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名古屋大学博士学位論文 学位の種類 : 博士(医学)(課程) 学位授与年月日:平成21年3月25日 靍見有史氏の博士論文として提出された

published_or_final_version / Sports Science / Master / Master of Science in Sports Science

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The effect of waveform shape and extension of negative flowrate are studied at two Reynolds numbers (Re = 80, Re = 200) on stented channels by looking at the kinematics and dynamics of the flow. The waveforms are reconstructed by Fourier decomposition of a waveform corresponding to left anterior descending (LAD) of coronary artery. The stents are modeled by an immersed boundary method. Two stent geometries are created which are the idealizations of two clinical ones. The first geometry is an idealization of XIENCE V stent which is called Lambda stent and the second one is the idealization of Endeavor stent and is called X stent. The former has larger inter-strut spacing and smaller thickness than the latter one. The use of immersed boundary method for creating the stents is validated, and the spatial resolution requirements are determined. The shape of the waveform is changed by systematically filtering out the higher modes of Fourier decomposition and the negative flowrate extension is reduced by shifting the waveform to the positive flowrate. The presence of the stent causes vortical structures to be created between stent struts. These vortices are migrating to the centre of the channel and disappear. It is observed that the confined geometric feature of X stent and its larger thickness, leads to larger areas of flow recirculation which causes smaller wall-shear-stress parameters with respect to Lambda stent and more deviation of the flow from a healthy vessel. The importance of the convective terms of the Navier-Stokes equations was studied at the two Reynolds numbers for both stents. It is observed that at high Reynolds number (Re = 200), the convective terms play significant role throughout the waveform cycle while at low Reynolds number (Re = 80), the effect of convective terms become negligible during negative flowrate. Moreover the convective terms become more significant for flow in a channel with Lambda stent than X stent due to the specific shape and size of the stents. The kinematics of the flow corresponds to the study of vortex timing. It was found that this timing is mainly affected by the waveform and Reynolds number rather than the stent geometry. The time at which vortex creation occurs is coincident with the time at which wall shear stress changes its sign in an unstented channel. Therefore the analytical solution of unsteady channel flow can be used as a tool for analysing the kinematics of the flow, / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2012-06-07 17:41:52.501

In this thesis, large-eddy simulation (LES) is used to simulate both Newtonian and non-Newtonian physiological pulsatile flows in constricted channels to gain insights into the physical phenomenon of laminar-turbulent flow transition due to the presence of an artificial arterial stenosis. The advanced dynamic nonlinear subgrid-scale stress (SGS) model of Wang and Bergstrom (DNM) was utilized to conduct numerical simulations and its predictive performance was examined in comparison with that of the conventional dynamic model (DM) of Lilly. An in-house LES code has been modified to conduct the unsteady numerical simulations, and the results obtained have been validated against available experimental and direct numerical simulation (DNS) results. The physical characteristics of the flow field have been thoroughly studied in terms of the resolved mean velocity, turbulence kinetic energy, viscous wall shear stress, and turbulence energy spectra along the central streamline of the domain.

In surgery for airway obstruction, the anesthetist and the ear-nose-throat surgeon share the approach to the airway and jet ventilation (JV) is a mutually convenient ventilation technique for both parties. As a consequence of the open system jet ventilation is applied in, bedside measurements of lung volumes are cumbersome to perform and thus, there is a lack of studies comparing different modes of JV or investigating the influence of ventilator settings on lung volumes and gas exchange. In this thesis, single frequency jet ventilation and superimposed high frequency jet ventilation (SHFJV) at different frequencies are systematically compared with respect to lung volume changes, underlying airway pressure variations and the resulting gas exchange. We compared three single-frequency JV modalities with SHFJV in patients. Moreover, we performed a systematic investigation of single frequency JV and SHFJV in a porcine model. Single frequency JV and SHFJV were compared frequency-wise in intact airways and in a newly developed model of tracheal obstruction. This model was also used to assess the influence of variable airway diameter on ventilation effectiveness during SHFJV. We measured chest wall volume variations with opto-electronic plethysmography and obtained airway pressures as well as gas exchange parameters. In unobstructed airways, both single-frequency JV and SHFJV provided adequate oxygenation, despite differences in lung volumes. Carbon dioxide removal was most effective using single frequency JV at a frequency of 150 min-1. During SHFJV, for both intact and obstructed airways, the choice of frequency for the high frequency component had little influence on lung volumes, airway pressures and gas exchange. With decreasing airway diameter and SHFJV, we observed air trapping and lower tidal volumes and acceptable oxygenation. Carbon dioxide removal, however, was insufficient at the narrowest airway diameter. In single frequency JV, very high frequencies resulted in negligible tidal volume and inacceptable gas exchange. Airway obstruction potentiated this frequency dependence. In conclusion, in intact airways, single frequency JV at sufficiently low frequencies provided adequate oxygenation and better CO2 removal than SHFJV. With decreasing airway diameter, SHFJV provided better oxygenation and CO2 removal and may therefore be the mode of choice in more complicated cases.

