Third-generation Blood Pumps With Mechanical Noncontact Magnetic Bearings

Numerical investigation on the effect of impeller axial position on hemodynamics of an extracorporeal centrifugal blood pump

Extracorporeal centrifugal blood pumps are used to treat cardiogenic shock. Owing to the imbalanced excitation or initial assembly configurations, the variation in the impeller axial position has the potential to affect the blood pump performance. This study compared the hydrodynamics and hemolysis outcomes at different impeller axial positions via numerical simulations. The result shows that pressure difference of the blood pump decreased with increasing impeller axial position, with decreasing by 4.5% at a flow rate of 2 L/min. Under axial impeller motion close to the top pump casing, average wall shear stress and scalar shear stress reached their maximum values (64.2 and 29.1 Pa, respectively). The residence time in the impeller center hole and bottom clearance were extended to 0.5 s by increasing impeller axial position. Compared to the baseline blood pump, hemolysis index increased by 12.3% and 24.3% when impeller axial position is 2.5 and 4.0 mm, respectively. As a novelty, the findings reveal that the impeller axial position adversely affects hemolysis performance when the impeller is close to the pump casing. Therefore, in the development process of centrifugal blood pumps, the optimal axial position of the impeller must be defined to ensure hemodynamic performance.

Prevention of thrombus formation in blood pump by mechanical circular orbital excitation of impeller in magnetically levitated centrifugal pump

BACKGROUND

Mechanical circulatory support devices, such as left ventricular assist devices, have recently been used in patients with heart failure as destination therapy but the formation of thrombus in blood pumps remains a critical problem. In this study, we propose a mechanical antithrombogenic method by impeller excitation using a magnetically levitated (Maglev) centrifugal pump. Previous studies have shown that one-directional excitation prevents thrombus; however, it is effective in only one direction. In this study, we aimed to obtain a better effect by vibrating it in a circular orbit to induce uniform changes in the shear-rate field entirely around the impeller.

METHODS

The blood coagulation time was compared using porcine blood. (1) The flow rate was set to 1 L/min, and applied excitation was at a frequency of 280 Hz and amplitude of 3 μm. (2) Moreover, the effect was compared by varying the frequency, amplitude, and direction of the excitation. In this experiment, the flow rate was set to 0.3 L/min.

RESULTS

(1) The thrombus formation time was 77 min without excitation and 133 min with excitation, which was 1.7 times longer. (2) The results showed no difference between (280 Hz, 3 μm) and (50 Hz, 16 μm) circular orbital excitations, and no directional difference, with thrombus formation of 2.5 times longer under all conditions than that without excitation.

CONCLUSION

In the case of simple reciprocating excitation, the time was approximately 1.2 times longer. This indicated that the circular orbital excitation is more effective.

Analysis of Plasma Skimming within a Hydrodynamic Bearing Gap for Designing Spiral Groove Bearings in Rotary Blood Pumps

The blood damage problem inside the narrow hydrodynamic bearing is potentially considered to be solved by applying plasma skimming. However, the consideration of improving plasma skimming has not been included in the design of hydrodynamic bearings. The absence of experimental investigation on revealing the relationship between blood flow and plasma skimming in the bearing gap impedes the design of groove shape for plasma skimming. Thus, the present study was undertaken to evaluate how the blood flow direction and the groove shape affect plasma skimming in the bearing gap. To this end, blood tests using porcine blood were repeated three times with a hematocrit of 0.8%. The bearing gap during the tests was adjusted to 25 µm and the rotational speed was adjusted from 50 rpm to 2500 rpm. The blood flow and plasma skimming effect was evaluated based on image analysis utilizing a high-speed microscope. Results of three tests indicated that the flow direction of RBCs was dominated by the rotating surface in the bearing gap when the rotational speed increased over 1200 rpm. The best plasma skimming effect was observed when the angle between the flow direction of RBCs and the tangent line of the groove was within -10 degrees to 10 degrees. The future study will be conducted with including the consideration of plasma skimming in the bearing shape design. The findings in this study aid the future design and development of hydrodynamic bearing for use in rotary blood pumps.

Hydrodynamic Bearing Structural Design of Blood Pump Based on Axial Passive Suspension Stability Analysis of Magnetic–Hydrodynamic Hybrid Suspension System

Rotor suspension stability is one of the important performance indexes of a blood pump and the basis of determining whether the blood pump can be used in a clinic. Compared with the traditional magnetic suspension system, a single-winding, bearingless motor has the advantages of a compact structure, simple control system and low power consumption. In this pursuit, the present study aimed to envisage and design the magnetic suspension system coupled with a single-winding bearingless motor and permanent magnet bearings, establish the theoretical models of axial force and electromagnetic torque, and calculate the stiffness of the magnetic suspension system at the equilibrium point. Addressing the problem of the negative axial stiffness of the magnetic suspension system being negative, which leads to the instability of the suspension rotor, the hydrodynamic bearing structure was proposed and designed, and the critical stiffness to realize the stable suspension of the rotor was obtained based on the stability criterion of the rotor dynamics model. The optimal structural parameters of the hydrodynamic bearing are selected by integrating various factors based on the solution of the Reynolds equation and a stiffness analysis. Furthermore, the vibration experiment results proved that the blood pump rotor exhibited a good suspension stability, and the maximum offset under the impact external fluid was no more than 2 μm.

