Quantifying the influence of combined lung and kidney support using a cardiovascular model and sensitivity analysis-informed parameter identification

The combination of extracorporeal membrane oxygenation (ECMO) and continuous renal replacement therapy (CRRT) pose complex hemodynamic challenges in intensive care. In this study, a comprehensive lumped parameter model (LPM) is developed to simulate the cardiovascular system, incorporating ECMO and CRRT circuit dynamics. A parameter identification framework based on global sensitivity analysis (GSA) and multi-start gradient-based optimization was developed and tested on 30 clinical data points from eight veno-arterial ECMO patients. To demonstrate feasibility, the model is used to analyze nine CRRT-ECMO connection schemes under varying flow conditions for a single patient. Our results indicate that CRRT has a notable impact on the cardiovascular system, with changes in pulmonary artery pressure of up to 203 %, highly dependent on ECMO flow. The GSA enabled the systematic and agnostic identification of a subset of model parameters used in the calibration process. The established parameter estimation framework is fast and robust, as no manual tuning of algorithm parameters is required, and achieves high correlations between simulation and experimental data with R2 > 0.98. It uses modeling methods that could pave the way for real-time applications in intensive care. This open-source framework provides a valuable tool for the systematic evaluation of combined ECMO and CRRT, which can be used to develop standardized treatment protocols and improve patient outcomes in critical care. This model provides a good basis for addressing research questions related to mechanical circulatory and respiratory support and presents tools to help move towards a digital twin in healthcare.

Dynamic modeling of variable speed left ventricular assist devices coupled to the cardiovascular system

BACKGROUND

Most of the modeling of the Left Ventricular Assist Devices (LVADs) coupled with the cardiovascular system is based on the assumption of constant rotational speed. Compared with the traditional inertial model, the validated hysteresis model can take into account the unsteady characteristics of LVADs, but it fails to work under the condition of variable speed modulation.

METHOD

This study takes into consideration the impact of speed variations on the unsteady hysteresis effects. The time constant in the hysteresis model is treated as a time-varying parameter, thereby developing a new model applicable to variable speed modulation. Under sinusoidal speed modulation at various phases, a comparative analysis was undertaken among the steady-state model, inertial model, and the new model. Transient Computational Fluid Dynamics (CFD) simulations and existing experimental results are used for validation.

RESULTS

The new model provides a more accurate method for the predicting the characteristics of LVAD in the coupled model under varying pump speeds, and exhibits higher linearity in the work done by the left ventricle and the blood pump, and R 2 = 0 . 9998 , which is aligning closely with the experimental results. This enhancement renders it applicable for proactive control predictions and passive control validations.

Interaction of a Ventricular Assist Device With Patient-Specific Cardiovascular Systems: In-Silico Study With Bidirectional Coupling

Ventricular assist devices (VADs) are used to assist the heart function of patients with advanced heart failure. Computational fluid dynamics in VADs are widely applied in the development and optimization, for example, to evaluate blood damage. For these simulations, the pulsating operating conditions, in which the VAD operates, should be included accurately. Therefore, this study aims to evaluate the flow in a VAD by interacting with patient-specific cardiovascular systems of heart failure patients. A numeric method will be presented, which includes a patient-specific cardiovascular system model that is bidirectionally coupled with a three-dimensional (3D) flow simulation of the HeartMate 3. The cardiovascular system is represented by a lumped parameter model. Three heart failure patients are considered, based on clinical data from end-stage heart failure patients. Various parameters of the cardiovascular system and the VAD are analyzed, for example, flow rates, pressures, VAD heads, and efficiencies. A further important parameter is the blood damage potential of the VAD, which varies significantly among different patients. Moreover, the predicted blood damage fluctuates within a single heartbeat. The increase in blood damage is evaluated based on the operating conditions. Both, overload and especially partial load conditions during the pulsating operation result in elevated blood damage.

