Implantable Rotary Blood Pump Research Articles

In Silico Evaluation of a Physiological Controller for a Rotary Blood Pump Based on a Sensorless Estimator

In this study, we present a sensorless, robust, and physiological tracking control method to drive the operational speed of implantable rotary blood pumps (IRBPs) for patients with heart failure (HF). The method used sensorless measurements of the pump flow to track the desired reference flow (Qr). A dynamical estimator model was used to estimate the average pump flow (Q^est) based on pulse-width modulation (PWM) signals. A proportional-integral (PI) controller integrated with a fuzzy logic control (FLC) system was developed to automatically adapt the pump flow. The Qr was modeled as a constant and trigonometric function using an elastance function (E(t)) to achieve a variation in the metabolic demand. The proposed method was evaluated in silico using a lumped parameter model of the cardiovascular system (CVS) under rest and exercise scenarios. The findings demonstrated that the proposed control system efficiently updated the pump speed of the IRBP to avoid suction or overperfusion. In all scenarios, the numerical results for the left atrium pressure (Pla), aortic pressure (Pao), and left ventricle pressure (Plv) were clinically accepted. The Q^est accurately tracked the Qr within an error of 0.25 L/min.

Miniaturized Fontan Circulation Assist Device: Chronic In Vivo Evaluation.

We have miniaturized and optimized our implantable rotary blood pump developed to provide long-term mechanical right heart support for patients who have failing Fontan circulation. The objective of this study was to evaluate the miniaturized Fontan circulation assist device (mini-FCAD) during 30-day sheep studies (n = 5). A complete right heart bypass was performed and all return flow was supported by the pump. Postoperatively, unfractionated heparin was given to maintain thromboelastography R times of 2× normal. The first two studies were terminated on day 0 and day 4 due to complications. In the final three studies, the animals remained healthy and were electively terminated at 30 ± 2 days. Pump flow was between 5 and 7 lpm, left atrial pressure remained normal, and inlet pressures were between 3 and 18 mm Hg with no incidents of suction. There was no evidence of hemolysis, end organ or pulmonary dysfunction, thromboembolic events, nor thermal damage to the surrounding tissue. Explanted devices from two studies were free of thrombi and in the third study there were unattached thrombi on the SVC inlet of the rotor. The mini-FCAD was successfully tested in vivo as a right heart replacement device demonstrating adequate circulatory support and normal physiologic pulmonary and venous pressures.

Chronic In Vivo Test of a Right Heart Replacement Blood Pump for Failed Fontan Circulation.

An implantable rotary blood pump was developed to provide long-term mechanical right heart support for patients who have failing Fontan circulation. The objective of this study was to evaluate the pump in vivo in a 30 day sheep study. Pump speed was set at 3,900 rpm for the duration of the study, and pump power was between 4.3 and 4.6 W. The pump inlet pressures for the superior vena cava (SVC) and inferior vena cava (IVC) were 14 ± 15 and 11 ± 15 mm Hg, respectively, over the duration of the study. Hematocrit remained stable at 30% ± 4%. Partial thromboplastin time (PTT) steadily increased from 30 s preoperatively to a high of 59 s on postoperative day 20, while prothrombin time (PT) remained at 20 ± 2 s for the duration of the study. The implantation and postoperative recovery were successful, and the animal demonstrated normal physiologic pulmonary and venous pressures and cardiac output. On pump inspection, the IVC and SVC inlets were completely clear of any deposits, but there were small thrombi (approximately 0.5 mm diameter) between each of the three rotor blades and along 20% of the parting line of the two volute halves. A complete right heart bypass was performed, postoperative recovery was successful, and the pump demonstrated adequate circulatory support and normal physiologic pulmonary and venous pressures. This study was the first successful test of a right heart replacement device in a chronic animal study.

