Numerical, hydraulic, and hemolytic evaluation of an intravascular axial flow blood pump to mechanically support Fontan patients

Empirical and Computational Evaluation of Hemolysis in a Microfluidic Extracorporeal Membrane Oxygenator Prototype

Microfluidic devices promise to overcome the limitations of conventional hemodialysis and oxygenation technologies by incorporating novel membranes with ultra-high permeability into portable devices with low blood volume. However, the characteristically small dimensions of these devices contribute to both non-physiologic shear that could damage blood components and laminar flow that inhibits transport. While many studies have been performed to empirically and computationally study hemolysis in medical devices, such as valves and blood pumps, little is known about blood damage in microfluidic devices. In this study, four variants of a representative microfluidic membrane-based oxygenator and two controls (positive and negative) are introduced, and computational models are used to predict hemolysis. The simulations were performed in ANSYS Fluent for nine shear stress-based parameter sets for the power law hemolysis model. We found that three of the nine tested parameters overpredict (5 to 10×) hemolysis compared to empirical experiments. However, three parameter sets demonstrated higher predictive accuracy for hemolysis values in devices characterized by low shear conditions, while another three parameter sets exhibited better performance for devices operating under higher shear conditions. Empirical testing of the devices in a recirculating loop revealed levels of hemolysis significantly lower (<2 ppm) than the hemolysis ranges observed in conventional oxygenators (>10 ppm). Evaluating the model's ability to predict hemolysis across diverse shearing conditions, both through empirical experiments and computational validation, will provide valuable insights for future micro ECMO device development by directly relating geometric and shear stress with hemolysis levels. We propose that, with an informed selection of hemolysis parameters based on the shear ranges of the test device, computational modeling can complement empirical testing in the development of novel high-flow blood-contacting microfluidic devices, allowing for a more efficient iterative design process. Furthermore, the low device-induced hemolysis measured in our study at physiologically relevant flow rates is promising for the future development of microfluidic oxygenators and dialyzers.

The Determination of the Biocompatibility of New Compositional Materials, including Carbamide-Containing Heterocycles of Anti-Adhesion Agents for Abdominal Surgery

Due to traumatic injuries, including those from surgical procedures, adhesions occur in over 50% of cases, necessitating exclusive surgical intervention for treatment. However, preventive measures can be implemented during abdominal organ surgeries. These measures involve creating a barrier around internal organs to forestall adhesion formation in the postoperative phase. Yet, the effectiveness of the artificial barrier relies on considerations of its biocompatibility and the avoidance of adverse effects on the body. This study explores the biocompatibility aspects, encompassing hemocompatibility, cytotoxicity, and antibacterial and antioxidant activities, as well as the adhesion of blood serum proteins and macrophages to the surface of new composite film materials. The materials, derived from the sodium salt of carboxymethylcellulose modified by glycoluril and allantoin, were investigated. The research reveals that film materials with a heterocyclic fragment exhibit biocompatibility comparable to commercially used samples in surgery. Notably, film samples developed with glycoluril outperform the effects of commercial samples in certain aspects.

Computational Modeling of the Penn State Fontan Circulation Assist Device

To address the increasing number of failing Fontan patients, Penn State University and the Penn State Hershey Medical Center are developing a centrifugal blood pump for long-term mechanical support. Computational fluid dynamics (CFD) modeling of the Penn State Fontan Circulatory Assist Device (FCAD) was performed to understand hemodynamics within the pump and its potential for hemolysis and thrombosis. CFD velocity and pressure results were first validated against experimental data and found to be within the standard deviations of the velocities and within 5% of the pressures. Further simulations performed with a human blood model found that most of the fluid domain was subjected to low shear stress (<50 Pa), with areas of highest stress around the rotor blade tips that increased with pump flow rate and rotor speed (138-178 Pa). However, the stresses compared well to previous CFD studies of commercial blood pumps and remained mostly below common thresholds of hemolysis and platelet activation. Additionally, few regions of low shear rate were observed within the FCAD, signifying minimal potential for platelet adhesion. These results further emphasize the FCAD's potential that has been observed previously in experimental and animal studies.

