Uniquely shaped cardiovascular stents enhance the pressure generation of intravascular blood pumps

In Silico Evaluation of a Self-powered Venous Ejector Pump for Fontan Patients

PURPOSE

The Fontan circulation carries a dismal prognosis in the long term due to its peculiar physiology and lack of a subpulmonic ventricle. Although it is multifactorial, elevated IVC pressure is accepted to be the primary cause of Fontan's high mortality and morbidity. This study presents a self-powered venous ejector pump (VEP) that can be used to lower the high IVC venous pressure in single-ventricle patients.

METHODS

A self-powered venous assist device that exploits the high-energy aortic flow to lower IVC pressure is designed. The proposed design is clinically feasible, simple in structure, and is powered intracorporeally. The device's performance in reducing IVC pressure is assessed by conducting comprehensive computational fluid dynamics simulations in idealized total cavopulmonary connections with different offsets. The device was finally applied to complex 3D reconstructed patient-specific TCPC models to validate its performance.

RESULTS

The assist device provided a significant IVC pressure drop of more than 3.2 mm Hg in both idealized and patient-specific geometries, while maintaining a high systemic oxygen saturation of more than 90%. The simulations revealed no significant caval pressure rise (< 0.1 mm Hg) and sufficient systemic oxygen saturation (> 84%) in the event of device failure, demonstrating its fail-safe feature.

CONCLUSIONS

A self-powered venous assist with promising in silico performance in improving Fontan hemodynamics is proposed. Due to its passive nature, the device has the potential to provide palliation for the growing population of patients with failing Fontan.

Analysis of flow field and hemolysis index in axial flow blood pump by computational fluid dynamics-discrete element method

To fully study the relationship between the internal flow field and hemolysis index in an axial flow blood pump, a computational fluid dynamics-discrete element method coupled calculation method was used. Through numerical analysis under conditions of 6000, 8000, and 10,000 r/min, it was found that there was flow separation of blood cell particles in the tip of the impeller and the guide vane behind the impeller. The flow field has a larger pressure gradient distribution, which reduces the lift ratio of the blood pump and easily causes blood cell damage. The study shows that the hemolysis index obtained by the computational fluid dynamics-discrete element method is 4.75% higher than that from the traditional computational fluid dynamics method, which indicates the impact of microcollision between erythrocyte particles and walls on hemolysis index and also further verifies the validity of the computational fluid dynamics-discrete element coupling method. Through the hydraulic and particle image velocimetry experiments of the blood pump, the coincidence between numerical calculation and experiment is analyzed from macro and micro aspects, which shows that the numerical calculation method is feasible.

Hemodynamic Effects of A Simplified Venturi Conduit for Fontan Circulation: A Pilot, In Silico Analysis

Objectives: To study the effects of a self-powered Fontan circulation in both idealized Fontan models and patient-specific models. Methods: In silico, a conduit with a nozzle was introduced from ascending aorta into the anastomosis of superior vena cava and pulmonary artery. Computational fluid dynamics (CFD) simulation was applied to calculate the fluid fields of models. Three 3-dimentional idealized models with different offsets were reconstructed by computer-aided design to evaluate the effects of the self-powered conduit. Furthermore, to validate the effects in patient-specific models, the conduit was introduced to three reconstructed models with different offsets. Results: The pressures at superior venae cavae and inferior venae cavae were decreased in both idealized models (0.4 mmHg) and patient-specific models (0.7 mmHg). In idealized models, the flows to left lungs were decreased (70%) by the jets from the conduits. However, in patient-specific models, the reductions of blood to the left lungs were relatively limited (30%) comparing to idealized models. Conclusions: CFD simulation was applied to analyze the effectiveness of the Fontan self-powered conduit. This self-powered conduit may help to decrease the venae cavae pressures and increase the flow to pulmonary arteries.

Computational fluid dynamic simulations of a cavopulmonary assist device for failing Fontan circulation

OBJECTIVES

Adult patients who have undergone the Fontan procedure are highly vulnerable to gradual, progressive circulatory failure, and options to reverse this situation are few. A cavopulmonary assist device could decongest the venous and lymphatic systems, overcome elevated pulmonary vascular resistance, increase cardiac output, and support some of these patients to heart transplant. This study characterizes the performance and challenges of a novel multilumen cannula coupled to an external blood pump proposed as a potential Fontan cavopulmonary assist strategy.

METHODS

Computational fluid dynamic simulations were conducted for 3 extracardiac Fontan geometries consisting of 1 idealized model and 2 patient-specific models. A range of physiologic flow rates and pump assist levels were simulated to calculate the pressure gain provided by the multilumen cannula. Hemolysis index was estimated for the idealized model with Lagrangian particle tracking and 2 variations of the power-law. Wall shear stresses were also examined.

RESULTS

Pressure gains up to 4 and 9 mm Hg were achieved for the idealized and patient-specific models, respectively. Pressure gains increased with both higher cardiac output and larger pump intake through the external pump. Flow-weighted hemolysis show hemoglobin damage levels to be several times lower than the 2% threshold at the highest pump intake flow cases. Wall shear stress predictions depict elevated areas in the pulmonary vessels and regions of the cannula device.

CONCLUSIONS

The cannula tested in this study shows promise as a percutaneous option to bridge support in some patients with a failing extracardiac Fontan. Limitations identified will be addressed in future design iterations and in ongoing experimental tests.

Experimental measurements of energy augmentation for mechanical circulatory assistance in a patient-specific Fontan model

A mechanical blood pump specifically designed to increase pressure in the great veins would improve hemodynamic stability in adolescent and adult Fontan patients having dysfunctional cavopulmonary circulation. This study investigates the impact of axial-flow blood pumps on pressure, flow rate, and energy augmentation in the total cavopulmonary circulation (TCPC) using a patient-specific Fontan model. The experiments were conducted for three mechanical support configurations, which included an axial-flow impeller alone in the inferior vena cava (IVC) and an impeller with one of two different protective stent designs. All of the pump configurations led to an increase in pressure generation and flow in the Fontan circuit. The increase in IVC flow was found to augment pulmonary arterial flow, having only a small impact on the pressure and flow in the superior vena cava (SVC). Retrograde flow was neither observed nor measured from the TCPC junction into the SVC. All of the pump configurations enhanced the rate of power gain of the cavopulmonary circulation by adding energy and rotational force to the fluid flow. We measured an enhancement of forward flow into the TCPC junction, reduction in IVC pressure, and only minimally increased pulmonary arterial pressure under conditions of pump support.