Biomedical subjects

Takami Yamaguchi

Publications and source records attributed to Takami Yamaguchi.

11 recordsLinked to original sources

PubMed2006

Particle method for computer simulation of red blood cell motion in blood flow.

A particle method for the computer simulation of blood flow was proposed to analyze the motion of a deformable red blood cell (RBC) in flowing blood plasma. The RBC and plasma were discretized by particles that have the characteristics of an elastic membrane and a viscous fluid, respectively. The membrane particles were connected to their neighboring membrane particles by springs, and the motion of the particles was determined on the basis of the minimum energy principle. The incompressible flow of plasma that was expressed by the motion of the fluid particles was determined by the moving-particle semi-implicit (MPS) method. The RBC motion and plasma flow were weakly coupled. The two-dimensional simulation of blood flow between parallel plates demonstrated the capability of the proposed method to express the blood flow phenomena observed in experiments, such as the downstream motion of the RBC and the deformation of the RBC into a parachute shape.

Blood Circulation↗

PubMed2006

Influence of the opening mode of the mitral valve orifice on intraventricular hemodynamics.

We analyzed intraventricular blood flow numerically to study the influence of the mode of mitral valve opening on the flow field in the left ventricle. Four different types of opening mode were examined: gradually axisymmetric, gradually anteroposterior (anatomical), gradually bilateral (anti-anatomical), or instantaneous opening and closing. In these models, the shape of the valve orifice was the same when the mitral valve was opened fully. The results demonstrated that the framework of the velocity profile of transmitral flow was built during the phase of mitral valve opening, which was characterized by the mode of valve opening. After the mitral valve opened completely, the transmitral velocity profile developed while maintaining its topological features. Consequently, each mode of mitral valve opening had its own pattern of intraventricular flow, although mitral valve opening accounted for less than 4% of a cardiac cycle. Particle tracking in the resulting flow field revealed that ventricular ejection was more efficient in the anteroposterior and axisymmetric opening modes. These results addressed the importance of the mode of mitral valve opening in intraventricular flow dynamics.

Blood Flow Velocity↗

PubMed2006

Computational flow dynamics in abdominal aortic aneurysm using multislice computed tomography.

Following the introduction of a new multislice computed tomography (MSCT) scanner, it has become possible to produce high-speed CT angiography (CTA), the preferred method for imaging in emergent abdominal vascular conditions. Unlike catheter angiography, multislice CTA not only depicts the vessels but also allows perfusion in adjacent organs to be assessed. To make the most effective diagnostic use of multi-detector row CTA and three-dimensional image post-processing, radiologists must be familiar with the optimal CTA protocols and the typical CT findings in various emergent vascular conditions using computational flow dynamics (CFD). This article describes a technical approach to estimating the blood flow state of human abdominal aortic aneurysms (AAA) in more detail by constructing realistic three-dimensional (3D) vessel models using CFD methods, focusing on pre- and postoperative cases.

Aged↗

PubMed2006

Computational analysis of blood flow in an integrated model of the left ventricle and the aorta.

To study the effects of intraventricular flow dynamics on the aortic flow, we created an integrated model of the left ventricle and aorta and conducted a computer simulation of diastolic and systolic blood flow within this model. The results demonstrated that the velocity profile at the aortic annulus changed dynamically, and was influenced by the intraventricular flow dynamics. The profile was almost flat in early systole but became nonuniform as systole progressed, and was skewed toward the posterior side in midsystole and toward the anterior side in later systole. At a distance from the aortic annulus, a different velocity profile was induced by the twisting and torsion of the aorta. In the ascending aorta, the fastest flow was initially located in the posteromedial sector, and it moved to the posterior section along the circumference as systole progressed. The nonuniformity of the aortic inflow gave rise to a complex wall shear stress (WSS) distribution in the aorta. A comparison of the WSS distribution obtained in this integrated analysis with that obtained in flow calculations using an isolated aorta model with Poiseuille and flat inlet conditions showed that intraventricular flow affected the WSS distribution in the ascending aorta. These results address the importance of an integrated analysis of flow in the left ventricle and aorta.

Animals↗

PubMed2005

Correlation of hemodynamic events with clinical and pathological observations.

The correlation of hemodynamic events with clinical or pathological observations is represented by a variety of applications reflecting the broad range of this theme. The position paper describes several cases in which benefits of combining imaging information with transport models of contrast material, can cause a gain in hemodynamic information. What appears to be lack of cohesiveness among the cases illustrates the variety in the application of hemodynamic research to the practice of medicine. Some of the contributions presented at the symposium do not directly apply to clinical medicine, but instead described mathematical models or applications to animal physiology or technical advancements in measuring blood rheology. Although related to this theme topic they fall somewhat outside the main scope. The topics summarized below demonstrate four examples in which translation of the research to the clinical arena can be realized in a short period of time. Overall recommendations for priority objectives related to this topic are provided at the end of this position paper.

