Control strategy for maintaining physiological perfusion with rotary blood pumps.

Interstitial lung disease (ILD) represents a collection of lung disorders with a lethal trajectory with few therapeutic options with the exception of lung transplantation. Various extracorporeal membrane oxygenation (ECMO) configurations have been used for bridge to transplant (BTT), yet no optimal configuration has been clearly demonstrated. Using a cardiopulmonary simulation, we assessed different ECMO configurations for patients with end-stage ILD to assess the physiologic deficits and help guide the development of new long-term pulmonary support devices. A cardiopulmonary ECMO simulation was created, and changes in hemodynamics and blood gases were compared for different inflow and outflow anatomic locations and for different sweep gas and blood pump flow rates. The system simulated the physiologic response of patients with severe ILD at rest and during exercise with central ECMO, peripheral ECMO, and with no ECMO. The output parameters were total cardiac output (CO), mixed venous oxygen (O2) saturation, arterial pH, and O2 delivery (DO2)/O2 utilization (VO2) at different levels of exercise. The model described the physiologic state of progressive ILD and showed the relative effects of using various ECMO configurations to support them. It elucidated the optimal device configurations and required physiologic pump performance and provided insight into the physiologic demands of exercise in ILD patients. The simulation program was able to model the pathophysiologic state of progressive ILD with PH and demonstrate how mechanical support devices can be implemented to improve cardiopulmonary function at rest and during exercise. The information generated from simulation can be used to optimize ECMO configuration selection for BTT patients and provide design guidance for new devices to better meet the physiologic demands of exercise associated with normal activities of daily living.

We have developed a tiny rotary centrifugal blood pump for the purpose of supporting circulation of children and infants. The pump is designed to provide a flow of 0.1-4.0 L/min against a head pressure of 50-120 mm Hg. The diameter of the impeller is 30 mm with six straight vanes. The impeller is supported by a hydrodynamic bearing at its center and rotated with a radial coupled magnetic driver. The bearing that supports rotation of the impeller of the tiny centrifugal blood pump is very critical to achieve durability, and clot-free and antihemolytic performance. In this study, computational fluid dynamics (CFD) analysis was performed to quantify the secondary flow through the hydrodynamic bearing at the center of the impeller and investigated the effects of bearing clearance on shear stress to optimize hemolytic performance of the pump. Two types of bearing clearance (0.1 and 0.2 mm) were studied. The wall shear stress of the 0.1-mm bearing clearance was lower than that of 0.2-mm bearing clearance at 2 L/min and 3000 rpm. This was because the axial component of the shear rate significantly decreased due to the narrower clearance even though the circumferential component of the shear rate increased. Hemolysis tests showed that the normalized index of hemolysis was reduced to 0.0076 g/100 L when the bearing clearance was reduced to 0.1 mm. It was found that the CFD prediction supported the experimental trend. The CFD is a useful tool for optimization of the hydrodynamic bearing design of the centrifugal rotary blood pump to optimize the performance of the pump in terms of mechanical effect on blood cell elements, durability of the bearing, and antithrombogenic performance.

As the clinical application of LVADs has increased, attempts have been made to develop smaller, less expensive, more durable and efficient implantable devices using rotary blood pumps. Since chronic circulatory support with implantable continuous-flow LVADs will be established in the near future, we need to determine the flow characteristics through an implantable continuous-flow LVAD. This study describes the flow characteristics through an implantable centrifugal blood pump as a left ventricular assist device (LVAD) to obtain a simple non-invasive algorithm to control its assist flow rate adequately. A prototype of the completely seal-less and pivot bearing-supported centrifugal blood pump was implanted into two calves, bypassing from the left ventricle to the descending aorta. Device motor speed, voltage, current, flow rate, and aortic blood pressure were monitored continuously. The flow patterns revealed forward flow in ventricular systole and backward flow in diastole. As the pump speed increased, an end-diastolic notch became evident in the flow profile. Although the flow rate (Q [l/min]) and rotational speed (R [rpm]) had a linear correlation (Q = 0.0042R - 5.159; r = 0.96), this linearity was altered after the end-diastolic notch was evident. The end-diastolic notch is considered to be a sign of the sucking phenomenon of the centrifugal pump. Also, although the consumed current (I [A]) and flow rate had a linear correlation (I = 0.212Q + 0.29; r = 0.97), this linearity also changed after the end-diastolic notch was evident. Based upon the above findings, we propose a simple algorithm to maintain submaximal flow without inducing sucking. To maintain the submaximal flow rate without measuring flow rate, the sucking point is determined by monitoring consumed current according to gradual increases in voltage.

