Mock Circulatory Loop Research Articles

Left Ventricular Assist Device Pump Obstruction Reduces Native Heart Efficiency.

Obstruction of the LVAD flow path can occur when blood clots or tissue overgrowth form within the inflow cannula, pump body, or outflow graft, and it can lead to thrombus, embolism, and stroke. The goal of this study was to measure the impact of progressive pump inflow obstruction on the pressure and flow dynamics of the LVAD-supported heart using a mock circulatory loop. Pump obstruction (PO) was produced by progressively blocking a fraction of the LVAD inlet area. Pressures, flows, and the midplane velocity field of the LV were measured for three LVAD speeds and six PO levels. Pressure and flow decreased with PO, shifting more of the flow through the aortic valve such that the total flow decreased by 6-11% and decreased the efficiency of the work of the native heart up to 60%. PO restricts diastolic flow through the LVAD, which reduces mitral inflow and decreases the strength and energy of the intraventricular vortices. The changes in flow architecture produced by PO include flow stasis and increased shear, which predispose the system to thromboembolic risk. Analysis of the contributions to external work may enable early detection, which allows time for therapeutic intervention, reducing the likelihood of pump replacement and the risk of complications.

Type III aortic arch angulation increases aortic stiffness: Analysis from an ex vivo porcine model

ObjectiveThe relationship among increased aortic arch angulation, aortic flow dynamics, and vessel wall stiffness remains unclear. This experimental ex vivo study investigated how increased aortic arch angulation affects aortic stiffness and stent-graft induced aortic stiffening, assessed by pulse wave velocity (PWV). MethodsPorcine thoracic aortas were connected to a circulatory mock loop in a Type I and Type III aortic arch configuration. Baseline characteristics and blood pressures were measured. Proximal and distal flow curves were acquired to calculate PWV in both arch configurations. After that, a thoracic stent-graft (VAMF2626C100TU) was deployed in aortas with adequate proximal landing zone diameters to reach 10% t0 20% oversizing. Acquisitions were repeated for both arch configurations after stent-graft deployment. ResultsTwenty-four aortas were harvested, surgically prepared, and mounted. Cardiac output was kept constant for both arch configurations (Type I: 4.74 ± 0.40 and Type III: 4.72 ± 0.38 L/minute; P = .703). Compared with a Type I arch, aortic PWV increased significantly in the Type III arch (3.53 ± 0.40 vs 3.83 ± 0.40 m/second; P < .001), as well as blood pressures. A stent-graft was deployed in 15 aortas. After deployment, Type I arch PWV increased (3.55 ± 0.39 vs 3.81 ± 0.44 m/second; P < .001) and Type III arch PWV increased although not significantly (3.86 ± 0.42 vs 4.03 ± 0.46 m/second; P = .094). Type III arch PWV resulted the highest and significantly higher compared with the Type I arch after stent-graft deployment (3.81 ± 0.44 vs 4.03 ± 0.46 m/second; P = .023). ConclusionsIncreased aortic arch angulation—as in a Type III arch—is associated with higher aortic PWV and blood pressures and this may negatively influence cardiovascular health.

Using a Mock Circulatory Loop as a Regulatory Science Tool to Simulate Different Heart Failure Conditions.

Mechanical circulatory support (MCS) device therapy is one of the primary treatment options for end-stage heart failure (HF), whereby a mechanical pump is integrated with the failing heart to maintain adequate tissue perfusion. The ISO 14708-5:2020 standard prescribes generic guidelines for nonclinical device evaluation and system performance testing of MCS devices using a mock circulatory loop (MCL). However, the utility of MCLs in premarket regulatory submissions of MCS devices is ambiguous, and the specific disease states that the device is intended to treat are not usually simulated. Hence, we aim to outline the potential of MCLs as a valuable regulatory science tool for characterizing MCS device systems by adequately representing target clinical-use HF conditions on the bench. Target pathophysiologic hemodynamics of HF conditions (i.e., cardiogenic shock (CS), left ventricular (LV) hypertrophy secondary to hypertension, and coronary artery disease), along with a healthy adult at rest and a healthy adult during exercise are provided as recommended test conditions. The conditions are characterized based on LV, aorta, and left atrium pressures using recommended cardiac hemodynamic indices such as systolic, diastolic, and mean arterial pressure, mean cardiac output (CO), cardiac cycle time, and systemic vascular resistance. This study is a first step toward standardizing MCLs to generate well-defined target HF conditions used to evaluate MCS devices.

