Circulatory Loop Research Articles

In Vitro Analysis of Left Ventricular Assist Device Outflow Graft Orientations and Their Effect on Aortic Hemodynamics.

Continuous-flow left ventricular assist devices have become an important treatment option for patients with advanced heart failure. However, adverse hemodynamic effects as consequence of an altered blood flow within the aorta and the aortic root remain a topic of concern. In this work, we investigated the influence of the outflow graft orientation on the hemodynamic profile and flow parameters within the thoracic aorta. Aortic models with different outflow graft orientations were designed and three-dimensional (3D) printed to mimic common implantation configurations and were integrated into a pulsatile mock circulatory flow loop. Assist device function was achieved using a rotary pump, replicating nonpulsatile, continuous support flows of 1-5 L/min. Flow velocity, wall shear stress, and pressure gradients were investigated for each configuration using sonography and four-dimensional (4D) flow magnetic resonance imaging. Mean wall shear stresses measured in 4D flow software were lowest for a graft inclination angle of 45°. Streamline visualization revealed areas of nonuniform, retrograde, and vortex flow in all models but most prominent for the aortic model with an outflow graft inclination of 60°. The insights gained from this research may aid in understanding clinical outcomes following assist device implantation and long-term mechanical circulatory support.

Real-time physiological environment emulation for the Istanbul heart ventricular assist device via acausal cardiovascular modeling.

The cost and complexity associated with animal testing are significantly reduced by using mock circulatory loops prior. Novel mock circulatory loops allow us to test biomedical devices preclinically due to their flexibility, scalability, and cost-effectiveness. The presented work describes the development of a hardware-in-the-loop platform to emulate human physiology for the Istanbul Heart (iHeart-II) LVAD. A closed-loop system is developed whereby the effect of the LVAD on the heart and vice versa can be studied. An acausal model of the cardiovascular system is calibrated to emulate advanced-stage heart failure. A new prototype of the iHeart-II LVAD is connected between two air-actuated chambers emulating the left ventricle and aortic chambers with PID controllers tracking numerically modeled pressures from the in silico model. A lead-lag compensator is used to maintain fluid level. Controllers are tuned using nonlinear Hammerstein-Weiner models identified using open-loop data. The iHeart-II LVAD is operated at various speeds in its operational range, and the resulting hemodynamics are visualized in real time. Hemodynamic variables, such as LVAD flow rate, aortic, left ventricular, and pulse pressure, demonstrate trends similar to clinical observations. The iHeart-II LVAD achieves hemodynamic normalization at ~3500 rpm for the emulated condition. A novel evaluation methodology is adopted to study the performance of the iHeart LVAD under advanced-stage heart failure emulation. The models and controllers used in the platform are readily replicable to facilitate VAD research, pedagogy, design, and development.

Investigation of stent retriever removal forces in an experimental model of acute ischemic stroke.

Mechanical thrombectomy becomes more complex when the occlusion occurs in a tortuous cerebral anatomy, increasing the puncture to reperfusion time and the number of attempts for clot removal. Therefore, an understanding of stent retriever performance in these locations is necessary to increase the efficiency and safety of the procedure. An in vitro investigation into the effects of occlusion site tortuosity, blood clot hematocrit, and device geometry was conducted to identify their individual influence on stent retriever removal forces. Embolus analogs were used to create occlusions in a mock circulatory flow loop, and in vitro mechanical thrombectomies were performed in arterial models of increasing tortuosity. The stent retriever removal forces of Solitaire Platinum and EmboTrap II devices were recorded through each geometry with and without embolus analogs present. Similar experiments were also conducted with Solitaire stent retrievers of varying lengths and diameters and 0, 25, and 50% hematocrit embolus analogs. The removal force increased as model tortuosity increased for both the Solitaire Platinum and EmboTrap II stent retriever devices. The average removal forces in the simplest geometry with the Solitaire Platinum and EmboTrap II were 0.24 ± 0.01 N and 0.37 ± 0.02 N, respectively, and increased to 1.2 ± 0.08 N and 1.6 ± 0.17 N, respectively, in the most complex geometry. Slight increases in removal force were found with 0% hematocrit embolus analogs, however, no statistical significance between removal force and EA hematocrit was observed. A comparison between stent retriever removal forces between devices of different diameters also proved to be significant (p < 0.01), while forces between devices of varying lengths were not (p > 0.05). Benchtop mechanical thrombectomies performed with commercial stent retrievers of varying geometry showed that device removal forces increase with increasing model tortuosity, clot hematocrit does not play a significant role in device removal force, and that a stent retriever's diameter has a greater impact on removal forces compared to its length. These results provide an improved understanding of the overall forces involved in mechanical thrombectomy and can be used to develop safer and more effective stent retrievers for the most difficult cases.

