坪田 健一

The in vitro experimental investigations provide an excellent approach to understand complex blood flow phenomena involved at a microscopic level. This paper emphasizes an emerging experimental technique capable to quantify the flow patterns inside microchannels with high spatial and temporal resolution. This technique, known as confocal micro-PIV, consists of a spinning disk confocal microscope, high speed camera and a diode-pumped solid state (DPSS) laser. Velocity profiles of pure water (PW), physiological saline (PS) and in vitro blood were measured in a 100 mu m glass square and rectangular polydimethysiloxane (PDMS) microchannel. The good agreement obtained between measured and estimated results suggests that this system is a very promising technique to obtain detail information about micro-scale effects in microchannels by using both homogeneous and non-homogeneous fluids such as blood flow.

We analyzed an acceleration pattern during natural walking and walking hampered by wearing weights to predict falls These two types of walking could be distinguished with a peak at the half of the principal frequency of the gait in anterior movement We measured walking while wearing each individual hampering weight and then analyzed. The peak was bigger when a subject wore the hampering weight that was restrictive and made the body unbalanced. As leg accidents are considered to occur with a change of the body balance, our system may be used to detect a leg accident by checking the peak at the half of the principal frequency of the gait in anterior movement

We construct numerical aneurysm models arisen from both straight and curved arteries, under the hypothesis that high local wall shear stress larger than a certain threshold value will lead to a linear decrease in the wall mechanical properties. Development of aneurysm is observed in both the straight and curved models. In the straight model, the growth of aneurysm is small and only at the distal neck region, and the aneurysm stops growing after several steps. In contrast, in the curved model, the aneurysm continues to grow in height and width. Our computer simulation study shows that even if the wall shear stress inside an aneurysm is low, aneurysm development can occur due to degeneration of the wall distal and proximal to the aneurysm. The interaction between the hemodynamic change (caused by the shape change) and the wall degeneration is key to the development of aneurysms. Our method demonstrates the potential utility of rule-based numerical methods in the investigation of developmental biology of cardiovascular diseases.

We previously developed a network-based medical care support system called the Hyper-Hospital, a computer network with an interface that is dedicated to patient care. In this paper, we described a wearable information system that is designed so that a caregiver can obtain information and control various support devices within the home-care environment. In our system, the wearable computer itself consists of a computer network built into a jacket. Each required function is implemented by a dedicated small computer connected to the in-jacket network. A new function may easily be added to the system by connecting additional computers. Functional modules implemented in our system are a WiFi system to act as a bridge type router, an authentication system, and a hands-free computer interface. A network comprising such a set of single-function computers becomes a highly efficient information system when applied to health care support.

A two-dimensional particle method simulation of blood flow was carried out to investigate effects of stenosis on primary thrombogenesis due to platelet aggregation. In the employed particle method, the blood region was discritized by moving particles that have the characteristics of plasma and platelets. Two geometrically different models were constructed for straight and stenosed vessels. As a result, it was shown that platelets adhered to cover the whole area of the injured wall in the straight model. In the case of the stenosed model, platelets adhered on the downstream side of the injured wall and not on that of the upstream side. This was caused by the disturbance of the blood flow due to the geometrical nonuniformity of stenosis, leading to local growth of the thrombus. These results suggest that thrombogensis is influenced by the blood flow pattern depending on the vessel geometry.

Deformability of red blood cells (RBC) plays an important role in determining the fluid mechanical properties of the blood. Important phenomena of blood flows in microcirculation depend on the combination of vessel geometry, RBC deformability and the collective behavior of RBC. Recently, we developed a computational model to analyze the dynamic behavior of RBCs in the blood flow using a spring network model based on the minimum energy principle. We also developed a large scale simulation method by using parallel computing technique. In the present study, a two dimensional simulation of multiple RBCs movement in a straight channel was conducted by using a massive parallel computer system and it was shown that the proposed model has a potential to represent the realistic behavior of multiple RBCs flowing in a microvascular vessel.

A two-dimensional computer simulation of blood flow between parallel plates was carried out using particle method to investigate effects of red blood cells (RBCs) on blood flow properties. The RBCs and plasma were discretized by the particles that have the characteristics of the elastic membrane and the viscous incompressible fluid, respectively. The simulation results demonstrated that apparent blood flow resistance was affected by hematocrit (HCT) that controlled degree of deformation of RBCs. The lower HCT led to the lower resistance because the RBCs were more concentrated in the center of flow channel due to their larger deformation.