Validation of a Multiscale Computational Model Using a Mock Circulatory Loop to Simulate Cardiogenic Shock.

The objectives of this study are to characterize the hemodynamics of cardiogenic shock (CS) through a computational model validated using a mock circulatory loop (MCL) and to perform sensitivity analysis and uncertainty propagation studies after the American Society of Mechanical Engineers (ASME) Validation and Verification (V&V) guidelines. The uncertainties in cardiac cycle time ( ), total resistance ( ), and total volume ( ) were quantified in the MCL and propagated in the computational model. Both models were used to quantify the pressure in the left atrium, aorta (Ao), and left ventricle (LV), along with the flow through the aortic valve, reaching a good agreement. The results suggest that 1) is the main source of uncertainty in the variables under study, 2) showed its greatest impact on the uncertainty of Ao hemodynamics, and 3) mostly affected the uncertainty of LV pressure and Ao flow at the late-systolic phase. Comparison of uncertainty levels in the computational and experimental results was used to infer the presence of additional contributing factors that were not captured and propagated during a first analysis. Future work will expand upon this study to analyze the impact of mechanical circulatory support devices, such as ventricular assist devices, under CS conditions.

Shear Forces Induced Platelet Clearance Is a New Mechanism of Thrombocytopenia.

Thrombocytopenia has been consistently described in patients with extracorporeal membrane oxygenation (ECMO) and associated with poor outcome. However, the prevalence and underlying mechanisms remain largely unknown, and a device-related role of ECMO in thrombocytopenia has been hypothesized. This study aims to investigate the mechanisms underlying thrombocytopenia in ECMO patients. In a prospective cohort of 107 ECMO patients, we investigated platelet count, functions, and glycoprotein shedding. In an ex vivo mock circulatory ECMO loop, we assessed platelet responses and VWF (von Willebrand factor)-GP Ibα (glycoprotein Ibα) interactions at low- and high-flow rates, in the presence or absence of red blood cells. The clearance of human platelets subjected or not to ex vivo perfusion was studied using an in vivo transfusion model in NOD/SCID (nonobese diabetic/severe combined Immunodeficient) mice. In ECMO patients, we observed a time-dependent decrease in platelet count starting 1 hour after device onset, with a mean drop of 7%, 35%, and 41% at 1, 24, and 48 hours post-ECMO initiation (P=0.00013, P<0.0001, and P<0.0001, respectively), regardless of the type of ECMO. This drop in platelet count was associated with a decrease in platelet GP Ibα expression (before: 47.8±9.1 versus 24 hours post-ECMO: 42.3±8.9 mean fluorescence intensity; P=0.002) and an increase in soluble GP Ibα plasma levels (before: 5.6±3.3 versus 24 hours post-ECMO: 10.8±4.1 µg/mL; P<0.0001). GP Ibα shedding was also observed ex vivo and was unaffected by (1) red blood cells, (2) the coagulation potential, (3) an antibody blocking VWF-GP Ibα interaction, (4) an antibody limiting VWF degradation, and (5) supraphysiological VWF plasma concentrations. In contrast, GP Ibα shedding was dependent on rheological conditions, with a 2.8-fold increase at high- versus low-flow rates. Platelets perfused at high-flow rates before being transfused to immunodeficient mice were eliminated faster in vivo with an accelerated clearance of GP Ibα-negative versus GP Ibα-positive platelets. ECMO-associated shear forces induce GP Ibα shedding and thrombocytopenia due to faster clearance of GP Ibα-negative platelets. Inhibiting GP Ibα shedding could represent an approach to reduce thrombocytopenia during ECMO.

A New Cardiovascular Mock Loop Driven by Novel Active Capacitance in Normal and Abnormal Conditions.

