Takami Yamaguchi

Three-Dimensional Simulation of Blood Flow in an Abdominal Aortic Aneurysm—Steady and Unsteady Flow Cases

Atherosclerosis and atherosclerotic aneurysms can occur in the abdominal aorta. Steady and unsteady three-dimensional flow cases were simulated in abdominal aortic aneurysm using a flow simulation package on a graphics workstation. In the steady case, three aneurysm models of 8.0 cm length were simulated using Reynolds numbers of 350 and 700. In the unsteady case, blood flow in a single asymmetric aneurysm of 8.0 cm length was simulated at Reynolds numbers of 350 and 700 and 1400. In the aneurysm center, two symmetric vortices were formed, and flow separation started at the aneurysm inlet. In the unsteady flow case, the main vortex appeared and disappeared and changed position in the unsteady flow case and induced vortices were formed. Although the centerline view shows the vortices change position with time, cross-sectional views show that two symmetric vortices are present or partially formed throughout the entire flow cycle. Regions of high pressure were observed at the aneurysm exit caused by the symmetric vortices that were formed, implying that this high-pressure region could be an area where rupture is most likely. In the unsteady case, regions of maximum pressure moved depending on the flow cycle time; at peak flow, local pressure maximums were observed at the distal aneurysm; these oscillated, tending to put an additional strain on the distal portion of the aneurysm. The shear stress was low in the aneurysm portion of the vessel, and local maximum values were observed at the distal aneurysm constriction.

Flow patterns in three-dimensional left ventricular systolic and diastolic flows determined from computational fluid dynamics

A realistic model of the left ventricle of the heart was previously constructed, using a cast from a dog heart which was in diastole. Previous studies of the three-dimensional heart model were conducted in systole only. The purpose of this investigation was to extend the model to both systole and diastole, and to determine what the effect of a previous cardiac cycle was on the next cardiac cycle. The 25.8 cc ventricular volume was reduced by 40% in 0.25 seconds, then increased to the original volume in another 0.25 seconds and then allowed to rest for 0.25 seconds. Runs done with an ejection fraction of 60% showed little variation from one cardiac cycle to another after the third cardiac cycle was completed; the maximum velocity could vary by over 30% between the first and second cardiac cycles. In systole, centerline and cross-sectional velocity vectors greatly increased in magnitude at the aortic outlet. Most of the pressure drop occurred in the top 15% of the heart. The diastolic phase showed complex vortex formation not seen in the systolic contractions; these complex vortices could account for experimentally observed turbulent blood flow fluctuations in the aorta.

Three-dimensional analysis of left ventricular ejection using computational fluid dynamics

We present in this study a method for constructing computational fluid mechanical models in order to study the effects of time-varying left ventricular ejection. A spherical left ventricular model was implemented in which three dimensional flow fields were obtained. The time course of the ventricular wall changes were assumed to have a trigonometrically varying nature. The wall grid was reformed 25 times during the calculation since the left ventricular wall motion was assumed to follow the blood flow, and the ventricle wall radius was reduced by 60 percent in 0.25 seconds. Centerline and cross-sectional velocity vectors greatly increased in magnitude at the aortic outlet, and pressure dropped from 1.17 x 10(4) dynes/cm2 (8.8 mmHg) to zero in the top 10 percent of the heart. The modeling framework will be used with left ventricular cast data coordinates in future studies. There is presently a lack of three-dimensional data based on a realistic model, and the computational method should make it possible to compare simulation results with important measurement techniques such as echocardiography and magnetic resonance imaging.

Realistic three-dimensional left ventricular ejection determined from computational fluid dynamics

A realistic model of the left ventricle of the human heart was constructed using a cast from a dog heart which was in diastole. A coordinate measuring machine was used to measure and digitize the coordinates of the left ventricle. From the complex measured left ventricle shape values, a three-dimensional finite volume representation was constructed using a simulation package. The left ventricular walls moved towards the centre of the aortic outlet in order to study the effects of time-varying left ventricular ejection. The left ventricular wall motion was assumed to follow the blood flow and the wall grid was reformed 25 times during the calculation. The 25.8 cm3 ventricular volume was reduced by 75% in 0.25 s. Centreline and cross-sectional velocity vectors greatly increased in magnitude at the aortic outlet, and most of the pressure occurred in the top 15% of the heart. The computational method should make it possible to compare simulation results with important measurement techniques such as ultrasound and magnetic resonance imaging, and this should allow a finer detail of flow understanding than is presently available using either a modelling or imaging method alone.