Dynamic VAD simulations: Performing accurate simulations of ventricular assist devices in interaction with the cardiovascular system

Medical advancements, particularly in ventricular assist devices (VADs), have notably advanced heart failure (HF) treatment, improving patient outcomes. However, challenges such as adverse events (strokes, bleeding and thrombosis) persist. Computational fluid dynamics (CFD) simulations are instrumental in understanding VAD flow dynamics and the associated flow-induced adverse events resulting from non-physiological flow conditions in the VAD.This study aims to validate critical CFD simulation parameters for accurate VAD simulations interacting with the cardiovascular system, building upon the groundwork laid by Hahne et al. A bidirectional coupling technique was used to model dynamic (pulsatile) flow conditions of the VAD CFD interacting with the cardiovascular system. Mesh size, time steps and simulation method (URANS, LES) were systematically varied to evaluate their impact on the dynamic pump performance (dynamic H - Q curve) of the HeartMate 3, aiming to find the optimal simulation configuration for accurately reproduce the dynamic H - Q curve. The new Overlapping Ratio (OR) method was developed and applied to quantify dynamic H - Q curves.In particular, mesh and time step sizes were found to have the greatest influence on the calculated pump performance. Therefore, small time steps and large mesh sizes are recommended to obtain accurate dynamic H - Q curves. On the other hand, the influence of the simulation method was not significant in this study. This study contributes to advancing VAD simulations, ultimately enhancing clinical efficacy and patient outcomes.

Toward an Adjustable Blood Pump for Wide-Range Operation: In-Vitro Results of Performance Curve and Hydraulic Efficiency

Rotary blood pumps in Extracorporeal Life Support (ECLS) applications are optimized for a specific design point. However, in clinical practice, these pumps are usually applied over a wide range of operation points. Studies have shown that a deviation from the design point in a rotary blood pump leads to an unexpected rise of hemolysis with corresponding clinical complications. Adjustable pumps that can adapt geometric parameters to the respective operation point are commonly used in other industrial branches, but yet not applied in blood pumps. We present a novel mechanism to adjust the impeller geometry of a centrifugal blood pump during operation together with in-vitro data of its hydraulic performance and efficiency. Three-dimensionalprinted prototypes of the adjustable impeller and a rigid impeller were manufactured and hydraulic performance and efficiency measured (n = 3). In a flow range of 1.5-9.5 L/min, the adjustable pump increased pump performance up to 47% and hydraulic efficiency by an average of 7.3 percentage points compared with a fixed setting. The adjustable pump allows customization of the pump's behavior (steepness of performance curve) according to individual needs. Furthermore, the hydraulic efficiency of the pump could be maintained at a high level throughout the complete flow range.

Real-time regurgitation estimation in percutaneous left ventricular assist device fully supported condition using an unscented Kalman filter

Objective.Significant aortic regurgitation is a common complication following left ventricular assist device (LVAD) intervention, and existing studies have not attempted to monitor regurgitation signals and undertake preventive measures during full support. Regurgitation is an adverse event that can lead to inadequate left ventricular unloading, insufficient peripheral perfusion, and repeated episodes of heart failure. Moreover, regurgitation occurring during full support due to pump position offset cannot be directly controlled through control algorithms. Therefore, accurate estimation of regurgitation during percutaneous left ventricular assist device (PLVAD) full support is critical for clinical management and patient safety.Approach.An estimation system based on the regurgitation model is built in this paper, and the unscented Kalman filter estimator (UKF) is introduced as an estimation approach. Three offset degrees and three heart failure states are considered in the investigation. Using the mock circulatory loop experimental platform, compare the regurgitation estimated by the UKF algorithm with the actual measured regurgitation; the errors are analyzed using standard confidence intervals of ±2 SDs, and the effectiveness of the mentioned algorithms is thus assessed. The generalization ability of the proposed algorithm is verified by setting different heart failure conditions and different rotational speeds. The root mean square error and correlation coefficient between the estimated and actual values are quantified and the statistical significance of accuracy differences in estimation is illustrated using one-way analysis of variance (One-Way ANOVA), which in turn assessed the accuracy and stability of the UKF algorithm.Main results.The research findings demonstrate that the regurgitation estimation system based on the regurgitation model and UKF can relatively accurately estimate the regurgitation status of patients during PLVAD full support, but the effect of myocardial contractility on the estimation accuracy still needs to be taken into account.Significance.The proposed estimation method in this study provides essential reference information for clinical practitioners, enabling them to promptly manage potential complications arising from regurgitation. By sensitively detecting LVAD adverse events, valuable insights into the performance and reliability of the LVAD device can be obtained, offering crucial feedback and data support for device improvement and optimization.

An Atraumatic Mock Loop for Realistic Hemocompatibility Assessment of Blood Pumps

OBJECTIVE

Conventional mock circulatory loops (MCLs) cannot replicate realistic hemodynamic conditions without inducing blood trauma. This constrains in-vitro hemocompatibility examinations of blood pumps to static test loops that do not mimic clinical scenarios. This study aimed at developing an atraumatic MCL based on a hardware-in-the-loop concept (H-MCL) for realistic hemocompatibility assessment.

