Eccentric Inlet Port Research Articles

The Pivot Wash in Two Impeller Modes for the Baylor/Miwatec Centrifugal Blood Pump

A centrifugal blood pump with a double pivot impeller and an eccentric inlet port is being developed as an implantable artificial heart by the Baylor College of Medicine and Miwatec Co. Ltd. Flow visualization measurements were conducted to compare the flow around the pivot for two impeller operational modes: the top and the bottom contact modes. In the top contact mode, one-way flow in the pivot gap due to the eccentric vortex was observed, and sufficient wall shear rate to prevent thrombus formation was attained around the bottom pivot for over 1,400 rpm. Computational fluid dynamic analyses confirmed that the causes of the eccentric vortex were the inlet eccentricity and the pressure imbalance in the volute.

Current status of the gyro centrifugal blood pump--development of the permanently implantable centrifugal blood pump as a biventricular assist device (NEDO project).

The New Energy and Industrial Technology Development Organization (NEDO) project was started in 1995. The goal is the development of a multipurpose, totally implantable biventricular assist device (BVAD) that can be used for any patient who suffers from severe heart failure. Our C1E3 (two-week pump) centrifugal pump, called the Gyro pump, has three design characteristics: a magnetic coupling and double pivot bearing system, an eccentric inlet port, and secondary vanes on the bottom of the impeller. The pump was miniaturized. The C1E3 evolved into the NEDO PI-601, a totally implantable centrifugal pump for BVAD. The current NEDO PI-710 pump (five-year pump) system includes a centrifugal pump with pivot bearings, a hydraulically-levitated impeller, an rpm-controlled miniaturized actuator (all-in-one actuator plus controller), an emergency clamp on the left outflow, and a Frank-Starling-type flow control. The final mass production model is now finalized, and the final animal study and two-year endurance studies are ongoing.

Flow visualization in a centrifugal blood pump with an eccentric inlet port.

Flow visualization analysis was applied to the Baylor/Miwatec centrifugal artificial heart to evaluate its fluid dynamic characteristics regarding antithrombogenicity. An eccentric vortex was found both in the upper and the lower gaps of the impeller, which is supposed to be caused by the eccentric inlet port. Therefore, one-way flow toward the outlet is formed and washes the pivot. The combination of an eccentric vortex and a pivot bearing that is washed is unique to the Baylor/Miwatec pump. For the male pivots exposed to periodic wash, the minimum shear rate around the bottom pivot was estimated to be 650/s, which is higher than the threshold for thrombus formation shown by other studies. The wall shear rate at the impeller bottom surface was found to be larger in the top contact mode than in the bottom contact mode.

Flow Visualization of a Centrifugal Blood Pump with an Eccentric Inlet Port and a Double Pivot(Cardiovascular Mechanics)

Flow Visualization of a Centrifugal Blood Pump with an Eccentric Inlet Port and a Double Pivot(Cardiovascular Mechanics)

偏心流入口を有する遠心血液ポンプの可視化解析

A centrifugal blood pump with a double pivot impeller and an eccentric inlet port is under development for implantable artificial heart by Baylor college of medicine/Miwatec Co.Ltd. To eliminate fluid dynamic causes for thrombus formation, flow visualization analysis was conducted to evaluate the flow patterns and the shear rate distributions. It was found that an eccentric vortex is formed in the pump apart from the pivot center as the prerotation caused by the eccentric inlet port. Since a similar eccentric vortex is also formed behind the impeller, the pivot is exposed to sinusoidally changing shear rate. The minimum value was found to be 650 sec-1. It was found that the value can be increased to more than 150% when the male pivot is lifted from the female pivot by 0.6 mm.

707 ダブルピボット遠心血液ポンプの可視化解析

A centrifugal blood pump with a double pivot impeller and an eccentric inlet port is under development for implantable artificial heart by Baylor college of medicine/Miwatec Co. Ltd. To eliminate fluid dynamic causes for thrombus formation, flow visualization analysis was conducted to evaluate the flow patterns and the shear rate distributions. It was found that an eccentric vortex is formed in the pump apart from the pivot center as the prerotation caused by the eccentric inlet port. Since a similar eccentric vortex is also formed behind the impeller, the pivot is exposed to sinusoidally changing shear rate. The minimum value was found to be 650(sec)_<-1>. It was found that the value can be increased to more than 150% when the male pivot is lifted from the female pivot by 0.6mm.