The hybrid mock circulatory loop (hMCL) serves as a crucial hemodynamic simulation tool, offering exceptional flexibility, controllability, and reproducibility for investigating the mechanisms underlying cardiovascular diseases (CVD) in a controlled environment, circumventing the limitations of live organism studies. This paper introduces a novel design and control strategy for hMCL, introducing a novel left ventricle volume-elastance (LVVE) equation that unifies the autoregulation of the Frank-Starling mechanism (FSM) with left ventricle contractility (LVC). LVVE establishes a dynamic link between left ventricular volume (LVV) and LVC, inherently satisfying the regulatory relationship between left ventricular pressure (LVP) and LVV through a mathematical equation. For the first time, LVVE integration significantly enhances the physiological relevance of hMCL by faithfully replicating FSM responses across diverse conditions, including aortic stenosis (AS), variations in systemic vascular resistance (SVR), and heart rate (HR) variations. Furthermore, this study introduces the stability proofs for the discrete closed-loop hMCL, enabling real-time proportional valve control through discrete feedback linearization-an innovative departure from conventional methods. Notably, FSM emulation is achieved by tracking reference maximum and minimum LVV values, eliminating the reliance on predefined functions or existing data, such as the maximum LV elastance value. Rigorous experimental validation, encompassing numerical simulations and comparative analyses with prior research, attests to the precision and efficacy of the proposed hMCL in faithfully replicating both normal and abnormal CV conditions. Significantly, the hMCL demonstrates that increasing HR enhances LVC while maintaining physiological pressures; however, this increase in LVC corresponds with a decrease in LVV, in alignment with human data and FSM principles. Crucially, the coupling mechanism between the FSM and LVC yields results of enhanced physiological fidelity, significantly advancing the hMCL's utility in physiological research. Moreover, the hMCL's capacity to simulate critical cardiovascular scenarios, including AS, SVR fluctuations, and HR variations, underscores its versatility and substantial potential for investigating complex CV dynamics.

Preservation of pulsatility with universal ventricular assist device: In vitro assessment for biventricular support.

The objective of this study was to assess the pulsatility preservation capability of the universal ventricular assist device (UVAD) when used as a biventricular assist device (BVAD). This evaluation was conducted through an in vitro experiment, utilizing a pulsatile biventricular circulatory mock loop. Two UVAD pumps were tested in a dual setup (BVAD) in the circulatory model with the simulated conditions of left heart failure (HF), right HF, and moderate/severe biventricular HF (BHF). The total flow, aortic pulse pressure, the pulse augmentation factor (PAF), the energy-equivalent pressure (EEP), and the surplus hemodynamic energy (SHE) were observed at various pump speeds to evaluate the pulsatility. The aortic pulse pressure increased from the baseline (without pump) in all simulated hemodynamic conditions. The PAF ranged from 17%-35% in healthy, left HF, right HF, and mild BHF conditions, with the highest PAF of 90% being observed in the severe BHF condition. The EEP correlated with LVAD flow in all groups (R2 = 0.87-0.97) and increased from the baseline in all cases. The SHE peaked at approximately 5-6 L/min of LVAD support and was likely to decrease at higher LVAD pump flow. The largest decrease in SHE from the baseline, 53%, was observed in the mild BHF conditions with the highest LVAD and RVAD support. The UVAD successfully demonstrated the ability to preserve pulsatility in vitro, and to optimize the cardiac output, as an isolated circulatory support device option (RVAD or LVAD) and when used for BVAD support.

Personalized Numerical Cardiovascular Model with Weight Growth for Evaluating Pediatric Left Ventricular Assist Devices: Derivation from an Experimental Mock Circulatory Loop.

Pediatric patients with heart failure have limited treatment options because of a shortage of donor hearts and compatible left ventricular assist devices (LVADs). To address this issue, our group is developing an implantable pediatric LVAD for patients weighing 5-20kg, capable of accommodating different physiological hemodynamic conditions as patients grow. To evaluate LVAD prototypes across a wide range of conditions, we developed a numerical cardiovascular model, using data from a mock circulatory loop (MCL) and patient-specific elastance functions. The numerical MCL was validated against experimental MCL results, showing good agreement, with differences ranging from 0 to 11%. The numerical model was also tested under left heart failure conditions and showed a worst-case difference of 16%. In an MCL study with a pediatric LVAD, a pediatric dataset was obtained from the experimental MCL and used to tune the numerical MCL. Then, the numerical model simulated LVAD flow by using an HQ curve obtained from the LVAD's impeller. When the numerical MCL was validated against the experimental MCL, hemodynamic differences ranged between 0 and 9%. These findings suggest that the numerical model can replicate various physiological conditions and impeller designs, indicating its potential as a tool for developing and optimizing pediatric LVADs.

Acausal Modelling of Advanced-Stage Heart Failure and the Istanbul Heart Ventricular Assist Device Support with Patient Data.