METHODS

The H-MCL was designed for 450 ± 50 ml of blood with the polycarbonate reservoirs, the silicone/polyvinyl-chloride tubing, and the blood pump under investigation as the sole blood-contacting components. To account for inherent coupling effects a decoupling pressure control was derived by feedback linearization, whereas the level control was addressed by an optimization task to overcome periodic loss of controllability. The HeartMate 3 was showcased to evaluate the H-MCL's accuracy at typical hemodynamic conditions. To verify the atraumatic properties of the H-MCL, hemolysis (bovine blood, n = 6) was evaluated using the H-MCL in both inactive (static) and active (minor pulsatility) mode, and compared to results achieved in conventional loops.

RESULTS

Typical hemodynamic scenarios were replicated with marginal coupling effects and root mean square error (RMSE) below 1.74 ± 1.37 mmHg while the fluid level remained within ±4% of its target value. The normalized indices of hemolysis (NIH) for the inactive H-MCL showed no significant differences to conventional loops ( ∆NIH = -1.6 mg/100 L). Further, no significant difference was evident between the active and inactive mode in the H-MCL ( ∆NIH = +0.3 mg/100 L).

CONCLUSION AND SIGNIFICANCE

Collectively, these findings indicated the H-MCL's potential for in-vitro hemocompatibility assessment of blood pumps within realistic hemodynamic conditions, eliminating inherent setup-related risks for blood trauma.

A Novel Pumping Principle for a Total Artificial Heart

OBJECTIVE

Total artificial hearts (TAH) serve as a temporary treatment for severe biventricular heart failure. The limited durability and complication rates of current devices hamper long-term cardiac replacement. The aim of this study was to assess the feasibility of a novel valveless pumping principle for a durable pulsatile TAH (ShuttlePump).

METHODS

The pump features a rotating and linearly shuttling piston within a cylindrical housing with two in- and outlets. With a single moving piston, the ShuttlePump delivers pulsatile flow to both systemic and pulmonary circulation. The pump and actuation system were designed iteratively based on analytical and in silico methods, utilizing finite element methods (FEM) and computational fluid dynamics (CFD). Pump characteristics were evaluated experimentally in a mock circulation loop mimicking the cardiovascular system, while hemocompatibility-related parameters were calculated numerically.

RESULTS

Pump characteristics cover the entire required operating range for a TAH, providing 2.5-9 L/min of flow rate against 50-160 mmHg arterial pressures at stroke frequencies of 1.5-5 Hz while balancing left and right atrial pressures. FEM analysis showed mean overall copper losses of 8.84 W, resulting in a local maximum blood temperature rise of <2 K. The CFD results of the normalized index of hemolysis were 3.57 mg/100 L, and 95% of the pump's blood volume was exchanged after 1.42 s.

CONCLUSION AND SIGNIFICANCE

This study indicates the feasibility of a novel pumping system for a TAH with numerical and experimental results substantiating further development of the ShuttlePump.

Computational evaluation of heart failure and continuous flow left ventricular assist device support in anaemia

Anaemia is common in end-stage heart failure patients supported with continuous flow left ventricular assist device (CF-LVAD) and is associated with adverse outcomes such as heart failure readmission. This study evaluates the haemodynamic effects of anaemia on cardiac function and cerebral blood flow in heart failure patients supported with CF-LVAD using computational simulations. A dynamic model simulating cardiac function, systemic, pulmonary and cerebral circulations, cerebral flow autoregulatory mechanisms and gas contents in blood was used to evaluate the effects of anaemia and iron deficiency in heart failure and during CF-LVAD support. CF-LVAD therapy was simulated by a model describing HeartMate 3. Anaemia and iron deficiency were simulated by reducing the haemoglobin level from 15 to 9 g/dL and modifying scaling coefficients in the models simulating heart chamber volumes. Reduced haemoglobin levels decreased the arterial O2 content, which increased cerebral blood flow rate by more than 50% in heart failure and during CF-LVAD assistance. Reduced haemoglobin levels simulating anaemia had minimal effect on the arterial and atrial blood pressures and ventricular volumes. In contrast, iron deficiency increased end-diastolic left and right ventricular diameters in heart failure from 6.6 cm to 7 cm and 2.9 cm to 3.1 cm and during CF-LVAD support from 6.1 to 6.4 cm and 3.1 to 3.3 cm. The developed numerical model simulates the effects of anaemia in failing heart and during CF-LVAD therapy. It is in good agreement with clinical data and can be utilised to assess CF-LVAD therapy.