Blood trauma potential of the HeartWare Ventricular Assist Device in pediatric patients

ObjectiveMechanical circulatory support has become a standard therapy for adult patients with end-stage heart failure. For pediatric patients, technologic development lags behind with no currently approved implantable rotary blood pump. As an alternative, the HeartWare Ventricular Assist Device (Medtronic, Minneapolis, Minn), originally designed for adults, is increasingly used in pediatric patients. The aim of this multicenter study was to assess in silico, in vitro, and in vivo the blood trauma potential of this pump in pediatric application. MethodsClinical outcome and indicators for in vivo blood trauma were investigated retrospectively in 14 pediatric patients with the HeartWare Ventricular Assist Device (age 11.3 ± 4.8 years). Blood trauma mechanisms of the HeartWare Ventricular Assist Device were examined in silico and in vitro at an adult and pediatric operating point (5 L/min and 2.5 L/min at 2800 rpm and 2200 rpm, respectively). The flow was simulated by computational fluid dynamics and analyzed regarding flow structures, shear stresses, and washout. Hemolysis was assessed with pumps circulating bovine blood in a temperate flow circuit. ResultsIn the retrospective in vivo analysis, lactate dehydrogenase and D-dimer values were 1.5- and 3-fold elevated, respectively, compared with adult patients with the HeartWare Ventricular Assist Device. Major bleedings were observed in 42.9%, and suspected pump thrombosis and neurologic dysfunction were observed in 14.3% of all patients. In the pediatric conditions, simulations predicted elevated mechanical stress profile below 50 Pa, more stagnant flow field, and longer washout times within the pump. In vitro measurements revealed an increased normalized index of hemolysis (17.5 vs 8.2 mg/100 L; P = .0021). ConclusionsThe HeartWare Ventricular Assist Device, operated at lower speeds and flows, induces elevated blood trauma. Further studies are required to assess the clinical implications of these findings.

A Valveless Pulsatile Pump for the Treatment of Heart Failure with Preserved Ejection Fraction: A Simulation Study.

Effective treatment of patients with terminal heart failure and preserved ejection fraction (HFpEF) is an unmet medical need. The aim of this study was to investigate a novel valveless pulsatile pump as a therapeutic option for the HFpEF population through comprehensive in silico investigations. The pump was simulated in a numerical model of the cardiovascular system of four HFpEF phenotypes and compared to a typical case of heart failure with reduced ejection fraction (HFrEF). The proposed pump, which was modeled as being directly connected to the left ventricle, features a single valveless inlet and outlet cannula and is driven in co-pulsation with the left ventricle. We collected hemodynamics for two different pump volumes (30 and 60mL). In all HFpEF conditions, the 30mL pump improved the cardiac output by approximately 1L/min, increased the mean arterial pressure by > 11% and lowered the mean left atrial pressure by > 30%. With the larger (60mL) stroke volume, these hemodynamic improvements were more pronounced. In the HFrEF condition however, these effects were three times less in magnitude. In this simulation study, the valveless pulsatile device improves hemodynamics in HFpEF patients by increasing the total stroke volume. The hemodynamic benefits are achieved with a small device volume comparable to implantable rotary blood pumps.

Hydraulic Characterization of Implantable Rotary Blood Pumps.

The hydraulic properties of implantable rotary blood pumps (RBPs) determine their interaction with the cardiovascular system. A systematic comparison in this regard has not yet been performed for different clinically used RBPs. The aim of this study is to describe the hydraulic characteristics of four RBPs with a universal mathematical model and to compare their behavior under clinical operating conditions. First, static and dynamic pump properties of four RBPs (HVAD, Heartmate II, Heartmate 3, and Incor) including their peripheral components were identified in an in vitro setup; results were translated into mathematical models based on principles of turbomachinery including the low and backflow regions. Second, the four hydraulic models were compared in a numerical simulation of the cardiovascular system for full- and partial-support conditions. A model structure applicable to each of the investigated RBPs was developed. Deviations between simulated and measured signals for static and dynamic properties were small (2.6 ± 0.5 mmHg, 0.38 ± 0.14 L/min, respectively). For a simulated partial support condition, flow pulsatility ranged from 4.1 (Incor) to 9.1 L/min (HVAD). Negative flow rates during diastole were observed in three out of four pumps. Hydraulic properties differ greatly between the investigated RBPs, with flat characteristics for the HVAD and Heartmate II and steeper curves for the Heartmate 3 and especially the Incor. Hydraulic characteristics of implantable RBPs are particularly important at lower pump flow rates if backflow is to be avoided. For further research, we provide dynamic hydraulic models of the four RBPs including their periphery.

