Stroke outcomes following durable left ventricular assist device implant in patients bridged with micro-axial flow pump: Insights from a large registry.

BACKGROUND: Stroke after durable left ventricular assist device (d-LVAD) implantation portends high mortality. The incidence of ischemic and hemorrhagic stroke and the impact on stroke outcomes of temporary mechanical circulatory support (tMCS) management among patients requiring bridge to d-LVAD with micro-axial flow-pump (mAFP, Abiomed) is unsettled. METHODS: Consecutive patients, who underwent d-LVAD implantation after being bridged with mAFP at 19 institutions, were retrospectively included. The incidence of early ischemic and hemorrhagic stroke after d-LVAD implantation (<60 days) and association of pre-d-LVAD characteristics and peri-procedural management with a specific focus on tMCS strategies were studied. RESULTS: Among 341 patients, who underwent d-LVAD implantation after mAFP implantation (male gender 83.6%, age 58 [48-65] years, mAFP 5.0/5.5 72.4%), the early ischemic stroke incidence was 10.8% and early hemorrhagic stroke 2.9%. The tMCS characteristics (type of mAFP device and access, support duration, upgrade from intra-aortic balloon pump, ECMELLA, ECMELLA at d-LVAD implantation, hemolysis, and bleeding) were not associated with ischemic stroke after d-LVAD implant. Conversely, the device model (mAFP 2.5/CP vs. mAFP 5.0/5.5: HR 5.6, 95%CI 1.4-22.7, p = 0.015), hemolysis on mAFP support (HR 10.5, 95% CI 1.3-85.3, p = 0.028) and ECMELLA at d-LVAD implantation (HR 5.0, 95% CI 1.4-18.7, p = 0.016) were associated with increased risk of hemorrhagic stroke after d-LVAD implantation. Both early ischemic (HR 2.7, 95% CI 1.9-4.5, p < 0.001) and hemorrhagic (HR 3.43, 95% CI 1.49-7.88, p = 0.004) stroke were associated with increased 1-year mortality. CONCLUSIONS: Among patients undergoing d-LVAD implantation following mAFP support, tMCS characteristics do not impact ischemic stroke occurrence, while several factors are associated with hemorrhagic stroke suggesting a proactive treatment target to reduce this complication.

Monitoring MCS patients on the intensive care unit: integrating haemodynamic assessment, laboratory data, and imaging techniques for timely detection of deterioration and recovery.

Monitoring of the patient supported with a temporary mechanical circulatory support (tMCS) is crucial in achieving the best possible outcome. Monitoring is a continuous and labour-intensive process, as cardiogenic shock (CS) patients can rapidly deteriorate and may require new interventions within a short time period. Echocardiography and invasive haemodynamic monitoring form the cornerstone of successful tMCS support. During monitoring, it is particularly important to ensure that adequate end-organ perfusion is achieved and maintained. Here, we provide a comprehensive overview of best practices for monitoring the CS patient supported by a micro-axial flow pump, veno-arterial extracorporeal membrane oxygenation, and both devices simultaneously (ECMELLA approach). It is a complex process that encompasses device control, haemodynamic control and stabilization, monitoring of interventions, and assessment of end-organ function. The combined, continuous, and preferably protocol-based approach of echocardiography, evaluation of biomarkers, end-organ assessment, and haemodynamic parameters is crucial in assessing this critically ill CS patient population.

Glimpse into the future.

Randomized studies attempting to prove benefit of mechanical circulatory support in cardiogenic shock have failed to reduce the risk of death. Further, both registry and randomized data suggest increased rates of serious complications associated with these devices. This last review in the supplement discusses current evidence and provides a perspective on how the scientific community could advance cardiogenic shock research focused on mechanical circulatory support.

Analysis of pressure pulsation and energy characteristics of guide vane for axial flow pump based on Hilbert-Huang transform considering impeller-guide vane interaction.

