The Nikkiso pump demonstrated easy manipulation and good controllability. This compact, atraumatic centrifugal pump meets the requirements for a second-generation cardiopulmonary by-pass pump.     

心肺转流术在犬心肺脑复苏中的应用

目的：观察犬在高钾停搏10分钟后行心肺转流术（CPB）复苏,并与常规心肺复苏（CPR）比较其自主循环恢复和脑复苏的效果。方法：将杂种家犬12只,以10％KCl静脉给药致心脏停搏（CA）10分钟后随机分为两组,每组6只。组1;用常规CPR法复苏;组2：用自行研制的心肺转流装置复苏。两组于CA前、CA10分钟,复苏后5分钟、10分钟和30分钟监测平均动脉压（MAP）、心率（HR)、心脏复跳时间、瞳孔大小、72小时存活率和动静脉血气并计算脑氧摄取率（CEO2)脑氧耗量（Ca-jvO2)。结果：组1中6只犬仅2只在CPR后10分钟、15分钟恢复自主心跳,但不稳定,并在60分钟内死亡;组2均于CPB后6－10分钟恢复自主心跳,CPB10分钟后MAP＞80mmHg,明显高于组1（P＜0．05）,其自主循环恢复率为100％,明显大于组1（P＜0．05）。两组CEO2和Ca-jvO2在CA10分钟、复苏后5分钟和10分钟均明显升高（P＜0．05）,且复苏后5分钟、10分钟和30分钟时组1明显高于组2（P＜0．05）。组2犬的瞳孔于复苏后第9－19分钟开始缩小,30分钟后恢复至正常,全组均存活72小时以上,72小时存活率为100％,明显高于组1（P＜0．05）。结论：CA10分钟后,用CPB复苏其自主循环恢复明显优于常规CPR,并有益于脑复苏。     

Hemolytic Effect of Surface Roughness of an Impeller in a Centrifugal Blood Pump

Abstract: The present study investigates how the surface roughness of an impeller affects hemolysis in the pivot bearing supported Gyro C1E3 pump. This study focuses on particular areas of the impeller surface in the impeller type centrifugal pump. Seven Gyro C1E3 pumps were prepared with smooth surface housings and different impeller parts with different surface roughnesses. The vanes, top side, and backside of the impeller were independently subjected to vapor polishing, fine sand blasting, or coarse sand blasting to produce three different grades of surface roughness. These surfaces were then examined by a surface profile instrument. Using these pumps with different impellers, in vitro hemolysis tests were performed simulating cardiopulmonary bypass (5 Wmin, 350 mm Hg). The findings of this study conclusively proved that surface roughness of the back side of the impeller has the greatest effect on hemolysis, followed by the top side and then the vanes. The following are reasons for these findings. First, the shear rate may be greater on the back side than on the top side because of the smaller gap between the back and the housing and the greater relative speed against the impeller. Second, the fluid beneath the impeller may have a longer exposure time because there is little chance for the fluid to mix beneath the impeller. Third, the shear rate may be greater on the top side of the impeller than on the vanes because a vortex formation occurs behind the vanes.     

Parametric Study of Blade Tip Clearance, Flow Rate, and Impeller Speed on Blood Damage in Rotary Blood Pump

Phenomenological studies on mechanical hemolysis in rotary blood pumps have provided empirical relationships that predict hemoglobin release as an exponential function of shear rate and time. However, these relations are not universally valid in all flow circumstances, particularly in small gap clearances. The experiments in this study were conducted at multiple operating points based on flow rate, impeller speed, and tip gap clearance. Fresh bovine red blood cells were resuspended in phosphate-buffered saline at about 30% hematocrit, and circulated for 30 min in a centrifugal blood pump with a variable tip gap, designed specifically for these studies. Blood damage indices were found to increase with increased impeller speed or decreased flow rate. The hemolysis index for 50-µm tip gap was found to be less than 200-µm gap, despite increased shear rate. This is explained by a cell screening effect that prevents cells from entering the smaller gap. It is suggested that these parameters should be reflected in the hemolysis model not only for the design, but for the practical use of rotary blood pumps, and that further investigation is needed to explore other possible factors contributing to hemolysis.     