Blood flow in the aorta is complex, being affected by both the geometry of the aorta and flow dynamics stemmed from the left ventricle. It has been suggested that such a complex flow plays an important role in the localization of vascular diseases such as aortic aneuysm and arteriosclerosis. The aim of this study is to investigate the effect of the inflow and geometry of the aorta on the aortic flow. We measured the velocity profile at a site just above the aortic valve using cine phase contrast MRI (PC-MRI), and then performed CFD analysis of blood flow in the aorta using the measured velocity as an inlet boundary condition. The results showed that the geometry of the aorta is influential in the hemodynamics in the whole region of the aorta while the effect of the aortic inflow remains up to the aortic arch.

The detail measurements of velocity profiles of physiological fluids in microchannels is fundamental for a better understanding on the biomechanics of the microcirculation. It is therefore very important to obtain measurements with high accuracy and spatial resolution. This paper presents for the first time measurements of physiological flows within rectangular rnicrochannels obtained by a confocal particle image velocimetry (PIV) system. This emerging technology by combining the conventional PIV system with a spinning disk confocal microscope has the ability to obtain not only high spatial resolution images but also three dimensional (3D) velocity profiles. Good agreement is obtained between measured and estimated results. Our results have demonstrated the potentiality of our system to generate 3D velocity profiles and consequently to obtain detail information about micro-scale effects in microchannels.

Hemodynamic stresses are known to degenerate the arterial wall and be involved in the pathogenesis of intracranial aneurysm formation and development. The present study simulates the formation and growth of aneurysms by focusing on the interplay between the wall shear stress, degeneration of the mechanical wall properties, and the wall deformation. We construct numerical aneurysm models arisen from both straight and curved arteries, and we hypothesize that high local wall shear stress larger than a certain threshold value will lead to a linear decrease in the mechanical property of the vessel wall. The degeneration of vessel wall leads to wall deformation and redistribution of the wall shear stress, which in turn leads to further degeneration of the wall. Development of aneurysm is observed in both the straight and curved models. In the straight model, the growth of aneurysm is small and mainly at the distal neck region, and the aneurysm stops growing after several steps. In contrast, in the curved model, the aneurysm continues to grow in height and width. Our computer simulation shows that even if the wall shear stress inside a saccular aneurysm is low, aneurysm development can occur due to degeneration of the wall distal and proximal to the aneurysm. The interaction between the geometry change and the wall degeneration is key to the development of aneurysms. The method demonstrates the potential utility of model-based numerical methods in the investigation of developmental biology of intracranial aneurysms.

Hemodynamics stresses are known to be able to degenerate the arterial wall and be involved in the pathogenesis of aneurysm formation and development. The present study numerically simulates the formation and growth of an aneurysm arising from a curved artery focusing on the interplay between the wall shear stress, arterial wall degeneration and deformation. It was hypothesized that if the local wall shear stress is higher than a threshold value, the Young's modulus of the wall is decreasedat'a fixed rate. The computer simulations clearly show the relationship among the change in the shape of the blood vessel, distribution of wall shear stress, and the degeneration of vessel wall during the progression of aneurysm, providing us new insight into the mechanism of aneurysm formation and development.

Blood flow in the aorta is affected by both the geometry of the aorta and the flow dynamics in the left ventricle, resulting in complex-flow patterns. It has been suggested that such a complex flow plays a role in the localization of the vascular diseases such as aortic aheurysm and arteriosclerosis. CFD analyses combined with in vivo measurements are useful to investigate these effects. In this study, we measured the velocity profiles at a site just above the aortic valve with cine MRI phase contrast method. Then, these velocity profiles are used as a boundary condition at the inlet in a computational simulation of blood flow in the aorta. The results show that the velocity profiles at the inlet of the aorta are not uniform, which affects the flow in the region from the ascending aorta to the aortic arch.

The aortic arch is characterized by its configuration, large diameter and strong bend, and torsion in the arterial system. These characteristics induce the complex blood flow in the aorta, therefore leading to the distribution of the wall shear stress (WSS). The exact cause of the aneurysm is not known. However, it is reported that the aneurysm are most likely to occur at the site where the WSS is relatively high. So we propose that the initiation and growth of aortic aneurysm is related to WSS distribution. In this study, we analyzed flow in aortic arch various models with development of aortic aneurysm using computational fluid dynamics simulation. The result showed that the distortion of the aortic arch strongly influences WSS distribution, which is suspected to be related to the development of the aortic aneurysms.