4D-Flow MRI and Vector Ultrasound in the In-Vitro Evaluation of Surgical Aortic Heart Valves - a Pilot Study.

The aim of this study was the initial investigation of 4D-Flow MRI and Vector Ultrasound as novel imaging techniques in the in-vitro analysis of hemodynamics in anatomical models. Specifically, by looking at the hemodynamic performance of state-of-the-art surgical heart valves in a 3D-printed aortic arch. The mock circulatory loop simulated physiological, pulsatile flow. Two mechanical and three biological aortic valves prostheses were compared in a 3D-printed aortic arch. 4D magnetic resonance imaging and vector flow Doppler ultrasound served as imaging methods. Hemodynamic parameters such as wall shear stress, flow velocities and pressure gradients were analyzed. The flow analysis revealed characteristic flow-patterns in the 3D-printed aortic arch. The blood-flow in the arch presented complex patterns, including the formation of helixes and vortices. Higher proximal peak velocities and lower flow volumes were found for biological valves. The mock circulatory loop in combination with modern radiological imaging provides a sufficient basis for the hemodynamic comparison of aortic valves.

Implantable continuous-flow total artificial heart for newborns and small pediatric patients: First report of working model

ObjectiveThe need for safe and reliable mechanical circulatory support (MCS) for smaller children with severe heart failure (HF) is well defined. More specifically, in pediatric patients with advanced congenital HF, there is no implantable total artificial heart (TAH) device available for small patients. Herein, we report the development of the infant continuous-flow total artificial heart (I-CFTAH), a fully implantable in infants and newborns. MethodsAfter extensive engineering analysis, we performed an unprecedented effort: reducing the I-CFTAH's displacement volume to be 14% of the adult CFTAH pump while simultaneously decreasing pump diameter (6.2 cm to 2.6 cm) and axial length (9.8 cm to 4.8 cm). Facilitated by these proportional reductions, for the first time, a durable total artificial heart device was successfully fit in the chest of infants and newborns (height of ≥50 cm). ResultsThe functional I-CFTAH prototype demonstrated capability to support stable hemodynamics and desired device performance. The pump flow range (0.5-1.5 L/min) was confirmed in a mock circulatory testing loop. Within the tested flow range, the I-CFTAH can support small patients that could benefit from the intended cardiac output. ConclusionsThis successful effort demonstrated the feasibility of the miniature continuous-flow total artificial heart, intended for very small patient populations. I-CFTAH showed stable hemodynamics and could, therefore, become one of the few therapeutic options as a bridge to transplantation, aiming to enhance both the quality and duration of life for pediatric patients with advanced HF.

A less-invasive left atrial assist device concept for diastolic heart failure: First in vitro and in vivo assessment

ObjectiveA less-invasive left atrial assist device (LAADx) is a novel and implantable, extracardiac blood pump concept, intended for the treatment of diastolic heart failure, represented by heart failure with preserved ejection fraction. MethodsA mixed-flow pump was used as the working LAADx model. Its performance was evaluated at 3 speeds, using an in vitro pulsatile mock circulatory loop, with a pneumatic pump that can simulate diastolic heart failure conditions by adjusting the diastolic drive pressure. The LAADx model was implanted in 4 healthy calves. The pump's inflow and outflow cannulas were inserted into the left atrium (LA) and left ventricle (LV), respectively, without cardiopulmonary bypass. The LAADx was operated at 3 speeds, and diastolic heart failure-like conditions were induced by inflating a balloon, inserted into the LV. ResultsWith the in vitro study, diastolic heart failure-like conditions were successfully induced, exhibiting decreased cardiac output and aortic pressure as well as increased mean LA pressure both mitigated with the LAADx support. With regard to the in vivo study, simulated diastolic heart failure conditions showed a decrease in aortic pressure and an increase in LA pressure and LV end-diastolic pressure, which were again mitigated by the LAADx. Echocardiography showed good positioning of the outflow cannula and neither cardiac dysfunction nor mitral interference was observed. ConclusionsInitial in vitro and in vivo results confirmed that the LAADx model, a device concept driven by creating an extracardiac route from the LA to LV, has the potential to mitigate high LA pressure and improve LV filling of heart failure with preserved ejection fraction pathology.

