Development of rotary blood pump technology: past, present, and future

Influence of circumferential annular grooving design of impeller on suspended fluid force of axial flow blood pump

Aiming at insufficient suspension force on the impeller when the hydraulic suspension axial flow blood pump is start at low speed, the impeller suspension stability is poor, and can't quickly enter the suspended working state. By establishing the mathematical model of the suspension force on the impeller, then the influence of the circumferential groove depth of the impeller on the suspension force is analyzed, and the annular groove depth on the impeller blade in the direction of fluid inlet and outlet was determined as (0.26, 0.02 mm). When the blood pump starts, there is an eccentricity between the impeller and the pump tube, the relationship between the suspension force and the speed of the impeller under different eccentricities is analyzed. Combined with the prototype experiment, the circumferential annular grooving design of the impeller can make the blood pump rotate at about 3500 rpm into the suspension state, when the impeller is at 8000 rpm, the impeller can basically achieve stable suspension at the eccentricity of 0.1 mm in the gravity direction, indicating that the reasonable circumferential annular grooving design of the impeller can effectively improve the suspension hydraulic force of the impeller and improve the stability of the hydraulic suspension axial flow blood pump.

Multiple parameters and target optimization of splitter blades for axial spiral blade blood pump using computational fluid mechanics, neural networks, and particle image velocimetry experiment

The blood pump is an implantable device with strict performance requirements. Any effective structural improvement will help to improve the treatment of patients. However, the research of blood pump structure improvement is a complex optimization problem with multiple parameters and objectives. This study takes the splitter blade as the object of structural improvement. Computational fluid mechanics and neural networks are combined in research and optimization. And hydraulic experiments and micro particle image velocimetry technology were used. In the optimization study, the number of blades, axial length and circumferential offset are optimization parameters, and hydraulic performance and hemolytic prediction index are optimization targets. The study analyzes the influence of each parameter on performance and completes the optimization of the parameters. In the results, the optimal parameters of number of blades, axial length ratio, and circumferential offset are 2.6° and 0.41°, respectively. Under optimized parameters, hydraulic performance can be significantly improved. And the results of hemolysis prediction and micro particle image velocimetry experiments reflect that there is no increase in the risk of hemolytic damage. The results of this study provide a method and ideas for improving the structure of the axial spiral blade blood pump. The established optimization method can be effectively applied to the design and research of axial spiral blade blood pumps with complex, high precision, and multiple parameters and targets.

Biologically Inspired, Open, Helicoid Impeller Design for Mechanical Circulatory Assist

Rotating impeller actuated by electromagnet has been a key technological innovation which surpassed earlier limitations of pulsatile pumps. Current impeller design, however, is alien to the functional unit of the human circulatory system and remains a potential cause of adverse prothrombotic events such as hemolysis or pump thrombosis by forcing blood cells to pass over a narrow space available within the rapidly alternating blades attached along its central hub, creating fundamentally a nonphysiologic flow, especially for miniaturized percutaneous blood pumps. Here, we present a biologically inspired, open, helicoid (BiO-H) impeller design for a circulatory assist device that has a fundamentally different footprint from the conventional Archimedean screw-based impeller designs by implementing new design features inspired by an avian right atrioventricular valve. Design parameters including an inner diameter, helix height, overall height, helix revolutions/pitch, blade length, blade thickness, introductory blade angle, number of blades, and blade shape were optimized for maximum output volumetric flow rate through the parametric analysis in computational fluid dynamics simulation. BiO-H shows an improved flow path with 2.25-fold less cross-sectional area loss than the conventional impeller designs. BiO-H with a diameter of 15 mm resulted in a maximum flow rate of 25 L/min at 15,000 revolutions per minute in simulation and showed further improved pressure-flow relationship in benchtop experiments. The design shows promise in increasing flow and could serve as a new impeller design for future blood pumps.