Trans-aortic Valvular Ejection Fraction for Monitoring Recovery of Patients with Ventricular Systolic Heart Failure

Durable mechanical circulatory support in the form of left ventricular (LV) assist device (LVAD) therapy is increasingly considered in the context of the recovery of native cardiac function. Progressive improvement in LV function may facilitate LVAD explantation and a resultant reduction in device-related risk. However, ascertaining LV recovery remains a challenge. In this study, we investigated the use of trans-aortic valvular flow rate and trans-LVAD flow rate to assess native LV systolic function using a well-established lumped parameter model of the mechanically assisted LV with pre-existing systolic dysfunction. Trans-aortic valvular ejection fraction (TAVEF) was specifically found to characterize the preload-independent contractility of the LV. It demonstrated excellent sensitivity to simulated pharmacodynamic stress tests and volume infusion tests. TAVEF may prove to be useful in the ascertainment of LV recovery in LVAD-supported LVs with pre-existing LV systolic dysfunction.

Evaluating Indices for Non-invasive Myocardial Recovery Assessment in LVAD-Supported Heart Failure Patients

Accurate assessment of myocardial recovery (MR) under left ventricular assist device (LVAD) support is essential for clinicians to manage heart failure patients. However, current techniques for assessing MR are time-consuming, invasive, and infrequent. Measuring MR using indices derived from LVAD operating data instead provides a potential real-time alternative. Several of these indices for assessing the MR of LVAD-supported heart failure patients were collated from the literature and subject to a comprehensive comparative analysis. The objective of this analysis was to determine the most accurate index for assessing systolic cardiac function under LVAD-support, characterized by maximal end-systolic elastance (Emax), while remaining insensitive to preload & afterload. The indices were compared in computational simulation, utilizing an LVAD + cardiovascular system model to sweep through a large array of Emax and resistance conditions. Results demonstrated the index that correlated best with Emax, showing the highest accuracy, was the ratio between maximum flow acceleration and flow pulsatility (average R2 =0.9790). The same index also exhibited the lowest % variation (sensitivity) to preload & afterload (1.32% & 13.53% respectively). However, opportunities for improvement remain among current recovery assessment indices, with this study providing a baseline of performance for potential future indices to improve upon.Clinical relevance- This study presents a potential real-time measure of native cardiac function in LVAD-supported heart failure patients to support patient management and further recovery.

Numerical analysis of different cardiac functions and support modes on blood damage potential in an axial pump

BACKGROUND

Cardiac functions and support modes of left ventricular assist device (LVAD) will influence the pump inner flow field and blood damage potential.

METHODS

Computational fluid dynamics (CFD) method and lumped-parameter-model (LPM) were applied to investigate the impacts of cardiac functions under full (9000 rpm) and partial (8000 rpm) support modes in an axial pump.

RESULTS

The constitution of hemolysis index (HI) in different components of the pump was investigated. HI was found to be more sensitive to positive incidence angles (i) compared with negative incidence angles in rotors. Negative incidence angles had little impact on HI both in rotors and the outlet guide vanes. The improved cardiac function made only a minor difference in HIave (estimated average HI in one cardiac cycle) by 9.88%, as the flow rate expanded mainly to higher flow range. Switching to partial support mode, however, would induce a periodic experience of severe flow separation and recirculation at low flow range. This irregular flow field increased HIave by 47.97%, remarkably increasing the blood damage potential.

CONCLUSION

This study revealed the relationship between the blade incidence angle i and HI, and recommended negative-incidence-angle blade designs as it yielded lower HI. Moreover, to avoid flow range below 50% of the design point, careful evaluations should be made before switching support modes as weaning procedures in clinical applications.

Dynamic characteristic modeling of left ventricular assist devices based on hysteresis effects

OBJECTIVE

The purpose of this study is to develop a new model for the dynamic characteristics of left ventricular assist devices (LVADs) interacting with the cardiovascular system under constant-speed modes.

METHODS

A new hysteresis model is established on the basis of the hysteresis effect and turbomachinery principles. The simulation results from the hysteresis model were compared with the inertia model. The in-vitro experiment results of a centrifugal pump (from literature) and the unsteady computational fluid dynamics (CFD) simulation results of an axial pump were used as the benchmarks.