Aortic Root Vortex Formation During Left Ventricular Assist Device Support.

The vortex that forms in the aortic sinus plays a vital role in optimizing blood flow. Disruption of the vortex can result in flow stagnation and activate thrombus formation in the aortic root, especially when aortic valve flow is reduced as during left ventricular assist device (LVAD) support. Our goal in this study was to visualize vortex formation in an experimental model of the aortic root as flow is progressively reduced. A mock circulatory loop that reproduces heart failure hemodynamics was combined with a HeartMate II LVAD and velocity measured in a transparent aortic root with a bioprosthetic valve. The aortic valve sinus vortices are clearly visible as counter-rotating structures in the velocity field at baseline and for all conditions with flow through the aortic valve. As LVAD speed increases, the central jet narrows but the vortices persist, disappearing only when the valve is completely closed. The vortices preserve fluid momentum and generate shear stress along the tissue surfaces which disrupts flow stasis. These features underscore the importance of maintaining "intermittent" aortic valve opening, as recommended for LVAD patients. This study is the first to report vortex formation in the aortic root during LVAD support, providing a motivation for further evaluation.

A Mock Circulatory Loop Analysis of Cardiorenal Hemodynamics With Intra-Aortic Mechanical Circulatory Support.

Type 1 cardiorenal syndrome is associated with significant excess morbidity and mortality in patients with severe acute decompensated heart failure. Previous trials of vasoactive drugs and ultrafiltration have not shown superiority over placebo or intravenous diuretics. Pilot data suggest short-term mechanical support devices may support diuresis in the cardiorenal syndrome. We evaluated the intra-aortic balloon pump (IABP) and a novel intra-aortic entrainment pump (IAEP) in a mock circulation loop (MCL) biventricular systolic heart failure model, to assess impact on renal flow and cardiac hemodynamics. Both devices produced similar and only modest increase in renal flow (IABP 3.3% vs. IAEP 4.3%) and cardiac output, with associated reduction in afterload elastance in the MCL. There were minor changes in coronary flow, increase with IABP and minor decrease with IAEP. Differences in device preload and afterload did not impact percentage change in renal flow with IABP therapy, however, there was a trend toward higher percentage flow change with IAEP in response to high baseline renal flow. The IAEP performed best in a smaller aorta and with more superior positioning within the descending aorta. Demonstrated changes in MCL flow during IAEP were of lower magnitude than previous animal studies, possibly due to lack of autoregulation and hormonal responses.

Collateral flow and pulsatility during large vessel occlusions: insights from a quantitative in vitro study.

Acute ischemic stroke caused by large vessel occlusions is being increasingly treated with neurovascular interventions. The hemodynamics within the collateral system of the circle of Willis (CoW) hemodynamics play a fundamental role in therapy success. However, transient in vivo data on pathological collateral flow during large vessel occlusions are not available. Moreover, there are no flow models that accurately simulate the hemodynamic conditions in the CoW during large vessel occlusions. We used a circulatory loop to generate highly reproducible cerebrovascular-like flows and pressures and used non-invasive flow visualization and high-resolution flow and pressure measurements to acquire detailed, time-dependent hemodynamics inside an anatomical phantom of the CoW. After calibrating a physiological reference case, we induced occlusions in the 1. middle cerebral artery, 2. terminal carotid artery, and 3. basilar artery; and measured the left posterior communicating artery flow. Mean arterial pressure and pulse pressure remained unchanged in the different occlusion cases compared to the physiological reference case, while total cerebral flow decreased by up to 19%. In all three occlusion cases, reversed flow was found in the left posterior communicating artery compared to the reference case with different flow magnitudes and pulsatility index values. The experimental results were compared with clinical findings, demonstrating the capability of this realistic cerebrovascular flow setup. This novel cerebrovascular flow setup opens the possibility for investigating different topics of neurovascular interventions under various clinical conditions in controlled preclinical laboratory studies.