Short- and long-term mechanical cardiac assistance

With the increase in high risk patients undergoing cardiac surgery and the substantial mortality among patients waiting for cardiac transplantation, the need for mechanical circulatory support is growing. Several devices are currently available, ranging from the intra-aortic balloon pump to fully implantable ventricular assist devices. Each system has its own features, and proper patient selection as well as the timing of implantation is sometimes difficult. Algorithms for stepwise management in subgroups of patients remain controversial and the concepts of weaning patients after myocardial recovery during mechanical circulatory support need further evaluation for their long-term effects. Future identification of valuable prognostic and risk factors may help in decision-making and allow for improved survival of these often very ill patients. In this report we review the concepts of mechanical circulatory support at our institution with emphasis on a detailed overview of technical features of extracorporeal life support.

Design and numerical evaluation of an axial partial-assist blood pump for Chinese and other heart failure patients

A fully implantable axial left ventricular assist device LAP31 was developed for Chinese or other heart failure patients who need partial support. Based on the 5-Lpm total cardiac blood output of Chinese without heart failure disease, the design point of LAP31 was set to a flow rate of 3 Lpm with 100-mmHg pressure head. To achieve the required pressure head and good hemolytic performance, a structure that includes a spindly rotor hub and a diffuser with splitter and cantilevered main blades was developed. Computational fluid dynamics (CFD) was used to analyze the hydraulic and hemodynamic performance of LAP31. Then in vitro hydraulics experiments were conducted. The numerical simulation results show that LAP31 could generate a 1 to 8 Lpm flow rate with a 60.9 to 182.7 mmHg pressure head when the pump was rotating between 9,000 and 12,000 rpm. The average scalar shear stress of the blood pump was 21.7 Pa, and the average exposure time was 71.0 milliseconds. The mean hemolysis index of LAP31 obtained using Heuser's hemolysis model and Giersiepen's model was 0.220% and 3.89 × 10-5% respectively. After adding the splitter blades, the flow separation at the suction surface of the diffuser was reduced. The cantilever structure reduced the tangential velocity from 6.1 to 4.7-1.4 m/s within the blade gap by changing the blade gap from shroud to hub. Subsequently, the blood damage caused by shear stress was reduced. In conclusion, the hydraulic and hemolytic characteristics of the LAP31 are acceptable for partial support.

Characteristics and Outcomes of Patients Bridged to Cardiac Transplantation on Centrifugal Ventricular Assist Devices: A Case Series of the Early Experience of One Canadian Transplant Centre

BACKGROUND

Centrifugal ventricular assist devices (VADs) have been used successfully to bridge patients in cardiogenic shock to cardiac transplantation, though complications are frequent and often life-threatening.

PURPOSE

To describe characteristics and examine outcomes of patients bridged to cardiac transplantation on centrifugal VADs.

METHODS

A retrospective health record review was conducted on all adults over a 12 year period (N=20) placed on centrifugal VADs with the intent to bridge to cardiac transplantation at a major Canadian transplant centre.

RESULTS

Complications of VAD support necessitated removal of 12 patients from the transplant list; seven (35%) survived to cardiac transplantation. Of the seven recipients, five survived to discharge and four remain alive and well.

CONCLUSIONS

Bridging patients on centrifugal VADs to cardiac transplantation requires improvement, including maintaining patient stability during the period of early VAD institution, aggressively managing complications of VAD support, and consideration of long-term pulsatile devices. However, if patients survive to transplantation, good long-term outcomes are expected.

A New Approach for Semiempirical Modeling of Mechanical Blood Trauma

Purpose

Two semi-empirical models were recently published, both making use of existing literature data, but each taking into account different physical phenomena that trigger hemolysis. In the first model, hemoglobin (Hb) release is described as a permeation procedure across the membrane, assuming a shear stress-dependent process (sublethal model). The second model only accounts for hemoglobin release that is caused by cell membrane breakdown, which occurs when red blood cells (RBC) undergo mechanically induced shearing for a period longer than the threshold time (nonuniform threshold model). In this paper, we introduce a model that considers the hemolysis generated by both these possible phenomena.

Methods

Since hemolysis can possibly be caused by permeation of hemoglobin through the RBC functional membrane as well as by release of hemoglobin from RBC membrane breakdown, our proposed model combines both these models. An experimental setup consisting of a Couette device was utilized for validation of our proposed model.