In order to explore the characteristics of pressure pulsation signals and energy distribution of water flow at the guide vane considering impeller-guide vane interaction. The numerical simulation of the vertical axial flow pump device's steady and unsteady three-dimensional flow fields was carried out. The Hilbert-Huang method was used to conduct empirical mode decomposition decomposition and Hilbert spectrum analysis of pressure pulsation signal at each monitoring point in the inlet and outlet regions of the guide vane. The results show: Under the condition of 0.3Qbep, the internal pressure of the guide vane is obviously affected by the impeller, and there are large block-shaped vortex structures in the guide vane. Under the operating conditions of 1.0Qbep and 1.2Qbep, the size of the pressure area in the guide vane is basically not affected by the impeller, and the vortex structures in the guide vane are concentrated near the outlet of the guide vanes, and there are long strip-shaped vortex structures at the edge of the guide vane. The size and number of vortex structures decrease with the increase in flow rate. The pressure pulsation signal at the inlet of the guide vane is affected by the rotation of the impeller and exhibits good periodicity, with the main frequency centered around 146 Hz, and the energy ratio of the main frequency is up to 97.7%. There are low-frequency signals below 100 Hz and high-frequency signals fluctuating around 146 Hz in all three flow conditions. When the flow rate increases, the fluctuation amplitude of the high-frequency signal increases. The flow rate has a significant impact on the water flow at the outlet of the guide vane. At 0.3Qbep, its frequency is distributed in the range of 0-500 Hz, mainly concentrated in the area below 400 Hz. At 1.0Qbep, the frequency of pressure pulsation is distributed below 250 Hz after the guiding function of the guide vane. At 1.2Qbep, the water flow is mainly controlled by the rotation of the impeller, and after the energy recovery of the guide vane, its main frequency is still concentrated around 150 Hz, which is 337.2% and 268.5% of 0.3Qbep and 1.0Qbep. Under the working condition of 0.3Qbep, the proportion of intrinsic mode function energy corresponding to the dominant frequency at the center of the guide vane inlet is as high as 95.9%, and the proportion of intrinsic mode function energy corresponding to the dominant frequency at the shroud side and hub side of the guide vane is rather low. If the flow rate rises from 0.3Qbep to 1.2Qbep, the proportion of intrinsic mode function energy increases by more than 42%. Under the working conditions of 0.3Qbep and 1.0Qbep, the main frequency of pressure pulsation signal of water flow at the guide vane outlet is less affected by the impeller and the corresponding energy proportion is low. Under the working condition of 1.2Qbep, the main frequency of pressure pulsation signal is 4 times the rotational frequency and the corresponding energy proportion is higher than 60%.

Substantial Reduction of Acute Ischemic Mitral Regurgitation Using Impella in AMI Complicated with Cardiogenic Shock.

A 77-year-old female presented with loss of consciousness, blood pressure of 90/60 mmHg, and heart rate of 47 bpm. At admission, highly sensitive Trop-T and lactate were elevated, and an electrocardiogram revealed an infero-posterior ST elevation myocardial infarction. Echocardiography revealed a depressed left ventricular ejection fraction with abnormal wall motion in the infero-posterior region and hyperkinetic apical movement along with severe mitral regurgitation (MR). Coronary angiography showed a hypoplastic right coronary artery, 100% thrombotic occlusion of the dominant left circumflex (LCx) artery, and 75% stenosis in the left anterior descending (LAD) artery. Substantial hemodynamic improvement with the reduction of acute ischemic MR was achieved by the initiation of an Impella 2.5, which is a transvalvular axial flow pump, and successful percutaneous coronary intervention (PCI) was conducted with stents to the LCx. The patient was weaned off the Impella 2.5 in 5 days, received staged PCI to LAD, and was later discharged after completion of the staged PCI to LAD.

Analysis of Energy Loss Characteristics of Vertical Axial Flow Pump Based on Entropy Production Method under Partial Conditions.