Study of Left Ventricular Bypass Using Wankel Type Semipulsatile Blood Pump

Abstract The influence of the Wankel type semipulsatile left ventricular assistance on hemodynamics was investigated with a computer simulation and an animal experiment. A simulation circuit was constructed to express the circulatory system. A current source was added to create a semipulsatile blood pump. The left and right ventricles were replaced by variable compliances. Left heart failure was simulated by decreasing the amount of compliance change of the left ventricle. Under the condition of heart failure when semipulsatile assist flow increased, the mean aortic pressure (AoP), tension time index (TTI), and diastolic pressure time index (DPTI) increased, and the cardiac output, pulse pressure (PP), and pulsatility indicator (PI) decreased. In an animal experiment, a Wankel type blood pump was used in a calf. With the increase of the assist flow, AoP curves became less pulsatile, and PP and PI decreased in accordance, which was predicted by the numerical simulation.     

Comparison of the Gyro C1E3 and BioMedicus Centrifugal Pump Performances During Cardiopulmonary Bypass

Abstract: The compact eccentric inlet port (ClE3) centrifugal blood pump was developed as a cardiopulmonary bypass (CPB) pump. The C1E3 pump incorporated a seal-less design with a blood stagnation free structure. The pump impeller was magnetically coupled to the driver magnet in a sealless manner. To develop an atraumatic and antithrombogenic centrifugal pump without a shaft seal junction, a double pivot bearing system was introduced. Recently, a mass production model of the C1E3 was fabricated and evaluated. The ratio of the normalized index of hemolysis (NIH) of the C1E3 was 0.007 g/ 100 L, in comparison to the NIH of the BP-80, 0.018 g/ 100 L, each in a CPB condition of 5 Limin against 325 mm Hg. Both pumps were compared in identical in vitro circuits. To further evaluate the pumps during cardio pulmonary bypass for reliability and function, 6 h of CPB was performed on each of 8 bovines using either the C1E3 or BP-80 centrifugal pump. The BP-80 and C1E3 provided pump flows of 5MO ml/kg/min without incident. The hemodynamics were stable, and the hematology and biochemistry data were within normal ranges. There were no statistically significant differences between the 2 groups. Concerning the plasma free hemoglobin values. a mass production model of the C1E3 pump had the same hemolysis levels as the BP-80. Our preliminary studies reveal that the C1E3 pump is reliable. Also, the C1E3 will satisfy clinical requirements as a cardiopulmonary bypass pump.     

Pulse Conductance and Flow‐induced Hemolysis During Pulsatile Cardiopulmonary Bypass

In this study, the hypothesis was tested that a low‐resistant, high‐compliant oxygenator provides better pulse conductance and less hemolysis than a high‐resistant, low‐compliant oxygenator during pulsatile cardiopulmonary bypass. Forty adults undergoing coronary artery bypass surgery were randomly divided into two groups using either an oxygenator with a relatively low hydraulic resistance (Quadrox BE‐HMO 2000, Maquet Cardiopulmonary AG, Hirrlingen, Germany) or with a relatively high hydraulic resistance (Capiox SX18, Terumo Cardiovascular Systems, Tokyo, Japan). The phase shift between the flow signals measured at the inlet and outlet of the oxygenator was used to assess compliance. Pulse conductance in terms of pressure attenuation was calculated by dividing the outlet pulse pressure of the oxygenator by the inlet pulse pressure. A normalized index was used to assess hemolysis. The phase shifts in time of the flow pulses were 36 ± 6 ms in the low‐resistant (high‐compliant) oxygenator, and 14 ± 2 ms in the high‐resistant (low‐compliant) oxygenator group (P < 0.001). The low‐resistant, high‐compliant oxygenator provided 27% better pulse conductance compared with the high‐resistant, low‐compliant oxygenator (0.84 ± 0.02 and 0.66 ± 0.01, respectively, P < 0.001). Inlet pulse pressures were significantly higher (29%) in the high‐resistant, low‐compliant (Capiox) group than in the low‐resistant, high‐compliant (Quadrox) group (838 ± 38 mm Hg and 648 ± 25 mm Hg respectively, P < 0.001), but no significant difference in hemolysis was found. A low‐resistant, high‐compliant oxygenator provides better pulse conduction than a high‐resistant, low‐compliant oxygenator. However, the study data could not confirm the association of high pressures with increased hemolysis.     