Results

A comparison is presented between the damage index (DI) predicted by the proposed model vs. the sublethal model vs. the nonthreshold model and experimental datasets. This comparison covers a wide range of shear stress for both human and porcine blood. An appropriate agreement between the measured DI and the DI predicted by the present model was obtained.

Conclusions

The semiempirical hemolysis model introduced in this paper aims for significantly enhanced conformity with experimental data. Two phenomenological outcomes become possible with the proposed approach: an estimation of the average time after which cell membrane breakdown occurs under the applied conditions, and a prediction of the ratio between the phenomena involved in hemolysis.

Classification of Implantable Rotary Blood Pump States With Class Noise

A medical case study related to implantable rotary blood pumps is examined. Five classifiers and two ensemble classifiers are applied to process the signals collected from the pumps for the identification of the aortic valve nonopening pump state. In addition to the noise-free datasets, up to 40% class noise has been added to the signals to evaluate the classification performance when mislabeling is present in the classifier training set. In order to ensure a reliable diagnostic model for the identification of the pump states, classifications performed with and without class noise are evaluated. The multilayer perceptron emerged as the best performing classifier for pump state detection due to its high accuracy as well as robustness against class noise.

Geometric optimization of a step bearing for a hydrodynamically levitated centrifugal blood pump for the reduction of hemolysis

A hydrodynamically levitated centrifugal blood pump with a semi-open impeller has been developed for mechanical circulatory assistance. However, a narrow bearing gap has the potential to cause hemolysis. The purpose of the present study is to optimize the geometric configuration of the hydrodynamic step bearing in order to reduce hemolysis by expansion of the bearing gap. First, a numerical analysis of the step bearing, based on lubrication theory, was performed to determine the optimal design. Second, in order to assess the accuracy of the numerical analysis, the hydrodynamic forces calculated in the numerical analysis were compared with those obtained in an actual measurement test using impellers having step lengths of 0%, 33%, and 67% of the vane length. Finally, a bearing gap measurement test and a hemolysis test were performed. As a result, the numerical analysis revealed that the hydrodynamic force was the largest when the step length was approximately 70%. The hydrodynamic force calculated in the numerical analysis was approximately equivalent to that obtained in the measurement test. In the measurement test and the hemolysis test, the blood pump having a step length of 67% achieved the maximum bearing gap and reduced hemolysis, as compared with the pumps having step lengths of 0% and 33%. It was confirmed that the numerical analysis of the step bearing was effective, and the developed blood pump having a step length of approximately 70% was found to be a suitable configuration for the reduction of hemolysis.

Control strategies for afterload reduction with an artificial vasculature device

Ventricular assist devices (VADs) have been used successfully as a bridge to transplant in heart failure patients by unloading ventricular volume and restoring the circulation. An artificial vasculature device (AVD) is being developed that may better facilitate myocardial recovery than VAD by controlling the afterload experienced by the native heart and controlling the pulsatile energy entering into the arterial system from the device, potentially reconditioning the arterial system properties. The AVD is a valveless, 80 ml blood chamber with a servo-controlled pusher plate connected to the ascending aorta by a vascular graft. Control algorithms for the AVD were developed to maintain any user-defined systemic input impedance (IM) including resistance, elastance, and inertial components. Computer simulation and mock circulation models of the cardiovascular system were used to test the efficacy of two control strategies for the AVD: 1) average impedance position control (AIPC)-to maintain an average value of resistance during left ventricular (LV) systole and 2) instantaneous impedance force feedback (IIFF) and position control (IIPC)-to maintain a desired value or profile of resistance and compliance. Computer simulations and mock loop tests were performed to predict resulting cardiovascular pressures, volumes, flows, and the resistance and compliance experienced by the native LV during ejection for simulated normal, failing, and recovering LV. These results indicate that the LV volume and pressure decreased, and the LV stroke volume increased with decreasing IM, resulting in an increased ejection fraction. Although the AIPC algorithm is more stable and can tolerate higher levels of sensor errors and noise, the IIFF and IIPC control algorithms are better suited to maintain any instantaneous IM or an IM profile. The developed AVD impedance control algorithms may be implemented with current VADs to promote myocardial recovery and facilitate weaning.