In object-oriented or acausal modelling, components of the model can be connected topologically, following the inherent structure of the physical system, and system equations can be formulated automatically. This technique allows individuals without a mathematics background to develop knowledge-based models and facilitates collaboration in multidisciplinary fields like biomedical engineering. This study conducts a preclinical evaluation of a ventricular assist device (VAD) in assisting advanced-stage heart failure patients in an acausal modelling environment. A comprehensive object-oriented model of the cardiovascular system with a VAD is developed in MATLAB/SIMSCAPE, and its hemodynamic behaviour is studied. An analytically derived pump model is calibrated for the experimental prototype of the Istanbul Heart VAD. Hemodynamics are produced under healthy, diseased, and assisted conditions. The study features a comprehensive collection of advanced-stage heart failure patients' data from the literature to identify parameters for disease modelling and tovalidate the resulting hemodynamics. Regurgitation, suction, and optimal speeds are identified, and trends in different hemodynamic parameters are observed for the simulated pathophysiological conditions. Using pertinent parameters in disease modelling allows for more accurate results compared to the traditional approach of arbitrary reduction in left ventricular contractility to model dilated cardiomyopathy. The current research provides a comprehensive and validated framework for the preclinical evaluation of cardiac assist devices. Due to its object-oriented nature, the featured model is readily modifiable for other cardiovascular diseases for studying the effect of pump operating conditions on hemodynamics and vice versa in silico and hybrid mock circulatory loops. The work also provides a potential teaching tool for understanding the pathophysiology of heart failure, diagnosis rationale, and degree of assist requirements.

Computational Fluid Dynamics Turbulence Model and Experimental Study for a Fontan Cavopulmonary Assist Device.

Head-flow HQ curves for a Fontan cavopulmonary assist device (CPAD) were measured using a blood surrogate in a mock circulatory loop and simulated with various computational fluid dynamics (CFD) models. The tests benchmarked the CFD tools for further enhancement of the CPAD design. Recommended Reynolds-Averaged Navier-Stokes (RANS) CFD approaches for the development of conventional ventricular assist devices (VAD) were found to have shortcomings when applied to the Fontan CPAD, which is designed to neutralize off-condition obstruction risks that could contribute to a major adverse event. The no-obstruction condition is achieved with a von Karman pump, utilizing large clearances and small blade heights, which challenge conventional VAD RANS-based CFD hemodynamic simulations. High-fidelity large eddy simulation (LES) is always recommended; however, this may be cost-inhibitive for optimization studies in commercial settings, thus the reliance on RANS models. This study compares head and power predictions of various RANS turbulence models, employing experimental measurements and LES results as a basis for comparison. The models include standard k-ϵ, re-normalization group k-ϵ, realizable k-ϵ, shear stress transport (SST) k-ω, SST with transitional turbulence, and Generalized k-ω. For the pressure head predictions, it was observed that the standard k-ϵ model provided far better agreement with experiment. For the rotor torque, k-ϵ predictions were 30% lower than LES, while the SST and LES torque values were near identical. For the Fontan CPAD, the findings support using LES for the final design simulations, k-ϵ model for head and general flow simulation, and SST for power, shear stress, hemolysis, and thrombogenicity predictions.

Regurgitation during the fully supported condition of the percutaneous left ventricular assist device

Objective. A percutaneous left ventricular assist device (PLVAD) can be used as a bridge to heart transplantation or as a temporary support for end-stage heart failure. Transvalvularly placed PLVADs may result in aortic regurgitation due to unstable pump position during fully supported operation, which may diminish the pumping effect of forward flow and predispose to complications. Therefore, accurate characterization of aortic regurgitation is essential for proper modeling of heart-pump interactions and validation of control strategies. Approach. In the present study, an improved aortic valve model was used to analyze the severity of regurgitation produced by different pump position offsets. The link between pump position offset degree and regurgitation is validated in the fixed speed mode, and the influence of pump speed on regurgitation is verified in the variable speed mode, using the mock circulatory loop (MCL) experimental platform. Main results. The greater the pump offset and the more severe the regurgitation, the more carefully the pump speed needs to be managed. To avoid over-pumping, the recommended pump speed in this study should not exceed 30 000 rpm. Significance. The modeling approach provide in this study not only makes it easier to comprehend the impact of regurgitation events on the entire interactive system during mechanical assistance, but it also aids in providing timely alerts and suitable management measures.

The role of innovative modeling and imaging techniques in improving outcomes in patients with LVAD.