Computational Investigation of Anastomosis Options of a Right-Heart Pump to Patient Specific Pulmonary Arteries

Patients with Fontan circulation have increased risk of heart failure, but are not always candidates for heart transplant, leading to the development of the subpulmonic Penn State Fontan Circulation Assist Device. The aim of this study was to use patient-specific computational fluid dynamics simulations to evaluate anastomosis options for implanting this device. Simulations were performed of the pre-surgical anatomy as well as four surgical options: a T-junction and three Y-grafts. Cases were evaluated based on several fluid-dynamic quantities. The impact of imbalanced left-right pulmonary flow distribution was also investigated. Results showed that a 12-mm Y-graft was the most energy efficient. However, an 8-mm graft showed more favorable wall shear stress distribution, indicating lower risk of thrombosis and endothelial damage. The 8-mm Y-grafts also showed a more balanced pulmonary flow split, and lower residence time, also indicating lower thrombosis risk. The relative performance of the surgical options was largely unchanged whether or not the pulmonary vascular resistance remained imbalanced post-implantation.

The Effect of Blood Viscosity on Shear-Induced Hemolysis using a Magnetically Levitated Shearing Device

INTRODUCTION

Blood contacting medical devices, including rotary blood pumps, can cause shear-induced blood damage that may lead to adverse effects in patients. Due in part to an inadequate understanding of how cell-scale fluid mechanics impact red blood cell membrane deformation and damage, there is currently not a uniformly accepted engineering model for predicting blood damage caused by complex flow fields within ventricular assist devices (VADs).

METHODS

We empirically investigated hemolysis in a magnetically levitated axial Couette flow device typical of a rotary VAD. The device is able to accurately control the shear rate and exposure time experienced by blood and to minimize the effects of other uncharacterized stresses. Using this device, we explored the effects of both hematocrit and plasma viscosity on shear-induced hemolysis to characterize blood damage based on the viscosity-independent shear rate, rather than on shear stress.

RESULTS

Over a shear rate range of 20,000-80,000 1/s, the Index of Hemolysis (IH) was found to be dependent upon and well-predicted by shear rate alone. IH was independent of hematocrit, bulk viscosity, or the suspension media viscosity, and less correlated to shear stress (MSE=0.46-0.75) than to shear rate (MSE=0.06-0.09).

CONCLUSION

This study recommends that future investigations of shear-induced blood damage report findings with respect to the viscosity-neutral term of shear rate, in addition to the bulk whole blood viscosity measured at an appropriate shear rate relevant to the flow conditions of the device.

Experimental Hemodynamics within the Penn State Fontan Circulatory Assist Device

For children born with a single functional ventricle, the Fontan operation bypasses the right ventricle by forming a four-way total cavopulmonary connection adapting the existing ventricle for the systemic circulation. However, upon adulthood, many Fontan patients exhibit low cardiac output and elevated venous pressure, eventually requiring a heart transplantation. Despite efforts to develop a Fontan pump or use an existing ventricular assist device for failing Fontan support, there is still no device designed or tested for subpulmonary support. Penn State University is developing a hydrodynamically levitated Fontan circulatory assist device (FCAD) for bridge-to-transplant or destination therapy. The FCAD hemodynamics, at both steady and pulsatile conditions for three pump operating conditions, were quantified using particle image velocimetry to determine the velocity magnitudes and Reynolds normal and shear stresses. Data were acquired at three planes (0 mm and ±25% of the radius) for the inferior and superior vena cavae inlets and the pulmonary artery outlet. The inlets had a blunt velocity profile that became skewed towards the collecting volute as fluid approached the rotor. At the outlet, regardless of the flow condition, a high-velocity jet exited the volute and moved downstream in a helical pattern. Turbulent stresses observed at the volute exit were influenced by the rotor's rotation. Regardless of inlet conditions, the pump demonstrated advantageous behavior for clinical use with a predictable flow field and a low risk of platelet adhesion and hemolysis based on calculated wall shear rates and turbulent stresses, respectively.