The need to change our objective for artificial heart development: from totally implantable permanent ventricular assist devices to wearable therapeutic ventricular assist devices

As a therapeutic VAD to be combined with drugs, apheresis, and cellular implants, it is advisable to develop a wearable VAD for less than 6 months of application. Such an example was shown by describing the therapeutic BCM Gyro centrifugal VAD.

Design analysis and performance assessment of hybrid magnetic bearings for a rotary centrifugal blood pump

A hybrid magnetic bearing system was designed for a rotary centrifugal blood pump being developed to provide long-term circulatory support for heart failure patients. This design consists of two compact bearings to suspend the rotor in five degrees-of-freedom with single axis active control. Permanent magnets are used to provide passive radial support and electromagnets to maintain axial stability of the rotor. Characteristics of the passive radial and active thrust magnetic bearing system were evaluated by the electromagnetic finite element analysis. A proportional-integral-derivative controller with force balance algorithm was implemented for closed loop control of the magnetic thrust bearing. The control position is continuously adjusted based on the electrical energy in the bearing coils, and thus passive magnetic forces carry static thrust loads to minimize the bearing current. Performance of the magnetic bearing system with associated control algorithm was evaluated at different operating conditions. The bearing current was significantly reduced with the force balance control method and the power consumption was below 0.5 W under various thrust loads. The bearing parameters predicted by the analysis were validated by the experimental data.

Hemolysis estimation in a centrifugal blood pump using a tensor-based measure

Hemolysis in the GYRO centrifugal blood pump, under development at the Baylor College of Medicine, Houston, TX, is numerically predicted using the newly proposed tensor-based blood-damage model, as well as a traditional model. Three typical operating conditions for the pump are simulated with a special-purpose finite element-based flow solver, and a novel approach for tracing the pathlines in discretely represented time-varying flow in a complex domain is presented, and 271 pathlines are traced through the pump. Hemolysis is computed along the pathlines, and the accumulated hemolysis at the outflow is converted into standard clinical units. The cumulative hemolysis at the outlet of the pump is weighted with the flow rate associated with the pathlines, and a temporal average is obtained by releasing the tracer particles at different time intervals. Numerical predictions are compared to experimental hemolysis studies performed according to the American Society for Testing and Materials standards at the Baylor College of Medicine. The tensor-based blood-damage model is found to match very well with the experimental results, whereas the traditional model overpredicts the hemolysis. The success of the tensor-based blood-damage model is attributed to its construction, which accounts for blood-specific physical properties and phenomena. Hemolysis values at the typical operating conditions of the pump are found to be within the clinically accepted range.

Effect of left ventricular assist device outflow conduit anastomosis location on flow patterns in the native aorta

Computational fluid dynamics (CFD) models were developed to investigate the altered fluid dynamics of the native aorta in patients with a left ventricular assist device (LVAD). The objective of this study was to simulate the effect of LVAD aortic outflow conduit location on the 3-D flow in the native aorta over a range of boundary conditions. The fluid mechanics of three different surgical geometries [(P), proximal, (D), distal and (IP), in-plane] were studied and the implications for short- and long-term medical consequences explored by evaluating the flow fields, wall shear, and hemolysis. The greatest disruptions in the normal aortic flow pattern occurred with series flow conditions, when flow through the aortic valve was minimal. Under series conditions, circulation in the proximal aorta is retrograde, originating from the LVAD outflow conduit. The (P) geometry provided the most blood washout of the proximal aorta, with a larger region of slow-moving flow observed in the (D) and (IP) models. Wall shear stress was reduced for the (IP) geometry, which lacks the direct flow impingement present in the (P) and (D) models. Clinically, the (D) and (IP) geometries require less traumatic surgeries and probably are better tolerated by the patient. In this situation, the (IP) geometry suggests improvement in both increased flow to the proximal aorta and decreased shear stress compared with (D). However, the (D) and (IP) configurations are not recommended for patients with low or no flow from the heart because of the lack of blood washout near the aortic valve and therefore possible thrombus formation in that area.