Heart failure remains a significant cause of mortality in the United States and around the world. While organ transplantation is acknowledged as the gold standard treatment for end stage heart failure, supply is limited, and many patients are treated with left ventricular assist devices (LVADs). LVADs extend and improve patients' lives, but they are not without their own complications, particularly the hemocompatibility related adverse events (HRAE) including stroke, bleeding and pump thrombosis. Mainstream imaging techniques currently in use to assess appropriate device function and troubleshoot complications, such as echocardiography and cardiac computed tomography, provide some insight but do not provide a holistic understanding of pump induced flow alterations that leads to HRAEs. In contrast, there are technologies restricted to the benchtop-such as computational fluid dynamics and mock circulatory loops paired with methods like particle image velocimetry-that can assess flow metrics but have not been optimized for clinical care. In this review, we outline the potential role and current limitations of converging available technologies to produce novel imaging techniques, and the potential utility in evaluating hemodynamic flow to determine whether LVAD patients may be at higher risk of HRAEs. This addition to diagnostic and monitoring capabilities could improve prevention and treatment of LVAD-induced complications in heart failure patients.

Passive performance evaluation and validation of a viscous impeller pump for subpulmonary fontan circulatory support

Patients with single ventricle defects undergoing the Fontan procedure eventually face Fontan failure. Long-term cavopulmonary assist devices using rotary pump technologies are currently being developed as a subpulmonary power source to prevent and treat Fontan failure. Low hydraulic resistance is a critical safety requirement in the event of pump failure (0 RPM) as a modest 2 mmHg cavopulmonary pressure drop can compromise patient hemodynamics. The goal of this study is therefore to assess the passive performance of a viscous impeller pump (VIP) we are developing for Fontan patients, and validate flow simulations against in-vitro data. Two different blade heights (1.09 mm vs 1.62 mm) and a blank housing model were tested using a mock circulatory loop (MCL) with cardiac output ranging from 3 to 11 L/min. Three-dimensional flow simulations were performed and compared against MCL data. In-silico and MCL results demonstrated a pressure drop of < 2 mmHg at a cardiac output of 7 L/min for both blade heights. There was good agreement between simulation and MCL results for pressure loss (mean difference − 0.23 mmHg 95% CI [0.24–0.71]). Compared to the blank housing model, low wall shear stress area and oscillatory shear index on the pump surface were low, and mean washout times were within 2 s. This study demonstrated the low resistance characteristic of current VIP designs in the failed condition that results in clinically acceptable minimal pressure loss without increased washout time as compared to a blank housing model under normal cardiac output in Fontan patients.

A Mock Circulation Loop to Characterize In Vitro Hemodynamics in Human Systemic Arteries with Stenosis

Vascular disease is the leading cause of morbidity and mortality and a major cause of disability for Americans, and arterial stenosis is its most common form in systemic arteries. Hemodynamic characterization in a stenosed arterial system plays a crucial role in the diagnosis of its lesion severity and the decision-making process for revascularization, but it is not readily available in the current clinical measurements. The newly emerged image-based computational hemodynamics (ICHD) technique provides great potential to characterize the hemodynamics with fine temporospatial resolutions in realistic human vessels, but medical data is rather limited for validation requirements. We present an image-based experimental hemodynamics (IEHD) technique through a mock circulation loop (MCL) to bridge this critical gap. The MCL mimics blood circulation in human stenosed systemic arterial systems that can be either 3D-printed silicone, artificial, or cadaver arteries and thus enables in vitro measurement of hemodynamics. In this work, we focus on the development and validation of the MCL for the in vitro measurement of blood pressure in stenosed silicone arteries anatomically extracted from medical imaging data. Five renal and six iliac patient cases are studied. The pressure data from IEHD were compared with those from ICHD and medical measurement. The good agreements demonstrate the reliability of IEHD. We also conducted two parametric studies to demonstrate the medical applicability of IEHD. One was the cardiovascular response to MCL parameters. We found that blood pressure has a linear correlation with stroke volume and heart rate. Another was the effect of arterial stenosis, characterized by the volumetric reduction (VR) of the arterial lumen, on the trans-stenotic pressure gradient (TSPG). We parametrically varied the stenosis degree and measured the corresponding TSPG. The TSPG-VR curve provides a critical VR that can be used to assess the true hemodynamic severity of the stenosis. Meanwhile, the TSPG at VR = 0 can predict the potential pressure improvement after revascularization. Unlike the majority of existing MCLs that are mainly used to test medical devices involving heart function, this MCL is unique in its specific focus on pressure measurement in stenosed human systemic arteries. Meanwhile, rigorous hemodynamic characterization through concurrent IEHD and ICHD will significantly enhance our current understanding of the pathophysiology of stenosis and contribute to advancements in the medical treatment of arterial stenosis.

Qualitative and Quantitative Assessment of Invasive Surgery Skill Based on a Custom Training Simulator.