A Mock Circulatory System for Testing Pediatric Rotary Blood Pumps

A mock circulatory system for simulating physiological characteristics of the cardiovascular system of pediatric heart failure patients is described. The system can also be used for preclinical testing of pediatric ventricular assist devices based on implantable rotary blood pumps.

Experimental Determination of the Normalized Index of Hemolysis for the Sputnik Implantable Pediatric Rotary Blood Pump

The paper describes the procedure for evaluation of hemolysis induced by the Sputnik implantable pediatric rotary blood pump. In a series of five experiments the normalized index of hemolysis (N.I.H) for the Sputnik pump was found to be 0.0099 ± 0.0015 g/100 L.

Development of Medical and Technical Requirements and Simulation of the Flow−Pressure Characteristics of the Sputnik Pediatric Rotary Blood Pump

This article discusses the first stages in the development of the Sputnik implantable pediatric rotary blood pump (Sputnik IPRBP). The requirements for the group of patients for whom the Sputnik IPRBP was developed were formulated. The design of the Sputnik IPRBP consists of a fixed flow tube, a straightener at the inflow, an impeller with an embedded magnet rotating at a rate of several thousand rpm, and a fixed diffuser on the output. Results of numerical simulation of liquid flow in the Sputnik IPRBP run in the Fluent ANSYS 16.2 hydrody-namics system are presented.

Slip and turbulence phenomena in journal bearings with application to implantable rotary blood pumps

This paper describes an investigation into journal bearings with geometries and working fluid similar to centrifugal blood pumps. The aim is to describe the phenomena that cause these journal bearings to deviate from classical predictions. Experimental, analytical and numerical methods are used to investigate the behaviour of a range of bearings with geometries and working fluid similar to blood pumps. It was found that the clearance had a significant effect on the force-eccentricity characteristic of the bearing, with smallest and largest clearances deviating from classical predictions. Experimentally measured pressure distributions show that slip occurs when the clearance is small and that turbulence occurs with the largest clearances. The effects of these phenomena on lubricant pressure and blood compatibility are discussed.

Sensorless Viscosity Measurement in a Magnetically-Levitated Rotary Blood Pump.

Controlling the flow rate in an implantable rotary blood pump based on the physiological demand made by the body is important. Even though various methods to estimate the flow rate without using a flow meter have been proposed, no adequate method for measuring the blood viscosity, which is necessary for an accurate estimate of the flow rate, without using additional sensors or mechanisms in a noninvasive way, has yet been realized. We have developed a sensorless method for measuring viscosity in magnetically levitated rotary blood pumps, which requires no additional sensors or mechanisms. By applying vibrational excitation to the impeller using a magnetic bearing, we measured the viscosity of the working fluid by measuring the phase difference between the current in the magnetic bearing and the displacement of the impeller. The measured viscosity showed a high correlation (R(2) > 0.992) with respect to a reference viscosity. The mean absolute deviation of the measured viscosity was 0.12 mPa·s for several working fluids with viscosities ranging from 1.18 to 5.12 mPa·s. The proposed sensorless measurement method has the possibility of being utilized for estimating flow rate.

Preload-based starling-like control for rotary blood pumps: numerical comparison with pulsatility control and constant speed operation.

