Control strategy for rotary blood pumps.

In this study, the effects on varying cardiac function during a left ventricular (LV) bypass from the apex to the descending aorta using a centrifugal blood pump were evaluated by analyzing the left ventricular pressure and the motor current of the centrifugal pump in a mock circulatory loop. Failing heart models (preload 15 mm Hg, afterload 40 mm Hg) and normal heart models (preload 5 mm Hg, afterload 100 mm Hg) were simulated by adjusting the contractility of the latex rubber left ventricle. In Study 1, the bypass flow rate, left ventricular pressure, aortic pressure, and motor current levels were measured in each model as the centrifugal pump rpm were increased from 1,000 to 1,500 to 2,000. In Study 2, the pump rpm were fixed at 1,300, 1,500, and 1,700, and at each rpm, the left ventricular peak pressure was increased from 40 to 140 mm Hg by steps of 20 mm Hg. The same measurements as in Study 1 were performed. In Study 1, the bypass flow rate and mean aortic pressure both increased with the increase in pump rpm while the mean left ventricular pressure decreased. In Study 2, a fairly good correlation between the left ventricular pressure and the motor current of the centrifugal pump was obtained. These results suggest that cardiac function as indicated by left ventricular pressure may be estimated from a motor current analysis of the centrifugal blood pump during left heart bypass.

A tri-pod supported, seal-less centrifugal blood pump has been developed as an implantable ventricular assist pump. The impeller is supported with a tri-pod made of 3mm ceramic balls attached to the bottom surface of the impeller and magnetically coupled to the driver magnet mounted on the motor shaft. As the motor turns, the impeller rotates with the tri-pod sliding in the polyethylene groove imbedded in the pump bottom casing. The dimension of the pump including the driver is 60mm ± 80mm with its weight being 450g. The pump can deliver flow of 5L/min against the 100mmHg head pressure at 1800RPM. The pumping efficiency is around 10%. The pump RPM control consists of two phases; The initial phase is rough adjustment of the RPM based on the native heart rate. The target RPM is preset based on the relationship between the cardiac output and heart rate, and pump RPM and pump output Fine turning of the pump RPM then follows by computing the waveform deformation index (WDI) through Fourier analysis of the motor current waveform. The threshold level of WDI for occurrence of suction is < 0.2 and if the WDI exceeds this number, the pump RPM is reduced in order to prevent the suction. The control system demonstrated a stable performance in response to a sudden change in the system parameter with the response time being around 3 seconds. The automatic control of the implantable centrifugal blood pump is feasible without relying on external sensors. The system is under evaluation in chronic animal models.

In this study, a tripod supported sealless centrifugal blood pump was designed and fabricated for implantable application using a specially designed DC brushless motor. The tripod structure consists of 3 ceramic balls mounted at the bottom surface of the impeller moving in a polyethylene groove incorporated at the bottom pump casing. The follower magnet inside the impeller is coupled to the driver magnet of the motor outside the bottom pump casing, thus allowing the impeller to slide-rotate in the polyethylene groove as the motor turns. The pump driver has a weight of 230 g and a diameter of 60 mm. The acrylic pump housing has a weight of 220 g with the priming volume of 25 ml. At the pump rpm of 1,000 to 2,200, the generated head pressure ranged from 30 to 150 mm Hg with the maximum system efficiency being 12%. When the prototype pump was used in the pulsatile mock loop to assist the ventricle from its apex to the aorta, a strong correlation was obtained between the motor current and bypass flow waveforms. The waveform deformation index (WDI), defined as the ratio of the fundamental to the higher order harmonics of the motor current power spectral density, was computed to possibly detect the suction occurring inside the ventricle due to the prototype centrifugal pump. When the WDI was kept under the value of 0.20 by adjusting the motor rpm, it was successful in suppressing the suction due to the centrifugal pump in the ventricle. The prototype sealless, centrifugal pump together with the control method based on the motor current waveform analysis may offer an intermediate support of the failing left or right ventricle bridging to heart transplantation.

Ventricular assist devices have been widely accepted as an alternative treatment for advanced heart failure, while heart transplantation is a limited procedure because of the shortage of donors. In face of a scarce availability of these devices, many centers around the world have developed their own technologies. We describe historical and general features of the main ventricular assist devices developed at the Instituto Dante Pazzanese de Cardiologia. The auxiliary total artificial heart is an electromechanical pulsatile blood pump with left and right chambers, being originally designed to work as a heterotopic artificial heart. The spiral pump is a disposable device and currently available for clinical use in cardiopulmonary bypass. It works through a combination of centrifugal and axial pumping principles coming from a conically shaped impeller. The implantable centrifugal blood pump was conceived for long-term circulatory assistance with a unique impeller design concept producing a mixed flow. The apico-aortic blood pump consists of a miniaturized centrifugal pump originally conceived for bridge to transplantation strategy. The temporary circulatory support device is a new centrifugal blood pump for temporary ventricular assistance developed with the purpose of bridge-to-decision or recovery strategies. Additionally, the hybrid cardiovascular simulator was developed as a tool to test blood pumps as they minimize the need for animal experiments. Brazil represents an important reference with a few academic groups with a considerable output in ventricular assist devices research and development. Notable devices produced at Instituto Dante Pazzanese de Cardiologia have demonstrated excellent results for clinical application.