Novel Copper Nanoparticles Intercalated Polyurethane Heparin/Poly-L-Lysine Chelates Coated Stents: Viability Study for Coronary Vascular Cells and Aneurysms Treatments

Continuous delayed endothelium regeneration and continues thrombosis development designate a task for coronary artery stent rehabilitation. To progress the direct vascular cell behavior, aneurysms treatments and compatibility of cardiovascular implants novel copper intercalated polyurethane heparin/poly-L-lysine chelates treated stent has established in this report. The functional group modifications, structural characteristics, and stability of the chelates have investigated for polyurethane heparin: poly-L-lysine, copper intercalated polyurethane heparin/poly-L-lysine coated stents. The FTIR results showed the copper intercalation at 446 cmr and the Cu 2s peak at 932 eV from XPS also indicated that the successful coating of copper, polyurethane heparin, poly-L-lysine. The relative surface geomorphology of the chelates displayed the uniform Cu coating consisting of multilayer poly-L-lysine on the substrate. The stability and biocompatibility studies indicated the significantly enhanced performance with clot the APTT and TT periods as clotting and cell proliferation assessments. This type of composite proposes a stage on a stent external area for discerning track of vascular cell performance and aneurysms treatments with low side effects.

Homopolar Bearingless Slice Motor with Flux-biasing Halbach Arrays

We present a new configuration of bearingless slice motor that levitates and rotates a ring-shaped solid steel reluctance rotor. The rotor is 50 mm in diameter and has salient features on the outer surface. Symmetric sets of Halbach magnet arrays, mounted on the tips of stator teeth, establish a homopolar bias flux around the rotor. The bias flux passively stabilizes the rotor in the out-of-plane tilts and axial translation, whereas the rotor's radial translations are actively stabilized by feedback control. The rotor saliencies spatially modulate the air-gap bias flux such that the resulting torque-current relationship is similar to that of permanent-magnet synchronous machines. We have designed, built, and tested a prototype bearingless motor and control system. The prototype system achieves a torque constant of 14.9mNm/A, maximum speed of 5500 rpm, and suspension bandwidth of 84 Hz with a phase margin of 11.3 deg. The rated torque and speed are 26.8 mNm and 3486 rpm, and the axial and tilting passive stiffnesses are 15.3 N/mm and 34.4 mNm/deg.

Study on Clearance-Rubbing Dynamic Behavior of 2-DOF Supporting System of Magnetic-Liquid Double Suspension Bearing

As a new type of suspension bearing, Magnetic-Liquid Double Suspension Bearing (MLDSB) is mainly supported by electromagnetic suspension and supplemented by hydrostatic supporting. Its bearing capacity and stiffness can be greatly improved. Because of the small liquid film thickness (it is smaller 10 times than air gap), the eccentricity, crack, bending of the rotor, and the assembly error, it is easy to cause a clearance-rubbing fault between the rotor and stator. The coating can be worn and peeled, the operating stability can be reduced, and then it is one of the key problems of restricting the development and application of MLDSB. Therefore, the clearance-rubbing dynamic equation of 2-DOF system of MLDSB is established and converted into Taylor Series form and the nonlinear components are retained. Dimensionless treatment is carried out by dimensional normalization method. Finally, the rotor displacement response under different rotor eccentricity ratio and rotating speeds is numerically simulated. The studies show that the trajectory of the rotor is periodic elliptic without clearance-rubbing phenomenon when the eccentricity ratio is less than 0.2, while the rotor is greatly affected by the rotation speed and a variety of motions, such as single-period, quasi-period, double-period and chaos, are presented when greater than 0.3. Within the largest range of rotating speed and eccentricity ratio, the rotor presents the single-period trajectory, and then the number of Poincare mapping point is 1, without a clearance-rubbing fault. When the rotational speed is in the scope of (9, 13) krpm and the eccentricity ratio is in the scope of (0.27, 0.4), the number of Poincare mapping point is more than one, the maximum dimensionless rubbing force is −5.7, and then clearance-rubbing fault occurs. The research can provide a theoretical basis for the safe and stable operation of MLDSB.

Evaluation method and platform of vibrational disturbance test for ventricular assist devices

OBJECTIVE

For ventricular assist devices utilizing levitation bearing technology, collision and wear of the rotor would occur if the bearing cannot resist disturbances from patient activities and vibration/shock impacts. The reliability of ventricular assist devices can be seriously affected, potentially impairing blood compatibility (e.g. thrombus generation) and threatening patient safety. In this article, we proposed a vibrational disturbance test protocol for ventricular assist devices.