The purpose of this study is to propose a computer simulation method using particle method to analyze aggregation process of platelets in blood flow. We applied the MPS method, which has been developed for incompressible fluid based on Navier-Stokes equations, to plasma flow analysis. Adhesion of platelets to exposed subendothelium was modeled by introducing attractive force between the platelets and the injured wall. In addition, force acted on among aggregated platelets was considered to express the deformation of the aggregation as a solid. Two-dimensional simulations revealed that the proposed method expresses initial thrombogenesis, growth of the thrombus, and the destruction of thrombus. It was shown that the Reynolds number affects the number of the aggregated platelets, indicating fluid mechanical factors play an important role in thrombosis caused by platelets aggregation.

The pulse wave propagating phenomenon is affected by changes in the mechanical properties and the geometry of the artery. The geometrical changes also affect the hemodynamics in the artery. In this study, to consider the hemodynamic effects on the pulse wave propagating phenomenon, we constructed computational aneurysmal models and analyzed the pulse wave propagation by a fluid-solid coupled method. The results show that vortices within the aneurysm caused vena contracta, which increased the pulse wave velocity locally, and the increased velocity was related to the maximum diameter of the aneurysm. This study shows the importance of the hemodynamic effects on the pulse wave propagation.

Distribution function of mechanical quantities at single trabecular level as remodeling stimuli was obtained by using digital image-based finite element models of normal vertebral body of rat. When a linear rate equation was assumed, integration of strain energy density (SED), von Mises equivalent stress, and local stress nonuniformity were more candidate stimuli of trabecular bone remodeling near remodeling equilibrium than SED. The sensitivity of distribution function of stress nonuniformity to change in physiological loading condition was the smallest in the four mechanical quantities.

Pulse Wave Velocity (PWV) is a very useful index for the systemic assessment of the cardio vascular diseases. To explore more effective usage of the PWV for the localized diseases, we analyzed the fluid-solid coupled problem of the stenosed artery with various area reductions ranging from 0% to 50% by using our application software. It was assumed that the stenosed artery is axisymmetric and the shape of the stenosis is given as the Gaussian curve. It was found that the PWV of the stenosed artery increases with the increase of the severity of the stenosis and the difference of the PWV between the stenosed and straight arteries reached 0.9m/s for the stenosed artery with an area reduction of 50%.

It is suggested that initiation and growth of an aortic aneurysm is related to the flow induced wall shear stress (WSS). The blood flow in the aorta with an aneurysm is affected not only by the geometry of the original aorta but also by the shape, location, size of the aneurysm. In this study, we constructed various CFD models of the aortic aneurysm by combining a three dimensionally bended aorta with an aneurysm whose shape is expressed as a two dimensional Gausian function. It was found that the location of the high wall shear stress region is discontinuously changed from upstream to downstream of the aneurysm by changing the size and location of the aneurysm.

It has been suggested that the development of aneurysms in the thoracic aorta is closely related to the torsion of the aortic arch. In this study, we analyzed flow in aortic arch models with various torsions using computational fluid dynamics simulation. The correlation between the aneurysm of the thoracic aorta and distortion of the arch was investigated from a fluid dynamics point of view. It was observed that the global feature of the secondary flow pattern, and the wall shear stress (WSS) distribution did not depend on the torsion of the arch from the qualitative viewpoint. However, the quantitative value of WSS appeared to be affected by the torsion. It was shown that WSS tends to increase when the torsion of the aortic arch increases. This result suggests that distortion of the aortic arch strongly influences WSS distribution, which is suspected to be related to the development of vascular diseases.

The blood flow regulation of the circle of Willis is thought to have a close correlation with the anatomy of the circle. In this study, we performed the computational fluid dynamics simulation with three-dimensional model in order to consider the relationship between the cerebral blood flow and the geometric configuration of blood vessels. The decrease of blood flow at the left internal carotid artery (LICA) led to the greater reduction of the blood flow at the left middle cerebral artery (LMCA) and the left anterior cerebral artery (LACA) which are near the LICA, and led to the smaller reduction at the left posterior artery (LPCA) and the blood vessels on the right side of the circle which are far from the LICA. Furthermore, the decrease of blood flow at the basilar artery (BA) led to the greater reduction of the blood flow at the left and right PCAs which are near the BA, and led to the smaller reduction at the MCAs and ACAs which are far from the BA. These results indicate that the redistribution of the blood flow in the circle of Willis is affected by the configuration, such as the spatial proximity of the blood vessels.

