Atsushi Shirai

Fundamental study of ultrasonic-measurement-integrated simulation of real blood flow in the aorta.

Acquisition of detailed information on the velocity and pressure fields of the blood flow is essential to achieve accurate diagnosis or treatment for serious circulatory diseases such as aortic aneurysms. A possible way to obtain such information is integration of numerical simulation and color Doppler ultrasonography in the framework of a flow observer. This methodology, namely, Ultrasonic-Measurement-Integrated (UMI) Simulation, consists of the following processes. At each time step of numerical simulation, the difference between the measurable output signal and the signal indicated by numerical simulation is evaluated. Feedback signals are generated from the difference, and numerical simulation is updated applying the feedback signal to compensate for the difference. This paper deals with a numerical study on the fundamental characteristics of UMI simulation using a simple two-dimensional model problem for the blood flow in an aorta with an aneurysm. The effect of the number of feedback points and the feedback formula are investigated systematically. It is revealed that the result of UMI simulation in the feedback domain rapidly converges to the standard solution, even with usually inevitable incorrect upstream boundary conditions. Finally, an example of UMI simulation with feedback from real color Doppler measurement also shows a good agreement with measurement.

Deformations of thin liquid spherical shells in liquid-liquid-gas systems

Deformation characteristics of a millimeter-sized thin liquid spherical shell moving at intermediate Reynolds numbers in immiscible liquid are investigated both numerically and experimentally. Experiments are made using the novel principle of sequential production of the shell developed by the authors. Numerical results of the flow pattern around the liquid shell, deformation ratio, and the drag coefficient are compared to experimental results for wide flow conditions. They are in reasonable agreement from the viewpoint of practical engineering. Furthermore, effects of shell deformation on heat transfer characteristics are also investigated numerically. The present research provides the fluid dynamical knowledge for various applications of liquid spherical shells.

Modeling neutrophil transport in pulmonary capillaries.

Neutrophils can be retained in the pulmonary microvasculature due to their low deformability, resulting in having a higher concentration there than in the systemic circulation, even in normal lungs. It is thought that this high concentration of the cells facilitates their effective recruitment to sites of inflammation. Thus, in order to understand their role in the immune system in the lungs, where blood comes in contact with outer air via thin septa of alveoli, it is important to clarify their flow characteristics in the pulmonary capillary bed. However, in contrast to erythrocytes in systemic capillaries, little research has been performed on the flow of neutrophils in pulmonary capillaries. This may be partly because no complete rheological model of the cell has been established yet, and partly because pulmonary capillaries are very short and closely interconnected, forming a complicated three-dimensional network, in addition to difficulty in in vivo experimental observations. Moreover, the neutrophils change their mechanical properties and show active motion in response to some chemoattractants. In this article, various proposed rheological models of the neutrophil, flow models of a cell through a single capillary segment, and alveolar capillary network models are introduced, aiming at the numerical simulation of neutrophil transport in the pulmonary microvasculature.

Numerical Simulation of Noninvasive Blood Pressure Measurement

In this paper, a simulation model based on the partially pressurized collapsible tube model for reproducing noninvasive blood pressure measurement is presented. The model consists of a collapsible tube, which models the pressurized part of the artery, rigid pipes connected to the collapsible tube, which model proximal and distal region far from the pressurized part, and the Windkessel model, which represents the capacitance and the resistance of the distal part of the circulation. The blood flow is simplified to a one-dimensional system. Collapse and expansion of the tube is represented by the change in the cross-sectional area of the tube considering the force balance acting on the tube membrane in the direction normal to the tube axis. They are solved using the Runge-Kutta method. This simple model can easily reproduce the oscillation of inner fluid and corresponding tube collapse typical for the Korotkoff sounds generated by the cuff pressure. The numerical result is compared with the experiment and shows good agreement.

Frictional Characteristics of Erythrocytes on Coated Glass Plates Subject to Inclined Centrifugal Forces

In recent years a diamond-like carbon (DLC) film and a 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer have attracted attention as coating materials for implantable artificial organs or devices. When these materials are coated on vascular devices, compatibility to blood is an important problem. The present paper focuses on friction characteristics of erythrocytes to these coating materials in a medium. With an inclined centrifuge microscope developed by the authors, observation was made for erythrocytes moving on flat glass plates with and without coating in a medium of plasma or saline under the effect of inclined centrifugal force. Friction characteristics of erythrocytes with respect to these coating materials were then measured and compared to each other to characterize DLC and MPC as coating materials. The friction characteristics of erythrocytes in plasma using the DLC-coated and noncoated glass plates are similar, changing approximately proportional to the 0.5th power of the cell velocity. The cells stick to these plates in saline as well, implying the influence of plasma protein. The results using the MPC-coated plate in plasma are similar to those of the other plates for large cell velocities, but deviate from the other results with decreased cell velocity. The results change nearly proportional to the 0.75th power of the cell velocity in the range of small velocities. The results for the MPC-coated plate in saline are similar to that in plasma but somewhat smaller, implying that the friction characteristics for the MPC-coated plate are essentially independent of plasma protein.