RESULTS

Compared with the inertia model, at the partial support mode, the relative estimation error of the time to the maximum and minimum pump flow (Q) in the hysteresis model decreased at least 16.3% cardiac cycle (T_c) in the centrifugal pump and at least 1.9% T_c in the axial pump, indicating its ability to simulate more realistic Q fluctuations. Moreover, the hysteresis model could predict an accurate time distribution of different Q.

CONCLUSION

The hysteresis model provides a general calculation method for simulating the dynamic characteristics of constant-speed LVADs under interaction with the cardiovascular system. It is more accurate than the inertia model.

SIGNIFICANCE

The hysteresis model is helpful for the rapid estimation of unsteady dynamic characteristics in absence of a physical pump prototype at the preliminary design stage.

Hemocompatibility and hemodynamic comparison of two centrifugal LVADs: HVAD and HeartMate3

Mechanical circulatory support using ventricular assist devices is a common technique for treating patients suffering from advanced heart failure. The latest generation of devices is characterized by centrifugal turbopumps which employ magnetic levitation bearings to ensure a gap clearance between moving and static parts. Despite the increasing use of these devices as a destination therapy, several long-term complications still exist regarding their hemocompatibility. The blood damage associated with different pump designs has been investigated profoundly in the literature, while the hemodynamic performance has been hardly considered. This work presents a novel comparison between the two main devices of the latest generation-HVAD and HM3-from both perspectives, hemodynamic performance and blood damage. Computational fluid dynamics simulations are performed to model the considered LVADs, and computational results are compared to experimental measurements of pressure head to validate the model. Enhanced performance and hemocompatibility are detected for HM3 owing to its design incorporating more conventional blades and larger gap clearances.

Comparison of device-based therapy options for heart failure with preserved ejection fraction: a simulation study

Successful therapy of heart failure with preserved ejection fraction (HFpEF) remains a major unmet clinical need. Device-based treatment approaches include the interatrial shunt device (IASD), conventional assist devices pumping blood from the left ventricle (LV-VAD) or the left atrium (LA-VAD) towards the aorta, and a valveless pulsatile assist device with a single cannula operating in co-pulsation with the native heart (CoPulse). Hemodynamics of two HFpEF subgroups during rest and exercise condition were translated into a lumped parameter model of the cardiovascular system. The numerical model was applied to assess the hemodynamic effect of each of the four device-based therapies. All four therapy options show a reduction in left atrial pressure during rest and exercise and in both subgroups (> 20%). IASDs concomitantly reduce cardiac output (CO) and shift the hemodynamic overload towards the pulmonary circulation. All three mechanical assist devices increase CO while reducing sympathetic activity. LV-VADs reduce end-systolic volume, indicating a high risk for suction events. The heterogeneity of the HFpEF population requires an individualized therapy approach based on the underlying hemodynamics. Whereas phenotypes with preserved CO may benefit most from an IASD device, HFpEF patients with reduced CO may be candidates for mechanical assist devices.

Insights Into the Low Rate of In-Pump Thrombosis With the HeartMate 3: Does the Artificial Pulse Improve Washout?

While earlier studies reported no relevant effect of the HeartMate 3 (HM3) artificial pulse (AP) on bulk pump washout, its effect on regions with prolonged residence times remains unexplored. Using numerical simulations, we compared pump washout in the HM3 with and without AP with a focus on the clearance of the last 5% of the pump volume. Results were examined in terms of flush-volume (V_f, number of times the pump was flushed with new blood) to probe the effect of the AP independent of changing flow rate. Irrespective of the flow condition, the HM3 washout scaled linearly with flush volume up to 70% washout and slowed down for the last 30%. Flush volumes needed to washout 95% of the pump were comparable with and without the AP (1.3–1.4 V_f), while 99% washout required 2.1–2.2 V_f with the AP vs. 2.5 V_f without the AP. The AP enhanced washout of the bend relief and near-wall regions. It also transiently shifted or eliminated stagnation regions and led to rapid wall shear stress fluctuations below the rotor and in the secondary flow path. Our results suggest potential benefits of the AP for clearance of fluid regions that might elicit in-pump thrombosis and provide possible mechanistic rationale behind clinical data showing very low rate of in-pump thrombosis with the HM3. Further optimization of the AP sequence is warranted to balance washout efficacy while limiting blood damage.