In der Literatur wird bei kleineren Patientenkohorten über eine erhöhte Prävalenz des linkskoronaren Versorgungstyps bei Patienten mit valvulärer Aortenklappenstenose berichet. Es wird auch postuliert, dass dies nur Patienten mit Aortenklappenstenose und bikuspider Aortenklappe betrifft. Die funktionelle Konsequenz der Kombination aus einem linksdominanten koronaren Versorgungstyp und valvulärer Aortenklappenstenose ist bisher nicht klar. Ziel der vorliegenden Arbeit war es, die Prävalenz des Linksversorgungstyps in einer großen Kohorte von Patienten mit diagnostizierter relevanter Aortenklappenstenose im Vergleich zu einer Kontrollkohorte ohne Aortenklappenstenose zu analysieren. Es galt ferner zu prüfen, ob sich eine etwaig höhere Prävalenz des koronaren Linksversorgungstyps auf Patienten mit bikuspider Aortenklappe beschränkt, ob der koronare Linksversorgungstyp ein unabhängiger Risikofaktor für die Progression einer Aortenklappenstenose ist und ob die koronare Linksdominanz Relevanz für das postoperative beziehungsweise postinterventionelle Outcome nach Aortenklappenersatz hat. Über eine Datenbankabfrage wurden alle Patienten identifiziert, die vom 01.01.2007 bis 31.12.2008 in der Klinik für Innere Medizin und Kardiologie im Herzzentrum der Universität Leipzig aufgenommen wurden. Zwei Subkohorten wurden extrahiert. Kohorte 1 umfasste alle Patienten mit einer bekannten oder neu diagnostizierten, symptomatischen und isolierten Stenose der nativen Aortenklappe. Kohorte 2 umfasste alle Patienten, welche einer invasiven Koronarangiographie unterzogen wurden und keine beginnende oder fortgeschrittene Aortenklappenstenose zeigten sowie ≥70 Jahre waren. Kohorte 1 umfasste 721, Kohorte 2 6990 Patienten. Der linkskoronare Versorgungstyp zeigte sich bei Patienten mit Aortenklappenstenose signifikant häufiger als bei Kontrollpatienten ohne Aortenklappenstenose (13.2% versus 10.2%, p=0.003). Eine signifikant niedrigere Prävalenz des rechtskoronaren Versorgungstypen fand sich bei Patienten mit einer Aortenklappenstenose (66.9% versus 71.6%, p=0.008). Beide Prävalenzen waren unabhängig vom Vorliegen einer bi- oder trikuspiden Klappenarchitektur. Es bestand lediglich ein geringer Trend zu einer höheren Prävalenz der linkskoronaren Dominanz bei Patienten mit bikuspider Klappe im Vergleich zu Patienten mit trikuspider Klappe (15 [20.8%] versus 60 [13.9%], p=0.12). Keine Unterschiede zeigten sich indessen für die intrahospitale Mortalität und Auftreten eines akuten Myokardinfarktes zwischen den koronaren Versorgungstypen. Die linkskoronare Dominanz ist kein Risikofaktor für eine Progression der Aortenklappenstenose.

In this thesis, large-eddy simulation (LES) is used to simulate both Newtonian and non-Newtonian physiological pulsatile flows in constricted channels to gain insights into the physical phenomenon of laminar-turbulent flow transition due to the presence of an artificial arterial stenosis. The advanced dynamic nonlinear subgrid-scale stress (SGS) model of Wang and Bergstrom (DNM) was utilized to conduct numerical simulations and its predictive performance was examined in comparison with that of the conventional dynamic model (DM) of Lilly. An in-house LES code has been modified to conduct the unsteady numerical simulations, and the results obtained have been validated against available experimental and direct numerical simulation (DNS) results. The physical characteristics of the flow field have been thoroughly studied in terms of the resolved mean velocity, turbulence kinetic energy, viscous wall shear stress, and turbulence energy spectra along the central streamline of the domain.

Platelets have been shown to be a main contributor to thrombus formation in stenotic arteries leading to acute coronary syndromes. It is thought that increased activation and adhesion of platelets under variable shear and complex flow conditions contribute to thrombosis. The objective of this work was to evaluate the relationship between asymmetric stenosis hemodynamics and platelet adhesion using in-vitro models developed to properly simulate physiological conditions. In this study, platelet rich plasma was circulated through stenotic and straight coronary artery models. Adhesion results were obtained by post-perfusion fluorescent labelling and imaging of adhered platelets. Analysis of platelet area coverage has shown maximum adhesion occurs in the distal region of the stenosis. Most likely this is due to increased exposure time of platelets to the wall of the recirculation zone following the stenosis and that exposure being directly after a period of high shear stress. This result gives us a better understanding of the importance of both shear and flow conditions in coronary artery thrombosis.