In this study, we evaluate a preload-based Starling-like controller for implantable rotary blood pumps (IRBPs) using left ventricular end-diastolic pressure (PLVED) as the feedback variable. Simulations are conducted using a validated mathematical model. The controller emulates the response of the natural left ventricle (LV) to changes in PLVED. We report the performance of the preload-based Starling-like controller in comparison with our recently designed pulsatility controller and constant speed operation. In handling the transition from a baseline state to test states, which include vigorous exercise, blood loss and a major reduction in the LV contractility (LVC), the preload controller outperformed pulsatility control and constant speed operation in all three test scenarios. In exercise, preload-control achieved an increase of 54% in mean pump flow () with minimum loading on the LV, while pulsatility control achieved only a 5% increase in flow and a decrease in mean pump speed. In a hemorrhage scenario, the preload control maintained the greatest safety margin against LV suction. PLVED for the preload controller was 4.9 mmHg, compared with 0.4 mmHg for the pulsatility controller and 0.2 mmHg for the constant speed mode. This was associated with an adequate mean arterial pressure (MAP) of 84 mmHg. In transition to low LVC, for preload control remained constant at 5.22 L/min with a PLVED of 8.0 mmHg. With regards to pulsatility control, fell to the nonviable level of 2.4 L/min with an associated PLVED of 16 mmHg and a MAP of 55 mmHg. Consequently, pulsatility control was deemed inferior to constant speed mode with a PLVED of 11 mmHg and a of 5.13 L/min in low LVC scenario. We conclude that pulsatility control imposes a danger to the patient in the severely reduced LVC scenario, which can be overcome by using a preload-based Starling-like control approach.

Classification of Implantable Rotary Blood Pump States With Class Noise

A medical case study related to implantable rotary blood pumps is examined. Five classifiers and two ensemble classifiers are applied to process the signals collected from the pumps for the identification of the aortic valve nonopening pump state. In addition to the noise-free datasets, up to 40% class noise has been added to the signals to evaluate the classification performance when mislabeling is present in the classifier training set. In order to ensure a reliable diagnostic model for the identification of the pump states, classifications performed with and without class noise are evaluated. The multilayer perceptron emerged as the best performing classifier for pump state detection due to its high accuracy as well as robustness against class noise.

Hemodynamic response to exercise and head-up tilt of patients implanted with a rotary blood pump: a computational modeling study.

The present study investigates the response of implantable rotary blood pump (IRBP)-assisted patients to exercise and head-up tilt (HUT), as well as the effect of alterations in the model parameter values on this response, using validated numerical models. Furthermore, we comparatively evaluate the performance of a number of previously proposed physiologically responsive controllers, including constant speed, constant flow pulsatility index (PI), constant average pressure difference between the aorta and the left atrium, constant average differential pump pressure, constant ratio between mean pump flow and pump flow pulsatility (ratioP I or linear Starling-like control), as well as constant left atrial pressure ( P l a ¯ ) control, with regard to their ability to increase cardiac output during exercise while maintaining circulatory stability upon HUT. Although native cardiac output increases automatically during exercise, increasing pump speed was able to further improve total cardiac output and reduce elevated filling pressures. At the same time, reduced venous return associated with upright posture was not shown to induce left ventricular (LV) suction. Although P l a ¯ control outperformed other control modes in its ability to increase cardiac output during exercise, it caused a fall in the mean arterial pressure upon HUT, which may cause postural hypotension or patient discomfort. To the contrary, maintaining constant average pressure difference between the aorta and the left atrium demonstrated superior performance in both exercise and HUT scenarios. Due to their strong dependence on the pump operating point, PI and ratioPI control performed poorly during exercise and HUT. Our simulation results also highlighted the importance of the baroreflex mechanism in determining the response of the IRBP-assisted patients to exercise and postural changes, where desensitized reflex response attenuated the percentage increase in cardiac output during exercise and substantially reduced the arterial pressure upon HUT.

(723) - The Initial Results of Implantable Rotary Blood Pumps from New Center in Istanbul, Turkey

(723) - The Initial Results of Implantable Rotary Blood Pumps from New Center in Istanbul, Turkey

Robust Aortic Valve Non-Opening Detection for Different Cardiac Conditions

In recent years, extensive studies have been conducted in the area of pumping state detection for implantable rotary blood pumps. However, limited studies have focused on automatically identifying the aortic valve non-opening (ANO) state despite its importance in the development of control algorithms aiming for myocardial recovery. In the present study, we investigated the performance of 14 ANO indices derived from the pump speed waveform using four different types of classifiers, including linear discriminant analysis, logistic regression, back propagation neural network, and k-nearest neighbors (KNN). Experimental measurements from four greyhounds, which take into consideration the variations in cardiac contractility, systemic vascular resistance, and total blood volume were used. By having only two indices, (i) the root mean square value, and (ii) the standard deviation, we were able to achieve an accuracy of 92.8% with the KNN classifier. Further increase of the number of indices to five for the KNN classifier increases the overall accuracy to 94.6%.