In Vitro Testing and Comparison of Additively Manufactured Polymer Impellers for the CentriMag Blood Pump

Additive manufacturing (AM) is an effective tool for accelerating knowledge gain in development processes, as it enables the production of complex prototypes at low cost and with short lead times. In the development of mechanical circulatory support, the use of cheap polymer-based AM techniques for prototype manufacturing allows more design variations to be tested, promoting a better understanding of the respective system and its optimization parameters. Here, we compare four commonly used AM processes for polymers with respect to manufacturing accuracy, surface roughness, and shape fidelity in an aqueous environment. Impeller replicas of the CentriMag blood pump were manufactured with each process and integrated into original pump housings. The assemblies were tested for hydraulic properties and hemolysis in reference to the commercially available pump. Computational fluid dynamic simulations were carried out to support the transfer of the results to other applications. In hydraulic testing, the deviation in pressure head and motor current of all additively manufactured replicas from the reference pump remained below 2% over the entire operating range of the pump. In contrast, significant deviations of up to 620% were observed in hemolysis testing. Only the replicas produced by stereolithography showed a nonsignificant deviation from the reference pump, which we attribute to the low surface roughness of parts manufactured thereby. The results suggest that there is a flow-dependent threshold of roughness above which a surface strongly contributes to cell lysis by promoting a hydraulically rough boundary flow.

Target Flow-Pressure Operating Range for Designing a Failing Fontan Cavopulmonary Support Device

Fontan operation as the current standard of care for the palliation of single ventricle defects results in significant late complications. Using a mechanical circulatory device for the right circulation to serve the function of the missing subpulmonary ventricle could potentially stabilize the failing Fontan circulation. This study aims to elucidate the hydraulic operating regions that should be targeted for designing cavopulmonary blood pumps. By integrating numerical analysis and available clinical information, the interaction of the cavopulmonary support via the IVC and full assist configurations with a wide range of simulated adult failing scenarios was investigated; with IVC and full assist corresponding to the inferior venous return or the entire venous return, respectively, being routed through the device. We identified the desired hydraulic operating regions for a cavopulmonary assist device by clustering all head pressures and corresponding pump flows that result in hemodynamic improvement for each simulated failing Fontan physiology. Results show that IVC support can produce beneficial hemodynamics in only a small fraction of failing Fontan scenarios. Cavopulmonary assist device could increase cardiac index by 35% and decrease the inferior vena cava pressure by 45% depending on the patient's pre-support hemodynamic state and surgical configuration of the cavopulmonary assist device (IVC or full support). The desired flow-pressure operating regions we identified can serve as the performance criteria for designing cavopulmonary assist devices as well as evaluating off-label use of commercially available left-side blood pumps for failing Fontan cavopulmonary support.

Fluid-structure interaction analysis of a collapsible axial flow blood pump impeller and protective cage for Fontan patients

Limited donor organs and alternative therapies have led to a growing interest in the use of blood pumps as a treatment strategy for patients with single functional ventricle. The present study examines the use of collapsible and flexible impeller, cage, and diffuser designs of an axial blood pump for Fontan patients. Using one-way fluid-structure interaction (FSI) studies, the impact of blade deformation on blood damage and pump performance was investigated for flexible impellers. We evaluated biocompatible materials, including Nitinol, Bionate 80A polyurethane, and silicone for flow rates between 2.0-4.0 L/min and rotational speeds of 3000-9000 rpm. The level of deformation experienced by a cage and diffuser made of surgical stainless steel (control), Nitinol, and Bionate 80A polyurethane was also predicted using one-way FSI. The fluid pressure on the surface of the impeller, cage, and diffuser was determined using computational fluid dynamics (CFD), and then, the surface pressure was exported and used to investigate the impeller, cage, and diffuser deformation using finite element analysis. Finally, deformed impeller geometries were imported into the CFD software to determine the implication of deformation on pressure generation, blood damage index, and fluid streamlines. It was found that rotational speed, and not flow rate, is the largest determinant of impeller deformation, occurring at the blade trailing edges. The models predicted the maximum impeller deformation for Nitinol to be 40 nm, Bionate 80A polyurethane to be 106 μm, and silicone to be 2.8 mm, all occurring at 9000 rpm. The effects of silicone deformation on performance were significant, particularly at speeds above 5000 rpm where a decrease in pressure generation of more than 10% was observed. Despite this loss, the pressure generation at 5000 rpm exceeded the level required to alleviate Fontan complications. A blood damage estimation was performed and levels remained low. The effect of significant impeller deformation on blood damage was inconsistent and requires additional investigation. Cage and diffuser geometries made of steel and Nitinol deformed minimally but Bionate 80A experienced unacceptable levels of deformation, particularly in the free-flow case without a spinning impeller. These results support the continued evaluation of a flexible, pitch-adjusting, axial-flow, mechanical assist device as a clinical therapeutic option for patients with dysfunctional Fontan physiology.