Fabrication, characterization and numerical validation of a novel thin-wall hydrogel vessel model for cardiovascular research based on a patient-specific stenotic carotid artery bifurcation

In vitro vascular models, primarily made of silicone, have been utilized for decades for studying hemodynamics and supporting the development of implants for catheter-based treatments of diseases such as stenoses and aneurysms. Hydrogels have emerged as prominent materials in tissue-engineering applications, offering distinct advantages over silicone models for fabricating vascular models owing to their viscoelasticity, low friction, and tunable mechanical properties. Our study evaluated the feasibility of fabricating thin-wall, anatomical vessel models made of polyvinyl alcohol hydrogel (PVA-H) based on a patient-specific carotid artery bifurcation using a combination of 3D printing and molding technologies. The model’s geometry, elastic modulus, volumetric compliance, and diameter distensibility were characterized experimentally and numerically simulated. Moreover, a comparison with silicone models with the same anatomy was performed. A PVA-H vessel model was integrated into a mock circulatory loop for a preliminary ultrasound-based assessment of fluid dynamics. The vascular model's geometry was successfully replicated, and the elastic moduli amounted to 0.31 ± 0.007 MPa and 0.29 ± 0.007 MPa for PVA-H and silicone, respectively. Both materials exhibited nearly identical volumetric compliance (0.346 and 0.342% mmHg−1), which was higher compared to numerical simulation (0.248 and 0.290% mmHg−1). The diameter distensibility ranged from 0.09 to 0.20% mmHg−1 in the experiments and between 0.10 and 0.18% mmHg−1 in the numerical model at different positions along the vessel model, highlighting the influence of vessel geometry on local deformation. In conclusion, our study presents a method and provides insights into the manufacturing and mechanical characterization of hydrogel-based thin-wall vessel models, potentially allowing for a combination of fluid dynamics and tissue engineering studies in future cardio- and neurovascular research.

An intelligent aortic valve model for complete cardiac cycle.

The aortic valve (AV) is crucial for cardiovascular (CV) hemodynamic, impacting cardiac output (CO) and left ventricular volumetric flow rate (LVQ). Its nonlinear behavior challenges standard LVQ prediction methods as well as CO one. This study presents a novel approach for modeling the AV in the CV system, offering an improved method for estimating crucial parameters like LVQ across various AV conditions, including aortic stenosis (AS). The model, based on AV channel length during the entire cardiac phase, introduces a time-varying AV resistance (TV-AVR) parameterized by the pressure ratio across the AV and LVQ, enabling the simulation of both healthy and AS-related conditions. To validate this model, in vitro measurements are compared using a hybrid mock circulatory loop device. An unconventional use of a convolutional neural network (CNN) corrects the model's estimates, eliminating the need for labeled datasets. This approach, incorporating real-time learning and transforming 1-D CV signals into 2-D tensors, significantly improves the accuracy of LVQ measurements, achieving an error rate of less than 3.41 ± 4.84% for CO in healthy conditions and 2.83 ± 1.35% in AS cases-a 33.13% enhancement over linear diode models. These results underscore the potential of this approach for enhancing the diagnosis, prediction, and treatment of AV diseases. The key contributions of the proposed method encompass nonlinear TV-AVR estimation, investigation of transient CV responses, prediction of instantaneous CO, development of a flexible framework for noninvasive measurements integration, and the introduction of an adjustable resistance model using an extended Kalman filter (EKF) and CNN combination, all without requiring labeled data.

Linking Computational Fluid Dynamics Modeling to Device-Induced Platelet Defects in Mechanically Assisted Circulation.

Thrombotic and bleeding events are the most common hematologic complications in patients with mechanically assisted circulation and are closely related to device-induced platelet dysfunction. In this study, we sought to link computational fluid dynamics (CFD) modeling of blood pumps with device-induced platelet defects. Fresh human blood was circulated in circulatory loops with four pumps (CentriMag, HVAD, HeartMate II, and CH-VAD) operated under a total of six clinically representative conditions. Blood samples were collected and analyzed for glycoprotein (GP) IIb/IIIa activation and receptor shedding of GPIbα and GPVI. In parallel, CFD modeling was performed to characterize the blood flow in these pumps. Numerical indices of platelet defects were derived from CFD modeling incorporating previously derived power-law models under constant shear conditions. Numerical results were correlated with experimental results by regression analysis. The results suggested that a scalar shear stress of less than 75 Pa may have limited contribution to platelet damage. The platelet defect indices predicted by the CFD power-law models after excluding shear stress <75 Pa correlated excellently with experimentally measured indices. Although numerical prediction based on the power-law model cannot directly reproduce the experimental data. The power-law model has proven its effectiveness, especially for quantitative comparisons.