Computational Evaluation of Cardiac Function in Children Supported with Heartware VAD, HeartMate 2 and HeartMate 3 Left Ventricular Assist Devices

Heart failure is one of the principal causes of morbidity and mortality in children. Treatment techniques may not work, and heart transplantation may be required as a result. The current state of donor-organ supply means that many patients cannot undergo transplantation. In these patients, ventricular assist devices (VADs) may be used to bridge the time until the transplantation. Continuous-flow VADs are increasingly being implanted to paediatric patients. The aim of this study was to evaluate cardiac function in children supported with Heartware HVAD, HeartMate2 and HeartMate3 devices using computational simulations. A lumped-parameter model simulating cardiac function in children around 12 years of age was used to simulate dilated cardiomyopathy and heart-pump support. The operating speeds in HVAD, HeartMate2 and HeartMate3 were selected as 2600 rpm, 8700 rpm and 5200 rpm constant speed, respectively, while the Lavare cycle and artificial-pulse modes were used to generate mean pump outputs at around 4.40 L/min and mean arterial pressures at around 82 mmHg in each device. Aortic pulse pressure was 11 mmHg, 14 mmHg and 6 mmHg under HVAD, HeartMate2 and HeartMate3 support, respectively. HVAD’s Lavare cycle and HeartMate3’s artificial pulse increased aortic pulse pressure to 15 mmHg and 20 mmHg. HeartMate3 with artificial-pulse mode may be more beneficial in reducing arterial-pulsatility-associated problems.

Hemolytic Footprint of Rotodynamic Blood Pumps

OBJECTIVE

In preclinical examinations, rotodynamic blood pumps (RBPs) are predominantly evaluated at design-point conditions. In clinical practice, however, they run at diversified modes of operation. This study aimed at extending current preclinical evaluation of hemolytic profiles in RBPs toward broader, clinically relevant ranges of operation.

METHODS

Two implantable RBPs the HeartMate 3 (HM3) and the HeartWare Ventricular Assist Device (HVAD) were analyzed at three pump speeds (HM3: 4300, 5600, 7000rpm; HVAD: 1800, 2760, 3600rpm) with three flow rates (1-9L/min) per speed setting. Hemolysis measurements were performed in heparinized bovine blood. The delta free hemoglobin (dfHb) and the normalized index of hemolysis (NIH) served as hemolytic measures. Statistical analysis was performed by multiple comparison of the 9 operating conditions. Moreover, computational fluid dynamics (CFD) was applied to provide mechanistic insights into the interrelation between hydraulics and hemolysis by correlating numerically computed hydraulic losses with in-vitro hemolytic measures.

RESULTS

In both devices, dfHb increased toward increasing speeds, particularly during low but also during high flow condition. By contrast, in both RBPs magnitudes of NIH were significantly elevated during low flow operation compared to high flow conditions (p<0.0036). Maps of hemolytic metrics revealed morphologically similar trends to in-silico hydraulic losses (r>0.793).

CONCLUSIONS

While off-design operation is associated with increased hemolytic profiles, the setting of different operating conditions render a preclinical prediction of clinical impact with current hemolysis metrics difficult.

SIGNIFICANCE

The identified increase in hemolytic measures during episodes of off-design operation is highlighting the need to consider worst-case operation during preclinical examinations.

Geometric Optimization of an Extracorporeal Centrifugal Blood Pump with an Unshrouded Impeller Concerning Both Hydraulic Performance and Shear Stress

Centrifugal blood pumps have provided a powerful artificial support system for patients with vascular diseases. In the design process, geometrical optimization is usually needed to acquire a more biocompatible model for clinical uses. In the current paper, we propose a method for multi-objective optimization concerning both the hydraulic and the hemolytic performances of the pump based on the near-orthogonal array in which the traditional hemolysis index (HI) is replaced with the maximum scalar shear stress criteria to reduce the computation load. The method is demonstrated with the optimization of an extracorporeal centrifugal blood pump with an unshrouded impeller. CFD studies on the original and nine modified pump models are carried out. The calculated hydraulic performances of the optimized model are also compared against the experiments for validation of the numeric method, with an error of 3.6% at the original design point. The resulting blood pump with low maximum scalar shear stress (132.2 Pa) shows a low degree of calculated HI (1.69 × 10−3).