Qualitative and quantitative assessment of interventional performance is a vital component in the evaluation of endovascular surgery skill training. We established a custom simulator with qualitative and quantitative metrics for endovascular performance training. The simulator included an in vitro silicone phantom, mock circulation loop, visual module, force-sensing module, and custom software for image and force data postprocessing. Two tasks to deliver the guidewire to the target location of the carotid artery were conducted by the expert (n=4), novice (n=6), and test (n=4) groups. Seven features with significant differences extracted from the expert and novice groups were applied for qualitative assessment using the support vector machine (SVM) and quantitative assessment using the Mahalanobis distance (MD). Significant differences were observed in kinematic and force data between experts and novices during the intervention procedure. The median value of finished time for task 1 was 26.88 seconds for experts and 63.36 seconds for novices. The maximum speed for experts and novices was 32.79 and 7.43 cm/s, respectively. Moreover, the classified results depicted that the accuracy of qualitative assessment for task 1 and task 2 was 96.67% and 90%, respectively. As for the quantitative data, the residents had higher scores than individuals majored in biomedical engineering at 2 tasks (70.06±5.30 vs 41.81±6.58 for task 1, p=0.001). The proposed endovascular intervention skill training simulator provides qualitative and quantitative metrics on intervention performance skills and may be a useful tool in future interventional surgical training. This simulator comprised an in-vitro silicone phantom, mock circulation loop, visual module, force-sensing module, and custom software for image and force data post-processing. Seven interventional performance features were used for qualitative assessment using the support vector machine and quantitative assessment using the Mahalanobis Distance. From the observations, we conclude that this endovascular intervention skill training simulator provides qualitative and quantitative metrics on intervention performance and may be a useful tool in future surgical training.

P76: Need for an Interlaboratory Study of Mock Circulatory Loops to Evaluate the Performance of Mechanical Circulatory Support Devices

Purpose of Study: Mechanical circulatory support (MCS) devices are a surgical therapeutic option for patients with advanced and end-stage heart failure (HF), but predictions of device performance are difficult after implantation and often rely on animal and human studies. There is an unmet need for standardized non-clinical test methods to assess MCS flow performance. Mock circulatory loops (MCLs) can fill this need by simulating healthy and pathophysiologic pressure and flow conditions on the bench. However, test methods and parameters are inconsistent among stakeholders (i.e., test laboratories), and there are no standardized acceptance criteria for using MCLs in the evaluation of MCS devices. Methods: Recognizing the need for a consensus test protocol, the FDA engaged with external partners who are currently using MCLs to develop and evaluate MCS devices. Through these collaborations, we resolved key components and characteristics of MCLs needed for assessing device performance. A test protocol with test parameters and operating conditions was proposed by the FDA and modified based on the input of the external partners for use in an interlaboratory study. Common pathophysiologic hemodynamics were identified through literature review, discussions with clinicians, real-world evidence from post-market studies, and annual reports. For each HF condition, clinically significant cardiac indices such as heart rate, cardiac output (CO), systolic and diastolic pressures (SP and DP), left ventricular (LV) volume, left atrial filling pressure, cardiac cycle time (CCT), and systemic vascular resistance were controlled. Results: An interlaboratory study is underway to evaluate consensus test methods and parameters using MCLs to assess MCS device performance under critical HF conditions. A standardized test protocol, including data acquisition time, fluid properties, and cardiac/device pressures and flows, has been developed to evaluate MCS device operating modes. The study participants are collecting cardiac and MCS device pressure-flow data, utilizing the standardized protocol to simulate patient conditions such as cardiogenic shock, hypertension, LV hypertrophy, coronary artery disease and congenital heart defects. Figure 1 shows the common elements of MCLs, along with pressure and flow waveforms representing cardiogenic shock. Initial results indicate that the differences between the target and simulated hemodynamics range between 3 – 9 mmHg for SP, 2 – 12 mmHg for DP, 0.3 – 1 L/min for CO, and 0.001 – 0.01 s for CCT. This study demonstrates that MCLs can be used as an alternative preclinical method to reliably generate waveforms mimicking healthy and pathophysiologic patient hemodynamics. Summary: This interlaboratory study aims to standardize the use and increase the utility of MCLs in the evaluation of MCS devices. The study results can be incorporated into consensus standards.Figure 1. A) A schematic of the key elements of mock circulatory loops used to evaluate mechanical circulatory support devices; B) Representative pressure waveforms generated by an MCL to simulate cardiogenic shock (simulated CO = 3.4 LPM).