The Evaluation of Leukocytes in Response to the In Vitro Testing of Ventricular Assist Devices

Infection is a clinically relevant adverse event in patients with ventricular assist device (VAD) support. The risk of infection could be linked to a reduced immune response resulting from damage to leukocytes during VAD support. The purpose of this study was to develop an understanding of leukocyte responses during the in vitro testing of VADs by analyzing the changes to their morphology and biochemistry. The VentrAssist implantable rotary blood pump (IRBP) and RotaFlow centrifugal pump (CP) were tested in vitro under constant hemodynamic conditions. Automated hematology analysis of samples collected regularly over 25-h tests was undertaken. A new flow cytometric assay was employed to measure biochemical alteration, necrosis (7-AAD) and morphological alteration (CD45 expression) of the circulating leukocytes during the pumping process. The results of hematology analysis show the total leukocyte number and subset counts decreased over the period of in vitro tests dependent on different blood pumps. The percentage of leukocytes damaged during 6-h tests was 40.8 ± 5.7% for the VentrAssist IRBP, 17.6 ± 5.4% for the RotaFlow CP, and 2.7 ± 1.8% for the static control (all n=5). Flow cytometric monitoring of CD45 expression and forward/side scatter characteristics revealed leukocytes that were fragmented into smaller pieces (microparticles). Scanning electron microscopy and imaging flow cytometry were used to confirm this. Device developers could use these robust cellular assays to gain a better understanding of leukocyte-specific VAD performance.

Evaluation of Suction Detection During Different Pumping States in an Implantable Rotary Blood Pump

In recent times, the problem of noninvasive suction detection for implantable rotary blood pumps has attracted substantial research interest. Here, we compare the performance of various suction indices for different types of suction and non-suction events based on pump speed irregularity. A total of 171 different indices that consist of previously proposed as well as newly introduced suction indices are tested using regularized logistic regression. These indices can be classified as amplitude based (derived from the mean, maximum, and minimum values of a cycle), duration based (derived from the duration of a cycle), gradient based (derived from the first order as well as higher order differences) and frequency based (derived from the power spectral density). The non-suction event data consists of ventricular ejection with or without arrhythmia and intermittent and continuous non-opening of the aortic valve. The suction event data consists of partial ventricular collapse that occurs intermittently as well as continuously with or without arrhythmia. In addition, we also attempted to minimize the usage of multiple indices by applying the sequential forward floating selection method to find which combination of indices gives the best performance. In general, the amplitude-based and gradient-based indices performed quite well while the duration-based and frequency-based indices performed poorly. By having only two indices ([i] the maximum gradient change in positive slope; and [ii] the standard deviation of the maximum value in a cycle), we were able to achieve a sensitivity of 98.9% and a specificity of 99.7%.