The energy loss of the vertical axial flow pump device increases due to the unstable internal flow, which reduces the efficiency of the pump device and increases its energy consumption of the pump device. The research results of the flow loss characteristics of the total internal conduit are still unclear. Therefore, to show the internal energy loss mechanism of the axial flow pump, this paper used the entropy production method to calculate the energy loss of the total conduit of the pump device to clarify the internal energy loss mechanism of the pump device. The results show that the energy loss of the impeller is the largest under various flow conditions, accounting for more than 40% of the total energy loss of the pump device. The variation trend of the volume average entropy production and the energy loss is similar under various flow coefficients (KQ). The volume average entropy production rate (EPR) and the energy loss decrease first and then increase with the increase of flow, the minimum volume average entropy production is 378,000 W/m3 at KQ = 0.52, and the area average EPR of the impeller increases gradually with the increase of flow. Under various flow coefficient KQ, the energy loss of campaniform inlet conduit is the smallest, accounting for less than 1% of the total energy loss. Its maximum value is 63.58 W. The energy loss of the guide vane and elbow increases with the increase of flow coefficient KQ, and the maximum ratio of energy loss to the total energy loss of the pump device is 29% and 21%, respectively, at small flow condition KQ = 0.38. The energy loss of straight outlet conduit reduces first and then increases with the increase of flow coefficient KQ. When flow coefficient KQ = 0.62, it accounts for 27% of the total energy loss of the pump device, but its area average entropy production rate (EPR) and volume average entropy production rate (EPR) are small. The main entropy production loss in the pump device is dominated by entropy production by turbulent dissipation (EPTD), and the proportion of entropy production by direct dissipation (EPDD) is the smallest.

Energy Characteristics of a Bidirectional Axial-Flow Pump with Two Impeller Airfoils Based on Entropy Production Analysis.

This research sought to determine the spatial distribution of hydraulic losses for a bidirectional axial-flow pump with arc- and S-shaped impellers. The unsteady Reynolds time-averaged Stokes (URANS) approach with the SST k-omega model was used to predict the internal flow field. The total entropy production (TEP) and total entropy production rate (TEPR) were used to evaluate the overall and local hydraulic losses. The results show that the distribution of TEP and TEPR was similar for both impeller cases. Under a forward condition, TEP mainly comes from the impeller and elbow pipe. The high TEPR inside the impeller can be found near the shroud, and it shifts from the leading edge to the trailing edge with an increase in the flow rate due to the decline in the attack angle. The high TEPR inside the elbow pipe can be seen near the inlet, and the area shrinks with an increase in the flow rate caused by a reduction in the velocity circulation. Under the reverse condition, TEP mainly comes from the impeller and the straight pipe. The TEPR of the region near the shroud is obviously higher than for other regions, and the area of high TEPR near the suction side shrinks with an increase in the flow rate. The high TEPR of the straight pipe can be found near the inlet, and declines in the flow direction. These results provide a theoretical reference for future work to optimize the design of the bidirectional axial-flow pump.

Concept, Design, and Early Prototyping of a Low-Cost, Minimally Invasive, Fully Implantable Left Ventricular Assist Device.

Despite evidence associating the use of mechanical circulatory support (MCS) devices with increased survival and quality of life in patients with advanced heart failure (HF), significant complications and high costs limit their clinical use. We aimed to design an innovative MCS device to address three important needs: low cost, minimally invasive implantation techniques, and low risk of infection. We used mathematical modeling to calculate the pump characteristics to deliver variable flows at different pump diameters, turbomachinery design software CFturbo (2020 R2.4 CFturbo GmbH, Dresden, Germany) to create the conceptual design of the pump, computational fluid dynamics analysis with Solidworks Flow Simulation to in silico test pump performance, Solidworks (Dassault Systèmes SolidWorks Corporation, Waltham, MA, USA) to further refine the design, 3D printing with polycarbonate filament for the initial prototype, and a stereolithography printer (Form 2, Formlabs, Somerville, MA, USA) for the second variant materialization. We present the concept, design, and early prototyping of a low-cost, minimally invasive, fully implantable in a subcutaneous pocket MCS device for long-term use and partial support in patients with advanced HF which unloads the left heart into the arterial system containing a rim-driven, hubless axial-flow pump and the wireless transmission of energy. We describe a low-cost, fully implantable, low-invasive, wireless power transmission left ventricular assist device that has the potential to address patients with advanced HF with higher impact, especially in developing countries. In vitro testing will provide input for further optimization of the device before proceeding to a completely functional prototype that can be implanted in animals.

Analysis of flow loss characteristics of slanted axial-flow pump device based on entropy production theory.