METHODS

Two kinds of vibrational disturbances-translational and rotational-were defined and the disturbance levels determined as 6G and 10 rad/s per possible patient activity impact. A test platform was built according to the disturbance level requirements.

RESULTS

The test platform successfully generated the required disturbance. The vibration test evaluation criteria for ventricular assist device assistance (characterized by the pressure head, flow rate, and driving current waveform) were well verified.

CONCLUSION

Compared with translational vibration, rotational vibration had a greater impact on the rotor. Accurate control of high-speed rotor is difficult because of the gyroscopic effect. As conventional random vibration tests cannot cover all risk situations, it is recommended that translational and rotational disturbance tests are carried out for levitation ventricular assist devices. We recommend that researchers and manufacturers pay attention to the vibrational impact of rotor-levitated ventricular assist devices.

Outcomes of percutaneous temporary biventricular mechanical support: a systematic review

Percutaneous biventricular assist devices (BiVAD) are a recently developed treatment option for severe cardiogenic shock. This systematic review sought to identify indications and outcomes of patients placed on percutaneous BiVAD support. An electronic search was performed to identify all appropriate studies utilizing a percutaneous BiVAD configuration. Fifteen studies comprising of 20 patients were identified. Individual patient survival and outcomes data were combined for statistical analysis. All 20 patients were supported with a microaxial LVAD, 12/20 (60%) of those patients were supported with a microaxial (RMA) right ventricular assist device (RVAD), and the remaining 8/20 (40%) patients were supported with a centrifugal extracorporeal RVAD (RCF). All patients presented with cardiogenic shock, and of these, 12/20 (60%) presented with a non-ischemic etiology vs 8/20 (40%) with ischemic disease. For the RMA group, RVAD support was significantly longer [RMA 5 (IQR 4-7) days vs RCF 1 (IQR 1-2) days, p = 0.03]. Intravascular hemolysis post-BiVAD occurred in three patients (27.3%) [RMA 3 (33.3%) vs RCF 0 (0%), p = 0.94]. Five patients received a durable left ventricular assist device, one patient received a total artificial heart, and one patient underwent a heart transplantation. Estimated 30-day mortality was 15.0%, and 78.6% were discharged alive. Both strategies for percutaneous BiVAD support appear to be viable options for severe cardiogenic shock.

Pediatric ventricular assist devices: what are the key considerations and requirements?

Introduction: The development of ventricular assist devices (VADs) have enabled myocardial recovery and improved patient survival until heart transplantation. However, device options remain limited for children and lag in development.Areas covered: This review focuses on the evolution of pediatric VADs in becoming to be an accepted treatment option in advanced heart failure, discusses the classification of VADs available for children, i.e. types of pumps and duration of support, and defines implantation indications and explantation criteria, describes attendant complications and long-term outcome of VAD support. Furthermore, we emphasize the key considerations and requirements in the application of these devices in infants, children and adolescents.Expert opinion: Increasing use of VADs has facilitated a leading edge in management of advanced heart failure either as a bridge to transplantation or as a bridge to myocardial recovery. In newborns and small children, the EXCOR Pediatric VAD remains the only reliable option. In some patients ventricular unloading may lead to complete myocardial recovery. There is a strong need for pumps that are fully implantable, suitable for single ventricle physiology, such as the right ventricle.

Performance Enhancement of a Magnetic System in a Ultra Compact 5-DOF-Controlled Self-Bearing Motor for a Rotary Pediatric Ventricular-Assist Device to Diminish Energy Input

Research interests of compact magnetically levitated motors have been strongly increased in development of durable and biocompatible mechanical circulatory support (MCS) devices for pediatric heart disease patients. In this study, an ultra-compact axial gap type self-bearing motor with 5-degrees of freedom (DOF) active control for use in pediatric MCS devices has been developed. The motor consists of two identical motor stators and a centrifugal levitated rotor. This paper investigated a design improvement of the magnetic circuit for the self-bearing motor undergoing development in order to diminish energy input by enhancing magnetic suspension and rotation performances. Geometries of the motor were refined based on numerical calculation and three-dimensional (3D) magnetic field analysis. The modified motor can achieve higher suspension force and torque characteristics than that of a previously developed prototype motor. Oscillation of the levitated rotor was significantly suppressed by 5-DOF control over rotating speeds up to 7000 rpm with lower energy input, indicating efficacy of the design refinement of the motor.