Open sesame from top of your head-an event related potential based interface for the control of the virtual reality system

We proposed a new concept of medical care system, named the hyper hospital which is constructed in computer based electronic information network. It is built as a distributed system on the network and consists of all kinds of conventional medical care facilities in both the real and the imaginary spaces. The virtual space of the hyper hospital and private information are owned and exclusively controlled by the patient, thus the maximum protection of the privacy of the patients can be observed. In the hyper hospital, an innovative human interface must be required for the consultation, treatment and other communication to the medical staff. This is especially true if the users are of severely disabled patients. The purpose of the present study is to establish a new human interface based on the event related potential, which enables those kind of patients to communicate with others including medical care staffs without any physical actions.<<ETX>>

The effects of supravalvular aortic stenosis on realistic three-dimensional left ventricular blood ejection.

The effect of supravalvular aortic stenosis on cardiac left ventricular ejection was determined from a realistic left ventricle (LV) model built from the profile of a diastolic dog LV. The ejection fraction was considered to be 75% of the diastolic volume. The maximum blood ejection velocities and ventricular pressure occurred at the start of the diastolic flow since the ventricular walls moved the fastest at this point. Going from a healthy non-stenotic LV to one with 64% stenosis increased the maximum ejection velocity from 117 cm/sec to 269 cm/sec, and the maximum relative pressure increased from 10,420 dynes/cm2 to 33,550 dynes/cm2 (7.82 to 25.16 mm Hg). The supravalvular stenotic aorta showed major flow disturbances as the degree of stenosis increased. The computational technique using a realistic model gives predictions in general agreement with observed experimental results, and allows a complex determination of the three-dimensional flow patterns.

Computational Visualization of Blood Flow

Computational bio-fluid mechanics, in the widest sense, is concerned with all aspects of biological flow, such as blood flow and respiratory flow. Tn this chapter, a general discussion of studies of blood flow by computational visualization emphasizing physiological relevance and pathological consequences is presented first. Further discussion follows on the extremely complex nature of blood flow, including its susceptibility to the geometrical configuration of blood vessels under unsteady conditions. A concise introduction of the basic governing equations, the methods of numerical computation, and the considerations of various computational conditions, particularly boundary conditions,.is also given. Modeling, which is the most important but the most time-consuming- part of computational studies, is also briefly discussed. Based on these fundamental discussions, two examples from both extremes of our multilevel computational bio-fluid mechanical studies are shown: realistic modeling and flow computation of the left ventricle, and the cellular-scale flow adjacent to cultured endothelial, cells.

Computational Visualization of Blood Flow in the Cardiovascular System

Fluid flow, such as blood flow and air flow, is a sine qua non mechanical phenomenon for maintaining the life of animals particularly vertebrates. Among them, blood flow is of vital concern not only from the view point of normal physiological conditions but also with respect to various disorders. It is, however, noteworthy that we can not clearly separate the physiological role and the pathological behavior of blood flow because the pathological process begins under normal physiological conditions. In other words, pathological phenomena should be regarded as being seamlessly continuous with the physiological state [1]. This is particularly true for some vascular diseases which start and develop under a strong influence of blood flow [2]. Atherosclerosis is representative among these diseases and is very important because its development finally results in the diminution and cessation of blood flow to crucial organs, particularly to the brain and the heart [3]. In westernized or industrial societies, death directly or indirectly caused by atherosclerosis usually occupies the top of the mortality statistics.

Which do you feel comfortable, interview by a real doctor or by a virtual doctor? A comparative study of responses to inquiries with various psychological intensities, for the development of the Hyper Hospital

The Hyper Hospital is a novel medical care system which will be constructed on an electronic information network. The human interface of the Hyper Hospital based on the modern virtual reality technology is expected to maximally enhance patients ability of healing illness by computer-supported online visual consultations. In order to investigate the effects and features of online visual consultations in the Hyper Hospital, we conducted an experiment to clarify the influence of electronic interviews on the talking behavior of interviewees in the similar context to real doctor-patient interactions. Four types of distant-confrontation interviews were presented to voluntary subjects and their verbal and nonverbal responses were analyzed from the human ethological viewpoints. In the media-mediated interviews both the latency and the duration of interviewees utterances in answering questions increased compared with those of live face to face interviews. These results suggest that the interviewee became more verbose or talkative in the mediated interviews, but his psychological tension was generally augmented.<<ETX>>

The hyper hospital-virtual reality based medical system on the computer network-its concept and user-configurable virtual world creating system

We have been developing a novel medical care system which is constructed on an electronic or computerized information network using virtual reality as the principal human interface. The major purpose of the hyper hospital is to restore humane interactions between patients and various medical caretakers by making a much closer contact between them in the real medical scene than that in current conventional medical practice. In the present study, we discuss the most fundamental part of the development of the virtual reality system for the medical use, that is, system software for the creation of the virtual world which can be defined and modified by users of various levels, not only by the medical caretakers, but particularly by patients.