SELCAB (self-lung cardiac bypass) procedures for pediatric patients

Cardiopulmonary bypass (CPB) for pediatric heart surgeries is not ideal. The currently available systems have a priming volume of 400-1,200 ml, requiring substantial hemodilution. CPB also subjects immature lung tissue to unphysiologic conditions. Exposure of the pediatric patient's blood to the large surface areas of foreign materials associated with an oxygenator results in humoral and cellular impacts on the pediatric patient's immature organs and should be avoided. For selected cases of pediatric heart surgeries, the SELCAB (self-lung cardiac bypass) procedure would be advantageous over CPB. This procedure is equivalent to a biventricular assist device (BVAD) implantation. To distinguish this procedure from long-term BVAD, a BVAD implantation of less than 2 weeks is referred to as SELCAB. Also, the SELCAB's inflow cannulations are either in atria or veins, whereas BVAD inflow cannulations are in ventricles. Advantages and disadvantages of SELCAB are discussed. The physiologic acceptance of SELCAB procedures in immature calves (pediatric model), with beating and nonbeating natural hearts for as long as 3 months, is described. The SELCAB and BVAD systems developed by these authors are also described in this article.

Right ventricular failure after left ventricular assist device implantation: the need for an implantable right ventricular assist device

Right ventricular failure after implantation of a left ventricular assist device is an unremitting problem. Consideration of portal circulation is important for reversing liver dysfunction and preventing multiple organ failure after left ventricular assist device implantation. To achieve these objectives, it is imperative to maintain the central venous pressure as low as possible. A more positive application of right ventricular assistance is recommended. Implantable pulsatile left ventricular assist devices cannot be used as a right ventricular assist device because of their structure and device size. To improve future prospects, it is necessary to develop an implantable right ventricular assist device based on a rotary blood pump.

Total Heart Replacement with Dual Centrifugal Ventricular Assist Devices

In an ovine feasibility study, we implanted two HeartMate-III centrifugal ventricular assist devices (VADs) for total heart replacement. With cardiopulmonary bypass support, both ventricles were transected at the atrioventricular groove, preserving a rim of ventricular tissue. The atrioventricular valves were excised, and the aorta and pulmonary artery were transected above the ventriculoarterial valves. An interatrial septal window was created by excising the foramen ovale. The VADs' sewing rings were attached to the left and right ventricular remnants, respectively. Outflow grafts were anastomosed to the aorta and pulmonary artery. The left VAD operated continuously at 4,500 rpm. Right VAD speed increased from 2,000 to 4,500 rpm in 500 rpm increments. Outflow graft flow, pressure, oxygen saturation, and shunt direction were recorded. The pulmonary artery to aortic ratio of flow and pressure increased from 0.26 and 0.15 (at 2,000 rpm) to 1.21 and 0.53, respectively (at 4,500 rpm). The interatrial shunt, which was right to left at lower right VAD speeds, progressed to bidirectional, then to left dominant as right VAD speed increased. Outflow-graft oxygen saturation was reflective of the shunt direction. In this acute experiment, total heart replacement with continuous flow VADs satisfactorily balanced left and right ventricular flows and preserved the physiologic circulatory response.

Cellular and Hemodynamics Responses of Failing Myocardium to Continuous Flow Mechanical Circulatory Support Using the DeBakey-Noon Left Ventricular Assist Device: a Comparative Analysis With Pulsatile-Type Devices

BACKGROUND

An increasing number of continuous flow pumps are currently under clinical studies, however very little data exist on the hemodynamic and cellular responses of the failing heart to continuous flow support. The purpose of this investigation was to characterize the response of the failing myocardium to continuous flow support.

METHODS

We compared echocardiographic and cellular markers of failing myocardium at the time of left ventricular assist device (LVAD) implantation and explantation in 20 consecutive patients (12 pulsatile flow [Novacor] and 8 continuous flow [DeBakey-Noon]).