Miniaturized centrifugal ventricular assist device for bridge to decision: Preclinical chronic study in a bovine model

We developed a novel miniaturized extracorporeal centrifugal pump "BIOFLOAT NCVC (Nipro Corporation Osaka, Japan) as a ventricular assist device (VAD) and performed a preclinical study that is part of the process for its approval as a bridge to decision by the pharmaceutical and medical device agencies. The aim of this study was to assess the postoperative performance, hemocompatibility, and anticoagulative status during an extended period of its use. A VAD system, consisting of a hydrodynamically levitated pump, measuring 64 mm by 131 mm in size and weighing 635 g, was used. We installed this assist system in 9 adult calves (body weight, 90 ± 13 kg): as left ventricular assist device (LVAD) in 6 calves and right ventricular assist device (RVAD) in 3 calves, for over 30 days. Perioperative hemodynamic, hematologic, and blood chemistry measurements were obtained and end-organ effects on necropsy were investigated. All calves survived for over 30 days, with a good general condition. The blood pump was operated at a mean rotational speed and a mean pump flow of 3482 ± 192 rpm and 4.08 ± 0.15 L/min, respectively, for the LVAD and 3902 ± 210 rpm and 4.24 ± 0.3 L/min, respectively, for the RVAD. Major adverse events, including neurological or respiratory complications, bleeding events, and infection were not observed. This novel VAD enabled a long-term support with consistent and satisfactory hemodynamic performance and hemocompatibility in the calf model. The hemodynamic performance, hemocompatibility, and anticoagulative status of this VAD system were reviewed.

Measuring real-time blood viscosity with a ventricular assist device

Ventricular assist devices assist in blood circulation and form a crucial component of artificial hearts. While it is important to measure parameters such as the flow rate, pressure head and viscosity of the blood, implanting additional devices to do such measurements is inadvisable. To this end, we demonstrate the adaptation of a ventricular assist device for the purpose of measuring blood viscosity. Such an approach eliminates the need for additional dedicated viscometers in artificial hearts. In the proposed method, the blood viscosity is measured by applying radial vibrational excitation to the impeller in a ventricular assist device using its magnetic levitation system. During the measurement, blood is exposed to a combination of a low shear rate (≈100/s) generated by the radial vibration of the impeller and a high shear rate (>10,000/s) generated by the impeller’s rotation. The apparent viscosity of blood depends on the shear rate, so we determined which shear rate was the dominant one in the proposed method. The measurement results showed that the viscosity measured by the proposed method was in good agreement with the reference viscosity measured with a high shear rate. The mean absolute deviation in the measurements using the proposed method and those obtained using a concentric cylindrical viscometer at a high shear rate was 0.12 mPa s for four samples of porcine blood, with viscosities ranging from 2.32 to 2.75 mPa s.

Assessment of Safety and Effectiveness of the Extracorporeal Continuous-Flow Ventricular Assist Device (BR16010) Use as a Bridge-to-Decision Therapy for Severe Heart Failure or Refractory Cardiogenic Shock: Study Protocol for Single-Arm Non-randomized, Uncontrolled, and Investigator-Initiated Clinical Trial

BACKGROUND

The management of heart failure patients presenting in a moribund state remains challenging, despite significant advances in the field of ventricular assist systems. Bridge to decision involves using temporary devices to stabilize the hemodynamic state of such patients while further assessment is performed and a decision can be made regarding patient management. The purpose of this study (NCVC-BTD_01, National Cerebral and Cardiovascular Center-Bridge to Dicision_01) is to assess the safety and effectiveness of the newly developed extracorporeal continuous-flow ventricular assist system employing a disposable centrifugal pump with a hydrodynamically levitated bearing (BR16010) use as a bridge-to-decision therapy for patients with severe heart failure or refractory cardiogenic shock.

METHOD/DESIGN

NCVC-BTD_01 is a single-center, single-arm, open-label, exploratory, medical device, investigator-initiated clinical study. It is conducted at the National Cerebral and Cardiovascular Center in Japan. A total of nine patients will be enrolled in the study. The study was planned using Simon's minimax two-stage phase design. The primary endpoint is a composite of survival free of device-related serious adverse events and complications during device support. For left ventricular assistance, withdrawal of a trial device due to cardiac function recovery or exchange to other ventricular assist devices (VADs) for the purpose of bridge to transplantation (BTT) during 30 days after implantation will be considered study successes. For right ventricular assistance, withdrawal of tal device due to right ventricular function recovery within 30 days after implantation will be considered a study success. Secondary objectives include changes in brain natriuretic peptide levels (7 days after implantation of a trial device and the day of withdrawal of a trial device), period of mechanical ventricular support, changes in left ventricular ejection fraction (7 days after implantation of a trial device and the day of withdrawal of a trial device), and changes in left ventricular diastolic dimension (7 days after implantation of a trial device and the day of withdrawal of a trial device).

ETHICS AND DISSEMINATION

We will disseminate the findings through regional, national, and international conferences and through peer-reviewed journals.

TRIAL REGISTRATION

UMIN Clinical Trials Registry (UMIN-CTR; R000033243) registered on 8 September 2017.