CARD13: INDUS: Economical Maglev Centrifugal Blood Pump for Developing Countries- Preliminary In-Vitro Hemolysis Testing

Purpose of Study: The Centrimag® is widely used for acute extracorporeal circulatory support. However, it is prohibitively expensive for low- and lower-middle-income countries (LMICs). In order to lower the costs associated with the use of Centrimag®, our India-US consortium is developing an economical centrifugal pump (INDUS), to improve accessibility of this lifesaving device. As a first step, a 3D printed magnetically levitated centrifugal pump head was designed and fabricated (Figure 1), that can fit into a standard Centrimag® motor unit. The objective of this study is to compare the hemolysis caused by the INDUS versus the original Centrimag® system in a mock circulatory loop, under realistic hemodynamic conditions. Methods: The prototype INDUS pump head was inserted into a simple mock-loop consisting of a blood reservoir, inlet and outlet tubing connections and the pump (Figure 2). A 3D printed clamp was used to control the resistance and develop pressure head. Pressure sensors were used to monitor pressure to a laptop using the DataQ system and non-contact Transonic flow probe provided a measure of the flow rate. The hemolysis tests were conducted as per the ASTM F1841-97 Standards using 400±20 mL of fresh, citrated, veni-puncture bovine blood at 30-35% haematocrit. The samples were collected at 0 Hr (baseline), 30 min., 1 Hr, 2 Hr, 3 Hr, and 4 Hr. The flow rate was maintained at 5±0.25 LPM and pressure at 110±15 mmHg. The samples were centrifuged, and the plasma was measured for plasma free hemoglobin, using a Multimode Reader. The normalized index of hemolysis (NIH) was calculated for both the pumps. Results: The NIH values for the original Centrimag® and the 3D printed INDUS were 0.00118 and 0.00166 respectively (Figure 3). Conclusion: The INDUS pump does not cause excessive hemolysis compared to the original Centrimag® pump. These encouraging in-vitro results encourages us to proceed with developing an injection moulded version and to launch further basic biocompatibility testing toward the goal of providing an inexpensive mechanical blood pump that can be accessible to patients in India and other LMICs.Figure 1. 3D Printed prototype of INDUS Pump (IAAHP: Indo-American Artificial Heart Program).Figure 2. Mock loop with Indus pump circulating bovine blood for hemolysis test.Figure 3. NIH comparison for Indus and Centrimag® pumps

P17: “Vadoscopy” Of Universal Ventricular Assist Device Shut-Off Feature During Pump Operation

Objective: The automatic, universal ventricular assist device has been designed for biventricular support (RVAD or LVAD). Device architecture (UVAD, Fig. 1A, B) enables a life-saving automatic forward flow shut-off function that, in the event of power interruption, helps mitigate patient hazard. Herein, we report the endoscopic visualization (“vadoscopy”) approach used to directly observe the UVAD shut-off function during device activation. Methods: The UVAD implanted in an ex vivo model and connected to a mock circulatory loop was used to simulate pump performance conditions. Device insertions in RVAD and LVAD positions were individually tested. The endoscopic visualization (Karl Storz 5 mm, 30° endoscope; Olympus CH-S190-XZ-E/Q Full HD 3CCD Camera) of the pump rotor occurred during operation and shut-off. The endoscope was placed through left and right atrial appendage and secured with a purse-string, respectively for UVAD used for left (LVAD) and right ventricular (RVAD) support. Results: The circulatory mock loop and ex vivo heart circulation were successfully maintained for both RVAD and LVAD settings. Endoscope was introduced through hermetically sealed insertion point. Direct visualization of the moving UVAD rotor was achieved at various modulated speeds and flows (continuous and pulsatile). The visual confirmation of sub-optimal and full rotor shut-off function (complete closure) was obtained in RVAD and LVAD conditions (Fig. 1C, D, E, F). Conclusion: The UVAD aperture mechanism enabled optimal forward flow shut-off in continuous and pulsatile speed and flow modulation. Direct endoscopic visualization of the UVAD with moving rotor has been feasible. Additional device feature assessment is ongoing.Figure 1. A - UVAD with open aperture; B - UVAD closed aperture; C - Rotor view via inflow; D - Rotor at nominal speed; E - Simulated sub-optimal rotor closure with large gap and regurgitant flow; F - Full rotor shut-off (nearly zero flow) through aperture area.