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.

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.

Recurrent orthostatic syncope due to left atrial and left ventricular collapse after a continuous-flow left ventricular assist device implantation

Reduced continuous-flow left ventricular assist device speed does not decrease von Willebrand factor degradation

Aortic valve regurgitation (AR) is a serious complication under left ventricular assist device (LVAD) support. AR causes LVAD-left ventricular (LV) recirculation, which makes it difficult to continue LVAD support. However, the hemodynamics and myocardial oxygen metabolism of LVAD support with AR have not been clarified, especially, how pump rotation speed influences them. An animal model of LVAD with AR was newly developed, and how pump rotation speed influences hemodynamics and myocardial oxygen metabolism was examined in acute animal experiments. Five goats (55±9.3kg) underwent centrifugal type LVAD, EVAHEART implantation. The AR model was established by placing a vena cava filter in the aortic valve. Hemodynamic values and the myocardial oxygen consumption, delivery, and oxygen extraction ratio (O2ER) were evaluated with changing pump rotation speeds with or without AR (AR+, AR-). AR+ was defined as Sellers classification 3 or greater. AR was successfully induced in five goats. Diastolic aortic pressure was significantly lower in AR+ than AR- (p=0.026). Central venous pressure, mean left atrial pressure, and diastolic left ventricular pressure were significantly higher in AR+ than AR- (p=0.010, 0.047, and 0.0083, respectively). Although systemic flow did not improve with increasing pump rotation speed, LVAD pump flow increased over systemic flow in AR+, which meant increasing pump rotation speed increased LVAD-LV recirculation and did not contribute to effective systemic circulation. O2ER in AR- decreased with increasing pump rotation speed, but O2ER in AR+ was hard to decrease. The O2ER in AR+ correlated positively with the flow rate of LVAD-LV recirculation (p=0.012). AR caused LVAD-LV recirculation that interfered with the cardiac assistance of LVAD support and made it ineffective to manage with high pump rotation speed.

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.

Artificial blood pumps are today's most promising bridge-to-recovery (BTR), bridge-to-transplant (BTT), and destination therapy solutions for patients suffering from intractable congestive heart failure (CHF). Due to an increased need for effective, reliable, and safe long-term artificial blood pumps, each new design must undergo failure and reliability testing, an important step prior to approval from the United States Food and Drug Administration (FDA), for clinical testing and commercial use. The FDA has established no specific standards or protocols for these testing procedures and there are only limited recommendations provided by the scientific community when testing an overall blood pump system and individual system components. Product development of any medical device must follow a systematic and logical approach. As the most critical aspects of the design phase, failure and reliability assessments aid in the successful evaluation and preparation of medical devices prior to clinical application. The extent of testing, associated costs, and lengthy time durations to execute these experiments justify the need for an early evaluation of failure and reliability. During the design stages of blood pump development, a failure modes and effects analysis (FMEA) should be completed to provide a concise evaluation of the occurrence and frequency of failures and their effects on the overall support system. Following this analysis, testing of any pump typically involves four sequential processes: performance and reliability testing in simple hydraulic or mock circulatory loops, acute and chronic animal experiments, human error analysis, and ultimately, clinical testing. This article presents recommendations for failure and reliability testing based on the National Institutes of Health (NIH), Society for Thoracic Surgeons (STS) and American Society for Artificial Internal Organs (ASAIO), American National Standards Institute (ANSI), the Association for Advancement of Medical Instrumentation (AAMI), and the Bethesda Conference. It further discusses studies that evaluate the failure, reliability, and safety of artificial blood pumps including in vitro and in vivo testing. A descriptive summary of mechanical and human error studies and methods of artificial blood pumps is detailed.

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.

Aortic regurgitation during continuous-flow left ventricular assist device support: An insufficient understanding of an insufficient lesion

A centrifugal blood pump for artificial heart has to have low hemolysis and no thrombus formation. For finding and removing the fluid dynamic causes of the above mentioned phenomena, flow visualization was utilized, as flow visualization can identify the high shear and stagnation locations which relate to hemolysis and thrombus formation respectively. In the present paper, general fluid dynamic characteristics of centrifugal blood pumps will be extracted, through analyzing four typical centrifugal pumps with flow visualization technique. Finding shear in the volute and diffuser regions, confirming vortex formation at washout holes, and quantitative analysis of the flow in the inlet regions are the shown examples. The obtained results correspond well to hemolysis tests, which proves that flow visualization is a useful tool in developing and analyzing blood pumps for artificial hearts.

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.