Slanted axial-flow pump devices are widely applied in urban water supply, irrigation and drainage engineering fields. The second law of thermodynamics is applied to investigate the flow loss characteristics of the 30° slanted axial-flow pump model according to the flow loss analysis method of entropy production theory, so that the hydraulic loss characteristics can be revealed in internal flow process of the slanted axial-flow pump. The three-dimensional numerical simulation of the whole flow conduit in slanted axial-flow pump was conducted and the entropy production increased in the flow process was calculated. The location and distribution characteristics of the flow loss of the pump were qualitatively analysed. The results show that the entropy production in impeller is the highest among the pump components. With the increase of flow rate, the proportion of the entropy production in impeller in total value of the pump device increases continuously. The wall entropy production of impeller, guide vane and outlet conduit are lower than the mainstream entropy production, and the mainstream entropy production occupies the dominant position. As the flow rate grows, the proportion of turbulent dissipation entropy production decreases, and the proportion of wall dissipation entropy production increases. At 0.8Q bep, the proportion of turbulent dissipation entropy production is close to 74%, which is about 2.8 times that of wall entropy production. Under 1.2Q bep condition, the proportion of turbulent dissipation entropy production is just 5.5% higher than that of wall dissipation entropy production.

Retrieval of Entrapped Catheter-Mounted Axial Flow Pump From Mitral Subvalvular Apparatus Using a Snare Catheter.

Axial-flow ventricular assist devices are being increasingly used to support hemodynamically compromised patients undergoing percutaneous coronary intervention. Periprocedural valvular complications have been recognized in a few case reports. We present a unique case of entanglement of the Impella within he mitral subvalvular apparatus, retrieved successfully using a snare under fluoroscopic guidance. (Level of Difficulty: Advanced.).

Impeller geometry definition of the transventricular assist device.

According to the World Health Organization, cardiovascular disease is the number one cause of death worldwide, except Africa, where Acquired Immune Deficiency Syndrome is the leading cause of death. In this scenario, the ventricular assist device (VAD) remains the unique alternative to extend patient life until heart transplantation. At Dante Pazzanese Institute of Cardiology, the research and development of an axial flow VAD to be fully implantable within the heart was started. This pump, denominated Transventricular Assist Device (TVAD), can be surgically implanted through a small left intercostal incision in a minimally invasive manner. The goal of this work is to analyze the impeller geometries of the TVAD, to avoid high shear stresses in the fluid and aim for the best conditions to support the circulatory system using computational fluid dynamics and in vitro tests. Different rotor geometries were selected according to the literature; based on the results, the best rotor was elected. This rotor contains a pair of spiral blades of constant and relatively high pitch, which pumps liquid at a flow rate of 3 L/min at 73 mm Hg. It is also expected that this rotor presents a moderate hemolysis since the shear rate is acceptable.

Perception and adoption of a new agricultural technology: Evidence from a developing country.

Adoption of new agricultural technologies is always at the center of policy interest in developing countries. In reality, despite the visible benefits of many of the new agricultural technologies, including machinery and management practices, farmers either do not adopt them or it takes a long time to begin the adoption process and scaling up. To enhance the provision of irrigation using surface water and to enhance irrigation efficiency, Bangladesh has been trying to introduce the axial-flow-pump (AFP) appropriate for surface water irrigation, which can lift up to 55% more water, conditional on the water head, than a conventional centrifugal pump. Despite the visible benefits of the AFP, the uptake of the AFP for irrigation is low in the targeted zone of Bangladesh. The present study demonstrates that the new technology must be modified to adapt to local demand and specifications. Most importantly, the price of the new technology must be competitive with the prices of the existing available substitute technologies to ensure a rapid uptake and scaling up of this new agricultural technology.

A Simplified Irrigation Pump Testing Method for Developing Countries: A Case Study in Bangladesh.

Much of South Asia experiences a monomodal rainfall pattern with a distinct dry season following the annual monsoon. Enabling irrigation during the dry season has therefore been crucial in assuring improved productivity and double-cropping. This is particularly the case in southern Bangladesh, where recent government initiatives have called for an expansion of surface water irrigation to reduce pressure on groundwater tables in intensively cultivated areas in the north of the country, where dry season boro rice is grown. This paper describes a method based on first principles of fluid mechanics to characterize the performance of surface water irrigation pumps used by small-scale farmers in South Asia and Bangladesh. This method is unique, as it incorporates an optimized protocol suitable for resource-limited conditions found in many developing countries and provides a comprehensive yet simple-to-use pump selection method for surface water irrigation pump customers. Using pump impellers as a case study, the method also characterizes the effect of pump geometric variations resulting from the variable production and assembly practices found in different manufacturing workshops. This method was validated with a case study in Bangladesh supported by both full-scale field testing and numerical simulation results. © 2018 The Authors. Irrigation and Drainage published by John Wiley & Sons Ltd on behalf of International Commission for Irrigation and Drainage.

