A blood pump consisting of an inflow cannula, a stator fixed to the pump housing, a flow straightener, an impeller, and a diffuser. The pump may include a flow straightener assembly consisting of the flow straightener body and front shaft. The pump may include an impeller assembly with a bearing on the front hub section. The pump may have a body contour which is shaped such that the rear section of the flow straightener body blends into the inserted shaft and there is no axial gap between the end of the flow straightener other than the ends of the blades and the front hub of the impeller.

Rotary blood pump

This study explores a quantitative evaluation of blood damage that occurs in a continuous flow left ventricular assist device (LVAD) due to fluid stress. Computational fluid dynamics (CFD) analysis is used to track the shear stress history of 388 particle streaklines. The accumulation of shear and exposure time is integrated along the streaklines to evaluate the levels of blood trauma. This analysis, which includes viscous and turbulent stresses, provides a statistical estimate of possible damage to cells flowing through the pump. Since experimental data for hemolysis levels in our LVAD are not available, in vitro normalized index of hemolysis values for clinically available ventricular assist devices were compared to our damage indices. This approach allowed for an order of magnitude comparison between our estimations and experimentally measured hemolysis levels, which resulted in a reasonable correlation. This work ultimately demonstrates that CFD is a convenient and effective approach to analyze the Lagrangian behavior of blood in a heart assist device

Quantitative Evaluation of Blood Damage in a Centrifugal VAD by Computational Fluid Dynamics

In this work, we propose a simple method to simultaneously match the refractive index and kinematic viscosity of a circulating blood analog in hydraulic models for optical flow measurement techniques (PIV, PMFV, LDA, and LIF). The method is based on the determination of the volumetric proportions and temperature at which two transparent miscible liquids should be mixed to reproduce the targeted fluid characteristics. The temperature dependence models are a linear relation for the refractive index and an Arrhenius relation for the dynamic viscosity of each liquid. Then the dynamic viscosity of the mixture is represented with a Grunberg-Nissan model of type 1. Experimental tests for acrylic and blood viscosity were found to be in very good agreement with the targeted values (measured refractive index of 1.486 and kinematic viscosity of 3.454 milli-m2/s with targeted values of 1.47 and 3.300 milli-m2/s).

A method for matching the refractive index and kinematic viscosity of a blood analog for flow visualization in hydraulic cardiovascular models.

Intravascular application of microaxial blood pumps as heart assist devices requires a maximum in size reduction of the pump components. These limitations affect the design process in many ways and restrict the number of applicable experimental procedures, but a detailed knowledge of the hemodynamics of the pump is of great interest for efficiency enhancement and reduction of blood trauma and thrombus formation. Computational fluid dynamics (CFD) offers a convenient approach to this goal. In this study, the inlet, vane, and outlet regions of a microaxial blood pump used as an intraaortic left ventricular assist device are analyzed by CFD and 3-dimensional (3-D) particle tracking velocimetry (PTV). For this purpose, a mock loop is set up that facilitates 3-D flow visualization. Flow in the main part of this testing device is modeled and computed by means of CFD. Pump head/flow (HQ) characteristics, axial pressure distribution, and particle images are then compared with numerical flow data. Results show that the pump performance characteristics, as well as inlet and outlet swirl predicted by the CFD model, are quite accurate compared with measured data. Proper boundary condition definitions and spatial discretization topology requirements for satisfactory results are discussed.

Computational fluid dynamics and experimental validation of a microaxial blood pump.

A collaborative effort between Baylor College of Medicine and NASA/Johnson Space Center is underway to develop an axial flow ventricular assist device (VAD). We evaluated inducer/impeller component designs in a series of in vitro hemolysis tests. As a result of computational fluid dynamic analysis, a flow inducer was added to the front of the pump impeller. According to the surface pressure distribution, the flow inducer blades were connected to the impeller long blades. This modification eliminated high negative pressure areas at the leading edge of the impeller. Comparative studies were performed between inducer blade sections that flowed smoothly into the impeller blades (continuous blades) and those that formed discrete separate pumping sections (discontinuous blades). The inducer/impeller with continuous blades showed significantly (p < 0.003) lower hemolysis with a normalized index of hemolysis (NIH) of 0.018 +/- 0.007 g/100 L (n = 3), compared with the discontinuous model, which demonstrated an NIH of 0.050 +/- 0.007 g/100 L (n = 3). The continuous blade model was evaluated in vivo for 2 days with no problems. One of the pumps evaluated ran for 5 days in vivo although thrombus formation was recognized on the flow straightener and the inducer/impeller. As a result of this study, the pump material was changed from polyether polyurethane to polycarbonate. The fabrication method was also changed to a computer numerically controlled (CNC) milling process with a final vapor polish. These changes resulted in an NIH of 0.0029 +/- 0.0009 g/100 L (n = 4), which is a significant (p < .0001) value 6 times less than that of the previous model.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of an Axial Flow Ventricular Assist Device: In Vitro and In Vivo Evaluation

The Baylor/NASA Axial Blood Flow Pump has been developed for use as an implantable left ventricular assist device (LVAD). The pump is intended as an assist device for either pulmonary or systemic circulatory support for more than 3-months' duration. To date the pump provides acceptable results in terms of thrombus formation and hemolysis (IH of 0.018 g/100 L). A fluid dynamics analysis using flow visualization was performed to investigate the flow fields and to determine areas within the pump that could be improved. These studies focused upon the inflow area in front of the pump. A prototype axial flow pump assembly was constructed to facilitate the flow visualization studies. Particle image tracking velocimetry techniques were used to measure Amberlite particles suspended in a blood analog fluid composed of 63% water and 37% glycerin. This method used a pulsed (612 Hz) laser light to determine flow velocity profiles, shear stress, Reynolds numbers, and stagnant areas within the axial pump. These studies showed that the flow straightener (a vaned assembly in the pump inflow) reduced Reynolds numbers from 4,640 to 2,540 (at 8.5 L/min) and that the flow straightener exacerbates a discontinuity found between it and the impeller. Within the inflow area, a maximum of 80 N/m2 shear stress was measured, which is well below published blood damage thresholds. Design variations were investigated resulting in a smoother flow transition between flow straightener and impeller. These variations must be investigated further to establish a correlation with hemolysis and thrombus formation.

A Fluid Dynamic Analysis Using Flow Visualization of the Baylor/NASA Implantable Axial Flow Blood Pump for Design Improvement

To analyze the flow patterns of the left blood chamber of the Baylor total artificial heart (TAH) and to evaluate influences of the inflow valve angle to the flow patterns, flow visualization studies were performed. The inflow valve angle of the left housing was changed by 20 degrees orthogonal to the inflow tube, and comparison studies of the modified and unmodified models were made. For evaluating sectional flow patterns, a laser light was used, the clear transparent housing was scanned segmentally, and flow patterns were recorded on high contrast film for measuring flow velocities. A signal was used that synchronized the timing of the camera shutter to the pusher-plate movement signal. With the modified 20 degree inflow valve direction, there were better closing characteristics of the inflow valve leaflets. At the same time, we could successfully reduce the vortex formation at the inflow port, which may cause thrombus formation. We also have improved the washout during the diastolic phase in not only the bottom area, but in the entire pumping chamber. This flow visualization setup is simple and inexpensive. It is useful not only for validation of global flow patterns, but also for validation of local flow velocities of various blood pumps.

Dirk Meier

Papers

A Fluid Dynamic Analysis Using Flow Visualization of the Baylor/NASA Implantable Axial Flow Blood Pump for Design Improvement

The Baylor total artificial heart. Flow visualization studies.