Prediction of mechanical hemolysis in medical devices via a Lagrangian strain-based multiscale model

This work introduces a new Lagrangian strain-based model to predict the shear-induced hemolysis in biomedical devices. Current computational models for device-induced hemolysis usually utilize empirical fitting of the released free hemoglobin (Hb) in plasma from damaged red blood cells (RBCs). These empirical correlations contain parameters that depend on specific device and operating conditions, thus cannot be used to predict hemolysis in a general device. The proposed algorithm does not have any empirical parameters, thus can presumably be used for hemolysis prediction in various blood-wetting medical devices. In contrast to empirical correlations in which the Hb release is related to the shear stress and exposure time without considering the physical processes, the proposed model links flow-induced deformation of the RBC membrane to membrane permeabilization and Hb release. In this approach, once the steady-state numerical solution of blood flow in the device is obtained under a prescribed operating condition, sample path lines are traced from the inlet of the device to the outlet to calculate the history of the shear stress tensor. In solving the fluid flow, it is assumed that RBCs do not have any influence on the flow pattern. Along each path line, shear stress tensor will be input into a coarse-grained (CG) RBC model to calculate the RBC deformation. Then the correlations obtained from molecular dynamics (MD) simulations are applied to relate the local areal RBC deformation to the perforated area on the RBC membrane. Finally, Hb released out of transient pores is calculated over each path line via a diffusion equation considering the effects of the steric hindrance and increased hydrodynamic drag due to the size of the Hb molecule. The total index of hemolysis (IH) is calculated by integration of released Hb over all the path lines in the computational domain. Hemolysis generated in the Food and Drug Administration (FDA) nozzle and two blood pumps, that is, a CentriMag blood pump (a centrifugal pump) and HeartMate II (an axial pump), for different flow regimes including the laminar and turbulent flows are calculated via the proposed algorithm. In all the simulations, the numerical predicted IH is close to the range of experimental data. The results promisingly indicate that this multiscale approach can be used as a tool for predicting hemolysis and optimizing the hematologic design of other types of blood-wetting devices.

3D Printing of Functional Assemblies with Integrated Polymer-Bonded Magnets Demonstrated with a Prototype of a Rotary Blood Pump

Conventional magnet manufacturing is a significant bottleneck in the development processes of products that use magnets, because every design adaption requires production steps with long lead times. Additive manufacturing of magnetic components delivers the opportunity to shift to agile and test-driven development in early prototyping stages, as well as new possibilities for complex designs. In an effort to simplify integration of magnetic components, the current work presents a method to directly print polymer-bonded hard magnets of arbitrary shape into thermoplastic parts by fused deposition modeling. This method was applied to an early prototype design of a rotary blood pump with magnetic bearing and magnetic drive coupling. Thermoplastics were compounded with 56 vol.% isotropic NdFeB powder to manufacture printable filament. With a powder loading of 56 vol.%, remanences of 350 mT and adequate mechanical flexibility for robust processability were achieved. This compound allowed us to print a prototype of a turbodynamic pump with integrated magnets in the impeller and housing in one piece on a low-cost, end-user 3D printer. Then, the magnetic components in the printed pump were fully magnetized in a pulsed Bitter coil. The pump impeller is driven by magnetic coupling to non-printed permanent magnets rotated by a brushless DC motor, resulting in a flow rate of 3 L/min at 1000 rpm. For the first time, an application of combined multi-material and magnet printing by fused deposition modeling was shown. The presented process significantly simplifies the prototyping of products that use magnets, such as rotary blood pumps, and opens the door for more complex and innovative designs. It will also help postpone the shift to conventional manufacturing methods to later phases of the development process.