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The main purpose is to compare the characteristics and performance of a centrifugal blood pump with and without center post. Furthermore, to propose a center post design guide for the development of centrifugal blood pumps: finding the appropriate height and diameter of the center post. A centrifugal blood pump with different center post configurations is investigated using Computational Fluid Dynamics (CFD) in an extensive parametric approach. Height and diameter of the center post are varied on 4 levels each. Pressure head and hydraulic efficiency curves, pressure and velocity contours and volumetric histograms of scalar shear stress (SSS) distribution are discussed in detail. The simulation results show uniform pressure distribution around the casing in the baseline design. Although obtaining the minimum Normalized Index of Hemolysis (NIH), average scalar shear stress (ASSS), and volumetric percentage ratios (SSS > 9, 50 and 150Pa), a stagnation and recirculation zone in the impeller eye above the casing bottom is detected in center post free (H = 0mm) pump. With the establishment and further increase of the center post height, the stagnation zone disappears gradually. The results also indicate that flow recirculation and stagnation around the circumference of the center post occurs when the center post has a small diameter. As the diameter increases, a reversed flow is formed between the impeller and the center post. The center post can greatly reduce the stagnation zone occurring in the center post free pump. The diameter of center post makes a difference to the flow field in the gap between the impeller and the center post.

Safe and effective pediatric blood pumps continue to lag far behind those developed for adults. To address this growing unmet clinical need, we are developing a hybrid, continuous-flow, magnetically levitated, pediatric total artificial heart (TAH). Our hybrid TAH design, the Dragon Heart (DH), integrates both an axial flow and centrifugal flow blood pump within a single, compact housing. The axial pump is embedded in the central hub region of the centrifugal pump, and both pumps rotate around a common central axis, while maintaining separate fluid domains. In this work, we concentrated our design and development effort on the centrifugal blood pump by performing computational modeling. An iterative process was employed to improve the DH design. The pressure generation, scalar stress levels, and fluid forces exerted on the magnetically levitated impellers were computationally estimated. A shaft driven centrifugal prototype was also manufactured and tested using a hydraulic flow loop circulating a water-glycerol blood analog. Pressure and flow performance of the pump prototype was measured for a given rotational speed for comparison to computational predictions. Our design achieved the target pump pressures of 60-140 mm Hg for flow rates of 1-5 L/min, and strong agreement in pressure rise was demonstrated between the experimental data and simulation results (less than 10% deviation on average). Fluid stress levels were, however, found to exceed thresholds in the outflow region of the pump, and fluid residence times were less than 600 ms. The findings of this work demonstrate that the more compact, next-gen DH's centrifugal pump design is able to achieve pressure-capacity requirements. Next steps will require a focused strategy to reduce hemolytic potential and to integrate magnetic suspension components for full rotor levitation.

To understand the needs and requirements in the development of rotary blood pumps, we have to consider the current use and limitations of blood pumps in cardiac surgery. There are 5 different fields of indications for blood pumps in cardiac surgery. First, there is the possibility to use rotary blood pumps in the cardiopulmonary bypass system. Second, miniaturized rotary blood pumps can be used to support beating heart surgery. Third, we expect a growing use of rotary blood pumps in short-term ventricular support. The same applies to the field of chronic cardiac failure and long-term myocardial support. Finally, miniaturized rotary blood pumps can be used to support the ventricle during myocardial infarction. Rotary blood pumps are expected, based on their features, to progress in all these indications.

This article presents a back-electromotive force (BEMF)-based technique of detection for sensorless brushless direct current motor (BLDCM) drivers. The BLDCM has been chosen as the energy converter in rotary or pulsatile blood pumps that use electrical motors for pumping. However, in order to operate properly, the BLDCM driver needs to know the shaft position. Usually, that information is obtained through a set of Hall sensors assembled close to the rotor and connected to the electronic controller by wires. Sometimes, a large distance between the motor and controller makes the system susceptible to interference on the sensor signal because of winding current switching. Thus, the goal of the sensorless technique presented in this study is to avoid this problem. First, the operation of BLDCM was evaluated on the electronic simulator PSpice. Then, a BEMF detector circuitry was assembled in our laboratories. For the tests, a sensor-dependent system was assembled where the direct comparison between the Hall sensors signals and the detected signals was performed. The obtained results showed that the output sensorless detector signals are very similar to the Hall signals at speeds of more than 2500 rpm. Therefore, the sensorless technique is recommended as a responsible or redundant system to be used in rotary blood pumps.

The previously more frequently implanted pulsatile blood pumps (PBPs) showed higher recovery rates than the currently preferred rotary blood pumps (RBPs), with unclear causality. The aim of this study was to comparatively assess the capability of PBPs and RPBs to unload the left ventricle and maintain cardiac energetics as a possible implication for recovery. An RBP and a heartbeat synchronized PBP were alternately connected to isolated porcine hearts. Rotational speed of RBPs was set to different support levels. For PBP support, the start of ejection was phased to different points during the cardiac cycle, prescribed as percentage delays from 0% to 90%. Cardiac efficiency, quantified by the ratio of external work over myocardial oxygen consumption, was determined. For RBP support, higher degrees of RBP support correlated with lower left atrial pressures (LAP) and lower cardiac efficiency (r = 0.91 ± 0.12). In contrast, depending on the phase delay of a PBP, LAP and cardiac efficiency exhibited a sinusoidal relationship with the LAP minimum at 90% and efficiency maximum at 60%. Phasing of a PBP offers the possibility to maintain a high cardiac efficiency and simultaneously unload the ventricle. These results warrant future studies investigating whether optimized cardiac energetics promotes functional recovery with LVAD therapy.