DEVELOPMENT OF A SINGLE-PIVOT, SEAL-LESS MAGNETICALLY DRIVEN CENTRIFUGAL BLOO PUMP

A single-pivot supported, compact, seal-less, magnetically drive centrifugal blood pump has been developed. The design concept wa based on a tri-pod supported centrifugal blood pump we previousl reported. The single-pivot concept was employed to reduce frictio force due to tri-pod mechanism. Additionally, single-pivot supporte system eliminated the upper bearing system, allowing incorporatio of the eccentric inlet port. In this study, we evaluated the performance of the prototype single-pivot centrifugal blood pum and impeller's stability. [Materials] Male pivot consisting of a ceramic ball (4mm was mounted on the bottom surface of the impeller, whil polyethylene groove female pivot was mounted on the bottom pum casing. The prototype pump had an impeller diameter of 50mm, priming volume of 25ml, and an outer diameter of 60mm. The pum driver used a specially designed brush-less DC motor. [Methods] Flow-Pressure characteristics and system efficiency were measured as the prototype pump performance in a moc circulatory loop. The impeller stability was evaluated by measuring the distance from impeller to the top housing using a Hall-effect sensor with a magnet incorporated inside the impeller. [Results] The pump performance of the prototype single-pivot pum was acceptable as a left-ventricular assist device. In order to obtain pum flow of 5L/min against the head pressure of 90–100mmHg, required pum speeds ranged from 1800 to 2000rpm. The maximum efficiency was 14 at 2200rpm. The Hall sensor signal level change became more stable with the increase in pump RPM. [Conclusion] This result indicates that the single-pivot supporte centrifugal pump can meet both flow and pressure requirements as a left ventricular assist device without requiring the upper bearing or magneti support system as incorporated in other existing systems.

Development of the NEDO implantable ventricular assist device with Gyro centrifugal pump.

The Gyro centrifugal pump, PI (permanently implantable) series, is being developed as a totally implantable artificial heart. Our final goal is to establish a "functional TAH," a totally implantable biventricular assist system (BiVAS) with centrifugal pumps. A plastic prototype pump, Gyro PI 601, was evaluated through in vitro and in vivo studies as a single ventricular assist device (VAD). Based upon these results, the pump head material was converted to a titanium alloy, and the actuator was modified. These titanium Gyro pumps, PI 700 series, also were subjected to in vitro and in vivo studies. The Gyro PI 601 and PI 700 series have the same inner dimensions and characteristics, such as the eccentric inlet port, double pivot bearing system, secondary vane, and magnet coupling system; however, the material of the PI 700 is different from the PI 601. The Gyro PI series is driven by the Vienna DC brushless motor actuator. The inlet cannula of the right ventricular assist system (RVAS) specially made for this system consists of 2 parts: a hat-shaped silicone tip biolized with gelatin and an angled wire reinforced tube made of polyvinylchloride. The pump-actuator package was implanted into 8 calves in the preperitoneal space, bypassing from the left ventricle apex to the descending aorta for the left ventricular assist system (LVAS) and bypassing the right ventricle to the main pulmonary artery for the RVAS. According to the PI 601 feasibility protocol, 2 LVAS cases were terminated after 2 weeks, and 1 LVAS case and 1 RVAS were terminated after 1 month. The PI 700 series was implanted into 4 cases: 3 LVAS cases survived for a long term, 2 of them over 200 days (72-283 days), and 1 RVAS case survived for 1 month and was terminated according to the protocol for a short-term antithrombogenic screening and system feasibility study. Regarding power consumption, the plastic pump cases demonstrated from 6.2 to 12.1 W as LVAS and 7.3 W as RVAS, the titanium pump cases showed from 10.4 to 14.2 W as LVAS and 15.8 W as RVAS. All cases exhibited low hemolysis. The renal function and the liver function were maintained normally in all cases throughout these experimental periods. In the 2 RVAS cases, pulmonary function was normally maintained. No calves demonstrated thromboembolic signs or symptoms throughout the experiments except Case 1 with the plastic pump. However, in the plastic pump cases, bilateral renal infarction was suspected in 2 cases during necropsy whereas no abnormal findings were revealed in the titanium pump cases. There were also no blood clots inside the PI 700 series. As for the 601, the explanted pumps demonstrated slight thrombus formations at the top and bottom pivots except in 1 case. The Gyro PI series, especially the PI 700 series, demonstrated superior performance, biocompatibility, antithrombogenicity and low hemolysis. Also, the durability of the actuator was demonstrated. Based on these results, this titanium centrifugal pump is suitable as an implantable LVAS and RVAS. It is likely that the Gyro PI series is a feasible component of the BiVAS functional TAH.