AvalonElite Double Lumen Cannula for Total Cavopulmonary Assist in Failing Fontan Sheep Model with Valved Extracardiac Conduit

The AvalonElite double lumen cannula (DLC) provides total cavopulmonary assist (CPA) in failing Fontan sheep, but recirculation limits reliability. To improve CPA performance, a two-valve extracardiac conduit (ECC) was used to bracket infusion blood toward pulmonary artery (PA). A total cavopulmonary connection with failing Fontan circulation adult sheep model was created with valved ECC (n = 6). The valved ECC was connected to superior/inferior venae cavae (SVC/IVC) and right PA. The AvalonElite DLC was inserted from right jugular vein with infusion opening between the ECC valves. The DLC drainage lumen withdrew blood from SVC/IVC, and the infusion lumen returned blood to ECC. A failing Fontan sheep model with valved ECC was successfully created. Central venous pressure increased from 9 ± 1 to 17 ± 1 mm Hg, systolic arterial pressure decreased from 103 ± 9 to 51 ± 13 mm Hg, and cardiac output decreased from 3.6 ± 0.3 to 1.4 ± 0.2 L/min. Serum lactate significantly increased, indicating poor tissue perfusion. At 4 L/min pumping flow, the AvalonElite DLC returned hemodynamics/lactate to baseline levels throughout 6 hour CPA. Necropsy revealed intact/well-functioning ECC valves and well-positioned DLC with no visible thrombosis. The AvalonElite DLC provides reliable CPA performance in failing Fontan sheep with valved ECC.

Development of a novel shrouded impeller pediatric blood pump

The aim of this work was to analyze a shrouded impeller pediatric ventricular assist device (SIP-VAD). This device has distinctive design characteristics and parameter optimizations for minimization of recirculation flow and reduction in high-stress regions that cause blood damage. Computational Fluid Dynamics (CFD) simulations were performed to analyze the optimized design. The bench-top prototype of SIP-VAD was manufactured with biocompatible stainless steel. A study on the hydrodynamic and hemodynamic performance of the SIP-VAD was conducted with predictions from CFD and actual experimentation values, and these results were compared. The CFD analysis yielded a pressure range of 29-90 mmHg corresponding to flow rates of 0.5-3 L/min over 9000-11000 rpm. The predicted value of the normalized index of hemolysis (NIH) was 0.0048 g/100 L. The experimental results with the bench-top prototype showed a pressure rise of 30-105 mmHg for the flow speed of 8000-12000 rpm and flow rate of 0.5-3.5 L/min. The maximum difference between CFD and experimental results was 4 mmHg pressure. In addition, the blood test showed the average NIH level of 0.00674 g/100 L. The results show the feasibility of shrouded impeller design of axial-flow pump for manufacturing the prototype for further animal trials.

Statistical Shape Modeling for Cavopulmonary Assist Device Development: Variability of Vascular Graft Geometry and Implications for Hemodynamics

Patients born with a single functional ventricle typically undergo three-staged surgical palliation in the first years of life, with the last stage realizing a cross-like total cavopulmonary connection (TCPC) of superior and inferior vena cavas (SVC and IVC) with both left and right pulmonary arteries, allowing all deoxygenated blood to flow passively back to the lungs (Fontan circulation). Even though within the past decades more patients survive into adulthood, the connection comes at the prize of deficiencies such as chronic systemic venous hypertension and low cardiac output, which ultimately may lead to Fontan failure. Many studies have suggested that the TCPC's inherent insufficiencies might be addressed by adding a cavopulmonary assist device (CPAD) to provide the necessary pressure boost. While many device concepts are being explored, few take into account the complex cardiac anatomy typically associated with TCPCs. In this study, we focus on the extra cardiac conduit vascular graft connecting IVC and pulmonary arteries as one possible landing zone for a CPAD and describe its geometric variability in a cohort of 18 patients that had their TCPC realized with a 20mm vascular graft. We report traditional morphometric parameters and apply statistical shape modeling to determine the main contributors of graft shape variability. Such information may prove useful when designing CPADs that are adapted to the challenging anatomical boundaries in Fontan patients. We further compute the anatomical mean 3D graft shape (template graft) as a representative of key shape features of our cohort and prove this template graft to be a significantly better approximation of population and individual patient's hemodynamics than a commonly used simplified tube geometry. We therefore conclude that statistical shape modeling results can provide better models of geometric and hemodynamic boundary conditions associated with complex cardiac anatomy, which in turn may impact on improved cardiac device development.