This paper presents the hydrodynamic design and performance analysis method for a miniaturized centrifugal blood pump using three-dimensional computational fluid dynamics (CFD) code. In order to obtain the hydraulically high efficient configuration of a miniaturized centrifugal blood pump for cardiopulmonary circulation, well-established commercial CFD codes were incorporated considering detailed flow dynamic phenomena in the blood pump system. A prototype of centrifugal blood pump developed by the present design and analysis method has been tested in the mock circulatory system. Predicted results by the CFD code agree very well with in vitro hydraulic performance data for a centrifugal blood pump over the entire operating conditions. Preliminary in vivo animal testing has also been conducted to demonstrate the haemodynamic feasibility for use of centrifugal blood pump as a mechanical circulatory support. A miniaturized centrifugal blood pump developed by the hydraulic design optimization and performance prediction method, presented herein, shows the possibility of a good candidate for intra and extracorporeal cardiopulmonary circulation pump in the near future.

Several types of centrifugal blood pump have been developed for artificial heart from its beneficial aspects compared with other types of blood pump. The designs of impeller and volute casing in a centrifugal blood pump are important factors affecting on its hydraulic performances. For initial evaluation of the impeller and the volute casing designed by 3-Dimensional modeling and Computational Fluidics Dynamics for its optimization, the animal experiments were conducted in comparison with Biopump™ (Medtronic BioMedicals, USA) as control group. Extracorporeal circulations with total cardiopulmonary bypass in swines (BW: 28.2±2.9 kg) were maintained for 2 hours at the flow rate of 1.5∼2 L/min in both groups. Hemodynamic and laboratory parameters, and pump performance parameters were measured during the experiments. The pressure differences between inlet and outlet in the study group were measured as 90–110 mmHg lower than that of control group as 150-200mmHg. But the higher motor speeds of 4700 rpm were required for maintaining the flow rate of 2 L/min than 2200 rpm in the control group. The plasma free hemoglobin data were higher than that of control group, possibly due to the impellar design or high motor speeds. More improvements including appropriate materials selection need to be done. This preliminary study shows the possibility of a centrifugal pump with optimized design of impeller and volute casing as a good candidate of artificial heart pumps in near future.

To reduce the energy consumption and blood damage of a centrifugal blood pump, this paper uses a permanent magnet bearing and blood flow pressure bearing to support blood pump impeller, design a magnetic fluid suspension centrifugal blood pump, three-dimensional numerical simulation of a magnetic fluid suspension centrifugal blood pump internal flow field, achieve the pressure of the blood pump flow channel and the velocity distribution, get the relationship between blood pressure and flow rate of the pump. The results can provide a theoretical basis for centrifugal blood pump design and improvement.

Secondary flow path is one of the crucial aspects during the design of centrifugal blood pumps. Small clearance size increases stress level and blood damage, while large clearance size can improve blood washout and reduce stress level. Nonetheless, large clearance also leads to strong secondary flows, causing further blood damage. Maglev blood pumps rely on magnetic force to achieve rotor suspension and allow more design freedom of clearance size. This study aims to characterize turbulent flow field and secondary flow as well as its effects on the primary flow and pump performance, in two representative commercial maglev blood pumps of CH-VAD and HeartMate III, which feature distinct designs of secondary flow path. The narrow and long secondary flow path of CH-VAD resulted in low secondary flow rates and low disturbance to the primary flow. The flow loss and blood damage potential of the CH-VAD mainly occurred at the secondary flow path, as well as the blade clearances. By contrast, the wide clearances in HeartMate III induced significant disturbance to the primary flow, resulting in large incidence angle, strong secondary flows and high flow loss. At higher flow rates, the incidence angle was even larger, causing larger separation, leading to a significant decrease of efficiency and steeper performance curve compared with CH-VAD. This study shows that maglev bearings do not guarantee good blood compatibility, and more attention should be paid to the influence of secondary flows on pump performance when designing centrifugal blood pumps.

Constant-speed methods are widely applied and studied in rotary blood pumps. However, various speed modulation which have been used in commercial blood pump lacks validation of the ventricular assist capability and hemolysis potential. This study investigates the hydrodynamic performance and hemolysis of a rotary ventricular assist device under sinusoidal speed modulation, focusing on the combined effects of phase, baseline speed, and speed fluctuation amplitude. Computational fluid dynamics (CFD) coupled with a dynamic cardiovascular model revealed that counter-phase modulation reduces hemolysis index (HI) fluctuations compared to in-phase conditions, while higher baseline speeds increase time-averaged HI due to prolonged exposure to non-physiological shear stress. Larger amplitudes expand the operational range but exacerbate HI variability. These findings demonstrate that phase synchronization critically balances pulsatility and hemocompatibility, providing actionable insights for adaptive speed control strategies in clinical practice.

A Novel Rotary Blood Pump for HFpEF