Long-term biventricular support with rotary blood pumps: prospects and pitfalls

Congestive heart failure affects 23 million people worldwide, including 7.5 million in North America (670 000 new cases per year) and 7 million in Europe [1]. Since 10% of those over 65 suffer from systolic left ventricular dysfunction, the number of patients with heart failure will double over the next 25 years. At any time, 10% of the heart failure cohort are categorized Stage D with advanced structural heart disease and symptoms at rest, despite detailed medical and cardiac resynchronization therapy. Twenty percent of these are younger than 65 years of age (around 140 000 in both the USA and Europe). The prognosis of Stage D heart failure is grim. In the REMATCH study, only 8% of the medically treated patients were alive at 2 years and continued to suffer in the interim [2]. A recurrent sentiment expressed by the Stage D patients is that they would sacrifice some duration of survival for a period of symptomatic relief [3]. Cardiac transplantation provides this for a highly selected tiny minority [4]. In contrast, cardiac resynchronization therapy is disappointing. A meta-analysis of 14 trials that randomized resynchronization against medical treatment showed only 59% of the NYHA IV device patients to have borderline symptomatic improvement to NYHA III with no survival benefit [5]. Boyle et al. [6] compared functional outcomes for NYHA IV patients after resynchronization or implantation of a left ventricular assist device (LVAD). At 6 months, resynchronized patients achieved only an additional 6 m in the 6 min walk test (insufficient to affect their daily living) and remained NYHA III or IV. In contrast, LVAD patients improved by 341 m, achieving NYHA I or II status. The study could not be randomized because 90% of the LVAD candidates were bed-bound on intravenous inotropes and could not walk beforehand. Long-term mechanical circulatory support is an increasingly realistic ‘off the shelf’ alternative to cardiac transplantation and an effective solution for those rendered ineligible through common heart failure comorbidities [7–9]. The treatment aims are uncontroversial. The first is to provide symptomatic relief and the second to achieve at least 5-year survival with a good quality of life. The third aim is cost containment by reducing the number of hospital admissions to palliate intolerable levels of breathlessness and fatigue. Hospital events account for $20.9 billion of an overall $35 billion heart failure budget in the USA. The rationale for a blood pump deployment is clear. The failing heart beats more than 120 000 times per day pumping around 7000 l of blood against an increasing afterload. As the heart dilates, the ventricular wall tension, myocardial energy and oxygen consumption increase, while sub-endocardial blood flow decreases. The LVAD unloads the failing ventricle resulting in beneficial structural and functional changes in the diseased myocardium [10–12]. Systemic blood flow returns to physiological levels to preserve the coronary and vital organ perfusion [13]. When native heart contractility and segmental wall motion improve, there is less propensity for intraventricular thrombus formation and thromboembolism. In September 2011, the Society of Thoracic Surgeons and the Food and Drugs Administration (USA) assembled a ‘Think Tank’ to focus on the need for long-term mechanical circulatory support in the USA. The group acknowledged the increasing safety profile and reliability of contemporary implantable rotary blood pumps together with the potential for stem cells to broaden the horizons of heart failure management. A need for 40 000 long-term LVADs per year was predicted, which would account for 50% of the heart failure annual budget. Between 15 and 30% of patients require biventricular support and there is no satisfactory long-term mechanical solution for these patients. The pulsatile total artificial hearts have numerous restrictions which confine their use as a bridge to transplantation [14]. INTERMACS data indicate that all total artificial heart patients are transplanted or dead within 6 months [15].

Theoretical Foundations of a Starling‐Like Controller for Rotary Blood Pumps

A clinically intuitive physiologic controller is desired to improve the interaction between implantable rotary blood pumps and the cardiovascular system. This controller should restore the Starling mechanism of the heart, thus preventing overpumping and underpumping scenarios plaguing their implementation. A linear Starling-like controller for pump flow which emulated the response of the natural left ventricle (LV) to changes in preload was then derived using pump flow pulsatility as the feedback variable. The controller could also adapt the control line gradient to accommodate longer-term changes in cardiovascular parameters, most importantly LV contractility which caused flow pulsatility to move outside predefined limits. To justify the choice of flow pulsatility, four different pulsatility measures (pump flow, speed, current, and pump head pressure) were investigated as possible surrogates for LV stroke work. Simulations using a validated numerical model were used to examine the relationships between LV stroke work and these measures. All were approximately linear (r(2) (mean ± SD) = 0.989 ± 0.013, n = 30) between the limits of ventricular suction and opening of the aortic valve. After aortic valve opening, the four measures differed greatly in sensitivity to further increases in LV stroke work. Pump flow pulsatility showed more correspondence with changes in LV stroke work before and after opening of the aortic valve and was least affected by changes in the LV and right ventricular (RV) contractility, blood volume, peripheral vascular resistance, and heart rate. The system (flow pulsatility) response to primary changes in pump flow was then demonstrated to be appropriate for stable control of the circulation. As medical practitioners have an instinctive understanding of the Starling curve, which is central to the synchronization of LV and RV outputs, the intuitiveness of the proposed Starling-like controller will promote acceptance and enable rational integration into patterns of hemodynamic management.