A Cellular Model of Shear-Induced Hemolysis

A novel model is presented to study red blood cell (RBC) hemolysis at cellular level. Under high shear rates, pores form on RBC membranes through which hemoglobin (Hb) leaks out and increases free Hb content of plasma leading to hemolysis. By coupling lattice Boltzmann and spring connected network models through immersed boundary method, we estimate hemolysis of a single RBC under various shear rates. First, we use adaptive meshing to find local strain distribution and critical sites on RBC membranes, and then we apply underlying molecular dynamics simulations to evaluate damage. Our approach comprises three sub-models: defining criteria of pore formation, calculating pore size, and measuring Hb diffusive flux out of pores. Our damage model uses information of different scales to predict cellular level hemolysis. Results are compared with experimental studies and other models in literature. The developed cellular damage model can be used as a predictive tool for hydrodynamic and hematologic design optimization of blood-wetting medical devices.

Does Pneumatic Tube System Transport Contribute to Hemolysis in ED Blood Samples?

INTRODUCTION

Our goal was to determine if the hemolysis among blood samples obtained in an emergency department and then sent to the laboratory in a pneumatic tube system was different from those in samples that were hand-carried.

METHODS

The hemolysis index is measured on all samples submitted for potassium analysis. We queried our hospital laboratory database system (SunQuest(®)) for potassium results for specimens obtained between January 2014 and July 2014. From facility maintenance records, we identified periods of system downtime, during which specimens were hand-carried to the laboratory.

RESULTS

During the study period, 15,851 blood specimens were transported via our pneumatic tube system and 92 samples were hand delivered. The proportions of hemolyzed specimens in the two groups were not significantly different (13.6% vs. 13.1% [p=0.90]). Results were consistent when the criterion was limited to gross (3.3% vs 3.3% [p=0.99]) or mild (10.3% vs 9.8% [p=0.88]) hemolysis. The hemolysis rate showed minimal variation during the study period (12.6%-14.6%).

CONCLUSION

We found no statistical difference in the percentages of hemolyzed specimens transported by a pneumatic tube system or hand delivered to the laboratory. Certain features of pneumatic tube systems might contribute to hemolysis (e.g., speed, distance, packing material). Since each system is unique in design, we encourage medical facilities to consider whether their method of transport might contribute to hemolysis in samples obtained in the emergency department.

A paired membrane umbrella double-lumen cannula ensures consistent cavopulmonary assistance in a Fontan sheep model

OBJECTIVES

The Avalon Elite (Macquet, Rastatt, Germany) double-lumen cannula can provide effective cavopulmonary assistance in a Fontan (total cavopulmonary connection) sheep model, but it requires strict alignment. The objective was to fabricate and test a newly designed paired umbrella double-lumen cannula without alignment requirement.

METHODS

The paired membrane umbrellas were designed on the double-lumen cannula to bracket infusion blood flow toward the pulmonary artery. Two umbrellas were attached, one 4 cm above and one 4 cm below the infusion opening. Umbrellas were temporarily wrapped and glued to the double-lumen cannula body to facilitate insertion. A total cavopulmonary connection mock loop was used to test cavopulmonary assistance performance and reliability with double-lumen cannula rotation and displacement. The paired umbrella double-lumen cannula also was tested in a total cavopulmonary connection adult sheep model (n = 6).

RESULTS

The bench test showed up to 4.5 L/min pumping flow and approximately 90% pumping flow efficiency at 360° rotation and 8-cm displacement of double-lumen cannula. The total cavopulmonary connection model with compromised hemodynamics was successfully created in all 6 sheep. The cavopulmonary assistance double-lumen cannula with paired umbrellas was smoothly inserted into the superior vena cava and extracardiac conduit in all sheep. At 3.5 to 4.0 L/min pump flow, the systolic arterial blood pressure and central venous pressure returned to normal baseline and remained stable throughout the 90-minute experiment, demonstrating effective cavopulmonary assistance support. Double-lumen cannula rotation and displacement did not affect performance. Autopsy revealed well-opened and positioned paired umbrellas, and double-lumen cannulas were easily removed from the right jugular vein.

CONCLUSIONS

Our double-lumen cannula with paired umbrellas is easy to insert and remove. The paired umbrellas eliminated the strict alignment requirement and ensured consistent cavopulmonary assistance performance.

Hemolysis associated with pneumatic tube system transport for blood samples

Objective: The frequency of hemolysis of blood samples may be increased by transport in a pneumatic tube system. The purpose of this study was to evaluate the effect of pneumatic tube system transport on hemolysis of blood samples.

Methods: Blood samples were transported from the emergency department to the hospital laboratory manually by hospital staff (49 patients) or with a pneumatic tube system (53 patients). The hemolysis index and serum chemistry studies were performed on the blood samples and compared between the different methods of transport.