Une grande partie de l'Asie du Sud connaît un régime pluviométrique monomodal avec une saison sèche distincte après la mousson annuelle. Permettre l'irrigation pendant la saison sèche a donc été crucial pour assurer une meilleure productivité et une double culture. C'est particulièrement le cas dans le sud du Bangladesh, où des initiatives gouvernementales récentes ont demandé une expansion de l'irrigation avec des eaux de surface pour réduire la pression sur les nappes phréatiques dans les zones intensément cultivées du nord du pays où pousse le riz boro de saison sèche. Cet article décrit une méthode basée sur les premiers principes de la mécanique des fluides pour caractériser les performances des pompes d'irrigation avec des eaux de surface utilisées par les petits agriculteurs en Asie du Sud et au Bangladesh. Cette méthode est unique car elle incorpore un protocole optimisé adapté aux conditions de ressources limitées dans de nombreux pays en développement et fournit une méthode de sélection de pompe complète mais simple à utiliser pour les clients de pompes d'irrigation d'eau de surface. En utilisant des turbines de pompage comme étude de cas, la méthode caractérise également l'effet des variations géométriques de la pompe résultant des pratiques variables de production et d'assemblage trouvées dans différents ateliers de fabrication. Cette méthode a été validée à l'aide d'une étude de cas au Bangladesh appuyée à la fois par des essais sur le terrain à grande échelle et des résultats de simulation numérique. © 2018 The Authors. Irrigation and Drainage published by John Wiley & Sons Ltd on behalf of International Commission for Irrigation and Drainage.

Systematic Design of a Magnetically Levitated Brushless DC Motor for a Reversible Rotary Intra-Aortic Blood Pump.

The IntraVAD is a miniature intra-aortic ventricular assist device (VAD) designed to work in series with the compromised left ventricle. A reverse-rotation control (RRc) mode has been developed to increase myocardial perfusion and reduce ventricular volume. The RRc mode includes forward rotation in systole and reverse rotation in diastole, which requires the IntraVAD to periodically reverse its rotational direction in synchrony with the cardiac cycle. This periodic reversal leads to changes in pressure force over the impeller, which makes the entire system less stable. To eliminate the mechanical wear of a contact bearing and provide active control over the axial position of the rotor, a miniature magnetically levitated bearing (i.e., the PM-Coil module) composed of two concentric permanent magnetic (PM) rings and a pair of coils-one on each side-was proposed to provide passive radial and active axial rotor stabilization. In the early design stage, the numerical finite element method (FEM) was used to optimize the geometry of the brushless DC (BLDC) motor and the maglev module, but constructing a new model each time certain design parameters were adjusted required substantial computation time. Because the design criteria for the module had to be modified to account for the magnetic force produced by the motor and for the hemodynamic changes associated with pump operation, a simplified analytic expression was derived for the expected magnetic forces. Suitable bearings could then be designed capable of overcoming these forces without repeating the complicated FEM simulation for the motor. Using this method at the initial design stage can inform the design of the miniature maglev BLDC motor for the proposed pulsatile axial-flow VAD.

Initial Acute Animal Experiment Using a New Miniature Axial Flow Pump in Series With the Natural Heart.

We have advocated an axial flow blood pump called "valvo pump" that is implanted at the aortic valve position, and we have developed axial flow blood pumps to realize the concept of the valvo pump. The latest model of the axial flow blood pump mainly consists of a stator, a directly driven impeller, and a hydrodynamic bearing. The axial flow blood pump has a diameter of 33 mm and length of 74 mm, and the length of anatomical occupation is 33 mm. The axial flow blood pump is anastomosed to the aorta with polytetrafluoroethylene (PTFE) cuffs worn on the inflow and outflow ports. Dp-Q curves of the axial flow blood pump are flatter than those of ordinary axial flow pumps, and pump outflow of 5 L/min was obtained against a pressure difference of 50 mm Hg at a rotational speed of 9000 rpm in vitro. The axial flow blood pump was installed in a goat by anastomosing with the thoracic descending aorta using PTFE cuffs, and it was rotated at a rotational speed of 8000 rpm. Unlike in case of the ventricular assistance in parallel with the natural heart, pulsatilities of aortic pressure and aortic flow were preserved even when the pump was on, and mean aortic flow was increased by 1.5 L/min with increase in mean aortic pressure of 30 mm Hg. In conclusion, circulatory assistance in series with the natural heart using the axial flow blood pump was able to improve hemodynamic pulsatility, and it would contribute to improvement of end-organ circulation. .