RESULTS

The use of mechanical support with both continuous- or pulsatile-type LVADs resulted in a reduction of left ventricular end-diastolic dimension (LVEDD), end-diastolic volume (EDV), end-systolic volume (ESV) and left atrial volume (LAV), as well as a decrease in mitral E/A ratio, tricuspid regurgitation velocity (TRV) and pulmonary valve acceleration time (PVAT). Comparative analyses for patients treated with a continuous- vs pulsatile-type LVAD support showed a greater degree of unloading with the latter type, as shown by the effect on LVEDD (-13.7% vs -33.7%, p = 0.0.004), EDV (-23.5% vs -41.2%, p = 0.015), ESV (-25.6% vs -57.6%, p = 0.001) and LAV (-25.2% vs -40.4%, p = 0.071). The hemodynamic effects of continuous vs pulsatile LVAD support were similar, as shown by their effect on mitral E/A ratio (-23.9% vs -39.9%, p = NS), TRV (-26.4% vs -23.8%, p = NS) and PVAT (28.5% vs 38.5%, p = NS). Only pulsatile support demonstrated a statistically significant percent change in mass (-6.3% vs -20.6%, p = 0.038). Continuous and pulsatile forms of mechanical support demonstrated equivalent reductions in myocardial tumor necrosis factor-alpha (TNF-alpha), total collagen and mycocyte size.

CONCLUSIONS

Our findings show that, although there are differences between these 2 devices in magnitude of unloading, both forms of support effectively normalize cellular markers of the failing phenotype.

Transient and quasi-steady computational fluid dynamics study of a left ventricular assist device

The HeartQuest continuous flow left ventricle assist device (LVAD) with a magnetically levitated impeller operates under highly transient flow conditions. Due to insertion of the in-flow cannula into the apex of the left ventricle, the inlet flow rate is transient because of ventricular contraction, and the pump's asymmetric circumferential configuration with five rotating blades forces blood intermittently through the pump to the great arteries. These two transient conditions correspond to time varying boundary conditions and transient rotational sliding interfaces in computational fluid dynamics (CFD). CFD was used to investigate the pump's performance under these dynamic flow conditions. A quasi-steady analysis was also conducted to evaluate the difference between the steady and transient analyses and demonstrate the significance of transient analysis, especially for transient rotational sliding interfaces transient simulations. This transient flow analysis can be applied generally in the design process of LVADs; it provides more reliable fluid forces and moments on the impeller for successful design of the magnetic suspension system and motor.

Design and transient computational fluid dynamics study of a continuous axial flow ventricular assist device

A ventricular assist device (VAD), which is a miniaturized axial flow pump from the point of view of mechanism, has been designed and studied in this report. It consists of an inducer, an impeller, and a diffuser. The main design objective of this VAD is to produce an axial pump with a streamlined, idealized, and nonobstructing blood flow path. The magnetic bearings are adapted so that the impeller is completely magnetically levitated. The VAD operates under transient conditions because of the spinning movement of the impeller and the pulsatile inlet flow rate. The design method, procedure, and iterations are presented. The VAD's performance under transient conditions is investigated by means of computational fluid dynamics (CFD). Two reference frames, rotational and stationary, are implemented in the CFD simulations. The inlet and outlet surfaces of the impeller, which are connected to the inducer and diffuser respectively, are allowed to rotate and slide during the calculation to simulate the realistic spinning motion of the impeller. The flow head curves are determined, and the variation of pressure distribution during a cardiac cycle (including systole and diastole) is given. The axial oscillation of impeller is also estimated for the magnetic bearing design. The transient CFD simulation, which requires more computer resources and calculation efforts than the steady simulation, provides a range rather than only a point for the VAD's performance. Because of pulsatile flow phenomena and virtual spinning movement of the impeller, the transient simulation, which is realistically correlated with the in vivo implant scenarios of a VAD, is essential to ensure an effective and reliable VAD design.

