Azuma Takahashi

Quantitative assessment of paravalvular leakage after transcatheter aortic valve replacement using a patient-specific pulsatile flow model

BACKGROUND Quantitative assessment of post-transcatheter aortic valve replacement (TAVR) aortic regurgitation (AR) remains challenging. We developed patient-specific anatomical models with pulsatile flow circuit and investigated factors associated with AR after TAVR. METHODS Based on pre-procedural computed tomography (CT) data of the six patients who underwent transfemoral TAVR using a 23-mm SAPIEN XT, anatomically and mechanically equivalent aortic valve models were developed. Forward flow and heart rate of each patient in two days after TAVR were duplicated under mean aortic pressure of 80mmHg. Paravalvular leakage (PVL) volume in basal and additional conditions was measured for each model using an electromagnetic flow sensor. Incompletely apposed tract between the transcatheter and aortic valves was examined using a micro-CT. RESULTS PVL volume in each patient-specific model was consistent with each patients PVL grade, and was affected by hemodynamic conditions. PVL and total regurgitation volume increased with the mean aortic pressure, whereas closing volume did not change. In contrast, closing volume increased proportionately with heart rate, but PVL did not change. The minimal cross-sectional gap had a positive correlation with the PVL volumes (r=0.89, P=0.02). The gap areas typically occurred in the vicinity of the bulky calcified nodules under the native commissure. CONCLUSIONS PVL volume, which could be affected by hemodynamic conditions, was significantly associated with the minimal cross-sectional gap area between the aortic annulus and the stent frame. These data may improve our understanding of the mechanism of the occurrence of post-TAVR PVL.

Controlling Sheer Stress in a Suspension Culture using Couette Flow forEfficient Proliferation of HEK 293 Cells

The suspension culture system is an increasingly popular method of culturing cells not only because of its up scaling ability, but also the non-enzymatic procurement of cells that is crucial for biomedical research, especially in the fields of pharmacology and regenerative medicine. Hypothetically, by controlling and reducing the shear stress applied to cells in a culture system, the higher viability and proliferation rates. In this study, we analyzed HEK 293 cells cultured with a commercially available spinner flask and our newly developed spinner flask which utilizes the theory of Couette flow for controlling shear stress. Fluid analysis and metabolic analysis of the cultured cells were measured at three different rotational speeds, 40, 50 and 60 rpm. It was apparent that 50 rpm was by far the best speed to proliferate the cells. A further viability test was also done in order to validate our hypothesis. Furthermore, by using the metabolic analysis results, it was observed that in the controlled stress system, the consumption of glucose doubled and lactate production was significantly higher compared to cells that were maintained in the conventional suspension method. Thus, Couette flow based suspension culture system will be a major contributor to the future biomedical and pharmacological field.

A three-dimensional strain measurement method in elastic transparent materials using tomographic particle image velocimetry

Background The mechanical interaction between blood vessels and medical devices can induce strains in these vessels. Measuring and understanding these strains is necessary to identify the causes of vascular complications. This study develops a method to measure the three-dimensional (3D) distribution of strain using tomographic particle image velocimetry (Tomo-PIV) and compares the measurement accuracy with the gauge strain in tensile tests. Methods and findings The test system for measuring 3D strain distribution consists of two cameras, a laser, a universal testing machine, an acrylic chamber with a glycerol water solution for adjusting the refractive index with the silicone, and dumbbell-shaped specimens mixed with fluorescent tracer particles. 3D images of the particles were reconstructed from 2D images using a multiplicative algebraic reconstruction technique (MART) and motion tracking enhancement. Distributions of the 3D displacements were calculated using a digital volume correlation. To evaluate the accuracy of the measurement method in terms of particle density and interrogation voxel size, the gauge strain and one of the two cameras for Tomo-PIV were used as a video-extensometer in the tensile test. The results show that the optimal particle density and interrogation voxel size are 0.014 particles per pixel and 40 × 40 × 40 voxels with a 75% overlap. The maximum measurement error was maintained at less than 2.5% in the 4-mm-wide region of the specimen. Conclusions We successfully developed a method to experimentally measure 3D strain distribution in an elastic silicone material using Tomo-PIV and fluorescent particles. To the best of our knowledge, this is the first report that applies Tomo-PIV to investigate 3D strain measurements in elastic materials with large deformation and validates the measurement accuracy.