Results: The blood samples that were transported by the pneumatic tube system had a greater frequency of hemolysis and greater mean serum potassium and median creatinine, aspartate aminotransferase, and lactate dehydrogenase levels than samples transported manually.

Conclusion: Blood samples transported from the emergency department to the hospital laboratory by a pneumatic tube system may have a greater frequency of hemolysis than samples transported manually. This may necessitate repeat phlebotomy and cause a delay in completing the laboratory analysis.

Effect of mechanical assistance of the systemic ventricle in single ventricle circulation with cavopulmonary connection

BACKGROUND

Previous attempts to support single ventricle circulation mechanically have suggested that a custom-built assist device is needed to push, rather than pull, through the pulmonary circulation. We hypothesized that using a conventional ventricular assist device, with or without conversion of a total cavopulmonary connection to a bidirectional Glenn cavopulmonary connection, would allow assistance by pulling blood through the circuit and improve the cardiac index (CI).

METHODS

Cavopulmonary connections were established in each of 5 Yorkshire pigs (25 kg) using ePTFE conduits in a Y configuration with appropriate clamping of the limbs of the Y to achieve a total cavopulmonary Fontan connection (TCPC), superior vena cava cavopulmonary connection (SVC Glenn), and inferior vena cava cavopulmonary connection (IVC Glenn). A common atrium had been established previously by balloon septostomy. Mechanical circulatory assistance of the single systemic ventricle was achieved using a centrifugal pump with common atrial inflow and proximal ascending aortic outflow. The CI was calculated using an ultrasonic flow meter placed on the distal ascending aorta and compared between the assisted and nonassisted circulation for 3 conditions: TCPC, SVC Glenn, and IVC Glenn. The mean pulmonary artery pressure, common atrial pressure, arterial oxygen saturation, partial pressure of arterial oxygen, and oxygen delivery were calculated.

RESULTS

The unassisted SVC Glenn CI tended to be greater than the TCPC or IVC Glenn CI. Significant augmentation of total CI was achieved with mechanical assistance for SVC Glenn (109% ± 24%, P = .04) and TCPC (130% ± 109%, P = .01). The assisted CI achieved at least a mean baseline biventricular CI for all 3 support modes. Oxygen delivery was greatest for assisted SVC Glenn (1786 ± 1307 mL/L/min) and lowest for TCPC (1146 ± 386 mL/L/min), with a trend toward lower common atrial and pulmonary artery pressures for SVC Glenn.

CONCLUSIONS

SVC bidirectional Glenn circulation might allow optimal augmentation of the CI and oxygen delivery in a failing single ventricle using a conventional pediatric ventricular assist device. The results from our model also suggest that the Fontan circulation itself can be supported with systemic ventricular assistance of the single ventricle.

A viable therapeutic option: mechanical circulatory support of the failing Fontan physiology

A blood pump specifically designed to augment flow from the great veins through the lungs would ameliorate the poor physiology of the failing univentricular circulation and result in a paradigm shift in the treatment strategy for Fontan patients. This study is the first to examine mechanical cavopulmonary assistance with a blood pump in the inferior vena cava (IVC) and hepatic blood flow. Five numerical models of mechanical cavopulmonary assistance were investigated using a three-dimensional, reconstructed, patient-specific Fontan circulation from magnetic resonance imaging data. Pressure flow characteristics of the axial blood pump, energy augmentation calculations for the cavopulmonary circulation with and without pump support, and hemolysis estimations were determined. In all of the pump-supported scenarios, a pressure increase of 7-9.5 mm Hg was achieved. The fluid power of the cavopulmonary circulation was also positive over the range of flow rates. No retrograde flow from the IVC into the hepatic circulation was evident during support cases. Vessel suction risk, however, was found for greater operating rotational speeds. Fluid shear stresses and hemolysis predictions remained at acceptable levels with normalized index of hemolysis estimations at 0.0001 g/100 L. The findings of this study support the continued design and development of this blood pump technology for Fontan patients with progressive cardiovascular insufficiency. Validation of these flow and performance predictions will be completed in the next round of experimental testing with blood bag evaluation.