Left Ventricular and Myocardial Perfusion Responses to Volume Unloading and Afterload Reduction in a Computer Simulation

Ventricular assist devices (VADs) have been used successfully as a bridge to transplant in heart failure patients by unloading ventricular volume and restoring the circulation. In a few cases, patients have been successfully weaned from these devices after myocardial recovery. To promote myocardial recovery and alleviate the demand for donor organs, we are developing an artificial vasculature device (AVD) that is designed to allow the heart to fill to its normal volume but eject against a lower afterload. Using this approach, the heart ejects its stroke volume (SV) into an AVD anastomosed to the aortic arch, which has been programmed to produce any desired afterload condition defined by an input impedance profile. During diastole, the AVD returns this SV to the aorta, providing counterpulsation. Dynamic computer models of each of the assist devices (AVD, continuous, and pulsatile flow pumps) were developed and coupled to a model of the cardiovascular system. Computer simulations of these assist techniques were conducted to predict physiologic responses. Hemodynamic parameters, ventricular pressure-volume loops, and vascular impedance characteristics were calculated with AVD, continuous VAD, and asynchronous pulsatile VAD support for a range of clinical cardiac conditions (normal, failing, and recovering left ventricle). These simulation results indicate that the AVD may provide better coronary perfusion, as well as lower vascular resistance and elastance seen by the native heart during ejection compared with continuous and pulsatile VAD. Our working hypothesis is that by controlling afterload using the AVD approach, ventricular cannulation can be eliminated, myocardial perfusion improved, myocardial compliance and resistance restored, and effective weaning protocols developed that promote myocardial recovery.

In vivo evaluation of the NEDO biventricular assist device with an RPM dynamic impeller suspension system

Since 1995, the Baylor College of Medicine group has been developing the NEDO Gyro permanent implantable (PI) pump. The Gyro PI pump has achieved outstanding results up to 284 days with no thrombus formation during the left ventricular assist device (LVAD) animal experiments. However, in biventricular assist device (BVAD) animal experiments, thrombus formation did occur. An in vitro experiment showed the reason for thrombus formation was caused by the missed magnetic balance between the impeller and the actuator. On the basis of this result, the revolutions per minute (RPM) impeller suspension system was developed. Six long-term animal studies were performed in bovine models. Survival periods were 90, 80, 60, 51, 48, and 37 days, respectively. No thrombus was observed in the pumps with the exception of one right pump. In that experiment, the thrombus formation may have occurred when the pump had a low flow because of outflow kinking. In this article, the antithrombogenic effect of this RPM impeller suspension system will be discussed.

Antithrombogenicity of the Gyro permanently implantable pump with the RPM dynamic suspension system for the impeller

In 1995, a group at Baylor College of Medicine started to develop the NEDO biventricular assist device (BVAD) using two Gyro permanently implantable (PI) centrifugal pumps. This pump consists of a sealless pump housing and an impeller supported with a double pivot bearing. In May 2001, an RPM dynamic suspension system (RPM-DS) for the impeller was developed to improve durability and antithrombogenicity without a complex magnetic suspension system. From March 2000 to March 2002, eight BVAD bovine experimental studies were performed for more than 1 month. Two pumps were implanted in two cases without the RPM-DS (group A) and in six cases with the RPM-DS (group B). In group A, the survival period was 45 and 50 days. The primary reason for termination was an increase in the requiring power, which was related to deposition of white thrombus on the bottom bearing. In group B, the survival period was 37, 48, 51, 60, 80, and 90 days. The reasons for termination were not related to thrombus formation. No thrombus was observed in the pumps except for one right pump. In that experiment, the thrombus formation may have occurred when that pump had a low flow rate at a level of 1 L/min for 6 hr. These studies demonstrate the apparent antithrombogenic effect of RPM-DS. The NEDO BVAD is ready to move into a 3-month preclinical system evaluation.

Development of totally implantable pulsatile biventricular assist device

Approximately 10% to 15% of all patients implanted with left ventricular assist devices (LVADs) have required right heart support with another device. The necessity of aggressive biventricular support has already been proposed. Therefore, the totally implantable biventricular assist device (BVAD) was developed. The width of the BVAD main body was 87 mm, the thickness 67 mm, and the height 106 mm, while the weight was 785 g. The automatic control algorithm was developed to prevent lung edema and atrial rupture.