Animals↗

PubMed2005

Effects of a ventricular untwisting on intraventricular diastolic flow and color M-mode Doppler echocardiograms.

Intraventricular hemodynamics during diastole was numerically analyzed in order to investigate effects of a ventricular untwisting on flow and a pattern of a color M-mode Doppler echocardiogram. Results showed that the ventricular untwisting affected secondary flows by inducing spiral flows in the ventricular cavity especially in the apical region. On the other hand, flows in the long-axis plane were not affected. Timing of formation, size and growing manner of the annular vortex were almost the same regardless of the presence of the ventricular untwisting; the vortex firstly arose in the base region, expanded towards the apex and eventually occupied the upper half of the ventricular cavity. A pattern of a color M-mode Doppler echocardiogram, that is, a spatiotemporal map of velocity along the long axis, was topologically the same as quantitatively confirmed by comparison of propagation velocity (0.43 m/s and 0.42 m/s for the case without and with the ventricular untwisting, respectively). These results suggested that this technique can exclusively capture flow dynamics produced by ventricular expansion with little influence of the ventricular untwisting. Therefore, we concluded that this is advantageous for assessing a left ventricular diastolic function.

Biomechanical Phenomena↗

PubMed2005

The application of computer simulation in the genesis and development of intracranial aneurysms.

The genesis and development of intracranial aneurysm have long been of interest but remain not understood. In the present study we simulate the progression of intracranial aneurysms by constructing a computational model of a curved artery. It is hypothesized that high local wall shear stress above a threshold value will lead to degeneration of the arterial wall mechanical properties. And this degenerative effect may continue even after the wall shear stress has become lower than the threshold, which is referred to as the "time remaining effect" in this study. We performed several groups of studies using both assumptions and aneurysm development is observed as result of the interplay between high wall shear stress, wall degeneration and wall deformation. In the growth of aneurysms with "time-remaining effect", the increase of aneurysmal height accelerates in later steps. It is concluded that computer simulation can yield insight into the understanding of the pathophysiology of aneurysmal initiation and growth, and help in clarifying the role of certain hemodynamic parameters.

Biomechanical Phenomena↗

PubMed2004

Patient Record Information System (PaRIS) for primary health care centers in Indonesia.

This study explores the Patient Record Information System (PaRIS) for primary health care centers in a developing country such as Indonesia. The specific geography of the thousand islands country Indonesia is the reason for transportation difficulties as well as communication problems. This causes a serious adverse effect on the public healthcare service especially in the rural area within the country. Hence, a sustainable system is required that makes use of appropriate Information and Communication Technology (ICT). We developed a clinical information system with modest communication technology combined with a unique database distribution system. The Internet and its free software are the main tools for this system. It is a good opportunity for a developing country such as Indonesia to apply open free software in regard to the healthcare sector. This cost effective and sustainable system can enhance the work of physicians in order to provide better and applicable public health care service.

Ambulatory Care Information Systems↗

PubMed2003

Formation and destruction of primary thrombi under the influence of blood flow and von Willebrand factor analyzed by a discrete element method.

Thrombogenesis and thrombolysis processes were simulated using a computational mechanics method called the discrete element method (DEM) to model the mechanical interactions between blood flow, platelets, the vessel wall, and von Willebrand factor (vWf). The inclusion of vWf and a complex blood flow field in the DEM are new developments used in this study. A primary thrombus did not form in the simulations if only the axial fluid force was considered, even when vWf was activated to simulate an endothelial injury. When the radial fluid force was considered to include the exclusion effect of erythrocytes, the modeled platelets formed primary thrombi at lesions where vWf was present. This suggests that activation of vWf is not sufficient to promote the formation of primary thrombi; a complex flow field that facilitates the transport of platelets towards the wall is also required.

Blood Platelets↗

PubMed2002

Computational fluid dynamics modeling and analysis of the effect of 3-D distortion of the human aortic arch.

An idealized CFD model and a realistic one were used to investigate the effect of the 3-D distortion of the aortic arch on the blood flow and its pathophysiological significance with respect to the pathogenesis of the aortic aneurysm. From the results of the flow simulations, the distortion of the centerline of the pipe was shown to affect significantly the flow structure. A right-handed vortex at the descending arch, and a left-handed one at the end of the arch tended to develop in the realistic model. But the secondary flow did not become a single helix. The top of the arch was the region where complex spatial and temporal WSS distributed. It was also observed that the direction of WSS had a significant circumferential component at the top of the arch.

Aorta, Thoracic↗

PubMed2002

A simple computational model of the right coronary artery on the beating heart--effects of the temporal change of curvature and torsion on the blood flow.

A computational fluid dynamics study was conducted using a simplified model of the right coronary artery, which deforms with contraction of the heart. The right coronary artery was modeled using an ordinary helix, whose torsion and curvature changed in time with the contraction and dilatation of the heart which was modeled as a cylinder. In the computational result, the flow in the model right coronary artery was thought to be more affected by the change of the curvature compared to that of the torsion.

Computational Biology↗