PreLoad-responsive,Pulsatile-Flow,Externally Valved Pump: Cardiopulmonary Bypass

Currently two pumps are used for cardiopulmonary bypass, the roller pump and the centrifugal or vortex pump. Both are steady-flow pumps. The procedure of cardiopulmonary bypass possesses a finite morbidity and mortality. The degree to which steady flow is responsible for this morbidity and mortality remains to be clarified, but investigators have established the fact that a physiologic degree of pulsatile flow must be achieved before its beneficial results, such as normal systemic resistance and absence of lactate production, can be demonstrated. Availability of a satisfactory pulsatile pump for cardiopulmonary bypass has been a problem in the past but the pump presented here may satisfy this need. It produces physiologic pulsatility with rate dependent ejection time equal to or less than that of humans (413 µs minus 1.7 times heart rate), and it is preload-responsive, varying its pumping rate and output with filling pressure. The pump is externally valved to minimize hemolysis, which has been demonstrated in two laboratory studies to be significantly less than with the roller pump. It produces pulsatile flow through membrane oxygenators. The pump is thought to have potential for several clinical applications in addition to (I) pulsatile-flow cardiopulmonary bypass, including (2) left, right, or combined transthoracic QRS synchronized ventricular assist, (3) femoral vein to femoral artery QRS synchronized left ventricular assist, (4) adult or infant ECMO, (5) pulsatile flow hemodialysis. In the latter, spallation and embolization of hemodialysis tubing particles should not be a problem as has proved to be the case with the present hemodialysis Pump.     

Design and Development Strategy for the Rotary Blood Pump

Development of an antitraumatic antithrombogenic and durable blood pump is a very difficult task. Based upon this author's experience of over 35 years in the development of various types of cardiac prostheses, development strategies for a rotary blood pump are described. A step-by-step development strategy is thus proposed. Initially, the development of a 2 day antitraumatic pump (Phase 1) would be made. Then, conversion of this pump to a 2 week antithrombogenic pump (Phase 2) should be attempted. After the successful development of the Phase 2 pump, the conversion of this device to a durable, implantable, and long-term blood pump (Phase 3) should be established. Based upon this development strategy, 2 rotary blood pumps, namely, the axial flow blood pump and the centrifugal blood pump, have been developed in less than 6 years with modest development costs.     

In Vitro Comparison of the Delivery of Gaseous Microemboli and Hemodynamic Energy for a Diagonal and a Roller Pump During Simulated Infantile Cardiopulmonary Bypass Procedures

Cardiopulmonary bypass (CPB) is used for a variety of procedures in pediatric patients. Flow settings of the CPB pump have dramatic effects on patient outcome, and gaseous microemboli delivery within the CPB circuit has been linked to neurological complications. To ensure the ongoing improvement of pediatric CPB, consistent evaluation and improvement of the equipment is necessary. In this study we analyze the Jostra HL‐20 roller pump (Jostra USA, Austin, TX, USA) and a Medos Deltastream DP3 diagonal pump (MEDOS Medizintechnik AG, Stolberg, Germany) which has not yet received Food and Drug Administration approval. An infant CPB model with heparinized human blood is used to quantify the gaseous microemboli delivery (via an Emboli Detection and Classification Quantifier), as well as the hemodynamic energy delivered under flow rates of 400, 800, and 1200 mL/min. Results show that at most flow settings the DP3 delivers fewer microemboli than the Jostra roller pump at the pre‐oxygenator site, with an exception at 1200 mL/min under pulsatile mode. The total volume and the number of gaseous microemboli greater than 40 μm in diameter were lower in the DP3 group. The HL‐20 exhibits less stolen blood flow (except at 1200 mL/min) and oxygenator pressure drops in both pulsatile and nonpulsatile mode. Additionally, under pulsatile flow the DP3 delivers greater surplus hemodynamic energy. Both pumps produce relatively few microemboli and deliver adequate hemodynamic energy to the pseudo‐patient, with the DP3 performing slightly better under most flow settings.     