Correlation between Myocardial Function and Electric Current Pulsatility of the Sputnik Left Ventricular Assist Device: In-Vitro Study

This study assesses the electric current parameters and reports on the analysis of the associated degree of myocardial function during left ventricular assist device (LVAD) support. An assumption is made that there is a correlation between cardiac output and the pulsatility index of the pump electric current. The experimental study is carried out using the ViVitro Pulse Duplicator System with Sputnik LVAD connected. Cardiac output and cardiac power output are used as a measure of myocardial function. Different heart rates (59, 73, 86 bpm) and pump speeds (7600–8400 rpm in 200 rpm steps) are investigated. In our methodology, ventricular stroke volumes in the range of 30–80 mL for each heart rate at a certain pump speed were used to simulate different levels of contractility. The correlation of the two measures of myocardial function and proposed pulsatility index was confirmed using different correlation coefficients (values ≥ 0.91). Linear and quadratic models for cardiac output and cardiac power output versus pulsatility index were obtained using regression analysis of measured data. Coefficients of determination for CO and CPO models were in the ranges of 0.914–0.982 and 0.817–0.993, respectively. Study findings suggest that appropriate interpretation of parameters could potentially serve as a valuable clinical tool to assess myocardial therapy using LVAD infrastructure.

A Sensorless Control System for an Implantable Heart Pump Using a Real-Time Deep Convolutional Neural Network

Left ventricular assist devices (LVADs) are mechanical pumps, which can be used to support heart failure (HF) patients as bridge to transplant and destination therapy. To automatically adjust the LVAD speed, a physiological control system needs to be designed to respond to variations of patient hemodynamics across a variety of clinical scenarios. These control systems require pressure feedback signals from the cardiovascular system. However, there are no suitable long-term implantable sensors available. In this study, a novel real-time deep convolutional neural network (CNN) for estimation of preload based on the LVAD flow was proposed. A new sensorless adaptive physiological control system for an LVAD pump was developed using the full dynamic form of model free adaptive control (FFDL-MFAC) and the proposed preload estimator to maintain the patient conditions in safe physiological ranges. The CNN model for preload estimation was trained and evaluated through 10-fold cross validation on 100 different patient conditions and the proposed sensorless control system was assessed on a new testing set of 30 different patient conditions across six different patient scenarios. The proposed preload estimator was extremely accurate with a correlation coefficient of 0.97, root mean squared error of 0.84 mmHg, reproducibility coefficient of 1.56 mmHg, coefficient of variation of 14.44%, and bias of 0.29 mmHg for the testing dataset. The results also indicate that the proposed sensorless physiological controller works similarly to the preload-based physiological control system for LVAD using measured preload to prevent ventricular suction and pulmonary congestion. This study shows that the LVADs can respond appropriately to changing patient states and physiological demands without the need for additional pressure or flow measurements.

Varying speed modulation of continuous-flow left ventricular assist device based on cardiovascular coupling numerical model

Continuous-flow left ventricular assist devices (CFLVADs) routinely operate at a constant speed for the support of a failing heart, which decreases the pulsatility in the arteries. Some late complications could be related to a long-term lack of pulsatility. Modulating the CFLVAD speed is a solution to enhance the pulsatility. The purpose of this study is to modulate multiple varying speed patterns and investigate their effects on the ventricle and vascular system. A cardiovascular coupling numerical model is developed to provide a simulation platform for testing the varying speed patterns. The varying speed patterns are modulated by combining the shape, amplitude, frequency, phase shift, and pulsatile duty cycle of the speed profile. The influence of varying speed support is examined by analyzing the indexes of pulsatility, indexes of ventricular unloading, and hemodynamic variables. The results show that the synchronous counterpulsation pattern can effectively reduce the ventricular unloading indexes, whereas the low-frequency asynchronous pattern can effectively increase the vascular pulsatility indexes. Also, the hemodynamics with synchronous varying speed support is more physiological than that with asynchronous varying speed support. This study provides valuable insight for further optimization of varying speed modulation by weighing vascular pulsatility, ventricular unloading, and hemodynamics.

Impeller (straight blade) design variations and their influence on the performance of a centrifugal blood pump

INTRODUCTION

The miniaturization of blood pumps has become a trend due to the advantage of easier transplantation, especially for pediatric patients. In small-scale pumps, it is much easier and more cost-efficient to manufacture the impeller with straight blades compared to spiral-profile blades.

METHODS

Straight-blade impeller designs with different blade angles, blade numbers, and impeller flow passage positions are evaluated using the computational fluid dynamics method. Blade angles (θ = 0°, 20°, 30°, and 40°), blade numbers (N = 5, 6, 7, and 8), and three positions of impeller flow passage (referred to as top, middle, and bottom) are selected as the studied parametric values.