Development of an Intelligent Ventricular Assist Device with a Function of Sensorless Thrombus Detection

Thrombus is one of the major problems in ventricular assist devices (VADs). However, method for detecting thrombus in early stage has not been established yet. In this study, we propose an intelligent function that the VAD itself can detect thrombus automatically and alert it to medical staffs. In the proposed method, thrombus formation inside a blood pump is detected by monitoring blood viscosity. This viscosity measurement is performed by using magnetic levitation system for the impeller. Hence, it can be implemented without any additional sensors or mechanisms in principle. For verification of the method, at first, we visualized inside of the pump during thrombus formation with measuring blood viscosity by using erythrocytes removed porcine blood. The result showed that the viscosity of the blood increased as blood coagulation progressed. Then, we conducted in vitro principle verification experiments with three different whole porcine blood. In all experiments, the measured blood viscosity increased and small thrombus was observed inside the pump. From these results, we confirmed that the proposed method has a possibility to detect and predict the thrombus in early stage.

Preoperative Predictors of Mortality in Short-Term Continuous-Flow Ventricular Assist Devices

Short-term continuous-flow ventricular assist devices (STCF-VADs) are increasingly being utilized to support critically ill patients, despite limited information regarding overall outcomes. All adult patients supported with an STCF-VAD between June 2009 and December 2015 were included in this retrospective single-center study. Associations between preoperative characteristics and unsuccessful bridge (death on device or within 30 days postdecannulation) were assessed using logistic regression. A total of 61 patients (77% male) were identified with a median age at implant of 54.6 years. Left VADs were implanted in 51%, right VADs in 21%, and both VADs in 28%, and patients were supported for a median of 11 days. Overall, 23% were weaned to recovery, 13% underwent heart transplantation, 16% converted to long-term VADs, and 48% had an unsuccessful bridge. In multivariable analysis, only renal insufficiency or dialysis (odds ratio = 7.53; p = 0.002) remained a significant independent predictor of an unsuccessful bridge. Short-term continuous-flow VADs can successfully bridge adult patients with mortality around 50%. Preimplant renal insufficiency or dialysis is correlated with an unsuccessful bridge in our patient population, likely reflecting the severity of illness preimplant. Further studies are required to determine whether this factor remains significant in a larger patient population.

HYDRAULICS AND IN VITRO HEMOLYSIS TEST OF A MAGLEV IMPLANTABLE VENTRICULAR ASSIST DEVICE

A small implantable centrifugal left ventricular assist device, the CH-VAD (CH Biomedical Inc, JiangSu, China), featuring a magnetically levitated impeller is under development. The goal of this study is to validate hydrodynamic performance and hemocompatibility of the pump through in vitro studies. The hydraulic performance was quantified experimentally by using in vitro circulation loop system, and it turned out that the pump could deliver 5[Formula: see text]L/min under a pressure of 100[Formula: see text]mmHg at a rotational speed of approximate 3400[Formula: see text]rpm. A series of in vitro tests were established according to ASTM F1841, the standard practice for the assessment of hemolysis in continuous-flow blood pumps. The results showed that the average normalized index of hemolysis (NIH) value of the VAD was 0.0007[Formula: see text][Formula: see text][Formula: see text]0.0003[Formula: see text]mg/dL. The magnetic levitation left ventricular assist device (LVAD) has good hemolytic performance and stable mechanical property. These acceptable performance results supported proceeding initial acute animal testing conditions.

Current State and Future Perspectives of Energy Sources for Totally Implantable Cardiac Devices

There is a large population of patients with end-stage congestive heart failure who cannot be treated by means of conventional cardiac surgery, cardiac transplantation, or chronic catecholamine infusions. Implantable cardiac devices, many designated as destination therapy, have revolutionized patient care and outcomes, although infection and complications related to external power sources or routine battery exchange remain a substantial risk. Complications from repeat battery replacement, power failure, and infections ultimately endanger the original objectives of implantable biomedical device therapy - eliminating the intended patient autonomy, affecting patient quality of life and survival. We sought to review the limitations of current cardiac biomedical device energy sources and discuss the current state and trends of future potential energy sources in pursuit of a lifelong fully implantable biomedical device.

Novel temporary left ventricular assist system with hydrodynamically levitated bearing pump for bridge to decision: initial preclinical assessment in a goat model

The management of heart failure patients presenting in a moribund state remains challenging, despite significant advances in the field of ventricular assist systems. Bridge to decision involves using temporary devices to stabilize the hemodynamic state of such patients while further assessment is performed and a decision can be made regarding patient management. We developed a new temporary left ventricular assist system employing a disposable centrifugal pump with a hydrodynamically levitated bearing. We used three adult goats (body weight, 58-68 kg) to investigate the 30-day performance and hemocompatibility of the newly developed left ventricular assist system, which included the pump, inflow and outflow cannulas, the extracorporeal circuit, and connectors. Hemodynamic, hematologic, and blood chemistry measurements were investigated as well as end-organ effect on necropsy. All goats survived for 30 days in good general condition. The blood pump was operated at a rotational speed of 3000-4500 rpm and a mean pump flow of 3.2 ± 0.6 L min. Excess hemolysis, observed in one goat, was due to the inadequate increase in pump rotational speed in response to drainage insufficiency caused by continuous contact of the inflow cannula tip with the left ventricular septal wall in the early days after surgery. At necropsy, no thrombus was noted in the pump, and no damage caused by mechanical contact was found on the bearing. The newly developed temporary left ventricular assist system using a disposable centrifugal pump with hydrodynamic bearing demonstrated consistent and satisfactory hemodynamic performance and hemocompatibility in the goat model.