Development of an implantable small right ventricular assist device.

Currently, at least two permanent implantable left ventricular assist devices (LVADs) are used clinically. Unfortunately, there is no small implantable right ventricular assist device (RVAD) available, even though at least 25-30% of this patient population has right ventricular failure. If a small implantable RVAD were available, biventricular assist could support patients with right ventricular failure. A small atraumatic and antithrombogenic RVAD is being developed to meet this clinical need. This small centrifugal blood pump, the Gyro PI pump, is 6.5 cm in diameter and 4.6 cm in height and has three unique characteristics to prevent thrombus formation: (1) the double pivot bearing and magnetic coupling system enable this pump to be completely sealless; (2) the secondary vanes at the bottom of the impeller accelerate the blood flow and prevent blood stagnation; and (3) the eccentric inlet port enables the top female bearing to be embedded into the top housing and decrease blood cell trauma. The inflow conduit consists of a wire reinforced tube and a hat-shaped tip that is biolized with gelatin to create a thrombus resistant material. This conduit is directly implanted into the right ventricle, and the outflow conduit is anastomosed to the PA. The pump can be implanted inside the abdominal wall or in the thoracic cavity. Biocompatibility of this pump was proved in two calves by thrombus free implantation as an LVAD for 284 days and 200 days. Two RVAD implantations were conducted, aiming for 1-month system feasibility studies. During the month, the RVADs operated satisfactorily without any thromboembolic incident. No blood clots or abnormal findings were seen inside the pump, nor were there abnormal findings in the explanted lungs except for small areas of atelectasis. The pump flow was 3.02 +/- 0.38 L/min in calf 1 and 3.75 +/- 1.18 L/min in calf 2. The power requirement was 7.28 +/- 0.43W for calf 1 and 14.52 +/- 3.93W for calf 2. The PaO2 was 72.0 +/- 3.60 mm Hg (calf 1) and 72.0 +/- 7.63 mm Hg (calf 2); PaCO2 was 38.3 +/- 2.17 mm Hg (calf 1) and 34.1 +/- 1.95 mm Hg (calf 2); and SaO2 was 94.1 +/- 1.37% (calf1) and 95.0 +/- 1.95% (calf 2). Gas exchange via the lungs was maintained. These studies indicate that the Gyro PI pump is suitable as a single implantable RVAD, and is a feasible RVAD as a part of a BiVAD system in terms of pump performance and thrombus resistance.

Clinical evaluation of the Gyro Pump C1E3 as a cardiopulmonary bypass pump.

The Gyro Pump C1E3 is a new centrifugal pump with numerous features, including a ceramic pivot bearing system, secondary vanes, and an eccentric inlet port. To evaluate its biocompatibility, antithrombogenicity, and produced hemolysis, we used the Gyro Pump during cardiopulmonary bypass (CPB) for coronary artery bypass grafting (CABG) cases to compare it with the BioMedicus pump. From September 1998 to February 1999, 30 consecutive patients underwent CABG under conventional CPB. Fifteen patients were supported by the Gyro Pump C1E3 (Group G), and the remaining 15 patients, by a BioMedicus BP-80 pump (Group B). In both groups, flow rate was equivalent. Blood samples were taken as follows: preoperative, 60 minutes after the end of the procedure, and at postoperative days (POD) 0, 1, and 2. We evaluated the plasma free hemoglobin (free Hb) as an indication of hemolysis; beta-thromboglobulin (beta-TG) and platelet factor four (PF-4) as an indication of platelet deterioration; C3, C4, CH50 for complement activation; coagulation parameters, fibrinolytic factor, thrombomodulin, nitric oxide (NO), and endothelin as an indication of endothelial deterioration. This was the first clinical sized Gyro Pump CIE3. De-airing from the pump was easily accomplished via the eccentric oblique inlet port. The system, including its console, was easily and simply controlled. Perioperative laboratory data were not markedly changed in either group with demonstrated equivalence for biocompatibility and hemolysis. After pumping, no thrombus formation or pivot wear were observed inside the pump. This atraumatic, small centrifugal pump appears well suited not only for CPB but also for circulatory support.

Long-term in vivo left ventricular assist device study for 284 days with Gyro PI pump.