Fluid dynamics aspects of miniaturized axial-flow blood pump.

Rotary blood pump (RBP) is a kind of crucial ventricular assist device (VAD) and its advantages have been evidenced and acknowledged in recent years. Among the factors that influence the operation performance and the durability of various rotary blood pumps, medium property and the flow features in pump's flow passages are conceivably significant. The major concern in this paper is the fluid dynamics aspects of such a kind of miniaturized pump. More specifically, the structural features of axial-flow blood pump and corresponding flow features are analyzed in detail. The narrow flow passage between blade tips and pump casing and the rotor-stator interaction (RSI) zone may exert a negative effect on the shear stress distribution in the blood flow. Numerical techniques are briefly introduced in view of their contribution to facilitating the optimal design of blood pump and the visualization of shear stress distribution and multiphase flow analysis. Additionally, with the development of flow measurement techniques, the high-resolution, effective and non-intrusive flow measurement techniques catering to the measurement of the flows inside rotary blood pumps are highly anticipated.

Initial clinical experience with the HeartMate II axial-flow left ventricular assist device.

The redesigned HeartMate II, an axial-flow left ventricular assist device, is simpler, smaller, and easier to operate than are pulsatile pumps. These design characteristics should make the HeartMate II more reliable and durable and broaden the eligible population base. We implanted the HeartMate II in 43 patients (average age, 42 yr). The indication for use was bridge-to-heart transplantation in 26 patients and destination therapy in 17. The average duration of device support was 258 days (range, 1-761 days), and cumulative duration, more than 31 patient-years. Hemodynamic function improved in all patients during support. By 48 hours after implantation, the mean cardiac index had increased from 1.9+/-0.27 L/(min.m(2)) (baseline) to 3.5+/-0.8 L/(min.m(2)), and the pulmonary capillary wedge pressure had decreased from 24.8+/-11 mmHg to 18.5+/-5.3 mmHg. Of the 43 patients, 35 were discharged from the hospital. Support is ongoing in 27 patients (longest duration, >700 days). Nine patients died during support. Four patients had sufficient heart recovery to undergo pump explantation. Three patients underwent transplantation. One patient underwent device replacement after the pump driveline was fractured in a skateboarding accident; the device was removed in another patient because of a pump-pocket infection after 749 days of support. Of the 10 patients in whom the HeartMate II replaced a failed HeartMate I, 8 were discharged from the hospital. We have seen excellent results with use of the HeartMate II. Functional status and quality of life have greatly improved in patients who survived the perioperative period.

Affection of guiding vane on axial flow pump heart assist device and its clinical relevancy / 医疗卫生装备

Objective To observe the response of the guiding vane to axial flow pump by testing two types of miniature axial flow pump,which have been developed by our group in recent years.Methods Two types of axial flow pump were tested in a mock circulation apparatus.Results The outputs of the two types of miniature axial flow pump all attain 5L/min against the pressure of 13.332kPa,which is enough for left ventricular assistance.The outputs are similarly related to their pre-load and after-load pressure.In this study,the guiding vane does not produce a significant affection on the hydrodynamic characteristic of the axial follow pump.Conclusion The guiding vane may be neglected in the design to improve the blood compatibility of a axial flow pump heart assist device.

A Ferrofluidic Seal Specially Designed for Rotary Blood Pumps.

One of the key technologies required for rotary blood pumps is sealing of the motor shaft. A ferrofluidic seal was developed for an axial flow pump. The seal body was composed of a plastic magnet and two pole pieces. This seal was formed by injecting ferrofluid into the gap between the pole pieces and the motor shaft. To contain the ferrofluid in the seal and to minimize the possibility of ferrofluid making contact with blood, a shield with a small cavity was provided on the pole piece. Sealing pressure of the seal was measured. The sealing pressure was maintained at more than 23.3 kPa (175 mm Hg) for a motor speed up to 11,000 rpm. The specially designed ferrofluidic seal for sealing out liquids is useful for axial flow blood pumps.