Rotary mechanical circulatory support systems

A detailed survey of the current trends and recent advances in rotary mechanical circulatory support systems is presented in this paper. Rather than clinical reports, the focus is on technological aspects of these rehabilitating devices as a reference for engineers and biomedical researchers. Existing trends in flow regimes, flow control, and bearing mechanisms are summarized. System specifications and applications of the most prominent continuous-flow ventricular assistive devices are provided. Based on the flow regime, pumps are categorized as axial flow, centrifugal flow, and mixed flow. Unique characteristics of each system are unveiled through an examination of the structure, bearing mechanism, impeller design, flow rate, and biocompatibility. A discussion on the current limitations is provided to invite more studies and further improvements.

Ventricular Assist Devices: Current State and Challenges

Cardiovascular disease (CVD), as the most prevalent human disease, incorporates a broad spectrum of cardiovascular system malfunctions/disorders. While cardiac transplantation is widely acknowledged as the optional treatment for patients suffering from end-stage heart failure (HF), due to its related drawbacks, such as the unavailability of heart donors, alternative treatments, i.e., implanting a ventricular assist device (VAD), it has been extensively utilized in recent years to recover heart function. However, this solution is thought problematic as it fails to satisfactorily provide lifelong support for patients at the end-stage of HF, nor does is solve the problem of their extensive postsurgery complications. In recent years, the huge technological advancements have enabled the manufacturing of a wide variety of reliable VAD devices, which provides a promising avenue for utilizing VAD implantation as the destination therapy (DT) in the future. Along with typical VAD systems, other innovative mechanical devices for cardiac support, as well as cell therapy and bioartificial cardiac tissue, have resulted in researchers proposing a new HF therapy. This paper aims to concisely review the current state of VAD technology, summarize recent advancements, discuss related complications, and argue for the development of the envisioned alternatives of HF therapy.

Machinability and Optimization of Shrouded Centrifugal Impellers for Implantable Blood Pumps

This paper describes the use of analytical methods to determine machinable centrifugal impeller geometries and the use of computational fluid dynamics (CFD) for predicting the impeller performance. An analytical scheme is described to determine the machinable geometries for a shrouded centrifugal impeller with blades composed of equiangular spirals. The scheme is used to determine the maximum machinable blade angles for impellers with three to nine blades in a case study. Computational fluid dynamics is then used to analyze all the machinable geometries and determine the optimal blade number and angle based on measures of efficiency and rotor speed. The effect of tip width on rotor speed and efficiency is also examined. It is found that, for our case study, a six- or seven-bladed impeller with a low blade angle provides maximum efficiency and minimum rotor speed.

Ventricular assist devices and sleep-disordered breathing

Congestive heart failure is one of the leading causes of morbidity and mortality in the United States, and left ventricular assist devices have revolutionized treatment of end-stage heart failure. Given that sleep apnea results in significant morbidity in these patients with advanced heart failure, practicing sleep physicians need to have an understanding of left ventricular assist devices. In this review, we summarize what is known about ventricular assist devices as they relate to sleep medicine.

Supporting pediatric patients with short-term continuous-flow devices

BACKGROUND

Short-term continuous-flow ventricular assist devices (STCF-VADs) are increasingly being used in the pediatric population. However, little is known about the outcomes in patients supported with these devices.

METHODS

All pediatric patients supported with a STCF-VAD, including the Thoratec PediMag or CentriMag, or the Maquet RotaFlow, between January 2005 and May 2014, were included in this retrospective single-center study.

RESULTS

Twenty-seven patients (15 girls [56%]) underwent 33 STCF-VAD runs in 28 separate hospital admissions. The STCF-VAD was implanted 1 time in 23 patients (85%), 2 times in 2 patients (7%), and 3 times in 2 patients (7%). Implantation occurred most commonly in the context of congenital heart disease in 14 runs (42.2%), cardiomyopathy in 11 (33%), and after transplant in 6 (18%). The median age at implantation was 1.7 (interquartile range [IQR] 0.1, 4.1) years, and median weight was 8.9 kg (IQR 3.7, 18 kg). Patients were supported for a median duration of 12 days (IQR 6, 23 days) per run; the longest duration was 75 days. Before implantation, 15 runs (45%) were supported by extracorporeal membrane oxygenation (ECMO). After implantation, an oxygenator was required in 20 runs (61%) and continuous renal replacement therapy in 21 (64%). Overall, 7 runs (21%) resulted in weaning for recovery, 14 (42%) converted to a long-term VAD, 4 (12%) resulted in direct transplantation, 3 (9%) were converted to ECMO, and 5 (15%) runs resulted in death on the device or within 1 month after decannulation. The most common complication was bleeding requiring reoperation in 24% of runs. In addition, 18% of runs were associated with neurologic events and 15% with a culture-positive infection. Hospital discharge occurred in 19 of 28 STCF-VAD admissions (67%). In follow-up, with a median duration of 9.2 months (IQR 2.3, 38.3 months), 17 patients (63%) survived.