A totally implantable centrifugal artificial heart has been developed. The plastic prototype, the Gyro PI 601, passed 2 day hemodynamic tests as a functional total artificial heart (TAH), 2 week screening tests for anti-thrombogenecity, and a 1 month system feasibility study. Based upon these results, a metallic prototype, the Gyro PI 700 series, was subjected to long-term in vivo left ventricular assist device (LVAD) studies of over 1 month. The Gyro PI 700 series has the same inner dimension and same characteristics of the Gyro PI 601 such as an eccentric inlet port, a double pivot bearing system, and a magnet coupling system. The PI metallic pump is also driven with the Vienna DC brushless motor actuator like the PI 601. The pump-actuator package was implanted in 3 calves in the preperitoneal space, bypassing from the left ventricular (LV) apex to the descending aorta. Case 1 achieved a 284 day survival. Case 2 was euthanized early at 72 postoperative days as a result of the functional obstruction of the inlet port due to the excessive growth of the calf. There was no blood clot inside the pumps of either case. Case 3 is on-going (22 days on July 24, 1998). During these periods, all cases showed no physiological abnormalities. In conclusion, the PI 700 series pump has excellent results as a long-term implantable LVAD.

Long-term in vivo left ventricular assist device study with a titanium centrifugal pump.

A totally implantable centrifugal artificial heart has been developed. The plastic prototype, Gyro PI 601, passed 2 day hemodynamic tests as a functional total artificial heart, 2 week screening tests for antithrombogenicity, and 1 month system feasibility. Based on these results, a metallic prototype, Gyro PI 702, was subjected to in vivo left ventricular assist device (LVAD) studies. The pump system employed the Gyro PI 702, which has the same inner dimensions and the same characteristics as the Gyro PI 601, including an eccentric inlet port, a double pivot bearing system, and a magnet coupling system. The PI 702 is driven with the Vienna DC brushless motor actuator. For the in vivo LVAD study, the pump actuator package was implanted in the preperitoneal space in two calves, from the left ventricular apex to the descending aorta. Case 1 achieved greater than 9 month survival without any complications, at an average flow rate of 6.6 L/min with 10.2 W input power. Case 2 was killed early due to the excessive growth of the calf, which caused functional obstruction of the inlet port. There was no blood clot inside the pump. During these periods, neither case exhibited any physiologic abnormalities. The PI 702 pump gives excellent results as a long-term implantable LVAD.

Simulation of the Piston Driven Flow Inside a Cylinder With an Eccentric Port

A grid-free Lagrangian approach is applied to simulate the high Reynolds number unsteady flow inside a three-dimensional domain with moving boundaries. For this purpose, the Navier-Stokes equations are expressed in terms of the vorticity transport formulation. The convection and stretch of vorticity are obtained using the Lagrangian vortex method, while diffusion is approximated by the random walk method. The boundary-element method is used to solve a potential flow problem formulated to impose the normal flux condition on the boundary of the domain. The no-slip condition is satisfied by a vortex tile generation mechanism at the solid boundary, which takes into account the time-varying boundary surfaces due to, e.g., a moving piston. The approach is entirely grid-free within the fluid domain, requiring only meshing of the surface boundary, and virtually free of numerical diffusion. The method is applied to study the evolution of the complex vortical structure forming inside the time-varying semi-confined geometry of a cylinder equipped with an eccentric inlet port and a harmonically driven piston. Results show that vortical structures resembling those observed experimentally in similar configurations dominate this unsteady flow. The roll-up of the incoming jet is responsible for the formation of eddies whose axes are nearly parallel to the cylinder axis. These eddies retain their coherence for most of the stroke length. Instabilities resembling conventional vortex ring azimuthal modes are found to be responsible for the breakup of these toroidal eddies near the end of the piston motion. The nondiffusive nature of the numerical approach allows the prediction of these essentially inviscid phenomena without resorting to a turbulence model or the need for extremely fine, adaptive volumetric meshes.

Preclinical evaluation of the Kyocera Gyro centrifugal blood pump for cardiopulmonary bypass.