We have been developing a network-based care supporting system called the Hyper Hospital. The Hyper Hospital is constructed on the computer based network whose interface is the virtual reality dedicated to the patients. As a part of the progress, we have been developing a wearable computer which enables a care-givers to operate various support devices connected to the network. In the process of study, we found that hands-free operation of the wearable computer is important for the care workers to keep continuous physical care works while accessing to the computer. In this paper, we proposed a method of the hands-free interface to utilize the ocular potential generated by dipolar potential of eyeball and carried out fundamental experiments to assure a usability of this method.

We have been developing a network-based care supporting system called the Hyper Hospital. The Hyper Hospital is constructed on the computer based network whose interface is the virtual reality dedicated to the patients. As a part of the progress, we have been developing a wearable computer which enables a care-givers to operate various support devices connected to the network. In the process of study, we found that hands-free operation of the wearable computer is important for the care workers to keep continuous physical care works while accessing to the computer. In this paper, we proposed a method of the hands-free interface to utilize the ocular potential generated by dipolar potential of eyeball and carried out fundamental experiments to assure a usability of this method.

Sustainable Patient Information Network for Primary Care Health Center is needed for Indonesia. There are many of remote, isolated or urban area, which causes transportation problems and telecommunication problems, for example: necessity of wireless infrastructure. The Internet and its free software is the main agent for this system combining with Information and Communication Technology. We develop low speed communication system to access the Internet using Internet radio packet and used PostgreSQL data base server on Linux machines. Our development is based on a data base managing system called Automatic Distributed Synchronizing Data Base System. This system connects every health center to each other and avoid central data storage which common use in this day. It is a good opportunity for developing country such as Indonesia to use open free software. And radio packet communication uses radio media is no connection charge like telephone line for data communication. A general practitioner in remote and isolated area can get assistance from a specialist in one urban area using email. The study opens perspective for a further data storage, distribution, synchronizing, maintenance and security.

Sustainable Patient Information Network for Primary Care Health Center is needed for Indonesia. There are many of remote, isolated or urban area, which causes transportation problems and telecommunication problems, for example: necessity of wireless infrastructure. The Internet and its free software is the main agent for this system combining with Information and Communication Technology. We develop low speed communication system to access the Internet using Internet radio packet and used PostgreSQL data base server on Linux machines. Our development is based on a data base managing system called Automatic Distributed Synchronizing Data Base System. This system connects every health center to each other and avoid central data storage which common use in this day. It is a good opportunity for developing country such as Indonesia to use open free software. And radio packet communication uses radio media is no connection charge like telephone line for data communication. A general practitioner in remote and isolated area can get assistance from a specialist in one urban area using email. The study opens perspective for a further data storage, distribution, synchronizing, maintenance and security.

We have been developing a network-based care supporting system called the Hyper Hospital. The Hyper Hospital is constructed on the computer based network whose interface is the virtual reality dedicated to the patients. As a part of the progress, we have been developing a wearable computer which enables a care-givers to operate various support devices connected to the network. In the process of study, we found that hands-free operation of the wearable computer is important for the care workers to keep continuous physical care works while accessing to the computer. In this paper, we proposed a method of the hands-free interface to utilize the ocular potential generated by dipolar potential of eyeball and carried out fundamental experiments to assure a usability of this method.

Characteristics of model parameters in the trabecular surface remodelling model were quantitatively examined by two-dimensional remodeling simulation for rectangular cancellous bone under simple loading condition. Parametric studies clarified that the parameters affected on the rate of changes and the spatial distribution of trabecular structure. Through the comparison of the structural indices to experimental observation, the parameters can be quantitatively determined.

For the cancellous bone with trabecular architecture, digital image-based finite element models are useful not only in modeling of the structure but also in simulating morphological changes of the architecture due to remodeling. In this study, a simulation method for trabecular surface remodeling was proposed using digital image-based finite element model, and the feasibility of the proposed method was demonstrated through the simulation study for cancellous bone cube under compressive loading.