Use of Percutaneous Cardiopulmonary Support System with Rotary Blood Pump in Graft Replacement of the Descending Thoracic and Thoracoabdominal Aorta

Abstract: Graft replacement of the descending thoracic or thoracoabdominal aorta was successfully performed in 3 patients using percutaneous cardiopulmonary bypass. Femoral inflow and outflow cannulas were inserted per-cutaneously after induction of anesthesia with the patient in supine position, and low flow normothermic bypass was established before thoracotomy. Next the patient was placed in a right lateral position to create an operating field. With this body position and even an almost prone position, which was sometimes necessary for easy dissection of adhesion of lung to the aneurysmal wall, the bypass flow was easily maintained adequately. The bypass circuit was coated with heparin, and the activated clotting time (ACT) was controlled to be between 150 and 200 s during the entire operating period. Percutaneous insertion of the cannulas avoided local bleeding in the groin, and the low ACT made control of hemorrhage in the operating field easy. For descending aortic surgery, heparin-coated percutaneous cardiopulmonary bypass proved to be a useful adjunctive measure.     

Heparin-Coated Equipment Reduces Complement Activation during Cardiopulmonary Bypass in the Pig

Complement activation was studied during cardiopulmonary bypass (CPB) in the pig. One group of animals was perfused for 2 h using a standard extracorporeal circuit including a hollow fiber membrane oxygenator with full systemic heparinization. Another group was treated in the same way, except that bypass was performed through a heparin-coated CPB circuit (Carmeda Bio-Active Surface, CBAS) and systemic heparinization was reduced by 75%. It was found that complement activation during CPB, measured as changes in the ratio C3d/C3, was significantly less in the CBAS group, most probably reflecting a better biocompatibility.     

Experimental Studies on Three Types of Heparin-Coated Cardiopulmonary Bypass Circuits

Abstract: In cardiovascular operations, we have usually used heparin-coated cardiopulmonary bypass circuits with low systemic heparinization. Three types of heparin-coated cardiopulmonary bypass circuits are available in Japan: 2 of the 3 have covalent heparin bonding, and the other has ionic heparin bonding. We studied these circuits in ex vivo experiments to explore which were the best in terms of biocompatibility. In this study we compared the Carmeda system (Medtronic) and the Capiox system (Terumo) with covalent heparin bonding, and the Duraflo-II (Baxter) with ionic heparin bonding, evaluating them in ex vivo experiments. They were primed with fresh human blood, and we studied and compared the platelet counts, fibrinogen, D-dimmer, beta-thioguanine (TG), thrombin-antithrombin complex (TAT), and C3a and C4a of each of them. Additional research will be presented in the future.     

抑肽酶在体外循环术中的应用

１０１例各种心脏直视手术病例在体外循环中应用抑肽酶，另以同期５２例心脏直视手术病例作为对照，研究大剂量抑肽酶在心脏直视手术中的作用，用药组转流结束后创面较对照组干燥，手术止血时间缩短，术中失血减少，术后２４小时出血量减少约５０％（用药组３１６±１１４ｍｌ，对照组５９８±１９７ｍｌ）；库血输入量抑肽酶组亦比对照组用量少（用药组４６８±１４８ｍｌ，对照组７８３±１２２ｍｌ）。大剂量抑肽酶在体外循环中的应用是安全有效的，它明显减少术中、术后的出血及库血用量。     

体外循环对血浆胰岛素分泌影响的观察

本文观察了１５例体外循环病人术中不同时期血浆胰岛素，血糖，肾上腺素及去甲肾上腺素改变。结果显示，尽管体外循环过程中血浆胰岛素和血糖溶液明显升高，但胰岛素／血糖比值明显下降，这提示胰岛素分泌功能降低或延迟。在影响胰岛素分泌的因素中，血浆肾上腺素浓度高可能起重要作用。