The Kyocera Gyro pump has been developed as a completely seal-less centrifugal pump to overcome the problems of the conventional centrifugal pumps. The Gyro pump is a double pivot bearing-supported centrifugal pump with several specific design features, including its eccentric inlet port. We investigated the feasibility of the Gyro pump for cardiopulmonary bypass (CPB) in a bovine model, comparing it with the BioMedicus pump (BP-80). Ten healthy calves (5: Gyro pump, 5: BP-80) underwent 6 h of mildly hypothermic CPB at approximately 33 degrees C. Both pumps provided more than 50 ml/kg/min without any incidents. The haemodynamics of both groups remained stable within the normal range. All haematology and biochemistry data demonstrated no significant differences between the two groups. However, values of plasma-free haemoglobin and lactate dehydrogenase were less throughout the experiments of the Gyro pump than those of the BP-80. To obtain flow equivalent to that of the BP-80, the Gyro pump needed less rotational speeds than the BP-80 (2749.7 +/- 233.3 versus 3170.6 +/- 300.8 rpm. p < 0.05). Less rotational speed in addition to the difference in operating principle may contribute to less blood damage during the CPB OF the Gyro pump. After pumping for CPB, no leakage or thrombus formation was observed in either pump. The present study indicated that the Kyocera Gyro pump can be applied as a centrifugal pump for CPB with the same performance as the BP-80 and with relatively less haemolysis than the BP-80.

Hydraulic assessment of the floating impeller phenomena in a centrifugal pump.

A compact eccentric inlet port centrifugal blood pump (C1E3) has been perfected for a long-term centrifugal ventricular assist device as well as a cardiopulmonary bypass pump. The C1E3 pump incorporates a sealless design and a blood stagnation free structure. The pump's impeller is magnetically coupled to the driver magnet in a sealless manner. The latest hemolysis study reveals that hemolysis is affected by the magnetic coupling distance between the driver and impeller magnet. Furthermore, a floating phenomenon can be observed in a pivot bearing supported pump. Attention was focused on the relationship between the floating phenomenon's characteristics and the magnetic coupling design in the C1E3 pump. Studies were conducted to evaluate the hydromechanical performance in the floating phenomenon. In this study, the relationship between the magnetic coupling design and the floating phenomenon was verified with a smooth spinning condition. The optimized magnetic coupling distance for the floating mode was estimated to be 12 mm for left ventricular assist device and 9 mm for cardiopulmonary bypass pump. Obtaining an optimal spinning condition is required for regulating the magnetic coupling force. To develop a double pivot bearing pump, it is necessary to establish an optimal spinning and/or floating condition and to determine the proper magnetic coupling and magnetic force between the impeller and driver.

Development and Evaluation of Antithrombogenic Centrifugal Pump: The Baylor C–Gyro Pump Eccentric Inlet Port Model

The Baylor C-Gyro Pump Eccentric Inlet Port Models (C1E) have been developed aiming for a long-term centrifugal ventricular assist device (VAD) as well as a cardiopulmonary bypass pump. The eccentric inlet port models are characterized by their unique inlet port and secondary impeller vanes. An inlet female pivot bearing, which was fixed to a supporting bar in the prototype model, is directly embedded into the ceiling of the pump casing. An inlet port is then placed off-center to avoid the bearing area, and it is angled between 0 to 90 degrees from the upright position. In addition, small secondary vanes were incorporated into the impeller bottom to accelerate the washout flow behind the impeller. These features attained design objectives proposed for higher antithrombogenicity: a seal-less pump chamber, no stationary parts in the blood path, and acceleration of the secondary flow behind the impeller. The first in vivo experiment using C1E pumps showed excellent antithrombogenicity for up to 18 days when the experiment ceased due to severe infection in the calf.

An ultimate, compact, seal-less centrifugal ventricular assist device: Baylor C-Gyro pump.

We have developed a compact, seal-less, all-purpose centrifugal pump, the Baylor C-Gyro pump, which is intended as a long-term ventricular assist device (VAD) as well as a cardiopulmonary bypass pump. In attaining this goal, we began with eliminating the shaft seals by adopting a pivot bearing system at the impeller shaft. In addition, a ring magnet encased in the bottom of the impeller was coupled magnetically to a driver magnet placed outside the pump housing (C1 Prototype). This first model yielded satisfactory performance in vitro with a flow rate of 8 L/min against 250 mm Hg at 2,400 rpm, and an index of hemolysis (IH) of 0.0083 g/100 L using bovine blood. In the second model, the C1 Eccentric Inlet Port Model, the inlet bearing support bar in the prototype were eliminated without reducing the prototype's performance. These designs for antithrombogenicity are being tested by the first in vivo experiment, which has lasted for more than 2 weeks.