Long-term ex vivo bovine experiments with the Gyro C1E3 centrifugal blood pump

Centrifugal blood pumps are used widely for cardiopulmonary bypass, as ventricular assist devices, and for extracorporeal membrane oxygenation (ECMO). However, there is no centrifugal blood pump that is suitable for long-term ECMO. The authors developed the Gyro C1E3 centrifugal blood pump (Kyocera Corporation, Kyoto, Japan), which has superior antithrombogenic, antitraumatic, and hydraulic features in comparison with the conventional centrifugal blood pumps. Five ex vivo long-term durability tests of the Gyro C1E3 were performed using healthy miniature calves. The ECMO circuit was composed of a prototype hollow fiber silicone membrane oxygenator and a Gyro C1E3 pump. Venous blood was drained from the left jugular vein of a calf, passed through the oxygenator and infused into the left carotid artery using a Gyro C1E3. Ex vivo studies were performed from 7 to 15 days at a blood flow rate of 1 L/min. During this period, the Gyro C1E3 demonstrated a stable performance without exchanging the pump. Bleeding complications were the major reason for termination of each experiment. Rotational speed was maintained around 2,000 rpm. All five calves demonstrated neither abnormal signs nor abnormal blood examination data throughout the experiment. Neither clot nor thrombus formations were found during the necropsy in the cannula or pump nor were infarctions observed in any of the major organs. In conclusion, the Gyro C1E3 showed a stable and reliable performance during long-term ex vivo bovine experiments under the conditions tested.

Centrifugal blood pumps for various clinical needs

During the past 10 years, different types of blood pumps were developed to address various clinical needs. The Nikkiso centrifugal blood pump was developed for cardiopulmonary bypass application. This blood pump has been widely used in Japan in more than 20% of the cardiopulmonary bypass procedures. The Kyocera C1E3 Gryo pump was developed for short-term circulatory assistance and extracorporeal membrane oxygenation application for up to 2 weeks. This blood pump has been clinically used for up to 28 days without any blood clot formation. Through Phase I of the Japanese government New Energy and Industrial Technology Development Organization (NEDO) program, a chronically implanted centrifugal pump for left ventricular assistance was developed. This pump has already demonstrated its effectiveness, safety, and durability as a 2 year blood pump through in vitro and in vivo experiments. Currently, it is in the process of being converted from an experimental to a clinical device. Through Phase II of the NEDO program, a permanently implantable biventricular assist centrifugal blood pump system is under development. It has demonstrated that the previously mentioned left ventricular assist device blood pump is easily converted into a right ventricular assist pump by simply adding a spacer between the pump and the actuator. This communication discusses the historical development strategies for centrifugal blood pumps and their current status for different clinical needs.

The seventh prototype of the mini-spindle-pump: does it fulfill the expectations of a short-term pump?

According to recent trends to develop implantable nonpulsatile blood pumps for different function modes and times, our intention was and still is to build a Mini-Spindle-Pump for a pumping duration of about 14 days. Initial conception for this plan was the premise that the device in a mock circuit should move 4 L of water/min at a speed of 12,000 to 15,000 rpm against a pressure difference of 90 mm Hg between pump inlet and outlet. Despite the development of 6 different prototypes, this project was not realized. Under the above-mentioned conditions, the main problem of this type of blood pump, the blood trauma, could not be reduced to an adequate level, i.e., the Mini-Spindle-Pump is not a high speed pump. Therefore, a revision of the conception was necessary. The device in a mock circuit should transport 5 L of water/min at a speed of about 9,000 rpm against a pressure difference of 90 mm Hg between its inlet and outlet. Considering the implantability of the blood pump, the following measurements for its components were arrived at. The U-shaped blockformed plexiglas housing was enlarged to 120 x 40 x 40 mm (length of blood chamber 86 mm, inner diameter 27 mm), and the rotor with 5 windings was redesigned at a length of 64 mm (outer diameter 25 mm, inner diameter 6.7 mm). In a mock circuit, this 7th prototype transported with a speed of 9,000 rpm about 10 L of water/min at an afterload of 80 mm Hg. In acute animal experiments with calves up to 15 h of pumping duration, the device showed the expected efficiency. Experiments with a longer pumping duration are necessary to confirm that this prototype will fulfill the criteria of a short-term pump according to Dr. Y. Nosé's advice.