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.

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. 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. 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). 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.

Development of the PSU Child Pump.

The Pennsylvania State University (PSU) Child Pump, a centrifugal continuous-flow ventricular assist device (cf-VAD), is being developed as a suitable long-term implantable device for pediatric heart failure patients between 10 and 35 kg, body surface area (BSA) of 0.5-1.2 m 2 , 1-11 years of age, and requiring a mean cardiac output of 1.0-3.5 L/min. In-vitro hydraulic and hemodynamic performances were evaluated on a custom mock circulatory loop with ovine blood. Normalized index of hemolysis (NIH) was evaluated under four conditions: 1) 8,300 rpm, 3.5 L/min, Δ P = 60 mm Hg, 2) 8,150 rpm, 5.1 L/min, Δ P = 20 mm Hg, 3) 8,400 rpm, 3.2 L/min, Δ P = 70 mm Hg, and 4) 9,850 rpm, 5.0 L/min, Δ P = 80 mm Hg, resulting in normalized index of hemolysis = 0.027 ± 0.013, 0.015 ± 0.006, 0.016 ± 0.008, and 0.026 ± 0.011 mg/dl, respectively. A mock fit study was conducted using a three-dimensional printed model of a 19 kg patient's thoracic cavity to compare the size of the PSU Child Pump to the HeartMate3 and the HVAD. Results indicate the PSU Child Pump will be a safer, appropriately sized device capable of providing the given patient cohort proper support while minimizing the risks of blood trauma as they wait for a transplant.

Fluid mechanics of aortic valve incompetence in the dilated left ventricle

Introduction: Aortic insufficiency (AI) occurs when the aortic valve fails to close completely, allowing backward blood flow into the left ventricle (LV). The progression of AI can lead to ventricular dysfunction and congestive heart failure, setting off a self-perpetuating cycle that worsens these conditions. This study employed models of repeatable and reversible AI within a simulated circulatory loop to analyze vortex dynamics, AI parameters, and gain insights into the efficiency of ventricular washout.Method: A transparent silicone model of an LV with an ejection fraction of 17% served as the baseline, simulating a condition without AI. Mild, moderate, and severe AI were induced using 3D-printed stents, obstructing the complete closure of the aortic valve while allowing unimpeded forward blood flow. Midplane velocity fields were analyzed to compute AI and vortex properties, energy dissipation rate, blood residence time, and shear activation potential.Results and discussion: With increasing AI severity, the regurgitant jet expanded, impeding the development and trajectory of mitral inflow. The inefficiency in fluid transport became apparent through a declining ratio of total kinetic energy rate to energy dissipation rate and an increasing residence time. Impaired ventricular washout resulted in the accumulation of fluid with elevated shear activation potential in the LV. These findings suggested that AI progressively induces abnormal intraventricular flow, heightening the thromboembolic risk in heart failure patients. The study also advocates for the potential application of mock circulatory system to explore the effects of various AI configurations, especially when combined with other cardiac implants like artificial heart valve or left ventricular assist device.

Experimental evaluation of the plunger technique: A method of cyclic manual aspiration thrombectomy for treatment of acute ischemic stroke.

Mechanical thrombectomy via direct aspiration is a rapid treatment for acute ischemic stroke. This method often results in the partial ingestion of the clot or "corking" of the catheter tip. Cyclic aspiration may take advantage of the mechanical properties of the clot, resulting in greater clot ingestion and overall procedure success. An in vitro analysis was performed comparing static and cyclic (plunger technique) aspiration. Embolus analogs were used to create occlusions in a mock circulatory flow loop, and one aspiration attempt (first pass effect) using either a static or plunger technique was performed. The percent ingestion of each embolus analog was recorded for each trial. Static aspiration for 0% and 50% hematocrit embolus analogs resulted in ingestions of 12.8 ± 4.6% and 15.1 ± 10.0%, respectively, while plunger technique (cyclic) aspiration resulted in 15.8 ± 7.3% and 34.4 ± 19.5% ingestion. Complete ingestion was observed only with 50% hematocrit analogs, occurring in 30% of plunger and 10% of static cases. Statistical differences were determined between the two aspiration techniques for the 50% hematocrit samples, with the plunger technique yielding significantly more ingestion. In addition, the plunger technique was shown to maintain a negative vacuum pressure throughout the duration of cyclic plunging. The plunger technique for manual cyclic aspiration resulted in higher rates of complete ingestion and greater average % ingestions when compared to static aspiration. Increased clot ingestion can result in a higher rate of complete reperfusion during the first aspiration attempt, maximizing the number of patients with good clinical outcomes.