RESULTS

The numerical results reveal that with increasing blade angle, the pressure head and the hydraulic efficiency increase, and the average scalar shear stress and the normalized index of hemolysis decrease. The minimum radial force and axial thrust are obtained when θ equals 20°. In addition, the minimum average scalar shear stress and normalized index of hemolysis values are obtained when N = 6, and the maximum values are obtained when N = 5. Regarding the impeller flow passage position, the axial thrust and the stagnation area forming in the impeller eye are reduced as the flow passage height declines.

CONCLUSION

The consideration of a blade angle can greatly improve the performance of blood pumps, although the influence of the blade number is not very easily determined. The bottom position of the impeller flow passage is the best design.

Short-term physiological response to high-frequency-actuated pVAD support

Ventricular assist devices (VADs) are an established treatment option for heart failure (HF). However, the devices are often plagued by material-related hemocompatibility issues. In contrast to continuous flow VADs with high shear stresses, pulsatile VADs (pVADs) offer the potential for an endothelial cell coating that promises to prevent many adverse events caused by an insufficient hemocompatibility. However, their size and weight often precludes their intracorporeal implantation. A reduction of the pump body size and weight of the pump could be achieved by an increase in the stroke frequency while maintaining a similar cardiac output. We present a new pVAD system consisting of a pump and an actuator specifically designed for actuation frequencies of up to 240 bpm. In vitro and in vivo results of the short-term reaction of the cardiovascular system show no significant changes in left ventricular and aortic pressure between actuation frequencies from 60 to 240 bpm. The aortic pulsatility increases when the actuation frequency is raised while the heart rate remains unaffected in vivo. These results lead us to the conclusion that the cardiovascular system tolerates short-term increases of the pVAD stroke frequencies.

Numerical modeling of continuous-flow left ventricular assist device performance

Responses of five rotary blood pumps, namely HeartAssist 5, HeartMate II, HeartWare, Sputnik 1, and Sputnik 2, were extensively assessed in six test cases using a mathematical model of the cardiovascular system. Data for the rotary pumps were derived from pressure-flow curves reported in the literature. The test cases were chosen to attempt to cover most common clinical conditions, such as partial or full support or transitions between different levels of ventricular support. The investigated parameters are collected in a table and presented in figures, such as pressure-volume loops, H-Q curves, pump flow, and aortic pressure waveforms. HeartAssist, Sputnik 1, and Sputnik 2 pumps provide comparable level of aortic pressure, pump flow pulsatility PI(Q_P), and aortic pressure pulsatility PI(AoP) due to the similarity of pressure-flow characteristic curves of these pumps. HeartMate II provides a minimal backflow among other investigated rotary blood pumps due to the maximum pressure head at zero flow. HeartWare provides minimal pulsation of flow, which is confirmed by a flow range from -2 to 7 L/min in case 1. At the same time, the greatest degree of unloading was demonstrated by the HeartWare due to the flatness of the pressure-flow curve shape. The conclusions were made based on the obtained results, including the influence of pressure-flow curve shape on the pump performance and occurrences of adverse events, such as backflow or suction. For example, the increase of the pressure head at zero flow decreases the likelihood of backflow through the pump, and with it, increasing the flow under minimal pressure head increases the likelihood of suction.

Influence of left ventricular assist device pressure-flow characteristic on exercise physiology: Assessment with a verified numerical model

Current left ventricular assist devices are designed to reestablish patient's hemodynamics at rest but they lack the suitability to sustain the heart adequately during physical exercise. Aim of this work is to assess the performance during exercise of a left ventricular assist device with flatter pump pressure-flow characteristic and increased pressure sensitivity (left ventricular assist device 1) and to compare it to the performance of a left ventricular assist device with a steeper characteristic (left ventricular assist device 2). The two left ventricular assist devices were tested at constant rotational speed with a verified computational cardiorespiratory simulator reproducing an average left ventricular assist device patient response to exercise (EXE↑) and a left ventricular assist device patient with no chronotropic and inotropic response (EXE→). According to the results, left ventricular assist device 1 pumps a higher flow than left ventricular assist device 2 both at EXE↑ (6.3 vs 5.6 L/min) and at EXE→ (6.7 vs 6.1 L/min), thus it better unloads the left ventricle. Left ventricular assist device 1 increases the power delivered to the circulation from 0.63 W at rest to 0.67 W at EXE↑ and 0.82 W at EXE→, while left ventricular assist device 2 power shows even a minimal decrease. Left ventricular assist device 1 better sustains exercise hemodynamics and can provide benefits in terms of exercise performance, especially for patients with a poor residual left ventricular function, for whom the heart can hardly accommodate an increase of cardiac output.