Design and evaluation of a single-pivot supported centrifugal blood pump

Mock circulatory loop applications for testing cardiovascular assist devices and in vitro studies

The mock circulatory loop (MCL) is an in vitro experimental system that can provide continuous pulsatile flows and simulate different physiological or pathological parameters of the human circulation system. It is of great significance for testing cardiovascular assist device (CAD), which is a type of clinical instrument used to treat cardiovascular disease and alleviate the dilemma of insufficient donor hearts. The MCL installed with different types of CADs can simulate specific conditions of clinical surgery for evaluating the effectiveness and reliability of those CADs under the repeated performance tests and reliability tests. Also, patient-specific cardiovascular models can be employed in the circulation of MCL for targeted pathological study associated with hemodynamics. Therefore, The MCL system has various combinations of different functional units according to its richful applications, which are comprehensively reviewed in the current work. Four types of CADs including prosthetic heart valve (PHV), ventricular assist device (VAD), total artificial heart (TAH) and intra-aortic balloon pump (IABP) applied in MCL experiments are documented and compared in detail. Moreover, MCLs with more complicated structures for achieving advanced functions are further introduced, such as MCL for the pediatric application, MCL with anatomical phantoms and MCL synchronizing multiple circulation systems. By reviewing the constructions and functions of available MCLs, the features of MCLs for different applications are summarized, and directions of developing the MCLs are suggested.

Single axis controlled hybrid magnetic bearing for left ventricular assist device: hybrid core and closed magnetic circuit

In previous studies, we presented main strategies for suspending the rotor of a mixed-flow type (centrifugal and axial) ventricular assist device (VAD), originally presented by the Institute Dante Pazzanese of Cardiology (IDPC), Brazil. Magnetic suspension is achieved by the use of a magnetic bearing architecture in which the active control is executed in only one degree of freedom, in the axial direction of the rotor. Remaining degrees of freedom, excepting the rotation, are restricted only by the attraction force between pairs of permanent magnets. This study is part of a joint project in development by IDPC and Escola Politecnica of São Paulo University, Brazil. This article shows advances in that project, presenting two promising solutions for magnetic bearings. One solution uses hybrid cores as electromagnetic actuators, that is, cores that combine iron and permanent magnets. The other solution uses actuators, also of hybrid type, but with the magnetic circuit closed by an iron core. After preliminary analysis, a pump prototype has been developed for each solution and has been tested. For each prototype, a brushless DC motor has been developed as the rotor driver. Each solution was evaluated by in vitro experiments and guidelines are extracted for future improvements. Tests have shown good results and demonstrated that one solution is not isolated from the other. One complements the other for the development of a single-axis-controlled, hybrid-type magnetic bearing for a mixed-flow type VAD.

Feasibility of a Miniature Centrifugal Rotary Blood Pump for Low-Flow Circulation in Children and Infants

In this study, a seal-less, tiny centrifugal rotary blood pump was designed for low-flow circulatory support in children and infants. The design was targeted to yield a compact and priming volume of 5 ml with a flow rate of 0.5-4 l/min against a head pressure of 40-100 mm Hg. To meet the design requirements, the first prototype had an impeller diameter of 30 mm with six straight vanes. The impeller was supported with a needle-type hydrodynamic bearing and was driven with a six-pole radial magnetic driver. The external pump dimensions included a pump head height of 20 mm, diameter of 49 mm, and priming volume of 5 ml. The weight was 150 g, including the motor driver. In the mock circulatory loop, using fresh porcine blood, the pump yielded a flow of 0.5-4.0 l/min against a head pressure of 40-100 mm Hg at a rotational speed of 1800-4000 rpm using 1/4" inflow and outflow conduits. The maximum flow and head pressure of 5.25 l/min and 244 mm Hg, respectively, were obtained at a rotational speed of 4400 rpm. The maximum electrical-to-hydraulic efficiency occurred at a flow rate of 1.5-3.5 l/min and at a rotational speed of 2000-4400 rpm. The normalized index of hemolysis, which was evaluated using fresh porcine blood, was 0.0076 g/100 l with the impeller in the down-mode and a bearing clearance of 0.1 mm. Further refinement in the bearing and magnetic coupler are required to improve the hemolytic performance of the pump. The durability of the needle-type hydrodynamic bearing and antithrombotic performance of the pump will be performed before clinical applications. The tiny centrifugal blood pump meets the flow requirements necessary to support the circulation of pediatric patients.

A Complete Mock Circulation Loop for the Evaluation of Left, Right, and Biventricular Assist Devices

A new mock circulation loop was developed to replicate the necessary features of the systemic and pulmonic circulatory systems, including pulsatile left and right ventricles coupled with vascular compliances and resistances. A brief description of the mock loop construction is provided before results are presented confirming the recreation of perfusion rates and pressures found in the natural systemic and pulmonic vascular trees for a normal and failing heart at rest. This rig provides the ability to evaluate the hemodynamic effect of left, right, and biventricular assist devices in vitro. The small and compact mock circulation rig has the potential to reduce device evaluation costs by simulating the natural circulatory system, thus providing valuable device performance feedback prior to expensive in vivo animal trials.