Dual-pump support in the inferior and superior vena cavae of a patient-specific fontan physiology

The implementation of simultaneous mechanical cavopulmonary assistance having blood pumps located in both of the vena cavae is investigated as an approach to treating patients with an ailing Fontan physiology. Identical intravascular blood pumps are employed to model the hemodynamic support of a patient-specific Fontan. Pressure flow characteristics, energy gain calculations, and blood damage analyses are assessed for each model. The performance of the dual-support scenario is compared to conditions of mechanical support in the inferior vena cava only and to a nonsupported cavopulmonary circuit. The blood pump in the superior vena cava generates pressures ranging from 1 to 22 mm Hg for flow rates of 1-4 L/min at operating speeds of 1250-2500 rpm. The blood pump in the inferior vena cava produces pressures at levels approximately 20% lower. The blood pumps positively augment the hydraulic energy in the total cavopulmonary connection circuit as a function of flow rate and rotational speed. Scalar stress levels and fluid residence times are at acceptable levels. Damage indices for the dual-support case, however, are elevated slightly above 3.5%. These results suggest that concurrent, mechanical assistance of the inferior vena cava and superior vena cava in Fontan patients has the potential to be beneficial, but additional studies are needed to further explore this approach.

Controlled pitch-adjustment of impeller blades for an intravascular blood pump

Thousands of mechanical blood pumps are currently providing circulatory support, and the incidence of their use continues to increase each year. As the use of blood pumps becomes more pervasive in the treatment of those patients with congestive heart failure, critical advances in design features to address known limitations and the integration of novel technologies become more imperative. To advance the current state-of-the-art in blood pump design, this study investigates the inclusion of pitch-adjusting blade features in intravascular blood pumps as a means to increase energy transfer; an approach not explored to date. A flexible impeller prototype was constructed with a configuration to allow for a variable range of twisted blade geometries of 60-250°. Hydraulic experiments using a blood analog fluid were conducted to characterize the pressure-flow performance for each of these twisted positions. The flexible, twisted impeller was able to produce 1-25 mmHg for 0.5-4 L/min at rotational speeds of 5,000-8,000 RPM. For a given twisted position, the pressure rise was found to decrease as a function of increasing flow rate, as expected. Generally, a steady increase in the pressure rise was observed as a function of higher twisted degrees for a constant rotational speed. Higher rotational speeds for a specific twisted impeller configuration resulted in a more substantial pressure generation. The findings of this study support the continued exploration of this unique design approach in the development of intravascular blood pumps.

Effect of pneumatic tube delivery system rate and distance on hemolysis of blood specimens

BACKGROUND

We evaluated the effects of pneumatic tube system (PTS) transport rates and distances on routine hematology and coagulation analysis. PTS effects on centrifuged blood samples were also examined.

METHOD

The study was completed at Dicle University Hospital, which has the longest pneumatic tube system in Turkey. Blood samples were collected at three different locations within the hospital and an emergency department, and delivered to the central laboratory by the PTS or a human carrier. Samples were transported at different rates and over varying distances. Each specimen's potassium (K) and lactic dehydrogenase (LDH) levels, in both the serum and plasma, were tracked to monitor hemolysis. Measurements of LDH and K were obtained using heparin or citrate.

RESULT

A positive correlation was observed between distance and hemolysis in serum samples transported at 4.2 m/sec, and at 3.1 m/sec for more than 2200 m (r = 0.774 and r = 0.766, respectively). Distance and hemolysis were also correlated in non-centrifuged samples (r = 0.871). The alterations in plasma LDH and K levels at different rates and PTS lengths were not statistically significant.

CONCLUSION

The rate of hemolysis in PTS transported samples, dependent on PTS length and rate, may seriously affect routine tests of non-centrifuged samples.

Heart transplantation in adults with end-stage congenital heart disease

Residual abnormalities in cardiac structure and function predispose adults with congenital heart disease to late-onset heart failure and its complications. Evaluation of this population requires collaboration between adult congenital and heart failure specialists. In addition to assessing heart transplant eligibility, clinicians must balance the risks of premature listing against progressive heart failure and increased waiting list mortality. Following heart transplantation, adults with congenital heart disease have higher mortality due to an increased risk of bleeding, infection and donor right heart failure secondary to pulmonary hypertension. Concerns relating to increased early mortality should be balanced against superior long-term survival in adult congenital heart disease patients surviving beyond the first year after heart transplantation.