CARD19: Hemodynamic Capabilities of biventricular HM3 Support

Background: Severe biventricular failure may necessitate the use of biventricular support using two HeartMate 3 (HM3) devices, with the right sided device in an off-label setting. Quantitative analysis of the hemodynamic capabilities has not yet been published. The aim of this study was to extensively investigate the balance between left and right flow, atrial pressures and septal positioning with and without pump speed changes during biventricular HM3 support. Methods: A mock circulation loop was configured to simulate a dual HM3 supported biventricular heart failure condition with left ventricular and right atrial inflows for the left and right pump respectively. Speed adjustments were made to balance systemic and pulmonary flow rates, atrial pressures (left atrial pressure (LAP) 10-15 mmHg, right atrial pressure (RAP) 7-12 mmHg), and septal position (ventricular end diastolic volume (VEDV) difference < 50 mL) to achieve a baseline condition. Systemic hypotension ((SHpo) mean arterial pressure (MAP) < 65 mmHg by decreasing SVR from 1000 to 600 dynes s/cm5), systemic hypertension ((SH) MAP > 106 mmHg by increasing from SVR 1000 to 2000 dynes s/cm5) and pulmonary hypertension ((PH) mean pulmonary arterial pressure (MPAP) > 20 mmHg by increasing PVR from 80 to 300 dynes s/cm5) were independently simulated and results recorded. Left and right pump speed manipulations were completed for each condition in an attempt to restore the flows, atrial pressures and septal position. Results: The largest change in pump speed (LVAD: 6000 to 8200 rpm, RVAD: 2950 to 4900 rpm), was required to restore the simulated condition of SHpo. PH had the biggest impact on the atrial pressures, with LAP down to 4.11 mmHg and RAP up to 13.29 mmHg compared to 10.88 mmHg and 11.11 mmHg at the restored baseline condition respectively. Through HM3 speed manipulation, the LAP was restored to 7.08 mmHg and the RAP to 12 mmHg. PH had the most significant impact on the left and right VEDV difference, with an increase from 28 mL at the restored baseline condition to 228 mL during PH. This imbalance was reduced to 133 mL by adjusting both pump speeds, but could not be restored to the target of 50 mL. Conclusion: Systemic and pulmonary flow and atrial pressures can be restored through pump speed manipulation with biventricular HM3 support during simulations of severe SH. Restoring flows, atrial pressures and septal position was not possible in all conditions when relying solely on pump speed changes.Figure 1. Atrial pressures at different conditions, HF – heart failure; SH – systemic hypertension; SHpo – systemic hypotension; PH – pulmonary hypertension; LAP, RAP – left and right atrial pressures.Figure 2. Ventricular end diastolic volume difference at different conditions, HF – heart failure; SH – systemic hypertension; SHpo – systemic hypotension; PH – pulmonary hypertension; LVEDV, RVEDV – left and right end diastolic volume.

P19: Modeling the Effects of Heartbeat Synchronized Speed Modulation for a Pediatric LVAD

Study: Increasing the pulsatility of combined LVAD and heart output can be done by modulating the speed of the pump driver in synchrony with the heart rhythm. Increased pulsatility is closer to the physiological norm, lessens blood stagnation, and improves baroreceptor feedback for pressure regulation. This study is a first step to model the systemic response to pump speed modulation to develop the precise synchronization timing and controls for an optimized outcome and to analyze the results. Methods: A previously validated computational model of a mock circulatory loop is used as a platform to observe the hemodynamic effects of synchronized pump speed modulation on the heart. A model of a brushless DC motor used to drive the pediatric LVAD is established using the speed, torque, and inertia constants of the manufacturer specification sheet to represent the motor’s ability to change speed. The pressure and flow HQ curve of the LVAD impeller is used to calculate the pump output flow at different pressures and impeller speeds. The flow of the set speed LVAD is 3L/min, and the flow of the speed modulated LVAD varies between 1 L/min and 5 L/min at diastole and systole respectively. A PID controller is used to control the pump speed to reach the desired flow output. Results: The modulated LVAD flow results in larger changes in aortic pressure. The speed modulated LVAD had an aortic pressure difference of 20 mmHg between the minimum diastole and maximum systole values while the set speed LVAD had a difference of 7 mmHg. The set speed LVAD and the speed modulated LVAD had similar average aortic pressure values of 93mmHg and 91mmHg respectively. The changes in aortic pressure at systole and diastole resulting from the speed modulated flow show that synchronized motor speed modulation results in physiologic conditions closer to the norm.Figure 1. Overview of the Mock Circulatory Loop model and LVAD motor speed controller.Figure 2. Left Ventricular and Aortic Pressure with a set speed LVAD and a speed modulated LVAD.