Three-Dimensional Flow Analysis in VFP Type Artificial Heart by Unstructured Grid

To effectively design the vibrating flow pump (VFP) for left ventricular assist device, the numerical codes were developed for three-dimensional blood flow based on the finite volume method. The numerical codes were also developed based on the artificial compressibility method by the use of unstructured grid. Three-dimensional numerical computations and the visualizations were made for flow patterns in the casing of VFP, which were closely connected with hemolysis and blood coagulation. We examined the three different inlet conditions, i.e., radial flow, flow considering the 2nd vibration mode of the jellyfish valve motion, and the swirling flow, to explore the suitable condition for preventing the hemolysis and the blood coagulation. It was found that the swirling flow could effectively decrease hemolysis. The effect of rheology model of the blood flow was also studied in detail.Copyright

A Stabilization Technique of Wobbly Images Taken by the Inclined Centrifuge Microscope

The authors have observed behavior of HL60 cells on endothelial cells cultured on a flat glass plate for the understanding of fundamental mechanism of the immune response of neutrophils using the inclined centrifuge microscope. The inclined centrifuge microscope applies a centrifugal force to the HL60 cells using a centrifuge and records motion of the cells on the plate as successive stroboscopic images synchronized with rotation of the rotor of the centrifuge. The successive images were wobbly by flatter of the rotor or vibration of the motor of the centrifuge. To stabilize the images, they drew cross lines on the glass plate, and adjusted the images by fixing the position of the crossing point of the lines. However, it was difficult to extract the lines accurately, because the lines were not clear on the low-contrast images. Therefore, in this research, the authors introduced the Hough transformation to extract the lines. Moreover, adherent cells on the plate were also used to compensate remaining shaking of the images. Consequently, the displacements of the images were decreased to almost within±1 pixel.

Numerical Analysis for Elucidation of Nonlinear Frictional Characteristics of a Deformed Erythrocyte Moving on a Plate in Medium Subject to Inclined Centrifugal Force

Complex interactions between blood cells, plasma proteins, and glycocalyx in the endothelial surface layer are crucial in microcirculation. To obtain measurement data of such interactions, we have previously performed experiments using an inclined centrifuge microscope, which revealed that the nonlinear velocity-friction characteristics of erythrocytes moving on an endothelia-cultured glass plate in medium under inclined centrifugal force are much larger than those on plain or material-coated glass plates. The purpose of this study was to elucidate the nonlinear frictional characteristics of an erythrocyte on plain or material-coated glass plates as the basis to clarify the interaction between the erythrocyte and the endothelial cells. We propose a model in which steady motion of the cell is realized as an equilibrium state of the force and moment due to inclined centrifugal force and hydrodynamic flow force acting on the cell. Other electrochemical effects on the surfaces of the erythrocyte and the plate are ignored for the sake of simplicity. Numerical analysis was performed for a three-dimensional flow of a mixture of plasma and saline around a rigid erythrocyte model of an undeformed biconcave shape and a deformed shape with a concave top surface and a flat bottom surface. A variety of conditions for the concentration of plasma in a medium, the velocity of the cell, and the minimum gap width and the angle of attack of the cell from the plate, were examined to obtain the equilibrium states. A simple flat plate model based on the lubrication theory was also examined to elucidate the physical meaning of the model. The equilibrium angle of attack was obtained only for the deformed cell model and was represented as a power function of the minimum gap width. A simple flat plate model qualitatively explains the power function relation of the frictional characteristics, but it cannot explain the equilibrium relation, confirming the computational result that the deformation of the cell is necessary for the equilibrium. The frictional characteristics obtained from the present computation qualitatively agree with those of former experiments, showing the validity of the proposed model.

Simultaneous analysis system for blood pressure and flow using photoplethysmography and ultrasonic-measurement-integrated simulation

We developed a simultaneous analysis system for blood pressure and flow using photoplethysmography and ultrasonic-measurement-integrated simulation. The validity of the system was confirmed by analysis of blood flow field in a carotid artery and corresponding wave intensity (WI) values.

Differentiation of neutrophil-like HL-60 cells strongly impacts their rolling on surfaces with various adhesive properties under a pressing force

BACKGROUND HL-60 cells have been used in in vitro experiments of neutrophils rolling. They lose uniform spherical appearance and enhance deformability by differentiation to neutrophil-like cells, which would affect their rolling characteristics. OBJECTIVE We investigate the influence of differentiation and coating of target substrate on the fundamental rolling characteristics of the cells under a constant pressing force which mimics the pressing force to the vessel wall by erythrocytes in vivo. METHODS Motions of undifferentiated and differentiated HL-60 cells on plain or MPC-polymer-coated flat glass substrate were compared using a homemade inclined centrifuge microscope system. RESULTS Most of the cells alternated between stop and go during the motion. The differentiation resulted in a high temporal ratio of the non-moving state and low mean velocity during the moving state, together with a high suppression performance of cell adhesion by the polymer. It was also suggested that the cells were mostly rolling but that the coating probably induced an infrequent slip on the substrate to stabilize the cells motion. CONCLUSIONS Differentiation strongly affects adhesivity of HL-60 cells but less affects the mean velocity. Our findings also demonstrate the importance of the pressing force and advantage of the present system with respect to classical flow chambers.