CONCLUSIONS

STCF-VADs can successfully bridge most pediatric patients to recovery, long-term device, or transplant, with an acceptable complication profile. Although these devices are designed for short-term support, longer support is possible and may serve as an alternative approach to patients not suitable for the current long-term devices.

Control of Magnetic Bearings for Rotor Unbalance With Plug-In Time-Varying Resonators

Rotor unbalance, common phenomenon of rotational systems, manifests itself as a periodic disturbance synchronized with the rotor's angular velocity. In active magnetic bearing (AMB) systems, feedback control is required to stabilize the open-loop unstable electromagnetic levitation. Further, feedback action can be added to suppress the repeatable runout but maintain closed-loop stability. In this paper, a plug-in time-varying resonator is designed by inverting cascaded notch filters. This formulation allows flexibility in designing the internal model for appropriate disturbance rejection. The plug-in structure ensures that stability can be maintained for varying rotor speeds. Experimental results of an AMB-rotor system are presented.

Computational Fluid Dynamics-Based Design Optimization Method for Archimedes Screw Blood Pumps

An optimization method suitable for improving the performance of Archimedes screw axial rotary blood pumps is described in the present article. In order to achieve a more robust design and to save computational resources, this method combines the advantages of the established pump design theory with modern computer-aided, computational fluid dynamics (CFD)-based design optimization (CFD-O) relying on evolutionary algorithms and computational fluid dynamics. The main purposes of this project are to: (i) integrate pump design theory within the already existing CFD-based optimization; (ii) demonstrate that the resulting procedure is suitable for optimizing an Archimedes screw blood pump in terms of efficiency. Results obtained in this study demonstrate that the developed tool is able to meet both objectives. Finally, the resulting level of hemolysis can be numerically assessed for the optimal design, as hemolysis is an issue of overwhelming importance for blood pumps.

Evaluation of a Spiral Groove Geometry for Improvement of Hemolysis Level in a Hydrodynamically Levitated Centrifugal Blood Pump

The purpose of this study is to evaluate a spiral groove geometry for a thrust bearing to improve the hemolysis level in a hydrodynamically levitated centrifugal blood pump. We compared three geometric models: (i) the groove width is the same as the ridge width at any given polar coordinate (conventional model); (ii) the groove width contracts inward from 9.7 to 0.5 mm (contraction model); and (iii) the groove width expands inward from 0.5 to 4.2 mm (expansion model). To evaluate the hemolysis level, an impeller levitation performance test and in vitro hemolysis test were conducted using a mock circulation loop. In these tests, the driving conditions were set at a pressure head of 200 mm Hg and a flow rate of 4.0 L/min. As a result of the impeller levitation performance test, the bottom bearing gaps of the contraction and conventional models were 88 and 25 μm, respectively. The impeller of the expansion model touched the bottom housing. In the hemolysis test, the relative normalized index of hemolysis (NIH) ratios of the contraction model in comparison with BPX-80 and HPM-15 were 0.6 and 0.9, respectively. In contrast, the relative NIH ratios of the conventional model in comparison with BPX-80 and HPM-15 were 9.6 and 13.7, respectively. We confirmed that the contraction model achieved a large bearing gap and improved the hemolysis level in a hydrodynamically levitated centrifugal blood pump.

Devices in heart failure--the new revolution

Heart failure is a growing epidemic, with more patients living longer and suffering from this disease. There is a growing segment of patients who have persistent symptoms despite pharmacologic therapy. In an era when transplants are rare, the need for devices and interventions that can assist ventricular function is paramount. This review goes through the devices used in heart failure, including left ventricular reconstruction, aortic counterpulsation, short-term mechanical circulatory support, long-term mechanical circulatory support, and right heart interventions.

Treatment strategies for patients with an INTERMACS I profile

Treatment of patients with INTERMACS class I heart failure can be very challenging, and temporary long-term device support may be needed. In this article, we review the currently available temporary support devices in order to support these severely ill patients with decompensated heart failure. Strategies of using a temporary assist as a bridge to long-term device support are also discussed.

Survival on biventricular mechanical support with the Centrimag® as a bridge to decision: a single-center risk stratification

Objective:

Temporary mechanical assist devices are increasingly being used as a lifesaving bridge to decision in patients requiring cardiopulmonary resuscitation. We report our single-center experience with biventricular Centrimag® pumps over a five-year period.