Disposable Magnetically Levitated Centrifugal Blood Pump: Design and In Vitro Performance

A magnetically levitated (MagLev) centrifugal blood pump (CBP) with a disposable pump head has been designed to realize a safe, easy-to-handle, reliable, and low-cost extracorporeal blood pump system. It consisted of a radial magnetic-coupled driver with a magnetic bearing having a two-degree freedom control and a disposable pump head unit with a priming volume of 24 mL. The easy on-off disposable pump head unit was made into a three-piece system consisting of the top and bottom housings, and the impeller-rotor assembly. The size and weight of the disposable pump unit were 75 mm x 45 mm and 100 g, respectively. Because the structure of the pump head unit is easily attachable and removable, the gap between the electromagnets of the stator and the target material in the rotor increased to 1.8 mm in comparison to the original integrated bearing system of 1.0 mm. The pump performance, power requirements, and controllability of the magnetic bearing revealed that from 1400 to 2400 rpm, the pump performance remained fairly unchanged. The amplitudes of the X- and Y-axis rotor oscillation increased to +/- 24 microm. The axial displacement of the rotor, 0.4 mm, toward the top housing was also observed at the pump rpm between 1400 and 2400. The axial and rotational stiffness of the bearing were 15.9 N/mm and 4.4 Nm/rad, respectively. The MagLev power was within 0.7 Watts. This study demonstrated the feasibility of a disposable, magnetically suspended CBP as the safe, reliable, easy-to-handle, low-cost extracorporeal circulation support device.

Magnetically Suspended Centrifugal Blood Pump With a Radial Magnetic Driver

A new magnetic bearing has been designed to achieve a low electronic power requirement and high stiffness. The magnetic bearing consists of 1) radial passive forces between the permanent magnet ring mounted inside the impeller rotor and the electromagnet core materials in the pump casing and 2) radial active forces generated by the electromagnets using the two gap sensor signals. The magnetic bearing was assembled into a centrifugal rotary blood pump (CRBP) driven with a radial, magnetic coupled driver. The impeller vane shape was designed based upon the computational fluid dynamic simulation. The diameter and height of the CRBP were 75 mm and 50 mm, respectively. The magnetic bearing system required the power of 1.0-1.4 W. The radial impeller movement was controlled to within +/- 10 microm. High stiffness in the noncontrolled axes, Z, phi, and theta, was obtained by the passive magnetic forces. The pump flow of 5 L/min against 100 mm Hg head pressure was obtained at 1,800 rpm with the electrical to hydraulic efficiency being greater than 15%. The Normalized Index of Hemolysis (NIH) of the magnetic bearing CRBP was one fifth of the BioPump BP-80 and one half of the NIKKISO HPM-15 after 4 hours. The newly designed magnetic bearing with two degrees of freedom control in combination with optimized impeller vane was successful in achieving an excellent hemolytic performance in comparison with the clinical centrifugal blood pumps.

Assessment and Improvement of the System Efficiency for the Moving-actuator Type Biventricular Assist Device

This is a test report on the efficiency of a moving-actuator type biventricular assist device (AnyHeart, Seoul National University). From the viewpoint of the various system mechanisms, the device can be subdivided into three separate parts: the motor and its associated controller, the actuator and motor assembly, and the blood sac and its associated components (including valves). The motor was operated under various conditions, including different torque, angular speed, and voltage pulses. The total system efficiency of 8% has been reported before, with subpart efficiencies of 50%, 85%, and 19%, respectively, for the motor and its associated controller, the actuator and motor assembly, and the blood sac and its associated components (including valves), under normal operating conditions (4 L/min pump output, 100 mm Hg aortic pressure [AoP]). This article focuses on the method of analyzing and improving the system efficiency. The applied input voltage under the normal operating conditions of the pump was determined using the analyzed results. Also, a speed profile that takes into consideration the filling state of the blood sac was provided. On the basis of tests performed involving in vitro mock circulation, experimental results are provided to demonstrate the effectiveness of the approach presented in this article.

Hydrodynamic and Static Performance Evaluation of the Moving-Actuator Type Biventricular Assist Device, AnyHeart

This study evaluated the hydrodynamic characteristics and efficiency of the moving-actuator type implantable biventricular assist device (BVAD), AnyHeart. A blood analog made of 52% glycerin and 48% water was used to simulate the density and viscosity of blood. The maximum pump flow was 9 L/min with 28.8 watts of power input, and the maximum electrical-to-hydraulic power conversion efficiency was approximately 11% at a pump flow of 3.5 L/min. The pump was able to generate 4 L/min output against 100 mm Hg afterload with less than 9 watts of power input. In addition to the overall system efficiency, the inner subpart power conversion efficiency was also evaluated. The system was subdivided according to system mechanism into three major parts: motor part, actuator part, and blood sac part. In normal working conditions (4 L/min, 100 mm Hg) with the AnyHeart, the total system efficiency was 8%, with subpart efficiencies of 50%, 85%, and 19% for motor part, actuator part, and blood sac part, respectively. The pump performance assessed in the in vitro Donovan-type mock circulation loop test was acceptable as a BVAD in terms of flow and pressure.