Real-Time Detection of Circulating Thrombi in an Extracorporeal Circuit Using Doppler Ultrasound: In-Vitro Proof of Concept Study.

Thromboembolic stroke continues to be by far the most common severe adverse event in patients supported with mechanical circulatory assist devices. Feasibility of using Doppler ultrasound to detect circulating thrombi in an extracorporeal circuit was investigated. A mock extracorporeal circulatory loop of uncoated cardiopulmonary bypass tubing and a roller pump was setup. A Doppler bubble counter was used to monitor the mean ultrasound backscatter signal (MUBS). The study involved two sets of experiments. In Scenario 1, the circuit was sequentially primed with human blood components, and the MUBS was measured. In Scenario 2, the circuit was primed with heparinized fresh porcine blood, and the MUBS was measured. Fresh blood clots (diameter <1,000 microns, 1,000-5,000 microns, >5,000 microns) were injected into the circuit followed by protamine administration. In Scenario 1 (n = 3), human platelets produced a baseline MUBS of 1.5 to 3.5 volts/s. Addition of packed human red blood cells increased the baseline backscatter to 17 to 21 volts/s. Addition of fresh frozen plasma did not change the baseline backscatter. In Scenario 2 (n = 5), the blood-primed circuit produced a steady baseline MUBS. Injection of the clots resulted in abrupt and transient increase (range: 3-30 volts/s) of the baseline MUBS. Protamine administration resulted in a sustained increase of MUBS followed by circuit thrombosis. Doppler ultrasound may be used for real-time detection of circulating solid microemboli in the extracorporeal circuit. This technology could potentially be used to design safety systems that can reduce the risk of thromboembolic stroke associated with mechanical circulatory support therapy.

Investigating the importance of left atrial compliance on fluid dynamics in a novel mock circulatory loop.

The left atrium (LA) hemodynamic indices hold prognostic value in various cardiac diseases and disorders. To understand the mechanisms of these conditions and to assess the performance of cardiac devices and interventions, in vitro models can be used to replicate the complex physiological interplay between the pulmonary veins, LA, and left ventricle. In this study, a comprehensive and adaptable in vitro model was created. The model includes a flexible LA made from silicone and allows distinct control over the systolic and diastolic functions of both the LA and left ventricle. The LA was mechanically matched with porcine LAs through expansion tests. Fluid dynamic measures were validated against the literature and pulmonary venous flows recorded on five healthy individuals using magnetic resonance flow imaging. Furthermore, the fluid dynamic measures were also used to construct LA pressure-volume loops. The in vitro pressure and flow recordings expressed a high resemblance to physiological waveforms. By decreasing the compliance of the LA, the model behaved realistically, elevating the a- and v-wave peaks of the LA pressure from 12 to 19mmHg and 22 to 26mmHg, respectively, while reducing the S/D ratio of the pulmonary venous flowrate from 1.5 to 0.3. This model provides a realistic platform and framework for developing and evaluating left heart procedures and interventions.

An Anatomically Shaped Mitral Valve for Hemodynamic Testing.

In vitro modeling of the left heart relies on accurately replicating the physiological conditions of the native heart. The targeted physiological conditions include the complex fluid dynamics coming along with the opening and closing of the aortic and mitral valves. As the mitral valve possess a highly sophisticated apparatus, thence, accurately modeling it remained a missing piece in the perfect heart duplicator puzzle. In this study, we explore using a hydrogel-based mitral valve that offers a full representation of the mitral valve apparatus. The valve is tested using a custom-made mock circulatory loop to replicate the left heart. The flow analysis includes performing particle image velocimetry measurements in both left atrium and ventricle. The results showed the ability of the new mitral valve to replicate the real interventricular and atrial flow patterns during the whole cardiac cycle. Moreover, the investigated valve has a ventricular vortex formation time of 5.2, while the peak e- and a-wave ventricular velocities was 0.9m/s and 0.4m/s respectively.