Method:

Data was retrospectively collected in consecutive patients who required biventricular support from 2008 to 2013. Patients who were supported with central cannulation using the Centrimag® system were analyzed. In addition to demographic information, data pertaining to indications, outcomes and mortality were collected.

Results:

The cohort consisted of 48 patients (19 women and 29 men, mean age of 56 years). The median duration of support was 14 days. The median duration to patient expiration while still on the Centrimag® was 12 days. Thirty-day survival was 56% (27/48). Nine patients were explanted to recovery, while fourteen patients were converted to a durable LVAD, two of whom were then transplanted. We stratified patients into two groups. Group I comprised patients who were either explanted to recovery, converted to durable LVAD or transplanted (23/48) and Group II consisted of patients who either died on the Centrimag® or were explanted for withdrawal of care (25/48). Statistical analysis did not reveal any clinically significant differences between the two groups in terms of age, sex, etiology, hemodynamic, co-morbidities or laboratory parameters.

Conclusion:

The biventricular Centrimag® can be used as a bridge to decision in patients with thirty-day survival of >50%. Parameters to predict 30-day survival in this high-risk cohort continue to remain elusive.

An insight into short- and long-term mechanical circulatory support systems

Cardiogenic shock due to acute myocardial infarction, postcardiotomy syndrome following cardiac surgery, or manifestation of heart failure remains a clinical challenge with high mortality rates, despite ongoing advances in surgical techniques, widespread use of primary percutaneous interventions, and medical treatment. Clinicians have, therefore, turned to mechanical means of circulatory support. At present, a broad range of devices are available, which may be extracorporeal, implantable, or percutaneous; temporary or long term. Although counter pulsation provided by intra-aortic balloon pump (IABP) and comprehensive mechanical support for both the systemic and the pulmonary circulation through extracorporeal membrane oxygenation (ECMO) remain a major tool of acute care in patients with cardiogenic shock, both before and after surgical or percutaneous intervention, the development of devices such as the Impella or the Tandemheart allows less invasive forms of temporary support. On the other hand, concerning mid-, or long-term support, left ventricular assist devices have evolved from a last resort life-saving therapy to a well-established viable alternative for thousands of heart failure patients caused by the shortage of donor organs available for transplantation. The optimal selection of the assist device is based on the initial consideration according to hemodynamic situation, comorbidities, intended time of use and therapeutic options. The present article offers an update on currently available mechanical circulatory support systems (MCSS) for short and long-term use as well as an insight into future perspectives.

Use of a single circuit to provide temporary mechanical respiratory and circulatory support in patients with LV apical thrombus and cardiogenic shock

Introduction:

Techniques to support patients with cardiogenic shock continue to improve. Patients with intracardiac thrombi pose a potential for additional complications. Novel methods of biventricular support are necessary to manage these patients.

Methods:

Two patients with refractory cardiogenic shock and left ventricular apical thrombi underwent mechanical circulatory support (MCS) as a bridge to decision, with a left ventricular assist device (LVAD) and extracorporeal mechanical oxygenation (ECMO). Instead of the conventional LV apical cannulation for LVAD, the left atrium (LA) was cannulated. The LA cannula was then integrated with the ECMO circuit via a ‘Y’ connection to a percutaneous right atrial cannula, enabling optimal drainage of both sides into one circuit through a single CentriMag® pump and ECMO into the aorta.

Results:

The first patient was converted to a durable LVAD and transplanted, while the second patient was explanted, after demonstrating significant LV recovery.

Conclusion:

We demonstrated the use of MCS as a bridge to decision in patients with LV thrombi, utilizing biatrial cannulation with a ‘Y’ connection to drain both right- and left-sided circulation through a single circuit and pump.

Noninvasive blood-flow meter using a curved cannula with zero compensation for an axial flow blood pump

In order to monitor the condition of a patient using a left ventricular assist system (LVAS), blood flow should be measured. However, the reliable determination of blood-flow rate has not been established. The purpose of the present study is to develop a noninvasive blood-flow meter using a curved cannula with zero compensation for an axial flow blood pump. The flow meter uses the centrifugal force generated by the flow rate in the curved cannula. Two strain gauges served as sensors. The first gauges were attached to the curved area to measure static pressure and centrifugal force, and the second gauges were attached to straight area to measure static pressure. The flow rate was determined by the differences in output from the two gauges. The zero compensation was constructed based on the consideration that the flow rate could be estimated during the initial driving condition and the ventricular suction condition without using the flow meter. A mock circulation loop was constructed in order to evaluate the measurement performance of the developed flow meter with zero compensation. As a result, the zero compensation worked effectively for the initial calibration and the zero-drift of the measured flow rate. We confirmed that the developed flow meter using a curved cannula with zero compensation was able to accurately measure the flow rate continuously and noninvasively.